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Hints of enhanced magnetic activity after the intermediate rotation period gap as traced by the chromospheric Ca ii infrared triplet
Authors:
Diego Godoy-Rivera,
Savita Mathur,
Tyler Richey-Yowell,
Angela R. G. Santos,
Rafael A. Garcia,
Desmond H. Grossmann,
Zachary R. Claytor,
Paul G. Beck
Abstract:
For low-mass stars (M < 1.4 Msun), the connection between stellar rotation and magnetic activity governs stellar spin-down, shapes the environments of their exoplanets, and provides an age-diagnostic via magneto-gyro-chronology. Recently, unexpected phenomena known as the intermediate rotation period gap and the rotational stalling have been discovered. These are likely due to internal angular mom…
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For low-mass stars (M < 1.4 Msun), the connection between stellar rotation and magnetic activity governs stellar spin-down, shapes the environments of their exoplanets, and provides an age-diagnostic via magneto-gyro-chronology. Recently, unexpected phenomena known as the intermediate rotation period gap and the rotational stalling have been discovered. These are likely due to internal angular momentum redistribution, and mark departures from a smooth spin-down evolution. These features have been shown to cause enhanced magnetic activity on the photosphere, as measured by the photometric index from light curves (Sph), in both cluster and field stars. However, their influence on other magnetic activity proxies, and particularly in field stars, remains poorly understood. In this work, we study the impact of the intermediate-period gap on chromospheric magnetic activity as traced by the Ca ii infrared triplet (IRT) index. We target the stars observed by the Kepler mission, as this is the largest and most reliable sample of field stars with measured rotation periods sensitive to the gap. We calculate the Ca ii IRT index for the Kepler stars using the spectroscopic information from the Gaia mission data release three (DR3). We study the rotation-activity relation as a function of spectral type, finding that K dwarfs are more active than G dwarfs, which in turn are more active than F dwarfs. For main-sequence stars, we find that chromospheric magnetic activity is also enhanced after the intermediate-period gap, mirroring its effect on the photospheric Sph index. Our work reveals that the intermediate-period gap marks a genuine transition in stellar magnetic behavior, not only at the photosphere but also at the chromosphere. This highlights the need to account for its signatures across activity proxies, as well as its impact on exoplanet habitability and the age-rotation-activity relation.
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Submitted 6 July, 2026;
originally announced July 2026.
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Quantifying isochrone-based age uncertainties for rapidly rotating A-type stars
Authors:
Simon J. Murphy,
Anuj Gautam,
Zachary R. Claytor
Abstract:
Accurate stellar ages and masses are essential for interpreting the demographics and physical properties of exoplanets, particularly for intermediate-mass, early-type stars where conventional age indicators are ineffective. Isochrone fitting remains the primary tool for characterising such stars, yet its uncertainties are often underestimated, especially in the presence of rapid rotation and unres…
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Accurate stellar ages and masses are essential for interpreting the demographics and physical properties of exoplanets, particularly for intermediate-mass, early-type stars where conventional age indicators are ineffective. Isochrone fitting remains the primary tool for characterising such stars, yet its uncertainties are often underestimated, especially in the presence of rapid rotation and unresolved binarity. We present a population-synthesis framework designed to quantify realistic mass and age uncertainties for intermediate-mass stars (1.4-2.5 M$_{\odot}$), incorporating distributions in rotation rate, mass, metallicity, binarity, inclination, and observational error. Rotational and geometric effects are applied a posteriori to stellar evolutionary models, enabling a continuous treatment of rotation and its impact on effective temperature and luminosity. By comparing synthetic populations against commonly used isochrone grids, we demonstrate that rotation and unresolved companions systematically bias inferred masses and ages, particularly for young stars, and introduce random uncertainties at the $\sim$0.1-M$_{\odot}$ and $\sim$180-Myr level, often exceeding formal fitting errors. The effect is strongest near the zero-age main sequence, where ages are underestimated by a factor of $\geq2$, while for older A stars ($>$10% of their main-sequence lifetime), ages are overestimated by 31% with 27% scatter. Our findings carry important consequences for planet detectability, characterisation, and population studies. We provide a publicly available tool, RAPID, for probabilistic inference of stellar parameters from these synthetic populations, and we demonstrate its application to known exoplanet hosts.
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Submitted 18 June, 2026; v1 submitted 8 June, 2026;
originally announced June 2026.
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The YREC Stellar Evolution Code: Public Data Release
Authors:
Marc H. Pinsonneault,
Jennifer L. van Saders,
Lyra Cao,
Jamie Tayar,
Franck Delahaye,
Leslie M. Morales,
Rachel A. Patton,
Matthew C. Rendina,
Joel C. Zinn,
Zachary R. Claytor,
Amanda L. Ash,
Susan Byrom,
Kaili Cao,
Vincent A. Smedile
Abstract:
In this paper we present the public release of the Yale Rotating Evolution Code (YREC). YREC is a stellar evolution code that covers brown dwarfs and stars across a wide range of masses, and evolutionary states from the pre-MS through helium burning. We summarize the key ingredients of the code, document the code performance, and discuss its strengths and limitations. We present libraries of input…
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In this paper we present the public release of the Yale Rotating Evolution Code (YREC). YREC is a stellar evolution code that covers brown dwarfs and stars across a wide range of masses, and evolutionary states from the pre-MS through helium burning. We summarize the key ingredients of the code, document the code performance, and discuss its strengths and limitations. We present libraries of input files, documentation, sample use cases, and scripts. In addition to usage as a research tool, we highlight the utility of the code for educational purposes.
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Submitted 26 March, 2026;
originally announced March 2026.
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The Impact of the MAST Data Archive
Authors:
Richard A. Shaw,
Jenny L. Novacescu,
Sarah Weissman,
Travis A. Berger,
Clara E. Brasseur,
Jeff Chamblee,
Brian Cherinka,
Zachary R. Claytor,
Theresa Dower,
Chinwe Edeani,
Scott W. Fleming,
Jonathan R. Hargis,
Julie Imig,
Tim Januario,
Karen Levay,
Tim Kimball,
Jenn Kotler,
Hannah M. Lewis,
Steve Lubow,
Adrian Lucy,
Brian McLean,
Sunita G. Malla,
Jacob Matuskey,
Sophie J. Miller,
Susan E. Mullally
, et al. (9 additional authors not shown)
Abstract:
The Barbara A. Mikulski Archive for Space Telescopes (MAST) hosts science-ready data products from over twenty NASA missions, plus community-contributed data collections, and other select surveys. The data support forefront research in the ultraviolet, optical, and near-infrared wavelength bands. We have constructed bibliographies for each mission from publications in nearly 40 professional journa…
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The Barbara A. Mikulski Archive for Space Telescopes (MAST) hosts science-ready data products from over twenty NASA missions, plus community-contributed data collections, and other select surveys. The data support forefront research in the ultraviolet, optical, and near-infrared wavelength bands. We have constructed bibliographies for each mission from publications in nearly 40 professional journals, and have identified more than 37,000 refereed articles where investigators made a science usage of data hosted in MAST. The publication rate over the last 50 years shows that most MAST missions have had very high productivity during their in-service lifetimes, and have remained so for years or decades afterward. Annual citations to these publications, a measure of impact on research, are robust for most missions, with citations that grow over more than a decade. Most of the citations come from about 10% of articles within each mission.
We examined the bibliographies of the active missions HST and JWST in greater detail. For HST the rate of archival publications exceeded those authored by the original observing teams within a decade of launch, and is now more than 3 times higher. Early indications hint that JWST archival articles could dominate the publication rate even sooner. The production of articles resulting from any given observing program can extend for decades. Programs with small and very large allocations of observing time tend to be particularly productive per unit of observing time. For HST in general, a first publication appears within 1.5 yr for 50% of observing programs, and within 3.8 yr for 80% of programs. We discuss various external factors that affect publication metrics, their strengths and limitations for measuring scientific impact, and the challenges of making meaningful comparisons of publication metrics across missions.
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Submitted 19 December, 2025;
originally announced December 2025.
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200,000+ Deep Learning-inferred Periods of Stellar Variability from the All-Sky Automated Survey for Supernovae
Authors:
Meir E. Schochet,
Penelope Planet,
Zachary R. Claytor,
Jamie Tayar,
Adina D. Feinstein
Abstract:
Stars exhibit a range of variability periods that depend on their mass, age, and evolutionary stage. For space-based photometric data, convolutional neural networks (CNNs) have demonstrated success in recovering and measuring periodic variability from photometric missions like Kepler and TESS. All-sky ground-based surveys can have similar if not longer baselines than space-based missions; however,…
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Stars exhibit a range of variability periods that depend on their mass, age, and evolutionary stage. For space-based photometric data, convolutional neural networks (CNNs) have demonstrated success in recovering and measuring periodic variability from photometric missions like Kepler and TESS. All-sky ground-based surveys can have similar if not longer baselines than space-based missions; however, these datasets are more challenging to work with due to irregular sampling, more complex systematics, and larger data gaps. In this work, we demonstrate that CNNs can be used to derive variability periods from ground-based surveys. From the All-Sky Automated Survey for Supernovae, we recover 208,260 variability periods between 1 and 30 days, approximately 60% of which are new detections. We recover periods for active RSCVn, anomalous sub-subgiants, and cool dwarfs that are consistent with previously measured rotation periods, while periods for stars above the Kraft break are generally spurious. We also identify periodic signals in tens of thousands of giant stars that correspond to frequencies of stellar oscillations rather than rotation. Our results highlight that CNNs can be used on sparsely sampled ground-based photometry to recover periodicity. We conclude that the findings of our work are very promising for the potential recovery of hundreds of thousands of stellar rotation periods in data from the Vera C. Rubin Observatory's Legacy Survey of Space and Time and the Nancy Grace Roman Space Telescopes Galactic Bulge Time Domain Survey.
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Submitted 23 December, 2025; v1 submitted 17 September, 2025;
originally announced September 2025.
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New Rotation Periods from the Kepler Bonus Background Light Curves
Authors:
Zachary R. Claytor,
Jamie Tayar
Abstract:
The Kepler field hosts the best studied sample of field star rotation periods. However, due to Kepler's large 4" pixels, many of its light curves are at high risk of contamination from background sources. The new Kepler Bonus Background light curves are de-blended using a PSF algorithm, providing light curves of over 400,000 new background sources in addition to over 200,000 re-analyzed Kepler pri…
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The Kepler field hosts the best studied sample of field star rotation periods. However, due to Kepler's large 4" pixels, many of its light curves are at high risk of contamination from background sources. The new Kepler Bonus Background light curves are de-blended using a PSF algorithm, providing light curves of over 400,000 new background sources in addition to over 200,000 re-analyzed Kepler prime targets. These light curves provide the opportunity to search for new rotation periods. Here we apply a convolutional neural network trained on synthetic spot-modulated light curves to regress rotation periods from the Kepler Bonus light curves. We obtained periods for 32,159 total sources, 19,650 of which had previously been measured and 9,811 of which are new periods for both Kepler prime and background sources. Our method also detected 608 pulsation frequencies from asteroseismic oscillations in red giants. We validate our Kepler prime periods against literature values and present the full period sample. We find excellent agreement with previously-known literature periods, validating deep learning as a viable class of period determination methods. Comparing the periods and light curves of foreground-background pairs, we find that as many as 63% of periodic background light curves are still blended with the foreground, highlighting limitations of the de-blending technique.
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Submitted 3 June, 2025;
originally announced June 2025.
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Model Choice Matters for Age Inference on the Red Giant Branch
Authors:
Leslie M. Morales,
Jamie Tayar,
Zachary R. Claytor
Abstract:
Galactic archaeology relies on accurate stellar parameters to reconstruct the galaxy's history, including information on stellar ages. While the precision of data has improved significantly in recent years, stellar models used for age inference have not improved at a similar rate. In fact, different models yield notably different age predictions for the same observational data. In this paper, we a…
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Galactic archaeology relies on accurate stellar parameters to reconstruct the galaxy's history, including information on stellar ages. While the precision of data has improved significantly in recent years, stellar models used for age inference have not improved at a similar rate. In fact, different models yield notably different age predictions for the same observational data. In this paper, we assess the difference in age predictions of various widely used model grids for stars along the red giant branch. Using open source software, we conduct a comparison of four different evolution grids and we find that age estimations become less reliable if stellar mass is not known, with differences occasionally exceeding $80\%$. Additionally, we note significant disagreements in the models' age estimations at non-solar metallicity. Finally, we present a method for including theoretical uncertainties from stellar evolutionary tracks in age inferences of red giants, aimed at improving the accuracy of age estimation techniques used in the galactic archaeology community.
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Submitted 24 April, 2025;
originally announced April 2025.
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Trials and Tribulations of Chemodynamical Tagging: Investigating the Recovery of Open Clusters in the Gaia DR3-GALAH DR4 Catalog
Authors:
Nicholas A. Barth,
David Mendez,
Rana Ezzeddine,
Yuxi,
Lu,
Leslie M. Morales,
Zachary R. Claytor,
Jamie Tayar
Abstract:
Chemodynamical tagging has been suggested as a powerful tool to trace stars back to their birth clusters. However, the efficacy of chemodynamical tagging as a means to recover individual stellar clusters is still under debate. In this study, we present a detailed investigation of chemodynamical tagging of open clusters using both dynamical and chemical data from the \textit{Gaia} DR3 and GALAH DR4…
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Chemodynamical tagging has been suggested as a powerful tool to trace stars back to their birth clusters. However, the efficacy of chemodynamical tagging as a means to recover individual stellar clusters is still under debate. In this study, we present a detailed investigation of chemodynamical tagging of open clusters using both dynamical and chemical data from the \textit{Gaia} DR3 and GALAH DR4 surveys, respectively. Using a sample of open clusters and mock field stars, we conduct a bootstrap analysis to evaluate every unique combination of orbital components ($E, J_R, J_φ, J_Z$) and chemical abundances ([X/Fe] for O, Na, Mg, Al, Si, K, Ca, Sc, Ti, Cr, Mn, Ni, Cu, Y, and Ba) on how well they recover open clusters when used as parameters in the clustering algorithm, HBDSCAN. We find that using primarily dynamical orbital parameters leads to the highest recovery rate of open cluster stars. Nevertheless, even employing the best performing parameter combinations leads to low open cluster recovery rates. We find that, in most cases, chemodynamical tagging of open clusters using blind clustering algorithms is not efficient, which is in line with previous theoretical and observational work. However, we show that the addition of cuts based on metallicity, age, and birth radii in order to reduce the size of the clustering catalog can marginally improve the recovery rate of open clusters.
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Submitted 15 April, 2025;
originally announced April 2025.
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Magnetic activity evolution of solar-like stars: II. $S_{\rm ph}$-Ro evolution of Kepler main-sequence targets
Authors:
Savita Mathur,
Angela R. G. Santos,
Zachary R. Claytor,
Rafael A. García,
Antoine Strugarek,
Adam J. Finley,
Quentin Noraz,
Louis Amard,
Paul G. Beck,
Alfio Bonanno,
Sylvain N. Breton,
Allan S. Brun,
Lyra Cao,
Enrico Corsaro,
Diego Godoy-Rivera,
Stéphane Mathis,
Dinil B. Palakkatharappil,
Marc H. Pinsonneault,
Jennifer van Saders
Abstract:
There is now a large sample of stars observed by the Kepler satellite with measured rotation periods and photometric activity index $S_{\rm ph}$. We use this data, in conjunction with stellar interiors models, to explore the interplay of magnetism, rotation, and convection. Stellar activity proxies other than $S_{\rm ph}$ are correlated with the Rossby number, $Ro$, or ratio of rotation period to…
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There is now a large sample of stars observed by the Kepler satellite with measured rotation periods and photometric activity index $S_{\rm ph}$. We use this data, in conjunction with stellar interiors models, to explore the interplay of magnetism, rotation, and convection. Stellar activity proxies other than $S_{\rm ph}$ are correlated with the Rossby number, $Ro$, or ratio of rotation period to convective overturn timescale. We compute the latter using the Yale Rotating Evolution Code stellar models. We observe different $S_{\rm ph}$-$Ro$ relationships for different stellar spectral types. Though the overall trend of decreasing magnetic activity versus $Ro$ is recovered, we find a localized dip in $S_{\rm ph}$ around $Ro/Ro_{\odot} \sim$\,0.3 for the G and K dwarfs. F dwarfs show little to no dependence of $S_{\rm ph}$ on $Ro$ due to their shallow convective zones; further accentuated as $T_{\rm eff}$ increases. The dip in activity for the G and K dwarfs corresponds to the intermediate rotation period gap, suggesting that the dip in $S_{\rm ph}$ could be associated with the redistribution of angular momentum between the core and convective envelope inside stars. For G-type stars, we observe enhanced magnetic activity above solar $Ro$. Compared to other Sun-like stars with similar effective temperature and metallicity, we find that the Sun's current level of magnetic activity is comparable to its peers and lies near the transition to increasing magnetic activity at high $Ro$. We confirm that metal-rich stars have a systematically larger $S_{\rm ph}$ level than metal-poor stars, which is likely a consequence of their deeper convective zones.
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Submitted 14 February, 2025;
originally announced February 2025.
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Evidence of Truly Young high-$α$ Dwarf Stars
Authors:
Yuxi Lu,
Isabel L. Colman,
Maryum Sayeed,
Louis Amard,
Sven Buder,
Catherine Manea,
Soichiro Hattori,
Marc H. Pinsonneault,
Adrian M. Price-Whelan,
Megan Bedell,
David Nidever,
Jennifer A. Johnson,
Melissa Ness,
Ruth Angus,
Zachary R. Claytor,
Danny Horta,
Aida Behmard
Abstract:
The existence of high-$α$ stars with inferred ages < 6 Gyr has been confirmed recently with large spectroscopic and photometric surveys. However, stellar mergers or binary interactions can induce properties associated with young ages, such as high mass, rapid rotation, or high activity, even in old populations. Literature studies have confirmed that at least some of these apparently young stars ar…
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The existence of high-$α$ stars with inferred ages < 6 Gyr has been confirmed recently with large spectroscopic and photometric surveys. However, stellar mergers or binary interactions can induce properties associated with young ages, such as high mass, rapid rotation, or high activity, even in old populations. Literature studies have confirmed that at least some of these apparently young stars are old merger products. However, none have ruled out the possibility of genuinely young high-$α$ stars. Because cool GKM dwarfs spin down, rapid rotation can be used to indicate youth. In this paper, we provide strong evidence that truly young high-$α$ stars exist by studying high-$α$ rotators in the Kepler and K2 field with abundance measurements from GALAH and APOGEE. After excluding close binaries using radial velocity (RV) measurements from Gaia DR3 and multi-epoch RVs from APOGEE, we find a total of 70 high-$α$ rapid rotators with periods ~10-30 days, 29 of which have lithium measurements from GALAH, indicating that they have not gone through past mass transfer or stellar merger events. We identify 10 young high-$α$ candidates with no signs of merger-induced mixing or close companions. One clear example is a G dwarf with a measurable rotation and an age of 1.98$^{+0.12}_{-0.28}$ Gyr that is likely a single star with multiple RV measurements from APOGEE, has significant lithium detection from GALAH (A(Li) = 1.79), and has no signs of planet engulfment.
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Submitted 3 October, 2024;
originally announced October 2024.
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TESS asteroseismology of $β$ Hydri: a subgiant with a born-again dynamo
Authors:
Travis S. Metcalfe,
Jennifer L. van Saders,
Daniel Huber,
Derek Buzasi,
Rafael A. Garcia,
Keivan G. Stassun,
Sarbani Basu,
Sylvain N. Breton,
Zachary R. Claytor,
Enrico Corsaro,
Martin B. Nielsen,
J. M. Joel Ong,
Nicholas Saunders,
Amalie Stokholm,
Timothy R. Bedding
Abstract:
The solar-type subgiant $β$ Hyi has long been studied as an old analog of the Sun. Although the rotation period has never been measured directly, it was estimated to be near 27 days. As a southern hemisphere target it was not monitored by long-term stellar activity surveys, but archival International Ultraviolet Explorer data revealed a 12 year activity cycle. Previous ground-based asteroseismolog…
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The solar-type subgiant $β$ Hyi has long been studied as an old analog of the Sun. Although the rotation period has never been measured directly, it was estimated to be near 27 days. As a southern hemisphere target it was not monitored by long-term stellar activity surveys, but archival International Ultraviolet Explorer data revealed a 12 year activity cycle. Previous ground-based asteroseismology suggested that the star is slightly more massive and substantially larger and older than the Sun, so the similarity of both the rotation rate and the activity cycle period to solar values is perplexing. We use two months of precise time-series photometry from the Transiting Exoplanet Survey Satellite (TESS) to detect solar-like oscillations in $β$ Hyi and determine the fundamental stellar properties from asteroseismic modeling. We also obtain a direct measurement of the rotation period, which was previously estimated from an ultraviolet activity-rotation relation. We then use rotational evolution modeling to predict the rotation period expected from either standard spin-down or weakened magnetic braking (WMB). We conclude that the rotation period of $β$ Hyi is consistent with WMB, and that changes in stellar structure on the subgiant branch can reinvigorate the large-scale dynamo and briefly sustain magnetic activity cycles. Our results support the existence of a "born-again" dynamo in evolved subgiants -- previously suggested to explain the cycle in 94 Aqr Aa -- which can best be understood within the WMB scenario.
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Submitted 10 August, 2024;
originally announced August 2024.
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A Testbed for Tidal Migration: the 3D Architecture of an Eccentric Hot Jupiter HD 118203 b Accompanied by a Possibly Aligned Outer Giant Planet
Authors:
Jingwen Zhang,
Daniel Huber,
Lauren M. Weiss,
Jerry W. Xuan,
Jennifer A. Burt,
Fei Dai,
Nicholas Saunders,
Erik A. Petigura,
Ryan A. Rubenzahl,
Joshua N. Winn,
Sharon X. Wang,
Judah Van Zandt,
Max Brodheim,
Zachary R. Claytor,
Ian Crossfield,
William Deich,
Benjamin J. Fulton,
Steven R. Gibson,
Grant M. Hill,
Bradford Holden,
Aaron Householder,
Andrew W. Howard,
Howard Isaacson,
Stephen Kaye,
Kyle Lanclos
, et al. (9 additional authors not shown)
Abstract:
Characterizing outer companions to hot Jupiters plays a crucial role in deciphering their origins. We present the discovery of a long-period giant planet, HD 118203 c ($m_{c}=11.79^{+0.69}_{-0.63}\ \mathrm{M_{J}}$, $a_{c}=6.28^{+0.10}_{-0.11}$ AU) exterior to a close-in eccentric hot Jupiter HD 118203 b ($P_{b}=6.135\ \mathrm{days}$, $m_{b}=2.14\pm{0.12}\ \mathrm{M_{J}}$,…
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Characterizing outer companions to hot Jupiters plays a crucial role in deciphering their origins. We present the discovery of a long-period giant planet, HD 118203 c ($m_{c}=11.79^{+0.69}_{-0.63}\ \mathrm{M_{J}}$, $a_{c}=6.28^{+0.10}_{-0.11}$ AU) exterior to a close-in eccentric hot Jupiter HD 118203 b ($P_{b}=6.135\ \mathrm{days}$, $m_{b}=2.14\pm{0.12}\ \mathrm{M_{J}}$, $r_{b}=1.14\pm{0.029}\ \mathrm{R_{J}}$, $e_{b}=0.31\pm{0.007}$) based on twenty-year radial velocities. Using Rossiter-McLaughlin (RM) observations from the Keck Planet Finder (KPF), we measured a low sky-projected spin-orbit angle $λ_{b}=-11^{\circ}.7^{+7.6}_{-10.0}$ for HD 118203 b and detected stellar oscillations in the host star, confirming its evolved status. Combining the RM observation with the stellar inclination measurement, we constrained the true spin-orbit angle of HD 118203 b as $Ψ_{b}<33^{\circ}.5\ (2σ)$, indicating the orbit normal of the hot Jupiter nearly aligned with the stellar spin axis. Furthermore, by combining radial velocities and Hipparcos-Gaia astrometric acceleration, we constrained the line-of-sight mutual inclination between the hot Jupiter and the outer planet to be $9^{\circ}.8^{+16.2}_{-9.3}$ at $2σ$ level. HD 118203 is one of first hot Jupiter systems where both the true spin-orbit angle of the hot Jupiter and the mutual inclination between inner and outer planets have been determined. Our results are consistent with a system-wide alignment, with low mutual inclinations between the outer giant planet, the inner hot Jupiter, and the host star. This alignment, along with the moderate eccentricity of HD 118203 c, implies that the system may have undergone coplanar high-eccentricity tidal migration. Under this framework, our dynamical analysis suggests an initial semi-major axis of 0.3 to 3.2 AU for the proto-hot Jupiter.
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Submitted 6 September, 2024; v1 submitted 31 July, 2024;
originally announced July 2024.
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TESS Stellar Rotation up to 80 days in the Southern Continuous Viewing Zone
Authors:
Zachary R. Claytor,
Jennifer L. van Saders,
Lyra Cao,
Marc H. Pinsonneault,
Johanna Teske,
Rachael L. Beaton
Abstract:
The TESS mission delivers time-series photometry for millions of stars across the sky, offering a probe into stellar astrophysics, including rotation, on a population scale. However, light curve systematics related to the satellite's 13.7-day orbit have prevented stellar rotation searches for periods longer than 13 days, putting the majority of stars beyond reach. Machine learning methods have the…
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The TESS mission delivers time-series photometry for millions of stars across the sky, offering a probe into stellar astrophysics, including rotation, on a population scale. However, light curve systematics related to the satellite's 13.7-day orbit have prevented stellar rotation searches for periods longer than 13 days, putting the majority of stars beyond reach. Machine learning methods have the ability to identify systematics and recover robust signals, enabling us to recover rotation periods up to 35 days for GK dwarfs and 80 days for M dwarfs. We present a catalog of 7245 rotation periods for cool dwarfs in the Southern Continuous Viewing Zone, estimated using convolutional neural networks. We find evidence for structure in the period distribution consistent with prior Kepler and K2 results, including a gap in 10--20-day cool star periods thought to arise from a change in stellar spin-down or activity. Using a combination of spectroscopic and gyrochronologic constraints, we fit stellar evolution models to estimate masses and ages for stars with rotation periods. We find strong correlations between the detectability of rotation in TESS and the effective temperature, age, and metallicity of the stars. Finally, we investigate the relationships between rotation and newly obtained spot filling fractions estimated from APOGEE spectra. Field star spot filling fractions are elevated in the same temperature and period regime where open clusters' magnetic braking stalls, lending support to an internal shear mechanism that can produce both phenomena.
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Submitted 10 January, 2024; v1 submitted 11 July, 2023;
originally announced July 2023.
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A close-in giant planet escapes engulfment by its star
Authors:
Marc Hon,
Daniel Huber,
Nicholas Z. Rui,
Jim Fuller,
Dimitri Veras,
James S. Kuszlewicz,
Oleg Kochukhov,
Amalie Stokholm,
Jakob Lysgaard Rørsted,
Mutlu Yıldız,
Zeynep Çelik Orhan,
Sibel Örtel,
Chen Jiang,
Daniel R. Hey,
Howard Isaacson,
Jingwen Zhang,
Mathieu Vrard,
Keivan G. Stassun,
Benjamin J. Shappee,
Jamie Tayar,
Zachary R. Claytor,
Corey Beard,
Timothy R. Bedding,
Casey Brinkman,
Tiago L. Campante
, et al. (17 additional authors not shown)
Abstract:
When main-sequence stars expand into red giants, they are expected to engulf close-in planets. Until now, the absence of planets with short orbital periods around post-expansion, core-helium-burning red giants has been interpreted as evidence that short-period planets around Sun-like stars do not survive the giant expansion phase of their host stars. Here we present the discovery that the giant pl…
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When main-sequence stars expand into red giants, they are expected to engulf close-in planets. Until now, the absence of planets with short orbital periods around post-expansion, core-helium-burning red giants has been interpreted as evidence that short-period planets around Sun-like stars do not survive the giant expansion phase of their host stars. Here we present the discovery that the giant planet 8 Ursae Minoris b orbits a core-helium-burning red giant. At a distance of only 0.5 au from its host star, the planet would have been engulfed by its host star, which is predicted by standard single-star evolution to have previously expanded to a radius of 0.7 au. Given the brief lifetime of helium-burning giants, the nearly circular orbit of the planet is challenging to reconcile with scenarios in which the planet survives by having a distant orbit initially. Instead, the planet may have avoided engulfment through a stellar merger that either altered the evolution of the host star or produced 8 Ursae Minoris b as a second-generation planet. This system shows that core-helium-burning red giants can harbour close planets and provides evidence for the role of non-canonical stellar evolution in the extended survival of late-stage exoplanetary systems.
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Submitted 27 June, 2023;
originally announced June 2023.
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Magnetic activity evolution of solar-like stars: I. S_ph-Age relation derived from Kepler observations
Authors:
Savita Mathur,
Zachary R. Claytor,
Angela R. G. Santos,
Rafael A. García,
Louis Amard,
Lisa Bugnet,
Enrico Corsaro,
Alfio Bonanno,
Sylvain N. Breton,
Diego Godoy-Rivera,
Marc H. Pinsonneault,
Jennifer van Saders
Abstract:
The ages of solar-like stars have been at the center of many studies such as exoplanet characterization or Galactic-archaeology. While ages are usually computed from stellar evolution models, relations linking ages to other stellar properties, such as rotation and magnetic activity, have been investigated. With the large catalog of 55,232 rotation periods, $P_{\rm rot}$, and photometric magnetic a…
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The ages of solar-like stars have been at the center of many studies such as exoplanet characterization or Galactic-archaeology. While ages are usually computed from stellar evolution models, relations linking ages to other stellar properties, such as rotation and magnetic activity, have been investigated. With the large catalog of 55,232 rotation periods, $P_{\rm rot}$, and photometric magnetic activity index, $S_{\rm ph}$ from Kepler data, we have the opportunity to look for such magneto-gyro-chronology relations. Stellar ages are obtained with two stellar evolution codes that include treatment of angular momentum evolution, hence using $P_{\rm rot}$ as input in addition to classical atmospheric parameters. We explore two different ways of predicting stellar ages on three subsamples with spectroscopic observations: solar analogs, late-F and G dwarfs, and K dwarfs. We first perform a Bayesian analysis to derive relations between $S_{\rm ph}$ and ages between 1 and 5 Gyr, and other stellar properties. For late-F and G dwarfs, and K dwarfs, the multivariate regression favors the model with $P_{\rm rot}$ and $S_{\rm ph}$ with median differences of 0.1%.and 0.2% respectively. We also apply Machine Learning techniques with a Random Forest algorithm to predict ages up to 14 Gyr with the same set of input parameters. For late-F, G and K dwarfs together, predicted ages are on average within 5.3% of the model ages and improve to 3.1% when including $P_{\rm rot}$. These are very promising results for a quick age estimation for solar-like stars with photometric observations, especially with current and future space missions.
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Submitted 20 June, 2023;
originally announced June 2023.
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Roman CCS White Paper: Adding Fields Hosting Globular Clusters To The Galactic Bulge Time Domain Survey
Authors:
Samuel K. Grunblatt,
Robert F. Wilson,
Andrew Winter,
B. Scott Gaudi,
Daniel Huber,
Daniel A. Yahalomi,
Andrea Bellini,
Zachary R. Claytor,
Jorge Martinez Palomera,
Thomas Barclay,
Guangwei Fu,
Adrian Price-Whelan
Abstract:
Despite multiple previous searches, no transiting planets have yet been identified within a globular cluster. This is believed to be due to a combination of factors: the low metallicities of most globular clusters suggests that there is significantly less planet-forming material per star in most globular clusters relative to the solar neighborhood, the high likelihood of dynamical interactions can…
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Despite multiple previous searches, no transiting planets have yet been identified within a globular cluster. This is believed to be due to a combination of factors: the low metallicities of most globular clusters suggests that there is significantly less planet-forming material per star in most globular clusters relative to the solar neighborhood, the high likelihood of dynamical interactions can also disrupt planetary orbits, and the data available for globular clusters is limited. However, transiting planets have been identified in open clusters, indicating that there may be planets in more massive clusters that have simply gone undetected, or that more massive clusters inhibit planet formation. Less than two degrees away from the nominal Galactic Bulge Time Domain Survey footprint, two globular clusters, NGC 6522 and NGC 6528, can be simultaneously observed by the Roman telescope during the Galactic Bulge Time Domain Survey. These clusters are comparable in mass (1-2 x 10$^5$ solar masses) and age (12 Gyr), but feature drastically different average metallicities: NGC 6522 has an average [Fe/H] $\sim$ -1.3, while NGC 6528 has an average [Fe/H] $\sim$ -0.1. If no transiting planets are detected in one season of time domain observations of these clusters, this would indicate a difference in planet occurrence among field stars and globular clusters at >3-$σ$ significance even after accounting for metallicity, which could be enhanced to >5-$σ$ significance with similar observations of another nearby field hosting a metal-rich globular cluster. Additionally, time domain observations of NGC 6522 and NGC 6528 will detect variable stars in both clusters, testing the connection between stellar variability and binary fraction to metallicity and cluster environment, as well as testing the dependence of exoplanet yields on stellar density and distance from the Galactic midplane.
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Submitted 18 June, 2023;
originally announced June 2023.
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Temporal variation of the photometric magnetic activity for the Sun and Kepler solar-like stars
Authors:
A. R. G. Santos,
S. Mathur,
R. A. García,
A. -M. Broomhall,
R. Egeland,
A. Jiménez,
D. Godoy-Rivera,
S. N. Breton,
Z. R. Claytor,
T. S. Metcalfe,
M. S. Cunha,
L. Amard
Abstract:
The photometric time series of solar-like stars can exhibit rotational modulation due to active regions co-rotating with the stellar surface, allowing us to constrain stellar rotation and magnetic activity. In this work we investigate the behavior, particularly the variability, of the photometric magnetic activity of Kepler solar-like stars and compare it with that of the Sun. We adopted the photo…
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The photometric time series of solar-like stars can exhibit rotational modulation due to active regions co-rotating with the stellar surface, allowing us to constrain stellar rotation and magnetic activity. In this work we investigate the behavior, particularly the variability, of the photometric magnetic activity of Kepler solar-like stars and compare it with that of the Sun. We adopted the photometric magnetic activity proxy Sph, which was computed with a cadence of 5 x the rotation period, Prot. The average Sph was taken as the mean activity level, and the standard deviation was taken as a measure of the temporal variation of the magnetic activity over the observations. We also analyzed Sun-as-a-star photometric data from VIRGO. Sun-like stars were selected from a very narrow parameter space around the solar properties. We also looked into KIC 8006161 (HD 173701), an active metal-rich G dwarf, and we compared its magnetic activity to that of stars with similar stellar parameters. We find that the amplitude of Sph variability is strongly correlated with its mean value, independent of spectral type. An equivalent relationship has been found for ground-based observations of chromospheric activity emission and magnetic field strength, but in this work we show that photometric Kepler data also present the same behavior. While, depending on the cycle phase, the Sun is among the less active stars, we find that the solar Sph properties are consistent with those observed in Kepler Sun-like stars. KIC 8006161 is, however, among the most active of its peers, which tend to be metal-rich. This results from an underlying relationship between Prot and metallicity and supports the following interpretation of the magnetic activity of KIC 8006161: its strong activity is a consequence of its high metallicity, which affects the depth of the convection zone and, consequently, the efficiency of the dynamo.
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Submitted 6 April, 2023;
originally announced April 2023.
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Kepler-102: Masses and Compositions for a Super-Earth and Sub-Neptune Orbiting an Active Star
Authors:
Casey Brinkman,
James Cadman,
Lauren Weiss,
Eric Gaidos,
Ken Rice,
Daniel Huber,
Zachary R. Claytor,
Aldo S. Bonomo,
Lars A. Buchhave,
Andrew Collier Cameron,
Rosario Cosentino,
Xavier Dumusque,
Aldo F Martinez Fiorenzano,
Adriano Ghedina,
Avet Harutyunyan,
Andrew Howard,
Howard Isaacson,
David W. Latham,
Mercedes Lopez-Morales,
Luca Malavolta,
Giuseppina Micela,
Emilio Molinari,
Francesco Pepe,
David F Philips,
Ennio Poretti
, et al. (2 additional authors not shown)
Abstract:
Radial velocity (RV) measurements of transiting multiplanet systems allow us to understand the densities and compositions of planets unlike those in the Solar System. Kepler-102, which consists of 5 tightly packed transiting planets, is a particularly interesting system since it includes a super-Earth (Kepler-102d) and a sub-Neptune-sized planet (Kepler-102e) for which masses can be measured using…
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Radial velocity (RV) measurements of transiting multiplanet systems allow us to understand the densities and compositions of planets unlike those in the Solar System. Kepler-102, which consists of 5 tightly packed transiting planets, is a particularly interesting system since it includes a super-Earth (Kepler-102d) and a sub-Neptune-sized planet (Kepler-102e) for which masses can be measured using radial velocities. Previous work found a high density for Kepler-102d, suggesting a composition similar to that of Mercury, while Kepler-102e was found to have a density typical of sub-Neptune size planets; however, Kepler-102 is an active star, which can interfere with RV mass measurements. To better measure the mass of these two planets, we obtained 111 new RVs using Keck/HIRES and TNG/HARPS-N and modeled Kepler-102's activity using quasi-periodic Gaussian Process Regression. For Kepler-102d, we report a mass upper limit of M$_{d} < $5.3 M$_{\oplus}$ [95\% confidence], a best-fit mass of M$_{d}$=2.5 $\pm$ 1.4 M$_{\oplus}$, and a density of $ρ_{d}$=5.6 $\pm$ 3.2 g/cm$^{3}$ which is consistent with a rocky composition similar in density to the Earth. For Kepler-102e we report a mass of M$_{e}$=4.7 $\pm$ 1.7 M$_{\oplus}$ and a density of $ρ_{e}$=1.8 $\pm$ 0.7 g/cm$^{3}$. These measurements suggest that Kepler-102e has a rocky core with a thick gaseous envelope comprising 2-4% of the planet mass and 16-50% of its radius. Our study is yet another demonstration that accounting for stellar activity in stars with clear rotation signals can yield more accurate planet masses, enabling a more realistic interpretation of planet interiors.
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Submitted 9 November, 2022;
originally announced November 2022.
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Is [Y/Mg] a Reliable Age Diagnostic for FGK Stars?
Authors:
Travis A. Berger,
Jennifer L. van Saders,
Daniel Huber,
Eric Gaidos,
Joshua E. Schlieder,
Zachary R. Claytor
Abstract:
Current spectroscopic surveys are producing large catalogs of chemical abundances for stars of all types. The yttrium to magnesium ratio, [Y/Mg], has emerged as a candidate age indicator for solar twins in the local stellar neighborhood. However, it is unclear whether it is a viable age diagnostic for more diverse stellar types, so we investigate [Y/Mg] as an age indicator for the FGK-type planet…
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Current spectroscopic surveys are producing large catalogs of chemical abundances for stars of all types. The yttrium to magnesium ratio, [Y/Mg], has emerged as a candidate age indicator for solar twins in the local stellar neighborhood. However, it is unclear whether it is a viable age diagnostic for more diverse stellar types, so we investigate [Y/Mg] as an age indicator for the FGK-type planet host stars observed by $Kepler$. We find that the [Y/Mg] "Clock" is most precise for solar twins, with a [Y/Mg]/Age slope of $m$ = $-$0.0370 $\pm$ 0.0071 dex/Gyr and $σ_{\mathrm{Age}}$ = 2.6 Gyr. We attribute the lower precision compared to literature results to non-solar twins contaminating our solar twin sample and recommend a 1.5 Gyr systematic uncertainty for stellar ages derived with any [Y/Mg]-Age relation. We also analyzed the [Y/Mg] Clock as a function of $T_{\mathrm{eff}}$, $\log g$, and metallicity individually and find no strong trends, but compute statistically significant [Y/Mg]-Age relations for subsamples defined by ranges in $T_{\mathrm{eff}}$, $\log g$, and metallicity. Finally, we compare [Y/Mg] and rotation ages and find statistically similar trends as for isochrone ages, although we find that rotation ages perform better for GK dwarfs while isochrones perform better for FG subgiants. We conclude that the [Y/Mg] Clock is most precise for solar twins and analogs but is also a useful age diagnostic for FGK stars.
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Submitted 4 August, 2022; v1 submitted 21 June, 2022;
originally announced June 2022.
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The TESS-Keck Survey. XI. Mass Measurements for Four Transiting sub-Neptunes orbiting K dwarf TOI-1246
Authors:
Emma V. Turtelboom,
Lauren M. Weiss,
Courtney D. Dressing,
Grzegorz Nowak,
Enric Pallé,
Corey Beard,
Sarah Blunt,
Casey Brinkman,
Ashley Chontos,
Zachary R. Claytor,
Fei Dai,
Paul A. Dalba,
Steven Giacalone,
Erica Gonzales,
Caleb K. Harada,
Michelle L. Hill,
Rae Holcomb,
Judith Korth,
Jack Lubin,
Thomas Masseron,
Mason MacDougall,
Andrew W. Mayo,
Teo Močnik,
Joseph M. Akana Murphy,
Alex S. Polanski
, et al. (56 additional authors not shown)
Abstract:
Multi-planet systems are valuable arenas for investigating exoplanet architectures and comparing planetary siblings. TOI-1246 is one such system, with a moderately bright K dwarf ($\rm{V=11.6,~K=9.9}$) and four transiting sub-Neptunes identified by TESS with orbital periods of $4.31~\rm{d},~5.90~\rm{d},~18.66~\rm{d}$, and $~37.92~\rm{d}$. We collected 130 radial velocity observations with Keck/HIR…
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Multi-planet systems are valuable arenas for investigating exoplanet architectures and comparing planetary siblings. TOI-1246 is one such system, with a moderately bright K dwarf ($\rm{V=11.6,~K=9.9}$) and four transiting sub-Neptunes identified by TESS with orbital periods of $4.31~\rm{d},~5.90~\rm{d},~18.66~\rm{d}$, and $~37.92~\rm{d}$. We collected 130 radial velocity observations with Keck/HIRES and TNG/HARPS-N to measure planet masses. We refit the 14 sectors of TESS photometry to refine planet radii ($\rm{2.97 \pm 0.06~R_\oplus},\rm{2.47 \pm 0.08~R_\oplus}, \rm{3.46 \pm 0.09~R_\oplus}$, $\rm{3.72 \pm 0.16~R_\oplus}$), and confirm the four planets. We find that TOI-1246 e is substantially more massive than the three inner planets ($\rm{8.1 \pm 1.1 M_\oplus}$, $\rm{8.8 \pm 1.2 M_\oplus}$, $\rm{5.3 \pm 1.7 M_\oplus}$, $\rm{14.8 \pm 2.3 M_\oplus}$). The two outer planets, TOI-1246 d and TOI-1246 e, lie near to the 2:1 resonance ($\rm{P_{e}/P_{d}=2.03}$) and exhibit transit timing variations. TOI-1246 is one of the brightest four-planet systems, making it amenable for continued observations. It is one of only six systems with measured masses and radii for all four transiting planets. The planet densities range from $\rm{0.70 \pm 0.24}$ to $3.21 \pm 0.44 \rm{g/cm^3}$, implying a range of bulk and atmospheric compositions. We also report a fifth planet candidate found in the RV data with a minimum mass of 25.6 $\pm$ 3.6 $\rm{M_\oplus}$. This planet candidate is exterior to TOI-1246 e with a candidate period of 93.8 d, and we discuss the implications if it is confirmed to be planetary in nature.
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Submitted 25 April, 2022;
originally announced April 2022.
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Worry No More, The Hubble Tension is Relieved: A Truly Direct Measurement of the Hubble Constant from Mooniversal Expansion
Authors:
Gagandeep S. Anand,
Zachary R. Claytor,
Ryan Dungee
Abstract:
Using sedimentary and eclipse-based measurements of the lunar recession velocity, we derive a new local-Universe measurement of the Hubble constant ($H_0$) from the recession rate of Earth's Moon. Taking into account the effects of tides, we find a value of $H_{0}$ = 63.01 $\pm$ 1.79 km s$^{-1}$ Mpc$^{-1}$, which is in approximate agreement with the Planck space mission's measurement using the cos…
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Using sedimentary and eclipse-based measurements of the lunar recession velocity, we derive a new local-Universe measurement of the Hubble constant ($H_0$) from the recession rate of Earth's Moon. Taking into account the effects of tides, we find a value of $H_{0}$ = 63.01 $\pm$ 1.79 km s$^{-1}$ Mpc$^{-1}$, which is in approximate agreement with the Planck space mission's measurement using the cosmic microwave background (CMB) and base $Λ$CDM. Our new measurement represents the first ever model-independent, single-step measurement of the Universe's current expansion rate. This is also the first major local Universe measurement of $H_0$ which is below the measurement from Planck. Importantly, it is robust to the systematic errors that may be present in other $H_0$ measurements using other cosmological probes such as type Ia supernovae, baryon acoustic oscillations, or lensed quasars. Our work provides key evidence towards the notion that the existing Hubble tension may indeed be a result of systematic uncertainties in the local distance ladder.
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Submitted 30 March, 2022;
originally announced March 2022.
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Rotation Distributions around the Kraft Break with TESS and Kepler: The Influences of Age, Metallicity, and Binarity
Authors:
Ellis A. Avallone,
Jamie N. Tayar,
Jennifer L. van Saders,
Travis A. Berger,
Zachary R. Claytor,
Rachael L. Beaton,
Johanna Teske,
Diego Godoy-Rivera,
Kaike Pan
Abstract:
Stellar rotation is a complex function of mass, metallicity, and age and can be altered by binarity. To understand the importance of these parameters in main sequence stars, we have assembled a sample of observations that spans a range of these parameters using a combination of observations from The Transiting Exoplanet Survey Satellite (TESS) and the Kepler Space Telescope. We find that while we…
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Stellar rotation is a complex function of mass, metallicity, and age and can be altered by binarity. To understand the importance of these parameters in main sequence stars, we have assembled a sample of observations that spans a range of these parameters using a combination of observations from The Transiting Exoplanet Survey Satellite (TESS) and the Kepler Space Telescope. We find that while we can measure rotation periods and identify other classes of stellar variability (e.g., pulsations) from TESS lightcurves, instrument systematics prevent the detection of rotation signals longer than the TESS orbital period of 13.7 days. Due to this detection limit, we also utilize rotation periods constrained using rotational velocities measured by the APOGEE spectroscopic survey and radii estimated using the Gaia mission for both TESS and Kepler stars. From these rotation periods, we 1) find we can track rotational evolution along discrete mass tracks as a function of stellar age, 2) find we are unable to recover trends between rotation and metallicity that were observed by previous studies, and 3) note that our sample reveals that wide binary companions do not affect rotation, while close binary companions cause stars to exhibit more rapid rotation than single stars.
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Submitted 28 March, 2022;
originally announced March 2022.
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TKS V. Twin sub-Neptunes Transiting the Nearby G Star HD 63935
Authors:
Nicholas Scarsdale,
Joseph M. Akana Murphy,
Natalie M. Batalha,
Ian J. M. Crossfield,
Courtney D. Dressing,
Benjamin Fulton,
Andrew W. Howard,
Daniel Huber,
Howard Isaacson,
Stephen R. Kane,
Erik A. Petigura,
Paul Robertson,
Arpita Roy,
Lauren M. Weiss,
Corey Beard,
Aida Behmard,
Ashley Chontos,
Jessie L. Christiansen,
David R. Ciardi,
Zachary R. Claytor,
Karen A. Collins,
Kevin I. Collins,
Fei Dai,
Paul A. Dalba,
Diana Dragomir
, et al. (34 additional authors not shown)
Abstract:
We present the discovery of two nearly identically-sized sub-Neptune transiting planets orbiting HD 63935, a bright ($V=8.6$ mag), sun-like ($T_{eff}=5560K$) star at 49 pc. TESS identified the first planet, HD 63935 b (TOI-509.01), in Sectors 7 and 34. We identified the second signal (HD 63935 c) in Keck HIRES and Lick APF radial velocity data as part of our followup campaign. It was subsequently…
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We present the discovery of two nearly identically-sized sub-Neptune transiting planets orbiting HD 63935, a bright ($V=8.6$ mag), sun-like ($T_{eff}=5560K$) star at 49 pc. TESS identified the first planet, HD 63935 b (TOI-509.01), in Sectors 7 and 34. We identified the second signal (HD 63935 c) in Keck HIRES and Lick APF radial velocity data as part of our followup campaign. It was subsequently confirmed with TESS photometry in Sector 34 as TOI-509.02. Our analysis of the photometric and radial velocity data yields a robust detection of both planets with periods of $9.0600 \pm 0.007$ and $21.40 \pm 0.0019$ days, radii of $2.99 \pm 0.14$ and $2.90 \pm 0.13$ $R_\oplus$, and masses of $10.8 \pm 1.8$ and $11.1 \pm 2.4$ $M_\oplus$. We calculate densities for planets b and c consistent with a few percent of the planet mass in hydrogen/helium envelopes. We also describe our survey's efforts to choose the best targets for JWST atmospheric followup. These efforts suggest that HD 63935 b will have the most clearly visible atmosphere of its class. It is the best target for transmission spectroscopy (ranked by Transmission Spectroscopy Metric, a proxy for atmospheric observability) in the so-far uncharacterized parameter space comprising sub-Neptune-sized (2.6 $R_\oplus$ $<$ $R_p$ $<$ 4 $R_\oplus$), moderately-irradiated (100 $F_\oplus$ $<$ $F_p$ $<$ 1000 $F_\oplus$) planets around G-stars. Planet c is also a viable target for transmission spectroscopy, and given the indistinguishable masses and radii of the two planets, the system serves as a natural laboratory for examining the processes that shape the evolution of sub-Neptune planets.
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Submitted 5 January, 2022; v1 submitted 13 October, 2021;
originally announced October 2021.
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The Second Discovery from the COol Companions ON Ultrawide orbiTS (COCONUTS) Program: A Cold Wide-Orbit Exoplanet around a Young Field M Dwarf at 10.9 pc
Authors:
Zhoujian Zhang,
Michael C. Liu,
Zachary R. Claytor,
William M. J. Best,
Trent J. Dupuy,
Robert J. Siverd
Abstract:
We present the identification of the COCONUTS-2 system, composed of the M3 dwarf L 34-26 and the T9 dwarf WISEPA J075108.79$-$763449.6. Given their common proper motions and parallaxes, these two field objects constitute a physically bound pair with a projected separation of 594$"$ (6471 au). The primary star COCONUTS-2A has strong stellar activity (H$α$, X-ray, and UV emission) and is rapidly rot…
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We present the identification of the COCONUTS-2 system, composed of the M3 dwarf L 34-26 and the T9 dwarf WISEPA J075108.79$-$763449.6. Given their common proper motions and parallaxes, these two field objects constitute a physically bound pair with a projected separation of 594$"$ (6471 au). The primary star COCONUTS-2A has strong stellar activity (H$α$, X-ray, and UV emission) and is rapidly rotating ($P_{\rm rot} = 2.83$ days), from which we estimate an age of 150-800 Myr. Comparing equatorial rotational velocity derived from the TESS light curve to spectroscopic $v\sin{i}$, we find COCONUTS-2A has a nearly edge-on inclination. The wide exoplanet COCONUTS-2b has an effective temperature of $T_{\rm eff}=434 \pm 9$ K, a surface gravity of $\log{g} = 4.11^{+0.11}_{-0.18}$ dex, and a mass of $M=6.3^{+1.5}_{-1.9}$ $M_{\rm Jup}$ based on hot-start evolutionary models, leading to a $0.016^{+0.004}_{-0.005}$ mass ratio for the COCONUTS-2 system. COCONUTS-2b is the second coldest (after WD 0806$-$661B) and the second widest (after TYC 9486-927-1 b) exoplanet imaged to date. Comparison of COCONUTS-2b's infrared photometry with ultracool model atmospheres suggests the presence of both condensate clouds and non-equilibrium chemistry in its photosphere. Similar to 51 Eri b, COCONUTS-2b has a sufficiently low luminosity ($\log{(L_{\rm bol}/L_{\odot})} = -6.384 \pm 0.028$ dex) to be consistent with the cold-start process that may form gas-giant (exo)planets, though its large separation means such formation would not have occurred in situ. Finally, at a distance of 10.9 pc, COCONUTS-2b is the nearest imaged exoplanet to Earth known to date.
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Submitted 6 July, 2021;
originally announced July 2021.
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Recovery of TESS Stellar Rotation Periods Using Deep Learning
Authors:
Zachary R. Claytor,
Jennifer L. van Saders,
Joe Llama,
Peter Sadowski,
Brandon Quach,
Ellis Avallone
Abstract:
We used a convolutional neural network to infer stellar rotation periods from a set of synthetic light curves simulated with realistic spot evolution patterns. We convolved these simulated light curves with real TESS light curves containing minimal intrinsic astrophysical variability to allow the network to learn TESS systematics and estimate rotation periods despite them. In addition to periods,…
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We used a convolutional neural network to infer stellar rotation periods from a set of synthetic light curves simulated with realistic spot evolution patterns. We convolved these simulated light curves with real TESS light curves containing minimal intrinsic astrophysical variability to allow the network to learn TESS systematics and estimate rotation periods despite them. In addition to periods, we predict uncertainties via heteroskedastic regression to estimate the credibility of the period predictions. In the most credible half of the test data, we recover 10%-accurate periods for 46% of the targets, and 20%-accurate periods for 69% of the targets. Using our trained network, we successfully recover periods of real stars with literature rotation measurements, even past the 13.7-day limit generally encountered by TESS rotation searches using conventional period-finding techniques. Our method also demonstrates resistance to half-period aliases. We present the neural network and simulated training data, and introduce the software butterpy used to synthesize the light curves using realistic star spot evolution.
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Submitted 29 April, 2021;
originally announced April 2021.
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TESS Asteroseismology of $α$ Mensae: Benchmark Ages for a G7 Dwarf and its M-dwarf Companion
Authors:
Ashley Chontos,
Daniel Huber,
Travis A. Berger,
Hans Kjeldsen,
Aldo M. Serenelli,
Victor Silva Aguirre,
Warrick H. Ball,
Sarbani Basu,
Timothy R. Bedding,
William J. Chaplin,
Zachary R. Claytor,
Enrico Corsaro,
Rafael A. García,
Steve B. Howell,
Mia S. Lundkvist,
Savita Mathur,
Travis S. Metcalfe,
Martin B. Nielsen,
Jia Mian Joel Ong,
Zeynep Çelik Orhan,
Sibel Örtel,
Maïssa Salama,
Keivan G. Stassun,
R. H. D. Townsend,
Jennifer L. van Saders
, et al. (5 additional authors not shown)
Abstract:
Asteroseismology of bright stars has become increasingly important as a method to determine fundamental properties (in particular ages) of stars. The Kepler Space Telescope initiated a revolution by detecting oscillations in more than 500 main-sequence and subgiant stars. However, most Kepler stars are faint, and therefore have limited constraints from independent methods such as long-baseline int…
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Asteroseismology of bright stars has become increasingly important as a method to determine fundamental properties (in particular ages) of stars. The Kepler Space Telescope initiated a revolution by detecting oscillations in more than 500 main-sequence and subgiant stars. However, most Kepler stars are faint, and therefore have limited constraints from independent methods such as long-baseline interferometry. Here, we present the discovery of solar-like oscillations in $α$ Men A, a naked-eye (V=5.1) G7 dwarf in TESS's Southern Continuous Viewing Zone. Using a combination of astrometry, spectroscopy, and asteroseismology, we precisely characterize the solar analog alpha Men A (Teff = 5569 +/- 62 K, R = 0.960 +/- 0.016 Rsun, M = 0.964 +/- 0.045 Msun). To characterize the fully convective M dwarf companion, we derive empirical relations to estimate mass, radius, and temperature given the absolute Gaia magnitude and metallicity, yielding M = 0.169 +/- 0.006, R = 0.19 +/- 0.01 and Teff = 3054 +/- 44 K. Our asteroseismic age of 6.2 +/- 1.4 (stat) +/- 0.6 (sys) Gyr for the primary places $α$ Men B within a small population of M dwarfs with precisely measured ages. We combined multiple ground-based spectroscopy surveys to reveal an activity cycle of 13.1 +/- 1.1 years, a period similar to that observed in the Sun. We used different gyrochronology models with the asteroseismic age to estimate a rotation period of ~30 days for the primary. Alpha Men A is now the closest (d=10pc) solar analog with a precise asteroseismic age from space-based photometry, making it a prime target for next-generation direct imaging missions searching for true Earth analogs.
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Submitted 4 December, 2021; v1 submitted 19 December, 2020;
originally announced December 2020.
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A Guide to Realistic Uncertainties on Fundamental Properties of Solar-Type Exoplanet Host Stars
Authors:
Jamie Tayar,
Zachary R. Claytor,
Daniel Huber,
Jennifer van Saders
Abstract:
Our understanding of the properties and demographics of exoplanets critically relies on our ability to determine fundamental properties of their host stars. The advent of Gaia and large spectroscopic surveys has now made it in principle possible to infer properties of individual stars, including most exoplanet hosts, to very high precision. However, we show that in practice, such analyses are limi…
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Our understanding of the properties and demographics of exoplanets critically relies on our ability to determine fundamental properties of their host stars. The advent of Gaia and large spectroscopic surveys has now made it in principle possible to infer properties of individual stars, including most exoplanet hosts, to very high precision. However, we show that in practice, such analyses are limited both by uncertainties in the fundamental scale, and by uncertainties in our models of stellar evolution, even for stars similar to the Sun. For example, we show that current uncertainties on measured interferometric angular diameters and bolometric fluxes set a systematic uncertainty floor of $\sim$2% in temperature, $\sim$2% in luminosity, and $\sim$4% in radius. Comparisons between widely available model grids suggest uncertainties of order $\sim$5% in mass and $\sim$20% in age for main sequence and subgiant stars. While the radius uncertainties are roughly constant over this range of stars, the model dependent uncertainties are a complex function of luminosity, temperature, and metallicity. We provide open-source software for approximating these uncertainties for individual targets, and discuss strategies for reducing these uncertainties in the future.
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Submitted 14 December, 2020;
originally announced December 2020.
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The TESS-Keck Survey II: An Ultra-Short Period Rocky Planet and its Siblings Transiting the Galactic Thick-Disk Star TOI-561
Authors:
Lauren M. Weiss,
Fei Dai,
Daniel Huber,
John M. Brewer,
Karen A. Collins,
David R. Ciardi,
Elisabeth C. Matthews,
Carl Ziegler,
Steve B. Howell,
Natalie M. Batalha,
Ian J. M> Crossfield,
Courtney Dressing,
Benjamin Fulton,
Andrew W. Howard,
Howard Isaacson,
Stephen R. Kane,
Erik A. Petigura,
Paul Robertson,
Arpita Roy,
Ryan A. Rubenzahl,
Joseph D. Twicken,
Zachary R. Claytor,
Keivan G. Stassun,
Mason G. MacDougall,
Ashley Chontos
, et al. (39 additional authors not shown)
Abstract:
We report the discovery of TOI-561, a multi-planet system in the galactic thick disk that contains a rocky, ultra-short period planet (USP). This bright ($V=10.2$) star hosts three small transiting planets identified in photometry from the NASA TESS mission: TOI-561 b (TOI-561.02, P=0.44 days, $R_b = 1.45\pm0.11\,R_\oplus$), c (TOI-561.01, P=10.8 days, $R_c=2.90\pm0.13\,R_\oplus$), and d (TOI-561.…
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We report the discovery of TOI-561, a multi-planet system in the galactic thick disk that contains a rocky, ultra-short period planet (USP). This bright ($V=10.2$) star hosts three small transiting planets identified in photometry from the NASA TESS mission: TOI-561 b (TOI-561.02, P=0.44 days, $R_b = 1.45\pm0.11\,R_\oplus$), c (TOI-561.01, P=10.8 days, $R_c=2.90\pm0.13\,R_\oplus$), and d (TOI-561.03, P=16.3 days, $R_d=2.32\pm0.16\,R_\oplus$). The star is chemically ([Fe/H]$=-0.41\pm0.05$, [$α$/H]$=+0.23\pm0.05$) and kinematically consistent with the galactic thick disk population, making TOI-561 one of the oldest ($10\pm3\,$Gyr) and most metal-poor planetary systems discovered yet. We dynamically confirm planets b and c with radial velocities from the W. M. Keck Observatory High Resolution Echelle Spectrometer. Planet b has a mass and density of $3.2\pm0.8\,M_\oplus$ and $5.5^{+2.0}_{-1.6}\,$g$\,$cm$^{-3}$, consistent with a rocky composition. Its lower-than-average density is consistent with an iron-poor composition, although an Earth-like iron-to-silicates ratio is not ruled out. Planet c is $7.0\pm2.3\,M_\oplus$ and $1.6\pm0.6\,$g$\,$cm$^{-3}$, consistent with an interior rocky core overlaid with a low-mass volatile envelope. Several attributes of the photometry for planet d (which we did not detect dynamically) complicate the analysis, but we vet the planet with high-contrast imaging, ground-based photometric follow-up and radial velocities. TOI-561 b is the first rocky world around a galactic thick-disk star confirmed with radial velocities and one of the best rocky planets for thermal emission studies.
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Submitted 14 December, 2020; v1 submitted 7 September, 2020;
originally announced September 2020.
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Chemical Evolution in the Milky Way: Rotation-based ages for APOGEE-Kepler cool dwarf stars
Authors:
Zachary R. Claytor,
Jennifer L. van Saders,
Angela R. G. Santos,
Rafael A. Garcia,
Savita Mathur,
Jamie Tayar,
Marc H. Pinsonneault,
Matthew Shetrone
Abstract:
We use models of stellar angular momentum evolution to determine ages for $\sim500$ stars in the APOGEE-\textit{Kepler} Cool Dwarfs sample. We focus on lower main-sequence stars, where other age-dating tools become ineffective. Our age distributions are compared to those derived from asteroseismic and giant samples and solar analogs. We are able to recover gyrochronological ages for old, lower-mai…
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We use models of stellar angular momentum evolution to determine ages for $\sim500$ stars in the APOGEE-\textit{Kepler} Cool Dwarfs sample. We focus on lower main-sequence stars, where other age-dating tools become ineffective. Our age distributions are compared to those derived from asteroseismic and giant samples and solar analogs. We are able to recover gyrochronological ages for old, lower-main-sequence stars, a remarkable improvement over prior work in hotter stars. Under our model assumptions, our ages have a median relative uncertainty of $14\%$, comparable to the age precision inferred for more massive stars using traditional methods. We investigate trends of galactic $α$-enhancement with age, finding evidence of a detection threshold between the age of the oldest $α$-poor stars and that of the bulk $α$-rich population. We argue that gyrochronology is an effective tool reaching ages of 10--12 Gyr in K- and early M-dwarfs. Finally, we present the first effort to quantify the impact of detailed abundance patterns on rotational evolution. We estimate a $\sim15\%$ bias in age for cool, $α$-enhanced (+ 0.4 dex) stars when standard solar-abundance-pattern rotational models are used for age inference, rather than models that appropriately account for $α$-enrichment.
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Submitted 11 November, 2019;
originally announced November 2019.