Macroturbulent and rotational broadening in the spectra of B-type supergiants

被引:74
作者
Ryans, RSI [1 ]
Dufton, PL
Rolleston, WRJ
Lennon, DJ
Keenan, FP
Smoker, JV
Lambert, DL
机构
[1] Queens Univ Belfast, Dept Phys, Belfast BT7 1NN, Antrim, North Ireland
[2] Isaac Newton Grp Telescopes, E-38700 Santa Cruz De La Palma, Canary Islands, Spain
[3] Univ Texas, Dept Astron, Austin, TX 78712 USA
关键词
stars : early-type; stars : fundamental parameters; stars : rotation; supergiants;
D O I
10.1046/j.1365-8711.2002.05780.x
中图分类号
P1 [天文学];
学科分类号
0704 ;
摘要
The absorption-line spectra of early B-type supergiants show significant broadening that implies that an additional broadening mechanism (characterized here as 'macroturbulence') is present in addition to rotational broadening. Using high-resolution spectra with signal-to-noise ratios of typically 500, we have attempted to quantify the relative contributions of rotation and macroturbulence, but even with data of this quality significant problems were encountered. However, for all our targets, a model where macroturbulence dominates and rotation is negligible is acceptable; the reverse scenario leads to poor agreement between theory and observation. Additionally, there is marginal evidence for the degree of broadening increasing with line strength, possibly a result of the stronger lines being formed higher in the atmosphere. Acceptable values of the projected rotational velocity are normally less than or equal to 50 km s(-1), which may also be a typical upper limit for the rotational velocity. Our best estimates for the projected rotational velocity are typically 10-20 km s(-1) and hence compatible with this limit. These values are compared with those predicted by single star evolutionary models, which are initially rapidly rotating. It is concluded that either these models underestimate the rate of rotational breaking or some of the targets may be evolving through a blue loop or are binaries.
引用
收藏
页码:577 / 586
页数:10
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