Letter to the Editor

The inner Galactic bar traced by the VVV survey^⋆

¹ European Southern Observatory, Karl-Schwarzschild-Strasse 2, 85748 Garching, Germany
e-mail:ogonzale@eso.org; mrejkuba@eso.org; evalenti@eso.org
² Departamento Astronomía y Astrofísica, Pontificia Universidad Católica de Chile, Av. Vicuña Mackenna 4860, Stgo., Chile
e-mail: mzoccali@astro.puc.cl; Dante@astro.puc.cl; rsaito@astro.puc.cl
³ Vatican Observatory, V00120 Vatican City State, Italy
⁴ European Southern Observatory, Ave. Alonso de Cordova 3107, Vitacura, Santiago, Chile

Received: 27 August 2011
Accepted: 3 October 2011

Abstract

Aims. We use the VVV survey observations in bulge regions close to the Galactic plane to trace the bar inclination at the Galactic latitude b ~  ±1 and to investigate a distinct structure in the inner regions of the bar that was previously detected at positive latitude (b =  +1).

Methods. We use the (J − K_s) colors of the red clump stars to obtain reddening values on 6 × 6 arcmin scale, minimizing the problems arising from differential extinction. Dereddened magnitudes are then used to build the luminosity function of the bulge in regions of  ~0.4 sq deg to obtain the mean red clump magnitudes. These are used as distance indicators to trace the bar structure.

Results. The luminosity function clearly shows the red clump mean magnitude variation with longitude, as expected from a large scale bar oriented towards us at positive Galactic longitude, with a dereddened magnitude varying from K_s0 = 13.4 at l = −10° to K_s0 = 12.4 at l =  +10°. We detect a change in the orientation of the bar in the central regions with |l| < 4° at b =  ±1°, in agreement with results obtained at positive latitudes by other authors. Our results are based on a different dataset and at different latitude, which shows that this change in the bar orientation is real. This suggests that there is an inner structure distinct to the large-scale Galactic bar, with a different orientation angle. This inner structure could be a secondary, inner bar, with a semi-major axis of  ~500 pc that is symmetric with respect to the Galactic plane.