Astronomy and Astrophysics – Astrophysics
Scientific paper
Apr 1994
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1994a%26a...284..491l&link_type=abstract
Astronomy and Astrophysics (ISSN 0004-6361), vol. 284, no. 2, p. 491-498
Astronomy and Astrophysics
Astrophysics
10
Linear Polarization, Magnetic Stars, Magnetic Variations, Periodic Variations, Stellar Magnetic Fields, Stellar Models, A Stars, Spectrum Analysis, Stellar Envelopes, Stellar Rotation
Scientific paper
We have discovered that the magnetic variable 49 Cam displays a remarkable linear polarization, with periodic variations larger than those of other Ap stars. The time variation of the Stokes parameters has been established with good accuracy for the standard B band and additional measurements in the U and V bands already give some insight into the spectral variation of the polarization. 49 Cam is expected to be closer than about 50 pc and its polarization, like that of most neighboring stars, suffers little contamination from the interstellar polarization. The hypothetical presence of continum polarization due to a circumstellar shell seems unlikely, given both the spectral dependence of the polarization and the negative result of our polarimetry bearing on several A-shell stars. Therefore, we think that the polarization of 49 Cam has to be understood, as for the other Ap stars, as the result of magnetic intensification in spectral lines. The interpretation of the polarization variation is much easier if one knows the magnetic phase derived from the classical longitudinal magnetic field measurements. The specific shape of the linear polarization diagram makes it difficult to interpret our observations in the customary framework of the oblique rotating dipole. Modifications of this model are necessary. One can reproduce fairly well the variations of the polarization of 49 Cam if the magnetic signal is not symmetrical with respect to the magnetic axis and has some peculiarities in the polar regions. The problem is not to find a magnetic solution but rather that there are too many possible solutions. While we cannot claim that we have already found a firm model for 49 Cam, there are serious guidelines for progress of the interpretation. In any case, it is clear that this star is one of the most peculiar objects among the 40 Ap stars considered in our investigation.
Bagnulo Stefano
Landstreet John Darlington
Leroy Jean-Louis
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