Photospheric velocity gradients in B1 supergiants

Details Photospheric velocity gradients in B1 supergiants Photospheric velocity gradients in B1 supergiants

Oct 1992

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1992a%26a...264..169m&link_type=abstract

Astronomy and Astrophysics (ISSN 0004-6361), vol. 264, no. 1, p. 169-172.

Astronomy and Astrophysics

Astrophysics

12

B Stars, Photosphere, Stellar Atmospheres, Supergiant Stars, Astronomical Spectroscopy, Iue, Local Thermodynamic Equilibrium, Stellar Luminosity, Stellar Mass Ejection, Stellar Models

Scientific paper

We present IUE spectra for a set of B1 supergiants. These data clearly demonstrate that the Si III 1300A multiplet (lower level 6.6 ev above ground) becomes progressively more asymmetric with increasing luminosity or, equivalently, mass loss. In the most luminous supergiants, the cores of the 1300A multiplets become displaced by up to -150 km/s relative to nearby, weaker lines. In addition, systematic velocity shifts and asymmetries are also present in the strong Si III singlets 1312A and 1417A in the more luminous stars. The obvious implication of these observations is that the outer photospheres of B supergiants are affected by radial expansion, and this may account for why even non-LTE line analyses of these stars require large micro-turbulent velocity fields, and why line blanketed LTE models underestimate their overall UV line blanketing.

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