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 -