New insights into the nature of the SMC WR/LBV Binary HD 5980¹

 

C. Foellmi,² G. Koenigsberger,³ L. Georgiev,⁴ O. Toledano,³ S. V. Marchenko, ⁵ P. Massey,⁶ T. H. Dall, ⁷ A. F. J. Moffat,⁸ N. Morrell,⁹ M. Corcoran,^10,11 A. Kaufer,¹² Y. Nazé,¹³ J. Pittard,¹⁴ N. St.–Louis,⁸ A. Fullerton,¹⁵ D. Massa,¹⁶ and A. M. T. Pollock,¹⁷

 

¹ Based on observations made with the NTT, MPI 2.2 m and Danish 1.5 m telescopes at ESO, La Silla, Chile.

² Laboratoire d'AstrOphysique de Grenoble, 414 Rue de la Piscine, Domaine Universitaire, 38400 Saint–Martin d'Héres, France (cedric.foellmi@obs.ujf-grenoble.fr)

³ Instituto de Ciencias Físicas, Universidad Nacional Autónoma de México, Av. Universidad s/n, Col. Chamilpa, Cuernavaca, Morelos, 62210, Mexico (gloria@fis.unam.mx, oswaldo–toledano@hotmail.com

⁴ Instituto de Astronomía, Universidad Nacional Autónoma de México, Apdo. Postal 70–264, 04510 México, D. F., Mexico (georgiev@astroscu.unam.mx)

⁵ Department of Physics and Astronomy, Western Kentucky University, 1906 College Heights Blvd #11001, Bowling Green, KY 42101–1101, USA (sergey@astro.wku.edu)

⁶ Lowell Observatory, 1400 W Mars Hill Road, Flagstaff, AZ, 86001, USA (Phil.Massey@lowell.edu)

⁷ Gemini Observatory, 670 N. A'ohoku Pl., Hilo, HI 96720, USA (tdall@gemini.edu)

⁸ Département de Physique, Université de Montréal, Quebec, Canada.St.–Louis: C.P. 6128, Succ. Centre–Ville, Montréal, QuebecC, H3C 3J7, and Observatoire du Mont Mégamtic, Canada (moffat@astro.umontreal.ca, st–louis@astro.umontreal.ca)

⁹ Las Campanas Observatory, Carnegie Observatories, Casilla 601, La Serena, Chile (nidia@lcoeps1.lco.cl; nidia@fcaglp.unlp.edu.ar

¹⁰ CRESST and X–ray Astrophysics Laboratory NASA/GSFC, Greenbelt, MD 20771, USA and Universities Space Research Association, 10211 Wincopin Circle, Suite 500 Columbia, MD 21044, USA (Michael.F.Corcoran.1@gsfc.nasa.gov)

¹¹ Universities Space Research Association, MD, USA. 10211 Wincopin Circle, Suite 500 Columbia, MD 21044, USA (Michael.F.Corcoran.1@gsfc.nasa.gov).

¹² European Southern Observatory, Santiago, Chile. Alonso de Cordova 3107, Casilla 19001, Santiago 19, Chile (akaufer@eso.org)

¹³ FNRS and Institut d'Astrophysique et de Géophysique, Université de Liège, Belgium. Allée du 6 Août 17, Bat B5C, B4000–Liège, Belgium (naze@astro.ulg.ac.be)

¹⁴ School of Physics and Astronomy, University of Leeds, UK. jmp@ast.leeds.ac.uk

¹⁵ Space Telescope Science Institute, MD, USA. 3700 San Martin Drive, Baltimore, MD 21218, USA (fullerton@stsci.edu)

¹⁶ NASA/GSFC, MD, USA. Mailstop 665.0, Greenbelt, MD 20771, USA (massa@taotaomona.gsfc.nasa.gov)

¹⁷ European Space Agency, XMM–Newton SOC, European Space Astronomy Centre, Apdo. 78, 28691 Villanueva de la Cañada, Madrid, Spain (Andy.Pollock@sciops.esa.int)

 

Received 2007 July 6
Accepted 2007 October 1

 

RESUMEN

Presentamos los resultados de una campaña de observaciones ópticas del sistema múltiple HD 5980, cuya estrella primaria sufrió una erupción importante en 1994. Atribuyendo la variabilidad de las líneas en emisión al movimiento orbital de las dos estrellas con un período de 19.3 días, deducimos sus masas. El comportamiento de las líneas fotosféricas indica que la fuente de "tercera luz" del sistema es probablemente también un sistema binario como fue propuesto por Schweickhardt (2000). Los datos presentados en este artículo estarán públicamente disponibles.

 

ABSTRACT

We present the results of optical wavelength observations of the unusual SMC eclipsing binary system HD 5980 obtained in 1999 and 2004–2005. Radial velocity curves for the erupting LBV/WR object (star A) and its close WR–like companion (star B) are obtained by deblending the variable emission–line profiles of NIV and NV lines. The derived masses M_A = 58 – 79 M and M_B = 51 – 67 M, are more consistent with the the stars' location near the top of the HRD than previous estimates. The presence of a wind–wind interaction region is inferred from the orbital phase–dependent behavior of He I P Cygni absorption components. The emission–line intensities continued with the declining trend previously seen in UV spectra. The behavior of the photospheric absorption lines is consistent with the results of Schweickhardt (2000) who concludes that the third object in the combined spectrum, star C, is also a binary system with P_starC96.5 days, e=0.83.

Key Words: binaries: close — stars: individual (HD 5980) — stars: mass loss

 

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