A search for rapidly pulsating hot subdwarf stars in the GALEX survey

TL;DR

This study utilizes GALEX UV data and the gPhoton tool to identify and confirm short-period pulsations in hot subdwarf B stars, discovering new variable stars and expanding the sdBVr class.

Contribution

First application of gPhoton to systematically search for pulsations in GALEX hot subdwarfs, leading to new pulsator discoveries and confirmation of variability.

Findings

Detected UV pulsations in four known sdB pulsators.

Identified promising signals in several non-variable targets.

Confirmed p-mode pulsations in LAMOST J082517.99+113106.3.

Abstract

NASA's Galaxy Evolution Explorer (GALEX) provided near- and far-UV observations for approximately 77 percent of the sky over a ten-year period; however, the data reduction pipeline initially only released single NUV and FUV images to the community. The recently released Python module gPhoton changes this, allowing calibrated time-series aperture photometry to be extracted easily from the raw GALEX data set. Here we use gPhoton to generate light curves for all hot subdwarf B (sdB) stars that were observed by GALEX, with the intention of identifying short-period, p-mode pulsations. We find that the spacecraft's short visit durations, uneven gaps between visits, and dither pattern make the detection of hot subdwarf pulsations difficult. Nonetheless, we detect UV variations in four previously known pulsating targets and report their UV pulsation amplitudes and frequencies. Additionally, we find that several other sdB targets not previously known to vary show promising signals in their periodograms. Using optical follow-up photometry with the Skynet Robotic Telescope Network, we confirm p-mode pulsations in one of these targets, LAMOST J082517.99+113106.3, and report it as the most recent addition to the sdBVr class of variable stars.