Astronomy and Astrophysics – Astronomy
Scientific paper
Dec 1994
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1994aj....108.2267p&link_type=abstract
Astronomical Journal (ISSN 0004-6256), vol. 108, no. 6, p. 2267-2272
Astronomy and Astrophysics
Astronomy
16
Binary Stars, Chronology, Main Sequence Stars, Metallicity, Radial Velocity, Stellar Color, Stellar Luminosity, Stellar Spectra, Astronomical Photometry, Echelle Gratings, Hydrogen, Iron, Reflecting Telescopes, Spectrographs
Scientific paper
CS 22873-139, a metal-deficient ((Fe/H) = -3.1), high-velocity (Vrad = +243 km/s) star with observed UBV colors (B-V = 0.37, U-B = -0.22) that locate it near the main-sequence turnoff of an old metal-poor population (Preston et al. (1991); Beers et al. (1992)), is, in fact, a double-lined spectroscopic binary with a period of 19.16 days, eccentricity e = 0.26, and a mass ratio of approximately 0.88. The observed colors, corrected for reddening, can be matched by those for a family of artificial binaries constructed by use of colors and luminosities taken from isochrones for ages between 3 and 13 Gy, but the strengths of metal lines in the primary and secondary spectra require that the age of the system be less than approximately 8 Gy. The inferred unreddened colors of the primary, (B-V)0,p = 0.30, (U-B)0,p = -0.19, lie blueward of any globular cluster turnoff and near the low-abundance (upper) U-B boundary of BMP stars in the UBV two-color diagram, as discussed by Preston et al. (1994). Were the primary product of binary merger in an initial triple star system, Harrington's (1977) stability criterion requires for the initial close binary a1 less than 5.2 solar radii and P less than 1.5 days. According to Vilhu (1982) such a system will merge in about 109 years, a time much shorter than the main-sequence age deduced for this system, so even if binary merger had taken place the conclusion that CS 22873-139 must be a relatively young metal-poor star is preserved.
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