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1. Photometry of Saturated Stars with Neural Networks

   https://doi.org/10.3847/1538-4357/ad5a0b  

   Winecki, Dominik; Kochanek, Christopher S (August 2024, The Astrophysical Journal)

   Abstract We use a multilevel perceptron (MLP) neural network to obtain photometry of saturated stars in the All-Sky Automated Survey for Supernovae (ASAS-SN). The MLP can obtain fairly unbiased photometry for stars fromg≃ 4 to 14 mag, particularly compared to the dispersion (15%–85% 1σrange around the median) of 0.12 mag for saturated (g< 11.5 mag) stars. More importantly, the light curve of a nonvariable saturated star has a median dispersion of only 0.037 mag. The MLP light curves are, in many cases, spectacularly better than those provided by the standard ASAS-SN pipelines. While the network was trained ong-band data from only one of ASAS-SN’s 20 cameras, initial experiments suggest that it can be used for any camera and the older ASAS-SNV-band data as well. The dominant problems seem to be associated with correctable issues in the ASAS-SN data reduction pipeline for saturated stars more than the MLP itself. The method is publicly available as a light-curve option on ASAS-SN Sky Patrol v1.0. 

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2. The Open Cluster Chemical Abundances and Mapping Survey. VII. APOGEE DR17 [C/N]–Age Calibration

   https://doi.org/10.3847/1538-3881/ac5d53  

   Spoo, Taylor; Tayar, Jamie; Frinchaboy, Peter M.; Cunha, Katia; Myers, Natalie; Donor, John; Majewski, Steven R.; Bizyaev, Dmitry; García-Hernández, D. A.; Jönsson, Henrik; et al (April 2022, The Astronomical Journal)

   Abstract Large-scale surveys open the possibility to investigate Galactic evolution both chemically and kinematically; however, reliable stellar ages remain a major challenge. Detailed chemical information provided by high-resolution spectroscopic surveys of the stars in clusters can be used as a means to calibrate recently developed chemical tools for age-dating field stars. Using data from the Open Cluster Abundances and Mapping survey, based on the Sloan Digital Sky Survey/Apache Point Observatory Galactic Evolution Experiment 2 survey, we derive a new empirical relationship between open cluster stellar ages and the carbon-to-nitrogen ([C/N]) abundance ratios for evolved stars, primarily those on the red giant branch. With this calibration, [C/N] can be used as a chemical clock for evolved field stars to investigate the formation and evolution of different parts of our Galaxy. We explore how mixing effects at different stellar evolutionary phases, like the red clump, affect the derived calibration. We have established the [C/N]–age calibration for APOGEE Data Release 17 (DR17) giant star abundances to be log [ Age ( yr ) ] DR 17 = 10.14 ( ± 0.08 ) + 2.23 ( ± 0.19 ) [ C / N ] , usable for 8.62 ≤ log ( Age [ yr ] ) ≤ 9.82 , derived from a uniform sample of 49 clusters observed as part of APOGEE DR17 applicable primarily to metal-rich, thin- and thick-disk giant stars. This measured [C/N]–age APOGEE DR17 calibration is also shown to be consistent with asteroseismic ages derived from Kepler photometry. 

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3. Data release of the AST3-2 automatic survey from Dome A, Antarctica

   https://doi.org/10.1093/mnras/stad498  

   Yang, Xu; Hu, Yi; Shang, Zhaohui; Ma, Bin; Ashley, Michael C; Cui, Xiangqun; Du, Fujia; Fu, Jianning; Gong, Xuefei; Gu, Bozhong; et al (February 2023, Monthly Notices of the Royal Astronomical Society)

   ABSTRACT AST3-2 is the second of the three Antarctic Survey Telescopes, aimed at wide-field time-domain optical astronomy. It is located at Dome A, Antarctica, which is by many measures the best optical astronomy site on the Earth’s surface. Here we present the data from the AST3-2 automatic survey in 2016 and the photometry results. The median 5σ limiting magnitude in i-band is 17.8 mag and the light-curve precision is 4 mmag for bright stars. The data release includes photometry for over 7 million stars, from which over 3500 variable stars were detected, with 70 of them newly discovered. We classify these new variables into different types by combining their light-curve features with stellar properties from surveys such as StarHorse. 

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4. Multiplicity of northern bright O-type stars with optical long baseline interferometry: Results of the pilot survey

   https://doi.org/10.1051/0004-6361/202245364  

   Lanthermann, C.; Le Bouquin, J.-B.; Sana, H.; Mérand, A.; Monnier, J. D.; Perraut, K.; Frost, A. J.; Mahy, L.; Gosset, E.; De Becker, M.; et al (April 2023, Astronomy & Astrophysics)

   Context . The study of the multiplicity of massive stars gives hints on their formation processes and their evolutionary paths, which are still not fully understood. Large separation binaries (>50 milliseconds of arc, mas) can be probed by adaptive-optics-assisted direct imaging and sparse aperture masking, while close binaries can be resolved by photometry and spectroscopy. However, optical long baseline interferometry is mandatory to establish the multiplicity of Galactic massive stars at the separation gap between 1 and 50 mas. Aims . In this paper, we aim to demonstrate the capability of the new interferometric instrument MIRC-X, located at the CHARA Array, to study the multiplicity of O-type stars and therefore probe the full range of separation for more than 120 massive stars ( H < 7 . 5 mag). Methods . We initiated a pilot survey of bright O-type stars ( H < 6.5 mag) observable with MIRC-X. We observed 29 O-type stars, including two systems in average atmospheric conditions around a magnitude of H = 7.5 mag. We systematically reduced the obtained data with the public reduction pipeline of the instrument. We analyzed the reduced data using the dedicated python software CANDID to detect companions. Results . Out of these 29 systems, we resolved 19 companions in 17 different systems with angular separations between ~0.5 and 50 mas. This results in a multiplicity fraction ƒ m = 17/29 = 0.59 ± 0.09, and an average number of companions ƒ c = 19/29 = 0.66 ± 0.13. Those results are in agreement with the results of the SMASH+ survey in the Southern Hemisphere. Thirteen of these companions have been resolved for the first time, including the companion responsible for the nonthermal emission in Cyg OB2-5 A and the confirmation of the candidate companion of HD 47129 suggested by SMASH+. Conclusions . A large survey on more than 120 northern O-type stars ( H < 7.5) is possible with MIRC-X and will be fruitful. 

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5. Mapping luminous hot stars in the Galaxy

   https://doi.org/10.1051/0004-6361/202039726  

   Zari, E.; Rix, H.-W.; Frankel, N.; Xiang, M.; Poggio, E.; Drimmel, R.; Tkachenko, A. (June 2021, Astronomy & Astrophysics)

   null (Ed.)

   Luminous hot stars ( M K s  ≲ 0 mag and T eff  ≳ 8000 K) dominate the stellar energy input to the interstellar medium throughout cosmological time, are used as laboratories to test theories of stellar evolution and multiplicity, and serve as luminous tracers of star formation in the Milky Way and other galaxies. Massive stars occupy well-defined loci in colour–colour and colour–magnitude spaces, enabling selection based on the combination of Gaia EDR3 astrometry and photometry and 2MASS photometry, even in the presence of substantive dust extinction. In this paper we devise an all-sky sample of such luminous OBA-type stars, which was designed to be complete rather than very pure, providing targets for spectroscopic follow-up with the SDSS-V survey. To estimate the purity and completeness of our catalogue, we derive stellar parameters for the stars in common with LAMOST DR6 and we compare the sample to other O and B-type star catalogues. We estimate ‘astro-kinematic’ distances by combining parallaxes and proper motions with a model for the expected velocity and density distribution of young stars; we show that this adds useful constraints on the distances and therefore luminosities of the stars. With these distances we map the spatial distribution of a more stringently selected subsample across the Galactic disc, and find it to be highly structured, with distinct over- and under-densities. The most evident over-densities can be associated with the presumed spiral arms of the Milky Way, in particular the Sagittarius-Carina and Scutum-Centaurus arms. Yet, the spatial picture of the Milky Way’s young disc structure emerging in this study is complex, and suggests that most young stars in our Galaxy ( t age  <  t dyn ) are not neatly organised into distinct spiral arms. The combination of the comprehensive spectroscopy to come from SDSS-V (yielding velocities, ages, etc.) with future Gaia data releases will be crucial in order to reveal the dynamical nature of the spiral arms themselves. 

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