Hostname: page-component-586b7cd67f-dlnhk Total loading time: 0 Render date: 2024-11-26T06:45:15.942Z Has data issue: false hasContentIssue false

The Chemical Composition of the Wolf-Rayet Stars

Published online by Cambridge University Press:  14 August 2015

Allan J. Willis*
Affiliation:
Dept. of Physics & Astronomy, University College London, Gower St., London WC1E 6BT, England

Extract

Core share and HTML view are not available for this content. However, as you have access to this content, a full PDF is available via the ‘Save PDF’ action button.

This review summarises current knowledge of the chemical composition of PopI WR stars, concentrating on work carried out in this area since the last IAU, No. 49, symposium devoted to this stellar class (Bappu & Sahade 1973). Earlier reviews of this topic are found in Gebbie & Thomas (1968). The dichotomy of the WR stars into the WN and WC sequences (Beals 1934) has generally been qualitatively interpreted as arising because of gross differences in the C and N abundances: WN stars which exhibit emission lines of predominantly He and N ions with little evidence for C, being inferred as C-poor objects, whilst WC stars, showing predominantly He and C lines and virtually no evidence for N being inferred as N-poor. In both sequences the visible spectra show little or no evidence for hydrogen. However, although the WR stars have been acknowledged as a class for over a century now, progress has been very slow in putting quantitative determinations of their physical and chemical properties on a firm basis, with the bulk of work in this area being conducted during the past decade. The chemical nature of the WR stars has always been a matter of considerable uncertainty, controversy and, quite often, passionate disagreement, arising from uncertainties in the interpretation of the, often ambiguous, observational material available, as well as from disagreements as to the reliability of the use of comparatively simple analytical models employed to date. Recent results strongly suggest that the WR stars are chemically evolved objects, with low H/He ratios and quite different C/N ratios in the WN and WC sequences, with some measure of agreement in these results with the chemistries predicted to arise at various stages of evolutionary theory for hot massive stars which, by one means or another, have shed much of their atmospheric material during their evolution. My purpose in this review is to summarise the investigations and results that lead to the above conclusions. §2 deals with an assessment of the atmospheric H/He ratio in both WN and WC stars: a parameter of fundamental importance in addressing their evolutionary status, as well as providing a base species with which to compare other derived chemical abundances. §3 briefly deals with the models generally employed and gives recent results for He, C and N abundances derived from both visible and UV line analyses. §4 summarises recent results from stellar evolutionary theory and in §5 compares these with those derived from observation, assessing the significance of these new results and their implications for the evolutionary status of the WR stars. Some areas for further advancement are identified.

Type
SESSION 2 — THE CHEMISTRY OF THE WOLF-RAYET STARS
Copyright
Copyright © Reidel 1982 

References

Bappu, M.K.V., 1973, IAU Symp. No. 49, ed. Bappu, M. & Sahade, J., D. Reidel Pub. Co., Holland, p.59.Google Scholar
Bappu, M.K.V., Sahade, J., 1973, eds. IAU Symp. No. 49, D. Reidel, Holland.Google Scholar
Barlow, M.J., Smith, L.J., Willis, A.J., 1981, M.N.R.A.S., 196, 101.Google Scholar
Barnes, T.G., Lambert, D.L., Potter, A.E., 1974, Astrophys. J., 187, 73.CrossRefGoogle Scholar
Castor, J.I., 1970, M.N.R.A.S., 149, 111.CrossRefGoogle Scholar
Castor, J.I., Nussbaumer, H., 1972, M.N.R.A.S., 155, 293.Google Scholar
Castor, J.I., van Blerkom, D., 1970, Astrophys. J., 161, 485.Google Scholar
Chiosi, C., Nasi, E., Bertelli, G., 1978, IAU Symp. No. 83, ed. Conti, P.S. & de Loore, C., D. Reidel Pub. Co., Holland, p.337.Google Scholar
Conti, P.S., 1976, Mem. Soc. r. Sci. Liege, Ser 6, 9, 193.Google Scholar
Conti, P.S., Garmany, K., 1980, Astrophys. J., 238, 190.Google Scholar
Conti, P.S., Massey, P., 1981, IAU Coll. No. 59, ed. Stalio, R. & Chiosi, C., D. Reidel Pub. Co., Holland, p.Google Scholar
De Loore, C., 1981, IAU Coll. No. 59, ed. Stalio, R. & Chiosi, C., D. Reidel Pub. Co., Holland, P.405.Google Scholar
Drescel, H., Rahe, J., 1981, Astron. Astrophys., in press.Google Scholar
Gabriel, M., Noels, A., 1981, Astron. Astrophys. Lett., 94, L1.Google Scholar
Gebbie, K.B., Thomas, R.N., 1968, NBS Spec. Pub., 307.Google Scholar
Kuhi, L.V., 1966, Astrophys. J., 145, 715.CrossRefGoogle Scholar
Kuhi, L.V., 1968, NBS Spec. Pub., 307, p.125.Google Scholar
Kwitter, K., 1981, Astrophys. J., 245, 154.CrossRefGoogle Scholar
Johnson, H.M., 1978, Astrophys. J. Suppl., 36, 217.CrossRefGoogle Scholar
Maeder, A., 1981, Astron. Astrophys., 99, 97.Google Scholar
Massey, P., 1980, Astrophys. J., 236, 526.Google Scholar
Massey, P., Conti, P.S., 1980, Astrophys. J., 242, 638.Google Scholar
Massey, P., Conti, P.S., 1981, Astrophys. J., 244, 173.Google Scholar
Noels, A., Conti, P.S., Gabriel, M., Vreux, J-M., 1980, Astron. Astrophys., 92, 242.Google Scholar
Nugis, T., 1975, IAU Symp. No. 67, D. Reidel Pub. Co., Holland, p.291.Google Scholar
Nugis, T., 1982, these proceedings.Google Scholar
Nussbaumer, H., Schmutz, W., Smith, L.J., Willis, A.J., 1981, Astron. Astrophys. Suppl., in press.Google Scholar
Oegerle, W.R., van Blerkom, D., 1976, Astrophys. J., 206, 150.Google Scholar
Paczynski, B., 1973, IAU Symp. No. 49, ed. Bappu, M. & Sahade, J., D. Reidel Pub. Co., Holland, p. 143.Google Scholar
Perry, D., Conti, P.S., 1982, these proceedings.Google Scholar
Rublev, S.V., 1972, Izv. Spets. Astrofiz. Obs., 4, 3.Google Scholar
Rumpl, W.M., 1980, Astrophys. J., 241, 1055.Google Scholar
Sahade, J., 1980, Astron. Astrophys. Lett., 87, L7.Google Scholar
Sahade, J., 1981, Rev. Mex. Ast. Astrophys., in press.Google Scholar
Smith, L.F., 1973, IAU Symp. No. 49, ed. Bappu, M. & Sahade, J., D. Reidel Pub. Co., Holland, p.15.Google Scholar
Smith, L.F., Kuhi, L.V., 1981, Atlas of WR Line Profiles, JILA Rep. 117.Google Scholar
Smith, L.J., Willis, A.J., 1981, M.N.R.A.S., submitted.Google Scholar
Sobolev, V.V., 1960, The Moving Envelopes of Stars, Har. Univ. Press.Google Scholar
Stecher, T.P., 1970, Astrophys. J., 159, 543.Google Scholar
Stothers, R., 1976a, Astrophys. J., 204, 853.Google Scholar
Stothers, R., 1976b, Astrophys. J., 209, 800.Google Scholar
Stothers, R., Chin, C., 1979, Astrophys. J., 233, 267.Google Scholar
Underhill, A.B., 1959, Pub. Dom. Ast. Obs., 11, 209.Google Scholar
Underhill, A.B., 1973, IAU Symp. No. 49, ed. Bappu, M. & Sahade, J., D. Reidel Pub. Co., Holland, p.37.Google Scholar
Underhill, A.B., 1980, Astrophys. J., 239, 220.Google Scholar
Underhill, A.B., 1981, Astrophys. J., 244, 963.Google Scholar
Vanbeveren, D., Doom, C., 1980, Astron. Astrophys., 87, 77.Google Scholar
Van Blerkom, D., Patton, D., 1972, Astrophys. J., 177, 547.Google Scholar
Williams, P.M., Adams, D.J., Arakdai, S., Beattie, D.H., Born, J., Lee, T.J., Robertson, D.J., Stewart, J.M., 1980, M.N.R.A.S., 192, 25p.CrossRefGoogle Scholar
Williams, P.M., Allen, L.R., 1980, Observatory, 100, 203.Google Scholar
Willis, A.J., 1980, in Symp: The 2nd European IUE Conf., ed. Battrick, B. & Mort, J., ESA Spec. Pub., 157, p.il.Google Scholar
Willis, A.J., 1981a, in IAU Coll. No. 59, ed. Stalio, R. & Chiosi, C., D. Reidel Pub. Co., Holland, p.27.Google Scholar
Willis, A.J., 1981, M.N.R.A.S., 198, in press.Google Scholar
Willis, A.J., Wilson, R., 1978, M.N.R.A.S., 182, 559.CrossRefGoogle Scholar
Willis, A.J., Wilson, R., 1979, in IAU Symp. No. 83, ed. Conti, P.S. & de Loore, C., D. Reidel Pub. Co., Holland, p.461.Google Scholar