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The nature of the runaways: old disk population OB stars?

Published online by Cambridge University Press:  14 August 2015

L. Carrasco
Affiliation:
Instituto de Astronomía, Universidad Nacional Autónoma de México
G. F. Bisiacchi
Affiliation:
Instituto de Astronomía, Universidad Nacional Autónoma de México
R. Costero
Affiliation:
Instituto de Astronomía, Universidad Nacional Autónoma de México
C. Firmani
Affiliation:
Instituto de Astronomía, Universidad Nacional Autónoma de México

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We propose that most of the OB runaway stars are Old Disk Population objects in the same evolutionary phase as the hot UV-bright stars in globular clusters. Bimodal Gaussian fits to the peculiar radial velocity distribution are computed for 386 O-type and 1093 B-type stars. Both samples independently yield one Gaussian with σ ≃ 13 km s−1, a value typical of extreme Population I objects, and a second one with σ ≃ 28 km s−1 which is characteristic of the Old Disk Population. The fraction of stars under the high velocity-dispersion distribution (HVD stars) is 47% of the 0 and 23% of the B stars. We analyze the kinematics of the sample of OB stars divided into low peculiar radial velocity, |Vrp|<20 km s−1, and high-velocity stars, |Vrp|> 45 km s−1. The results for the solar motion and mean peculiar velocity of the groups are the expected ones for the extreme Population I objects in the case of the low-velocity group (U= 9.1±0.1;V= 14.8±0.1 km s−1) and an asymmetric drift of approximately 20 km s−1 for the high velocity stars (U=2.7±1.4; V= 32.7±1.4 km s−1). This lag behind circular motion also corresponds to Old Disk Population objects.

Type
Session 5: Theory and Mass Loss Rates Binary Stars - Miscellaneous Topics
Copyright
Copyright © Reidel 1979