Photometric quality of Dome C for the winter 2008 from ASTEP South

TL;DR

This study assesses the photometric quality of Dome C in Antarctica during winter 2008 using ASTEP South, demonstrating high potential for nearly continuous astronomical observations due to favorable weather conditions.

Contribution

It introduces a method to evaluate photometric night fractions sensitive to thin cirrus clouds and provides empirical data on Dome C's observing conditions during winter 2008.

Findings

74% of nights had at least 50% star detection

Extended clear weather periods observed, e.g., 60% of time in July-August 2008

High potential for continuous observations at Dome C

Abstract

ASTEP South is an Antarctic Search for Transiting Exo- Planets in the South pole field, from the Concordia station, Dome C, Antarctica. The instrument consists of a thermalized 10 cm refractor observing a fixed 3.88\degree x 3.88\degree field of view to perform photometry of several thousand stars at visible wavelengths (700-900 nm). The first winter campaign in 2008 led to the retrieval of nearly 1600 hours of data. We derive the fraction of photometric nights by measuring the number of detectable stars in the field. The method is sensitive to the presence of small cirrus clouds which are invisible to the naked eye. The fraction of night-time for which at least 50% of the stars are detected is 74% from June to September 2008. Most of the lost time (18.5% out of 26%) is due to periods of bad weather conditions lasting for a few days ("white outs"). Extended periods of clear weather exist. For example, between July 10 and August 10, 2008, the total fraction of time (day+night) for which photometric observations were possible was 60%. This confirms the very high quality of Dome C for nearly continuous photometric observations during the Antarctic winter.