The ASAS-SN Catalog of Variable Stars VI: An All-Sky Sample of $\hat{I}´$ Scuti Stars

Abstract

We characterize an all-sky catalog of $\sim 8,400$ $\hat{I}´$ Scuti variables in ASAS-SN, which includes $\sim 3,300$ new discoveries. Using distances from \textit{Gaia} DR2, we derive period-luminosity relationships (PLRs) for both the fundamental mode and overtone pulsators in the $W_{JK}$, $V$, Gaia DR2 $G$, $J$, $H$, $K_s$ and $W_1$ 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 ${\log }_{10}(\mathrm{P})\sim -1.1$ for $[Fe/H]<-0.3$ and ${\log }_{10}(\mathrm{P})\sim -0.9$ for $[Fe/H]>0$ which leads to a period-dependant scale height. Stars with $\mathrm{P}>0.100\mathrm{d}$ are predominantly located close to the Galactic disk ($|Z|<0.5\mathrm{kpc}$). The median period at a scale height of $\mathrm{Z}\sim 0\mathrm{kpc}$ also increases with the Galactocentric radius $\mathrm{R}$, from ${\log }_{10}(\mathrm{P})\sim -0.94$ for sources with $\mathrm{R}>9\mathrm{kpc}$ to ${\log }_{10}(\mathrm{P})\sim -0.85$ for sources with $\mathrm{R}<7\mathrm{kpc}$, which is indicative of a radial metallicity gradient. To illustrate potential applications of this all-sky catalog, we obtained 30 min cadence, image subtraction TESS light curves for a sample of 10 fundamental mode and 10 overtone $\hat{I}´$ Scuti stars discovered by ASAS-SN. From this sample, we identified two new $\hat{I}´$ Scuti eclipsing binaries, ASASSN-V J071855.62$-$434247.3 and ASASSN-V J170344.20$-$615941.2 with short orbital periods of ${\mathrm{P}}_{\mathrm{orb}}=2.6096$ d and ${\mathrm{P}}_{\mathrm{orb}}=2.5347$ d respectively.

Accepted by MNRAS