The magnetic fields and magnetospheres of hot stars

Strong advances in direct evidence of magnetic fields in hot massive stars have been possible thanks to the new generation of high-resolution spectropolarimeters such as ESPaDOnS (on the Canada-France-Hawaii Telescope) or HARPSpol (on the 3.6m ESO telescope). UV and optical high-resolution spectroscopy has also been very useful to study the magnetospheres of massive stars. In this contribution I review the observing tools and our current knowledge concerning the detection and characterisation of the magnetic fields and magnetospheres in hot stars.Comment: 10 pages, 3 figures, to appear in the proceedings of "Circumstellar Dynamics at High Resolution", Foz do Iguacu, Feb. 201

Discovery of fossil magnetic fields in the intermediate-mass pre-main sequence stars

It is now well-known that the surface magnetic fields observed in cool, lower-mass stars on the main sequence (MS) are generated by dynamos operating in their convective envelopes. However, higher-mass stars (above 1.5 Msun) pass their MS lives with a small convective core and a largely radiative envelope. Remarkably, notwithstanding the absence of energetically-important envelope convection, we observe very strong (from 300 G to 30 kG) and organised (mainly dipolar) magnetic fields in a few percent of the A and B-type stars on the MS, the origin of which is not well understood. In this poster we propose that these magnetic fields could be of fossil origin, and we present very strong observational results in favour of this proposal.Comment: To appear in Proceedings IAU Symposium No. 259, 2009. Cosmic Magnetic Fields: From Planets, to Stars and Galaxie

Searching for magnetic fields in the descendants of massive OB stars

We present the results of a recent survey of cool, late-type supergiants - the descendants of massive O- and B-type stars - that has systematically detected magnetic fields in these stars using spectropolarimetric observations obtained with ESPaDOnS at the Canada-France-Hawaii Telescope. Our observations reveal detectable, often complex, Stokes V Zeeman signatures in Least-Squares Deconvolved mean line profiles in a significant fraction of the observed sample of ~30 stars.Comment: 2 pages, 1 figure, IAUS 272 - Active OB Stars: Structure, Evolution, Mass Loss and Critical Limit

HD 35502: a hierarchical triple system with a magnetic B5IVpe primary

We present our analysis of HD~35502 based on high- and medium-resolution spectropolarimetric observations. Our results indicate that the magnetic B5IVsnp star is the primary component of a spectroscopic triple system and that it has an effective temperature of $18.4\pm0.6\,{\rm kK}$, a mass of $5.7\pm0.6\,M_\odot$, and a polar radius of $3.0^{+1.1}_{-0.5}\,R_\odot$. The two secondary components are found to be essentially identical A-type stars for which we derive effective temperatures ($8.9\pm0.3\,{\rm kK}$), masses ($2.1\pm0.2\,M_\odot$), and radii ($2.1\pm0.4\,R_\odot$). We infer a hierarchical orbital configuration for the system in which the secondary components form a tight binary with an orbital period of $5.66866(6)\,{\rm d}$ that orbits the primary component with a period of over $40\,{\rm yrs}$. Least-Squares Deconvolution (LSD) profiles reveal Zeeman signatures in Stokes $V$ indicative of a longitudinal magnetic field produced by the B star ranging from approximately $-4$ to $0\,{\rm kG}$ with a median uncertainty of $0.4\,{\rm kG}$. These measurements, along with the line variability produced by strong emission in H$\alpha$, are used to derive a rotational period of $0.853807(3)\,{\rm d}$. We find that the measured $v\sin{i}=75\pm5\,{\rm km\,s}^{-1}$ of the B star then implies an inclination angle of the star's rotation axis to the line of sight of $24^{+6}_{-10}\degree$. Assuming the Oblique Rotator Model, we derive the magnetic field strength of the B star's dipolar component ($14^{+9}_{-3}\,{\rm kG}$) and its obliquity ($63\pm13\degree$). Furthermore, we demonstrate that the calculated Alfv\'{e}n radius ($41^{+17}_{-6}\,R_\ast$) and Kepler radius ($2.1^{+0.4}_{-0.7}\,R_\ast$) place HD~35502's central B star well within the regime of centrifugal magnetosphere-hosting stars.Comment: 24 pages, 14 figures, Accepted for publication in MNRA

The Effect of Neutron Star Binding Energy on Gravitational-Radiation-Driven Mass-Transfer Binaries

In a relativistic model of a neutron star, the star's mass is less than the mass of the individual component baryons. This is due to the fact that the star's negative binding energy makes a contribution to the star's total energy and its mass. A consequence of this relativistic mass deficit is that a neutron star that is accreting matter increases its mass at a rate which is slower than the mass of a baryon times the rate that baryons are accreted. This difference in the rate of change of the masses has a simple relation with the star's gravitational redshift. We show that this effect has the potential to be observed in binaries where the mass transfer is driven by angular momentum losses from the gravitational radiation emitted by the binary motion.Comment: 9 pages, 3 figures, accepted by Ap

Discovery of Magnetospheric Interactions in the Doubly-Magnetic Hot Binary ϵ\epsilon Lupi

Magnetic fields are extremely rare in close, hot binaries, with only 1.5\% of such systems known to contain a magnetic star. The eccentric $\epsilon$ Lupi system stands out in this population as the only close binary in which both stars are known to be magnetic. We report the discovery of strong, variable radio emission from $\epsilon$ Lupi using the upgraded Giant Metrewave Radio Telescope (uGMRT) and the MeerKAT radio telescope.The light curve exhibits striking, unique characteristics including sharp, high-amplitude pulses that repeat with the orbital period, with the brightest enhancement occurring near periastron. The characteristics of the light curve point to variable levels of magnetic reconnection throughout the orbital cycle, making $\epsilon$ Lupi the first known high-mass, main sequence binary embedded in an interacting magnetosphere. We also present a previously unreported enhancement in the X-ray light curve obtained from archival XMM-Newton data. The stability of the components' fossil magnetic fields, the firm characterization of their relatively simple configurations, and the short orbital period of the system make $\epsilon$ Lupi an ideal target to study the physics of magnetospheric interactions. This system may thus help us to illuminate the exotic plasma physics of other magnetically interacting systems such as moon-planet, planet-star, and star-star systems including T Tauri binaries, RS CVn systems, and neutron star binaries.Comment: Accepted for publication in MNRAS, 16 pages, 12 figure