Showing 1–50 of 161 results for author: Geballe, T R

Ultraviolet to Infrared Spectroscopy of the Type Ibn SN 2023tsz Suggests a Lower-mass Progenitor

Authors: Sergiy S. Vasylyev, Griffin Hosseinzadeh, Luc Dessart, Ori Fox, David J. Sand, Alexei V. Filippenko, Qinan Wang, D. Andrew Howell, Jennifer E. Andrews, Moira Andrews, Pallas Beddow, K. Azalee Bostroem, Thomas G. Brink, Peter J. Brown, Asia deGraw, Yize Dong, Joseph Farah, Thomas R. Geballe, Sebastian Gomez, Emily T. Hoang, Brian Hsu, Saurabh W. Jha, Patrick Kelly, Curtis McCully, Darshana Mehta , et al. (20 additional authors not shown)

Abstract: Type Ibn supernovae are stripped-envelope explosions whose spectra indicate interaction with dense, helium-rich and hydrogen-poor circumstellar material (CSM), making them important probes of late-stage mass loss and progenitor stripping. We present extensive ultraviolet-to-near-infrared spectrophotometry of the Type Ibn SN 2023tsz, including two epochs of HST/STIS ultraviolet (UV) spectroscopy an… ▽ More Type Ibn supernovae are stripped-envelope explosions whose spectra indicate interaction with dense, helium-rich and hydrogen-poor circumstellar material (CSM), making them important probes of late-stage mass loss and progenitor stripping. We present extensive ultraviolet-to-near-infrared spectrophotometry of the Type Ibn SN 2023tsz, including two epochs of HST/STIS ultraviolet (UV) spectroscopy and ground-based optical and near-infrared follow-up observations. The spectra are dominated by intermediate-width emission lines at all phases after maximum light, suggesting that much of the luminosity originates in a cold dense shell (CDS) formed by interaction between the ejecta and CSM. We compare the observations to one-dimensional non-local-thermodynamic-equilibrium radiative-transfer models of a helium-star explosion with a mass of $4 M_{\odot}$ at the onset of helium burning. The models reproduce the strong optical and near-infrared He I lines and require an added X-ray irradiation field to match the highly ionized UV features. The spectra are best reproduced by models with an X-ray irradiation power of $L_X \approx 10^8 L_{\odot}$, with the preferred models favoring CDS radii of order $(1.5$--$2) \times 10^{15}$ cm, velocities of $\sim 5 \times 10^7$ cm s$^{-1}$, and interaction powers of a few times $10^{42}$ erg s$^{-1}$. In the optical, the preferred models shift from higher interaction power and smaller radii at early times to lower power and larger radii at later times. These results add to the growing evidence that at least some SNe Ibn arise from lower-mass helium stars whose final evolution is shaped by binary interaction. △ Less

Submitted 16 July, 2026; originally announced July 2026.

Comments: Submitted to ApJ

JWST Reveals Large Reservoirs of Dust and Ongoing Circumstellar Interaction in SN Ibn/Icn 2023xgo over a Year Post-Explosion

Authors: Kyle W. Davis, Kirsty Taggart, Samaporn Tinyanont, Ryan J. Foley, Jeonghee Rho, Katie Auchettl, Diego Farias, Ori D. Fox, Joel Johansson, Charles D. Kilpatrick, Kishore C. Patra, Craig Pellegrino, Enrico Ramirez-Ruiz, David A. Coulter, Yize Dong, Alexander T. Gagliano, T. R. Geballe, Wynn V. Jacobson-Galán, Jenna Karcheski, Ravjit Kaur, Ryan M. Lau, Thomas Moore, Seong Hyun Park, Armin Rest, Tamás Szalai , et al. (1 additional authors not shown)

Abstract: We present infrared (IR) photometric and spectroscopic observations of SN 2023xgo, a recent and nearby Type Ibn/Icn supernova (SN Ibn/Icn) which shows shock interaction with a He/C-rich and H-poor circumstellar medium (CSM). Although interacting SNe are predicted to produce large amounts of dust, the rarity of SNe Ibn and Icn has resulted in few opportunities to observe these objects in the IR at… ▽ More We present infrared (IR) photometric and spectroscopic observations of SN 2023xgo, a recent and nearby Type Ibn/Icn supernova (SN Ibn/Icn) which shows shock interaction with a He/C-rich and H-poor circumstellar medium (CSM). Although interacting SNe are predicted to produce large amounts of dust, the rarity of SNe Ibn and Icn has resulted in few opportunities to observe these objects in the IR at late times. Here, we report observations of SN 2023xgo from JWST (NIRSpec and MIRI), WISE, and Gemini taken out to +377 days post-explosion. At +377 days, the JWST spectrum is consistent with both emission from cool (~300-600 K) silicate dust with $M \gtrsim 3 \times 10^{-2}$ M$_{\odot}$ at a radius similar to the shock radius ($2.3 \times 10^{16}$ cm), and optically thin carbonaceous dust with $M = 8 \times 10^{-3}$ M$_{\odot}$. We also detect narrow (FWHM = 520+/-130 km s$^{-1}$) He I $λ$2.06 micron emission at +377 days, indicating that the SN shock continues to encounter material shed from the star to this late epoch. The emission line is blueshifted from the rest frame by 340+/-40 km s$^{-1}$. The Gemini and WISE observations at ~70-100 days reveal emission from 6.8$\times$10$^{-5}$ M$_{\odot}$ of hot (~1300 K) dust, which we interpret as a lower limit of the total dust mass at that phase. Molecular gas emission is not detected in any data, though emission line profiles in the optical and NIR taken at ~70 days after explosion show progressively less redshifted emission, attributed to attenuation from dust and suggesting that some dust is rapidly forming interior to the unshocked CSM. The large dust mass and rapid onset of dust formation observed in SN 2023xgo show that the unique physical environments of SNe Ibn/Icn facilitate substantial dust formation both before and after the SN. △ Less

Submitted 29 May, 2026; originally announced June 2026.

Comments: 22 pages, 11 figures; to be submitted to OJAp

Near-Infrared and Optical Observations of SN 2024rbc: The First Early Detection of CO and Dust in a Type Ib Supernova

Authors: Ryan Hwangbo, Jeonghee Rho, Aravind P. Ravi, Seong Hyun Park, Harim Jin, Sung-Chul Yoon, T. R. Geballe, Ryan Foley, Kirsty Taggart, Kyle W. Davis, Kishore C. Patra, S. Tinyanont, Jesper Sollerman, Steve Schulze, Natalie LeBaron, Chang Liu, Charles D. Kilpatrick, David O. Jones, C. Tanner Murphey

Abstract: We present optical and near-infrared (NIR) observations of the Type Ib supernova (SN) 2024rbc. Emission from the first CO overtone, resting on a dust continuum at $2.3-2.4$ $μ$m, was observed at 62 days post-explosion. The CO band heads are not resolved, and the emission appears broad, lacking sharp spectral features. This is the first observation of CO in the ejecta of a Type Ib SN reported in li… ▽ More We present optical and near-infrared (NIR) observations of the Type Ib supernova (SN) 2024rbc. Emission from the first CO overtone, resting on a dust continuum at $2.3-2.4$ $μ$m, was observed at 62 days post-explosion. The CO band heads are not resolved, and the emission appears broad, lacking sharp spectral features. This is the first observation of CO in the ejecta of a Type Ib SN reported in literature. The spectra of SN 2024rbc exhibit strong He I lines and numerous neutral and ionized metal lines. Comparing the spectral evolution of SN 2024rbc to other Type Ib, Ic, and IIb SNe indicates it is a Type Ib SN. We compare the velocities of key optical lines to examine the evolution of the ejecta. Additionally, fitting SN light curve models of helium star progenitors computed with the STELLA code to photometric observations indicates a $^{56}$Ni mass of $0.07$ $M_\odot$ and an ejecta mass of $1.7$ $M_\odot$. Fitting a LTE model to the CO overtone implies a CO mass of 5.2 $\times$ 10$^{-4}$ $M_{\odot}$, a CO temperature of $4040$ K, and a CO velocity width of $5905$ km s$^{-1}$. We also fitted a modified blackbody model to the dust continuum, deriving a dust temperature of $910$ K and a dust mass of $1.3$ $\times$ $10^{-3}$ $M_{\odot}$. The CO provides direct evidence for the onset of dust formation, and the observed dust continuum likely originates from newly formed dust in the ejecta. However, robust dust mass estimates require MIR observations. △ Less

Submitted 8 August, 2026; v1 submitted 24 March, 2026; originally announced March 2026.

Comments: 24 pages, 14 figures, 5 tables; Accepted to ApJ

Detection of a molecular hydrogen envelope around nova GK Persei

Authors: D. P. K. Banerjee, A. Evans, T. Liimets, C. E. Woodward, T. R. Geballe, V. Joshi, S. Starrfield

Abstract: The eruption of Nova Persei 1901 (GK Per) occurred 125 yrs ago; remarkably it still holds major surprises. Using data from the Spectro-Photometer for the History of the Universe, Epoch of Reionization, and Ices Explorer (SPHEREx), we find it has a bipolar molecular hydrogen shell. This shell, which has dimensions 18'x10', is co-spatial with the Halpha nebulosity surrounding the nova, which is purp… ▽ More The eruption of Nova Persei 1901 (GK Per) occurred 125 yrs ago; remarkably it still holds major surprises. Using data from the Spectro-Photometer for the History of the Universe, Epoch of Reionization, and Ices Explorer (SPHEREx), we find it has a bipolar molecular hydrogen shell. This shell, which has dimensions 18'x10', is co-spatial with the Halpha nebulosity surrounding the nova, which is purported to be an ancient planetary nebula (PN). The shell is detected most strongly in the 0--0 S(9) 4.6947 micron line. A filament of emission in the S(9) 4.6947 micron line is seen 45" SW of GKPer. This coincides, over much of its length, with the site of X-ray and non-thermal radio emission where the 1901 nova ejecta impinges on the ambient medium. We propose that the H_2 emission from the filament arises from the predicted neutral zone between the forward and reverse shocks. Since it is common for bipolar PNe to be accompanied by H_2 envelopes, it ostensibly suggests that the 18'x10' nebulosity is a conventional PN with a luminous, ionizing central source. We show this is not the case, and that the H$α$ nebulosity may be surrounding gas belonging to pre-existing material that was ionized during the 1901 eruption. The ionized gas is presently undergoing recombination on a timescale of ~3000 years, explaining why the nebulosity is still visible. △ Less

Submitted 13 March, 2026; originally announced March 2026.

Comments: 9 pages, 3 figures, 1 table to appear in the ApJ Letters

An infrared echo from a circumstellar disk in the hydrogen- and helium-poor SN 2024aecx

Authors: Samaporn Tinyanont, Kittipong Wangnok, Jennifer E. Andrews, Ryan J. Foley, Methawee Kaewmookda, Jacob E. Jencson, Armin Rest, Katie Auchettl, K. A. Bostroem, David A. Coulter, Poemwai Chainakun, Ryan Chornock, Kyle W. Davis, Ori D. Fox, Lluís Galbany, Thomas R. Geballe, Brian Hsu, Wynn Jacobson-Galán, Saurabh W. Jha, Ravjit Kaur, Mansi M. Kasliwal, Ryan M. Lau, Natalie LeBaron, Raffaella Margutti, Seong Hyun Park , et al. (12 additional authors not shown)

Abstract: We present near-infrared (NIR) spectroscopy of the hydrogen- and helium-poor (Type Ic) supernova (SN) 2024aecx, which displays a strong NIR excess emerging 32 days post peak. SN 2024aecx is a peculiar SN Ic that exhibited luminous shock-cooling emission at early times, suggestive of close-in circumstellar medium (CSM), unexpected for this class of SNe. Its early NIR spectra are typical for a SN Ic… ▽ More We present near-infrared (NIR) spectroscopy of the hydrogen- and helium-poor (Type Ic) supernova (SN) 2024aecx, which displays a strong NIR excess emerging 32 days post peak. SN 2024aecx is a peculiar SN Ic that exhibited luminous shock-cooling emission at early times, suggestive of close-in circumstellar medium (CSM), unexpected for this class of SNe. Its early NIR spectra are typical for a SN Ic but with strong C I absorption features. By $\sim$32 days post peak, the spectra show a strong NIR excess, while maintaining normal optical colors, unprecedented for SNe Ic. We find that the NIR excess is well fit with a single-temperature, optically thin dust model with declining temperature, increasing mass, and roughly constant luminosity over time. The NIR excess appears too promptly for dust to have formed in the SN ejecta, indicating an IR echo from pre-existing dust in the CSM. The IR echo is likely powered by the relatively slowly evolving SN peak light, and not the brief shock cooling emission, as the latter requires unrealistically high CSM densities to explain the observed dust mass. We consider different potential CSM geometries and find that a thick face-on disk with an inner edge of around $5\times 10^{16} \rm \ cm$ can best explain the dust mass and temperature evolution. In this scenario, the SN shock should start interacting with this CSM $440\pm200$ days post explosion. CSM around SN Ic is rare, and follow-up observations of SN 2024aecx will probe the mass-loss process responsible for removing hydrogen and helium from their progenitor star. △ Less

Submitted 18 June, 2026; v1 submitted 2 February, 2026; originally announced February 2026.

Comments: Published in the ApJ

The [Fe XIII] Infrared 10747 Angstrom and 10798 Angstrom Lines in Novae

Authors: D. P. K. Banerjee, C. E. Woodward, A. Evans, T. R. Geballe, V. Joshi, S. Starrfield

Abstract: The forbidden lines of [Fe XIII] at 10,747 Angstrom and 10,798 Angsrtom are among the most prominent lines in the near-infrared spectrum of the solar corona. They have been used routinely, both outside and during eclipses, as sensitive probes of the electron density and polarization in the solar corona. Many novae pass through a coronal phase, wherein the highly ionized nova ejecta have physical c… ▽ More The forbidden lines of [Fe XIII] at 10,747 Angstrom and 10,798 Angsrtom are among the most prominent lines in the near-infrared spectrum of the solar corona. They have been used routinely, both outside and during eclipses, as sensitive probes of the electron density and polarization in the solar corona. Many novae pass through a coronal phase, wherein the highly ionized nova ejecta have physical conditions that are remarkably similar to those of the solar corona. Many of the coronal emission lines that are seen are common to the spectra of both the Sun and novae. Yet, it appears that no robust detection of the [Fe XIII] lines has been made in a nova. Here we report the detection of these two infrared [Fe XIII]lines in the spectrum of the recurrent nova V3890 Sgr, taken 23.43 and 31.35 days after its August 2019 outburst. From their line strengths, we derive values of 10^10 per cubic cm and 10^[8.5-9] per cubic cm for the electron density on the two. The decrease in density between epochs can be explained if the density decreased with a power law n ~ r**alpha with a alpha inferred to be -3. The average temperature of the coronal gas is estimated to be T = (2.51\pm0.06) x 10^6~K. We find that recurrent novae with giant secondaries, including T CrB whose eruption is imminent, are the most suitable sources for further detections of the [Fe XIII] lines. epochs. △ Less

Submitted 20 January, 2026; originally announced January 2026.

Comments: 8 Page, 5 Figures, 1 Table, To Appear in the Astrophysical J

A Tale of Two Sightlines: Comparison of Hydrocarbon Dust Absorption Bands toward Cygnus OB2-12 and the Galactic Center

Authors: Yvonne J. Pendleton, T. R. Geballe, Laurie E. U. Chu, Marjorie Decleir, Karl D. Gordon, A. G. G. M. Tielens, Louis J. Allamandola, Jeroen Bouwman, J. E. Chiar, Curtis Dewitt, Burcu Gunay, Thomas Henning, Vito Mennella, M. E. Palumbo, Alexey Potapov, Maisie Rashman, Sascha Zeegers

Abstract: Infrared spectra of hydrocarbon dust absorption bands toward the bright hypergiant Cygnus OB2-12 are compared to published spectra of the Quintuplet Cluster, a sightline to the Galactic center. The Cyg OB2-12 data include a new ground-based 2.86-3.70 microns spectrum and a previously published, but here further analyzed, spectrum of the 5.50-7.34 microns region. Higher spectral resolution data for… ▽ More Infrared spectra of hydrocarbon dust absorption bands toward the bright hypergiant Cygnus OB2-12 are compared to published spectra of the Quintuplet Cluster, a sightline to the Galactic center. The Cyg OB2-12 data include a new ground-based 2.86-3.70 microns spectrum and a previously published, but here further analyzed, spectrum of the 5.50-7.34 microns region. Higher spectral resolution data for the Cyg OB2-12 sightline in the 3 micron region allows a detailed comparison of the 3.4 micron aliphatic bands to those observed toward the Quintuplet. Despite differences in interstellar environments along each sightline, strong similarities are observed in the central wavelengths and relative strengths for bands at 3.3, 3.4, 5.85, 6.2, and 6.85 microns. Analysis of these bands, produced by aromatic, aliphatic, olefinic, hydrogenated, and oxygenated components, shows that carbonaceous dust is a significant component of the diffuse interstellar medium, second in abundance only to silicates, and is primarily aromatic in nature. The grains producing these bands likely consist of large aromatic carbon cores with thin aliphatic mantles composed of hydrogenated amorphous carbon (HAC). Laboratory analog spectra reproduce the observed aliphatic absorption bands well, supporting the presence of such mantles. We present evidence that the carriers of both the 3.4 micron aliphatic and the 3.3 micron aromatic bands reside exclusively in the diffuse ISM, and that the 3.3 micron bands observed in the diffuse ISM differ from the 3.25 micron band seen in dense clouds, implying chemically distinct carriers. △ Less

Submitted 27 September, 2025; v1 submitted 17 August, 2025; originally announced August 2025.

Comments: 28 pages, 7 figures, accepted by ApJ; one typo corrected; two minor clarifying changes to text

Infrared Spectroscopy of V838 Monocerotis in 2015 and 2022

Authors: T. R. Geballe, B. M. Kaminskiy, D. P. K. Banerjee, A. Evans, Y. Pavlenko, M. T. Rushton, M. Popescu, S. P. S. Eyres

Abstract: We report medium-resolution $0.85-2.45\,μ$m spectroscopy obtained in 2015 and 2022 and high resolution $2.27-2.39\,μ$m and $4.59-4.77\,μ$m spectroscopy obtained in 2015 of V838 Monocerotis, along with modeling of the $0.85-2.45\,μ$ spectrum. V838 Mon underwent a series of eruptions and extreme brightenings in 2002, which are thought to have occured as a result of a stellar merger. The new spectra… ▽ More We report medium-resolution $0.85-2.45\,μ$m spectroscopy obtained in 2015 and 2022 and high resolution $2.27-2.39\,μ$m and $4.59-4.77\,μ$m spectroscopy obtained in 2015 of V838 Monocerotis, along with modeling of the $0.85-2.45\,μ$ spectrum. V838 Mon underwent a series of eruptions and extreme brightenings in 2002, which are thought to have occured as a result of a stellar merger. The new spectra and modelling of them reveal a disturbed red giant photosphere that is probably continuing to contract and ejecta that are cooling and continuing to disperse at velocities up to 200kms$^{-1}$. △ Less

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

Comments: Accepted for publication in MNRAS. Updated to make minor corrections identified at the proof stage

Near-Infrared Spectroscopy and Detection of Carbon Monoxide in the Type II Supernova SN 2023ixf

Authors: Seong Hyun Park, Jeonghee Rho, Sung-Chul Yoon, Jeniveve Pearson, Manisha Shrestha, Samaporn Tinyanont, T. R. Geballe, Ryan J. Foley, Aravind P. Ravi, Jennifer Andrews, David J. Sand, K. Azalee Bostroem, Chris Ashall, Peter Hoeflich, Stefano Valenti, Yize Dong, Nicolas Meza Retamal, Emily Hoang, Darshana Mehta, D. Andrew Howell, Joseph R. Farah, Giacomo Terreran, Estefania Padilla Gonzalez, Moira Andrews, Megan Newsome , et al. (11 additional authors not shown)

Abstract: Core-collapse supernovae (CCSNe) may contribute a significant amount of dust in the early universe. Freshly formed coolant molecules (e.g., CO) and warm dust can be found in CCSNe as early as ~100 d after the explosion, allowing the study of their evolution with time series observations. In the Type II SN 2023ixf, we aim to investigate the temporal evolution of the temperature, velocity, and mass… ▽ More Core-collapse supernovae (CCSNe) may contribute a significant amount of dust in the early universe. Freshly formed coolant molecules (e.g., CO) and warm dust can be found in CCSNe as early as ~100 d after the explosion, allowing the study of their evolution with time series observations. In the Type II SN 2023ixf, we aim to investigate the temporal evolution of the temperature, velocity, and mass of CO and compare them with other CCSNe, exploring their implications for the dust formation in CCSNe. From observations of velocity profiles of lines of other species (e.g., H and He), we also aim to characterize and understand the interaction of the SN ejecta with preexisting circumstellar material (CSM). We present a time series of 16 near-infrared spectra of SN 2023ixf from 9 to 307 d, taken with multiple instruments: Gemini/GNIRS, Keck/NIRES, IRTF/SpeX, and MMT/MMIRS. The early (t<70 d) spectra indicate interaction between the expanding ejecta and nearby CSM. At t<20 d, intermediate-width line profiles corresponding to the ejecta-wind interaction are superposed on evolving broad P Cygni profiles. We find intermediate-width and narrow lines in the spectra until t<70 d, which suggest continued CSM interaction. We also observe and discuss high-velocity absorption features in H $α$ and H $β$ line profiles formed by CSM interaction. The spectra contain CO first overtone emission between 199 and 307 d after the explosion. We model the CO emission and find the CO to have a higher velocity (3000-3500 km/s) than that in Type II-pec SN 1987A (1800-2000 km/s) during similar phases (t=199-307 d) and a comparable CO temperature to SN 1987A. A flattened continuum at wavelengths greater than 1.5 $μ$m accompanies the CO emission, suggesting that the warm dust is likely formed in the ejecta. The warm dust masses are estimated to be on the order of ~10$^{-5} M_{\odot}$.} △ Less

Submitted 31 July, 2025; v1 submitted 15 July, 2025; originally announced July 2025.

Comments: 14 pages, 7 figures, 1 additional figure, submitted to A&A

Journal ref: A&A 703, A227 (2025)

Investigating silicate, carbon, and water in the diffuse interstellar medium: the first shots from WISCI

Authors: S. T. Zeegers, Jonathan P. Marshall, Karl D. Gordon, Karl A. Misselt, G. P. P. L. Otten, Jeroen Bouwman, Jean Chiar, Marjorie Decleir, Thavisha Dharmawardena, F. Kemper, Aigen Li, Mayank Narang, Alexey Potapov, Manoj Puravankara, Peter Scicluna, Himanshu Tyagi, Eleonora Zari, ChuanYu Wei, Lex Kaper, Frank Backs, Stefan T. Bromley, Laurie Chu, Elisa Costantini, T. R. Geballe, Joel D. Green , et al. (11 additional authors not shown)

Abstract: The dusty interstellar medium (ISM) of the Milky Way is distributed in a complex, cloudy structure. It is fundamental to the radiation balance within the Milky Way, provides a reaction surface to form complex molecules, and is the feedstock for future generations of stars and planets. The life cycle of interstellar dust is not completely understood, and neither are its structure nor composition. T… ▽ More The dusty interstellar medium (ISM) of the Milky Way is distributed in a complex, cloudy structure. It is fundamental to the radiation balance within the Milky Way, provides a reaction surface to form complex molecules, and is the feedstock for future generations of stars and planets. The life cycle of interstellar dust is not completely understood, and neither are its structure nor composition. The abundance, composition, and structure of dust in the diffuse ISM can be determined by combining infrared, optical and ultraviolet spectroscopy. JWST enables measurement of the faint absorption of ISM dust grains against bright stars at kiloparsec distances across the infrared spectrum. Here we present an overview of the project `Webb Investigation of Silicates, Carbons, and Ices' (WISCI) along with interpretation of two targets, GSC 08152-02121 and CPD-59 5831. Observations of 12 WISCI target stars were taken by JWST, the Hubble Space Telescope, Himalayan Chandra Telescope, and the Very Large Telescope. We use these to characterize the targets' spectral types and calculate their line-of-sight extinction parameters, $A_{\rm V}$ and $R_{\rm V}$. We find absorption in the JWST spectra of GSC 08152-02121, and CPD-59 5831 associated with carbonaceous dust around 3.4 and 6.2 micron and amorphous silicates at 9.7 micron. In GSC 08152-02121 we also find indications of absorption by trapped water around 3 micron. This first look from WISCI demonstrates the line-of-sight variability within the sample, and the program's potential to identify and correlate features across ultraviolet to mid-infrared wavelengths. △ Less

Submitted 24 June, 2025; originally announced June 2025.

Comments: Accepted for publication in ApJ

Near-Infrared Spectroscopy of the Recurrent Nova M31N 2008-12a

Authors: D. P. K. Banerjee, T. R. Geballe, A. Evans, C. E. Woodward, K. L. Page, S. Starrfield

Abstract: Near infrared (NIR) 0.9--2.5$μ$m spectra of the remarkable recurrent nova M31N 2008-12a were obtained on days 6.3 and 10.3 after discovery of its 2024 outburst, and are the first NIR spectra of this object. The only prominent line seen in the spectra is that of HeI 1.083$μ$m, on day 6.3. Apart from this HeI line, there are only two other weak emission features: one at 1.0786$μ$m, suggested to be t… ▽ More Near infrared (NIR) 0.9--2.5$μ$m spectra of the remarkable recurrent nova M31N 2008-12a were obtained on days 6.3 and 10.3 after discovery of its 2024 outburst, and are the first NIR spectra of this object. The only prominent line seen in the spectra is that of HeI 1.083$μ$m, on day 6.3. Apart from this HeI line, there are only two other weak emission features: one at 1.0786$μ$m, suggested to be the [FeXIII] 1.075$μ$m coronal line, and one unidentified feature at 1.0969$μ$m. The observed full width at half maximum of the HeI line on day 6.3 (1350 km s$^{-1}$) is consistent with the behaviour of optical HeI lines during earlier eruptions of this RN, which show that the nova ejecta decelerate as they interact with the secondary's wind. The HeI 1.083$μ$m line faded rapidly, and was absent in the day 10.3 spectrum, along with any other emission lines. We use the relative strengths of optical He and H lines in previous eruptions to estimate the expected strengths of the HeI 1.083$μ$m line and of other infrared (including coronal) lines at 6.3 days after eruption. Our findings are consistent with the infrared spectra we observed during the 2024 eruption. We apply our analysis to account for the relative weakness of NIR coronal emission in known Galactic recurrent novae with giant secondaries. △ Less

Submitted 15 May, 2025; originally announced May 2025.

Comments: Accepted for publication in MNRAS

Hydrodynamic Predictions for the Next Outburst of T Coronae Borealis: It will be the Brightest Classical or Recurrent Nova Ever Observed in X-rays

Authors: S. Starrfield, M. Bose, C. E. Woodward, C. Iliadis, W. R. Hix, A. Evans, G. Shaw, D. P. K. Banerjee, T. Liimets, K. L. Page, T. R. Geballe, I. Ilyin, I. Perron, R. M. Wagner

Abstract: T Coronae Borealis (TCrB) is a recurrent nova (RN) with recorded outbursts in 1866, and 1946 and possible outbursts in 1217 and 1787. It is predicted to explode again in 2025 or 2026 based on multiple observational studies. The system consists of a massive (M$_{wd}$ $\gtrsim$ 1.35 M$_\odot$) white dwarf (WD) and a red giant (M3-M4 III). We have performed 1-D hydrodynamic simulations with NOVA to p… ▽ More T Coronae Borealis (TCrB) is a recurrent nova (RN) with recorded outbursts in 1866, and 1946 and possible outbursts in 1217 and 1787. It is predicted to explode again in 2025 or 2026 based on multiple observational studies. The system consists of a massive (M$_{wd}$ $\gtrsim$ 1.35 M$_\odot$) white dwarf (WD) and a red giant (M3-M4 III). We have performed 1-D hydrodynamic simulations with NOVA to predict the behavior of the next outburst. These simulations consist of a range of mass accretion rates onto $\sim$1.35 M$_\odot$ WDs, designed to bound the conditions necessary to achieve ignition of an explosion after an $\approx$80 year inter-outburst period. We have used both carbon-oxygen and oxygen-neon initial compositions, in order to include the possible ejecta abundances to be measured in the observations of the next outburst. As the WD in the TCrB system is observed to be massive, theoretical predictions reported here imply that the WD is growing in mass as a consequence of the TNR. Therefore, the secular evolution of the WD may allow it to approach the Chandrasekhar limit and either explode as a Type Ia supernova or undergo accretion induced collapse, depending on its underlying composition. We have followed the evolution of just the WD, after removing the ejected matter from the surface layers. Our intent is to illuminate the mystery of the unique, second, maximum in the two well observed outbursts and we have found conditions that bracket the predictions. △ Less

Submitted 15 February, 2025; originally announced February 2025.

Comments: 34 pages, 7 tables, 11 figures, Submitted to Astrophysical Journal

Near-infrared spectroscopy of the LMC recurrent nova LMCN 1968-12a

Authors: A. Evans, D. P. K. Banerjee, T. R. Geballe, A. Polin, E. Y. Hsiao, K. L. Page, C. E. Woodward, S. Starrfield

Abstract: We have obtained near-infrared ($0.80-2.45μ$m) spectra of the recurrent nova LMCN 1968-12a on two occasions during its 2024 August eruption. This is the first near-infrared spectroscopy of an extragalactic nova. The initial spectrum, on day 8.48, caught the nova in the coronal phase, with the [SiX] $1.43μ$m line being extremely strong. This line had a luminosity of $\sim95$L$_\odot$, and is clearl… ▽ More We have obtained near-infrared ($0.80-2.45μ$m) spectra of the recurrent nova LMCN 1968-12a on two occasions during its 2024 August eruption. This is the first near-infrared spectroscopy of an extragalactic nova. The initial spectrum, on day 8.48, caught the nova in the coronal phase, with the [SiX] $1.43μ$m line being extremely strong. This line had a luminosity of $\sim95$L$_\odot$, and is clearly a very powerful coolant. Its presence, together with the absence of [SiIX] 1.56$μ$m, implies a coronal temperature $\gtrsim3\times10^6$K, possibly amongst the highest recorded coronal temperature in a nova eruption. With the exception of the [SiX] line, the near-infrared spectra are remarkable for being devoid of metal lines. We suggest that this is due, in part, to the exceptionally high temperature of the coronal gas, causing ions, whose emission lines would normally appear in the near-infrared spectrum, to be collisionally ionised to higher stages. △ Less

Submitted 5 December, 2024; originally announced December 2024.

Comments: Accepted for publication in MNRAS, 4 December 2024

Protosolar D-to-H abundance and one part-per-billion PH$_{3}$ in the coldest brown dwarf

Authors: Melanie J. Rowland, Caroline V. Morley, Brittany E. Miles, Genaro Suárez, Jacqueline K. Faherty, Andrew J. Skemer, Samuel A. Beiler, Michael R. Line, Gordon L. Bjoraker, Jonathan J. Fortney, Johanna M. Vos, Sherelyn Alejandro Merchan, Mark Marley, Ben Burningham, Richard Freedman, Ehsan Gharib-Nezhad, Natasha Batalha, Roxana Lupu, Channon Visscher, Adam C. Schneider, T. R. Geballe, Aarynn Carter, Katelyn Allers, James Mang, Dániel Apai , et al. (2 additional authors not shown)

Abstract: The coldest Y spectral type brown dwarfs are similar in mass and temperature to cool and warm ($\sim$200 -- 400 K) giant exoplanets. We can therefore use their atmospheres as proxies for planetary atmospheres, testing our understanding of physics and chemistry for these complex, cool worlds. At these cold temperatures, their atmospheres are cold enough for water clouds to form, and chemical timesc… ▽ More The coldest Y spectral type brown dwarfs are similar in mass and temperature to cool and warm ($\sim$200 -- 400 K) giant exoplanets. We can therefore use their atmospheres as proxies for planetary atmospheres, testing our understanding of physics and chemistry for these complex, cool worlds. At these cold temperatures, their atmospheres are cold enough for water clouds to form, and chemical timescales increase, increasing the likelihood of disequilibrium chemistry compared to warmer classes of planets. JWST observations are revolutionizing the characterization of these worlds with high signal-to-noise, moderate resolution near- and mid-infrared spectra. The spectra have been used to measure the abundances of prominent species like water, methane, and ammonia; species that trace chemical reactions like carbon monoxide; and even isotopologues of carbon monoxide and ammonia. Here, we present atmospheric retrieval results using both published fixed-slit (GTO program 1230) and new averaged time series observations (GO program 2327) of the coldest known Y dwarf, WISE 0855-0714 (using NIRSpec G395M spectra), which has an effective temperature of $\sim$ 264 K. We present a detection of deuterium in an atmosphere outside of the solar system via a relative measurement of deuterated methane (CH$_{3}$D) and standard methane. From this, we infer the D/H ratio of a substellar object outside the solar system for the first time. We also present a well-constrained part-per-billion abundance of phosphine (PH$_{3}$). We discuss our interpretation of these results and the implications for brown dwarf and giant exoplanet formation and evolution. △ Less

Submitted 25 November, 2024; v1 submitted 21 November, 2024; originally announced November 2024.

Comments: 17 pages, 7 figures, accepted to ApJ Letters

Diffuse interstellar bands in the near-infrared: Expanding the reddening range

Authors: R. Castellanos, F. Najarro, M. Garcia, L. R. Patrick, T. R. Geballe

Abstract: We have investigated the behaviour of three strong near-infrared diffuse interstellar bands (DIBs) at λ13177 Å, λ14680 Å, and λ15272 Å, on a larger sample of sightlines and over a wider range of extinctions than previously studied, utilizing spectra from three observatories. We applied two telluric correction techniques to reduce atmospheric contamination and have used Gaussian fits to characteris… ▽ More We have investigated the behaviour of three strong near-infrared diffuse interstellar bands (DIBs) at λ13177 Å, λ14680 Å, and λ15272 Å, on a larger sample of sightlines and over a wider range of extinctions than previously studied, utilizing spectra from three observatories. We applied two telluric correction techniques to reduce atmospheric contamination and have used Gaussian fits to characterise the DIB profiles and measure equivalent widths. We confirmed strong and approximately linear correlations with reddening of the λ13177 Å, λ14680 Å and λ15272 Å DIBs, extending them to higher reddening values and strengthening their link to interstellar matter. Modelling of the λ14680 Å DIB profiles revealed intrinsic variations, including line broadening, linked to their formation processes. This effect is particularly pronounced in the Galactic Centre (GC) environment, where multiple diffuse molecular clouds along the line of sight contribute to line broadening. We have detected one new DIB candidate at λ14795 Å on sightlines with high reddening. △ Less

Submitted 27 June, 2024; originally announced June 2024.

Comments: Accepted for publication in Monthly Notices of the Royal Astronomical Society (MNRAS)

Haro 5-2: A New Pre-Main Sequence Quadruple Stellar System

Authors: Bo Reipurth, C. Briceno, T. R. Geballe, C. Baranec, S. Mikkola, A. M. Cody, M. S. Connelley, C. Flores, B. A. Skiff, J. D. Armstrong, N. M. Law, R. Riddle

Abstract: We have discovered that the Halpha emission line star Haro 5-2, located in the 3-6 Myr old Ori OB1b association, is a young quadruple system. The system has a 2+2 configuration with an outer separation of 2.6 arcseconds and with resolved subarcsecond inner binary components. The brightest component, Aa, dominates the A-binary, it is a weakline T Tauri star with spectral type M2.5pm1. The two stars… ▽ More We have discovered that the Halpha emission line star Haro 5-2, located in the 3-6 Myr old Ori OB1b association, is a young quadruple system. The system has a 2+2 configuration with an outer separation of 2.6 arcseconds and with resolved subarcsecond inner binary components. The brightest component, Aa, dominates the A-binary, it is a weakline T Tauri star with spectral type M2.5pm1. The two stars of the B component are equally bright at J, but the Bb star is much redder. Optical spectroscopy of the combined B pair indicates a rich emission line spectrum with a M3pm1 spectral type. The spectrum is highly variable and switches back and forth between a classical and a weakline T Tauri star. In the near-infrared, the spectrum shows Paschen beta and Brackett gamma in emission, indicative of active accretion. A significant mid-infrared excess reveals the presence of circumstellar or circumbinary material in the system. Most multiple systems are likely formed during the protostellar phase, involving flybys of neighboring stars followed by an in-spiraling phase driven by accretion from circumbinary material and leading to compact sub-systems. However, Haro 5-2 stands out among young 2+2 quadruples as the two inner binaries are unusually wide relative to the separation of the A and B pair, allowing future studies of the individual components. Assuming the components are coeval, the system could potentially allow stringent tests of PMS evolutionary models. △ Less

Submitted 16 May, 2024; originally announced May 2024.

Comments: 21 pages, 10 figures. Accepted by The Astronomical Journal

Analysis of the 3.2-3.3 $μ$m Interstellar Absorption Feature on Three Milky Way Sightlines

Authors: L. S. Bernstein, T. R. Geballe

Abstract: We report new analyses of spectra of the $3.2-3.3~μ$m absorption feature observed in the diffuse interstellar medium toward three Milky Way sources: 2MASS $J17470898-2829561$ (2M1747) and the Quintuplet Cluster, both located in the Galactic center, and Cygnus OB2-12. The $3.2-3.3~μ$m interval coincides with the CH-stretching region for compact polycyclic aromatic hydrocarbons (PAHs). We focus on t… ▽ More We report new analyses of spectra of the $3.2-3.3~μ$m absorption feature observed in the diffuse interstellar medium toward three Milky Way sources: 2MASS $J17470898-2829561$ (2M1747) and the Quintuplet Cluster, both located in the Galactic center, and Cygnus OB2-12. The $3.2-3.3~μ$m interval coincides with the CH-stretching region for compact polycyclic aromatic hydrocarbons (PAHs). We focus on the 2M1747 spectrum. Its published optical depth spectrum contains residual telluric transmission features, which arise from the 0.06 difference in mean airmasses between the observations of the source and its telluric standard star. We corrected the published spectrum by adding the airmass residual optical depth spectrum. The corrected spectrum is well fit by a superposition of four Gaussians. The absorption spectra of the other two sources were also fit by four Gaussians, with similar central wavelengths, widths, and relative peak opacities. We associate the three longer wavelength Gaussians covering the $3.23-3.31~μ$m interval with compact PAHs in positive, neutral, and negative charge states. We identify the shortest wavelength Gaussian, near 3.21 $μ$m, with irregularly-shaped PAHs. Constraints imposed by spectral smoothness on the corrected 2M1747 spectrum, augmented by a PAH cluster formation model for post-asymptotic giant branch stars, suggests that $> 99$\%\ of the PAHs in the diffuse interstellar medium reside in small clusters. This study supports the PAH hypothesis, and suggests that a family of primarily compact PAHs with a C$_{66}$H$_{20}$ (circumvalene) parent is consistent with the observed mid-infrared and ultraviolet interstellar absorption spectrum. △ Less

Submitted 15 February, 2024; v1 submitted 5 December, 2023; originally announced December 2023.

Comments: 17 pages, 8 figures, ApJ in press (accepted 2023 December 5

The HH 24 Complex: Jets, Multiple Star Formation, and Orphaned Protostars

Authors: Bo Reipurth, J. Bally, Hsi-Wei Yen, H. G. Arce, L. -F. Rodriguez, A. C. Raga, T. R. Geballe, R. Rao, F. Comeron, S. Mikkola, C. A. Aspin, J. Walawender

Abstract: The HH 24 complex harbors five collimated jets emanating from a small protostellar multiple system. We have carried out a multi-wavelength study of the jets, their driving sources, and the cloud core hosting the embedded stellar system, based on data from the HST, Gemini, Subaru, APO 3.5m, VLA, and ALMA telescopes. The data show that the multiple system, SSV 63, contains at least 7 sources, rangin… ▽ More The HH 24 complex harbors five collimated jets emanating from a small protostellar multiple system. We have carried out a multi-wavelength study of the jets, their driving sources, and the cloud core hosting the embedded stellar system, based on data from the HST, Gemini, Subaru, APO 3.5m, VLA, and ALMA telescopes. The data show that the multiple system, SSV 63, contains at least 7 sources, ranging in mass from the hydrogen-burning limit to proto-Herbig Ae stars. The stars are in an unstable non-hierarchical configuration, and one member, a borderline brown dwarf, is moving away from the protostellar system with 25 km/s, after being ejected about 5,800 yr ago as an orphaned protostar. Five of the embedded sources are surrounded by small, possibly truncated, disks resolved at 1.3 mm with ALMA. Proper motions and radial velocities imply jet speeds of 200-300 km/s. The two main HH 24 jets, E and C, form a bipolar jet system which traces the innermost portions of parsec-scale chains of Herbig-Haro and H2 shocks with a total extent of at least 3 parsec. H2CO and C18O observations show that the core has been churned and continuously fed by an infalling streamer. 13CO and 12CO trace compact, low-velocity, cavity walls carved by the jets and an ultra-compact molecular outflow from the most embedded object. Chaotic N-body dynamics likely will eject several more of these objects. The ejection of stars from their feeding zones sets their masses. Dynamical decay of non-hierarchical systems can thus be a major contributor to establishing the initial mass function. △ Less

Submitted 4 January, 2023; originally announced January 2023.

Comments: 57 pages, 61 figures, 12 tables; accepted to Astron.J

Analysis of the first infrared spectrum of quasi-bound H2 line emission in Herbig-Haro 7

Authors: Evelyne Roueff, Michael G. Burton, Thomas R. Geballe, Hervé Abgrall

Abstract: Context. Highly excited molecular hydrogen H2 has been observed in many regions of shocked molecular gas. A recently published $K$-band spectrum of Herbig-Haro 7 (HH7) contains several vibration-rotation lines of H2 from highly excited energy levels that have not been detected elsewhere, including a line at 2.179 $μ$m identified as arising from the $v$=2 $J$=29 level, which lies above the dissocia… ▽ More Context. Highly excited molecular hydrogen H2 has been observed in many regions of shocked molecular gas. A recently published $K$-band spectrum of Herbig-Haro 7 (HH7) contains several vibration-rotation lines of H2 from highly excited energy levels that have not been detected elsewhere, including a line at 2.179 $μ$m identified as arising from the $v$=2 $J$=29 level, which lies above the dissociation limit of H2. One emission line at 2.104 $μ$m in this spectrum was unidentified. Aims. We aim to complete the analysis of the spectrum of HH7 by including previously missing molecular data that have been recently computed. Methods. We re-analysed the $K$-band spectrum, emphasising the physics of quasi-bound upper levels that can produce infrared emission lines in the $K$ band. Results. We confirm the identification of the $2-1$ $S$(27) line at 2.1785 $μ$m and identify the line at 2.1042 $μ$m as due to the 1-0 $S$(29) transition of H2, whose upper level energy is also higher than the dissociation limit. This latter identification, its column density, and the energy of its upper level further substantiate the existence of a hot thermal component at 5000 K in the HH7 environment.} Conclusion. The presence of the newly identified $1-0$ $S$(29) line, whose quasi-bound upper level ($v$=1, $J$=31) has a significant spontaneous dissociation probability, shows that dissociation of H2 is occurring. The mechanism by which virtually all of the H2 levels with energies from 20,000 K to 53,000 K is maintained in local thermodynamic equilibrium at a single temperature of $\sim$5,000 K remains to be understood. △ Less

Submitted 2 January, 2023; originally announced January 2023.

Comments: 5 pages, 3 figures, accepted in Astronomy and Astrophysics Letters 22/12/2022

Journal ref: A&A 669, L7 (2023)

Near-Infrared and Optical Observations of Type Ic SN 2021krf: Luminous Late-time Emission and Dust Formation

Authors: Aravind P. Ravi, Jeonghee Rho, Sangwook Park, Seong Hyun Park, Sung-Chul Yoon, T. R. Geballe, Jozsef Vinko, Samaporn Tinyanont, K. Azalee Bostroem, Jamison Burke, Daichi Hiramatsu, D. Andrew Howell, Curtis McCully, Megan Newsome, Estefania Padilla Gonzalez, Craig Pellegrino, Regis Cartier, Tyler Pritchard, Morten Andersen, Sergey Blinnikov, Yize Dong, Peter Blanchard, Charles D. Kilpatrick, Peter Hoeflich, Stefano Valenti , et al. (7 additional authors not shown)

Abstract: We present near-infrared (NIR) and optical observations of the Type Ic supernova (SN Ic) SN 2021krf obtained between days 13 and 259 at several ground-based telescopes. The NIR spectrum at day 68 exhibits a rising $K$-band continuum flux density longward of $\sim$ 2.0 $μ$m, and a late-time optical spectrum at day 259 shows strong [O I] 6300 and 6364 Å emission-line asymmetry, both indicating the p… ▽ More We present near-infrared (NIR) and optical observations of the Type Ic supernova (SN Ic) SN 2021krf obtained between days 13 and 259 at several ground-based telescopes. The NIR spectrum at day 68 exhibits a rising $K$-band continuum flux density longward of $\sim$ 2.0 $μ$m, and a late-time optical spectrum at day 259 shows strong [O I] 6300 and 6364 Å emission-line asymmetry, both indicating the presence of dust, likely formed in the SN ejecta. We estimate a carbon-grain dust mass of $\sim$ 2 $\times$ 10$^{-5}$ M$_{\odot}$ and a dust temperature of $\sim$ 900 - 1200 K associated with this rising continuum and suggest the dust has formed in SN ejecta. Utilizing the one-dimensional multigroup radiation hydrodynamics code STELLA, we present two degenerate progenitor solutions for SN 2021krf, characterized by C-O star masses of 3.93 and 5.74 M$_{\odot}$, but with the same best-fit $^{56}$Ni mass of 0.11 M$_{\odot}$ for early times (0-70 days). At late times (70-300 days), optical light curves of SN 2021krf decline substantially more slowly than that expected from $^{56}$Co radioactive decay. Lack of H and He lines in the late-time SN spectrum suggests the absence of significant interaction of the ejecta with the circumstellar medium. We reproduce the entire bolometric light curve with a combination of radioactive decay and an additional powering source in the form of a central engine of a millisecond pulsar with a magnetic field smaller than that of a typical magnetar. △ Less

Submitted 19 April, 2023; v1 submitted 31 October, 2022; originally announced November 2022.

Comments: Accepted for publication in ApJ, 27 pages, 21 figures, 6 tables. Previous arXiv submission (arXiv:2211.00205) replaced after acceptance

Infrared spectroscopy of the 2019 eruption of the recurrent nova V3890 Sgr: separation into equatorial and polar winds revealed

Authors: A. Evans, T. R. Geballe, C. E. Woodward, D. P. K. Banerjee, R. D. Gehrz, S. Starrfield, M. Shahbandeh

Abstract: We present infrared spectroscopy of the 2019 eruption of the recurrent nova V3890 Sgr, obtained over the period 5.1-46.3 days after the eruption. The spectrum of the red giant became more prominent as the flux declined, and by day 46.3 dominated the spectrum. Hydrogen and helium emission lines consisted of a narrow component superposed on a broad pedestal. The full width at half maximum of the nar… ▽ More We present infrared spectroscopy of the 2019 eruption of the recurrent nova V3890 Sgr, obtained over the period 5.1-46.3 days after the eruption. The spectrum of the red giant became more prominent as the flux declined, and by day 46.3 dominated the spectrum. Hydrogen and helium emission lines consisted of a narrow component superposed on a broad pedestal. The full width at half maximum of the narrow components declined with time $t$ as the eruption progressed, as ${t}^{-0.74}$, whereas those of the broad components remained essentially constant. Conversely, the line fluxes of the narrow components of Pa,$β$ remained roughly constant, while those of the broad components declined by a factor $\sim30$ over a period of $\lesssim25$~days. The behaviour of the broad components is consistent with them arising in unencumbered fast-flowing ejecta perpendicular to the binary plane, in material that was ejected in a short $\sim3.3$-day burst. The narrow components arise in material that encounters the accumulated circumstellar material. The outburst spectra were rich in coronal lines. There were two coronal line phases, one that originated in gas ionised by supersoft X-ray source, the other in shocked gas. From the relative fluxes of silicon and sulphur coronal lines on day 23.4 - when the emitting gas was shocked - we deduce that the temperature of the coronal gas was $9.3\times10^5$~K, and that the abundances are approximately solar. △ Less

Submitted 19 August, 2022; originally announced August 2022.

Comments: Accepted for publication in MNRAS on 2022 August 1. 19 pages, 10 figures

V4334 Sgr (Sakurai's Object): still churning out the dust

Authors: A. Evans, D. P. K. Banerjee, T. R. Geballe, R. D. Gehrz, C. E. Woodward, K. Hinkle, R. R. Joyce, M. Shahbandeh

Abstract: We present a $0.8-2.5\,μ$m spectrum of the Very Late Thermal Pulse object V4334 Sgr (Sakurai's Object), obtained in 2020 September. The spectrum displays a continuum that rises strongly to longer wavelengths, and is considerably brighter than the most recent published spectrum obtained seven years earlier. At the longer wavelengths the continuum is well fitted by a blackbody with a temperature of… ▽ More We present a $0.8-2.5\,μ$m spectrum of the Very Late Thermal Pulse object V4334 Sgr (Sakurai's Object), obtained in 2020 September. The spectrum displays a continuum that rises strongly to longer wavelengths, and is considerably brighter than the most recent published spectrum obtained seven years earlier. At the longer wavelengths the continuum is well fitted by a blackbody with a temperature of $624\pm8$ K. However, there is excess continuum at the shortest wavelengths that we interpret as being due to hot dust that has very recently formed in an environment with C/O $\simeq2.5$. Other possible sources for this excess continuum are discussed - such as the stellar photosphere dimly seen through the dust shell, and light scattered off the inner wall of the dust torus - but these interpretations seem unlikely. Numerous emission lines are present, including those of HeI, CI, [CI], and OI. Our observations confirm that emission in the HeI 1.083$\,μ$m and [CI] 0.9827/0.9852$\,μ$m lines is spatially extended. The [CI] line fluxes suggest that the electron density increased by an order of magnitude between 2013 and 2020, and that these two lines may soon disappear from the spectrum. The flux ratio of the 1.083$\,μ$m and 2.058$\,μ$m HeI lines is consistent with the previously-assumed interstellar extinction. The stellar photosphere remains elusive, and the central star may not be as hot as suggested by current evolutionary models. △ Less

Submitted 11 January, 2022; originally announced January 2022.

Comments: MNRAS, accepted

The Central 300 pc of the Galaxy Probed by Infrared Spectra of H$_3^+$ and CO: III. Locations of Sgr B2 and Star $ι$

Authors: Takeshi Oka, T. R. Geballe

Abstract: Using a simple relation between the radial expansion velocity of diffuse gas in the Central Molecular Zone (CMZ) of the Galaxy and its distance from Sgr A$^\ast$ we estimate the physical depths within the CMZ of Star $ι$ (2MASS $J$17470898-2829561) and two Sgr B2 far-infrared continuum sources with respect to the location of Sgr A$^\ast$. To do this we use velocity profiles of mid-infrared absorpt… ▽ More Using a simple relation between the radial expansion velocity of diffuse gas in the Central Molecular Zone (CMZ) of the Galaxy and its distance from Sgr A$^\ast$ we estimate the physical depths within the CMZ of Star $ι$ (2MASS $J$17470898-2829561) and two Sgr B2 far-infrared continuum sources with respect to the location of Sgr A$^\ast$. To do this we use velocity profiles of mid-infrared absorption lines of H$_3^+$ and of far-infrared absorption lines of H$_2$O$^+$, OH$^+$, and $^{13}$CH$^+$. The distances to Star $ι$ and to the Sgr B2 sources are found to be $\sim$90 pc greater than the distance to Sgr A$^\ast$. Our conclusion that Sgr B2 lies toward the rear of the CMZ is contrary to many previous models in which it has been placed shallower than Sgr A$^\ast$. △ Less

Submitted 12 February, 2022; v1 submitted 10 November, 2021; originally announced November 2021.

Comments: 9 pages, 10 figures. Accepted by ApJ

Near-infrared studies of nova V1674 Herculis: A shocking record-breaker

Authors: C. E. Woodward, D. P. K. Banerjee, T. R. Geballe, K. L. Page, S. Starrfield, R. M. Wagner

Abstract: We present near infrared spectroscopy of Nova Herculis 2021 (V1674 Her), obtained over the first 70 days of its evolution. This fastest nova on record displays a rich emission line spectrum, including strong coronal line emission with complex structures. The hydrogen line fluxes, combined with a distance of 4.7 (+1.3 / -1.0) kpc, give an upper limit to the hydrogen ejected mass of 1.4 (+0.8 / -1.2… ▽ More We present near infrared spectroscopy of Nova Herculis 2021 (V1674 Her), obtained over the first 70 days of its evolution. This fastest nova on record displays a rich emission line spectrum, including strong coronal line emission with complex structures. The hydrogen line fluxes, combined with a distance of 4.7 (+1.3 / -1.0) kpc, give an upper limit to the hydrogen ejected mass of 1.4 (+0.8 / -1.2) 10^{-3} solar masses. The coronal lines appeared at day 11.5, the earliest onset yet observed for any classical nova, before there was an obvious source of ionizing radiation. We argue that the gas cannot be photoionized, at least in the earliest phase, and must be shocked. Its temperature is estimated to be 10^{5.57 +/- 0.05} K on day 11.5. Tentative analysis indicates a solar abundance of aluminum and an underabundance of calcium, relative to silicon, with respect to solar values in the ejecta. Further, we show that the vexing problem of whether collisional or photoionization is responsible for coronal emission in classical novae can be resolved by correlating the temporal sequence in which the X-ray supersoft phase and the near-infrared coronal line emission appear. △ Less

Submitted 25 October, 2021; originally announced October 2021.

Comments: 8 pages, 3 figures, 2 tables

The 2019 outburst of the 2005 classical nova V1047 Cen: a record breaking dwarf nova outburst or a new phenomenon?

Authors: E. Aydi, K. V. Sokolovsky, J. S. Bright, E. Tremou, M. M. Nyamai, A. Evans, J. Strader, L. Chomiuk, G. Myers, F-J. Hambsch, K. L. Page, D. A. H. Buckley, C. E. Woodward, F. M. Walter, P. Mróz, P. J. Vallely, T. R. Geballe, D. P. K. Banerjee, R. D. Gehrz, R. P. Fender, M. Gromadzki, A. Kawash, C. Knigge, K. Mukai, U. Munari , et al. (6 additional authors not shown)

Abstract: We present a detailed study of the 2019 outburst of the cataclysmic variable V1047~Cen, which hosted a classical nova eruption in 2005. The peculiar outburst occurred 14 years after the classical nova event and lasted for more than 400 days, reaching an amplitude of around 6 magnitudes in the optical. Early spectral follow-up revealed what could be a dwarf nova (accretion disk instability) outburs… ▽ More We present a detailed study of the 2019 outburst of the cataclysmic variable V1047~Cen, which hosted a classical nova eruption in 2005. The peculiar outburst occurred 14 years after the classical nova event and lasted for more than 400 days, reaching an amplitude of around 6 magnitudes in the optical. Early spectral follow-up revealed what could be a dwarf nova (accretion disk instability) outburst. However, the outburst duration, high velocity ($>$2000\,km\,s$^{-1}$) features in the optical line profiles, luminous optical emission, and presence of prominent long-lasting radio emission together suggest a phenomenon more exotic and energetic than a dwarf nova outburst. The outburst amplitude, radiated energy, and spectral evolution are also not consistent with a classical nova eruption. There are similarities between V1047~Cen's 2019 outburst and those of classical symbiotic stars, but pre-2005 images of the field of V1047~Cen indicate that the system likely hosts a dwarf companion, implying a typical cataclysmic variable system. Based on our multi-wavelength observations, we suggest that the outburst may have started with a brightening of the disk due to enhanced mass transfer or disk instability, possibly leading to enhanced nuclear shell burning on the white dwarf, which was already experiencing some level of quasi-steady shell burning. This eventually led to the generation of a wind and/or bipolar, collimated outflows. The 2019 outburst of V1047~Cen appears to be unique, and nothing similar has been observed in a typical cataclysmic variable system before, hinting at a potentially new astrophysical phenomenon. △ Less

Submitted 13 September, 2022; v1 submitted 17 August, 2021; originally announced August 2021.

Comments: 36 pages, 24 figures, 9 tables. Accepted in ApJ

Observations and analysis of CH$^+$ vibrational emissions from the young, carbon-rich planetary nebula NGC 7027: a textbook example of chemical pumping

Authors: David A. Neufeld, Benjamin Godard, P. Bryan Changala, Alexandre Faure, T. R. Geballe, Rolf Güsten, Karl M. Menten, Helmut Wiesemeyer

Abstract: We discuss the detection of 14 rovibrational lines of CH$^+$, obtained with the iSHELL spectrograph on NASA's Infrared Telescope Facility (IRTF) on Maunakea. Our observations in the 3.49 - 4.13 $μ$m spectral region, obtained with a 0.375" slit width that provided a spectral resolving power $λ/Δλ\sim 80,000$, have resulted in the unequivocal detection of the $R(0) - R(3)$ and $P(1)-P(10)$ transitio… ▽ More We discuss the detection of 14 rovibrational lines of CH$^+$, obtained with the iSHELL spectrograph on NASA's Infrared Telescope Facility (IRTF) on Maunakea. Our observations in the 3.49 - 4.13 $μ$m spectral region, obtained with a 0.375" slit width that provided a spectral resolving power $λ/Δλ\sim 80,000$, have resulted in the unequivocal detection of the $R(0) - R(3)$ and $P(1)-P(10)$ transitions within the $v=1-0$ band of CH$^+$. The $R$-branch transitions are anomalously weak relative to the $P$-branch transitions, a behavior that is explained accurately by rovibronic calculations of the transition dipole moment reported in a companion paper (Changala et al. 2021). Nine infrared transitions of H$_2$ were also detected in these observations, comprising the $S(8)$, $S(9)$, $S(13)$ and $S(15)$ pure rotational lines; the $v=1-0$ $O(4) - O(7)$ lines, and the $v=2-1$ $O(5)$ line. We present a photodissociation region model, constrained by the CH$^+$ and H$_2$ line fluxes that we measured, that includes a detailed treatment of the excitation of CH$^+$ by inelastic collisions, optical pumping, and chemical ("formation") pumping. The latter process is found to dominate the excitation of the observed rovibrational lines of CH$^+$, and the model is remarkably successful in explaining both the absolute and relative strengths of the CH$^+$ and H$_2$ lines. △ Less

Submitted 28 May, 2021; originally announced May 2021.

Comments: 38 pages, 15 figures, accepted for publication in the Astrophysical Journal

The Interstellar Medium toward the Galactic Center Source 2MASS J17470898-2829561

Authors: T. R. Geballe, Yvonne Pendleton, Jean Chiar, Alexander G . G. M. Tielens

Abstract: We describe and discuss remarkable infrared spectra, covering key portions of the $2-5$ $μ$m wavelength interval, of the probable OH/IR supergiant 2MASS J17470898$-$2829561 (2M1747), located in direction of the Sgr B molecular cloud complex within the Central Molecular Zone (CMZ) of the Galaxy. This star was originally singled out for examination based on its suitability for spectroscopy of lines… ▽ More We describe and discuss remarkable infrared spectra, covering key portions of the $2-5$ $μ$m wavelength interval, of the probable OH/IR supergiant 2MASS J17470898$-$2829561 (2M1747), located in direction of the Sgr B molecular cloud complex within the Central Molecular Zone (CMZ) of the Galaxy. This star was originally singled out for examination based on its suitability for spectroscopy of lines of H$_3^+$ in the CMZ. Analysis of the spectra shows that 2M1747 is deeply embedded within Sgr B1, with A$_V$ $\gtrsim$ 100 mag, making it the only star within Sgr B for which infrared spectra have been obtained at present, and thereby a unique infrared probe of the dense interstellar medium within the CMZ. Despite the high extinction, spectra of 2M1747 reveal a veiled photosphere in the $K$ band and circumstellar gas in the $M$ band, giving clues as to its nature. Its $ 3.5-4.0$ $μ$m spectrum contains the strongest absorption lines of H$_3^+$ observed toward any object to date. The $4.5-4.8$ $μ$m spectrum has impressively deep and wide absorption lines of interstellar CO, most of which arise in dense gas within Sgr B1. The $3-5$ $μ$m spectrum also contains several solid state absorption features, which are characteristic of both dense and diffuse clouds, and which raise questions about the identifications of some of these features. We discuss the nature of the star, the extinction to it, the extinction law for dust in the CMZ, and the identifications of the various solid-state features and where they are produced along this complex line of sight. △ Less

Submitted 12 April, 2021; v1 submitted 11 March, 2021; originally announced March 2021.

Comments: 17 pages, 10 figures; accepted by ApJ 2021 March 10

Infrared spectroscopy of CK Vulpeculae: revealing a remarkably powerful blast from the past

Authors: D. P. K. Banerjee, T. R. Geballe, A. Evans, M. Shahbandeh, C. E. Woodward, R. D. Gehrz, S. P. S. Eyres, S. Starrfield, A. Zijlstra

Abstract: CK Vulpeculae, which erupted in AD 1670-71, was long considered to be a nova outburst; however, recent observations have required that alternative scenarios be considered. Long slit infrared spectroscopy of a forbidden line of iron reported here has revealed high line-of-sight velocities ($\sim\pm900$~km~s$^{-1}$) of the ansae at the tips of the bipolar lobes imaged in H$α$ in 2010. The deprojecte… ▽ More CK Vulpeculae, which erupted in AD 1670-71, was long considered to be a nova outburst; however, recent observations have required that alternative scenarios be considered. Long slit infrared spectroscopy of a forbidden line of iron reported here has revealed high line-of-sight velocities ($\sim\pm900$~km~s$^{-1}$) of the ansae at the tips of the bipolar lobes imaged in H$α$ in 2010. The deprojected velocities of the tips are approximately $\pm2130$~km~s$^{-1}$ assuming the previously derived inclination angle of $65^\circ$ for the axis of cylindrical symmetry of the bipolar nebula. Such high velocities are in stark contrast to previous reports of much lower expansion velocities in CK~Vul. Based on the deprojected velocities of the tips and their angular expansion measured over a 10-year baseline, we derive a revised estimate, with estimated uncertainties, of $3.2^{+0.9}_{-0.6}$~kpc for the distance to CK~Vul. This implies that the absolute visual magnitude at the peak of the 1670 explosion was $M_V = -12.4^{+1.3}_{-2.4}$, indicating that the 1670 event was far more luminous than previous estimates and brighter than any classical nova or any Galactic stellar merger. We propose that CK~Vul belongs to the class of Intermediate Luminosity Optical Transients (ILOTs), objects which bridge the luminosity gap between novae and supernovae. While eruptions in lower luminosity ILOTs are attributed to merger events, the origin of the highly luminous ILOT outbursts is currently not known. △ Less

Submitted 5 November, 2020; originally announced November 2020.

Comments: Submitted to ApJ Letters 3 October 2020, accepted 4 November 2020. Seven pages, three figures

Near-Infrared and Optical Observations of Type Ic SN2020oi and broad-lined Ic SN2020bvc: Carbon Monoxide, Dust and High-Velocity Supernova Ejecta

Authors: J. Rho, A. Evans, T. R. Geballe, D. P. K. Banerjee, P. Hoeflich, M. Shahbandeh, S. Valenti, S. -C. Yoon, H. Jin, M. Williamson, M. Modjaz, D. Hiramatsu, D. A. Howell, C. Pellegrino, J. Vinko, R. Cartier, J. Burke, C. McCully, H. An, H. Cha, T. Pritchard, X. Wang, J. Andrews, L. Galbany, M. L. Graham , et al. (11 additional authors not shown)

Abstract: We present near-infrared and optical observations of the Type Ic Supernova (SN) 2020oi in the galaxy M100 and the broad-lined Type Ic SN2020bvc in UGC 9379, using Gemini, LCO, SOAR, and other ground-based telescopes. The near-IR spectrum of SN2020oi at day 63 since the explosion shows strong CO emissions and a rising K-band continuum, which is the first unambiguous dust detection from a Type Ic SN… ▽ More We present near-infrared and optical observations of the Type Ic Supernova (SN) 2020oi in the galaxy M100 and the broad-lined Type Ic SN2020bvc in UGC 9379, using Gemini, LCO, SOAR, and other ground-based telescopes. The near-IR spectrum of SN2020oi at day 63 since the explosion shows strong CO emissions and a rising K-band continuum, which is the first unambiguous dust detection from a Type Ic SN. Non-LTE CO modeling shows that CO is still optically thick, and that the lower limit to the CO mass is 0.001 Msun. The dust temperature is 810 K, and the dust mass is ~10^(-5) Msun. We explore the possibilities that the dust is freshly formed in the ejecta, heated dust in the pre-existing circumstellar medium, and an infrared echo. The light curves of SN2020oi are consistent with a STELLA model with canonical explosion energy, 0.07 Msun Ni mass, and 0.7 Msun ejecta mass. A model of high explosion energy of ~10^(52) erg, 0.4 Msun Ni mass, 6.5 Msun ejecta mass with the circumstellar matter, reproduces the double-peaked light curves of SN2020bvc. We observe temporal changes of absorption features of the IR Ca~II triplet, S~I at 1.043 micron, and Fe~II at 5169 Angstrom. The blue-shifted lines indicate high velocities, up to 60,000 km/s for SN2020bvc and 20,000 km/s for SN2020oi, and the expansion velocity rapidly declines before the optical maximum. We present spectral signatures and diagnostics of CO and SiO molecular bands between 1.4 and 10 microns. △ Less

Submitted 7 January, 2021; v1 submitted 1 October, 2020; originally announced October 2020.

Comments: accepted for the ApJ; data files are available for Figures 1 and 4

Isotopic ratios in the red giant component of the recurrent nova T Coronae Borealis

Authors: Ya. V. Pavlenko, A. Evans, D. P. K. Banerjee, T. R. Geballe, U. Munari, R. D. Gehrz, C. E. Woodward, S. Starrfield

Abstract: We report the determination of abundances and isotopic ratios for C, O and Si in the photosphere of the red giant component of the recurrent nova T Coronae Borealis from new 2.284--2.402 $μ$m and 3.985--4.155 $μ$m spectroscopy. Abundances and isotopic ratios in the photosphere may be affected by (i) processes in the red giant interior which are brought to the surface during dredge-up, (ii) contami… ▽ More We report the determination of abundances and isotopic ratios for C, O and Si in the photosphere of the red giant component of the recurrent nova T Coronae Borealis from new 2.284--2.402 $μ$m and 3.985--4.155 $μ$m spectroscopy. Abundances and isotopic ratios in the photosphere may be affected by (i) processes in the red giant interior which are brought to the surface during dredge-up, (ii) contamination of the red giant, either during the common envelope phase of the binary evolution or by material synthesised in recurrent nova eruptions, or a combination of the two. We find that the abundances of C, O and Si are reasonably consistent with the expected composition of a red giant after first dredge-up, as is the $^{16}$O/$^{17}$O ratio. The $^{28}$Si/$^{29}$Si ratio is found to be $8.6\pm3.0$, and that for $^{28}$Si/$^{30}$Si is $21.5\pm3.0$. The $^{12}$C/$^{13}$C ratio ($10\pm2$) is somewhat lower than expected for first dredge-up. The $^{16}$O/$^{18}$O ratio ($41\pm3$) is highly inconsistent with that expected either from red giant evolution ($\sim550$) or from contamination of the red giant by the products of a nova thermonuclear runaway. In particular the C and O isotopic ratios taken in combination are a puzzle. We urge confirmation of our results using spectroscopy at high resolution. We also encourage a thorough theoretical study of the effects on the secondary star in a recurrent nova system of contamination by ejecta having anomalous abundances and isotopic ratios. △ Less

Submitted 27 August, 2020; originally announced August 2020.

Comments: Accepted for publication in Monthly Notices of the Royal Astronomical Society on August 26th. 11 pages, 10 figures

The Central 300 pc of the Galaxy probed by infrared spectra of H3+ and CO: II. Expansion and morphology of the warm diffuse gas

Authors: Takeshi Oka, T. R. Geballe

Abstract: Velocity profiles of a line of H$_3^+$ at 3.7 $μ$m produced in warm diffuse gas have been observed toward 18 stars in the Central Molecular Zone (CMZ) of the Galaxy. Their longitude-velocity diagram indicates that the gas is radially expanding within the CMZ at speeds up to a maximum of $\sim$150 km s$^{-1}$. The current momentum and energy in the gas are $\sim 5 \times 10^8 M_\odot$ km s$^{-1}$ a… ▽ More Velocity profiles of a line of H$_3^+$ at 3.7 $μ$m produced in warm diffuse gas have been observed toward 18 stars in the Central Molecular Zone (CMZ) of the Galaxy. Their longitude-velocity diagram indicates that the gas is radially expanding within the CMZ at speeds up to a maximum of $\sim$150 km s$^{-1}$. The current momentum and energy in the gas are $\sim 5 \times 10^8 M_\odot$ km s$^{-1}$ and $\sim 5\times 10^{53}$ erg. The motion is similar to that of the Expanding Molecular Ring (EMR) discovered in 1972 by Kaifu et al. and by Scoville. We propose that the expanding gas seen in H$_3^+$ is part of the same phenomenon, in spite of differences in estimates of density, morphology, and degree of rotation. The outward motion suggests that one or more ejection events occurred near the center of the CMZ (0.5$-$1) $\times$ 10$^6$ years ago, which may be related to creation of the recently observed microwave bubble. These observations revive the circular face-on view of the CMZ proposed in 1972, which fell out of favor after 1991 when Binney et al. proposed that a face-on view of the CMZ would show it to have an elliptical shape, with high eccentricity. While that model may apply on kiloparsec scales, we argue that it is incorrect to apply it to the much smaller CMZ. We discuss the fate of the expanding gas, which appears to be eventual infall into the center, leading to episodes of star formation and violent events associated with accretion onto Sgr~A$^\ast$. △ Less

Submitted 18 September, 2020; v1 submitted 24 August, 2020; originally announced August 2020.

Comments: 21 pages incl. 12 figures and 1 table; accepted for publication in The Astrophysical Journal. Minor typos corrected in this version

Observations of Disequilibrium CO Chemistry in the Coldest Brown Dwarfs

Authors: Brittany E. Miles, Andrew J. I. Skemer, Caroline V. Morley, Mark S. Marley, Jonathan J. Fortney, Katelyn N. Allers, Jacqueline K. Faherty, Thomas R. Geballe, Channon Visscher, Adam C. Schneider, Roxana Lupu, Richard S. Freedman, Gordon L. Bjoraker

Abstract: Cold brown dwarfs are excellent analogs of widely separated, gas giant exoplanets, and provide insight into the potential atmospheric chemistry and physics we may encounter in objects discovered by future direct imaging surveys. We present a low resolution R $\sim$ 300 $M$-band spectroscopic sequence of seven brown dwarfs with effective temperatures between 750 K and 250 K along with Jupiter. Thes… ▽ More Cold brown dwarfs are excellent analogs of widely separated, gas giant exoplanets, and provide insight into the potential atmospheric chemistry and physics we may encounter in objects discovered by future direct imaging surveys. We present a low resolution R $\sim$ 300 $M$-band spectroscopic sequence of seven brown dwarfs with effective temperatures between 750 K and 250 K along with Jupiter. These spectra reveal disequilibrium abundances of carbon monoxide (CO) produced by atmospheric quenching. We use the eddy diffusion coefficient (K$_{zz}$) to estimate the strength of vertical mixing in each object. The K$_{zz}$ values of cooler gaseous objects are close to their theoretical maximum and warmer objects show weaker mixing, likely due to less efficient convective mixing in primarily radiative layers. The CO-derived K$_{zz}$ values imply that disequilibrium phosphine (PH$_{3}$) should be easily observable in all of the brown dwarfs, but none as yet show any evidence for PH$_{3}$ absorption. We find that ammonia is relatively insensitive to atmospheric quenching at these effective temperatures. We are able to improve the fit to WISE 0855's $M$-band spectrum by including both CO and water clouds in the atmospheric model. △ Less

Submitted 27 April, 2020; v1 submitted 22 April, 2020; originally announced April 2020.

Comments: Accepted to the Astronomical Journal. 24 Pages, 16 Figures, 4 Tables. take care

The infrared view of dust and molecules around V4334 Sgr (Sakurai's Object): a 20-year retrospective

Authors: A. Evans, R. D. Gehrz, C. E. Woodward, D. P. K. Banerjee, T. R. Geballe, G. C. Clayton, P. J. Sarre, S. Starrfield, K. Hinkle, R. R. Joyce, Foteini Lykou, L. A. Helton, S. P. S. Eyres, H. Worters, E. J. Montiel, T. Liimets, A. Zijlstra, M. Richter, J. Krautter

Abstract: We present an analysis of the evolution of circumstellar dust and molecules in the environment of the very late thermal pulse object V4334 Sgr (Sakurai's Object) over a $\sim20$-year period, drawing on ground-, airborne- and space-based infrared photometry and spectroscopy. The dust emission, which started in 1997, resembles a blackbody that cooled from $\sim1200$K in 1998 August to $\sim180$K in… ▽ More We present an analysis of the evolution of circumstellar dust and molecules in the environment of the very late thermal pulse object V4334 Sgr (Sakurai's Object) over a $\sim20$-year period, drawing on ground-, airborne- and space-based infrared photometry and spectroscopy. The dust emission, which started in 1997, resembles a blackbody that cooled from $\sim1200$K in 1998 August to $\sim180$K in 2016 July. The dust mass, assuming amorphous carbon, was $\sim5\times10^{-10}$M$_\odot$ in 1998 August, and we estimate that the total dust mass was $\sim2\times10^{-5}$M$_\odot$ by $\sim2016$. The appearance of a near infrared excess in 2008 suggests a new episode of (or renewed) mass loss began then. We infer lower limits on the bolometric luminosity of the embedded star from that of the dust shell, which rose to $\sim16000$L$_\odot$ before declining to $\sim3000$L$_\odot$. There is evidence for weak 6-7$μ$m absorption, which we attribute to hydrogenated amorphous carbon formed in material ejected by Sakurai's Object during a mass ejection phase that preceded the 1997 event. We detect small hydrocarbon and other molecules in the spectra, and trace the column densities in hydrogen cyanide (HCN) and acetylene (C$_2$H$_2$). We use the former to determine the $^{12}$C/$^{13}$C ratio to be $6.4\pm0.7$, 14 times smaller than the Solar System value. △ Less

Submitted 3 February, 2020; originally announced February 2020.

Detection of vibrational emissions from the helium hydride ion (HeH$^+$) in the planetary nebula NGC 7027

Authors: David A. Neufeld, Miwa Goto, T. R. Geballe, Rolf Güsten, Karl M. Menten, Helmut Wiesemeyer

Abstract: We report the detection of emission in the v=1-0 P(1) (3.51629 micron) and P(2) (3.60776 micron) rovibrational lines of the helium hydride cation (HeH+) from the planetary nebula NGC 7027. These detections were obtained with the iSHELL spectrograph on NASA's Infrared Telescope Facility (IRTF) on Maunakea. The confirm the discovery of HeH+ reported recently by Guesten et al. (2019), who used the GR… ▽ More We report the detection of emission in the v=1-0 P(1) (3.51629 micron) and P(2) (3.60776 micron) rovibrational lines of the helium hydride cation (HeH+) from the planetary nebula NGC 7027. These detections were obtained with the iSHELL spectrograph on NASA's Infrared Telescope Facility (IRTF) on Maunakea. The confirm the discovery of HeH+ reported recently by Guesten et al. (2019), who used the GREAT instrument on the SOFIA airborne observatory to observe its pure rotational J=1-0 transition at 149.137 micron. The flux measured for the HeH+ v=1-0 P(1) line is in good agreement with our model for the formation, destruction and excitation of HeH+ in NGC 7027. The measured strength of the J=1-0 pure rotational line, however, exceeds the model prediction significantly, as does that of the v=1-0 P(2) line, by factors of 2.9 and 2.3 respectively. Possible causes of these discrepancies are discussed. Our observations of NGC 7027, covering the 3.26 - 3.93 micron spectral region, have led to the detection of more than sixty spectral lines including nine rovibrational emissions from CH+. The latter are detected for the first time in an astronomical source. △ Less

Submitted 30 January, 2020; originally announced January 2020.

Comments: 49 pages, including 17 figures. Accepted for publication in ApJ

The Giant Herbig-Haro Flow HH 212 and Associated Star Formation

Authors: Bo Reipurth, C. J. Davis, John Bally, A. C. Raga, B. P. Bowler, T. R. Geballe, Colin Aspin, Hsin-Fang Chiang

Abstract: The bipolar jet HH 212, among the finest collimated jets known, has so far been detected only in near-infrared H$_2$ emission. Here we present deep optical images that show two of the major bow shocks weakly detected in optical [SII] emission, as expected for a bona fide Herbig-Haro jet. We present widefield H$_2$ images which reveal two more bow shocks located symmetrically around the source and… ▽ More The bipolar jet HH 212, among the finest collimated jets known, has so far been detected only in near-infrared H$_2$ emission. Here we present deep optical images that show two of the major bow shocks weakly detected in optical [SII] emission, as expected for a bona fide Herbig-Haro jet. We present widefield H$_2$ images which reveal two more bow shocks located symmetrically around the source and along the main jet axis. Additionally, examination of Spitzer 4.5 $μ$m images reveals yet another bright bow shock further to the north along the jet axis; no corresponding bow shock is seen to the south. In total, the HH 212 flow has an extent of 1050 arcsec, corresponding to a projected dimension of 2.0 pc. HH 212 thus joins the growing group of parsec-scale Herbig-Haro jets. Proper motion measurements indicate a velocity of about 170 km/sec, highly symmetric around the source, with an uncertainty of $\sim$30 km/sec, suggesting a probable age of the giant HH 212 flow of about 7000 yr. The jet is driven by a deeply embedded source, known as IRAS 05413-0104. We draw attention to a Spitzer near- and mid-infrared source, which we call IRS-B, located only 7 arcsec from the driving source, towards the outskirts of the dense cloud core. Infrared photometry and spectroscopy suggests that IRS-B is a K-type star with a substantial infrared excess, except that for an extinction of A$_V$ = 44 the star would have only a weakinfrared excess, and so in principle it could be a K-giant at a distance of about 2 kpc. △ Less

Submitted 13 November, 2019; originally announced November 2019.

Comments: 17 pages, 10 figures, 2 tables

Journal ref: Astron. J. 158:107, 2019

Infrared spectroscopy of the recent outburst in V1047 Cen (Nova Centauri 2005)

Authors: T. R. Geballe, D. P. K. Banerjee, A. Evans, R. D. Gehrz, C. E. Woodward, P. Mroz, A. Udalski, U. Munari, S. Starrfield, K. L. Page, K. Sokolovsky, F. -J. Hambsch, G. Myers, E. Aydi, D. A. H. Buckley, F. Walter, R. M. Wagner

Abstract: Fourteen years after its eruption as a classical nova (CN), V1047 Cen (Nova Cen 2005) began an unusual re-brightening in 2019 April. The amplitude of the brightening suggests that this is a dwarf nova (DN) eruption in a CN system. Very few CNe have had DN eruptions within decades of the main CN outburst. The 14 years separating the CN and DN eruptions of V1047 Cen is the shortest of all instances… ▽ More Fourteen years after its eruption as a classical nova (CN), V1047 Cen (Nova Cen 2005) began an unusual re-brightening in 2019 April. The amplitude of the brightening suggests that this is a dwarf nova (DN) eruption in a CN system. Very few CNe have had DN eruptions within decades of the main CN outburst. The 14 years separating the CN and DN eruptions of V1047 Cen is the shortest of all instances recorded thus far. Explaining this rapid succession of CN and DN outbursts in V1047 Cen may be challenging within the framework of standard theories for DN outbursts. Following a CN eruption, the mass accretion rate is believed to remain high $(\dot{M}\sim10^{-8}$M$_\odot$yr$^{-1})$ for a few centuries, due to the irradiation of the secondary star by the still-hot surface of the white dwarf. Thus a DN eruption is not expected to occur during this high mass accretion phase as DN outbursts, which result from thermal instabilities in the accretion disk, and arise during a regime of low mass accretion rate $(\dot{M}\sim10^{-10}$M$_\odot$yr$^{-1})$. Here we present near-infrared spectroscopy to show that the present outburst is most likely a DN eruption, and discuss the possible reasons for its early occurrence. Even if the present re-brightening is later shown to be due to a cause other than a DN outburst, the present study provides invaluable documentation of this unusual event. △ Less

Submitted 28 October, 2019; originally announced October 2019.

Comments: Astrophysical Journal Letters, in press. Data in Figure 2 will be available as "Data behind the Figure" in the published version of the paper

The Central 300 pc of the Galaxy probed by infrared spectra of H$_3^+$ and CO: part I. Predominance of warm and diffuse gas and high H$_2$ ionization rate

Authors: Takeshi Oka, T. R. Geballe, Miwa Goto, Tomonori Usuda, Benjamin, J. McCall, Nick Indriolo

Abstract: The molecular gas in the Central Molecular Zone (CMZ) of the Galaxy has been studied using infrared absorption spectra of H$_3^+$ lines at 3.5-4.0 $μ$m and CO lines near 2.34 $μ$m. In addition to the previously reported spectra of these lines toward 8 stars located within 30 pc of Sgr A$^\ast$, there are now spectra toward $\sim$30 bright stars located from 140 pc west to 120 pc east of Sgr A… ▽ More The molecular gas in the Central Molecular Zone (CMZ) of the Galaxy has been studied using infrared absorption spectra of H$_3^+$ lines at 3.5-4.0 $μ$m and CO lines near 2.34 $μ$m. In addition to the previously reported spectra of these lines toward 8 stars located within 30 pc of Sgr A$^\ast$, there are now spectra toward $\sim$30 bright stars located from 140 pc west to 120 pc east of Sgr A$^\ast$. The spectra show the presence of warm ($T\sim 200$ K) and diffuse ($n < 100 $cm$^{-3}$) gas with $N$(H$_3^+$) $\sim 3 \times 10^{15} $cm$^{-2}$ on majority of sightlines. Instead of our previous analysis in which only electrons from photoionization of carbon atoms were considered, we have developed a simple model calculation in which the cosmic ray ionization of H$_2$ and H are also taken into account. We conclude: (1) Warm and diffuse gas dominates the volume of the CMZ. The volume filling factor of dense gas must be much less than 0.1 and the CMZ is not as opaque as previously considered. The X-ray emitting ultra-hot 10$^8 $K plasma, which some thought to dominate the CMZ, does not exist over extended regions. (2) The cosmic ray ionization rate is $ζ\sim 2 \times 10^{-14} $s$^{-1}$, higher than in Galactic dense clouds and diffuse clouds by factors of $\sim$1000 and $\sim$100, respectively. If the equipartition law stands, this suggests a pervading magnetic field on the order of $\sim$100 $μ$G. △ Less

Submitted 10 October, 2019; originally announced October 2019.

Comments: 39 pages, 7 tables, 10 figures, published at the ApJ

Search for H$_3^+$ isotopologues toward CRL 2136 IRS 1

Authors: Miwa Goto, T. R. Geballe, Jorma Harju, Paola Caselli, Olli Sipilä, Karl M. Menten, Tomonori Usuda

Abstract: Deuterated interstellar molecules frequently have abundances relative to their main isotopologues much higher than the overall elemental D-to-H ratio in the cold dense interstellar medium. The H$_3^+$ and its isotopologues play a key role in the deuterium fractionation; however, the abundances of these isotopologues have not been measured empirically with respect to H$_3^+$ to date. Our aim was to… ▽ More Deuterated interstellar molecules frequently have abundances relative to their main isotopologues much higher than the overall elemental D-to-H ratio in the cold dense interstellar medium. The H$_3^+$ and its isotopologues play a key role in the deuterium fractionation; however, the abundances of these isotopologues have not been measured empirically with respect to H$_3^+$ to date. Our aim was to constrain the relative abundances of H$_2$D$^+$ and D$_3^+$ in the cold outer envelope of the hot core CRL 2136 IRS 1. We carried out three observations targeting H$_3^+$ and its isotopologues using the spectrographs CRIRES at the VLT, iSHELL at IRTF, and EXES on board SOFIA. In addition, the CO overtone band at 2.3 $μ$m was observed by iSHELL to characterize the gas on the line of sight. The H$_3^+$ ion was detected toward CRL 2136 IRS 1 as in previous observations. Spectroscopy of lines of H$_2$D$^+$ and D$_3^+$ resulted in non-detections. The 3$σ$ upper limits of $N({\rm H_2D^+})/N({\rm H_3^+})$ and $N({\rm D_3^+})/N({\rm H_3^+})$ are 0.24 and 0.13, respectively. The population diagram for CO is reproduced by two components of warm gas with the temperatures 58 K and 530 K, assuming a local thermodynamic equilibrium (LTE) distribution of the rotational levels. Cold gas ($<$20 K) makes only a minor contribution to the CO molecular column toward CRL 2136 IRS 1. The critical conditions for deuterium fractionation in a dense cloud are low temperature and CO depletion. Given the revised cloud properties, it is no surprise that H$_3^+$ isotopologues are not detected toward CRL 2136 IRS 1. The result is consistent with our current understanding of how deuterium fractionation proceeds. △ Less

Submitted 9 October, 2019; originally announced October 2019.

Comments: 9 pages, 3 tables, 8 figures, accepted for publication at A&A

Journal ref: A&A 632, A29 (2019)

3.8um Imaging of 400-600K Brown Dwarfs and Orbital Constraints for WISEP J045853.90+643452.6AB

Authors: S. K. Leggett, Trent J. Dupuy, Caroline V. Morley, Mark S. Marley, William M. J. Best, Michael C. Liu, D. Apai, S. L. Casewell, T. R. Geballe, John E. Gizis, J. Sebastian Pineda, Marcia Rieke, G. S. Wright

Abstract: Half of the energy emitted by late-T- and Y-type brown dwarfs emerges at 3.5 < lambda um < 5.5. We present new L' (3.43 < lambda um < 4.11) photometry obtained at the Gemini North telescope for nine late-T and Y dwarfs, and synthesize L' from spectra for an additional two dwarfs. The targets include two binary systems which were imaged at a resolution of 0.25". One of these, WISEP J045853.90+64345… ▽ More Half of the energy emitted by late-T- and Y-type brown dwarfs emerges at 3.5 < lambda um < 5.5. We present new L' (3.43 < lambda um < 4.11) photometry obtained at the Gemini North telescope for nine late-T and Y dwarfs, and synthesize L' from spectra for an additional two dwarfs. The targets include two binary systems which were imaged at a resolution of 0.25". One of these, WISEP J045853.90+643452.6AB, shows significant motion, and we present an astrometric analysis of the binary using Hubble Space Telescope, Keck Adaptive Optics, and Gemini images. We compare lambda ~4um observations to models, and find that the model fluxes are too low for brown dwarfs cooler than ~700K. The discrepancy increases with decreasing temperature, and is a factor of ~2 at T_eff=500K and ~4 at T_eff=400K. Warming the upper layers of a model atmosphere generates a spectrum closer to what is observed. The thermal structure of cool brown dwarf atmospheres above the radiative-convective boundary may not be adequately modelled using pure radiative equilibrium; instead heat may be introduced by thermochemical instabilities (previously suggested for the L- to T-type transition) or by breaking gravity waves (previously suggested for the solar system giant planets). One-dimensional models may not capture these atmospheres, which likely have both horizontal and vertical pressure/temperature variations. △ Less

Submitted 21 August, 2019; v1 submitted 17 July, 2019; originally announced July 2019.

Comments: Accepted for publication in The Astrophysical Journal, July 17 2019. This revision includes changes to the Appendix only. Additional new W1 photometry is given and Figure 11 is updated; Figure 13 contained erroneous data and is corrected; Figure 14 is new and shows the new relationships derived for transforming from ground-based L or M magnitudes to Spitzer [3.6] and [4.5]

Astro2020 Science White Paper: Are Supernovae the Dust Producer in the Early Universe?

Authors: Jeonghee Rho, Danny Milisavljevic, Arkaprabha Sarangi, Raffaella Margutti, Ryan Chornock, Armin Rest, Melissa Graham, J. Craig Wheeler, Darren DePoy, Lifan Wang, Jennifer Marshall, Grant Williams, Rachel Street, Warren Skidmore, Yan Haojing, Joshua Bloom, Sumner Starrfield, Chien-Hsiu Lee, Philip S. Cowperthwaite, Guy S. Stringfellow, Deanne Coppejans, Giacomo Terreran, Niharika Sravan, Thomas R. Geballe, Aneurin Evans , et al. (1 additional authors not shown)

Abstract: Whether supernovae are a significant source of dust has been a long-standing debate. The large quantities of dust observed in high-redshift galaxies raise a fundamental question as to the origin of dust in the Universe since stars cannot have evolved to the AGB dust-producing phase in high-redshift galaxies. In contrast, supernovae occur within several millions of years after the onset of star for… ▽ More Whether supernovae are a significant source of dust has been a long-standing debate. The large quantities of dust observed in high-redshift galaxies raise a fundamental question as to the origin of dust in the Universe since stars cannot have evolved to the AGB dust-producing phase in high-redshift galaxies. In contrast, supernovae occur within several millions of years after the onset of star formation. This white paper focuses on dust formation in supernova ejecta with US-Extremely Large Telescope (ELT) perspective during the era of JWST and LSST. △ Less

Submitted 17 April, 2019; originally announced April 2019.

Comments: Astro2020 Science White Paper: Dust Formation in Supernovae with US-ELT Perspective

New Near-Infrared Imaging and Spectroscopy of NGC 2071-IR

Authors: D. M. Walther, T. R. Geballe

Abstract: We present high resolution images of NGC 2071-IR in the $J$, $H$, and $K$ bands and in the emission at 2.12 $μ$m of the v=$1-0$ $S$(1) line of molecular hydrogen. We also present moderate resolution K-band spectra of two young stellar objects, IRS 1 and IRS 3, within NGC 2071-IR, that are candidates sources of one or more of the outflows observed in the region. Two of the eight originally identifi… ▽ More We present high resolution images of NGC 2071-IR in the $J$, $H$, and $K$ bands and in the emission at 2.12 $μ$m of the v=$1-0$ $S$(1) line of molecular hydrogen. We also present moderate resolution K-band spectra of two young stellar objects, IRS 1 and IRS 3, within NGC 2071-IR, that are candidates sources of one or more of the outflows observed in the region. Two of the eight originally identified infrared point sources in NGC 2071-IR are binaries, and we identifiy two new sources, one coincident with the radio source VLA-1 and highly reddened. The H2 $Q$(3)/$S$(1) line intensity ratios at IRS 1 and IRS 3 yield high and very high extinctions, respectively, to them, as is implied by their near-infrared colors and K-band continuum slopes. The spectra also reveal the presence of hot, dense circumstellar molecular gas in each, suggesting that both are strong candidates for having energetic molecular outflows. We agree with a previous suggestion that IRS 1 is the likely source of an E-W-oriented outflow and conclude that this outflow is probably largely out of the plane of the sky. We also conclude that if IRS 3 is the source of the large scale NE-SW outflow, as has been previously suggested, its jet/wind must precess in order to explain the angular width of that outflow. We discuss the natures of the point sources and their probable contributions, if any, to the complex morphology of the H2 line emission. △ Less

Submitted 10 March, 2021; v1 submitted 8 March, 2019; originally announced March 2019.

Comments: 30 pages, 5 figures; accepted by ApJ 6 March 2019. Offset to VLA-1 in Table 1 corrected

Background Infrared Sources for Studying the Galactic Center's Interstellar Gas

Authors: T. R. Geballe, E. Lambrides, B. Schlegelmilch, S. C. C. Yeh, M. Goto, Calvin Westrick, T. Oka, F. Najarro

Abstract: We briefy describe the results of a K-band spectroscopic survey of over 500 highly reddened point-like objects on sightlines toward the Central Molecular Zone (CMZ) of the Galaxy. The goal was to find stars with featureless or nearly featureless spectra suitable for near- and mid-infrared absorption spectroscopy of the Galactic center's interstellar gas on sightlines spread across the CMZ. Until r… ▽ More We briefy describe the results of a K-band spectroscopic survey of over 500 highly reddened point-like objects on sightlines toward the Central Molecular Zone (CMZ) of the Galaxy. The goal was to find stars with featureless or nearly featureless spectra suitable for near- and mid-infrared absorption spectroscopy of the Galactic center's interstellar gas on sightlines spread across the CMZ. Until recently only a few such stars have been known outside of very localized sightlines in the vicinity of the Quintuplet and Central clusters. We have used Spitzer Space Telescope (GLIMPSE) and 2MASS photometry to select promising candidates, and over the last ten years have been acquiring low-resolution K-band spectra of them. As expected, the vast majority are cool and/or highly reddened red giants with complex photospheric spectra unsuitable for measuring faint interstellar lines. Approximately ten percent of them, whose observations are reported here, have featureless or nearly featureless spectra. Although not evenly distributed in Galactic longitude, these stars are scattered across the CMZ. Many of them are luminous stars that are deeply embedded in warm dust cocoons, and have K-band continua rising steeply to longer wavelengths. A significant fraction of them are hot stars of a variety of spectral types, including at least five newly discovered Wolf-Rayet stars. All of them should be suitable for spectroscopy of interstellar absorption lines at infrared wavelengths greater than 3 microns and many are also suitable at shorter wavelengths. △ Less

Submitted 9 February, 2019; originally announced February 2019.

Comments: 24 pages, 6 figures; ApJ, in press

Early formation of carbon monoxide in the Centaurus A supernova SN 2016adj

Authors: D. P. K. Banerjee, Vishal Joshi, A. Evans, Mudit Srivastava, N. M. Ashok, R. D. Gehrz, M. S. Connelley, T. R. Geballe, J. Spyromilio, J. Rho, R. Roy

Abstract: We present near-infrared spectroscopy of the NGC 5128 supernova SN 2016adj in the first 2 months following discovery. We report the detection of first overtone carbon monoxide emission at $\sim58.2$ d after discovery, one of the earliest detections of CO in an erupting supernova. We model the CO emission to derive the CO mass, temperature and velocity, assuming both pure $^{12}$CO and a compositio… ▽ More We present near-infrared spectroscopy of the NGC 5128 supernova SN 2016adj in the first 2 months following discovery. We report the detection of first overtone carbon monoxide emission at $\sim58.2$ d after discovery, one of the earliest detections of CO in an erupting supernova. We model the CO emission to derive the CO mass, temperature and velocity, assuming both pure $^{12}$CO and a composition that includes $^{13}$CO; the case for the latter is the isotopic analyses of meteoritic grains, which suggest that core collapse supernovae can synthesise significant amounts of $^{13}$C. Our models show that, while the CO data are adequately explained by pure $^{12}$CO, they do not preclude the presence of $^{13}$CO, to a limit of $^{12}$C/$^{13}$C $> 3$, the first constraint on the $^{12}$C/$^{13}$C ratio determined from near-infrared observations. We estimate the reddening to the object, and the effective temperature from the energy distribution at outburst. We discuss whether the ejecta of SN 2016adj may be carbon-rich, what the infrared data tell us about the classification of this supernova, and what implications the early formation of CO in supernovae may have for CO formation in supernovae in general. △ Less

Submitted 14 August, 2018; originally announced August 2018.

Comments: MNRAS, in press. Accepted 2018 August 13

Near-Infrared Spectroscopy of SN 2017eaw in 2017: Carbon Monoxide and Dust Formation in a Type II-P Supernova

Authors: J. Rho, T. R. Geballe, D. P. K. Banerjee, L. Dessart, A. Evans, V. Joshi

Abstract: The origin of dust in the early Universe has been the subject of considerable debate. Core-collapse supernovae (ccSNe), which occur several million years after their massive progenitors form, could be a major source of that dust, as in the local universe several ccSNe have been observed to be copious dust producers. Here we report nine near-infrared (0.8 - 2.5 micron) spectra of the Type II-P SN 2… ▽ More The origin of dust in the early Universe has been the subject of considerable debate. Core-collapse supernovae (ccSNe), which occur several million years after their massive progenitors form, could be a major source of that dust, as in the local universe several ccSNe have been observed to be copious dust producers. Here we report nine near-infrared (0.8 - 2.5 micron) spectra of the Type II-P SN 2017eaw in NGC 6946, spanning the time interval 22 - 205 days after discovery. The specta show the onset of CO formation and continuum emission at wavelengths greater than 2.1 micron from newly-formed hot dust, in addition to numerous lines of hydrogen and metals, which reveal the change in ionization as the density of much of the ejecta decreases. The observed CO masses estimated from an LTE model are typically 10^{-4} Msun during days 124 - 205, but could be an order of magnitude larger if non-LTE conditions are present in the emitting region. The timing of the appearance of CO is remarkably consistent with chemically controlled dust models of Sarangi & Cherchneff. △ Less

Submitted 2 August, 2018; originally announced August 2018.

Comments: Accepted for publication in the ApJL

An L Band Spectrum of the Coldest Brown Dwarf

Authors: Caroline V. Morley, Andrew J. Skemer, Katelyn N. Allers, Mark. S. Marley, Jacqueline K. Faherty, Channon Visscher, Samuel A. Beiler, Brittany E. Miles, Roxana Lupu, Richard S. Freedman, Jonathan J. Fortney, Thomas R. Geballe, Gordon L. Bjoraker

Abstract: The coldest brown dwarf, WISE 0855, is the closest known planetary-mass, free-floating object and has a temperature nearly as cold as the solar system gas giants. Like Jupiter, it is predicted to have an atmosphere rich in methane, water, and ammonia, with clouds of volatile ices. WISE 0855 is faint at near-infrared wavelengths and emits almost all its energy in the mid-infrared. Skemer et al. 201… ▽ More The coldest brown dwarf, WISE 0855, is the closest known planetary-mass, free-floating object and has a temperature nearly as cold as the solar system gas giants. Like Jupiter, it is predicted to have an atmosphere rich in methane, water, and ammonia, with clouds of volatile ices. WISE 0855 is faint at near-infrared wavelengths and emits almost all its energy in the mid-infrared. Skemer et al. 2016 presented a spectrum of WISE 0855 from 4.5-5.1 micron (M band), revealing water vapor features. Here, we present a spectrum of WISE 0855 in L band, from 3.4-4.14 micron. We present a set of atmosphere models that include a range of compositions (metallicities and C/O ratios) and water ice clouds. Methane absorption is clearly present in the spectrum. The mid-infrared color can be better matched with a methane abundance that is depleted relative to solar abundance. We find that there is evidence for water ice clouds in the M band spectrum, and we find a lack of phosphine spectral features in both the L and M band spectra. We suggest that a deep continuum opacity source may be obscuring the near-infrared flux, possibly a deep phosphorous-bearing cloud, ammonium dihyrogen phosphate. Observations of WISE 0855 provide critical constraints for cold planetary atmospheres, bridging the temperature range between the long-studied solar system planets and accessible exoplanets. JWST will soon revolutionize our understanding of cold brown dwarfs with high-precision spectroscopy across the infrared, allowing us to study their compositions and cloud properties, and to infer their atmospheric dynamics and formation processes. △ Less

Submitted 20 April, 2018; originally announced April 2018.

Comments: 19 pages, 21 figures. Accepted for publication in ApJ

Emission Lines in the Near-infrared Spectra of the Infrared Quintuplet Stars in the Galactic Center

Authors: F. Najarro, T. R. Geballe, D. F. Figer, D. de la Fuente

Abstract: We report the detection of a number of emission lines in the 1.0--2.4~$μ$m spectra of four of the five bright infrared dust-embedded stars at the center of the Galactic center's Quintuplet Cluster. Spectroscopy of the central stars of these objects is hampered not only by the large interstellar extinction that obscures all objects in the Galactic center, but also by the large amounts of warm circu… ▽ More We report the detection of a number of emission lines in the 1.0--2.4~$μ$m spectra of four of the five bright infrared dust-embedded stars at the center of the Galactic center's Quintuplet Cluster. Spectroscopy of the central stars of these objects is hampered not only by the large interstellar extinction that obscures all objects in the Galactic center, but also by the large amounts of warm circumstellar dust surrounding each of the five. The pinwheel morphologies of the dust observed previously around two of them are indicative of Wolf-Rayet colliding wind binaries; however, infrared spectra of each of the five have until now revealed only dust continua steeply rising to long wavelengths and absorption lines and bands from interstellar gas and dust. The emission lines detected, from ionized carbon and from helium, are broad and confirm that the objects are dusty late-type carbon Wolf-Rayet stars. △ Less

Submitted 21 July, 2017; originally announced July 2017.

Comments: 12 pages, 7 figures, 3 tables. Accepted for publication in ApJ

Very High Excitation Lines of H$_{2}$ in the Orion Molecular Cloud Outflow

Authors: T. R. Geballe, M. G. Burton, R. E. Pike

Abstract: Vibration-rotation lines of H$_{2}$ from highly excited levels approaching the dissociation limit have been detected at a number of locations in the shocked gas of the Orion Molecular Cloud (OMC-1), including in a Herbig-Haro object near the tip of one of the OMC-1 "fingers." Population diagrams show that while the excited H$_{2}$ is almost entirely at a kinetic temperature of $\sim$1,800 K, (typi… ▽ More Vibration-rotation lines of H$_{2}$ from highly excited levels approaching the dissociation limit have been detected at a number of locations in the shocked gas of the Orion Molecular Cloud (OMC-1), including in a Herbig-Haro object near the tip of one of the OMC-1 "fingers." Population diagrams show that while the excited H$_{2}$ is almost entirely at a kinetic temperature of $\sim$1,800 K, (typical for vibrationally shock-excited H$_{2}$), as in the previously reported case of Herbig-Haro object HH 7 up to a few percent of the H$_{2}$ is at a kinetic temperature of $\sim$5,000~K. The location with the largest fraction of hot H$_{2}$ is the Herbig-Haro object, where the outflowing material is moving at a higher speed than at the other locations. Although theoretical work is required for a better understanding of the 5,000 K H$_{2}$, (including how it cools), its existence and the apparent dependence of its abundance relative to that of the cooler component on the relative velocities of the outflow and the surrounding ambient gas appear broadly consistent with it having recently reformed. The existence of this high temperature H$_{2}$ appears to be a common characteristic of shock-excited molecular gas. △ Less

Submitted 20 February, 2017; originally announced February 2017.

Comments: 20 pages, 5 figures, accepted by ApJ 2017 Feb. 18

Highly Excited H2 in Herbig-Haro 7: Formation Pumping in Shocked Molecular Gas?

Authors: R. E. Pike, T. R. Geballe, M. G. Burton, A. Chrysostomou

Abstract: We have obtained K-band spectra at R~5,000 and angular resolution 0.3" of a section of the Herbig-Haro 7 (HH7) bow shock, using the Near-Infrared Integral Field Spectrograph at Gemini North. Present in the portion of the data cube corresponding to the brightest part of the bow shock are emission lines of H2 with upper state energies ranging from ~6,000 K up to the dissociation energy of H2, ~50,00… ▽ More We have obtained K-band spectra at R~5,000 and angular resolution 0.3" of a section of the Herbig-Haro 7 (HH7) bow shock, using the Near-Infrared Integral Field Spectrograph at Gemini North. Present in the portion of the data cube corresponding to the brightest part of the bow shock are emission lines of H2 with upper state energies ranging from ~6,000 K up to the dissociation energy of H2, ~50,000 K. Because of low signal-to-noise ratios, the highest excitation lines cannot be easily seen elsewhere in the observed region. However, excitation temperatures, measured throughout much of the observed region using lines from levels as high as 25,000 K, are a strong function of upper level energy, indicating that the very highest levels are populated throughout. The level populations in the brightest region are well fit by a two-temperature model, with 98.5% of the emitting gas at T=1800 K and 1.5% at T=5200 K. The bulk of the H2 line emission in HH7, from the 1,800 K gas, has previously been well modeled by a continuous shock, but the 5,200 K component is inconsistent with standalone standard continuous shock models. We discuss various possible origins for the hot component and suggest that this component is H2 newly reformed on dust grains and then ejected from them, presumably following dissociation of some of the H2 by the shock. △ Less

Submitted 23 March, 2016; originally announced March 2016.

Outflowing Diffuse Gas in the Active Galactic Nucleus of NGC 1068

Authors: T. R. Geballe, R. E. Mason, T. Oka

Abstract: Spectra of the archetypal Type II Seyfert galaxy NGC 1068 in a narrow wavelength interval near 3.7 microns have revealed a weak absorption feature due to two lines of the molecular ion H3+. The observed wavelength of the feature corresponds to velocity of -70 km/s relative to the systemic velocity of the galaxy, implying an outward flow from the nucleus along the line of sight. The absorption by H… ▽ More Spectra of the archetypal Type II Seyfert galaxy NGC 1068 in a narrow wavelength interval near 3.7 microns have revealed a weak absorption feature due to two lines of the molecular ion H3+. The observed wavelength of the feature corresponds to velocity of -70 km/s relative to the systemic velocity of the galaxy, implying an outward flow from the nucleus along the line of sight. The absorption by H3+ along with the previously known broad hydrocarbon absorption at 3.4~microns probably are formed in diffuse gas that is in close proximity to the continuum source, i.e. within a few tens of parsecs of the central engine. Based on that conclusion and the measured H3+ absorption velocity and with the assumption of a spherically symmetric wind we estimate a rate of mass outflow from the AGN of ~1 Msun/yr. △ Less

Submitted 2 September, 2015; originally announced September 2015.

Comments: Accepted by ApJ 2 Sep 2015

The Brightening of Re50N: Accretion Event or Dust Clearing?

Authors: Hsin-Fang Chiang, Bo Reipurth, Josh Walawender, Michael S. Connelley, Peter Pessev, Tom R. Geballe, William M. J. Best, Martin Paegert

Abstract: The luminous Class I protostar HBC 494, embedded in the Orion A cloud, is associated with a pair of reflection nebulae, Re50 and Re50N, which appeared sometime between 1955 and 1979. We have found that a dramatic brightening of Re50N has taken place sometime between 2006 and 2014. This could result if the embedded source is undergoing a FUor eruption. However, the near-infrared spectrum shows a fe… ▽ More The luminous Class I protostar HBC 494, embedded in the Orion A cloud, is associated with a pair of reflection nebulae, Re50 and Re50N, which appeared sometime between 1955 and 1979. We have found that a dramatic brightening of Re50N has taken place sometime between 2006 and 2014. This could result if the embedded source is undergoing a FUor eruption. However, the near-infrared spectrum shows a featureless very red continuum, in contrast to the strong CO bandhead absorption displayed by FUors. Such heavy veiling, and the high luminosity of the protostar, is indicative of strong accretion but seemingly not in the manner of typical FUors. We favor the alternative explanation that the major brightening of Re50N and the simultaneous fading of Re50 is caused by curtains of obscuring material that cast patterns of illumination and shadows across the surface of the molecular cloud. This is likely occurring as an outflow cavity surrounding the embedded protostar breaks through to the surface of the molecular cloud. Several Herbig-Haro objects are found in the region. △ Less

Submitted 13 March, 2015; originally announced March 2015.

Comments: 8 pages, accepted by ApJ