Mauricio Tapia,1 Luis F. Rodríguez,2,4 Gagik Tovmassian,1 Vicente Rodríguez-Gómez,3 Diego González-Buitrago,1 Sergei Zharikov,1 and Gisela N. Ortiz-León2
1 Instituto de Astronomía, Universidad Nacional Autónoma de México, Apdo. Postal 877, Ensenada, Baja California, C.P. 22830, Mexico. (mt@astrosen.unam.mx, gag@astrosen.unam.mx, zhar@astrosen.unam.mx).
2 Centro de Radiostronomía y Astrofísica, Universidad Nacional Autónoma de México, Apdo. Postal 3-72, (Xangari), C.P. 58089 Morelia, Michoacán, Mexico. (g.ortiz@crya.unam.mx).
3 Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138, USA.
4 Astronomy Department, Faculty of Science, King Abdulaziz University, P.O. Box 80203, Jeddah 21589, Saudi Arabia. (l.rodriguez@crya.unam.mx).
]]> Received 2013 August 27.
RESUMEN
Presentamos fotometría y espectroscopía de mediana resolución de V2187 Cyg. Confirmamos que es una estrella tipo β Cephei de tipo espectral B2-3 V. Tiene variaciones sinusoidales con un período de 0.2539 días y amplitudes medias de 0.037 y 0.042 magnitudes en i y V, respectivamente. No encontramos evidencia de variaciones en los perfiles de líneas de absorción en escalas de tiempo de horas o días y tampoco líneas de emisión. Reportamos también la sorpresiva detección de emisión de radiocontinuo de esta estrella con un espectro térmico. La emisión de radio presenta variaciones con un periodo de 12.8 días. Del archivo del Very Large Array encontramos que ninguna de las otras 15 estrellas de tipo β Cephei que han sido observadas con este instrumento muestra emisión de radio detectable, aunque muchas de ellas se encuentran mucho más cercanas al Sol que V2187 Cyg. La emisión de radio es, entonces, un fenómeno extremadamente raro en las estrellas tipo β Cephei.
ABSTRACT
We present new optical time-resolved photometry and medium-resolution spectroscopy of V2187 Cyg. We confirm its classification as a β Cephei star based on sinusoidal light variations with a period of 0.2539 days and mean amplitudes of 0.037 and 0.042 magnitudes in i and V, respectively. We classified the spectrum of this star as B2-3 V with no evidence of variations in the profiles of its absorption lines in timescales of hours or days. The stellar spectrum is totally absent of emission lines. We detected unexpected faint radio continuum emission (between 0.4 and 0.8 mJy at 6-cm) showing a sinusoidal variation with a period of 12.8 days. The radio spectrum is thermal. We searched in the Very Large Array archive for radio continuum emission toward 15 other β Cephei stars. None of these additional stars, some of them much closer to the Sun than V2187 Cyg, was detected, indicating that radio emission from β Cephei stars is extremely uncommon.
Key Words: radio continuum: stars — stars: individual (V1287 Cyg, β Cephei).
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ACKNOWLEDGMENTS
LFR acknowledges the support of DGAPA-UNAM, and of CONACyT (México). MT acknowledges the support from grant PAPIIT/DGAPA IN-101813. GT, SZ and DGB are supported by CONACyT grant 166376 and PAPIIT/DGAPA projects IN-107712 and IN-103912. This research has made use of the SIMBAD database, operated at CDS, Strasbourg, France.
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