The OmegaWhite survey for Short-Period Variable Stars III: Follow-up Photometric and Spectroscopic Observations

TL;DR

This paper reports follow-up photometric and spectroscopic observations of short-period variable stars from the OmegaWhite survey, identifying pulsating stars, potential white dwarf/subdwarf pulsators, eclipsing binaries, and a possible Bump Cepheid phenomenon.

Contribution

It provides validation of period estimates, spectroscopic classification of variables, and reports potential first detections of rare phenomena in short-period variables.

Findings

Many variables are delta Scuti pulsators.

Detected four possible pulsating white dwarf/subdwarfs.

Reported potential first detection of Bump Cepheid in a delta Scuti star.

Abstract

We present photometric and spectroscopic follow-up observations of short-period variables discovered in the OmegaWhite survey: a wide-field high-cadence g-band synoptic survey targeting the Galactic Plane. We have used fast photometry on the SAAO 1.0-m and 1.9-m telescopes to obtain light curves of 27 variables, and use these results to validate the period and amplitude estimates from the OmegaWhite processing pipeline. Furthermore, 57 sources (44 unique, 13 also with new light curves) were selected for spectroscopic follow-up using either the SAAO 1.9-m telescope or the Southern African Large Telescope. We find many of these variables have spectra which are consistent with being delta Scuti type pulsating stars. At higher amplitudes, we detect four possible pulsating white dwarf/subdwarf sources and an eclipsing cataclysmic variable. Due to their rarity, these targets are ideal candidates for detailed follow-up studies. From spectroscopy, we confirm the symbiotic binary star nature of two variables identified as such in the SIMBAD database. We also report what could possibly be the first detection of the `Bump Cepheid' phenomena in a delta Scuti star, with OW J175848.21-271653.7 showing a pronounced 22% amplitude dip lasting 3 minutes during each pulsational cycle peak. However, the precise nature of this target is still uncertain as it exhibits the spectral features of a B-type star.