Four winters of photometry with ASTEP South at Dome C, Antarctica

TL;DR

This study presents four years of continuous photometric observations from Dome C, Antarctica, demonstrating its suitability for high-quality time series astronomy and variable star detection.

Contribution

The paper provides the first extensive four-year dataset from Dome C, improving instrumentation and data reduction methods, and characterizes the site's photometric quality and variable star population.

Findings

Dome C offers 67.1% photometric weather conditions.

Achieved nearly continuous four-year observations with high phase coverage.

Detected 34 new variable stars and 8 eclipsing binaries.

Abstract

Dome C in Antarctica is a promising site for photometric observations thanks to the continuous night during the Antarctic winter and favorable weather conditions. We developed instruments to assess the quality of this site for photometry in the visible and to detect and characterize variable objects through the Antarctic Search for Transiting ExoPlanets (ASTEP) project. We present the full analysis of four winters of data collected with ASTEP South, a 10 cm refractor pointing continuously toward the celestial south pole. We improved the instrument over the years and developed specific data reduction methods. We achieved nearly continuous observations over the winters. We measure an average sky background of 20 mag arcsec$^{-2}$ in the 579-642 nm bandpass. We built the lightcurves of 6000 stars and developed a model to infer the photometric quality of Dome C from the lightcurves themselves. The weather is photometric $67.1\pm4.2$ % of the time and veiled $21.8\pm2.0$ % of the time. The remaining time corresponds to poor quality data or winter storms. We analyzed the lightcurves of $\sigma$ Oct and HD 184465 and find that the amplitude of their main frequency varies by a factor of 3.5 and 6.7 over the four years, respectively. We also identify 34 new variable stars and eight new eclipsing binaries with periods ranging from 0.17 to 81 days. The phase coverage that we achieved with ASTEP South is exceptional for a ground-based instrument and the data quality enables the detection and study of variable objects. These results demonstrate the high quality of Dome C for photometry in the visible and for time series observations in general.