Multiperiodicity in the newly discovered mid-late Be star V2104 Cygni

Free access article

Issue		A&A Volume 470, Number 3, August II 2007


Page(s)		1051 - 1057
Section		Stellar structure and evolution
DOI		http://dx.doi.org/10.1051/0004-6361:20077657

A&A 470, 1051-1057 (2007)
DOI: 10.1051/0004-6361:20077657

Multiperiodicity in the newly discovered mid-late Be star V2104 Cygni

K. Uytterhoeven¹, E. Poretti¹, E. Rodríguez², P. De Cat³, P. Mathias⁴, J. H. Telting⁵, V. Costa², and A. Miglio⁶

¹ INAF-Osservatorio Astronomico di Brera, via E. Bianchi 46, 23807 Merate
    e-mail: [katrien.uytterhoeven;ennio.poretti]@brera.inaf.it
² Instituto de Astrofísica de Andalucía (CSIC), Apartado 3004, 18080 Granada, Spain
    e-mail: [eloy;victor]@iaa.es
³ Royal Observatory of Belgium, Ringlaan 3, 1180 Brussel, Belgium
    e-mail: peter@oma.be
⁴ Observatoire de la Côte d'Azur, GEMINI, CNRS, Université Nice Sophia-Antipolis, BP 4229, 06304 Nice Cedex 4, France
    e-mail: Philippe.Mathias@oca.eu
⁵ Nordic Optical Telescope, Apartado 474, 38700 Santa Cruz de La Palma, Spain
    e-mail: jht@not.iac.es
⁶ Institut d'Astrophysique et de Géophysique de l'Université de Liège, Allée du 6 Août 17, 4000 Liège, Belgium
    e-mail: a.miglio@ulg.ac.be

(Received 17 April 2007 / Accepted 15 May 2007)

Abstract
Aims.We obtained the first long, homogenous time-series of V2104 Cyg, consisting of 679 datapoints, with the $uvby\beta$ photometers of the Sierra Nevada and San Pedro Mártir Observatories. Our aim was to detect and subsequently interpret the intrinsic frequencies of this previously unstudied variable star, which turned out to be a Be star. We evaluate its place among the variable B stars on the upper Main Sequence. To obtain additional information on physical parameters we collected a few spectra with the Elodie and FIES instruments.
Methods.We searched for frequencies in the uvby passbands using 2 different frequency analysis methods and used the S/N > 4 criterion to select the significant periodicities. We obtained an estimate of the physical parameters of the underlying B star of spectral type between B5 and B7, by correcting for the presence of a circumstellar disk using a formalism based on the strength of the H $\alpha$ line emission.
Results.We detected 3 independent frequencies with amplitudes below 0.01 mag, $\nu_1$ = 4.7126 d^-1 , $\nu_2$ = 2.2342 d^-1 and $\nu_3$ = 4.671 d^-1 , and discovered that V2104 Cyg is a Be star. The fast rotation ( $v\sin i$ = 290 $\pm$ 10 km s^-1, and 27°< i < 45°) hampered the investigation of the associated pulsational parameters $\ell$ .
Conclusions.The most plausible explanation for the observed variability of this mid-late type Be star is a non-radial pulsation model.

Key words: stars: oscillations -- stars: emission-line, Be -- stars: individual: V2104 Cyg

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