Identification of the Dominant Luminosity Sources at the Galactic Center Through Infrared Imaging and Spectroscopy.

Details Identification of the Dominant Luminosity Sources at the Galactic Center Through Infrared Imaging and Spectroscopy. Identification of the Dominant Luminosity Sources at the Galactic Center Through Infrared Imaging and Spectroscopy.

Jan 1995

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1995phdt.........5l&link_type=abstract

Thesis (PH.D.)--THE UNIVERSITY OF ROCHESTER, 1995.Source: Dissertation Abstracts International, Volume: 56-03, Section: B, page:

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Scientific paper

Two sources for the luminosity of the Galactic center (LGC = 10 ^7 solar luminosities) have been proposed: an accretion disk about a 10^6 solar mass black hole, and a clueter of massive stars, formed in a starburst 10^6--10 ^7 years ago. In this thesis we attempt to identify the dominant luminosity source(s) in the central parsec through new infrared broad band and spectroscopic observations. At the position of the putative black hole (Sgr A^{*}) we find only a weak source of near infrared emission whose intrinsic (H-K) color is consistent with a T ~ 10,000 K blackbody. We find that the stellar surface density (stars arcsec^{-2}) is well fit by a model assuming an isothermal cluster of stars with a core mass of 5 x 10^5-1 x 10^6 solar masses and a core radius of 0.15 parsec, constraining the mass of any black hole to be less than ~ 5 x 10 ^5 solar masses. We have identified a group of objects in the central parsec that have spectral characteristics of evolved massive stars (LBVs and/or WN9/Ofpe stars, plus one WN8 star). We show that they are of sufficient number to account for a significant fraction of LGC , but an additional population of normal OB stars is required to account for the deduced excitation temperatures. The existence of the prescribed OB cluster is supported by the fact that we find sources in the central parsec with intrinsic (H-K) and (K-3.3) colors of hot massive stars (mostly in the vicinity of IRS 16). Thus, our observations support the hypothesis that a cluster of evolved massive stars now powers the central parsec. The fact that we identify several LBVs and/or WN9/Ofpe stars, but only one WN8 star is interesting because the Wolf-Rayet phase is expected to last ~ 100 times longer than the LBV and WN9/Ofpe phases. If star formation were proceeding continuously in the central parsec we would expect to detect ~100 times more Wolf-Rayet stars than LBVs. Thus we conclude that the massive stars were formed in a starburst 10 ^6-10^7 years ago, and the more massive or more evolved members of this cluster have just reached the LBV and late-type Wolf-Rayet stages of post-main sequence evolution.

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