Searching for faint comoving companions to the alpha Centauri system in the VVV survey infrared images

Abstract

The VVV survey has observed the southern disc of the Milky Way in the near-infrared, covering 240 deg(2) in the ZYJHKs filters. We search the VVV survey images in a similar to 19 deg(2) field around alpha Centauri, the nearest stellar system to the Sun, to look for possible overlooked companions that the baseline in time of VVV would be able to uncover. The photometric depth of our search reaches Y similar to 19.3mag, J similar to 19 mag, and K-s similar to 17 mag. This search has yielded no new companions in a Centauri system, setting an upper mass limit for any unseen companion well into the brown dwarf/planetary mass regime. The apparent magnitude limits were turned into effective temperature limits, and the presence of companion objects with effective temperatures warmer than 325K can be ruled out using different state-of-the-art atmospheric models. These limits were transformed into mass limits using evolutionary models, companions with masses above 11M(Jup) were discarded, extending the constraints recently provided in the literature up to projected distances of d < 7000 au from alpha Cen AB and similar to 1200 au from Proxima. In the next few years, the VVV extended survey (VVVX) will allow us to extend the search and place similar limits on brown dwarfs/planetary companions to a Cen AB for separations up to 20 000 au.