stars: early-type; stars: emission-line; Be; stars: individual: HD 45314; stars: individual: HD 60848; stars: winds; outflows
Abstract :
[en] Context. The two Oe stars HD 45 314 and HD 60 848 have recently been found to exhibit very different X-ray properties: whilst HD 60 848 has an X-ray spectrum and the emission level typical of most OB stars, HD 45 314 features a much harder and brighter X-ray emission, making it a so-called γ Cas analogue. Aims: Monitoring the optical spectra could provide hints towards the origin of these very different behaviours. Methods: We analyse a large set of spectroscopic observations of HD 45 314 and HD 60 848, extending over 20 years. We further attempt to fit the Hα line profiles of both stars with a simple model of emission line formation in a Keplerian disk. Results: Strong variations in the strengths of the Hα, Hβ, and He i λ 5876 emission lines are observed for both stars. In the case of HD 60 848, we find a time lag between the variations in the equivalent widths of these lines, which is currently not understood. The emission lines are double peaked with nearly identical strengths of the violet and red peaks. The Hα profile of this star can be successfully reproduced by our model of a disk seen under an inclination of 30°. In the case of HD 45 314, the emission lines are highly asymmetric and display strong line profile variations. We find a major change in behaviour between the 2002 outburst and the one observed in 2013. This concerns both the relationship between the equivalent widths of the various lines and their morphologies at maximum strength (double-peaked in 2002 versus single-peaked in 2013). Our simple disk model fails to reproduce the observed Hα line profiles of HD 45 314. Conclusions: Our results further support the interpretation that Oe stars do have decretion disks similar to those of Be stars. Whilst the emission lines of HD 60 848 are explained well by a disk with a Keplerian velocity field, the disk of HD 45 314 seems to have a significantly more complex velocity field that could be another signature of the phenomenon that produces its peculiar X-ray emission.
Research Center/Unit :
LiSRI - Liège Space Research Institute - ULiège
Disciplines :
Space science, astronomy & astrophysics
Author, co-author :
Rauw, Grégor ; Université de Liège - ULiège > Groupe d'astrophysique des hautes énergies (GAPHE)
Morel, Thierry ; Université de Liège - ULiège > Groupe d'astrophysique des hautes énergies (GAPHE)
Nazé, Yaël ; Université de Liège - ULiège > Groupe d'astrophysique des hautes énergies (GAPHE)
Eversberg, T.; Schnörringen Telescope Science Institute, Waldbröl, Germany
Alves, F.; Av. Portugal 616C, 2765-272, Estoril, Portugal
Knapen, J. H.; Instituto de Astrofísica de Canarias, 38200 La Laguna, Tenerife, Spain ; Departamento de Astrofísica de Canarias, Universidad de La Laguna, 38205 La Laguna, Tenerife, Spain
Leadbeater, R.; Three Hills Observatory, The Birches, Torpenhow, CA7 1JF, United Kingdom
Mittag, M.; Hamburger Sternwarte, Universität Hamburg, Germany
Moffat, A. F. J.; Département de Physique, Université de Montréal, and, Centre de Recherche en Astrophysique du Québec, Canada
Reinecke, N.; Nurda-Park 13, 53562, St. Katharinen, Germany
Ribeiro, J.; R. Venezuela 29 3 Esq., 1500-618, Lisbon, Portugal
Romeo, N.; Virulylaan 30, 2267 BS, Leidschendam, The Netherlands
Sánchez Gallego, J.; Instituto de Astrofísica de Canarias, 38200 La Laguna, Tenerife, Spain ; Department of Physics & Astronomy, University of Kentucky, Lexington, USA
Dos Santos, E. M.; Rua Nuno Ataide Mascarenhas 47, 2. Esq., 8100-610, Loule, Portugal
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