Discovery of Fluorine in Cool Extreme Helium Stars
نویسنده
چکیده
Neutral fluorine (F i) lines are identified in the optical spectra of cool EHe stars. These are the first identification of F i lines in a star’s spectrum, and provide the first measurement of fluorine abundances in EHe stars. The results show that fluorine is overabundant in EHe stars. The overabundance of fluorine provides evidence for the synthesis of fluorine in these stars, that is discussed in the light of asymptotic giant branch (AGB) evolution, and the expectation from accretion of an He white dwarf by a C-O white dwarf. Subject headings: stars: abundances – stars: chemically peculiar – stars: evolution
منابع مشابه
Abundance analysis of cool extreme helium star : LSS 3378
Abundance analysis of the cool extreme helium (EHe) star LSS 3378 is presented. The abundance analysis is done using LTE line formation and LTE model atmospheres constructed for EHe stars. The atmosphere of LSS 3378 shows evidence of H-burning, He-burning, and sprocess nucleosynthesis. The derived abundances of iron-peak and α-elements indicate absence of selective fractionation or any other pr...
متن کاملModel Atmosphere Analysis of Two Very Cool White Dwarfs
A detailed analysis of the very cool white dwarfs SDSS 1337+00 and LHS 3250 is presented. Model atmosphere calculations with improved collision-induced absorptions by molecular hydrogen indicate that a pure hydrogen composition can be ruled out, and that the strong infrared absorption observed in these cool stars is better explained in terms of collisions of H 2 with neutral helium. It is shown...
متن کاملA model for the Globular Cluster extreme anomalies
In spite of the efforts made in the latest years, still there is no comprehensive explanation for the chemical anomalies of globular cluster stars. Among these, the most striking is oxygen depletion, which reaches values down to [O/Fe]∼ −0.4 in most clusters, but in M13 it goes down to less than [O/Fe]∼ −1. In this work we suggest that the anomalies are due to the super position of two differen...
متن کاملWhite Dwarfs in Ngc 6791: Avoiding the Helium Flash
We propose that the anomalously bright white dwarf luminosity function observed in NGC 6791 (Bedin et al 2005) is the consequence of the formation of 0.5M⊙ white dwarfs with Helium cores instead of Carbon cores. This may happen if mass loss during the ascent of the Red Giant Branch is strong enough to prevent a star from reaching the Helium flash. Such a model can explain the slower white dwarf...
متن کاملOn the Dissociation Equilibrium of H2 in Very Cool, Helium-Rich White Dwarf Atmospheres
We investigate the dissociation equilibrium of H2 in very cool, helium-rich white dwarf atmospheres. We present the solution of the non-ideal chemical equilibrium for the dissociation of molecular hydrogen in a medium of dense helium. We find that at the photosphere of cool white dwarfs of Teff = 4000K, the non-ideality results in an increase of the mole fraction of molecular hydrogen by up to ...
متن کامل