Bibcode
Dufton, P. L.; Ryans, R. S. I.; Simón-Díaz, S.; Trundle, C.; Lennon, D. J.
Referencia bibliográfica
Astronomy and Astrophysics, Volume 451, Issue 2, May IV 2006, pp.603-611
Advertised on:
5
2006
Revista
Número de citas
43
Número de citas referidas
37
Descripción
High-resolution spectra for 24 SMC and Galactic B-type supergiants have
been analysed to estimate the contributions of both macroturbulence and
rotation to the broadening of their metal lines. Two different
methodologies are considered, viz. goodness-of-fit comparisons between
observed and theoretical line profiles and identifying zeros in the
Fourier transforms of the observed profiles. The advantages and
limitations of the two methods are briefly discussed with the latter
techniques being adopted for estimating projected rotational velocities
(v sin i) but the former being used to estimate macroturbulent
velocities. The projected rotational velocity estimates range from
approximately 20 to 60 km s-1, apart from one SMC supergiant,
Sk 191, with a v sin i ≃ 90 km s-1. Apart from Sk 191,
the distribution of projected rotational velocities as a function of
spectral type are similar in both our Galactic and SMC samples with
larger values being found at earlier spectral types. There is marginal
evidence for the projected rotational velocities in the SMC being higher
than those in the Galactic targets but any differences are only of the
order of 5-10 km s-1, whilst evolutionary models predict
differences in this effective temperature range of typically 20 to 70 km
s-1. The combined sample is consistent with a linear
variation of projected rotational velocity with effective temperature,
which would imply rotational velocities for supergiants of 70 km
s-1 at an effective temperature of 28 000 K (approximately B0
spectral type) decreasing to 32 km s-1 at 12 000 K (B8
spectral type). For all targets, the macroturbulent broadening would
appear to be consistent with a Gaussian distribution (although other
distributions cannot be discounted) with an 1/e half-width varying from
approximately 20 km s-1 at B8 to 60 km s-1 at B0
spectral types.