Are the UV Stars Nuclear Powered?

Abstract

view Abstract Citations (8) References (22) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Are the UV Stars Nuclear Powered? Hills, J. G. Abstract The UV stars (hot pre-white dwarfs) may be fueled by nuclear energy rather than merely by gravitational contraction as has usually been assumed. Evolutionary models of white dwarfs without nuclear burning are used to determine their contribution to the observed far-ultraviolet excess in galaxies and their frequency in stellar systems. It is found that white dwarfs with an average mass of 0.7 are able to produce the ultraviolet excess observed in the nucleus of M31 only if they do not emit neutrinos as directed by the theory of universal Fermi interactions. It is further found that the observed number of UV stars in the globular cluster M3 greatly exceeds that expected for these white dwarfs. The observed UV stars in this cluster are almost certainly evolving on a nuclear time scale. These UV stars may be powered by the conversion of their residual helium to carbon near the helium-burning main sequence for pure helium stars. There is enough of this fuel to permit the UV stars to emit up to 10 percent of the total radiation from a stellar system. This is adequate to explain both the far-ultraviolet flux in galaxies and the number of UV stars in M3. UV stars more massive than about 0.8 may even be able to burn their carbon to magnesium, and this process could release an additional quantity of energy about equal to that released by helium burning. The theory that the UV stars are responsible for the ionization of the inter- cloud medium (1CM) is in better agreement with observations if the UV stars are nuclear-powered rather than powered only by gravitational contraction. Because of their lower average surface temperatures the nuclearpowered UV stars would produce a much less highly ionized 1CM than that produced exclusively by the much hotter white dwarfs powered only by gravitational contraction. A less highly ionized 1CM is supported by recent observations by the Copernicus satellite. The longer average lifetime of the nuclear-powered stars increases the theoretical space density of the UV stars, which is also in better agreement with observations. Subject headings: globular clusters - interiors, stellar - interstellar matter nucleosynthesis - white dwarf stars Publication: The Astrophysical Journal Pub Date: May 1974 DOI: 10.1086/152853 Bibcode: 1974ApJ...190..109H full text sources ADS |