Article (Scientific journals)
Irregular emission cycles in the Oe star HD 60 848
Rauw, Grégor; Nazé, Yaël; Campos, Fran et al.
2021In New Astronomy, 83, p. 101462 (14
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Keywords :
stars: Oe; stars: individual (HD 60 848); X-rays: stars; stars: individual (HD 60 848); Astrophysics - Solar and Stellar Astrophysics
Abstract :
[en] We analyse the spectroscopic and photometric variability of the Oe star HD 60 848 over the last twenty five years. The spectra reveal recurrent, but irregular cycles of increased circumstellar emission lines. These cycles are highly asymmetric displaying a slow increase over about 6 years, followed by a fast decay within about 6 months. Our analysis focuses on the most recent cycle (2013 - 2020). The equivalent width and velocity separation of the emission peaks indicate variations of the outer disk radius by a factor ~ 2.2, although the variability appears more complex than expected from first principle relations for optically thin Keplerian disks. We observe a time delay between the variations of the strengths of He Iλ 5876 on the one hand and Hα and Hβ on the other hand. We interpret this behaviour in a two-step disk growth scenario, where the disk first expands radially before its density increases. A difference in behaviour is also seen between Hα and the H I Paschen lines, with the latter displaying a more symmetric cycle, similar to the photometric variability. The rather fast decays of the Hα emission observed in 2001, 2009 and 2018 - 2019 suggest that the strong radiation field and early spectral type of the star lead to a faster dissipation of the disk than in later-type Be stars, as theoretically expected. We discuss X-ray observations of the star both during a high and a low- emission state. The X-ray spectrum is soft at both epochs, and the X-ray fluxes are only marginally different and remain consistent with the canonical L[SUB]X[/SUB]/L[SUB]bol[/SUB] relation of O-type stars. These results indicate that the circumstellar decretion disk of HD 60 848 has essentially no impact on the star's X-ray emission, and that the latter most likely arises inside the stellar wind.
Disciplines :
Space science, astronomy & astrophysics
Author, co-author :
Rauw, Grégor  ;  Université de Liège - ULiège > Groupe d'astrophysique des hautes énergies (GAPHE)
Nazé, Yaël  ;  Université de Liège - ULiège > Groupe d'astrophysique des hautes énergies (GAPHE)
Campos, Fran;  Observatori Puig d'Agulles, Passatge Bosc 1, Vallirana 08759, Barcelona, Spain
Fló, Joan Guarro;  Observatori de Piera, Balmes, 2, 08784 Piera, Barcelona, Spain
Sollecchia, Umberto;  Via dei Malatesta 10, L'Aquila 67100, Italy)
Language :
English
Title :
Irregular emission cycles in the Oe star HD 60 848
Publication date :
01 February 2021
Journal title :
New Astronomy
ISSN :
1384-1076
eISSN :
1384-1092
Publisher :
Elsevier, Netherlands
Volume :
83
Pages :
101462 (14p)
Peer reviewed :
Peer Reviewed verified by ORBi
Available on ORBi :
since 08 October 2020

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