Infrared photometry of the inner regions of the dwarf irregular galaxy NGC3109

We present VIJHK photometry for stars in a 0.8 x 2.0 kpc(2) inner field of the dwarf irregular galaxy NGC 3109. The infrared photometry reaches 3 magn itudes fainter than previous work. Optical and infrared color-color and col or-magnitude diagrams, and a bolometric luminosity function are constructed , confirming the presence of an intermediate-age stellar population. We als o present a logL/L-. vs logT(eff) diagram of the galaxy and compare the res ults with the theoretical isochrones of Bertelli et al. (1994) for Z = 0.00 4 and Y = 0.24. The comparison suggests that most of the stars detected in the IR are 10(9) yr or younger. We compare the infrared color-magnitude dia grams of NGC 3 109 with the composite color-magnitude diagrams of LMC clust ers and of the outer disk of the Scd galaxy M33. They show similar stellar content in these late-type systems.