Difference Image Analysis of Defocused Observations with CSTAR

TL;DR

This paper presents a novel difference imaging method to analyze defocused and crowded astronomical images from CSTAR, enabling the detection of variable stars despite technical challenges during Antarctic winter observations.

Contribution

The authors developed a combined difference imaging and aperture photometry technique tailored for defocused, crowded frames, improving variable star detection in challenging observational conditions.

Findings

Recovered 68 known variable stars

Detected variability in 37 new objects

Achieved high-quality photometry despite defocus and technical issues

Abstract

The Chinese Small Telescope ARray (CSTAR) carried out high-cadence time-series observations of 27 square degrees centered on the South Celestial Pole during the Antarctic winter seasons of 2008, 2009 and 2010. Aperture photometry of the 2008 and 2010 i-band images resulted in the discovery of over 200 variable stars. Yearly servicing left the array defocused for the 2009 winter season, during which the system also suffered from intermittent frosting and power failures. Despite these technical issues, nearly 800,000 useful images were obtained using g, r & clear filters. We developed a combination of difference imaging and aperture photometry to compensate for the highly crowded, blended and defocused frames. We present details of this approach, which may be useful for the analysis of time-series data from other small-aperture telescopes regardless of their image quality. Using this approach, we were able to recover 68 previously-known variables and detected variability in 37 additional objects. We also have determined the observing statistics for Dome A during the 2009 winter season; we find the extinction due to clouds to be less than 0.1 and 0.4 mag for 40% and 63% of the dark time, respectively.