Article (Scientific journals)
Tracing back the evolution of the candidate LBV HD 168625
Mahy, Laurent; Hutsemekers, Damien; Royer, P. et al.
2016In Astronomy and Astrophysics, 594, p. 94, pp. 1-13
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Keywords :
stars: massive; stars: mass-loss; stars: abundances; stars: individual: HD168625; circumstellar matter; stars: individual: HD168607
Abstract :
[en] Context. The luminous blue variable phase is a crucial transitory phase that is not clearly understood in the massive star evolution. <BR /> Aims: We have obtained far-infrared Herschel/PACS imaging and spectroscopic observations of the nebula surrounding the candidate LBV HD 168625. By combining these data with optical spectra of the central star, we want to constrain the abundances in the nebula and in the star and compare them to trace back the evolution of this object. <BR /> Methods: We use the CMFGEN atmosphere code to determine the fundamental parameters and the CNO abundances of the central star whilst the abundances of the nebula are derived from the emission lines present in the Herschel/PACS spectrum. <BR /> Results: The far-infrared images show a nebula composed of an elliptical ring/torus of ejecta with a ESE-WNW axis and of a second perpendicular bipolar structure composed of empty caps/rings. We detect equatorial shells composed of dust and ionized material with different sizes when observed at different wavelengths, and bipolar caps more of less separated from the central star in Hα and mid-IR images. This complex global structure seems to show two different inclinations: ~40° for the equatorial torus and ~ 60° for the bipolar ejections. From the Herschel/PACS spectrum, we determine nebular abundances of N/H = 4.1 ± 0.8 × 10[SUP]-4[/SUP] and , as well as a mass of ionized gas of 0.17 ± 0.04 M[SUB]⊙[/SUB] and a neutral hydrogen mass of about 1.0 ± 0.3 M[SUB]⊙[/SUB] which dominates. Analysis of the central star reveals T[SUB]eff[/SUB] = 14 000 ± 2000 K, log g = 1.74 ± 0.05 and log (L/L[SUB]⊙[/SUB]) = 5.58 ± 0.11. We derive stellar CNO abundances of about N/H = 5.0 ± 1.5 × 10[SUP]-4[/SUP], C/H = 1.4 ± 0.5 × 10[SUP]-4[/SUP] and O/H = 3.5 ± 1.0 × 10[SUP]-4[/SUP], not significantly different from nebular abundances. All these measurements taken together are compatible with the evolutionary tracks of a star with an initial mass between 28 and 33 M[SUB]⊙[/SUB] and with a critical rotational rate between 0.3 and 0.4 that has lost its material during or just after the blue supergiant phase. Based in part on observations taken by Herschel satellite. Herschel is an ESA space observatory with science instruments provided by European-led Principal Investigator consortia and with important participation from NASA.Based in part on observations collected at the European Southern Observatory, in Chile.
Disciplines :
Space science, astronomy & astrophysics
Author, co-author :
Mahy, Laurent ;  Université de Liège > Département d'astrophys., géophysique et océanographie (AGO) > Astroph. extragalactique et observations spatiales (AEOS)
Hutsemekers, Damien ;  Université de Liège > Département d'astrophys., géophysique et océanographie (AGO) > Astroph. extragalactique et observations spatiales (AEOS)
Royer, P.;  Instituut voor Sterrenkunde, KU Leuven, Celestijnenlaan 200D, Bus 2401, 3001, Leuven, Belgium
Waelkens, C.;  Instituut voor Sterrenkunde, KU Leuven, Celestijnenlaan 200D, Bus 2401, 3001, Leuven, Belgium)
Language :
English
Title :
Tracing back the evolution of the candidate LBV HD 168625
Publication date :
01 October 2016
Journal title :
Astronomy and Astrophysics
ISSN :
0004-6361
eISSN :
1432-0746
Publisher :
EDP Sciences, Les Ulis, France
Volume :
594
Pages :
A94, pp. 1-13
Peer reviewed :
Peer Reviewed verified by ORBi
Available on ORBi :
since 15 November 2016

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