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

The All-Sky Automated Survey for Supernovae provides long baseline (similar to 4 yr) V-band light curves for sources brighter than V less than or similar to 17 mag across the whole sky. We produced V-band light curves for a total of similar to 61.5 million sources and systematically searched these sources for variability. We identified similar to 426 000 variables, including similar to 219 000 new discoveries. Most (similar to 74 per cent) 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 (greater than or similar to 80 per cent) of the rotating giants have large v(rot) or large near-ultraviolet excesses also indicative of fast rotation. The rotational variables have unusual abundances suggestive of analysis problems. Semiregular variables tend to be lower metallicity ([Fe/H]similar to- 0.5) than most giant stars. We find that the APOGEE DR16 temperatures of oxygen-rich semiregular variables are strongly correlated with the W-RP - W-JK colour index for T-eff less than or similar to 3800 K. Using abundance measurements from APOGEE DR16, we find evidence for Mg and N enrichment in the semiregular variables. We find that the Aluminum abundances of the semiregular variables are strongly correlated with the pulsation period, where the variables with P greater than or similar to 60 d are significantly depleted in Al.