Adaptive Optics Used to Measure Proper Motion in Distant Star Cluster

Gemini Multi-Object Spectrograph (GMOS-South) of the Pyxis field (left image), with the center of the cluster marked with a red star. A zoom of the pseudo color image of Pyxis observed with the Gemini South Adaptive Optics Imager (GSAOI) used with the Gemini Multi-conjugate adaptive optics System (GeMS) is shown at right. The field of view of GMOS is 5 x 5 arcminutes, 85 x 85 arcseconds for GeMS.

Tobias Fritz (University of Virginia) and team combined images from Gemini South’s wide-field adaptive optics system (GeMS/GSAOI) with data from the Hubble Space Telescope (HST) to determine the proper motion of a distant cluster of stars. The observations, the first to use ground-based adaptive optics to precisely measure the motion of a cluster at such a large distance, allowed astronomers to set a lower limit for the mass of our Milky Way while providing clues about the cluster’s origin.

The paper, titled: The Proper Motion of Pyxis: The First Use of Adaptive Optics in Tandem with HST on a Faint Halo Object is published in The Astrophysical Journal. The work is part of a Large and Long program at Gemini that is also targeting other clusters, dwarf galaxies, and individual stars in stellar streams. Read more at http://www.gemini.edu/node/12662