Discovery of periodic variables in the hot subdwarf catalogue through a systematic search in Zwicky Transient Facility data

TL;DR

This study systematically identifies and classifies periodic variable stars in the hot subdwarf catalogue using Zwicky Transient Facility data, discovering 486 new variables and analyzing their properties and distribution.

Contribution

It introduces a comprehensive method combining Lomb-Scargle and Box Least Squares periodograms with manual inspection to discover and classify new hot subdwarf variables, including a new mass-transferring binary candidate.

Findings

486 new variable hot subdwarfs discovered

60% of variables would be missed by traditional variability cuts

Higher concentration of variables near the Galactic Plane

Abstract

We conduct a systematic search for periodic variables in the hot subdwarf catalogue using data from the Zwicky Transient Facility. We present the classification of 67 HW Vir binaries, 496 reflection effect, pulsation or rotation sinusoids, 11 eclipsing signals, and 4 ellipsoidally modulated binaries. Of these, 486 are new discoveries that have not been previously published including a new mass-transferring hot subdwarf binary candidate. These sources were determined by applying the Lomb-Scargle and Box Least Squares periodograms along with manual inspection. We calculated variability statistics on all periodic sources, and compared our results to traditional methods of determining astrophysical variability. We find that $\approx60$\% percent of variable targets, mostly sinusoidal variability, would have been missed using a traditional $varindex$ cut. Most HW Virs, eclipsing systems and all ellipsoidal variables were recovered with a $varindex\,>0.02$. We also find a significant reddening effect, with some variable hot subdwarfs meshing with the main sequence stripe in the Hertzprung-Russell Diagram. Examining the positions of the variable stars in Galactic coordinates, we discover a higher proportion of variable stars within $|b|<25^\circ$ of the Galactic Plane, suggesting that the Galactic Plane may be fertile grounds for future discoveries if photometric surveys can effectively process the clustered field.