The ASAS-SN Catalog of Variable Stars VI: An All-Sky Sample of $\delta$ Scuti Stars

TL;DR

This paper presents an extensive all-sky catalog of approximately 8,400 $\delta$ Scuti stars, including new discoveries, and derives period-luminosity relationships using Gaia data, revealing spatial and metallicity-dependent properties.

Contribution

The study provides the first comprehensive all-sky catalog of $\delta$ Scuti stars with new discoveries and detailed period-luminosity relations across multiple bands, enhancing understanding of their galactic distribution.

Findings

Overtone pulsators often pulsate in second or higher modes.

Fundamental mode periods depend on metallicity, affecting scale height.

Identified two new $\delta$ Scuti eclipsing binaries.

Abstract

We characterize an all-sky catalog of ${\sim} 8,400$ $\delta$ 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 $\log_{10} (\rm P){\sim}-1.1$ for $\rm [Fe/H]<-0.3$ and $\log_{10} (\rm P){\sim}-0.9$ for $\rm [Fe/H]>0$ which leads to a period-dependant scale height. Stars with $\rm P>0.100\,d$ are predominantly located close to the Galactic disk ($\rm |Z|<0.5\,kpc$). The median period at a scale height of $\rm Z{\sim}0\, kpc$ also increases with the Galactocentric radius $\rm R$, from $\log_{10} (\rm P){\sim}-0.94$ for sources with $\rm R>9\, kpc$ to $\log_{10} (\rm P){\sim}-0.85$ for sources with $\rm R<7\, kpc$, 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 $\delta$ Scuti stars discovered by ASAS-SN. From this sample, we identified two new $\delta$ Scuti eclipsing binaries, ASASSN-V J071855.62$-$434247.3 and ASASSN-V J170344.20$-$615941.2 with short orbital periods of $\rm P_{orb}=2.6096$ d and $\rm P_{orb}=2.5347$ d respectively.