eprintid: 1494039
rev_number: 43
eprint_status: archive
userid: 608
dir: disk0/01/49/40/39
datestamp: 2016-05-29 04:28:39
lastmod: 2021-10-14 22:46:30
status_changed: 2018-01-04 14:23:06
type: article
metadata_visibility: show
creators_name: Martins, F
creators_name: Simon-Diaz, S
creators_name: Palacios, A
creators_name: Howarth, I
creators_name: Georgy, C
creators_name: Walborn, NR
creators_name: Bouret, J-C
creators_name: Barba, R
title: Surface abundances of ON stars
ispublished: pub
divisions: UCL
divisions: B04
divisions: C06
divisions: F60
keywords: stars: massive – stars: abundances – stars: evolution – stars: atmospheres
note: This version is the version of record. For information on re-use, please refer to the publisher’s terms and conditions.
abstract: Context. Massive stars burn hydrogen through the CNO cycle during most of their evolution. When mixing is efficient or when mass
transfer in binary systems occurs, chemically processed material is observed at the surface of O and B stars.
Aims. ON stars show stronger lines of nitrogen than morphologically normal counterparts. Whether this corresponds to the presence
of material processed through the CNO cycle is not known. Our goal is to answer this question.
Methods. We performed a spectroscopic analysis of a sample of ON stars with atmosphere models. We determined the fundamental
parameters as well as the He, C, N, and O surface abundances. We also measured the projected rotational velocities. We compared the
properties of the ON stars to those of normal O stars.
Results. We show that ON stars are usually rich in helium. Their CNO surface abundances are fully consistent with predictions of
nucleosynthesis. ON stars are more chemically evolved and rotate − on average − faster than normal O stars. Evolutionary models
including rotation cannot account for the extreme enrichment observed among ON main sequence stars. Some ON stars are members
of binary systems, but others are single stars as indicated by stable radial velocities. Mass transfer is therefore not a simple explanation
for the observed chemical properties.
Conclusions. We conclude that ON stars show extreme chemical enrichment at their surface, consistent with nucleosynthesis through
the CNO cycle. Its origin is not clear at present.
date: 2015-06-01
date_type: published
publisher: EDP SCIENCES S A
official_url: http://doi.org/10.1051/0004-6361/201526130
oa_status: green
full_text_type: pub
language: eng
primo: open
primo_central: open_green
verified: verified_manual
elements_id: 1053710
doi: 10.1051/0004-6361/201526130
lyricists_name: Howarth, Ian
lyricists_id: IDHOW62
actors_name: Waragoda Vitharana, Nimal
actors_id: NWARR44
actors_role: owner
full_text_status: public
publication: Astronomy & Astrophysics
volume: 578
number: A10
pages: 16
issn: 1432-0746
citation:        Martins, F;    Simon-Diaz, S;    Palacios, A;    Howarth, I;    Georgy, C;    Walborn, NR;    Bouret, J-C;           Martins, F;  Simon-Diaz, S;  Palacios, A;  Howarth, I;  Georgy, C;  Walborn, NR;  Bouret, J-C;  Barba, R;   - view fewer <#>    (2015)    Surface abundances of ON stars.                   Astronomy & Astrophysics , 578  (A10)      10.1051/0004-6361/201526130 <https://doi.org/10.1051/0004-6361%2F201526130>.       Green open access   
 
document_url: https://discovery.ucl.ac.uk/id/eprint/1494039/1/Howarth_aa26130-15.pdf