Variability and stellar populations with deep optical-IR images of the Milky Way disc: matching VVV with VLT/VIMOS data^⋆,⋆⋆

¹ Warsaw University Observatory, Al. Ujazdowskie 4, 00-478 Warszawa, Poland
e-mail: pietruk@astrouw.edu.pl
² Departamento de Astronomía y Astrofísica, Pontificia Universidad Católica de Chile, Av. Vicuña MacKenna 4860, Casilla 306, Santiago 22, Chile
³ Vatican Observatory, Vatican City State 00120, Italy

Received: 12 March 2011
Accepted: 10 October 2011

Abstract

Aims. We have used deep V-band and JHK_s-band observations to investigate variability and stellar populations near the Galactic plane in Centaurus, and compared the observations with the Galactic model of Besançon.

Methods. By applying image subtraction technique to a series of over 580 V-band frames taken with the ESO VLT/VIMOS instrument during two contiguous nights in April 2005, we have detected 333 variables among 84 734 stars in the brightness range 12.7 < V < 26.0 mag. Infrared data collected in March 2010 with the new ESO VISTA telescope allowed us to construct deep combined optical-IR colour–magnitude and colour–colour diagrams.

Results. All detected variables but four transit candidates are reported for the first time. The majority of the variables are eclipsing/ellipsoidal binaries and δ Scuti-type pulsators. The occurrence rate of eclipsing/ellipsoidal variables reached  ~0.28% of all stars. This is very close to the highest fraction of binary systems detected using ground-based data so far (0.30%), but still about four times less than the average occurrence rate recently obtained from the Kepler space mission after 44 days of operation. Comparison of the observed K_s vs. V − K_s diagram with a diagram based on the Besançon model shows significant effects of both distance and reddening in the investigated direction of the sky. We demonstrate that the best model indicates the presence of absorbing clouds at distances 11–13 kpc from the Sun in the minor Carina-Sagittarius arm.