Astronomy and Astrophysics – Astronomy
Scientific paper
Oct 1995
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1995apjs..100..461u&link_type=abstract
Astrophysical Journal Supplement v.100, p.461
Astronomy and Astrophysics
Astronomy
5
Line: Profiles, Stars: Atmospheres, Stars: Early-Type, Stars: Emission-Line, Be
Scientific paper
Seven Of stars (HD 17603, HD 34656, HD 188001 9 Sge, HD 190864, HD 192639, HD 193514, and HD 210839 λ Cep) have been observed in the blue-violet, yellow-green, and red spectral regions, chiefly at 30 Å mm-1. The equivalent widths and FWHM measures of the prominent absorption and emission lines in these spectra are presented here, and this new information is used with information presented in Underhill 1995 (Paper I) to study what the spectra of stars of types 08-06 imply.
It was noted in Paper I that the character of the profiles of Hα and He II N4686, both being lines formed in the winds from the stars, has been observed to vary. The other absorption and emission lines of H, He I, He II, C III, C iv, N III, and Si IV have not been observed to change by an amount in excess of 5%. It is argued that the photosphere and line-emitting plasma of the program stars are more constant in behavior than the winds of the program stars. An index measuring the amount of Stark broadening of the He II lines is derived, and it is argued that this index can be used as a criterion of the density in the photosphere of an O star. This index correlates fairly well with the luminosity classes assigned by Walborn from inspection of the spectra of the stars.
The appearance of N III λλ4634, 4641 emission lines in all O spectral types bearing an Of tag of any description is noted to mean that heated plasma is present in the line-forming regions of some, but not all, main-sequence, giant, and supergiant 0 stars. It is suggested that the heating may be a result of the transformation of mechanical energy to heat in the presence of small magnetic fields on the surfaces of Of stars. A specific agent must be invoked to explain why only some stars in each spectral type-luminosity class box show selected weak sharp emission lines.
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