@article{JaervinenHubrigIlyinetal.2017, author = {Jaervinen, S. P. and Hubrig, Swetlana and Ilyin, Ilya and Shenar, Tomer and Schoeller, M.}, title = {A search for spectral variability in the highly magnetized O9.7 V star HD 54879}, series = {Astronomische Nachrichten = Astronomical notes}, volume = {338}, journal = {Astronomische Nachrichten = Astronomical notes}, publisher = {Wiley-VCH}, address = {Weinheim}, issn = {0004-6337}, doi = {10.1002/asna.201713402}, pages = {952 -- 958}, year = {2017}, abstract = {The O9.7 V star HD 54879 possesses the second strongest magnetic field among the single, magnetic, O-type stars. In contrast to other magnetic O-type stars, the chemical abundance analysis of HD 54879 indicated a rather normal optical spectrum without obvious element enhancements or depletions. Furthermore, spectral variability was detected only in lines partly formed in the magnetosphere. As this star shows such a deviate, almost nonvariable, spectral behavior, we performed a deeper analysis of its spectral variability on different timescales using all currently available HARPSpol and FORS 2 spectropolarimetric observations. The longitudinal magnetic field strengths measured at different epochs indicate the presence of variability possibly related to stellar rotation, but the current data do not allow us yet to identify the periodicity of the field variation. As spectropolarimetric observations obtained at different epochs consist of subexposures with different integration times, we investigated spectral variability on timescales of minutes. The detected level of variability in line profiles of different elements is rather low, between 0.2 and 1.7\%, depending on the integration time of the exposures and the considered element.}, language = {en} } @article{ShenarOskinovaJaervinenetal.2017, author = {Shenar, Tomer and Oskinova, Lida and Jaervinen, S. P. and Luckas, P. and Hainich, Rainer and Todt, Helge Tobias and Hubrig, Swetlana and Sander, Andreas Alexander Christoph and Ilyin, Ilya and Hamann, Wolf-Rainer}, title = {Constraining the weak-wind problem}, series = {Contributions Of The Astronomical Observatory Skalnate Pleso}, volume = {48}, journal = {Contributions Of The Astronomical Observatory Skalnate Pleso}, number = {1}, publisher = {Astronomick{\´y} {\´U}stav SAV}, address = {Tatransk{\´a} Lomnica}, issn = {1335-1842}, doi = {10.1051/0004-6361/201731291}, pages = {139 -- 143}, year = {2017}, abstract = {Mass-loss rates of massive, late type main sequence stars are much weaker than currently predicted, but their true values are very difficult to measure. We suggest that confined stellar winds of magnetic stars can be exploited to constrain the true mass-loss rates M of massive main sequence stars. We acquired UV, X-ray, and optical amateur data of HD 54879 (09.7 V), one of a few O-type stars with a detected atmospheric magnetic field (B-d greater than or similar to 2 kG). We analyze these data with the Potsdam Wolf-Rayet (PoWR) and XSPEC codes. We can roughly estimate the mass-loss rate the star would have in the absence of a magnetic field as log M-B=0 approximate to -9.0 M-circle dot yr(-1). Since the wind is partially trapped within the Alfven radius rA greater than or similar to 12 R-*,, the true mass-loss rate of HD 54879 is log M less than or similar to -10.2 M-circle dot yr(-1). Moreover, we find that the microturbulent, macroturbulent, and projected rotational velocities are lower than previously suggested (< 4 km s(-1)). An initial mass of 16 M-circle dot and an age of 5 Myr are inferred. We derive a mean X-ray emitting temperature of log T-x = 6.7 K and an X-ray luminosity of log L-x = 32 erg s(-1). The latter implies a significant X-ray excess (log L-x/L-Bol approximate to - 6.0), most likely stemming from collisions at the magnetic equator. A tentative period of P approximate to 5 yr is derived from variability of the Ha line. Our study confirms that strongly magnetized stars lose little or no mass, and supplies important constraints on the weak-wind problem of massive main sequence stars.}, language = {en} } @article{SchoellerHubrigFossatietal.2017, author = {Sch{\"o}ller, Markus and Hubrig, Swetlana and Fossati, L. and Carroll, Thorsten Anthony and Briquet, Maryline and Oskinova, Lida and J{\"a}rvinen, S. and Ilyin, Ilya and Castro, N. and Morel, T. and Langer, N. and Przybilla, N. and Nieva, M. -F. and Kholtygin, A. F. and Sana, H. and Herrero, A. and Barba, R. H. and de Koter, A.}, title = {B fields in OB stars (BOB)}, series = {Astronomy and astrophysics : an international weekly journal}, volume = {599}, journal = {Astronomy and astrophysics : an international weekly journal}, publisher = {EDP Sciences}, address = {Les Ulis}, organization = {BOB Collaboration}, issn = {1432-0746}, doi = {10.1051/0004-6361/201628905}, pages = {11}, year = {2017}, abstract = {Aims. The B fields in OB stars (BOB) Collaboration is based on an ESO Large Programme to study the occurrence rate, properties, and ultimately the origin of magnetic fields in massive stars. Methods. In the framework of this program, we carried out low-resolution spectropolarimetric observations of a large sample of massive stars using FORS2 installed at the ESO VLT 8m telescope. Results. We determined the magnetic field values with two completely independent reduction and analysis pipelines. Our in-depth study of the magnetic field measurements shows that differences between our two pipelines are usually well within 3 sigma errors. From the 32 observations of 28 OB stars, we were able to monitor the magnetic fields in CPD -57 degrees 3509 and HD164492C, confirm the magnetic field in HD54879, and detect a magnetic field in CPD -62 degrees 2124. We obtain a magnetic field detection rate of 6 +/- 3\% for the full sample of 69 OB stars observed with FORS 2 within the BOB program. For the preselected objects with a nu sin i below 60 km s(-1), we obtain a magnetic field detection rate of 5 +/- 5\%. We also discuss X-ray properties and multiplicity of the objects in our FORS2 sample with respect to the magnetic field detections.}, language = {en} }