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

We present VIJHK photometry for stars in a 0.82.0 kpc 2 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 di- agrams, and a bolometric luminosity function are constructed, confirming the presence of an intermediate-age stellar popu- lation. We also present a logL=L vs logTeff diagram of the galaxy and compare the results with the theoretical isochrones of Bertelli et al. (1994) for Z =0 :004 and Y =0 :24. The compar- ison suggests that most of the stars detected in the IR are 10 9 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.