Astronomy and Astrophysics, volume 602A, 92-92 (2017/6-1)
The early B-type star Rho Ophiuchi A is an X-ray lighthouse.
PILLITTERI I., WOLK S.J., REALE F. and OSKINOVA L.
Abstract (from CDS):
We present the results of a 140ks XMM-Newton observation of the B2 star ρ 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 104ks, 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 60MK (kT∼5keV). From the analysis of its rise, we infer a magnetic field of ≥300G and a size of the flaring region of ∼1.4-1.9x1011cm, which corresponds 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 ≥2.5yr, 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 ρ Oph would constitute an extreme system that is worthy of further investigation.
© ESO, 2017
stars: activity - stars: individual: Rho Ophiuchi - stars: early-type - stars: magnetic field - starspots - X-rays: stars - X-rays: stars
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