Logo image
Back
The abundances of carbon and nitrogen in the atmospheres of classical Be stars
Journal article   Open access   Peer reviewed

The abundances of carbon and nitrogen in the atmospheres of classical Be stars

Geraldine J Peters, Kenneth G Gayley, Rina G Rast, Jorick S Vink and Jeremy J Drake
Astrophysics and space science, Vol.371(1), 9
2026
DOI: 10.1007/s10509-026-04538-8
PMCID: PMC12835015
PMID: 41608613
url
https://doi.org/10.1007/s10509-026-04538-8View
Published (Version of record) Open Access

Abstract

Hot stars born as rapid rotators are expected to induce meridional currents that mix hydrogen from the envelope into the core and return CNO-cycle processed material to the envelope, which should enhance the N at the surface at the expense of C and possibly also O depending on the ambient conditions. But the photospheric C and N abundances could also be influenced by mass transfer in a close binary system which spins up the mass gainer and deposits either processed or unprocessed material to its surface depending on just how much material has been peeled off the mass donor. We focus on the chemical composition of Be star photospheres to infer the present and past evolution of rapidly rotating early B stars. To mitigate the effects of gravity darkening and photospheric line blending on the abundances, we chose 8 Be stars with low that have good high-resolution FUV spectra in the archive. We carried out a conventional NLTE abundance analysis of selected N iii, N i, and C iii lines in the FUV spectral region. We find clear evidence that the C iii 1176 Å multiplet is weak in the core region in most program stars, suggesting CNO processing. However, in all cases we infer a N abundance that is solar or less, raising a conundrum as to what happened to the "missing C." Since a similar pattern of weak C yet normal N is also found in the mass gainer in some Algol binaries, there appears to be an emerging challenge to explain this apparent abundance anomaly. We speculate that the excess N from CNO processing might be converted into O (and perhaps on to Ne) by fusion with He in the hot but low-density regions either in the trail of ashes just outside the receding carbon-fusing core, or in He-shell flash regions, of a highly evolved mass loser in its final stage of mass transfer.
 Algol binaries UV astronomy OB subdwarf stars Close binary stars Circumstellar matter Stellar mass loss Be stars Early-type emission line stars

Details

Metrics

1 Record Views
1 Times Cited - Web of Science
Logo image