EDP Sciences
Free access
Volume 414, Number 2, February I 2004
Page(s) 591 - 600
Section Stellar atmospheres
DOI http://dx.doi.org/10.1051/0004-6361:20031689

A&A 414, 591-600 (2004)
DOI: 10.1051/0004-6361:20031689

Polarimetric evolution of V838 Monocerotis

S. Desidera1, E. Giro1, U. Munari2, Y. S. Efimov3, A. Henden4, S. Benetti1, T. Tomov5, A. Bianchini6 and C. Pernechele1

1  INAF - Osservatorio Astronomico di Padova, Vicolo dell' Osservatorio 5, 35122, Padova, Italy
2  INAF - Osservatorio Astronomico di Padova - Sede di Asiago, 36012, Asiago, Italy
3  Crimean Astrophysical Observatory and Isaac Newton Institute of Chile, Crimean Branch, Ukraine
4  Universities Space Research Association/US Naval Observatory Flagstaff Station, PO Box 1149, Flagstaff AZ 86002-1149, USA
5  Centre for Astronomy Nicholaus Copernicus University, ul. Gagarina 11, 87-100 Torun, Poland
6  Universitá di Padova, Dipartimento di Astronomia, Vicolo dell'Osservatorio 2, 35122, Padova, Italy

(Received 28 April 2003 / Accepted 30 September 2003)

We present the results of our polarimetric and spectropolarimetric monitoring of V838 Monocerotis, performed at the Asiago and Crimean observatories during and after the multiple outbursts that occurred in January-March 2002. The polarization of the object is mainly due to interstellar polarization ( $P\sim 2.48$%). Intrinsic polarization up to $\sim $0.7% at 5000 Å is present during the second maximum of the object (February 2002). This intrinsic component increases toward shorter wavelengths but our limited spectral coverage (5000-7500 Å) does not allow conclusive inferences about its origin. A strong depolarization across the H $_{\alpha}$ profile is observed. The interstellar polarization gives a lower limit to the reddening of E(B-V) >0.28, with $E(B-V)\sim 0.5$ being the most probable value. A normal ratio of total to selective absorption ( $R_{V}=3.22\pm0.17$) was derived from the wavelength of maximum interstellar polarization. This suggests a low (if any) contribution by circumstellar material with a peculiar dust to gas ratio. A polarimetric map of a portion of the light echo shows a complex polarization distribution reaching $P_{\max}=45$%.

Key words: stars: individual: V838Mon -- techniques: polarimetric -- stars: peculiar (except chemically peculiar)

Offprint request: S. Desidera, desidera@pd.astro.it

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