Astronomy and Astrophysics – Astronomy
Scientific paper
Nov 1993
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1993a%26a...279...90o&link_type=abstract
Astronomy and Astrophysics (ISSN 0004-6361), vol. 279, no. 1, p. 90-106
Astronomy and Astrophysics
Astronomy
52
Astronomical Models, Galactic Structure, Infrared Astronomy, Infrared Stars, Mathematical Models, Milky Way Galaxy, Star Distribution, Cosmic Dust, Disks (Shapes), Infrared Astronomy Satellite, Interstellar Extinction, Interstellar Matter, Stellar Envelopes, Stellar Luminosity, Stellar Magnitude
Scientific paper
We present a model of the Galaxy to reproduce star counts in the R, I, J, H, K, L, (12 micrometer) and (25 micrometer) bands, for any given direction and sensitivity. The Galaxy is represented as the sum of a spheroidal component given by a Hernquist density law, two disk components with scale heights 100 pc and 390 pc, and a spiral arm structure. Absolute magnitudes in each spectral band and for each luminosity class are obtained from V-lambda color indices, presented in form of polynomial fits as a function of spectral type. The interstellar extinction is taken into account, based on the known distribution of galactic gas in atomic and molecular forms. The contribution of circumstellar dust shells to the luminosity of late type giants and supergiants is studied and taken into account; all giant stars later than M6 are found to present a dust shell. The effect of the large amplitude of variability of these stars is also considered. The model predictions have not been compared with observations for all the bands included in our code due to the lack of observational data. Extensive comparisons are presented for the K band, over the 1-11 magnitude range for many directions in the Galaxy, and comparisons with the IRAS point source catalog (PSC) are presented at 12 micrometers and 25 micrometers. The model reproduces correctly the overall star counts in the K band, at 12 micrometers and at 25 micrometers, although an increase of the parameter representing the intensity of the spiral structure is required for the IRAS bands, and our description of the local arm (l = 80 deg) is not yet satisfactory. The scale-length of the disk is found to be about 2.6 kpc for the 390 pc disk, and seems to be larger (about 4 kpc) for the 100 pc disk, which contains a younger population.
Lépine Jacques R. D.
Ortiz Roberto
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