A Hot Subdwarf in NGC 1851

Details A Hot Subdwarf in NGC 1851 A Hot Subdwarf in NGC 1851

May 1993

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1993aas...182.5005l&link_type=abstract

American Astronomical Society, 182nd AAS Meeting, #50.05; Bulletin of the American Astronomical Society, Vol. 25, p.884

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Scientific paper

Images of the globular cluster NGC 1851 obtained with the Ultraviolet Imaging Telescope (UIT) reveal the presence of a hot (Teff ~ 30,000 K) optically faint (V ~ 18.2) star about 3' from the cluster center. We have obtained a CTIO 4-m spectrum of this star, which is # 43 in the UIT color-magnitude study of Parise et al. (1992, submitted to ApJ). The CTIO spectrum shows only weak Balmer absorption lines. The measured radial velocity of 330 km s(-1) confirms the membership of UIT-43 in NGC 1851. By simultaneously fitting the Balmer lines, we derive Teff = 29700 +/- 1630 K and log g= 5.39 +/- 0.27. These values place UIT-43 somewhat above the zero-age extended horizontal branch (HB). The other HB stars in NGC 1851 detected in the Parise study, and in the ground-based study of Walker (1992, PASP, 104, 1063), are all cooler than 12,000 K. If UIT-43 is a product of single star evolution, then a mechanism must be found to explain its large separation in effective temperature from the remaining HB stars. Alternatively, UIT-43 could be a merger product of a white dwarf pair, as outlined by Bailyn and Iben (1989, ApJL, L21).

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