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1. The loudest stellar heartbeat: characterizing the most extreme amplitude heartbeat star system

   https://doi.org/10.1093/mnras/stab1920  

   Jayasinghe, T; Kochanek, C S; Strader, J; Stanek, K Z; Vallely, P J; Thompson, Todd A; Hinkle, J T; Shappee, B J; Dupree, A K; Auchettl, K; et al (July 2021, Monthly Notices of the Royal Astronomical Society)

   null (Ed.)

   ABSTRACT We characterize the extreme heartbeat star system MACHO 80.7443.1718 in the Large Magellanic Cloud using Transiting Exoplanet Survey Satellite (TESS) photometry and spectroscopic observations from the Magellan Inamori Kyocera Echelle (MIKE) and SOAR Goodman spectographs. MACHO 80.7443.1718 was first identified as a heartbeat star system in the All-Sky Automated Survey for SuperNovae (ASAS-SN) with $$P_{\rm orb}=32.836\pm 0.008\, {\rm d}$$. MACHO 80.7443.1718 is a young (∼6 Myr), massive binary, composed of a B0 Iae supergiant with $$M_1 \simeq 35\, {\rm M}_\odot$$ and an O9.5V secondary with $$M_2 \simeq 16\, {\rm M}_\odot$$ on an eccentric (e = 0.51 ± 0.03) orbit. In addition to having the largest variability amplitude amongst all known heartbeats stars, MACHO 80.7443.1718 is also one of the most massive heartbeat stars yet discovered. The B[e] supergiant has Balmer emission lines and permitted/forbidden metallic emission lines associated with a circumstellar disc. The disc rapidly dissipates at periastron that could indicate mass transfer to the secondary, but re-emerges immediately following periastron passage. MACHO 80.7443.1718 also shows tidally excited oscillations at the N = 25 and N = 41 orbital harmonics and has a rotational period of 4.4 d. 

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2. The ASAS-SN catalogue of variable stars X: discovery of 116 000 new variable stars using G -band photometry

   https://doi.org/10.1093/mnras/stac3801  

   Christy, C. T.; Jayasinghe, T.; Stanek, K. Z.; Kochanek, C. S.; Thompson, T. A.; Shappee, B. J.; Holoien, T. W-S; Prieto, J. L.; Dong, Subo; Giles, W. (December 2022, Monthly Notices of the Royal Astronomical Society)

   ABSTRACT The All-Sky Automated Survey for Supernovae (ASAS-SN) is the first optical survey to monitor the entire sky, currently with a cadence of ≲ 24 h down to g ≲ 18.5 mag. ASAS-SN has routinely operated since 2013, collecting ∼ 2 000 to over 7 500 epochs of V- and g-band observations per field to date. This work illustrates the first analysis of ASAS-SN’s newer, deeper, and higher cadence g-band data. From an input source list of ∼55 million isolated sources with g < 18 mag, we identified 1.5 × 106 variable star candidates using a random forest (RF) classifier trained on features derived from Gaia, 2MASS, and AllWISE. Using ASAS-SN g-band light curves, and an updated RF classifier augmented with data from Citizen ASAS-SN, we classified the candidate variables into eight broad variability types. We present a catalogue of ∼116 000 new variable stars with high-classification probabilities, including ∼111 000 periodic variables and ∼5 000 irregular variables. We also recovered ∼263 000 known variable stars. 

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3. The ASAS-SN catalogue of variable stars – V. Variables in the Southern hemisphere

   https://doi.org/10.1093/mnras/stz2711  

   Jayasinghe, T.; Stanek, K. Z.; Kochanek, C. S.; Shappee, B. J.; Holoien, T. W-S; Thompson, T. A.; Prieto, J. L.; Dong, S.; Pawlak, M.; Pejcha, O.; et al (September 2019, Monthly Notices of the Royal Astronomical Society)

   ABSTRACT The All-Sky Automated Survey for Supernovae (ASAS-SN) provides long baseline (∼4 yr) light curves for sources brighter than V ≲ 17 mag across the whole sky. As part of our effort to characterize the variability of all the stellar sources visible in ASAS-SN, we have produced ∼30.1 million V-band light curves for sources in the Southern hemisphere using the APASS DR9 (AAVSO Photometric All-Sky Survey Data Release) catalogue as our input source list. We have systematically searched these sources for variability using a pipeline based on random forest classifiers. We have identified $${\sim } 220\, 000$$ variables, including $${\sim } 88\, 300$$ new discoveries. In particular, we have discovered $${\sim }48\, 000$$ red pulsating variables, $${\sim }23\, 000$$ eclipsing binaries, ∼2200 δ-Scuti variables, and $${\sim }10\, 200$$ rotational variables. The light curves and characteristics of the variables are all available through the ASAS-SN variable stars data base (https://asas-sn.osu.edu/variables). The pre-computed ASAS-SN V-band light curves for all the ∼30.1 million sources are available through the ASAS-SN photometry data base (https://asas-sn.osu.edu/photometry). This effort will be extended to provide ASAS-SN light curves for sources in the Northern hemisphere and for V ≲ 17 mag sources across the whole sky that are not included in APASS DR9. 

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4. 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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5. Spectroscopic properties of stars in young binaries: fundamental data for understanding binary formation and disk evolution

   https://doi.org/10.1140/epjp/s13360-023-03854-0  

   Prato, Lisa (March 2023, The European Physical Journal Plus)

   Abstract This contribution combines a relatively comprehensive review of the spectroscopic study of the individual component stars and their associated disks in young binary systems, outlines the need for more in-depth studies, and previews the results of a high-spectral and high-angular resolution survey of $$\sim$$ ∼ 100 young binaries located primarily in the Taurus and Ophiuchus star forming regions. Observed spectra, synthetic spectral analysis, and preliminary outcomes for 3 systems are presented, illustrating the power and potential of adaptive optics-fed, high-resolution, infrared spectroscopy for our understanding of the dynamical and physical properties of young binary stars and their circumstellar disks and environments, especially when combined with ancillary data from ALMA, K2, TESS, and other facilities. This new survey will deepen our understanding of disk evolution and planet formation in close binaries and, more broadly, will provide clues to disk dissipation processes in both singles and binaries. 

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