Comparison of Astrometry and Photometry of the Galactic Bulge Between HST-NICMOS and NACO Data

Abstract

We present a preliminary study of photometric and astrometric measurements from adaptive optics (AO) observations of the Galactic Bulge. We compare two different observations of the same crowded stellar region in H-band, one detected with the NICMOS camera on HST and one using NACO, the AO system on the VLT at ESO. The AO image field is affected by anisoplanatism, with the natural guide star just outside the 27.6x27.6 field of view. We want to address the question of the AO images photometric and astrometric precision, compared with analogous HST data taken as the truth, even in presence of anisoplanatism. To do so we have divided the NACO image in 9 sections, derived for each section the corresponding PSF using myopic deconvolution, and then applied the StarFinder program to derive photometry and astrometry in each subfield. We compare astrometry, photometry and depth of sensitivity between the data by HST-NICMOS and NACO. We find that the astrometry from NACO images was equivalent to HST within 32 mas rms and the derived photometry with our method was good as well, within 0.18 stellar magnitudes rms.