Peter Tamblyn: Dissertation

The Peculiar Population of Helium Emission Stars at the Galactic Center

Peter Tamblyn Ph.D. Dissertation, The University of Arizona, 1996 Directors: George H. Rieke and Fulvio Melia

Abstract:

We show that extremely luminous, blue stars are present at the Galactic Center (GC) in numbers that are incompatible with normal stellar evolution. Helium 2.058 micrometer images with a spatial resolution of 1 arcsecond show that the helium emission is concentrated on point sources, most of which are bright in the infrared, indicating they are warm and very luminous. Comparison with Monte-Carlo stellar population models demonstrates that normal evolution is incapable of producing this population. Near-infrared spectroscopy at high angular and spectral resolutions has been obtained, along with spectra of an extensive suite of other warm, luminous stars. These spectra provide new constraints on the mass in the central 1/2 parsec and the spectral comparisons confirm the peculiarity of the GC stars. The brightest have few, if any, analogues known in the Galaxy. Constraints from space-based observations on the blue light associated with nuclear populations in nearby galaxies demonstrate that the GC is unique or in a time-dependent phase. We have examined and rejected a number of models expected to produce this density of luminous, blue stars in the central parsec. A possibility remains that they are recently formed massive stars with unusual evolution forced by close binary companions. This model predicts similar populations of peculiar stars only in other dense galactic nuclei which have undergone very recent star formation.

Name	Size	Description
Tamblyn_dissertation.pdf	1.5MB	Complete text with figures
Tamblyn_ch1.pdf	64KB	Abstract, Contents, Introduction
Tamblyn_ch2.pdf	433KB	Stellar Population Models I
Tamblyn_ch3.pdf	728KB	Emission-Line Observations
Tamblyn_ch4.pdf	298KB	Kinematics
Tamblyn_ch5.pdf	408KB	Population Models II, Comparisons
Tamblyn_ch6.pdf	188KB	Unusual Stellar Evolution
Tamblyn_ch7-refs.pdf	49KB	Conclusions, References

Comments or difficulties can be addressed to Peter Tamblyn.