Milliarcsecond angular resolution of reddened stellar sources in the vicinity of the Galactic center. II. Additional observations

Abstract

Context: Interstellar extinction in the inner regions of the Galactic bulge amounts to tens of magnitudes at visual wavelengths. As a consequence, the majority of sources in that area are poorly studied and large numbers of potentially interesting sources such as late-type giants with circumstellar shells, stellar masers and infrared stars, remain excluded from the typical investigations that are carried out in less problematic regions. Also undetected are a large numbers of binaries.Aims: We present lunar occultation (LO) observations obtained in August 2006 with the recently demonstrated burst mode of the ISAAC instrument at the ESO VLT. The results presented here follow the previously reported observations carried out in March 2006 on a similar but unrelated set of sources. By observing LO events in this region, we gain the means to investigate at least a selected number of sources with an unprecedented combination of sensitivity and angular resolution.Methods: The LO technique permits milliarcsecond resolution with a sensitivity of K≈ 12 mag at a very large telescope. We used the opportunity of a favorable passage of the Moon over a crowded region in the general direction of the Galactic center to observe 78 LO events of heavily reddened stellar sources.Results: We detected six new binary and one triple star, with typical projected separation of ≈0farcs01. We also detected the compact circumstellar emission around one maser and one central star of a planetary nebula. We measured the diameter and/or circumstellar shell of two carbon stars and other IR sources.Conclusions: We used the upper limits on the size of about 60 unresolved or marginally resolved sources to confirm the performance of the method. In agreement with our previous result, we conclude that lunar occultations in fast read-out mode on a detector subwindow at an 8 m-class telescope can achieve an angular resolution close to 0farcs001 with a sensitivity K≈ 12 mag.