Ground-based astrometry with wide field imagers. V. Application to near-infrared detectors: HAWK-I@VLT/ESO

摘要

High-precision astrometry requires accurate point-spread function modelingand accurate geometric-distortion corrections. This paper demonstrates that itis possible to achieve both requirements with data collected at the high acuitywide-field K-band imager (HAWK-I), a wide-field imager installed at the Nasmythfocus of UT4/VLT ESO 8m telescope. Our final astrometric precision reaches ~3mas per coordinate for a well-exposed star in a single image with a systematicerror less than 0.1 mas. We constructed calibrated astro-photometric catalogsand atlases of seven fields: the Baade's Window, NGC 6656, NGC 6121, NGC 6822,NGC 6388, NGC 104, and the James Webb Space Telescope calibration field in theLarge Magellanic Cloud. We make these catalogs and images electronicallyavailable to the community. Furthermore, as a demonstration of the efficacy ofour approach, we combined archival material taken with the optical wide-fieldimager at the MPI/ESO 2.2m with HAWK-I observations. We showed that we are ableto achieve an excellent separation between cluster members and field objectsfor NGC 6656 and NGC 6121 with a time base-line of about 8 years. Using bothHST and HAWK-I data, we also study the radial distribution of the SGBpopulations in NGC 6656 and conclude that the radial trend is flat within ouruncertainty. We also provide membership probabilities for most of the stars inNGC 6656 and NGC 6121 catalogs and estimate membership for the publishedvariable stars in these two fields.