Diffracto-Astrometry with Hubble Space Telescope and Adaptive Optics Images

Abstract

Following the lead established by Allen et al. (1974, 2004) in the study of internal movements in Trapezium-type systems, we decided to investigate the possibility of performing precision astrometry on Hubble Space Telescope (HST) images and on images obtained with Adaptive Optics (AO) systems. A region widely observed by the HST is that of the Orion Trapezium. The HST archive contains public domain observations of this Trapezium obtained with the WFPC/WFPC2 during a 16 year time interval (1991-2007). Applying new techniques (which we call Diffracto-Astrometry) we have determined the separation between components A and E of the Orion Trapezium with a precision reaching down to 0.03" on saturated images. These techniques appear to be very promising for exploiting, not only the important HST public image data base but also images obtained at telescopes using AO techniques. In order to demonstrate this last point, we use these same techniques to carry out precision astrometry on IR images of the Orion Trapezium obtained with the Multi-Conjugate Adaptive Optics (MCAO) system at the VLT.