@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{KelesMallomvonEssenetal.2021, author = {Keles, Engin and Mallom, Matthias and von Essen, Carolina and Caroll, Thorsten A. and Alexoudi, Xanthippi and Pino, Lorenzo and Ilyin, Ilya and Poppenh{\"a}ger, Katja and Kitzmann, Daniel and Nascimbeni, Valerino and Turner, Jake D. and Strassmeier, Klaus G.}, title = {The potassium absorption on HD189733b and HD209458b}, series = {Monthly Notices of the Royal Astronomical Society: Letters}, volume = {489}, journal = {Monthly Notices of the Royal Astronomical Society: Letters}, number = {1}, publisher = {Oxford Univ. Press}, address = {Oxford}, doi = {10.1093/mnrasl/slz123}, pages = {L37 -- L41}, year = {2021}, abstract = {In this work, we investigate the potassium excess absorption around 7699 {\AA} of the exoplanets HD189733b and HD209458b. For this purpose, we used high-spectral resolution transit observations acquired with the 2 × 8.4 m Large Binocular Telescope (LBT) and the Potsdam Echelle Polarimetric and Spectroscopic Instrument (PEPSI). For a bandwidth of 0.8 {\AA}, we present a detection >7σ with an absorption level of 0.18 per cent for HD189733b. Applying the same analysis to HD209458b, we can set 3σ upper limit of 0.09 per cent, even though we do not detect a K-excess absorption. The investigation suggests that the K feature is less present in the atmosphere of HD209458b than in the one of HD189733b. This comparison confirms previous claims that the atmospheres of these two planets must have fundamentally different properties.}, language = {en} } @article{KelesKitzmannMallonnetal.2020, author = {Keles, Engin and Kitzmann, Daniel and Mallonn, Matthias and Alexoudi, Xanthippi and Fossati, Luca and Pino, Lorenzo and Seidel, Julia Victoria and Caroll, Thorsten A. and Steffen, M. and Ilyin, Ilya and Poppenh{\"a}ger, Katja and Strassmeier, Klaus G. and von Essen, Carolina and Nascimbeni, Valerio and Turner, Jake D.}, title = {Probing the atmosphere of HD189733b with the Na i and K i lines}, series = {Monthly Notices of the Royal Astronomical Society}, volume = {498}, journal = {Monthly Notices of the Royal Astronomical Society}, number = {1}, publisher = {Oxford Univ. Press}, address = {Oxford}, doi = {10.1093/mnras/staa2435}, pages = {1033}, year = {2020}, abstract = {High spectral resolution transmission spectroscopy is a powerful tool to characterize exoplanet atmospheres. Especially for hot Jupiters, this technique is highly relevant, due to their high-altitude absorption, e.g. from resonant sodium (Na i) and potassium (K i) lines. We resolve the atmospheric K i absorption on HD189733b with the aim to compare the resolved K i line and previously obtained high-resolution Na i-D line observations with synthetic transmission spectra. The line profiles suggest atmospheric processes leading to a line broadening of the order of ∼10 km/s for the Na i-D lines and only a few km/s for the K i line. The investigation hints that either the atmosphere of HD189733b lacks a significant amount of K i or the alkali lines probe different atmospheric regions with different temperature, which could explain the differences we see in the resolved absorption lines.}, 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{CastroFossatiHubrigetal.2015, author = {Castro, Norberto and Fossati, Luca and Hubrig, Swetlana and Simon D{\´i}az, Sergio and Schoeller, Markus and Ilyin, Ilya and Carrol, Thorsten A. and Langer, Norbert and Morel, Thierry and Schneider, Fabian R. N. and Przybilla, Norbert and Herrero, Artemio and de Koter, Alex and Oskinova, Lida and Reisenegger, Andreas and Sana, Hugues}, title = {B fields in OB stars (BOB) Detection of a strong magnetic field in the O9.7 V star HD 54879}, series = {Astronomy and astrophysics : an international weekly journal}, volume = {581}, journal = {Astronomy and astrophysics : an international weekly journal}, publisher = {EDP Sciences}, address = {Les Ulis}, organization = {BOB Collaboration}, issn = {1432-0746}, doi = {10.1051/0004-6361/201425354}, pages = {14}, year = {2015}, abstract = {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.}, 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{FossatiCastroMoreletal.2015, author = {Fossati, Luca and Castro, Norberto and Morel, Thierry and Langer, Norbert and Briquet, Maryline and Carroll, Thorsten Anthony and Hubrig, Swetlana and Nieva, Maria-Fernanda and Oskinova, Lida and Przybilla, Norbert and Schneider, Fabian R. N. and Schoeller, Magnus and Simon D{\´i}az, Sergio and Ilyin, Ilya and de Koter, Alex and Reisenegger, Andreas and Sana, Hugues}, title = {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}, series = {Astronomy and astrophysics : an international weekly journal}, volume = {574}, journal = {Astronomy and astrophysics : an international weekly journal}, publisher = {EDP Sciences}, address = {Les Ulis}, organization = {BOB Collaboration}, issn = {0004-6361}, doi = {10.1051/0004-6361/201424986}, pages = {15}, year = {2015}, abstract = {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.}, language = {en} } @article{HubrigFossatiCarrolletal.2014, author = {Hubrig, Swetlana and Fossati, Luca and Carroll, Thorsten Anthony and Castro, Norberto and Gonzalez, J. F. and Ilyin, Ilya and Przybilla, Norbert and Schoeller, M. and Oskinova, Lida and Morel, T. and Langer, N. and Scholz, Ralf-Dieter and Kharchenko, N. V. and Nieva, M. -F.}, title = {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}, series = {Astronomy and astrophysics : an international weekly journal}, volume = {564}, journal = {Astronomy and astrophysics : an international weekly journal}, publisher = {EDP Sciences}, address = {Les Ulis}, organization = {BOB Collaboration}, issn = {0004-6361}, doi = {10.1051/0004-6361/201423490}, pages = {5}, year = {2014}, abstract = {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.}, 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{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} }