Showing 1–50 of 203 results for author: Nazé, Y

Expanding stellar horizons with polarized light

Authors: J. Vandersnickt, R. Ochoa Armenta, V. Vanlaer, A. David-Uraz, C. Aerts, S. B. Das, J. -C. Bouret, D. M. Bowman, L. Bugnet, V. Khalack, J. Labadie-Bartz, S. Mathis, Y. Nazé, C. Neiner, P. Petit, V. Petit, K. Thomson-Paressant, T. Van Doorsselaere, M. Vanrespaille

Abstract: The polarization of light is a critically under-utilized, rich source of information in astronomy. For stars in particular, surface magnetism polarization that can be detected and measured with spectro-polarimetry. Many questions about these surface fields remain unanswered due to a lack of dedicated instruments capable of probing weak and strong surface magnetic fields for the entire mass range o… ▽ More The polarization of light is a critically under-utilized, rich source of information in astronomy. For stars in particular, surface magnetism polarization that can be detected and measured with spectro-polarimetry. Many questions about these surface fields remain unanswered due to a lack of dedicated instruments capable of probing weak and strong surface magnetic fields for the entire mass range of stars, from M-dwarfs (and even substellar objects) to massive O-type stars at different evolutionary stages and metallicities. These questions range from the origin of these fields to their true incidence rate throughout the stellar population and the dependence on metallicity. Magnetic fields, although currently often excluded from stellar evolution models, play an important role in stellar evolution. Connecting the surface fields to internal fields through asteroseismology will instigate a new era of understanding stellar evolution and the transport of angular momentum and chemical elements throughout stellar interiors, also impacting our understanding of star-planet interactions and stellar remnants. Polarimetry is also an under-utilized tool to observationally constrain the mode identification of nonradial oscillations, which lies at the basis of accurate asteroseismic parameter estimation at percentage-level for stellar radii, masses, ages, internal rotation, and magnetic field strengths. Combining strong constraints on mode identification and surface magnetic properties through the acquisition of time-resolved, high-resolution and high-signal-to-noise (S/N) spectro-polarimetry and spectroscopy promises to bring leaps forward in our understanding of stellar structure, particularly when combined with long-term space photometric data from past, current, and future missions. △ Less

Submitted 17 December, 2025; originally announced December 2025.

Comments: White paper in response to ESO call Expanding Horizons (4 pages)

Exploring the binary origin of B and Be rapid rotators

Authors: Jonathan Labadie-Bartz, Mark Suffak, Carol Jones, Yaël Nazé, Ken Gayley, Geraldine Peters, Rina Rast, Anusha Ravikumar, Asif ud-Doula, Coralie Neiner, Jeremy J. Drake

Abstract: Observational evidence has continued to mount that a significant fraction of rapidly rotating early-B type stars are products of binary mass transfer. However, very few mid- and late-type B stars with rapid rotation have been demonstrated to be post-interaction products, despite a growing sample of SB1 binaries among stars within this range of spectral types. By considering the currently available… ▽ More Observational evidence has continued to mount that a significant fraction of rapidly rotating early-B type stars are products of binary mass transfer. However, very few mid- and late-type B stars with rapid rotation have been demonstrated to be post-interaction products, despite a growing sample of SB1 binaries among stars within this range of spectral types. By considering the currently available information over the entire range of rapidly rotating B-type binaries, we argue that a significant fraction of the mid- and late-type rapid rotators found in binaries are also likely the result of past mass transfer episodes. The observed properties of this sample are compared to the predictions from the Binary Population and Spectral Synthesis code (BPASS), with attention given to the expected evolutionary pathways of stripped stars and the stellar and binary properties of both components of post-interaction systems across a range of initial conditions. Prospects for directly detecting and characterizing the stripped cores of the previous mass donors in such systems are described, and the implications for the role of binary interaction in causing rapid rotation are discussed. An accurate description of prevalence of binary interaction, the physics of mass transfer, and the post-interaction configuration of systems over a range of initial conditions has far-reaching implications including double-degenerate binaries and their eventual mergers, the output of ionizing UV flux of stellar populations, and the supernova explosions that can arise from stripped or rapidly-rotating progenitors. △ Less

Submitted 9 December, 2025; originally announced December 2025.

Comments: 40 pages, 12 figures, 4 tables, Accepted for publication in Astrophysics and Space Science

The Advanced X-ray Imaging Satellite Community Science Book

Authors: Michael Koss, Nafisa Aftab, Steven W. Allen, Roberta Amato, Hongjun An, Igor Andreoni, Timo Anguita, Riccardo Arcodia, Thomas Ayres, Matteo Bachetti, Maria Cristina Baglio, Arash Bahramian, Marco Balboni, Ranieri D. Baldi, Solen Balman, Aya Bamba, Eduardo Banados, Tong Bao, Iacopo Bartalucci, Antara Basu-Zych, Rebeca Batalha, Lorenzo Battistini, Franz Erik Bauer, Andy Beardmore, Werner Becker , et al. (373 additional authors not shown)

Abstract: The AXIS Community Science Book represents the collective effort of more than 500 scientists worldwide to define the transformative science enabled by the Advanced X-ray Imaging Satellite (AXIS), a next-generation X-ray mission selected by NASA's Astrophysics Probe Program for Phase A study. AXIS will advance the legacy of high-angular-resolution X-ray astronomy with ~1.5'' imaging over a wide 24'… ▽ More The AXIS Community Science Book represents the collective effort of more than 500 scientists worldwide to define the transformative science enabled by the Advanced X-ray Imaging Satellite (AXIS), a next-generation X-ray mission selected by NASA's Astrophysics Probe Program for Phase A study. AXIS will advance the legacy of high-angular-resolution X-ray astronomy with ~1.5'' imaging over a wide 24' field of view and an order of magnitude greater collecting area than Chandra in the 0.3-12 keV band. Combining sharp imaging, high throughput, and rapid response capabilities, AXIS will open new windows on virtually every aspect of modern astrophysics, exploring the birth and growth of supermassive black holes, the feedback processes that shape galaxies, the life cycles of stars and exoplanet environments, and the nature of compact stellar remnants, supernova remnants, and explosive transients. This book compiles over 140 community-contributed science cases developed by five Science Working Groups focused on AGN and supermassive black holes, galaxy evolution and feedback, compact objects and supernova remnants, stellar physics and exoplanets, and time-domain and multi-messenger astrophysics. Together, these studies establish the scientific foundation for next-generation X-ray exploration in the 2030s and highlight strong synergies with facilities of the 2030s, such as JWST, Roman, Rubin/LSST, SKA, ALMA, ngVLA, and next-generation gravitational-wave and neutrino networks. △ Less

Submitted 31 October, 2025; originally announced November 2025.

Comments: 595 pages, 225 figures

A family of binaries with an extreme mass ratio

Authors: Yael Naze, Gregor Rauw, Piotr A. Kolaczek-Szymanski, Nikolay Britavskiy, Jonathan Labadie-Bartz

Abstract: Multiplicity is ubiquitous among massive stars. While the stellar components usually display similar masses, some binaries with extremely low mass ratios were also observed. Some of them are primordial, while others arise from binary interactions. The identification of systems with extreme mass ratios brings valuable information, notably on the origin of fast rotation in massive stars. We identify… ▽ More Multiplicity is ubiquitous among massive stars. While the stellar components usually display similar masses, some binaries with extremely low mass ratios were also observed. Some of them are primordial, while others arise from binary interactions. The identification of systems with extreme mass ratios brings valuable information, notably on the origin of fast rotation in massive stars. We identify new short-period systems with extreme mass ratios through the detection of eclipses and reflection effects. The physical properties of a dozen newly identified cases were precisely evaluated through high-quality photometry and spectroscopy. In addition to characterizing these binaries, we found a clear signature of apsidal motion in one system, and three other systems display long-term shifts in eclipse times. All systems we reported here are composed of a massive star and a cool low-mass companion. They are therefore primordial cases. This doubles the known number of these systems in the Galaxy. In this context, it is important to note that most massive stars in these systems, as well as in previous systems reported in the literature, rotate fast (supersynchronous compared to the orbital motion). The high incidence of fast rotation in these nascent binaries provides strong constraints for star formation models. △ Less

Submitted 27 October, 2025; v1 submitted 17 October, 2025; originally announced October 2025.

Comments: accepted by A&A

High energy emission powered by accreting companions of Be/gamma Cas stars

Authors: Rina G. Rast, Yael Naze, Jonathan Labadie-Bartz, Carol E. Jones, Christiana Erba, Ken Gayley, Asif ud-Doula, Coralie Neiner, Jeremy J. Drake

Abstract: The origin of the hard, bright X-ray emission that defines the gamma Cas analog class of Be stars remains an outstanding question in Be star literature. This work explores the possibility that the X-ray flux is produced by accretion onto a white dwarf companion. We use three-dimensional smoothed particle hydrodynamics simulations to model the prototype gamma Cas system assuming a white dwarf compa… ▽ More The origin of the hard, bright X-ray emission that defines the gamma Cas analog class of Be stars remains an outstanding question in Be star literature. This work explores the possibility that the X-ray flux is produced by accretion onto a white dwarf companion. We use three-dimensional smoothed particle hydrodynamics simulations to model the prototype gamma Cas system assuming a white dwarf companion and investigate the accretion of the circumstellar material by the secondary star. We contrast these results to a model for 59 Cyg, a non-gamma Cas Be star system with a stripped companion. We find that the secondary stars in both systems form disk-like accretion structures with Keplerian characteristics, similar to those seen in the Be decretion disks. We also find that white dwarf accretion can produce X-ray fluxes that are consistent with the observed values for gamma Cas, while the predicted X-ray luminosities are significantly lower for the non-degenerate companion in 59 Cyg. In addition, using the three-dimensional radiative transfer code, HDUST, we find that these models produce H-alpha emission consistent with the observations for both gamma Cas and 59 Cyg, and that the predicted polarization degrees across optical and UV wavelengths are at detectable levels. Finally, we discuss the impact that future UV spectropolarimetry missions could have on our understanding of these systems. △ Less

Submitted 1 October, 2025; originally announced October 2025.

Comments: 29 pages, 9 figures, accepted for publication in Astrophysics and Space Science

Apsidal motion and proximity effects in the massive binary BD+60 497

Authors: Gregor Rauw, Piotr A. Kolaczek-Szymanski, Yael Naze, Lucas Nys

Abstract: The eccentric short-period O-star binary BD+60 497 is an interesting laboratory in which to study tidal interactions in massive binary systems, notably via the detection and characterisation of apsidal motion. The rate of apsidal motion in such systems can help constrain their age and provide insight into the degree of mass concentration in the interior of massive stars. We used spectroscopic data… ▽ More The eccentric short-period O-star binary BD+60 497 is an interesting laboratory in which to study tidal interactions in massive binary systems, notably via the detection and characterisation of apsidal motion. The rate of apsidal motion in such systems can help constrain their age and provide insight into the degree of mass concentration in the interior of massive stars. We used spectroscopic data collected over two decades to reconstruct the individual spectra of the stars and to establish their epoch-dependent radial velocities. An orbital solution, explicitly accounting for apsidal motion was adjusted to the data. Space-borne photometric time series were analysed with Fourier methods and with binary models. We derived a rate of apsidal motion of $6.15^{+1.05}_{-1.65}$ degree/yr, which suggests an age of $4.13^{+0.42}_{-1.37}$ Myr. The disentangled spectra unveiled a curious change in the spectral properties of the secondary star between the epochs 2002-2003 and 2018-2022 with the secondary spectrum appearing to be of an earlier spectral type over recent years. Photometric data show variability at the 6 mmag level on the period of the binary system, which is hard to explain in terms of proximity effects. Whilst the rate of apsidal motion agrees well with theoretical expectations, the changes in the reconstructed secondary spectrum hint at a highly non-uniform surface temperature distribution for this star. Different effects are discussed that could contribute to the photometric variations. The current most-likely explanation is a mix of proximity effects and tidally excited oscillations △ Less

Submitted 2 October, 2025; v1 submitted 16 September, 2025; originally announced September 2025.

Comments: Accepted for publication in A&A

Journal ref: A&A 702, A274 (2025)

X-ray Polarimetry of Accreting White Dwarfs: A Case Study of EX Hydrae

Authors: Sean J. Gunderson, Swati Ravi, Herman L. Marshall, Dustin K. Swarm, Richard Ignace, Yael Naze, David P. Huenemoerder, Pragati Pradhan

Abstract: We present the first first X-ray polarization measurements of a white dwarf, the intermediate polar EX Hya. We measured significant polarization only in the 2 -- 3 keV energy band with a polarization degree of 8 percent at a $3σ$ significance. No significant polarization was detected above 3 keV, which we attribute to the higher energy bands having lower signal-to-noise. We found that the scatteri… ▽ More We present the first first X-ray polarization measurements of a white dwarf, the intermediate polar EX Hya. We measured significant polarization only in the 2 -- 3 keV energy band with a polarization degree of 8 percent at a $3σ$ significance. No significant polarization was detected above 3 keV, which we attribute to the higher energy bands having lower signal-to-noise. We found that the scattering surface detected by the IXPE is nearly perpendicular to the optical scattering plane, showing that the X-ray scattering surface is the WD and close to the base of the accretion column. Finally, we show how the polarization can be used to estimate the height of the accretion shock above the white dwarf's surface. △ Less

Submitted 30 September, 2025; v1 submitted 5 August, 2025; originally announced August 2025.

Comments: 8 pages, 3 figures. Submitted to ApJ

The multi-faceted variability of HD 192639: Stochastic behaviour, regularities, and an exceptional mass-ejection event

Authors: Gregor Rauw, Yaël Nazé, Charles-Antoine Gilon

Abstract: Spectroscopic and photometric variability is widespread among O-type supergiants. It is linked to various phenomena affecting the star and its circumstellar environment, thereby providing direct information concerning them. To investigate such connections, we decided to revisit the prototypical O7.5 Iabf supergiant HD 192639. High-cadence spectroscopic monitoring was performed simultaneously with… ▽ More Spectroscopic and photometric variability is widespread among O-type supergiants. It is linked to various phenomena affecting the star and its circumstellar environment, thereby providing direct information concerning them. To investigate such connections, we decided to revisit the prototypical O7.5 Iabf supergiant HD 192639. High-cadence spectroscopic monitoring was performed simultaneously with intensive space-borne photometric observations. The data were analysed with several methods to characterise the variability. Besides the usual stochastic, low-frequency photometric variability, our observations reveal the presence of recurrent - but transient - modulations on a timescale of about five days. The same signal is present in the spectroscopic data and was already seen two decades ago. This stability suggests that this timescale corresponds to the stellar rotation. Furthermore, our observations unveil, for the first time, an unusually strong dimming event in the light curve associated with absorption and emission changes in H I and He I lines. This unprecedented trough corresponds to an episodic ejection of a rather large amount of mass (its column density being comparable to that of the steady wind). While rare, such an event could hint at an overlooked aspect of mass loss in massive stars. △ Less

Submitted 3 August, 2025; originally announced August 2025.

Comments: Accepted for publucation in A&A

New Frontiers in the Study of Magnetic Massive Stars with the Habitable Worlds Observatory

Authors: Alexandre David-Uraz, Véronique Petit, Coralie Neiner, Jean-Claude Bouret, Yaël Nazé, Christiana Erba, Miriam Garcia, Kenneth Gayley, Richard Ignace, Jiři Krtička, Hugues Sana, Nicole St-Louis, Asif ud-Doula

Abstract: High-mass stars are notable for several reasons: they are characterized by strong winds, which inject momentum and enriched material into their surroundings, and die spectacularly as supernovae, leaving behind compact remnants and heavy elements (such as those that make life on Earth possible). Despite their relative rarity, they play a disproportionate role in the evolution of the galaxies that h… ▽ More High-mass stars are notable for several reasons: they are characterized by strong winds, which inject momentum and enriched material into their surroundings, and die spectacularly as supernovae, leaving behind compact remnants and heavy elements (such as those that make life on Earth possible). Despite their relative rarity, they play a disproportionate role in the evolution of the galaxies that host them, and likely also played a significant role in the early days of the Universe. A subset ($\sim$10\%) of these stars was also found to host magnetic fields on their surface. These fields impact their evolution, and may lead to exotic physics (e.g., heavy stellar-mass black holes, pair-instability supernovae, magnetars, etc.). However, the detection and measurement of magnetic fields is limited, due to current instrumentation, to nearby massive stars in the Milky Way. To truly understand how magnetism arises in massive stars, and what role it might have played in earlier stages of our Universe, we require next-generation hardware, such as the proposed near-infrared-to-ultraviolet spectropolarimeter Pollux, on the Habitable Worlds Observatory (HWO). In this contribution, we detail how Pollux @ HWO will enable new frontiers in the study of magnetic massive stars, delivering results that will profoundly impact the fields of stellar formation, stellar evolution, compact objects, and stellar feedback. △ Less

Submitted 18 July, 2025; originally announced July 2025.

Comments: 11 pages, 4 figures. HWO science case, to be presented at the conference "Towards the Habitable Worlds Observatory: Visionary Science and Transformational Technology" and to be submitted to Astronomical Society of the Pacific

The birth of Be star disks I. From localized ejection to circularization

Authors: J. Labadie-Bartz, A. C. Carciofi, A. C. Rubio, D. Baade, R. Siverd, C. Arcos, A. L. Figueiredo, Y. Nazé, C. Neiner, T. Rivinius, N. D. Richardson, S. Nova, M. L. Pinho, S. Bhattacharyya, R. Leadbeater, J. Guarro Fló, V. Lecocq, G. Piehler, J. Kozok, U. Sollecchia, E. Bryssinck, C. Buil, J. Martin, V. Desnoux, B. Heathcote , et al. (13 additional authors not shown)

Abstract: Classical Be stars are well known to eject mass, but the details governing the initial distribution and evolution of this matter into a disk are poorly constrained by observations. By combining high-cadence spectroscopy with contemporaneous space photometry from TESS, we have sampled about 30 mass ejection events in 13 Be stars. Our goal is to constrain the geometrical and kinematic properties of… ▽ More Classical Be stars are well known to eject mass, but the details governing the initial distribution and evolution of this matter into a disk are poorly constrained by observations. By combining high-cadence spectroscopy with contemporaneous space photometry from TESS, we have sampled about 30 mass ejection events in 13 Be stars. Our goal is to constrain the geometrical and kinematic properties of the ejecta, facilitating the investigation into the initial conditions and evolution, and understanding its interactions with preexisting material. The photometric variability is analyzed together with measurements of the rapidly changing emission features to identify the onset of outburst events and obtain information about the geometry of the ejecta and its evolution. All Be stars observed with sufficiently high cadence exhibit rapid oscillations of line asymmetry with a single frequency in the days following the start of the event. The emission asymmetry cycles break down after roughly 5 - 10 cycles, with the emission line profile converging toward approximate symmetry. In photometry, several frequencies typically emerge at relatively high amplitude at some point during the mass ejection process. In all observed cases, freshly ejected material was initially within a narrow azimuthal range, indicating it was launched from a localized region on the star. The material orbits the star with a frequency consistent with the near-surface Keplerian orbital frequency. This material circularizes into a disk configuration after several orbital timescales. This is true whether or not there was a preexisting disk. We find no evidence for precursor phases prior to the ejection of mass in our sample. The several photometric frequencies that emerge during outburst are at least partially stellar in origin. (Abstract abridged) △ Less

Submitted 10 April, 2025; originally announced April 2025.

Comments: 41 pages, 31 figures, 4 tables

Another one (BH+OB pair) bites the dust

Authors: Yael Naze, Gregor Rauw

Abstract: Most (or possibly all) massive stars reside in multiple systems. From stellar evolution models, numerous systems with an OB star coupled to a black hole would be expected to exist. There have been several claimed detections of such pairs in recent years and this is notably the case of HD96670. Using high-quality photometry and spectroscopy in the optical range, we revisited the HD96670 system. We… ▽ More Most (or possibly all) massive stars reside in multiple systems. From stellar evolution models, numerous systems with an OB star coupled to a black hole would be expected to exist. There have been several claimed detections of such pairs in recent years and this is notably the case of HD96670. Using high-quality photometry and spectroscopy in the optical range, we revisited the HD96670 system. We also examined complementary X-ray observations to provide a broader view of the system properties. The TESS light curves of HD96670 clearly show eclipses, ruling out the black hole companion scenario. This does not mean that the system is not of interest. Indeed, the combined analysis of photometric and spectroscopic data indicates that the system most likely consists of a O8.5 giant star paired with a stripped-star companion with a mass of ~4.5Msol, a radius of ~1Rsol, and a surface temperature of ~50kK. While several B+sdOB systems have been reported in the literature, this would be the first case of a Galactic system composed of an O star and a faint stripped star. In addition, the system appears brighter and harder than normal OB stars in the X-ray range, albeit less so than for X-ray binaries. The high-energy observations provide hints of phase-locked variations, as typically seen in colliding wind systems. As a post-interaction system, HD96670 actually represents a key case for probing binary evolution, even if it is not ultimately found to host a black hole. △ Less

Submitted 11 March, 2025; originally announced March 2025.

Comments: accepted for publication in A&A

The X-ray Integral Field Unit at the end of the Athena reformulation phase

Authors: Philippe Peille, Didier Barret, Edoardo Cucchetti, Vincent Albouys, Luigi Piro, Aurora Simionescu, Massimo Cappi, Elise Bellouard, Céline Cénac-Morthé, Christophe Daniel, Alice Pradines, Alexis Finoguenov, Richard Kelley, J. Miguel Mas-Hesse, Stéphane Paltani, Gregor Rauw, Agata Rozanska, Jiri Svoboda, Joern Wilms, Marc Audard, Enrico Bozzo, Elisa Costantini, Mauro Dadina, Thomas Dauser, Anne Decourchelle , et al. (257 additional authors not shown)

Abstract: The Athena mission entered a redefinition phase in July 2022, driven by the imperative to reduce the mission cost at completion for the European Space Agency below an acceptable target, while maintaining the flagship nature of its science return. This notably called for a complete redesign of the X-ray Integral Field Unit (X-IFU) cryogenic architecture towards a simpler active cooling chain. Passi… ▽ More The Athena mission entered a redefinition phase in July 2022, driven by the imperative to reduce the mission cost at completion for the European Space Agency below an acceptable target, while maintaining the flagship nature of its science return. This notably called for a complete redesign of the X-ray Integral Field Unit (X-IFU) cryogenic architecture towards a simpler active cooling chain. Passive cooling via successive radiative panels at spacecraft level is now used to provide a 50 K thermal environment to an X-IFU owned cryostat. 4.5 K cooling is achieved via a single remote active cryocooler unit, while a multi-stage Adiabatic Demagnetization Refrigerator ensures heat lift down to the 50 mK required by the detectors. Amidst these changes, the core concept of the readout chain remains robust, employing Transition Edge Sensor microcalorimeters and a SQUID-based Time-Division Multiplexing scheme. Noteworthy is the introduction of a slower pixel. This enables an increase in the multiplexing factor (from 34 to 48) without compromising the instrument energy resolution, hence keeping significant system margins to the new 4 eV resolution requirement. This allows reducing the number of channels by more than a factor two, and thus the resource demands on the system, while keeping a 4' field of view (compared to 5' before). In this article, we will give an overview of this new architecture, before detailing its anticipated performances. Finally, we will present the new X-IFU schedule, with its short term focus on demonstration activities towards a mission adoption in early 2027. △ Less

Submitted 15 February, 2025; originally announced February 2025.

Comments: 44 pages, 14 figures, accepted for publication in Experimental Astronomy

X-raying the wind-wind collisions in HD 168112 and HD 167971

Authors: Gregor Rauw, Ronny Blomme, Yaël Nazé, Delia Volpi

Abstract: The O-type long-period binary HD 168112 and triple HD 167971 star systems have been known for several decades for their non-thermal synchrotron radio emission. This emission arises from relativistic electrons accelerated in the hydrodynamic shocks of the wind collisions in these systems. Such wind collisions are expected to produce a strong X-ray emission that varies as a function of orbital phase… ▽ More The O-type long-period binary HD 168112 and triple HD 167971 star systems have been known for several decades for their non-thermal synchrotron radio emission. This emission arises from relativistic electrons accelerated in the hydrodynamic shocks of the wind collisions in these systems. Such wind collisions are expected to produce a strong X-ray emission that varies as a function of orbital phase. In wide eccentric binaries, such as our targets, the X-ray emission arises from an adiabatic plasma and its intensity should scale as the inverse of the orbital separation. We present a set of XMM-Newton observations of these systems which help us gain insight into the properties of their wind interactions. △ Less

Submitted 18 October, 2024; originally announced October 2024.

Comments: in French language. Accepted for publication in the Bulletin de la Société Royale des Sciences de Liège, Proceedings of the 41st Liège Astrophysical Colloquium, held in Liège 15-19 July 2024, edited by Y. Nazé, & E. Bozzo

TESS observations of non-Be fast rotators

Authors: Yael Naze, Nikolay Britavskiy, Jonathan Labadie-Bartz

Abstract: The variability of fast-rotating Oe/Be stars has been reported in detail in recent years. However, much less known about the behaviour of fast-rotating OB stars without known decretion disks, and hence it is difficult to identify the commonalities and differences in the photometric variability of these two populations, especially with regards to their pulsational properties and their link with the… ▽ More The variability of fast-rotating Oe/Be stars has been reported in detail in recent years. However, much less known about the behaviour of fast-rotating OB stars without known decretion disks, and hence it is difficult to identify the commonalities and differences in the photometric variability of these two populations, especially with regards to their pulsational properties and their link with the presence of circumstellar material. Via an in-depth literature search, we identified a set of fast-rotating (v sin(i)>200 km/s) early B-type stars not known to have disks. TESS and Kepler light curves were built for 58 stars that appear isolated (no bright neighbour within 1 arcmin and no known companion) to avoid contamination of the light curves. Frequency spectra were calculated and then analysed to determine the noise level and the presence of significant signals above the noise. Red noise is detected in all targets, without obvious correlations between noise and stellar parameters. Long-term changes are much less frequent than in Be stars, with only 12% of our targets having the variability below 0.5/d dominating their frequency spectrum. In contrast, strong frequency groups are detected in about a third of targets, as in Be stars. These groups generally occur in pairs with harmonic frequencies, as is usually seen in Be stars, but with the first group more often displaying larger amplitudes. Finally, the most frequent variability is due to isolated frequencies in the 0.5-6./d range (which is found in two-thirds of cases and dominates the spectra in 42% of the sample). Higher-frequency signals (up to 40/d) are sometimes also detected but rarely (only 12% of stars) appear as the strongest ones of the frequency spectra. Overall, fast-rotating B-type stars, with or without disks, display similar photometric properties, except as regards their longer-term behaviour. △ Less

Submitted 11 July, 2024; originally announced July 2024.

Comments: accepted for publication by A&A

X-raying the zeta Tau binary system

Authors: Yael Naze, Christian Motch, G. Rauw, Myron A. Smith, Jan Robrade

Abstract: The Be star zeta Tau was recently reported to be a gamma Cas analog; that is, it displays an atypical (bright and hard) X-ray emission. The origin of these X-rays remains debated.The first X-ray observations indicated a very large absorption of the hot plasma component (N_H~ 10^{23}/cm^2). This is most probably related to the edge-on configuration of the zeta Tau disk. If the X-ray emission arises… ▽ More The Be star zeta Tau was recently reported to be a gamma Cas analog; that is, it displays an atypical (bright and hard) X-ray emission. The origin of these X-rays remains debated.The first X-ray observations indicated a very large absorption of the hot plasma component (N_H~ 10^{23}/cm^2). This is most probably related to the edge-on configuration of the zeta Tau disk. If the X-ray emission arises close to the companion, an orbital modulation of the absorption could be detected as the disk comes in and out of the line of sight. New XMM-Newton data were obtained to characterize the high-energy properties of zeta Tau in more detail. They are complemented by previous Chandra and SRG/eROSITA observations as well as by optical spectroscopy and TESS photometry. The high-quality XMM-Newton data reveal the presence of a faint soft X-ray emission, which appears in line with that recorded for non-gamma Cas Be stars. In addition, zeta Tau exhibits significant short-term variability at all energies, with larger amplitudes at lower frequencies (``red noise''), as is found in X-ray data of other gamma Cas stars. Transient variability (softness dip, low-frequency signal) may also be detected at some epochs. In addition, between X-ray exposures, large variations in the spectra are detected in the 1.5-4.keV energy band. They are due to large changes in absorption toward the hottest (9keV) plasma. These changes are not correlated with either the orbital phase or the depth of the shell absorption of the Halpha line. These observed properties are examined in the light of proposed gamma Cas models. △ Less

Submitted 11 July, 2024; v1 submitted 21 June, 2024; originally announced June 2024.

Comments: accepted for publication by A&A

Ups and downs in the X-ray emission of the colliding wind binaries HD 168112 and HD 167971

Authors: Gregor Rauw, Ronny Blomme, Yael Naze, Delia Volpi, Sorenza Fernandez-Vera

Abstract: The long-period O-star binary system HD 168112 and the triple O-star system HD 167971 are well-known sources of non-thermal radio emission that arises from a colliding wind interaction. The wind-wind collisions in these systems should result in phase-dependent X-ray emissions. The presence of a population of relativistic electrons in the wind interaction zone could affect the properties of the X-r… ▽ More The long-period O-star binary system HD 168112 and the triple O-star system HD 167971 are well-known sources of non-thermal radio emission that arises from a colliding wind interaction. The wind-wind collisions in these systems should result in phase-dependent X-ray emissions. The presence of a population of relativistic electrons in the wind interaction zone could affect the properties of the X-ray emission and make it deviate from the behaviour expected for adiabatic shocks. We investigate the X-ray emission of these systems with the goals of quantifying the fraction of the X-ray flux arising from wind interactions and determining whether these emissions follow the predictions for adiabatic wind-wind collisions. Six X-ray observations were collected with XMM-Newton. Three observations were scheduled around the most recent periastron passage of HD 168112. Spectra and light curves were analysed and compared with simple predictions of model calculations for X-ray emission from colliding wind systems. The X-ray emission of HD 168112 varies as the inverse of the orbital separation, as expected for an adiabatic wind interaction zone. The relative contribution of intrinsic X-ray emission from wind-embedded shocks varies between 38% at periastron to 81% at apastron. The wind-wind collision zone remains adiabatic even around periastron passage. The X-ray emission of HD 167971 displays variations on the orbital timescale of the inner eclipsing binary. The existing data of this system do not allow us to probe variations on the timescale of the outer orbit. Shock modification due to the action of relativistic electrons does not seem to be efficiently operating in the HD 168112 system. In the existing observations, a significant part of the emission of HD 167971 must arise in the inner eclipsing binary. The origin of this emission is as yet unclear. △ Less

Submitted 13 June, 2024; originally announced June 2024.

Comments: Accepted for publication in Astronomy & Astrophysics

The colliding-wind binary HD 168112

Authors: R. Blomme, G. Rauw, D. Volpi, Y. Nazé, M. Abdul-Masih

Abstract: Radio surveys of early-type stars have revealed a number of non-thermal emitters. Most of these have been shown to be binaries, where the collision between the two stellar winds is responsible for the non-thermal emission. HD 168112 is a non-thermal radio emitter, whose binary nature has only recently been confirmed spectroscopically. We obtained independent spectroscopic observations to determine… ▽ More Radio surveys of early-type stars have revealed a number of non-thermal emitters. Most of these have been shown to be binaries, where the collision between the two stellar winds is responsible for the non-thermal emission. HD 168112 is a non-thermal radio emitter, whose binary nature has only recently been confirmed spectroscopically. We obtained independent spectroscopic observations to determine its orbit, in addition to radio observations to see if the thermal or non-thermal nature of the emission changes during the periastron passage. We monitored HD 168112 spectroscopically for a 13 year time span. From these data, we determined the orbital parameters, which we compared to the previous results in the literature. From the spectral index of the radio observations, we found how the nature of the emission changes as the system goes through periastron. Combining our results with other literature data allowed us to further constrain the orbital and stellar parameters. We find HD 168112 to have an orbital period of P = 512.17+0.41-0.11 d, an eccentricity of e = 0.7533+0.0053-0.0124, and a mass ratio close to one. From our spectroscopic modelling, we derived the stellar parameters, but we had difficulty arriving at a spectroscopic mass ratio of one. The radio observations around periastron show only thermal emission, suggesting that most of the synchrotron photons are absorbed in the two stellar winds at that phase. Combining our data with the optical interferometry detection, we could constrain the inclination angle to i ~ 63 deg, and the mass of each component to ~ 26 Msun. We have provided an independent spectroscopic confirmation of the binary nature of HD 168112. Although detected as a non-thermal radio emitter, near periastron the radio emission of this highly eccentric system is thermal and is mainly formed in the colliding-wind region. [abridged] △ Less

Submitted 3 June, 2024; v1 submitted 6 May, 2024; originally announced May 2024.

Comments: 13 pages, 7 figures, accepted for publication in Astronomy & Astrophysics. Corrected values of Omega on p. 9

Tracing the evolution of short-period binaries with super-synchronous fast rotators

Authors: N. Britavskiy, M. Renzo, Y. Nazé, G. Rauw, P. Vynatheya

Abstract: The initial distribution of rotational velocities of stars is still poorly known, and how the stellar spin evolves from birth to the various end points of stellar evolution is an actively debated topic. Binary interactions are often invoked to explain the existence of extremely fast-rotating stars ($v\sin\,i$ $\gtrsim$ 200 $km\,s^{-1}$). The primary mechanisms through which binaries can spin up st… ▽ More The initial distribution of rotational velocities of stars is still poorly known, and how the stellar spin evolves from birth to the various end points of stellar evolution is an actively debated topic. Binary interactions are often invoked to explain the existence of extremely fast-rotating stars ($v\sin\,i$ $\gtrsim$ 200 $km\,s^{-1}$). The primary mechanisms through which binaries can spin up stars are tidal interactions, mass transfer, and possibly mergers. To evaluate these scenarios, we investigated in detail the evolution of three known fast-rotating stars in short-period spectroscopic and eclipsing binaries, namely HD 25631, HD 191495, and HD 46485, with primaries of masses of 7, 15, and 24 $M_{\odot}$, respectively, with companions of $\sim1\,M_\odot$ and orbital periods of less than 7 days. These systems belong to a recently identified class of binaries with extreme mass ratios, whose evolutionary origin is still poorly understood. We evaluated in detail three scenarios that could explain the fast rotation observed in these binaries: it could be primordial, a product of mass transfer, or the result of a merger within an originally triple system. We computed grids of single and binary MESA models varying tidal forces and initial binary architectures to investigate the evolution and reproduce observational properties of these systems. We find that, because of the extreme mass-ratio between binary components, tides have a limited impact, regardless of the prescription used, and that the observed short orbital periods are at odds with post-mass-transfer scenarios. The most likely scenario to form such young, rapidly rotating, and short-period binaries is primordial rotation, implying that the observed binaries are pre-interaction ones. These binaries show that the initial spin distribution of massive stars can have a wide range of rotational velocities. △ Less

Submitted 20 January, 2024; originally announced January 2024.

Comments: Accepted for publication in the Astronomy & Astrophysics journal. 20 pages, 17 figures. Reproducible at https://github.com/NikolayBritavskiyAstro/fast_rotating_binaries; the input and output MESA data are available at https://zenodo.org/records/10479754

Reysa Bernson, the unconventional head of the first French planetarium

Authors: Yael Naze

Abstract: The first modern planetarium was presented in 1923 in Jena, Germany. Very soon in the subsequent years, planetariums were installed in other parts of Europe as well as in America. France, however, got its first planetarium only in 1937, for the World Exhibition organized in Paris. The team that took care of that planetarium was headed by a female amateur astronomer named Reysa Bernson. This choice… ▽ More The first modern planetarium was presented in 1923 in Jena, Germany. Very soon in the subsequent years, planetariums were installed in other parts of Europe as well as in America. France, however, got its first planetarium only in 1937, for the World Exhibition organized in Paris. The team that took care of that planetarium was headed by a female amateur astronomer named Reysa Bernson. This choice might seem surprising, but it was not made at random, thanks to her never-ending astronomical activities at that time. This paper aims to bring back memories of this very active amateur astronomer of the 1920s and 1930s, and show the many ways in which astronomy was disseminated a century ago. △ Less

Submitted 4 January, 2024; originally announced January 2024.

Comments: published in JAHH, see complements on https://hdl.handle.net/2268/310591

Journal ref: JAHH, vol 26(4), pages 816-832 (2023)

A Morpho-Kinematic Study of the Enigmatic Emission Nebula NGC 6164/5 Surrounding the Magnetic O-type Star HD 148937

Authors: Beomdu Lim, Yael Naze, Seok-Jun Chang, Damien Hutsemekers

Abstract: HD 148937 is a peculiar massive star (Of?p) with a strong magnetic field (1kG). The hourglass-shaped emission nebula NGC 6164/5 surrounds this star. This nebula is presumed to originate from episodic mass-loss events of the central O-type star, but the detailed formation mechanism is not yet well understood. Grasping its three-dimensional structure is essential to uncover the origin of this nebula… ▽ More HD 148937 is a peculiar massive star (Of?p) with a strong magnetic field (1kG). The hourglass-shaped emission nebula NGC 6164/5 surrounds this star. This nebula is presumed to originate from episodic mass-loss events of the central O-type star, but the detailed formation mechanism is not yet well understood. Grasping its three-dimensional structure is essential to uncover the origin of this nebula. Here we report the high-resolution multi-object spectroscopic observation of NGC 6164/5 using the GIRAFFE on the 8.2m Very Large Telescope. Integrated intensity maps constructed from several spectral lines delineate well the overall shape of this nebula, such as the two bright lobes and the inner gas region. The position-velocity diagrams show that the two bright lobes are found to be redshifted and blueshifted, respectively, while the inner region has multiple layers. We consider a geometric model composed of a bilateral outflow harboring nitrogen-enriched knots and expanding inner shells. Its spectral features are then simulated by using a Monte-Carlo radiative transfer technique for different sets of velocities. Some position-velocity diagrams from simulations are very similar to the observed ones. According to the model that best reproduces the observational data, the two bright lobes and the nitrogen-enriched knots are moving away from HD 148937 at about 120 km s$^{-1}$. Their minimum kinematic age is estimated to be about 7,500 years. We discuss possible formation mechanisms of this nebula in the context of binary interaction. △ Less

Submitted 5 December, 2023; originally announced December 2023.

Comments: 14 pages, 11 figures, accepted for publication in ApJ

Addressing Outstanding Problems in the Physics of Massive Stars with the Line Emission Mapper X-ray Probe

Authors: Jeremy J. Drake, David Cohen, Michael Corcoran, Maurice Leutenegger, Kristina Monsch, Yaël Nazé, Lidia Oskinova, Vallia Antoniou

Abstract: We present some of the salient aspects of the scientific motivation for high resolution soft X-ray spectroscopy of early-type stars with the Line Emission Mapper X-ray Probe. The major strength of {\it LEM} for hot star physics is its large effective area, aided by the inherent energy resolution of its microcalorimeter that readily achieves resolving powers of 1000 and obviates the need for relati… ▽ More We present some of the salient aspects of the scientific motivation for high resolution soft X-ray spectroscopy of early-type stars with the Line Emission Mapper X-ray Probe. The major strength of {\it LEM} for hot star physics is its large effective area, aided by the inherent energy resolution of its microcalorimeter that readily achieves resolving powers of 1000 and obviates the need for relatively inefficient dispersive optical elements. This increased sensitivity enables much fainter and more distant high mass stars to be observed than are accessible with present-day facilities, greatly increasing the pool of potential targets. For brighter sources, the sensitivity opens up time domain studies, wherein sufficient signal can be garnered in short order and exposure times, probing source variations on ks timescales. We argue that these capabilities of {\it LEM} will yield breakthroughs in all types of hot star systems, from understanding single OB and WR star winds and how they vary with metallicity, to probing the shocks of colliding wind systems and the magnetically channeled winds of magnetic OB stars. {\it LEM} will also study the energetics of WR star bubbles and feedback from their powerful pre-SN stellar winds. △ Less

Submitted 25 October, 2023; originally announced October 2023.

Comments: A Line Emission Mapper White Paper

Colliding winds in WR21 and WR31 -- I. The X-ray view

Authors: Yael Naze, Gregor Rauw, Rachel Johnson, Eric Gosset, Jennifer L. Hoffman

Abstract: WR21 and WR31 are two WR+O binaries with short periods, quite similar to the case of V444 Cyg. The XMM-Newton observatory has monitored these two objects and clearly revealed phase-locked variations as expected from colliding winds. The changes are maximum in the soft band (0.5--2.keV, variations by a factor 3--4) where they are intrinsically linked to absorption effects. The increase in absorptio… ▽ More WR21 and WR31 are two WR+O binaries with short periods, quite similar to the case of V444 Cyg. The XMM-Newton observatory has monitored these two objects and clearly revealed phase-locked variations as expected from colliding winds. The changes are maximum in the soft band (0.5--2.keV, variations by a factor 3--4) where they are intrinsically linked to absorption effects. The increase in absorption due to the dense WR wind is confirmed by the spectral analysis. The flux maximum is however not detected exactly at conjunction with the O star in front but slightly afterwards, suggesting Coriolis deflection of the collision zone as in V444 Cyg. In the hard band (2.--10. keV), the variations (by a factor of 1.5--2.0) are much more limited. Because of the lower orbital inclinations, eclipses as observed for V444 Cyg are not detected in these systems. △ Less

Submitted 12 September, 2023; v1 submitted 1 September, 2023; originally announced September 2023.

Comments: accepted for publication by MNRAS

Extreme mass ratios and fast rotation in three massive binaries

Authors: Yael Naze, Nikolay Britavskiy, Gregor Rauw, Jonathan Labadie-Bartz, S. Simon-Diaz

Abstract: The origin of rapid rotation in massive stars remains debated, although binary interactions are now often advocated as a cause. However, the broad and shallow lines in the spectra of fast rotators make direct detection of binarity difficult. In this paper, we report on the discovery and analysis of multiplicity for three fast-rotating massive stars: HD25631 (B3V), HD191495 (B0V), and HD46485 (O7V)… ▽ More The origin of rapid rotation in massive stars remains debated, although binary interactions are now often advocated as a cause. However, the broad and shallow lines in the spectra of fast rotators make direct detection of binarity difficult. In this paper, we report on the discovery and analysis of multiplicity for three fast-rotating massive stars: HD25631 (B3V), HD191495 (B0V), and HD46485 (O7V). They display strikingly similar TESS light curves, with two narrow eclipses superimposed on a sinusoidal variation due to reflection effects. We complement these photometric data by spectroscopy from various instruments (X-Shooter, Espadons, FUSE...), to further constrain the nature of these systems. The detailed analyses of these data demonstrates that the companions of the massive OB stars have low masses (~1Msol) with rather large radii (2-4 Rsol) and low temperatures (<15 kK). These companions display no UV signature, which would exclude a hot subdwarf nature, but disentangling of the large set of X-Shooter spectra of HD25631 revealed the typical signature of chromospheric activity in the companion's spectrum. In addition, despite the short orbital periods (P=3-7d), the fast-rotating OB-stars still display non-synchronized rotation and all systems appear young (<20Myr). This suggests that, as in a few other cases, these massive stars are paired in those systems with non-degenerate, low-mass PMS companions, implying that fast rotation would not be a consequence of a past binary interactions in their case. △ Less

Submitted 7 August, 2023; v1 submitted 4 August, 2023; originally announced August 2023.

Comments: accepted for publication by MNRAS

SRG/eROSITA survey of Be stars

Authors: Yael Naze, Jan Robrade

Abstract: Massive stars are known X-ray emitters and those belonging to the Be category are no exception. One type of X-ray emission even appears specific to that category, the gamma Cas phenomenon. Its actual incidence has been particularly difficult to assess. Thanks to four semesters of sky survey data taken by SRG (Spectrum Roentgen Gamma)/eROSITA, we revisit the question of the X-ray properties of Be s… ▽ More Massive stars are known X-ray emitters and those belonging to the Be category are no exception. One type of X-ray emission even appears specific to that category, the gamma Cas phenomenon. Its actual incidence has been particularly difficult to assess. Thanks to four semesters of sky survey data taken by SRG (Spectrum Roentgen Gamma)/eROSITA, we revisit the question of the X-ray properties of Be stars. Amongst a large catalog of Be stars, eROSITA achieved 170 detections (20% of sample), mostly corresponding to the earliest spectral types and/or close objects. While X-ray luminosities show an uninterrupted increasing trend with the X-ray-to-bolometric luminosity ratios, the X-ray hardness was split between a large group of soft (and fainter on average) sources and a smaller group of hard (and brighter on average) sources. The latter category gathers at least 34 sources, nearly all displaying early spectral types. Only a third of them were known before to display such X-ray properties. The actual incidence of hard and bright X-rays amongst early-type Be stars within 100--1000pc appears to be ~12%, which is far from negligible. At the other extreme, no bright supersoft X-ray emission seem to be associated to any of our targets. △ Less

Submitted 22 August, 2023; v1 submitted 25 July, 2023; originally announced July 2023.

Comments: accepted for publication by MNRAS

Revisiting the orbital motion of WR 138

Authors: Gregor Rauw, Yaël Nazé, Eric Gosset

Abstract: The optical spectrum of WR 138 exhibits emission lines typical of a WN6o star and absorption lines from a rapidly-rotating OB star. Using a large set of spectroscopic data, we establish a new orbital solution of the WN6o star based on the radial velocities of highly-ionized nitrogen lines. We show that the WN6o star moves on a 4.3 yr orbit with a comparatively low eccentricity of 0.16. The radial… ▽ More The optical spectrum of WR 138 exhibits emission lines typical of a WN6o star and absorption lines from a rapidly-rotating OB star. Using a large set of spectroscopic data, we establish a new orbital solution of the WN6o star based on the radial velocities of highly-ionized nitrogen lines. We show that the WN6o star moves on a 4.3 yr orbit with a comparatively low eccentricity of 0.16. The radial velocities of the OB star display considerable scatter. Our best estimates of the velocities of He I absorption lines result in a mass-ratio of $m_{\rm WN6o}/m_{\rm OB} = 0.53 \pm 0.09$. We disentangle the spectra of the two stars and derive a projected rotational velocity of $v\,\sin{i} = 350 \pm 10$ km s$^{-1}$ for the OB star. Our best orbital parameters, combined with the Gaia parallax of WR 138, are at odds with a previous interferometric detection of the companion, suggesting that there is either a bias in this detection or that WR 138 is actually a triple system. △ Less

Submitted 22 May, 2023; originally announced May 2023.

Comments: accepted for publication by New Astronomy

Discovery of extraordinary X-ray emission from magnetospheric interaction in the unique binary stellar system $ε$ Lupi

Authors: B. Das, V. Petit, Y. Nazé, M. F. Corcoran, D. H. Cohen, A. Biswas, P. Chandra, A. David-Uraz, M. A. Leutenegger, C. Neiner, H. Pablo, E. Paunzen, M. E. Shultz, A. ud-Doula, G. A. Wade

Abstract: We report detailed X-ray observations of the unique binary system $ε$ Lupi, the only known short-period binary consisting of two magnetic early-type stars. The components have comparably strong, but anti-aligned magnetic fields. The orbital and magnetic properties of the system imply that the magnetospheres overlap at all orbital phases, suggesting the possibility of variable inter-star magnetosph… ▽ More We report detailed X-ray observations of the unique binary system $ε$ Lupi, the only known short-period binary consisting of two magnetic early-type stars. The components have comparably strong, but anti-aligned magnetic fields. The orbital and magnetic properties of the system imply that the magnetospheres overlap at all orbital phases, suggesting the possibility of variable inter-star magnetospheric interaction due to the non-negligible eccentricity of the orbit. To investigate this effect, we observed the X-ray emission from $ε$ Lupi both near and away from periastron passage, using the Neutron Star Interior Composition Explorer mission (NICER) X-ray Telescope. We find that the system produces excess X-ray emission at the periastron phase, suggesting the presence of variable inter-star magnetospheric interaction. We also discover that the enhancement at periastron is confined to a very narrow orbital phase range ($\approx 5\%$ of the orbital period), but the X-ray properties close to periastron phase are similar to those observed away from periastron. From these observations, we infer that the underlying cause is magnetic reconnection heating the stellar wind plasma, rather than shocks produced by wind-wind collision. Finally, by comparing the behavior of $ε$ Lupi with that observed for cooler magnetic binary systems, we propose that elevated X-ray flux at periastron phase is likely a general characteristic of interacting magnetospheres irrespective of the spectral types of the constituent stars. △ Less

Submitted 29 June, 2023; v1 submitted 25 April, 2023; originally announced April 2023.

Comments: Accepted for publication in MNRAS (20 pages, 17 figures)

Diving into the magnetosphere of the Of?p star HD108

Authors: Gregor Rauw, Yaël Nazé, Asif ud-Doula, Coralie Neiner

Abstract: We analyse optical and X-ray spectroscopy of the Of?p star HD108, known for its strong dipolar magnetic field and its optical line profile variability with a timescale of $54 \pm 3$ yrs, interpreted as the stellar rotation period. Optical emission lines have now recovered from their minimum emission state reached in 2007 - 2008. The variations of the equivalent width of the H$α$ emission provide c… ▽ More We analyse optical and X-ray spectroscopy of the Of?p star HD108, known for its strong dipolar magnetic field and its optical line profile variability with a timescale of $54 \pm 3$ yrs, interpreted as the stellar rotation period. Optical emission lines have now recovered from their minimum emission state reached in 2007 - 2008. The variations of the equivalent width of the H$α$ emission provide constraints on the inclination of the rotation axis ($i$) and the obliquity of the magnetic axis ($β$). The best agreement between model and observations is found for ($i$, $β$) pairs with $i + β\simeq 85^{\circ}$ and $i \in [30^{\circ},55^{\circ}]$. The Balmer emission lines display stochastic variability at the $\sim 5$ % level on timescales of a few days. TESS photometry unveils transient modulations on similar timescales in addition to prominent red noise variations. A Chandra X-ray observation of December 2021, when the star was at a higher emission level, indicates a slight increase of the flux and a spectral hardening compared to the August 2002 XMM-Newton observation, taken near minimum emission state. Magnetohydrodynamic simulations are used to compute synthetic X-ray spectra. With our current best estimate of the $\dot{M}_{B=0}$ mass-loss rate, the simulated X-ray luminosity and spectral energy distribution agree very well with the observations. Finally, the radial velocities vary on a period of 8.5 years with a peak-to-peak amplitude of 10 - 11 km s$^{-1}$, suggesting orbital motion with an unseen companion of at least 4 M$_{\odot}$. △ Less

Submitted 2 March, 2023; originally announced March 2023.

Comments: Accepted for publication in MNRAS

The IACOB project VIII. Searching for empirical signatures of binarity in fast-rotating O-type stars

Authors: N. Britavskiy, S. Simón-Díaz, G. Holgado, S. Burssens, J. Maíz Apellániz, J. J. Eldridge, Y. Nazé, M. Pantaleoni González, A. Herrero

Abstract: The empirical distribution of projected rotational velocities (vsini) in massive O-type stars is characterized by a dominant slow velocity component and a tail of fast rotators. Binary interaction has been proposed to play a dominant role in the formation of this tail. We perform a complete and homogeneous search for empirical signatures of binarity in a sample of 54 fast-rotating stars with the a… ▽ More The empirical distribution of projected rotational velocities (vsini) in massive O-type stars is characterized by a dominant slow velocity component and a tail of fast rotators. Binary interaction has been proposed to play a dominant role in the formation of this tail. We perform a complete and homogeneous search for empirical signatures of binarity in a sample of 54 fast-rotating stars with the aim of evaluating this hypothesis. This working sample has been extracted from a larger sample of 415 Galactic O-type stars which covers the full range of vsini values. We use new and archival multi-epoch spectra in order to detect spectroscopic binary systems. We complement this information with Gaia proper motions and TESS photometric data to aid in the identification of runaway stars and eclipsing binaries, respectively. The identified fraction of single-lined spectroscopic binary (SB1) systems and apparently single stars among the fast-rotating sample is $\sim$18% and $\sim$70%, respectively. When comparing these percentages with those corresponding to the slow-rotating sample we find that our sample of fast rotators is characterized by a slightly larger percentage of SB1 systems ($\sim$18% vs. $\sim$13%) and a considerably smaller fraction of clearly detected SB2 systems (8% vs. 33%). Overall, there seems to be a clear deficit of spectroscopic binaries (SB1+SB2) among fast-rotating O-type stars ($\sim$26% vs. $\sim$46%). On the contrary, the fraction of runaway stars is significantly higher in the fast-rotating domain ($\sim$33-50%) than among those stars with vsini < 200 km/s. Lastly, almost 65% of the apparently single fast-rotating stars are runaways. Our empirical results seem to be in good agreement with the idea that the tail of fast-rotating O-type stars (with vsini > 200 km/s) is mostly populated by post-interaction binary products. △ Less

Submitted 15 March, 2023; v1 submitted 2 February, 2023; originally announced February 2023.

Comments: 33 pages, 16 figures, accepted for publication in "Astronomy and Astrophysics"

Journal ref: A&A 672, A22 (2023)

The Athena X-ray Integral Field Unit: a consolidated design for the system requirement review of the preliminary definition phase

Authors: Didier Barret, Vincent Albouys, Jan-Willem den Herder, Luigi Piro, Massimo Cappi, Juhani Huovelin, Richard Kelley, J. Miguel Mas-Hesse, Stéphane Paltani, Gregor Rauw, Agata Rozanska, Jiri Svoboda, Joern Wilms, Noriko Yamasaki, Marc Audard, Simon Bandler, Marco Barbera, Xavier Barcons, Enrico Bozzo, Maria Teresa Ceballos, Ivan Charles, Elisa Costantini, Thomas Dauser, Anne Decourchelle, Lionel Duband , et al. (274 additional authors not shown)

Abstract: The Athena X-ray Integral Unit (X-IFU) is the high resolution X-ray spectrometer, studied since 2015 for flying in the mid-30s on the Athena space X-ray Observatory, a versatile observatory designed to address the Hot and Energetic Universe science theme, selected in November 2013 by the Survey Science Committee. Based on a large format array of Transition Edge Sensors (TES), it aims to provide sp… ▽ More The Athena X-ray Integral Unit (X-IFU) is the high resolution X-ray spectrometer, studied since 2015 for flying in the mid-30s on the Athena space X-ray Observatory, a versatile observatory designed to address the Hot and Energetic Universe science theme, selected in November 2013 by the Survey Science Committee. Based on a large format array of Transition Edge Sensors (TES), it aims to provide spatially resolved X-ray spectroscopy, with a spectral resolution of 2.5 eV (up to 7 keV) over an hexagonal field of view of 5 arc minutes (equivalent diameter). The X-IFU entered its System Requirement Review (SRR) in June 2022, at about the same time when ESA called for an overall X-IFU redesign (including the X-IFU cryostat and the cooling chain), due to an unanticipated cost overrun of Athena. In this paper, after illustrating the breakthrough capabilities of the X-IFU, we describe the instrument as presented at its SRR, browsing through all the subsystems and associated requirements. We then show the instrument budgets, with a particular emphasis on the anticipated budgets of some of its key performance parameters. Finally we briefly discuss on the ongoing key technology demonstration activities, the calibration and the activities foreseen in the X-IFU Instrument Science Center, and touch on communication and outreach activities, the consortium organisation, and finally on the life cycle assessment of X-IFU aiming at minimising the environmental footprint, associated with the development of the instrument. Thanks to the studies conducted so far on X-IFU, it is expected that along the design-to-cost exercise requested by ESA, the X-IFU will maintain flagship capabilities in spatially resolved high resolution X-ray spectroscopy, enabling most of the original X-IFU related scientific objectives of the Athena mission to be retained. (abridged). △ Less

Submitted 28 November, 2022; v1 submitted 30 August, 2022; originally announced August 2022.

Comments: 48 pages, 29 figures, Accepted for publication in Experimental Astronomy with minor editing

The X-ray emission of Be+stripped star binaries

Authors: Yael Naze, Gregor Rauw, Myron A. Smith, Christian Motch

Abstract: Using observations from Chandra, Swift and XMM-Newton, we investigate the high-energy properties of all known (18) Be+sdO systems as well as 7 additional Be binaries suspected to harbour stripped stars. The observed X-ray properties are found to be similar to those observed for other Be samples. The vast majority of these systems (15 out of 25) display very faint (and soft) X-ray emission, and six… ▽ More Using observations from Chandra, Swift and XMM-Newton, we investigate the high-energy properties of all known (18) Be+sdO systems as well as 7 additional Be binaries suspected to harbour stripped stars. The observed X-ray properties are found to be similar to those observed for other Be samples. The vast majority of these systems (15 out of 25) display very faint (and soft) X-ray emission, and six others are certainly not bright X-ray sources. Only two systems display gamma-Cas characteristics (i.e. bright and hard X-rays), and one of them is a new detection: HD37202 (zeta Tau). It presents an extremely hard spectrum, due to a combination of high temperature and high absorption (possibly due to its high inclination). In parallel, it may be noted that the previously reported cyclic behaviour of this Be star has disappeared in recent years. Instead, shorter cycles and symmetric line profiles are observed for the Halpha line. It had been recently suggested that the peculiar X-ray emissions observed in gamma-Cas stars could arise from a collision between the disk of a Be star and the wind of its hot, stripped-star companion. The small fraction of gamma-Cas analogs in this sample, as well as the properties of the known companions of the gamma-Cas cases (low mass or not extremely hot, contrary to predictions), combined to the actual stripped-star and colliding-wind empirical knowledge, make the disk-wind collision an unlikely scenario to explain the gamma-Cas phenomenon. △ Less

Submitted 25 August, 2022; v1 submitted 8 August, 2022; originally announced August 2022.

Comments: accepted for publication by MNRAS

Ultraviolet Spectropolarimetry With Polstar: Using Polstar to test Magnetospheric Mass-loss Quenching

Authors: M. E. Shultz, R. Casini, M. C. M. Cheung, A. David-Uraz, T. del Pino Alemán, C. Erba, C. P. Folsom, K. Gayley, R. Ignace, Z. Keszthelyi, O. Kochukhov, Y. Nazé, C. Neiner, M. Oksala, V. Petit, P. A. Scowen, N. Sudnik, A. ud-Doula, J. S. Vink, G. A. Wade

Abstract: Polstar is a proposed NASA MIDEX space telescope that will provide high-resolution, simultaneous full-Stokes spectropolarimetry in the far ultraviolet, together with low-resolution linear polarimetry in the near ultraviolet. This observatory offers unprecedented capabilities to obtain unique information on the magnetic and plasma properties of the magnetospheres of hot stars. We describe an observ… ▽ More Polstar is a proposed NASA MIDEX space telescope that will provide high-resolution, simultaneous full-Stokes spectropolarimetry in the far ultraviolet, together with low-resolution linear polarimetry in the near ultraviolet. This observatory offers unprecedented capabilities to obtain unique information on the magnetic and plasma properties of the magnetospheres of hot stars. We describe an observing program making use of the known population of magnetic hot stars to test the fundamental hypothesis that magnetospheres should act to rapidly drain angular momentum, thereby spinning the star down, whilst simultaneously reducing the net mass-loss rate. Both effects are expected to lead to dramatic differences in the evolution of magnetic vs. non-magnetic stars. △ Less

Submitted 26 July, 2022; originally announced July 2022.

Comments: 20 pages, 10 figures, accepted for publication in ApSS. arXiv admin note: substantial text overlap with arXiv:2111.06434

UV Spectropolarimetry with Polstar: Massive Star Binary Colliding Winds

Authors: Nicole St-Louis, Kenneth Gayley, D. John Hillier, Richard Ignace, Carol E. Jones, Alexandre David-Uraz, Noel D. Richardson, Jorick S. Vink, Geraldine J. Peters, Jennifer L. Hoffman, Yael Nazé, Heloise Stevance, Tomer Shenar, Andrew G. Fullard, Jaimie R. Lomax, Paul A. Scowen

Abstract: The winds of massive stars are important for their direct impact on the interstellar medium, and for their influence on the final state of a star prior to it exploding as a supernova. However, the dynamics of these winds is understood primarily via their illumination from a single central source. The Doppler shift seen in resonance lines is a useful tool for inferring these dynamics, but the mappi… ▽ More The winds of massive stars are important for their direct impact on the interstellar medium, and for their influence on the final state of a star prior to it exploding as a supernova. However, the dynamics of these winds is understood primarily via their illumination from a single central source. The Doppler shift seen in resonance lines is a useful tool for inferring these dynamics, but the mapping from that Doppler shift to the radial distance from the source is ambiguous. Binary systems can reduce this ambiguity by providing a second light source at a known radius in the wind, seen from orbitally modulated directions. From the nature of the collision between the winds, a massive companion also provides unique additional information about wind momentum fluxes. Since massive stars are strong ultraviolet (UV) sources, and UV resonance line opacity in the wind is strong, UV instruments with a high resolution spectroscopic capability are essential for extracting this dynamical information. Polarimetric capability also helps to further resolve ambiguities in aspects of the wind geometry that are not axisymmetric about the line of sight, because of its unique access to scattering direction information. We review how the proposed MIDEX-scale mission Polstar can use UV spectropolarimetric observations to critically constrain the physics of colliding winds, and hence radiatively-driven winds in general. We propose a sample of 20 binary targets, capitalizing on this unique combination of illumination by companion starlight, and collision with a companion wind, to probe wind attributes over a range in wind strengths. Of particular interest is the hypothesis that the radial distribution of the wind acceleration is altered significantly, when the radiative transfer within the winds becomes optically thick to resonance scattering in multiple overlapping UV lines. △ Less

Submitted 14 July, 2022; originally announced July 2022.

Comments: 26 pages, 12 figures, Review in a topical collection series of Astrophysics and Space Sciences on the proposed Polstar satellite. arXiv admin note: substantial text overlap with arXiv:2111.11552

Ultraviolet Spectropolarimetric Diagnostics of Hot Star Magnetospheres

Authors: Asif ud-Doula, M. C. M. Cheung, A. David-Uraz, C. Erba, C. P. Folsom, K. Gayley, Y. Naze, C. Neiner, V. Petit, R. Prinja, M. E. Shultz, N. Sudnik, J. S. Vink, G. A. Wade

Abstract: Several space missions and instruments for UV spectropolarimetry are in preparation, such as the proposed NASA MIDEX Polstar project, the proposed ESA M mission Arago, and the Pollux instrument on the future LUVOIR-like NASA flagship mission. In the frame of Polstar, we have studied the capabilities these observatories would offer to gain information on the magnetic and plasma properties of the ma… ▽ More Several space missions and instruments for UV spectropolarimetry are in preparation, such as the proposed NASA MIDEX Polstar project, the proposed ESA M mission Arago, and the Pollux instrument on the future LUVOIR-like NASA flagship mission. In the frame of Polstar, we have studied the capabilities these observatories would offer to gain information on the magnetic and plasma properties of the magnetospheres of hot stars, helping us test the fundamental hypothesis that magnetospheres should act to rapidly drain angular momentum, thereby spinning the star down, whilst simultaneously reducing the net mass-loss rate. Both effects are expected to lead to dramatic differences in the evolution of magnetic vs. non-magnetic stars. △ Less

Submitted 26 June, 2022; originally announced June 2022.

Comments: Accepted for publication in Astrophysics and Space Science. arXiv admin note: substantial text overlap with arXiv:2111.06434

Report number: ASTR-D-22-00095R3

The X-ray emission of gamma Cassiopeiae during the 2020-2021 disc eruption

Authors: Gregor Rauw, Yaël Nazé, Christian Motch, Myron A. Smith, Joan Guarro Fló, Raimundo Lopes de Oliveira

Abstract: gamma Cas is known for its hard and intense X-ray emission that could trace accretion by a compact companion, wind interaction with a hot sub-dwarf companion, or magnetic interaction between the star and its Be decretion disc. These scenarios should lead to diverse dependences of the hard X-ray emission on disc density. We collected X-ray observations of gamma Cas during an episode of enhanced dis… ▽ More gamma Cas is known for its hard and intense X-ray emission that could trace accretion by a compact companion, wind interaction with a hot sub-dwarf companion, or magnetic interaction between the star and its Be decretion disc. These scenarios should lead to diverse dependences of the hard X-ray emission on disc density. We collected X-ray observations of gamma Cas during an episode of enhanced disc activity around January 2021. We investigate the variations in the disc properties using time series of dedicated optical spectroscopy and existing broadband photometry. Epoch-dependent Doppler maps of the H-alpha, H-beta, and He I 5876 emission lines are built to characterise the emission regions in velocity space. We analyse 4 XMM-Newton observations taken at key phases of the enhanced disc activity episode. Archival data are used to study the long-term correlation between optical and X-ray emission. Optical spectroscopy unveils an increase in the radial extent of the emission regions during the episode of enhanced disc activity, whilst no increase in the V-band flux is recorded. Doppler maps do not reveal any stable feature in the disc resulting from the putative action of the companion on the outer parts of the Be disc. No increase in the hard emission is observed in relation to the enhanced disc activity. However, at two occasions, the soft X-ray emission of gamma Cas is strongly attenuated, suggesting more efficient obscuration by a large flaring Be disc. There is a strong correlation between the long-term variations in the X-ray flux and in the V-band photometry. The observed behaviour of gamma Cas suggests no direct link between the properties of the outer regions of the Be disc and the hard X-ray emission, but favours a link between the level of X-ray emission and the properties of the inner part of the Be disc. These results thus disfavour an accretion or colliding wind scenario. △ Less

Submitted 17 June, 2022; originally announced June 2022.

Comments: Accepted for publication in A&A

Journal ref: A&A 664, A184 (2022)

Eight years of TIGRE robotic spectroscopy: Operational experience and selected scientific results

Authors: J. N. González-Perez, M. Mittag, J. H. M. M. Schmitt, K. -P. Schröder, D. Jack, G. Rauw, Y. Nazé

Abstract: TIGRE (Telescopio Internacional de Guanajuato Robótico Espectroscópico) has been operating in fully robotic mode in the Observatory La Luz (Guanajuato, Mexico) since the end of 2013. With its sole instrument, HEROS, an échelle spectrograph with a spectral resolution R~20000, TIGRE has collected more than 48000 spectra of 1151 different sources with a total exposure time of more than 11000 hours in… ▽ More TIGRE (Telescopio Internacional de Guanajuato Robótico Espectroscópico) has been operating in fully robotic mode in the Observatory La Luz (Guanajuato, Mexico) since the end of 2013. With its sole instrument, HEROS, an échelle spectrograph with a spectral resolution R~20000, TIGRE has collected more than 48000 spectra of 1151 different sources with a total exposure time of more than 11000 hours in these eight years. Here we briefly describe the system and the upgrades performed during the last years. We present the statistics of the weather conditions at the La Luz Observatory, emphasizing the characteristics that affect the astronomical observations. We evaluate the performance and efficiency of TIGRE, both optical and operational, and describe the improvements of the system implemented to optimize the telescope's performance and meet the requirements of the astronomer in terms of timing constraints for the observations and the quality of the spectra. We describe the actions taken to slow down the optical efficiency loss due to the aging of the optical surfaces as well as the upgrades of the scheduler and the observing procedures to minimize the time lost due to interrupted observations or observations that do not reach the required quality. Finally, we highlight a few of the main scientific results obtained with TIGRE data. △ Less

Submitted 6 June, 2022; originally announced June 2022.

Comments: 26 pages, 14 figures, accepted in Frontiers in Astronomy and Space Sciences

Apsidal motion in massive eccentric binaries: The case of CPD-41$^\circ$7742, and HD 152218 revisited

Authors: Sophie Rosu, Gregor Rauw, Yaël Nazé, Eric Gosset, Christiaan Sterken

Abstract: This paper is part of a study of the apsidal motion in close eccentric massive binary systems, which aims to constrain the internal structure of the stars. We focus on the binary CPD-41°7742 and revisit HD152218. Independent studies of CPD-41°7742 in the past showed large discrepancies in the longitude of periastron of the orbit, hinting at the presence of apsidal motion. We perform a consistent a… ▽ More This paper is part of a study of the apsidal motion in close eccentric massive binary systems, which aims to constrain the internal structure of the stars. We focus on the binary CPD-41°7742 and revisit HD152218. Independent studies of CPD-41°7742 in the past showed large discrepancies in the longitude of periastron of the orbit, hinting at the presence of apsidal motion. We perform a consistent analysis of all observational data, explicitly accounting for the apsidal motion. We use spectroscopic and photometric observations of CPD-41°7742 to infer values for the fundamental stellar and binary parameters. We apply a disentangling method to the spectra to simultaneously derive the RVs at the times of observation and reconstruct the individual stellar spectra. These are analysed by means of CMFGEN to determine the stellar properties. We determine the apsidal motion rate in two ways: We complement our RVs with those reported in the literature and we use the phase shifts between the primary and secondary eclipses. The light curves are analysed by means of Nightfall to constrain the orbital inclination and stellar masses. Stellar structure and evolution models are constructed with Cles. Different prescriptions for the mixing are adopted. Photometric data of HD152218 are analysed and stellar evolution models are built. The binary CPD-41°7742 displays apsidal motion at a rate of 15.38+0.42-0.51° yr-1. Our analysis of the observational data of CPD-41°7742 explicitly accounting for the apsidal motion allows us to explain the discrepancy in periastron longitudes. The age estimates are in good agreement with estimates obtained for other massive binaries in NGC 6231. This study confirms the need for enhanced mixing in the stellar evolution models to reproduce the observational stellar properties; this points towards larger convective cores than usually considered. △ Less

Submitted 25 May, 2022; v1 submitted 23 May, 2022; originally announced May 2022.

Comments: arXiv admin note: text overlap with arXiv:2202.02012

Journal ref: A&A 664, A98 (2022)

Modeling the Optical to Ultraviolet Polarimetric Variability from Thomson Scattering in Colliding Wind Binaries

Authors: Richard Ignace, Andrew Fullard, Manisha Shrestha, Yael Naze, Kenneth Gayley, Jennifer L Hoffman, Jamie R Lomax, Nicole St-Louis

Abstract: Massive star binaries are critical laboratories for measuring masses and stellar wind mass-loss rates. A major challenge is inferring viewing inclination and extracting information about the colliding wind interaction (CWI) region. Polarimetric variability from electron scattering in the highly ionized winds provides important diagnostic information about system geometry. We combine for the first… ▽ More Massive star binaries are critical laboratories for measuring masses and stellar wind mass-loss rates. A major challenge is inferring viewing inclination and extracting information about the colliding wind interaction (CWI) region. Polarimetric variability from electron scattering in the highly ionized winds provides important diagnostic information about system geometry. We combine for the first time the well-known generalized treatment of \citet{brown_polarisation_1978} for variable polarization from binaries with the semi-analytic solution for the geometry and surface density CWI shock interface between the winds based on Canto et al 1996. Our calculations include some simplifications in the form of inverse square-law wind densities and the assumption of axisymmetry, but in so doing arrive at several robust conclusions. One is that when the winds are nearly equal (e.g., O\,+\,O binaries), the polarization has a relatively mild decline with binary separation. Another is that despite Thomson scattering being a gray opacity, the continuum polarization can show chromatic effects at ultraviolet wavelengths but will be mostly constant at longer wavelengths. Finally, when one wind dominates the other, as for example in WR+OB binaries, the polarization is expected to be larger at wavelengths where the OB component is more luminous, and generally smaller at wavelengths where the WR component is more luminous. This behavior arises because from the perspective of the WR star, the distortion of the scattering envelope from spherical is a minor perturbation situated far from the WR star. By contrast, the polarization contribution from the OB star is dominated by the geometry of the CWI shock. △ Less

Submitted 16 May, 2022; originally announced May 2022.

Comments: accepted for publication in the Astrophysical Journal. arXiv admin note: text overlap with arXiv:2111.11552

A Gaia view on the star formation in the Monoceros OB1 and R1 associations

Authors: Beomdu Lim, Yael Naze, Jongsuk Hong, Sung-yong Yoon, Jinhee Lee, Narae Hwang, Byeong-Gon Park, Jeong-Eun Lee

Abstract: Stellar kinematics provides the key to understanding star formation process. In this respect, we present a kinematic study of the Monoceros OB1 (Mon OB1) and R1 (Mon R1) associations using the recent Gaia data and radial velocities of stars derived from high-resolution spectroscopy and the literature. A total of 728 members are selected using the criteria based on the intrinsic properties of young… ▽ More Stellar kinematics provides the key to understanding star formation process. In this respect, we present a kinematic study of the Monoceros OB1 (Mon OB1) and R1 (Mon R1) associations using the recent Gaia data and radial velocities of stars derived from high-resolution spectroscopy and the literature. A total of 728 members are selected using the criteria based on the intrinsic properties of young stars, parallaxes, and proper motions. The spatial distribution and kinematic properties of members show that these associations have distinct substructures. In Mon OB1, we find one northern group and two southern groups. Mon R1 is composed of three small stellar groups that are spatially and kinematically distinct. Some stars are found in a halo around these two associations. We detect patterns of expansion for most stellar groups in the associations. In addition, two stellar groups in Mon OB1 show the signature of rotation, which provides an important constraint on cluster formation. The star formation history of Mon OB1 is slightly revised. Star formation first occurred in the southern region and subsequently in the northern region. Recent star-forming events ignited deeper into the southern region, while some stars are escaping from Mon OB1, forming a halo. Mon R1 might have formed at the same epoch as the formation of the northern group in Mon OB1. Given that star formation is taking place on different scales along a large arc-like structure, Mon OB1 and Mon R1 may be the results of hierarchical star formation. △ Less

Submitted 1 April, 2022; originally announced April 2022.

Comments: 18 pages, 16 figures, accepted for publication in AJ

X-ray response to disk evolution in two gamma-Cas stars

Authors: Yael Naze, Gregor Rauw, Terrence Bohlsen, Bernard Heathcote, Padric Mc Gee, Paulo Cacella, Christian Motch

Abstract: The Halpha emission of a set of southern gamma-Cas stars was monitored since 2019, with the aim of detecting transition events and examining how their peculiar X-ray emission would react in such cases. Two stars, HD119682 and V767Cen, were found to display slowly decreasing disk emissions. These decreases were not perfectly monotonic and several temporary and limited re-building events were observ… ▽ More The Halpha emission of a set of southern gamma-Cas stars was monitored since 2019, with the aim of detecting transition events and examining how their peculiar X-ray emission would react in such cases. Two stars, HD119682 and V767Cen, were found to display slowly decreasing disk emissions. These decreases were not perfectly monotonic and several temporary and limited re-building events were observed. For HD119682, the emission component in Halpha disappeared in mid-July 2020. In X-rays, the X-ray flux was twice smaller than recorded two decades ago but of a similar level as observed a decade ago. The X-ray flux decreased over the campaign by 30%, but the hardness remained similar in datasets of all epochs. In particular, the gamma-Cas character remained as clear as before even when there was no trace of disk emission in the Halpha line. For V767Cen, the full disappearance of disk emission in Halpha never occurred. We followed closely a disk rebuilding event, but no significant change in flux or hardness was detected. These behaviours are compared to those of other gamma-Cas stars and their consequences on the X-ray generation are discussed. △ Less

Submitted 1 February, 2022; originally announced February 2022.

Comments: accepted by MNRAS

Science with the Ultraviolet Explorer (UVEX)

Authors: S. R. Kulkarni, Fiona A. Harrison, Brian W. Grefenstette, Hannah P. Earnshaw, Igor Andreoni, Danielle A. Berg, Joshua S. Bloom, S. Bradley Cenko, Ryan Chornock, Jessie L. Christiansen, Michael W. Coughlin, Alexander Wuollet Criswell, Behnam Darvish, Kaustav K. Das, Kishalay De, Luc Dessart, Don Dixon, Bas Dorsman, Kareem El-Badry, Christopher Evans, K. E. Saavik Ford, Christoffer Fremling, Boris T. Gansicke, Suvi Gezari, Y. Goetberg , et al. (31 additional authors not shown)

Abstract: UVEX is a proposed medium class Explorer mission designed to provide crucial missing capabilities that will address objectives central to a broad range of modern astrophysics. The UVEX design has two co-aligned wide-field imagers operating in the FUV and NUV and a powerful broadband medium resolution spectrometer. In its two-year baseline mission, UVEX will perform a multi-cadence synoptic all-sky… ▽ More UVEX is a proposed medium class Explorer mission designed to provide crucial missing capabilities that will address objectives central to a broad range of modern astrophysics. The UVEX design has two co-aligned wide-field imagers operating in the FUV and NUV and a powerful broadband medium resolution spectrometer. In its two-year baseline mission, UVEX will perform a multi-cadence synoptic all-sky survey 50/100 times deeper than GALEX in the NUV/FUV, cadenced surveys of the Large and Small Magellanic Clouds, rapid target of opportunity followup, as well as spectroscopic followup of samples of stars and galaxies. The science program is built around three pillars. First, UVEX will explore the low-mass, low-metallicity galaxy frontier through imaging and spectroscopic surveys that will probe key aspects of the evolution of galaxies by understanding how star formation and stellar evolution at low metallicities affect the growth and evolution of low-metallicity, low-mass galaxies in the local universe. Such galaxies contain half the mass in the local universe, and are analogs for the first galaxies, but observed at distances that make them accessible to detailed study. Second, UVEX will explore the dynamic universe through time-domain surveys and prompt spectroscopic followup capability will probe the environments, energetics, and emission processes in the early aftermaths of gravitational wave-discovered compact object mergers, discover hot, fast UV transients, and diagnose the early stages of stellar explosions. Finally, UVEX will become a key community resource by leaving a large all-sky legacy data set, enabling a wide range of scientific studies and filling a gap in the new generation of wide-field, sensitive optical and infrared surveys provided by the Rubin, Euclid, and Roman observatories. This paper discusses the scientific potential of UVEX, and the broad scientific program. △ Less

Submitted 17 January, 2023; v1 submitted 30 November, 2021; originally announced November 2021.

Comments: 69 pages, 43 figures

Ultraviolet Spectropolarimetry:Conservative and Nonconservative Mass Transfer in OB Interacting Binaries

Authors: Geraldine J. Peters, Ken Gayley, Richard Ignace, Carol E. Jones, Yael Naze, Nicole St-Louis, Heloise Stevance, Jorick S. Vink, Noel D. Richardson, Jennifer L. Hoffman, Jamie R. Lomax, Tomer Shenar, Andrew G. Fullard, Paul A. Scowen

Abstract: One objective of the Polstar spectropolarimetry mission is to characterize the degree of nonconservative mass transfer that occurs at various stages of binary evolution, from the initial mass reversal to the late Algol phase. The proposed instrument combines spectroscopic and polarimetric capabilities, where the spectroscopy can resolve Doppler shifts in UV resonance lines with 10 km/s precision,… ▽ More One objective of the Polstar spectropolarimetry mission is to characterize the degree of nonconservative mass transfer that occurs at various stages of binary evolution, from the initial mass reversal to the late Algol phase. The proposed instrument combines spectroscopic and polarimetric capabilities, where the spectroscopy can resolve Doppler shifts in UV resonance lines with 10 km/s precision, and polarimetry can resolve linear polarization with 1e-3 precision or better. The spectroscopy will identify absorption by mass streams seen in projection against the stellar disk as a function of orbital phase, hot accretion spots, as well as scattering from extended splash structures, circumbinary disks, and other flows in and above/below the orbital plane (e.g. jets) that fail to be transferred conservatively. The polarimetry affects more the light coming from material not seen against the stellar disk, allowing the geometry of the scattering to be tracked, resolving ambiguities left by the spectroscopy and light-curve information. For example, nonconservative mass streams ejected in the polar direction will produce polarization of the opposite sign from conservative transfer accreting in the orbital plane. Also, time domain coverage over a range of phases of the binary orbit are well supported by the Polstar observing strategy. Combining these elements will significantly improve our understanding of the mass transfer process and the amount of mass that can escape from the system, an important channel for changing the final mass, and ultimate supernova, of the large number of massive stars found in binaries at close enough separation to undergo interaction. △ Less

Submitted 12 October, 2022; v1 submitted 27 November, 2021; originally announced November 2021.

Comments: Refereed paper in Ap&SS 367:Topical Collection, 23 pages, 10 figures

Ultraviolet Spectropolarimetry with Polstar: Clumping and Mass-loss Rate Corrections

Authors: Ken Gayley, Jorick S. Vink, Asif ud-Doula, Alexandre David-Uraz, Richard Ignace, Raman Prinja, Nicole St-Louis, Sylvia Ekström, Yaël Nazé, Tomer Shenar, Paul A. Scowen, Natallia Sudnik, Stan P. Owocki, Jon O. Sundqvist, Florian A. Driessen, Levin Hennicker

Abstract: The most massive stars are thought to lose a significant fraction of their mass in a steady wind during the main-sequence and blue supergiant phases. This in turn sets the stage for their further evolution and eventual supernova, with consequences for ISM energization and chemical enrichment. Understanding these processes requires accurate observational constraints on the mass-loss rates of the mo… ▽ More The most massive stars are thought to lose a significant fraction of their mass in a steady wind during the main-sequence and blue supergiant phases. This in turn sets the stage for their further evolution and eventual supernova, with consequences for ISM energization and chemical enrichment. Understanding these processes requires accurate observational constraints on the mass-loss rates of the most luminous stars, which can also be used to test theories of stellar wind generation. In the past, mass-loss rates have been characterized via collisional emission processes such as H$α$ and free-free radio emission, but these so-called "density squared" diagnostics require correction in the presence of widespread clumping. Recent observational and theoretical evidence points to the likelihood of a ubiquitously high level of such clumping in hot-star winds, but quantifying its effects requires a deeper understanding of the complex dynamics of radiatively driven winds. Furthermore, large-scale structures arising from surface anisotropies and propagating throughout the wind can further complicate the picture by introducing further density enhancements, affecting mass-loss diagnostics. Time series spectroscopy of UV resonance lines with high resolution and high signal-to-noise are required to better understand this complex dynamics, and help correct "density squared" diagnostics of mass-loss rates. The proposed Polstar mission easily provides the necessary resolution at the sound-speed scale of 20 km s$^{-1}$, on three dozen bright targets with signal-to noise an order of magnitude above that of the celebrated IUE MEGA campaign, via continuous observations that track structures advecting through the wind in real time. △ Less

Submitted 12 December, 2021; v1 submitted 22 November, 2021; originally announced November 2021.

Comments: white paper

Ultraviolet Spectropolarimetry with Polstar: Massive Star Binary Colliding Winds

Authors: Nicole St-Louis, Kenneth Gayley, Desmond John Hillier, Richard Ignace, Carol E. Jones, Alexandre David-Uraz, Noel D. Richardson, Jorick S. Vink, Geraldine J. Peters, Jennifer L. Hoffman, Yael Naze, Heloise Stevance, Tomer Shenar, Andrew G. Fullard, Jamie R. Lomax, Paul A. Scowen

Abstract: As sources of chemical enrichment, ionizing radiation and energetic feedback, massive stars drive the ecology of their host galaxies despite their relative rarity, additionally to yielding compact remnants, which can generate gravitational waves. The evolution of massive stars is crucially informed by their detailed mass-loss history; however, wind structures on a variety of scales cause important… ▽ More As sources of chemical enrichment, ionizing radiation and energetic feedback, massive stars drive the ecology of their host galaxies despite their relative rarity, additionally to yielding compact remnants, which can generate gravitational waves. The evolution of massive stars is crucially informed by their detailed mass-loss history; however, wind structures on a variety of scales cause important uncertainties on their mass-loss rates. Binary systems can place further constraints on the mass-loss properties of massive stars, especially colliding-wind binaries. In this paper, we review how the proposed MIDEX-scale mission Polstar can critically constrain the physics of colliding winds (and hence radiatively-driven winds in general) with ultraviolet spectropolarimetric observations, providing an unprecedented improvement on the accuracy of the determination of both mass-loss rates and the velocity structure of the winds of massive stars. We propose a sample of 17 targets that will allow us to study a variety of wind-colliding systems spanning a large parameter space using the spatial information yielded by both spectroscopic and polarimetric data obtained with Polstar. △ Less

Submitted 16 December, 2021; v1 submitted 22 November, 2021; originally announced November 2021.

Comments: 21 pages, 12 figures 1 table, Whitepaper

Velocity monitoring of gamma-Cas stars reveals their binarity status

Authors: Yael Naze, Gregor Rauw, Stefan Czesla, Myron A. Smith, Jan Robrade

Abstract: The binary status of gamma-Cas stars has been discussed while theoretically examining the origin of their peculiar X-ray emission. However, except in two cases, no systematic radial velocity monitoring of these stars had been undertaken yet to clarify their status. We now fill this gap using TIGRE, CARMENES, and UVES high-resolution spectroscopy. Velocities were determined for 16 stars, revealing… ▽ More The binary status of gamma-Cas stars has been discussed while theoretically examining the origin of their peculiar X-ray emission. However, except in two cases, no systematic radial velocity monitoring of these stars had been undertaken yet to clarify their status. We now fill this gap using TIGRE, CARMENES, and UVES high-resolution spectroscopy. Velocities were determined for 16 stars, revealing shifts and/or changes in line profiles. The orbit of six new binaries could be determined: the long periods (80-120d) and small velocity amplitudes (5-7km/s) suggest low mass companions (0.6-1 M$_{\odot}$). The properties of the known gamma-Cas binaries appear similar to those of other Be systems, with no clear-cut separation between them. One of the new systems is a candidate for a rare case of quadruple system involving a Be star. Five additional gamma-Cas stars display velocity variations compatible with the presence of companions, but no orbital solution could yet be formally established for them hence they only receive the status of "binary candidate". △ Less

Submitted 18 November, 2021; originally announced November 2021.

Comments: accepted by MNRAS

Ultraviolet Spectropolarimetry: on the origin of rapidly rotating B stars

Authors: C. E. Jones, J. Labadie-Bartz, D. V. Cotton, Y. Nazé, G. J. Peters, D. J. Hillier, C. Neiner, N. D. Richardson, J. L. Hoffman, A. C. Carciofi, J. P. Wisniewski, K. G. Gayley, M. W. Suffak, R. Ignace, P. A. Scowen

Abstract: UV spectroscopy and spectropolarimetry hold the key to understanding certain aspects of massive stars that are largely inaccessible with optical or longer wavelength observations. This is especially true for the rapidly-rotating Be and Bn stars, owing to their high temperatures, geometric asymmetries, binary properties, and evolutionary history. UV spectropolarimetric observations are extremely se… ▽ More UV spectroscopy and spectropolarimetry hold the key to understanding certain aspects of massive stars that are largely inaccessible with optical or longer wavelength observations. This is especially true for the rapidly-rotating Be and Bn stars, owing to their high temperatures, geometric asymmetries, binary properties, and evolutionary history. UV spectropolarimetric observations are extremely sensitive to the photospheric consequences of rapid rotation (i.e. oblateness, temperature, and surface gravity gradients). Our polarized radiative-transfer modelling predicts that with low-resolution UV spectropolarimetry covering 120 -- 300 nm the inclination angle of a rapid rotator can be determined to within 5 degrees, and the rotation rate to within 1%. The origin of rapid rotation in Be/n stars can be explained by either single-star or binary evolution, but their relative importance is largely unknown. Some Be stars have hot sub-luminous (sdO) companions, which at an earlier phase transferred their envelope (and with it mass and angular momentum) to the present-day rapid rotator. Through spectral modelling of a wide range of simulated Be/n+sdO configurations, we demonstrate that high-resolution high-SNR UV spectroscopy can detect an sdO star even when $\sim$1,000 times fainter in the UV than its Be/n star companion. This degree of sensitivity is needed to more fully explore the parameter space of Be/n+sdO binaries, which so far has been limited to about a dozen systems with relatively luminous sdO stars. We suggest that a UV spectropolarimetric survey of Be/n stars is the next step forward in understanding this population. Such a dataset would, when combined with population synthesis models, allow for the determination of the relative importance of the possible evolutionary pathways traversed by these stars, which is also crucial for understanding their future evolution and fate. △ Less

Submitted 27 December, 2022; v1 submitted 15 November, 2021; originally announced November 2021.

Comments: 38 pages, 16 figures, 1 table, topical collection in Astrophysics and Space Science: UV Spectropolarimetry for Stellar, Interstellar, and Exoplanetary Astrophysics with Polstar

Journal ref: Astrophysics and Space Science, Volume 367, Issue 12, article id.124, December 2022

Ultraviolet Spectropolarimetry With Polstar: Hot Star Magnetospheres

Authors: M. E. Shultz, R. Casini, M. C. M. Cheung, A. David-Uraz, T. del Pino Alemán, C. Erba, C. P. Folsom, K. Gayley, R. Ignace, Z. Keszthelyi, O. Kochukhov, Y. Nazé, C. Neiner, M. Oksala, V. Petit, P. A. Scowen, N. Sudnik, A. ud-Doula, J. S. Vink, G. A. Wade

Abstract: Polstar is a proposed NASA MIDEX space telescope that will provide high-resolution, simultaneous full-Stokes spectropolarimetry in the far ultraviolet, together with low-resolution linear polarimetry in the near ultraviolet. In this white paper, we describe the unprecedented capabilities this observatory would offer in order to obtain unique information on the magnetic and plasma properties of the… ▽ More Polstar is a proposed NASA MIDEX space telescope that will provide high-resolution, simultaneous full-Stokes spectropolarimetry in the far ultraviolet, together with low-resolution linear polarimetry in the near ultraviolet. In this white paper, we describe the unprecedented capabilities this observatory would offer in order to obtain unique information on the magnetic and plasma properties of the magnetospheres of hot stars. This would enable a test of the fundamental hypothesis that magnetospheres should act to rapidly drain angular momentum, thereby spinning the star down, whilst simultaneously reducing the net mass-loss rate. Both effects are expected to lead to dramatic differences in the evolution of magnetic vs. non-magnetic stars. △ Less

Submitted 9 December, 2021; v1 submitted 11 November, 2021; originally announced November 2021.

Comments: White paper, 40 pages

Ultraviolet Line Profiles of Slowly Rotating Massive Star Winds Using the "Analytic Dynamical Magnetosphere" Formalism

Authors: C. Erba, A. David-Uraz, V. Petit, L. Hennicker, C. Fletcher, A. W. Fullerton, Y. Nazé, J. Sundqvist, A. ud-Doula

Abstract: Recent large-scale spectropolarimetric surveys have established that a small but significant percentage of massive stars host stable, surface dipolar magnetic fields with strengths on the order of kG. These fields channel the dense, radiatively driven stellar wind into circumstellar magnetospheres, whose density and velocity structure can be probed using ultraviolet (UV) spectroscopy of wind-sensi… ▽ More Recent large-scale spectropolarimetric surveys have established that a small but significant percentage of massive stars host stable, surface dipolar magnetic fields with strengths on the order of kG. These fields channel the dense, radiatively driven stellar wind into circumstellar magnetospheres, whose density and velocity structure can be probed using ultraviolet (UV) spectroscopy of wind-sensitive resonance lines. Coupled with appropriate magnetosphere models, UV spectroscopy provides a valuable way to investigate the wind-field interaction, and can yield quantitative estimates of the wind parameters of magnetic massive stars. We report a systematic investigation of the formation of UV resonance lines in slowly rotating magnetic massive stars with dynamical magnetospheres. We pair the Analytic Dynamical Magnetosphere (ADM) formalism with a simplified radiative transfer technique to produce synthetic UV line profiles. Using a grid of models, we examine the effect of magnetosphere size, the line strength parameter, and the cooling parameter on the structure and modulation of the line profile. We find that magnetic massive stars uniquely exhibit redshifted absorption at most viewing angles and magnetosphere sizes, and that significant changes to the shape and variation of the line profile with varying line strengths can be explained by examining the individual wind components described in the ADM formalism. Finally, we show that the cooling parameter has a negligible effect on the line profiles. △ Less

Submitted 25 June, 2021; originally announced June 2021.

Comments: 16 pages, 15 figures, accepted to MNRAS

A kinematic perspective on the formation process of the stellar groups in the Rosette Nebula

Authors: Beomdu Lim, Yael Naze, Jongsuk Hong, Byeong-Gon Park, Hyeong-Sik Yun, Hee-Weon Yi, Sunkyung Park, Narae Hwang, Jeong-Eun Lee

Abstract: Stellar kinematics is a powerful tool for understanding the formation process of stellar associations. Here, we present a kinematic study of the young stellar population in the Rosette nebula using the recent Gaia data and high-resolution spectra. We first isolate member candidates using the published mid-infrared photometric data and the list of X-ray sources. A total of 403 stars with similar pa… ▽ More Stellar kinematics is a powerful tool for understanding the formation process of stellar associations. Here, we present a kinematic study of the young stellar population in the Rosette nebula using the recent Gaia data and high-resolution spectra. We first isolate member candidates using the published mid-infrared photometric data and the list of X-ray sources. A total of 403 stars with similar parallaxes and proper motions are finally selected as members. The spatial distribution of the members shows that this star-forming region is highly substructured. The young open cluster NGC 2244 in the center of the nebula has a pattern of radial expansion and rotation. We discuss its implication on the cluster formation, e.g., monolithic cold collapse or hierarchical assembly. On the other hand, we also investigate three groups located around the border of the H II bubble. The western group seems to be spatially correlated with the adjacent gas structure, but their kinematics is not associated with that of the gas. The southern group does not show any systematic motion relative to NGC 2244. These two groups might be spontaneously formed in filaments of a turbulent cloud. The eastern group is spatially and kinematically associated with the gas pillar receding away from NGC 2244. This group might be formed by feedback from massive stars in NGC 2244. Our results suggest that the stellar population in the Rosette Nebula may form through three different processes: the expansion of stellar clusters, hierarchical star formation in turbulent clouds, and feedback-driven star formation. △ Less

Submitted 8 May, 2021; originally announced May 2021.

Comments: 23 pages, 16 figures, accepted for publication in the Astronomical Journal

Two proto-science-fiction novels written in French by 18th century women

Authors: Yael Naze

Abstract: With Cyrano, Voltaire, and Verne, France provided important milestones in the history of early science fiction. However, even if the genre was not very common a few centuries ago, there were numerous additional contributions by French-speaking writers. In this paper, we review two cases of interplanetary novels written in the second half of the eighteenth century and sharing a rare particularity:… ▽ More With Cyrano, Voltaire, and Verne, France provided important milestones in the history of early science fiction. However, even if the genre was not very common a few centuries ago, there were numerous additional contributions by French-speaking writers. In this paper, we review two cases of interplanetary novels written in the second half of the eighteenth century and sharing a rare particularity: their authors were female. Voyages de Milord Ceton was imagined by Marie-Anne de Roumier-Robert whereas Cornelie Wouters de Wasse conceived Le Char Volant. While their personal lives were very different, and their writing style too, both authors share in these novels a common philosophy in which equality -- between ranks but also between genders -- takes an important place. Their works thus clearly fit into the context of the Enlightenment. △ Less

Submitted 11 March, 2021; originally announced March 2021.

Comments: published in Journal of Astronomical History and Heritage, 24(1), 125-136 (2021)

Journal ref: JAHH, 24, 125-136 (2021)

Red noise and pulsations in evolved massive stars

Authors: Yael Naze, Gregor Rauw, Eric Gosset

Abstract: We examine high-cadence space photometry taken by the Transiting Exoplanet Survey Satellite (TESS) of a sample of evolved massive stars (26 Wolf-Rayet stars and 8 Luminous Blue Variables or candidate LBVs). To avoid confusion problems, only stars without bright Gaia neighbours and without evidence of bound companions are considered. This leads to a clean sample, whose variability properties should… ▽ More We examine high-cadence space photometry taken by the Transiting Exoplanet Survey Satellite (TESS) of a sample of evolved massive stars (26 Wolf-Rayet stars and 8 Luminous Blue Variables or candidate LBVs). To avoid confusion problems, only stars without bright Gaia neighbours and without evidence of bound companions are considered. This leads to a clean sample, whose variability properties should truly reflect the properties of the WR and LBV classes. Red noise is detected in all cases and its fitting reveals characteristics very similar to those found for OB-stars. Coherent variability is also detected for 20% of the WR sample. Most detections occur at moderately high frequency (3--14/d), hence are most probably linked to pulsational activity. This work doubles the number of WRs known to exhibit high-frequency signals. △ Less

Submitted 14 January, 2021; originally announced January 2021.

Comments: accepted by MNRAS - the arxiv version has some figures in low-resolution