SB 21, an extremely helium-rich subdwarf O-star

Details SB 21, an extremely helium-rich subdwarf O-star SB 21, an extremely helium-rich subdwarf O-star

Aug 1980

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1980a%26a....88l...4h&link_type=abstract

Astronomy and Astrophysics, vol. 88, no. 1-2, Aug. 1980, p. L4, L5.

Astronomy and Astrophysics

Astrophysics

2

Helium, O Stars, Spectrum Analysis, Stellar Spectra, Stellar Spectrophotometry, Subdwarf Stars, Early Stars, H Gamma Line, Image Processing, Stellar Evolution, Stellar Models, Stellar Temperature, Thermodynamic Equilibrium

Scientific paper

Spectral observations of the subdwarf O star SB 21 are reported. The observations were made at a dispersion of 29 A/mm in the spectral range 4250-4800 A using a 3.6-m telescope and an image dissector scanner. The H gamma line is found to be absent in SB 21, while the He I lines at 4388, 4471 and 4713 A and the He II lines at 4686 and possibly 4542 are detected. A detailed nonlocal thermodynamic equilibrium model analysis of the data indicates an effective temperature of 35,000 K, log g of 5.5 and a He/H density ratio greater than 10. Differences between the extremely helium rich objects SB 21, CPD-31 1701 and BD + 48 177 and other extremely helium-rich objects such as BD +37 1877 and BD +37 442 are pointed out.

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