Wind Structure of the Wolf–Rayet Star EZ CMa = HD 50896
Aaron Flores,1 Gloria Koenigsberger,2 Octavio Cardona,3 and Lelio de la Cruz1
1 Facultad de Ingeniería, Universidad Autónoma del Carmen, Calle 56, 4. Cd. del Carmen, Campeche, Mexico (aflores, ldelacruz@pampano.unacar.mx).
2 Instituto de Ciencias Físicas, Universidad Nacional Autónoma de México, Ave. Universidad S/N, Col. Chamilpa, Cuernavaca 62210, Mexico (gloria@fis.unam.mx).
3 Instituto Nacional de Astrofísica Óptica y Electrónica, Luis Enrique Erro 1, Tonantzintla, Puebla, Mexico. (ocardona@inaoep.mx).
Received 2011 March 22 ]]> Accepted 2011 May 9
RESUMEN
Presentamos los resultados del analisis de la línea de N V 4604 observada en espectros de la estrella Wolf–Rayet HD 50896 obtenidos en 1991, 1999, 2005 y 2009. Mostramos que la variabilidad de esta línea es consistente con un modelo en el que la opacidad del viento sufre cambios cíclicos con un periodo de 3.76 d o bien con un modelo de un viento con estructura cuadrupolar donde cada sector tiene una opacidad distinta.
ABSTRACT
The Wolf–Rayet star HD 50896 (EZ CMa=WR6) is well–known for the emission–line profile variability that occurs on a 3.7–day timescale. In particular, the shape of the N V 4604–21 doublet changes from a P Cygni profile to one in which no blue–shifted absorption component is present. In this paper we use spectroscopic observations obtained in 1991, 1999, 2005 and 2009 to glean physical conditions within the stellar wind that may give rise to these changes. We find that variations in the opacity at a distance r/Rmax ~ 0.3–0.5 of the stellar surface can produce the observed effects. Here, Rmax is the extent of the N V line–forming region. The results are consistent either with a scenario in which the opacity of the inner wind region of HD 50896 undergoes cyclical variations over the 3.76 d period or with a quadrupolar wind distribution in which the sectors having different opacities rotate in and out of our line–of–sight on this periodic timescale.
Key Words: stars: individual (EZ CMa = HD 50896) — stars: winds, outflows — stars: Wolf–Rayet.
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]]>ACKNOWLEDGMENTS
GK acknowledges support from PAPIIT/Universidad Nacional Autónoma de Mexico grant and computing support from Ulises Amaya. AF acknowledges the sabbatical stay in the INAOE and support from Conacyt under the target financed project 121166 "Spectroscopy Variations of Wolf–Rayet Stars", and by the UNACAR grant 1320.
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