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

¹ Instituto de Astrofísica de Canarias, C. Vía Láctea s/n, 38205 La Laguna, Tenerife, Spain
e-mail: ncrouzet@iac.es
² Dept. de Astrofísica, Universidad de La Laguna, 38206 La Laguna, Tenerife, Spain
³ Université Côte d’Azur, Observatoire de la Côte d’Azur, CNRS, Laboratoire Lagrange, CS 34229 06304 Nice Cedex 4, France
⁴ Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138, USA
⁵ Observatoire Midi-Pyrénées, 14 avenue Edouard Belin, 31400 Toulouse, France
⁶ Concordia Station, Dome C, Antarctica
⁷ Optique et Vision, 6 bis avenue de l’Esterel, 06160 Juan-les Pins, France
⁸ Department of Physics, University of Warwick, Gibbet Hill Road, Coventry CV4 7AL, UK

Received: 29 December 2017
Accepted: 28 June 2018

Abstract

Context. Dome C in Antarctica is a promising site for photometric observations thanks to the continuous night during the Antarctic winter and favorable weather conditions.

Aims.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.

Methods. Here, 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.

Results. 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 ± 4.2% of the time and veiled 21.8 ± 2.0% of the time. The remaining time corresponds to poor quality data or winter storms. We analyzed the lightcurves of σ 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.

Conclusion. 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.