@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}
}
@article{SchoellerHubrigIlyinetal.2011,
  author    = {Schoeller, M. and Hubrig, Swetlana and Ilyin, Ilya and Kharchenko, N. V. and Briquet, Maryline and Gonzalez, J. F. and Langer, Norbert and Oskinova, Lida},
  title     = {Magnetic field studies of massive main sequence stars},
  series = {Astronomische Nachrichten = Astronomical notes},
  volume    = {332},
  journal   = {Astronomische Nachrichten = Astronomical notes},
  number    = {9-10},
  publisher = {Wiley-Blackwell},
  address   = {Malden},
  organization    = {MAGORI Collaboration},
  issn      = {0004-6337},
  doi       = {10.1002/asna.201111606},
  pages     = {994 -- 997},
  year      = {2011},
  abstract  = {We report on the status of our spectropolarimetric observations of massive stars. During the last years, we have discovered magnetic fields in many objects of the upper main sequence, including Be stars, beta Cephei and Slowly Pulsating B stars, and a dozen O stars. Since the effects of those magnetic fields have been found to be substantial by recent models, we are looking into their impact on stellar rotation, pulsation, stellar winds, and chemical abundances. Accurate studies of the age, environment, and kinematic characteristics of the magnetic stars are also promising to give us new insight into the origin of the magnetic fields. Furthermore, longer time series of magnetic field measurements allow us to observe the temporal variability of the magnetic field and to deduce the stellar rotation period and the magnetic field geometry. Studies of the magnetic field in massive stars are indispensable to understand the conditions controlling the presence of those fields and their implications on the stellar physical parameters and evolution.},
  language  = {en}
}
@article{PrzybillaFossatiHubrigetal.2016,
  author    = {Przybilla, Norbert and Fossati, Luca and Hubrig, Swetlana and Nieva, M. -F. and Jaervinen, S. P. and Castro, Norberto and Schoeller, M. and Ilyin, Ilya and Butler, Keith and Schneider, F. R. N. and Oskinova, Lida and Morel, T. and Langer, N. and de Koter, A.},
  title     = {B fields in OB stars (BOB): Detection of a magnetic field in the He-strong star CPD-57 degrees 3509},
  series = {Organic letters},
  volume    = {587},
  journal   = {Organic letters},
  publisher = {EDP Sciences},
  address   = {Les Ulis},
  organization    = {BOB Collaboratio},
  issn      = {1432-0746},
  doi       = {10.1051/0004-6361/201527646},
  pages     = {15},
  year      = {2016},
  abstract  = {Methods. Spectropolarimetric observations with FORS2 and HARPSpol are analysed using two independent approaches to quantify the magnetic field strength. A high-S/N FLAMES/GIRAFFE spectrum is analysed using a hybrid non-LTE model atmosphere technique. Comparison with stellar evolution models constrains the fundamental parameters of the star. Results. We obtain a firm detection of a surface averaged longitudinal magnetic field with a maximum amplitude of about 1 kG. Assuming a dipolar configuration of the magnetic field, this implies a dipolar field strength larger than 3.3 kG. Moreover, the large amplitude and fast variation (within about 1 day) of the longitudinal magnetic field implies that CPD-57 degrees 3509 is spinning very fast despite its apparently slow projected rotational velocity. The star should be able to support a centrifugal magnetosphere, yet the spectrum shows no sign of magnetically confined material; in particular, emission in H alpha is not observed. Apparently, the wind is either not strong enough for enough material to accumulate in the magnetosphere to become observable or, alternatively, some leakage process leads to loss of material from the magnetosphere. The quantitative spectroscopic analysis of the star yields an effective temperature and a logarithmic surface gravity of 23 750 +/- 250 K and 4.05 +/- 0.10, respectively, and a surface helium fraction of 0.28 +/- 0.02 by number. The surface abundances of C, N, O, Ne, S, and Ar are compatible with the cosmic abundance standard, whereas Mg, Al, Si, and Fe are depleted by about a factor of 2. This abundance pattern can be understood as the consequence of a fractionated stellar wind. CPD-57 degrees 3509 is one of the most evolved He-strong stars known with an independent age constraint due to its cluster membership.},
  language  = {en}
}
@misc{MorelCastroFossatietal.2014,
  author    = {Morel, T. and Castro, Norberto and Fossati, Luca and Hubrig, Swetlana and Langer, N. and Przybilla, Norbert and Sch{\"o}ller, Markus and Carroll, Thorsten Anthony and Ilyin, Ilya and Irrgang, Andreas and Oskinova, Lida and Schneider, Fabian R. N. and Simon D{\´i}az, Sergio and Briquet, Maryline and Gonz{\´a}lez, Jean-Francois and Kharchenko, Nina and Nieva, M.-F. and Scholz, Ralf-Dieter and de Koter, Alexander and Hamann, Wolf-Rainer and Herrero, Artemio and Ma{\´i}z Apell{\´a}niz, Jesus and Sana, Hugues and Arlt, Rainer and Barb{\´a}, Rodolfo H. and Dufton, Polly and Kholtygin, Alexander and Mathys, Gautier and Piskunov, Anatoly E. and Reisenegger, Andreas and Spruit, H. and Yoon, S.-C.},
  title     = {The B fields in OB stars (BOB) survey},
  series = {Postprints der Universit{\"a}t Potsdam : Mathematisch-Naturwissenschaftliche Reihe},
  journal   = {Postprints der Universit{\"a}t Potsdam : Mathematisch-Naturwissenschaftliche Reihe},
  number    = {821},
  issn      = {1866-8372},
  doi       = {10.25932/publishup-41523},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-415238},
  pages     = {8},
  year      = {2014},
  abstract  = {The B fields in OB stars (BOB) survey is an ESO large programme collecting spectropolarimetric observations for a large number of early-type stars in order to study the occurrence rate, properties, and ultimately the origin of magnetic fields in massive stars. As of July 2014, a total of 98 objects were observed over 20 nights with FORS2 and HARPSpol. Our preliminary results indicate that the fraction of magnetic OB stars with an organised, detectable field is low. This conclusion, now independently reached by two different surveys, has profound implications for any theoretical model attempting to explain the field formation in these objects. We discuss in this contribution some important issues addressed by our observations (e.g., the lower bound of the field strength) and the discovery of some remarkable objects.},
  language  = {en}
}
@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{HubrigSchoellerKholtyginetal.2015,
  author    = {Hubrig, Swetlana and Sch{\"o}ller, Markus and Kholtygin, Alexander F. and Tsumura, Hiroki and Hoshino, Akio and Kitamoto, Shunji and Oskinova, Lida and Ignace, Richard and Todt, Helge Tobias and Ilyin, Ilya},
  title     = {New multiwavelength observations of the Of?p star CPD-28 degrees 2561},
  series = {Monthly notices of the Royal Astronomical Society},
  volume    = {447},
  journal   = {Monthly notices of the Royal Astronomical Society},
  number    = {2},
  publisher = {Oxford Univ. Press},
  address   = {Oxford},
  issn      = {0035-8711},
  doi       = {10.1093/mnras/stu2516},
  pages     = {1885 -- 1894},
  year      = {2015},
  abstract  = {A rather strong mean longitudinal magnetic field of the order of a few hundred gauss was detected a few years ago in the Of?p star CPD -28 degrees 2561 using FORS2 (FOcal Reducer low dispersion Spectrograph 2) low-resolution spectropolarimetric observations. In this work, we present additional low-resolution spectropolarimetric observations obtained during several weeks in 2013 December using FORS 2 mounted at the 8-m Antu telescope of the Very Large Telescope (VLT). These observations cover a little less than half of the stellar rotation period of 73.41 d mentioned in the literature. The behaviour of the mean longitudinal magnetic field is consistent with the assumption of a single-wave variation during the stellar rotation cycle, indicating a dominant dipolar contribution to the magnetic field topology. The estimated polar strength of the surface dipole B-d is larger than 1.15 kG. Further, we compared the behaviour of the line profiles of various elements at different rotation phases associated with different magnetic field strengths. The strongest contribution of the emission component is observed at the phases when the magnetic field shows a negative or positive extremum. The comparison of the spectral behaviour of CPD -28 degrees 2561 with that of another Of?p star, HD 148937 of similar spectral type, reveals remarkable differences in the degree of variability between both stars. Finally, we present new X-ray observations obtained with the Suzaku X-ray Observatory. We report that the star is X-ray bright with log L-X/L-bol approximate to -5.7. The low-resolution X-ray spectra reveal the presence of a plasma heated up to 24 MK. We associate the 24 MK plasma in CPD -28 degrees 2561 with the presence of a kG strong magnetic field capable to confine stellar wind.},
  language  = {en}
}
@article{HubrigScholzHamannetal.2016,
  author    = {Hubrig, Swetlana and Scholz, Kathleen and Hamann, Wolf-Rainer and Schoeller, M. and Ignace, R. and Ilyin, Ilya and Gayley, K. G. and Oskinova, Lida},
  title     = {Searching for a magnetic field in Wolf-Rayet stars using FORS 2 spectropolarimetry},
  series = {Monthly notices of the Royal Astronomical Society},
  volume    = {458},
  journal   = {Monthly notices of the Royal Astronomical Society},
  publisher = {Oxford Univ. Press},
  address   = {Oxford},
  issn      = {0035-8711},
  doi       = {10.1093/mnras/stw558},
  pages     = {3381 -- 3393},
  year      = {2016},
  abstract  = {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 European Southern Observatory FORS 2 (FOcal Reducer low dispersion Spectrograph) 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 WR 6, WR 7, WR 18, and WR 23 in our Galaxy. The second run in service mode was focused on monitoring the star WR 6. Linear polarization was recorded immediately after the observations of circular polarization. During our visitor observing run, the magnetic field for the cyclically variable star WR 6 was measured at a significance level of 3.3 sigma (< B-z > = 258 +/- 78 G). Among the other targets, the highest value for the longitudinal magnetic field, < B-z > = 327 +/- 141 G, was measured in the LMC star BAT99 7. Spectropolarimetric monitoring of the star WR 6 revealed a sinusoidal nature of the < B-z > variations with the known rotation period of 3.77 d, 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 of 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 WR 6. BAT99 7, WR 7, and WR 23 do not show variability of the linear polarization over two nights.},
  language  = {en}
}
@article{HubrigSchoellerIlyinetal.2013,
  author    = {Hubrig, Swetlana and Schoeller, M. and Ilyin, Ilya and Kharchenko, N. V. and Oskinova, Lida and Langer, N. and Gonzalez, J. F. and Kholtygin, A. F. and Briquet, Maryline},
  title     = {Exploring the origin of magnetic fields in massive stars - II. New magnetic field measurements in cluster and field stars},
  series = {Astronomy and astrophysics : an international weekly journal},
  volume    = {551},
  journal   = {Astronomy and astrophysics : an international weekly journal},
  publisher = {EDP Sciences},
  address   = {Les Ulis},
  organization    = {MAGORI Collaboration},
  issn      = {0004-6361},
  doi       = {10.1051/0004-6361/201220721},
  pages     = {13},
  year      = {2013},
  abstract  = {Context. Theories on the origin of magnetic fields in massive stars remain poorly developed, because the properties of their magnetic field as function of stellar parameters could not yet be investigated. Additional observations are of utmost importance to constrain the conditions that are conducive to magnetic fields and to determine first trends about their occurrence rate and field strength distribution. Aims. To investigate whether magnetic fields in massive stars are ubiquitous or appear only in stars with a specific spectral classification, certain ages, or in a special environment, we acquired 67 new spectropolarimetric observations for 30 massive stars. Among the observed sample, roughly one third of the stars are probable members of clusters at different ages, whereas the remaining stars are field stars not known to belong to any cluster or association. Methods. Spectropolarimetric observations were obtained during four different nights using the low-resolution spectropolarimetric mode of FOcal Reducer low dispersion Spectrograph (FORS 2) mounted on the 8-m Antu telescope of the VLT. Furthermore, we present a number of follow-up observations carried out with the high-resolution spectropolarimeters SOFIN mounted at the Nordic Optical Telescope (NOT) and HARPS mounted at the ESO 3.6 m between 2008 and 2011. To assess the membership in open clusters and associations, we used astrometric catalogues with the highest quality kinematic and photometric data currently available. Results. The presence of a magnetic field is confirmed in nine stars previously observed with FORS 1/2: HD36879, HD47839, CPD-28 2561, CPD-47 2963, HD93843, HD148937, HD149757, HD328856, and HD164794. New magnetic field detections at a significance level of at least 3 sigma were achieved in five stars: HD92206c, HD93521, HD93632, CPD-46 8221, and HD157857. Among the stars with a detected magnetic field, five stars belong to open clusters with high membership probability. According to previous kinematic studies, five magnetic O-type stars in our sample are candidate runaway stars.},
  language  = {en}
}
@article{HubrigKholtyginIlyinetal.2016,
  author    = {Hubrig, Swetlana and Kholtygin, A. and Ilyin, Ilya and Sch{\"o}ller, M. and Oskinova, Lida},
  title     = {THE FIRST SPECTROPOLARIMETRIC MONITORING OF THE PECULIAR O4 Ief SUPERGIANT zeta PUPPIS},
  series = {The astrophysical journal : an international review of spectroscopy and astronomical physics},
  volume    = {822},
  journal   = {The astrophysical journal : an international review of spectroscopy and astronomical physics},
  publisher = {IOP Publ. Ltd.},
  address   = {Bristol},
  issn      = {0004-637X},
  doi       = {10.3847/0004-637X/822/2/104},
  pages     = {7},
  year      = {2016},
  abstract  = {The origin of the magnetic field in massive O-type stars is still under debate. To model the physical processes responsible for the generation of O star magnetic fields, it is important to understand whether correlations between the presence of a magnetic field and stellar evolutionary state, rotation velocity, kinematical status, and surface composition can be identified. The O4 Ief supergiant zeta Pup is a fast rotator and a runaway star, which may be a product of a past binary interaction, possibly having had an encounter with the cluster Trumper 10 some 2 Myr ago. The currently available observational material suggests that certain observed phenomena in this star may be related to the presence of a magnetic field. We acquired spectropolarimetric observations of zeta Pup with FORS 2 mounted on the 8 m Antu telescope of the Very Large Telescope to investigate if a magnetic field is indeed present in this star. We show that many spectral lines are highly variable and probably vary with the recently detected period of 1.78 day. No magnetic field is detected in zeta Pup, as no magnetic field measurement has a significance level higher than 2.4 sigma. Still, we studied the probability of a single sinusoidal explaining the variation of the longitudinal magnetic field measurements.},
  language  = {en}
}