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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)

   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)

   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. Where are the missing symbiotic stars? Uncovering hidden symbiotic stars in public catalogues

   https://doi.org/10.1093/mnras/stad096  

   Akras, Stavros ( January 2023 , Monthly Notices of the Royal Astronomical Society)

   Theoretical predictions of the population of Galactic symbiotic stars (SySts) are highly inconsistent with the current known population. Despite intense effort over the past decades, observations are still far below the predictions. The majority of known SySts so far are identified based on selection criteria established in the optical regime. The recent discovery of SU Lyn with very faint optical emission lines uncloaked a subgroup of SySts with accreting-only white dwarfs. In this particular case, the luminous red giant may overshadow the dimmed white dwarf companion. A new approach to search for this subgroup of SySts is presented, employing GALEX UV and 2MASS/AllWISE IR photometry. The FUV-NUV colour index is an indicator, direct or indirect, for the presence of hot compact companions. The cross-match of the Catalogue of Variable Stars III obtained from the All-Sky Automated Survey for SuperNovae (ASAS-SN) with the GALEX, 2MASS, and AllWISE catalogues result in a sample of 814 potential SySt candidates. From them, 105 sources have photometric measurements from both FUV and NUV bands and 35 exhibit FUV-NUV<1, similar to what it is expected from known SySts. Five known SySts are recovered, while two new genuine SySts are discovered in spectroscopic follow-up observations after the detection of the typical emission lines.

    

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5. The ASAS-SN catalogue of variable stars VI: an all-sky sample of δ Scuti stars

   https://doi.org/10.1093/mnras/staa499  

   Jayasinghe, T ; Stanek, K Z ; Kochanek, C S ; Vallely, P J ; Shappee, B J ; Holoien, T W-S ; Thompson, Todd A ; Prieto, J L ; Pejcha, O ; Fausnaugh, M ; et al ( April 2020 , Monthly Notices of the Royal Astronomical Society)

   ABSTRACT We characterize an all-sky catalogue of ∼8400 δ Scuti variables in ASAS-SN, which includes ∼3300 new discoveries. Using distances from Gaia DR2, we derive period–luminosity relationships for both the fundamental mode and overtone pulsators in the WJK, V, Gaia DR2 G, J, H, Ks, and W1 bands. We find that the overtone pulsators have a dominant overtone mode, with many sources pulsating in the second overtone or higher order modes. The fundamental mode pulsators have metallicity-dependent periods, with log10(P) ∼ −1.1 for $\rm [Fe/H]\lt -0.3$ and log10(P) ∼ −0.9 for $\rm [Fe/H]\gt 0$, which leads to a period-dependent scale height. Stars with $P\gt 0.100\, \rm d$ are predominantly located close to the Galactic disc ($\rm |\mathit{ Z}|\lt 0.5\, kpc$). The median period at a scale height of $Z\sim 0\, \rm kpc$ also increases with the Galactocentric radius R, from log10(P) ∼ −0.94 for sources with $R\gt 9\, \rm kpc$ to log10(P) ∼ −0.85 for sources with $R\lt 7\, \rm kpc$, which is indicative of a radial metallicity gradient. To illustrate potential applications of this all-sky catalogue, we obtained 30 min cadence, image subtraction TESS light curves for a sample of 10 fundamental mode and 10 overtone δ Scuti stars discovered by ASAS-SN. From this sample, we identified two new δ Scuti eclipsing binaries, ASASSN-V J071855.62−434247.3 and ASASSN-V J170344.20−615941.2 with short orbital periods of Porb = 2.6096 and 2.5347 d, respectively. 

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