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Session 38 - Dwarf Galaxies.
Display session, Tuesday, January 14
We present the J, H, K surface photometry of 6 Blue Compact Dwarf Galaxies, obtained last winter at the 2.2m telescope in La Silla (ESO) equipped with IRAC2b (IR camera). These BCDGs belong to our larger sample that we have studied in B and R broad band (Doublier et al. 1997 I and II), aimed to study the properties of the stellar population of blue compact dwarf galaxies chosen in isolated environments. The IR observations were obtained following the technique of in-field chopping.
In this poster, we first present the images for all 6 galaxies in J, H and K. From these images , we can compare the different morphologies in these bands, in order to study how the elliptical BCDGs (36% of the sample), the disk BCDGs (39%) and the mixed-profile BCDGs (25%) behave in the near IR. As discussed in our previous B and R photometric papers, these observations are aimed at distinguishing the young supergiant stars from the old giant stars. This distinction can be done, in principle, using the B--K index that is a direct indicator of the effective temperature of the giant stars. However, due to the metallicity--age degeneracy, and correction uncertainties, the old red giants and the young supergiants have indistinguishable IR colors (in the J--H vs. H--K diagrams, and B--K index); the better method used for discriminating the two populations is to obtain the CO and H_2O indexes as a function of J--K, that vary, in principle less ambiguously with the stellar type.
Nonetheless, with this degeneracy in mind, and looking for hints, we present the 2--color plots, J--H vs. H---K; while in the future, we plan CO and H-2O observations to lift up the degeneracy.
Program listing for Tuesday