TY - JOUR A1 - Schöller, Markus A1 - Hubrig, Swetlana A1 - Fossati, L. A1 - Carroll, Thorsten Anthony A1 - Briquet, Maryline A1 - Oskinova, Lida A1 - Järvinen, S. A1 - Ilyin, Ilya A1 - Castro, N. A1 - Morel, T. A1 - Langer, N. A1 - Przybilla, N. A1 - Nieva, M. -F. A1 - Kholtygin, A. F. A1 - Sana, H. A1 - Herrero, A. A1 - Barba, R. H. A1 - de Koter, A. T1 - B fields in OB stars (BOB) BT - Concluding the FORS2 observing campaign JF - Astronomy and astrophysics : an international weekly journal N2 - 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. KW - polarization KW - stars: early-type KW - stars: magnetic field KW - stars: massive Y1 - 2017 U6 - https://doi.org/10.1051/0004-6361/201628905 SN - 1432-0746 VL - 599 PB - EDP Sciences CY - Les Ulis ER - TY - JOUR A1 - Shenar, Tomer A1 - Oskinova, Lida A1 - Jaervinen, S. P. A1 - Luckas, P. A1 - Hainich, Rainer A1 - Todt, Helge Tobias A1 - Hubrig, Swetlana A1 - Sander, Andreas Alexander Christoph A1 - Ilyin, Ilya A1 - Hamann, Wolf-Rainer T1 - Constraining the weak-wind problem BT - an XMM-HST campaign for the magnetic 09.7 V star HD 54879 JF - Contributions Of The Astronomical Observatory Skalnate Pleso N2 - 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. KW - stars: massive KW - stars: magnetic field KW - stars: mass-loss Y1 - 2017 U6 - https://doi.org/10.1051/0004-6361/201731291 SN - 1335-1842 SN - 1336-0337 VL - 48 IS - 1 SP - 139 EP - 143 PB - Astronomický Ústav SAV CY - Tatranská Lomnica ER - TY - JOUR A1 - Pillitteri, Ignazio A1 - Fossati, Luca A1 - Rodriguez, N. Castro A1 - Oskinova, Lida A1 - Wolk, Scott J. T1 - Detection of magnetic field in the B2 star rho Ophiuchi A with ESO FORS2 JF - Astronomy and astrophysics : an international weekly journal N2 - Circumstantial evidence suggests that magnetism and enhanced X-ray emission are likely correlated in early B-type stars: similar fractions of them (similar to 10%) are strong and hard X-ray sources and possess strong magnetic fields. It is also known that some B-type stars have spots on their surface. Yet up to now no X-ray activity associated with spots on early-type stars was detected. In this Letter we report the detection of a magnetic field on the B2V star rho Oph A. Previously, we assessed that the X-ray activity of this star is associated with a surface spot, herewith we establish its magnetic origin. We analyze spectra of rho Oph A obtained with the FORS2 spectrograph at ESO Very Large Telescope (VLT) at two epochs, and detect a longitudinal component of the magnetic field of the order of similar to 500 G in one of the datasets. The detection of the magnetic field only at one epoch can be explained by stellar rotation which is also invoked to explain observed periodic X-ray activity. From archival HARPS ESO VLT high resolution spectra we derived the fundamental stellar parameters of rho Oph A and further constrained its age. We conclude that rho Oph A provides strong evidence for the presence of active X-ray emitting regions on young magnetized early type stars. KW - stars: activity KW - stars: early-type KW - stars: magnetic field KW - pulsars: individual: rho Ophiuchi A Y1 - 2017 U6 - https://doi.org/10.1051/0004-6361/201732078 SN - 1432-0746 VL - 610 PB - EDP Sciences CY - Les Ulis ER - TY - JOUR A1 - Leto, Paolo A1 - Trigilio, C. A1 - Oskinova, Lida A1 - Ignace, R. A1 - Buemi, C. S. A1 - Umana, G. A1 - Ingallinera, A. A1 - Leone, Francesco A1 - Phillips, N. M. A1 - Agliozzo, Claudia A1 - Todt, Helge Tobias A1 - Cerrigone, L. T1 - A combined multiwavelength VLA/ALMA/Chandra study unveils the complex magnetosphere of the B-type star HR5907 JF - Monthly notices of the Royal Astronomical Society N2 - We present new radio/millimeter measurements of the hot magnetic star HR5907 obtained with the VLA and ALMA interferometers. We find that HR5907 is the most radio luminous early type star in the cm-mm band among those presently known. Its multi-wavelength radio light curves are strongly variable with an amplitude that increases with radio frequency. The radio emission can be explained by the populations of the non-thermal electrons accelerated in the current sheets on the outer border of the magnetosphere of this fast-rotating magnetic star. We classify HR5907 as another member of the growing class of strongly magnetic fast-rotating hot stars where the gyro-synchrotron emission mechanism efficiently operates in their magnetospheres. The new radio observations of HR5907 are combined with archival X-ray data to study the physical condition of its magnetosphere. The X-ray spectra of HR5907 show tentative evidence for the presence of non-thermal spectral component. We suggest that non-thermal X-rays originate a stellar X-ray aurora due to streams of non-thermal electrons impacting on the stellar surface. Taking advantage of the relation between the spectral indices of the X-ray power-law spectrum and the non-thermal electron energy distributions, we perform 3-D modelling of the radio emission for HR5907. The wavelength-dependent radio light curves probe magnetospheric layers at different heights above the stellar surface. A detailed comparison between simulated and observed radio light curves leads us to conclude that the stellar magnetic field of HR 5907 is likely non-dipolar, providing further indirect evidence of the complex magnetic field topology of HR5907. KW - stars: chemically peculiar KW - stars: early-type KW - stars: individual: HR 5907 KW - stars: magnetic field KW - radio continuum: stars KW - X-rays: stars Y1 - 2018 U6 - https://doi.org/10.1093/mnras/sty244 SN - 0035-8711 SN - 1365-2966 VL - 476 IS - 1 SP - 562 EP - 579 PB - Oxford Univ. Press CY - Oxford ER - TY - JOUR A1 - Robrade, Jan A1 - Oskinova, Lida A1 - Schmitt, J. H. M. M. A1 - Leto, Paolo A1 - Trigilio, C. T1 - Outstanding X-ray emission from the stellar radio pulsar CU Virginis JF - Astronomy and astrophysics : an international weekly journal N2 - Context. Among the intermediate-mass magnetic chemically peculiar (MCP) stars, CU Vir is one of the most intriguing objects. Its 100% circularly polarized beams of radio emission sweep the Earth as the star rotates, thereby making this strongly magnetic star the prototype of a class of nondegenerate stellar radio pulsars. While CU Vir is well studied in radio, its high-energy properties are not known. Yet, X-ray emission is expected from stellar magnetospheres and confined stellar winds. Aims. Using X-ray data we aim to test CU Vir for intrinsic X-ray emission and investigate mechanisms responsible for its generation. Methods. We present X-ray observations performed with XMM-Newton and Chandra and study obtained X-ray images, light curves, and spectra. Basic X-ray properties are derived from spectral modelling and are compared with model predictions. In this context we investigate potential thermal and nonthermal X-ray emission scenarios. Results. We detect an X-ray source at the position of CU Vir. With LX approximate to 3 x 10(28) erg s(-1) it is moderately X-ray bright, but the spectrum is extremely hard compared to other Ap stars. Spectral modelling requires multi-component models with predominant hot plasma at temperatures of about T-X = 25MK or, alternatively, a nonthermal spectral component. Both types of model provide a virtually equivalent description of the X-ray spectra. The Chandra observation was performed six years later than those by XMM-Newton, yet the source has similar X-ray flux and spectrum, suggesting a steady and persistent X-ray emission. This is further confirmed by the X-ray light curves that show only mild X-ray variability. Conclusions. CU Vir is also an exceptional star at X-ray energies. To explain its full X-ray properties, a generating mechanism beyond standard explanations, like the presence of a low-mass companion or magnetically confined wind-shocks, is required. Magnetospheric activity might be present or, as proposed for fast-rotating strongly magnetic Bp stars, the X-ray emission of CU Vir is predominantly auroral in nature. KW - individual: CU Vir KW - stars: activity KW - stars: chemically peculiar KW - stars: magnetic field KW - X-rays: stars Y1 - 2018 U6 - https://doi.org/10.1051/0004-6361/201833492 SN - 1432-0746 VL - 619 PB - EDP Sciences CY - Les Ulis ER - TY - JOUR A1 - Reindl, Nicole A1 - Bainbridge, M. A1 - Przybilla, Norbert A1 - Geier, Stephan Alfred A1 - Prvak, M. A1 - Krticka, Jiri A1 - Ostensen, R. H. A1 - Telting, J. A1 - Werner, K. T1 - Unravelling the baffling mystery of the ultrahot wind phenomenon in white dwarfs JF - Monthly notices of the Royal Astronomical Society N2 - The presence of ultrahigh excitation (UHE) absorption lines (e.g. OVIII) in the optical spectra of several of the hottest white dwarfs poses a decades-long mystery and is something that has never been observed in any other astrophysical object. The occurrence of such features requires a dense environment with temperatures near 10(6) K, by far exceeding the stellar effective temperature. Here we report the discovery of a new hot wind white dwarf, GALEXJ014636.8+323615. Astonishingly, we found for the first time rapid changes of the equivalent widths of the UHE features, which are correlated to the rotational period of the star (P=0.242035 d). We explain this with the presence of a wind-fed circumstellar magnetosphere in which magnetically confined wind shocks heat up the material to the high temperatures required for the creation of the UHE lines. The photometric and spectroscopic variability of GALEXJ014636.8+323615 can then be understood as consequence of the obliquity of the magnetic axis with respect to the rotation axis of the white dwarf. This is the first time a wind-fed circumstellar magnetosphere around an apparently isolated white dwarf has been discovered and finally offers a plausible explanation of the ultrahot wind phenomenon. KW - stars: AGB and post-AGB KW - stars: evolution KW - stars: magnetic field Y1 - 2018 U6 - https://doi.org/10.1093/mnrasl/sly191 SN - 0035-8711 SN - 1365-2966 VL - 482 IS - 1 SP - L93 EP - L98 PB - Oxford Univ. Press CY - Oxford ER - TY - JOUR A1 - Leto, Paolo A1 - Trigilio, C. A1 - Oskinova, Lida A1 - Ignace, R. A1 - Buemi, C. S. A1 - Umana, G. A1 - Cavallaro, Francesco A1 - Ingallinera, A. A1 - Bufano, F. A1 - Phillips, N. M. A1 - Agliozzo, Claudia A1 - Cerrigone, L. A1 - Todt, Helge Tobias A1 - Riggi, S. A1 - Leone, Francesco T1 - The polarization mode of the auroral radio emission from the early-type star HD 142301 JF - Monthly notices of the Royal Astronomical Society N2 - We report the detection of the auroral radio emission from the early-type magnetic star HD142301. New VLA observations of HD142301 detected highly polarized amplified emission occurring at fixed stellar orientations. The coherent emission mechanism responsible for the stellar auroral radio emission amplifies the radiation within a narrow beam, making the star where this phenomenon occurs similar to a radio lighthouse. The elementary emission process responsible for the auroral radiation mainly amplifies one of the two magneto-ionic modes of the electromagnetic wave. This explains why the auroral pulses are highly circularly polarized. The auroral radio emission of HD142301 is characterized by a reversal of the sense of polarization as the star rotates. The effective magnetic field curve of HD142301 is also available making it possible to correlate the transition from the left to the right-hand circular polarization sense ( and vice versa) of the auroral pulses with the known orientation of the stellar magnetic field. The results presented in this letter have implications for the estimation of the dominant magneto-ionic mode amplified within the HD142301 magnetosphere. KW - masers KW - polarization KW - stars: early-type KW - stars: individual: HD142301 KW - stars: magnetic field KW - radio continuum: stars Y1 - 2018 U6 - https://doi.org/10.1093/mnrasl/sly179 SN - 0035-8711 SN - 1365-2966 VL - 482 IS - 1 SP - L4 EP - L8 PB - Oxford Univ. Press CY - Oxford ER - TY - JOUR A1 - Leto, Paolo A1 - Trigilio, C. A1 - Oskinova, Lida A1 - Ignace, R. A1 - Buemi, C. S. A1 - Umana, G. A1 - Ingallinera, A. A1 - Todt, Helge Tobias A1 - Leone, F. T1 - The detection of variable radio emission from the fast rotating magnetic hot B-star HR 7355 and evidence for its X-ray aurorae JF - Monthly notices of the Royal Astronomical Society N2 - In this paper, we investigate the multiwavelength properties of the magnetic early B-type star HR 7355. We present its radio light curves at several frequencies, taken with the Jansky Very Large Array, and X-ray spectra, taken with the XMM-Newton X-ray telescope. Modelling of the radio light curves for the Stokes I and V provides a quantitative analysis of the HR 7355 magnetosphere. A comparison between HR 7355 and a similar analysis for the Ap star CU Vir allows us to study how the different physical parameters of the two stars affect the structure of the respective magnetospheres where the non-thermal electrons originate. Our model includes a cold thermal plasma component that accumulates at high magnetic latitudes that influences the radio regime, but does not give rise to X-ray emission. Instead, the thermal X-ray emission arises from shocks generated by wind stream collisions close to the magnetic equatorial plane. The analysis of the X-ray spectrum of HR 7355 also suggests the presence of a non-thermal radiation. Comparison between the spectral index of the power-law X-ray energy distribution with the non-thermal electron energy distribution indicates that the non-thermal X-ray component could be the auroral signature of the non-thermal electrons that impact the stellar surface, the same non-thermal electrons that are responsible for the observed radio emission. On the basis of our analysis, we suggest a novel model that simultaneously explains the X-ray and the radio features of HR 7355 and is likely relevant for magnetospheres of other magnetic early-type stars. KW - stars: chemically peculiar KW - stars: early-type KW - stars: individual: HR 7355 KW - stars: magnetic field KW - radio continuum: stars KW - X-rays: stars Y1 - 2017 U6 - https://doi.org/10.1093/mnras/stx267 SN - 0035-8711 SN - 1365-2966 VL - 467 SP - 2820 EP - 2833 PB - Oxford Univ. Press CY - Oxford ER - TY - JOUR A1 - Pillitteri, Ignazio A1 - Wolk, Scott J. A1 - Reale, Fabio A1 - Oskinova, Lida T1 - The early B-type star Rho Ophiuchi A is an X-ray lighthouse JF - Astronomy and astrophysics : an international weekly journal N2 - We present the results of a 140 ks XMM-Newton observation of the B2 star rho Oph A. The star has exhibited strong X-ray variability: a cusp-shaped increase of rate, similar to that which we partially observed in 2013, and a bright flare. These events are separated in time by about 104 ks, which likely correspond to the rotational period of the star (1.2 days). Time resolved spectroscopy of the X-ray spectra shows that the first event is caused by an increase of the plasma emission measure, while the second increase of rate is a major flare with temperatures in excess of 60 MK (kT similar to 5 keV). From the analysis of its rise, we infer a magnetic field of >= 300 G and a size of the flaring region of similar to 1.4-1.9 x 10(11) cm, which corresponds to similar to 25%-30% of the stellar radius. We speculate that either an intrinsic magnetism that produces a hot spot on its surface or an unknown low mass companion are the source of such X-rays and variability. A hot spot of magnetic origin should be a stable structure over a time span of >= 2.5 yr, and suggests an overall large scale dipolar magnetic field that produces an extended feature on the stellar surface. In the second scenario, a low mass unknown companion is the emitter of X-rays and it should orbit extremely close to the surface of the primary in a locked spin-orbit configuration, almost on the verge of collapsing onto the primary. As such, the X-ray activity of the secondary star would be enhanced by its young age, and the tight orbit as in RS Cvn systems. In both cases rho Oph would constitute an extreme system that is worthy of further investigation. KW - stars: activity KW - stars: individual: Rho Ophiuchi KW - stars: early-type KW - stars: magnetic field KW - starspots KW - X-rays: stars Y1 - 2017 U6 - https://doi.org/10.1051/0004-6361/201630070 SN - 1432-0746 VL - 602 PB - EDP Sciences CY - Les Ulis ER - TY - JOUR A1 - Przybilla, Norbert A1 - Fossati, Luca A1 - Hubrig, Swetlana A1 - Nieva, M. -F. A1 - Jaervinen, S. P. A1 - Castro, Norberto A1 - Schoeller, M. A1 - Ilyin, Ilya A1 - Butler, Keith A1 - Schneider, F. R. N. A1 - Oskinova, Lida A1 - Morel, T. A1 - Langer, N. A1 - de Koter, A. T1 - B fields in OB stars (BOB): Detection of a magnetic field in the He-strong star CPD-57 degrees 3509 JF - Organic letters N2 - 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. KW - stars: abundances KW - stars: atmospheres KW - stars: evolution KW - stars: magnetic field KW - stars: individual: CPD-57 degrees 3509 KW - stars: massive Y1 - 2016 U6 - https://doi.org/10.1051/0004-6361/201527646 SN - 1432-0746 VL - 587 PB - EDP Sciences CY - Les Ulis ER -