Volume 575, March 2015
|Number of page(s)||11|
|Published online||03 March 2015|
Spectroscopic variability of two Oe stars
1 Groupe d’Astrophysique des Hautes Énergies, Institut d’Astrophysique et de Géophysique, Université de Liège, Allée du 6 Août, Bât. B5c, 4000 Liège, Belgium
2 Schnörringen Telescope Science Institute, Waldbröl, Germany
3 Av. Portugal 616C, 2765-272 Estoril, Portugal
4 Burggraben 3, 61206 Wöllstadt, Germany
5 Eichendorffstraße 8, 63538 Großkrotzenburg, Germany
6 Rua Nuno Ataide Mascarenhas 47, 2. Esq. 8100-610 Loule, Portugal
7 Département de Physique, Université de Montréal, and Centre de Recherche en Astrophysique du Québec, Canada
8 Alto Ajuda, Rua 27 - No 215, 1300-581 Lisbon, Portugal
9 Hamburger Sternwarte, Universität Hamburg, Germany
10 R. Rego de Agua LT 24 RC Esq., Marrazes, 2400 Leiria, Portugal
11 Normannenweg 39, 59519 Möhnesee-Körbecke, Germany
12 Instituto de Astrofísica de Canarias, 38200 La Laguna, Tenerife, Spain
13 Departamento de Astrofísica de Canarias, Universidad de La Laguna, 38205 La Laguna, Tenerife, Spain
14 Three Hills Observatory, The Birches, Torpenhow, CA7 1JF, United Kingdom
15 Rua Almirante Campos Rodrigues, Edf. Girassol, 5F, 1500-036 Lisbon, Portugal
16 Nurda-Park 13, 53562 St. Katharinen, Germany
17 R. Venezuela 29 3 Esq., 1500-618 Lisbon, Portugal
18 Virulylaan 30, 2267 BS Leidschendam, The Netherlands
19 Department of Physics & Astronomy, University of Kentucky, Lexington, USA
20 Hohlstraße 19, 66333 Völklingen, Germany
21 Departamento de Astronomía, Universidad de Guanajuato, Guanajuato, Mexico
22 Zentrum für Astronomie der Universität Heidelberg, Landessternwarte Königstuhl, Heidelberg, Germany
23 Nelkenweg 14, 66907 Glan-Münchweiler, Germany
G. Rauw, e-mail: firstname.lastname@example.org
Received: 13 October 2014
Accepted: 15 December 2014
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.
Key words: stars: early-type / stars: emission-line, Be / stars: individual: HD 45314 / stars: individual: HD 60848 / stars: winds, outflows
© ESO, 2015
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