The ASAS-SN catalogue of variable stars IX: The spectroscopic properties of Galactic variable stars

Abstract

The All-Sky Automated Survey for Supernovae (ASAS-SN) provides long baseline (∼4 yrs) V −band light curves for sources brighter than V≲ 17 mag across the whole sky. We produced V-band light curves for a total of ∼61.5 million sources and systematically searched these sources for variability. We identified ∼426, 000 variables, including ∼219, 000 new discoveries. Most (${\sim }74\%$) of our discoveries are in the Southern hemisphere. Here we use spectroscopic information from LAMOST, GALAH, RAVE, and APOGEE to study the physical and chemical properties of these variables. We find that metal-poor eclipsing binaries have orbital periods that are shorter than metal-rich systems at fixed temperature. We identified rotational variables on the main-sequence, red giant branch and the red clump. A substantial fraction (${\gtrsim }80\%$) of the rotating giants have large vrot or large NUV excesses also indicative of fast rotation. The rotational variables have unusual abundances suggestive of analysis problems. Semi-regular variables tend to be lower metallicity ($\rm [Fe/H]{\sim }-0.5$) than most giant stars. We find that the APOGEE DR16 temperatures of oxygen-rich semi-regular variables are strongly correlated with the WRP − WJK color index for $\rm T_{eff}\lesssim 3800$ K. Using abundance measurements from APOGEE DR16, we find evidence for Mg and N enrichment in the semi-regular variables. We find that the Aluminum abundances of the semi-regular variables are strongly correlated with the pulsation period, where the variables with $\rm P\gtrsim 60$ days are significantly depleted in Al.

A unicorn in monoceros: the 3 M⊙ dark companion to the bright, nearby red giant V723 Mon is a non-interacting, mass-gap black hole candidate

“…A particularly important synergy is the ability to combine photometric surveys with these spectroscopic surveys to search for non-interacting compact object binaries like V723 Mon. For example, for the vast majority of these relatively bright stars, the ASAS-SN survey (Shappee et al 2014;Kochanek et al 2017;Jayasinghe et al 2018Jayasinghe et al , 2021 will supply all-sky, well-sampled light curves spanning multiple years. If we make a conservative assumption that ASAS-SN can characterize the variability of most giants up to ∼3 kpc away (not accounting for extinction), there may be ∼20 red giants with non-interacting companions that have ASAS-SN light curves.…”

The "Giraffe": Discovery of a stripped red giant in an interacting binary with a ${\sim}2~M_\odot$ lower giant

“…It was first classified as an 'NSINE' variable star (ATO J063.1314+67.6468) in the the Asteroid Terrestrial-impact Last Alert System (ATLAS; Tonry et al 2018;Heinze et al 2018) catalog of variable stars with a period of ∼80.36 days. It was classified as a semi-regular variable (ASASSN-V J041231.49+673848.6, ZTF J041231.52+673848.6) by the All-Sky Automated Survey for SuperNovae (ASAS-SN; Jayasinghe et al 2018Jayasinghe et al , 2021aShappee et al 2014), and the Zwicky Transient Facility (ZTF; Chen et al 2020;Bellm et al 2019) with periods of ∼40.65 days and ∼41.20 days respectively.…”

Citizen ASAS-SN: Citizen Science with The All-Sky Automated Survey for SuperNovae (ASAS-SN)

“…We used the refcat2 catalog (Tonry et al 2018) as our catalog of targets. The g-band light curves for candidate variables were extracted as described in Jayasinghe et al (2021). We corrected the zero point offsets between the different cameras as described in Jayasinghe et al (2021) and calculated periodograms using the Generalized Lomb- Scargle (GLS, Zechmeister & Kürster 2009;Scargle 1982) periodogram.…”

“…ASAS-SN uses image subtraction (Alard & Lupton 1998) for the detection of transients and to generate light curves. Recently, we have been using ASAS-SN data to study bright variable stars (see, for e.g., Jayasinghe et al 2021). In the V -band catalog, ∼60 million stars were classified using machine learning, resulting in a catalog of ∼426, 000 variables, of which ∼220, 000 were new discoveries.…”