The spectra of Wolf-Rayet stars. I - Optical line strengths and the hydrogen-to-helium ratios in WN type stars

Abstract

view Abstract Citations (172) References (37) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS The spectra of Wolf-Rayet stars. I. Optical line strengths and the hydrogen-to-helium ratios in WN type stars. Conti, P. S. ; Leep, M. E. ; Perry, D. N. Abstract We begin a series of systematic studies of spectra of Wolf-Rayet stars by examining the optical line strengths of WN stars in the Galaxy and the Large Magellanic Cloud to see what similarities and differences exist among them. Tables of equivalent widths extracted from spectra are presented and some conclusions are drawn. We have found that there is a wide dispersion, up to a factor of 10 or more, in line strengths for all ions even among stars of the same subtype, with WN 7 stars weaker overall than surrounding types. Type-to-type trends are consistent with changing ionization balance in the stellar wind. Nitrogen line ratios indicate that the WN subtypes represent an ionization sequence, but one with considerable overlap: the classification scheme is not single valued; other physical parameters must play a role. The line strength dispersion does not appear to be primarily due to ionization, or luminosity. The Balmer-Pickering decrement has been used to estimate the H/He ratio for most of the WN stars with available spectra; semi-quantitative results are presented. Significant differences in H/He are observed (10 stars may have H/He > 2). At a given subclass, the strongest line stars have no detectable H. The abundance of H probably relates to structural differences in the winds that, in part, give rise to a dispersion in observed line strengths. Finally, we have estimated the C/N ratio from the C IV λ5805/N IV λ4057 line ratio. In most cases our observations suggest that the C/N ratio is consistent with "evolved" models for WN stars. A few stars show strong C IV implying much larger values for C/N, but hydrogen was not detected in them. These stars may be in transition from the WN to WC classes. Publication: The Astrophysical Journal Pub Date: May 1983 DOI: 10.1086/160948 Bibcode: 1983ApJ...268..228C Keywords: Abundance; Helium Hydrogen Atmospheres; Optical Emission Spectroscopy; Spectral Line Width; Stellar Spectra; Wolf-Rayet Stars; Carbon Stars; Emission Spectra; Gas Ionization; Nitrogen; Stellar Magnitude; Stellar Winds; Visible Spectrum; Astrophysics full text sources ADS | data products SIMBAD (70) NED (1) Related Materials (5) Part 2: 1984ApJ...280..181T Part 3: 1986ApJ...300..379T Part 4: 1989ApJ...337..251C Part 5: 1989ApJ...341..113C Part 6: 1990ApJ...354..359C