The helium abundance in the population II Cepheid, W Virginis

Details The helium abundance in the population II Cepheid, W Virginis The helium abundance in the population II Cepheid, W Virginis

Dec 1989

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1989apj...347.1107r&link_type=abstract

Astrophysical Journal, Part 1 (ISSN 0004-637X), vol. 347, Dec. 15, 1989, p. 1107-1113.

Astronomy and Astrophysics

Astrophysics

18

Abundance, Cepheid Variables, Helium, Stellar Atmospheres, Stellar Spectra, Emission Spectra, Hydrogen, Line Spectra, Radial Velocity

Scientific paper

Emission in H-alpha, H-beta, and He I 5876A has been observed in W Virginis during rising light from phase 0.84 to 1.01. Radial velocities show that the emission comes from the recombination region behind a shock wave moving out at 65 km/s. The line ratios are sensitive to the helium-to-hydrogen ratio and yield a value of y/x = N(He)/N(H) = 0.12 compared with a value of 0.08 for metal-poor systems. The uncertainties depend more upon the model than the data, so no formal probable error may be assigned to y/x; however, reasonable extreme limits are 0.08 to 0.18. Hence, it appears that the helium abundance in the atmosphere of W Vir is typical of Population II objects, with the distinct possibility that some helium has been added to its atmosphere during its evolution.

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