Abundance analyses of cool extreme helium stars

Details Abundance analyses of cool extreme helium stars Abundance analyses of cool extreme helium stars

2001-01-29

arxiv.org/abs/astro-ph/0101518v1

Mon.Not.Roy.Astron.Soc. 324 (2001) 937

Astronomy and Astrophysics

Astrophysics

24 pages (MNRAS Journal style), 7 tables, 19 figures, Accepted for publication in MNRAS

Scientific paper

10.1046/j.1365-8711.2001.04371.x

Extreme helium stars (EHe) with effective temperatures from 8000K to 13000K are among the coolest EHe stars and overlap the hotter R CrB stars in effective temperature. The cool EHes may represent an evolutionary link between the hot EHes and the R CrBs. Abundance analyses of four cool EHes are presented. To test for an evolutionary connection, the chemical compositions of cool EHes are compared with those of hot EHes and R CrBs. Relative to Fe, the N abundance of these stars is intermediate between those of hot EHes and R CrBs. For the R CrBs, the metallicity M derived from the mean of Si and S appears to be more consistent with the kinematics than that derived from Fe. When metallicity M derived from Si and S replaces Fe, the observed N abundances of EHes and R CrBs fall at or below the upper limit corresponding to thorough conversion of initial C and O to N. There is an apparent difference between the composition of R CrBs and EHes; the former having systematically higher [N/M] ratios. The material present in the atmospheres of many R CrBs is heavily CN- and ON-cycled. Most of the EHes have only CN-cycled material in their atmospheres. There is an indication that the CN- and ON-cycled N in EHes was partially converted to Ne by $\alpha$-captures. If EHes are to evolve to R CrBs, fresh C in EHes has to be converted to N. If Ne is found to be normal in R CrBs, the proposal that EHes evolve to R CrBs fails. The idea that R CrBs evolve to EHes is ruled out; the N abundance in R CrBs has to be reduced to the level of EHes, as the C/He which is observed to be uniform across EHes, has to be maintained. Hence, the inferred [N/M], C/He, [Ne/M], and the H-abundances of these two groups indicate that the EHes and the R CrBs may not be on the same evolutionary path.

Affiliated with

Also associated with

No associations

Rating

Abundance analyses of cool extreme helium stars does not yet have a rating. At this time, there are no reviews or comments for this scientific paper.

If you have personal experience with Abundance analyses of cool extreme helium stars, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Abundance analyses of cool extreme helium stars will most certainly appreciate the feedback.

Rate now

Comments { 0 }

Profile ID: LFWR-SCP-O-279344