The OmegaWhite Survey for Short-Period Variable Stars I: Overview and First Results

TL;DR

The OmegaWhite survey is a high-cadence, wide-field optical survey aiming to discover and analyze short-period variable stars in the Galactic Plane, providing initial results including candidate identifications and follow-up spectroscopy.

Contribution

This paper introduces the OmegaWhite survey's strategy, initial data, and candidate variable stars, including potential ultracompact binaries and pulsators, expanding the understanding of short-period stellar variability.

Findings

Identified 613 variable star candidates in 26 square degrees.

Presented light curves and properties of 20 high-likelihood variables.

Follow-up spectroscopy suggests some candidates are low-amplitude δ Sct pulsators.

Abstract

We present the goals, strategy and first results of the OmegaWhite survey: a wide-field high-cadence $g$-band synoptic survey which aims to unveil the Galactic population of short-period variable stars (with periods $<$ 80 min), including ultracompact binary star systems and stellar pulsators. The ultimate goal of OmegaWhite is to cover 400 square degrees along the Galactic Plane reaching a depth of $g = $ 21.5 mag (10$\sigma$), using OmegaCam on the VLT Survey Telescope (VST). The fields are selected to overlap with surveys such as the Galactic Bulge Survey (GBS) and the VST Photometric H$\alpha$ Survey of the Southern Galactic Plane (VPHAS+) for multi-band colour information. Each field is observed using 38 exposures of 39 s each, with a median cadence of $\sim$2.7 min for a total duration of two hours. Within an initial 26 square degrees, we have extracted the light curves of 1.6 million stars, and have identified 613 variable candidates which satisfy our selection criteria. Furthermore, we present the light curves and statistical properties of 20 sources which have the highest-likelihood of being variable stars. One of these candidates exhibits the colours and light curve properties typically associated with ultracompact AM CVn binaries, although its spectrum exhibits weak Balmer absorption lines and is thus not likely to be such a binary system. We also present follow-up spectroscopy of five other variable candidates, which identifies them as likely low-amplitude $\delta$ Sct pulsating stars.