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Дата индексирования: Tue Oct 2 09:36:10 2012
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CONCLUSIONS

The highly-processed surfaces of extreme helium stars point to an extremely unusual evolutionary history. In order to test candidate theories it is necessary to make reliable measurements of, in particular, stellar masses. Three methods are available; all depend on a measurement of the surface gravity $g$. The spectroscopic mass $M_{\rm S}$ requires a suitable mass-luminosity relation. The pulsation mass $M_{\rm P}$ is obtained from a pulsation period and linear pulsation theory, and the direct mass $M_{\rm D}$ is provided directly by the pulsation properties.

Data now exists to provide direct masses for five EHes. That for V652Her is well established and agrees well with evolution models involving the merger of two helium white dwarfs. The result demonstrates that pulsations are an essential and successful tool for determining the evolutionary origin of extreme helium stars.

Direct masses for two agree well with the spectroscopic and pulsation masses, although much may be done to reduce the errors. Further painstaking observations and analyses are also required for another others.