Discovery of a probable CH star in the globular cluster M14 and implications for the evolution of binaries in clusters

被引:21
作者
Cote, P
Hanes, DA
McLaughlin, DE
Bridges, TJ
Hesser, JE
Harris, GLH
机构
[1] QUEENS UNIV, DEPT PHYS, KINGSTON, ON K7L 3N6, CANADA
[2] MCMASTER UNIV, DEPT PHYS & ASTRON, HAMILTON, ON L8S 4M1, CANADA
[3] ROYAL GREENWICH OBSERV, CAMBRIDGE CBS 6EZ, ENGLAND
[4] UNIV WATERLOO, DEPT PHYS, GUELPH WATERLOO PROGRAM GRAD WORK PHYS, ASTRON PROGRAM, WATERLOO, ON N2L 3G1, CANADA
基金
美国国家科学基金会; 加拿大自然科学与工程研究理事会;
关键词
binaries; general; galaxies; stellar content; Galaxy; globular clusters; individual; (M14); Local Group; stars; carbon;
D O I
10.1086/310488
中图分类号
P1 [天文学];
学科分类号
0704 ;
摘要
We report the discovery of a probable CH star in the core of the Galactic globular duster M14 (=NGC 6402 = C1735-032), identified from an integrated-light spectrum of the cluster obtained with the MOS spectrograph on the Canada-France-Hawaii telescope. From a high-resolution echelle spectrum of the same star obtained with the Hydra fiber positioner and bench spectrograph on the WIYN telescope, we measure a radial velocity of -53.0 +/- 1.2 km s(-1). Although this velocity is inconsistent with published estimates of the systemic radial velocity of M14 (e.g., upsilon(r)(-) approximate to -123 km s(-1)), we use high-precision Hydra velocities for 20 stars in the central 2'.6 of M14 to calculate improved values for the cluster mean velocity and one-dimensional velocity dispersion: -59.5 +/- 1.9 km s(-1) and 8.2 +/- 1.4 km s(-1), respectively. Both the star's location near the tip of the red giant branch in the cluster color-magnitude diagram and its radial velocity therefore argue for membership in M14. Since the intermediate-resolution MOS spectrum shows not only enhanced CH absorption but also strong Swan bands of C-2, M14 joins omega Cen as the only globular clusters known to contain ''classical'' CH stars. Although evidence for its duplicity must await additional radial velocity measurements, the CH star in M14 is probably, like all field CH stars, a spectroscopic binary with a degenerate (white dwarf) secondary. The candidate and confirmed CH stars in M14 and omega Cen, and in a number of Galactic dSph galaxies, may then owe their existence to the long timescales for the shrinking and coalescence of hard binaries in low-concentration environments.
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页码:L15 / +
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