Small Nebulae Associated with Wolf-Rayet Stars.

Abstract

view Abstract Citations (4) References Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Small Nebulae Associated with Wolf-Rayet Stars. Smith, Lindsey F. Abstract We now know of six Woif-Rayet (WR) stars that are situated at the center of curvature of an arc or arcs of nebulosity. All of these are WX stars; none are believed to be binary systems. Total masses have been derived for three of the nebulae from (a) total fluxes 9btained from 11-cm observations with the 2 10-ft radio telescope of the Australian X ational Radio Astronomical Observatory, (b) electron densities derived from spectra of the N3727 doublet, (c) photometric distances for the central WR stars. Similar data are given by Johnson and Hogg (Astrophys. J. 142, 1033, 1965) for two other nebulae, and their mass estimates have been revised in accord with the new photometric distances for the stars concerned. The derived masses range from 7 to 700 solar masses. The conclusions drawn by Johnson and Hogg are confirmed: (1) that the nebulae are in the form of extremely thin shells, and (2) that this characteristic shape may arise from a situation in which the interstellar matter is swept up by matter ejected from the WR star. Assuming that the nebulae are formed in this way, and assuming continuous ejection, the ages of the nebulae may be calculated for a range of values of the assumed rate of mass loss and velocity of ejection. The derived ages lie in the range 10~ to 106 yr for rates of mass loss between 10-~ and 10-6 solar masses per year. There is a monotonic relationship between the derived ages of the nebulae and their observed masses, in the sense that the more massive nebulae are older. This is reasonable since the formation, persistence and total mass of such a nebula will depend on the density of the interstellar medium in which the star is situated. The absence of nebulae associated with WC stars therefore implies either that the WC stars do not eject matter, or that they are situated in regions of low density of the interstellar gas. The latter explanation is favored. Publication: The Astronomical Journal Pub Date: September 1967 DOI: 10.1086/110559 Bibcode: 1967AJ.....72S.829S full text sources ADS |