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Astron. Astrophys. 326, 936-940 (1997)

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Stellar populations from adaptive optics observations: four test cases

T.R. Bedding 1, 2, D. Minniti 2, 3, F. Courbin 2, 4, 5 and B. Sams 6, 7

1 Chatterton Astronomy Department, School of Physics, University of Sydney 2006, Australia
2 European Southern Observatory, Karl-Schwarzschild-Str. 2, D-85748 Garching bei München, Germany
3 IGPP, Lawrence Livermore National Laboratory, P.O. Box 808, MS L-413, Livermore, CA 94550
4 Institut d'Astrophysique, 5 Avenue de Cointe, B-4000 Liege, Belgium
5 URA 173 CNRS-DAEC, Observatoire de Paris, F-92195 Meudon Principal Cédex, France
6 Max Plank Institut für Astrophysik, Karl-Schwarzschild-Str. 1, D-85748 Garching bei München, Germany
7 Current address: mediateam, Weidenweg 2c, D-85375 Neufahrn, Germany

Received 17 February 1997 / Accepted 4 June 1997

Abstract

We describe a first attempt to apply adaptive optics to the study of resolved stellar populations in galaxies. Advantages over traditional approaches are (i) improved spatial resolution and point-source sensitivity through adaptive optics, and (ii) use of the near-infrared region, where the peak of the spectral energy distribution for old populations is found. Disadvantages are the small area covered and the need for excellent seeing. We made observations with the ADONIS system at the European Southern Observatory of the peculiar elliptical galaxy NGC 5128; the irregular galaxy IC 5152 (a possible outer member of the Local Group); the Sc galaxy NGC 300 (a member of the Sculptor group); and the Sgr window in the bulge of the Milky Way. These different fields give excellent test cases for the potential of adaptive optics. In the first two cases, we failed to obtain photometry of individual stars, which would have required excellent seeing. For NGC 300 we measured magnitudes for nine individual supergiants ([FORMULA] -20.2), but did not go deep enough to detect the tip of the RGB of an old population. For the Sgr field we produced a infrared luminosity function and colour-magnitude diagram for 70 stars down to [FORMULA]. These are the deepest yet measured for the Galactic bulge, reaching beyond the turn-off.

Key words: techniques: miscellaneous galaxies: stellar content – galaxies: individual: NGC 5128, IC 5152, NGC 300 – galaxy: stellar content

Send offprint requests to: Tim Bedding (bedding@physics.usyd.edu.au)

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© European Southern Observatory (ESO) 1997

Online publication: April 8, 1998
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