Dec 1999: CFHT Adaptive Optics Observations of the Central Kinematics in M15 by Gebhardt, Pryor, O'Connell, Williams, and Hesser, AJ in press.
This page compares imaging with the Adaptive Optics Bonnette (AOB) on the Canada- France-Hawaii Telescope (CFHT) to that with the Hubble Space Telescope (HST). Both pictures show the central 9x9 arcsec of the globular cluster M15. Clicking on the images will retreive larger versions.
The upper image is the average of four of our best 15 minute exposures from the CFHT. They were taken through a Rutgers Fabry-Perot etalon behind the AOB and have a pass band of about 2 Angstroms centered near the 8542 A calcium triplet line. They have been averaged with sigma clipping to suppress cosmic rays. The profile of the point-spread function in the original images has a sharp core surrounded by a more diffuse halo. The sharp cores have FWHM's, measured approximately using imexamine in IRAF, of 0.10 - 0.13 arcsec. The pixels in the original and combined images are 0.0305 arcsec across. The display uses a logarithmic mapping of intensity values to show both bright and faint stars. The image was rotated to match the orientation of the HST image.
The lower image is the beautiful color composite picture created from HST images by Guhathakurta et al. (1996, AJ 111, 267).
While the HST image clearly goes deeper than the CFHT image (it is made from images with bandpasses of about 800 Angstroms instead of 2 Angstroms!), the angular resolution of the two is comparable.
The CFHT images were obtained by C. Pryor, R. O'Connell (Rutgers), K. Gebhardt (UCSC), and J. Hesser (DAO). Processing and analysis of the images from our run has just begun. Our goal is to use these Fabry-Perot images to measure radial velocities for stars at the centers of globular clusters.
Revised January 20, 2000