The correlations between various parameters of the WN b stars supports the idea that they are an essentially one-parameter family. Specifically, the WN b stars follow, within the observational uncertainty, one-to-one relationships the following plots:
The primary parameter defining the properties of a WN b stars is certainly its present mass. Fig. 13 shows the mass-luminosity relationship for WN stars without hydrogen from models by Meynet et al. (1994). Models of different initial metallicities obey the same, well defined relationship. The mass-luminosity relationship is independent of the local Z and of the previous history of the star. This will eventually allow the assignment of masses corresponding to the other tightly correlated parameters: , , and EW 5411.
The actual mass of a WN b star is also related to its initial stellar mass. Fig. 14 shows the relationship for different metallicities from the models by Meynet et al. (1994). The relationship is very sensitive to Z and, for Z 0.02, it is double valued; i.e. a given WN b star mass can result from two different initial stellar masses, even at the same Z. Thus it does not appear possible to assign an initial mass to a WN b star on the basis of its present mass or other properties.
While most parameters of WN b stars are well correlated with each other, the line width, represented by FWHM 4686, is an exception (Fig. 9). This suggests the presence of a second parameter that affects the mass flux and the terminal velocity of the optically thick wind. The discussion in the previous section suggests that this second parameter may be either (or a combination of) internal mean molecular weight or rotation rate.
© European Southern Observatory (ESO) 1998
Online publication: June 2, 1998