Deep imaging survey of the environment of Alpha Centauri - II. CCD imaging with the NTT-SUSI2 camera

Abstract

Context: The nearby pair of solar-type stars Alpha Centauri is a favorable target for an imaging search for extrasolar planets. Indications exist that the gravitational mass of Alpha Cen B could be higher than its modeled mass, the difference being consistent with a substellar companion of a few tens of Jupiter masses. However, Alpha Centauri usually appears in star catalogues surrounded by a large void area, due to the strong diffused light. Aims: We searched for faint comoving companions to Alpha Cen located at angular distances of the order of a few tens of arcseconds, up to 2-3 arcmin. As a secondary objective, we built a catalogue of the detected background sources. Methods: In order to complement our adaptive optics search at small angular distances (Paper I), we used atmosphere limited CCD imaging from the NTT-SUSI2 instrument in the Bessel V, R, I, and Z bands. Results: We present the results of our search in the form of a catalogue of the detected objects inside a 5.5 arcmin box around this star. A total of 4313 sources down to mV~24 and mI~22 were detected from this wide-field survey. We extracted the infrared photometry of part of the detected sources from archive images of the 2MASS survey (JHK bands). We investigate briefly the nature of the detected sources, many of them presenting extremely red color indices (V-K > 14). Conclusions: We did not detect any companion to Alpha Centauri between 100 and 300 AU, down to a maximum mass of ~15 times Jupiter. We also mostly exclude the presence of a companion more massive than 30 MJup between 50 and 100 AU.