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Astron. Astrophys. 346, 33-44 (1999)

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Infrared photometry of the inner regions of the dwarf irregular galaxy NGC 3109 *

M. Victoria Alonso **  1, Dante Minniti 2,3, Albert A. Zijlstra 4,5 and Eline Tolstoy 6

1 Observatorio Astronómico de Córdoba, Laprida 854, 5000 Córdoba, Argentina
2 Lawrence Livermore National Laboratory, MS L-413, P.O.Box 808, Livermore, CA 94550, USA
3 Departamento de Astronomía y Astrofísica, P. Universidad Católica, Casilla 104, Santiago 22, Chile
4 European Southern Observatory, D-85748 Garching bei München, Germany
5 Department of Physics, UMIST, P.O.Box 88, Manchester M60 1QD, UK
6 Space Telescope European Coordinating Facility, D-85748 Garching bei München, Germany

Received 18 August 1998 / Accepted 18 February 1999


We present VIJHK photometry for stars in a 0.8[FORMULA]2.0 kpc2 inner field of the dwarf irregular galaxy NGC 3109. The infrared photometry reaches 3 magnitudes fainter than previous work. Optical and infrared color-color and color-magnitude diagrams, and a bolometric luminosity function are constructed, confirming the presence of an intermediate-age stellar population. We also present a [FORMULA] vs [FORMULA] diagram of the galaxy and compare the results with the theoretical isochrones of Bertelli et al. (1994) for [FORMULA] and [FORMULA]. The comparison suggests that most of the stars detected in the IR are 109 yr or younger. We compare the infrared color-magnitude diagrams of NGC 3109 with the composite color-magnitude diagrams of LMC clusters and of the outer disk of the Scd galaxy M33. They show similar stellar content in these late-type systems.

Key words: stars: Hertzsprung – Russel (HR) and C-M diagrams – galaxies: abundances – galaxies: evolution – galaxies: individual: NGC 3109 – galaxies: irregular – infrared: galaxies

* Based on observations collected at La Silla Observatory
** Visiting Astronomer, European Southern Observatory, D-85748 Garching bei München, Germany

Send offprint requests to: M. Victoria Alonso

Correspondence to: vicky@oac.uncor.edu

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© European Southern Observatory (ESO) 1999

Online publication: May 6, 1999