Searching for a magnetic field in Wolf-Rayet stars using FORS2 spectropolarimetry
Autor: | Markus Schöller, Lidia M. Oskinova, K. G. Gayley, Ilya Ilyin, Wolf-Rainer Hamann, Richard Ignace, K. Scholz, Swetlana Hubrig |
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Jazyk: | angličtina |
Rok vydání: | 2016 |
Předmět: |
Rotation period
Physics 010308 nuclear & particles physics Linear polarization Institut für Physik und Astronomie Astronomy FOS: Physical sciences Astronomy and Astrophysics Astrophysics 01 natural sciences Galaxy Stars Wolf–Rayet star Astrophysics - Solar and Stellar Astrophysics Space and Planetary Science 0103 physical sciences Variable star Large Magellanic Cloud 010303 astronomy & astrophysics Circular polarization Solar and Stellar Astrophysics (astro-ph.SR) |
Popis: | To investigate if magnetic fields are present in Wolf-Rayet stars, we selected a few stars in the Galaxy and one in the Large Magellanic Cloud (LMC). We acquired low-resolution spectropolarimetric observations with the ESO FORS2 instrument during two different observing runs. During the first run in visitor mode, we observed the LMC Wolf-Rayet star BAT99 7 and the stars WR6, WR7, WR18, and WR23 in our Galaxy. The second run in service mode was focused on monitoring the star WR6. Linear polarization was recorded immediately after the observations of circular polarization. During our visitor observing run, the magnetic field for the cyclically variable star WR6 was measured at a significance level of 3.3sigma ( = 258+-78G). Among the other targets, the highest value for the longitudinal magnetic field, = 327+-141G, was measured in the LMC star BAT99 7. Spectropolarimetric monitoring of the star WR6 revealed a sinusoidal nature of the variations with the known rotation period of 3.77d, significantly adding to the confidence in the detection. The presence of the rotation-modulated magnetic variability is also indicated in our frequency periodogram. The reported field magnitude suffers from significant systematic uncertainties at the factor 2 level, in addition to the quoted statistical uncertainties, owing to the theoretical approach used to characterize it. Linear polarization measurements showed no line effect in the stars, apart from WR6. BAT99 7, WR7, and WR,23 do not show variability of the linear polarization over two nights. Comment: 14 pages, 6 tables, 14 figures, accepted for publication in MNRAS |
Databáze: | OpenAIRE |
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