A STELLAR ROTATION CENSUS OF B STARS: FROM ZAMS TO TAMS

被引:193
作者
Huang, Wenjin [1 ]
Gies, D. R. [2 ]
McSwain, M. V. [3 ]
机构
[1] Univ Washington, Dept Astron, Seattle, WA 98195 USA
[2] Georgia State Univ, Ctr High Angular Resolut Astron, Dept Phys & Astron, Atlanta, GA 30302 USA
[3] Lehigh Univ, Dept Phys, Bethlehem, PA 18015 USA
基金
美国国家科学基金会;
关键词
line: profiles; open clusters and associations: individual (IC 4996; NGC; 581; 869; 884; 1893; 1960); stars: early-type; stars: fundamental parameters; stars: rotation; LARGE-MAGELLANIC-CLOUD; M-CIRCLE-DOT; YOUNG CLUSTERS; EVOLUTIONARY STATUS; MASSIVE STARS; VELOCITIES; FIELD; PARAMETERS; MECHANISM; DENSITY;
D O I
10.1088/0004-637X/722/1/605
中图分类号
P1 [天文学];
学科分类号
0704 ;
摘要
Two recent observing campaigns provide us with moderate dispersion spectra of more than 230 cluster and 370 field B stars. Combining them and the spectra of the B stars from our previous investigations (similar to 430 cluster and similar to 100 field B stars) yields a large, homogeneous sample for studying the rotational properties of B stars. We derive the projected rotational velocity V sin i, effective temperature, gravity, mass, and critical rotation speed V-crit for each star. We find that the average V sin i is significantly lower among field stars because they are systematically more evolved and spun down than their cluster counterparts. The rotational distribution functions of V-eq/V-crit for the least evolved B stars show that lower mass B stars are born with a larger proportion of rapid rotators than higher mass B stars. However, the upper limit of V-eq/V-crit that may separate normal B stars from emission-line Be stars (where rotation promotes mass loss into a circumstellar disk) is smaller among the higher mass B stars. We compare the evolutionary trends of rotation (measured according to the polar gravity of the star) with recent models that treat internal mixing. The spin-down rates observed in the high-mass subset (similar to 9 M-circle dot) agree with predictions, but the rates are larger for the low-mass group (similar to 3 M-circle dot). The faster spin-down in the low-mass B stars matches well with the predictions based on conservation of angular momentum in individual spherical shells. Our results suggest that the fastest rotators (that probably correspond to the emission-line Be stars) are probably formed by evolutionary spin-up (for the more massive stars) and by mass transfer in binaries (for the full range of B star masses).
引用
收藏
页码:605 / 619
页数:15
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