TY  - JOUR
A1  - Castro, Norberto
A1  - Fossati, Luca
A1  - Hubrig, Swetlana
A1  - Simon Díaz, Sergio
A1  - Schoeller, Markus
A1  - Ilyin, Ilya
A1  - Carrol, Thorsten A.
A1  - Langer, Norbert
A1  - Morel, Thierry
A1  - Schneider, Fabian R. N.
A1  - Przybilla, Norbert
A1  - Herrero, Artemio
A1  - de Koter, Alex
A1  - Oskinova, Lida
A1  - Reisenegger, Andreas
A1  - Sana, Hugues
T1  - B fields in OB stars (BOB) Detection of a strong magnetic field in the O9.7 V star HD 54879
JF  - Astronomy and astrophysics : an international weekly journal
N2  - The number of magnetic stars detected among massive stars is small; nevertheless, the role played by the magnetic field in stellar evolution cannot be disregarded. Links between line profile variability, enhancements/depletions of surface chemical abundances, and magnetic fields have been identified for low-mass B-stars, but for the O-type domain this is almost unexplored. Based on FORS 2 and HARPS spectropolarimetric data, we present the first detection of a magnetic field in HD54879, a single slowly rotating O9.7 V star. Using two independent and different techniques we obtained the firm detection of a surface average longitudinal magnetic field with a maximum amplitude of about 600 G, in modulus. A quantitative spectroscopic analysis of the star with the stellar atmosphere code FASTWIND results in an effective temperature and a surface gravity of 33 000 +/- 1000K and 4.0 +/- 0.1 dex. The abundances of carbon, nitrogen, oxygen, silicon, and magnesium are found to be slightly lower than solar, but compatible within the errors. We investigate line-profile variability in HD54879 by complementing our spectra with spectroscopic data from other recent OB-star surveys. The photospheric lines remain constant in shape between 2009 and 2014, although H alpha shows a variable emission. The H alpha emission is too strong for a standard O9.7 V and is probably linked to the magnetic field and the presence of circumstellar material. Its normal chemical composition and the absence of photospheric line profile variations make HD54879 the most strongly magnetic, non-variable single O-star detected to date.
KW  - stars: atmospheres
KW  - stars: evolution
KW  - stars: magnetic field
KW  - stars: massive
KW  - stars: individual: HD 54879
Y1  - 2015
U6  - https://doi.org/10.1051/0004-6361/201425354
SN  - 1432-0746
VL  - 581
PB  - EDP Sciences
CY  - Les Ulis
ER  - 
TY  - JOUR
A1  - Fossati, Luca
A1  - Castro, Norberto
A1  - Morel, Thierry
A1  - Langer, Norbert
A1  - Briquet, Maryline
A1  - Carroll, Thorsten Anthony
A1  - Hubrig, Swetlana
A1  - Nieva, Maria-Fernanda
A1  - Oskinova, Lida
A1  - Przybilla, Norbert
A1  - Schneider, Fabian R. N.
A1  - Schoeller, Magnus
A1  - Simon Díaz, Sergio
A1  - Ilyin, Ilya
A1  - de Koter, Alex
A1  - Reisenegger, Andreas
A1  - Sana, Hugues
T1  - B fields in OB stars (BOB): on the detection of weak magnetic fields in the two early B-type stars beta CMa and epsilon CMa Possible lack of a "magnetic desert" in massive stars
JF  - Astronomy and astrophysics : an international weekly journal
N2  - Only a small fraction of massive stars seem to host a measurable structured magnetic field, whose origin is still unknown and whose implications for stellar evolution still need to be assessed. Within the context of the "B fields in OB stars (BOB)" collaboration, we used the HARPSpol spectropolarimeter to observe the early B-type stars beta CMa (HD 44743; B1 II/III) and epsilon CMa (HD 52089; B1.5II) in December 2013 and April 2014. For both stars, we consistently detected the signature of a weak (<30 G in absolute value) longitudinal magnetic field, approximately constant with time. We determined the physical parameters of both stars and characterise their X-ray spectrum. For the beta Cep star beta CMa, our mode identification analysis led to determining a rotation period of 13.6 +/- 1.2 days and of an inclination angle of the rotation axis of 57.6 +/- 1.7 degrees, with respect to the line of sight. On the basis of these measurements and assuming a dipolar field geometry, we derived a best fitting obliquity of about 22 degrees and a dipolar magnetic field strength (B-d) of about 100 G (60 < B-d < 230 G within the 1 sigma level), below what is typically found for other magnetic massive stars. This conclusion is strengthened further by considerations of the star's X-ray spectrum. For epsilon CMa we could only determine a lower limit on the dipolar magnetic field strength of 13 G. For this star, we determine that the rotation period ranges between 1.3 and 24 days. Our results imply that both stars are expected to have a dynamical magnetosphere, so the magnetic field is not able to support a circumstellar disk. We also conclude that both stars are most likely core hydrogen burning and that they have spent more than 2/3 of their main sequence lifetime. A histogram of the distribution of the dipolar magnetic field strength for the magnetic massive stars known to date does not show the magnetic field "desert" observed instead for intermediate-mass stars. The biases involved in the detection of (weak) magnetic fields in massive stars with the currently available instrumentation and techniques imply that weak fields might be more common than currently observed. Our results show that, if present, even relatively weak magnetic fields are detectable in massive stars and that more observational effort is probably still needed to properly access the magnetic field incidence.
KW  - stars: atmospheres
KW  - stars: evolution
KW  - stars: magnetic field
KW  - stars: individual: epsilon CMa
KW  - stars: individual: beta CMa
KW  - stars: massive
Y1  - 2015
U6  - https://doi.org/10.1051/0004-6361/201424986
SN  - 0004-6361
SN  - 1432-0746
VL  - 574
PB  - EDP Sciences
CY  - Les Ulis
ER  - 
TY  - JOUR
A1  - Hubrig, Swetlana
A1  - Fossati, Luca
A1  - Carroll, Thorsten Anthony
A1  - Castro, Norberto
A1  - Gonzalez, J. F.
A1  - Ilyin, Ilya
A1  - Przybilla, Norbert
A1  - Schoeller, M.
A1  - Oskinova, Lida
A1  - Morel, T.
A1  - Langer, N.
A1  - Scholz, Ralf-Dieter
A1  - Kharchenko, N. V.
A1  - Nieva, M. -F.
T1  - B fields in OB stars (BOB): The discovery of a magnetic field in a multiple system in the Trifid nebula, one of the youngest star forming regions
JF  - Astronomy and astrophysics : an international weekly journal
N2  - Aims. Recent magnetic field surveys in O- and B-type stars revealed that about 10% of the core-hydrogen-burning massive stars host large-scale magnetic fields. The physical origin of these fields is highly debated. To identify and model the physical processes responsible for the generation of magnetic fields in massive stars, it is important to establish whether magnetic massive stars are found in very young star-forming regions or whether they are formed in close interacting binary systems.
 Methods. In the framework of our ESO Large Program, we carried out low-resolution spectropolarimetric observations with FORS 2 in 2013 April of the three most massive central stars in the Trifid nebula, HD 164492A, HD 164492C, and HD 164492D. These observations indicated a strong longitudinal magnetic field of about 500-600 G in the poorly studied component HD 164492C. To confirm this detection, we used HARPS in spectropolarimetric mode on two consecutive nights in 2013 June.
 Results. Our HARPS observations confirmed the longitudinal magnetic field in HD 164492C. Furthermore, the HARPS observations revealed that HD 164492C cannot be considered as a single star as it possesses one or two companions. The spectral appearance indicates that the primary is most likely of spectral type B1-B1.5 V. Since in both observing nights most spectral lines appear blended, it is currently unclear which components are magnetic. Long-term monitoring using high-resolution spectropolarimetry is necessary to separate the contribution of each component to the magnetic signal. Given the location of the system HD 164492C in one of the youngest star formation regions, this system can be considered as a Rosetta Stone for our understanding of the origin of magnetic fields in massive stars.
KW  - binaries: close
KW  - stars: early-type
KW  - stars: fundamental parameters
KW  - stars: magnetic field
KW  - stars: variables: general
KW  - stars: individual: HD 164492C
Y1  - 2014
U6  - https://doi.org/10.1051/0004-6361/201423490
SN  - 0004-6361
SN  - 1432-0746
VL  - 564
PB  - EDP Sciences
CY  - Les Ulis
ER  - 
TY  - JOUR
A1  - Hubrig, Swetlana
A1  - Kholtygin, A.
A1  - Ilyin, Ilya
A1  - Schöller, M.
A1  - Oskinova, Lida
T1  - THE FIRST SPECTROPOLARIMETRIC MONITORING OF THE PECULIAR O4 Ief SUPERGIANT zeta PUPPIS
JF  - The astrophysical journal : an international review of spectroscopy and astronomical physics
N2  - 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.
KW  - stars: atmospheres
KW  - stars: early-type
KW  - stars: individual (zetaPup)
KW  - stars: magnetic field
KW  - stars: variables: general
Y1  - 2016
U6  - https://doi.org/10.3847/0004-637X/822/2/104
SN  - 0004-637X
SN  - 1538-4357
VL  - 822
PB  - IOP Publ. Ltd.
CY  - Bristol
ER  - 
TY  - JOUR
A1  - Hubrig, Swetlana
A1  - Oskinova, Lida
A1  - Schoeller, M.
T1  - First detection of a magnetic field in the fast rotating runaway Oe star zeta Ophiuchi
JF  - Astronomische Nachrichten = Astronomical notes
N2  - The star zeta Ophiuchi is one of the brightest massive stars in the northern hemisphere and was intensively studied in various wavelength domains. The currently available observational material suggests that certain observed phenomena are related to the presence of a magnetic field. We acquired spectropolarimetric observations of zeta Oph with FORS 1 mounted on the 8-m Kueyen telescope of the VLT to investigate if a magnetic field is indeed present in this star. Using all available absorption lines, we detect a mean longitudinal magnetic field < B(z)>(all) = 141 +/- 45 G, confirming the magnetic nature of this star. We review the X-ray properties of zeta Oph with the aim to understand whether the X-ray emission of zeta Oph is dominated by magnetic or by wind instability processes.
KW  - stars: mass-loss
KW  - stars: early-type
KW  - stars: magnetic field
KW  - stars: kinematics and dynamics
KW  - X-rays: stars
KW  - stars: individual: zeta Ophiuchi
Y1  - 2011
U6  - https://doi.org/10.1002/asna.201111516
SN  - 0004-6337
VL  - 332
IS  - 2
SP  - 147
EP  - 152
PB  - Wiley-Blackwell
CY  - Malden
ER  - 
TY  - JOUR
A1  - Hubrig, Swetlana
A1  - Schoeller, M.
A1  - Ilyin, Ilya
A1  - Kharchenko, N. V.
A1  - Oskinova, Lida
A1  - Langer, N.
A1  - Gonzalez, J. F.
A1  - Kholtygin, A. F.
A1  - Briquet, Maryline
T1  - Exploring the origin of magnetic fields in massive stars - II. New magnetic field measurements in cluster and field stars
JF  - Astronomy and astrophysics : an international weekly journal
N2  - 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.
KW  - polarization
KW  - stars: early-type
KW  - stars: kinematics and dynamics
KW  - stars: magnetic field
KW  - stars: massive
KW  - open clusters and associations: general
Y1  - 2013
U6  - https://doi.org/10.1051/0004-6361/201220721
SN  - 0004-6361
VL  - 551
PB  - EDP Sciences
CY  - Les Ulis
ER  - 
TY  - JOUR
A1  - Hubrig, Swetlana
A1  - Schoeller, Markus
A1  - Fossati, Luca
A1  - Morel, Thierry
A1  - Castro, Neves
A1  - Oskinova, Lida
A1  - Przybilla, Norbert
A1  - Eikenberry, Stephen S.
A1  - Nieva, Maria Fernanda
A1  - Langer, Norbert
T1  - B fields in OB stars (BOB): FORS2 spectropolarimetric follow-up of the two rare rigidly rotating magnetosphere stars HD 23478 and HD 345439
JF  - Astronomy and astrophysics : an international weekly journal
N2  - Aims. Massive B-type stars with strong magnetic fields and fast rotation are very rare and pose a mystery for theories of star formation and magnetic field evolution. Only two such stars, called sigma Ori E analogues, were known until recently. A team involved in APOGEE, one of the Sloan Digital Sky Survey III programs, announced the discovery of two additional rigidly rotating magnetosphere stars, HD 23478 and HD 345439. The magnetic fields in these newly discovered sOri E analogues have not been investigated so far.
 Methods. In the framework of our ESO Large Programme and one normal ESO programme, we carried out low-resolution FORS 2 spectropolarimetric observations of HD 23478 and HD 345439.
 Results. In the measurements of hydrogen lines, we discover a rather strong longitudinal magnetic field of up to 1.5 kG in HD 23478 and up to 1.3 kG using the entire spectrum. The analysis of HD 345439 using four subsequent spectropolarimetric subexposures does not reveal a magnetic field at a significance level of 3 sigma. On the other hand, individual subexposures indicate that HD 345439 may host a strong magnetic field that rapidly varies over 88 min. The fast rotation of HD 345439 is also indicated by the behaviour of several metallic and He I lines in the low-resolution FORS 2 spectra that show profile variations already on this short time-scale.
KW  - stars: early-type
KW  - stars: fundamental parameters
KW  - stars: variables: general
KW  - stars: magnetic field
KW  - stars: individual: HD 23478
KW  - stars: individual: HD 345439
Y1  - 2015
U6  - https://doi.org/10.1051/0004-6361/201526262
SN  - 0004-6361
SN  - 1432-0746
VL  - 578
PB  - EDP Sciences
CY  - Les Ulis
ER  - 
TY  - JOUR
A1  - Hubrig, Swetlana
A1  - Scholz, Kathleen
A1  - Hamann, Wolf-Rainer
A1  - Schoeller, M.
A1  - Ignace, R.
A1  - Ilyin, Ilya
A1  - Gayley, K. G.
A1  - Oskinova, Lida
T1  - Searching for a magnetic field in Wolf-Rayet stars using FORS 2 spectropolarimetry
JF  - Monthly notices of the Royal Astronomical Society
N2  - 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.
KW  - techniques: polarimetric
KW  - stars: individual: WR 6
KW  - stars: magnetic field
KW  - stars: variables: general
KW  - stars: Wolf-Rayet
Y1  - 2016
U6  - https://doi.org/10.1093/mnras/stw558
SN  - 0035-8711
SN  - 1365-2966
VL  - 458
SP  - 3381
EP  - 3393
PB  - Oxford Univ. Press
CY  - Oxford
ER  - 
TY  - JOUR
A1  - Hubrig, Swetlana
A1  - Schöller, Markus
A1  - Kholtygin, Alexander F.
A1  - Tsumura, Hiroki
A1  - Hoshino, Akio
A1  - Kitamoto, Shunji
A1  - Oskinova, Lida
A1  - Ignace, Richard
A1  - Todt, Helge Tobias
A1  - Ilyin, Ilya
T1  - New multiwavelength observations of the Of?p star CPD-28 degrees 2561
JF  - Monthly notices of the Royal Astronomical Society
N2  - 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.
KW  - stars: atmospheres
KW  - stars: individual: CPD-28 degrees 2561
KW  - stars: magnetic field
KW  - stars: mass-loss
KW  - stars: variables: general
KW  - X-rays: stars
Y1  - 2015
U6  - https://doi.org/10.1093/mnras/stu2516
SN  - 0035-8711
SN  - 1365-2966
VL  - 447
IS  - 2
SP  - 1885
EP  - 1894
PB  - Oxford Univ. Press
CY  - Oxford
ER  - 
TY  - JOUR
A1  - Ignace, Richard
A1  - Oskinova, Lida
A1  - Massa, D.
T1  - A report on the X-ray properties of the tau Sco-like stars
JF  - Monthly notices of the Royal Astronomical Society
N2  - An increasing number of OB stars have been shown to possess magnetic fields. Although the sample remains small, it is surprising that the magnetic and X-ray properties of these stars appear to be far less correlated than expected. This contradicts model predictions, which generally indicate that the X-rays from magnetic stars are harder and more luminous than their non-magnetic counterparts. Instead, the X-ray properties of magnetic OB stars are quite diverse.
 tau Sco is one example where the expectations are better met. This bright main-sequence, early B star has been studied extensively in a variety of wavebands. It has a surface magnetic field of around 500 G, and Zeeman Doppler tomography has revealed an unusual field configuration. Furthermore, tau Sco displays an unusually hard X-ray spectrum, much harder than similar, non-magnetic OB stars. In addition, the profiles of its UV P Cygni wind lines have long been known to possess a peculiar morphology.
 Recently, two stars, HD 66665 and HD 63425, whose spectral types and UV wind line profiles are similar to those of tau Sco, have also been determined to be magnetic. In the hope of establishing a magnetic field - X-ray connection for at least a subset of the magnetic stars, we obtained XMM-Newton European Photon Imaging Camera spectra of these two objects. Our results for HD 66665 are somewhat inconclusive. No especially strong hard component is detected; however, the number of source counts is insufficient to rule out hard emission. Longer exposure is needed to assess the nature of the X-rays from this star. On the other hand, we do find that HD 63425 has a substantial hard X-ray component, thereby bolstering its close similarity to tau Sco.
KW  - stars: early-type
KW  - stars: individual: HD 63425
KW  - stars: individual: HD 66665
KW  - stars: magnetic field
KW  - X-rays: stars
Y1  - 2013
U6  - https://doi.org/10.1093/mnras/sts358
SN  - 0035-8711
VL  - 429
IS  - 1
SP  - 516
EP  - 522
PB  - Oxford Univ. Press
CY  - Oxford
ER  -