Astronomy and Astrophysics – Astronomy
Scientific paper
Dec 2001
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2001phdt.........8w&link_type=abstract
Thesis (PhD). THE UNIVERSITY OF NEW MEXICO, Source DAI-B 62/06, p. 2759, Dec 2001, 104 pages.
Astronomy and Astrophysics
Astronomy
3
Scientific paper
The hot subdwarfs are evolved stars intermediate between the hydrogen burning main sequence and the white dwarfs. As the immediate precursors of white dwarfs they are essential to a complete understanding of the end points of stellar evolution, and as exemplars of extreme mass- loss stars they may be windows on one of astronomy's least understood problems. But the origins of the hot subdwarfs are obscure. Duplicity may play a role in the enhanced mass-loss hot subdwarfs must suffer, and it is known that the hydrogen-rich sdB hot subdwarfs show a high binary fraction. The helium-rich hot subdwarfs, the putative descendants of the sdB stars, are only weakly characterized with respect to binarity. The helium-rich hot subdwarfs are the subject of this research, and the question of their duplicity is its focus. Sixty-four helium-rich hot subdwarfs drawn from the Palomar-Green Survey of UV-Excess Stellar Objects were observed on the Cousins BV RI photometric system. A subset of twenty-five of the 64 program stars were observed in the IR J and K pass-bands. Spectroscopic data were obtained for thirty-two members of the sample, including seven that have not been observed in either the BV RI or the JK filter sets. A total of sixteen binary candidates were identified, twelve for the first time. Binary candidates were identified by their intrinsic color excesses in two-color plots of the extinction-corrected BV RI and JK data, and by comparison to synthetic binary system colors. Spectrophotometric color indices were derived from the spectroscopic data and used to identify binary candidates by their excess color in two color plots. The binary fraction of the sdOC stars in the sample is predicted to be at least 64% and potentially 100%. A binary fraction for the whole sample of sdOs may have limited meaning, given the probable inhomogeneity of the sample. However, performing the calculation for the whole sample again produces the estimate that at least 64% and at most 100% of the sample is binary.
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