Simultaneous Multi-Wavelength Observations of Magnetic Activity in Ultracool Dwarfs. I. The Complex Behavior of the M8.5 Dwarf TVLM513-46546 - AstrophysicsReportar como inadecuado




Simultaneous Multi-Wavelength Observations of Magnetic Activity in Ultracool Dwarfs. I. The Complex Behavior of the M8.5 Dwarf TVLM513-46546 - Astrophysics - Descarga este documento en PDF. Documentación en PDF para descargar gratis. Disponible también para leer online.

Abstract: Abridged We present the first simultaneous radio, X-ray, ultraviolet, andoptical spectroscopic observations of the M8.5 dwarf TVLM513-46546, with aduration of 9 hours. These observations are part of a program to study theorigin of magnetic activity in ultracool dwarfs, and its impact onchromospheric and coronal emission. Here we detect steady quiescent radioemission superposed with multiple short-duration, highly polarized flares;there is no evidence for periodic bursts previously reported for this object,indicating their transient nature. We also detect soft X-ray emission, withL X-L bol~10^-4.9, the faintest to date for any object later than M5, and apossible weak X-ray flare. TVLM513-46546 continues the trend of severeviolation of the radio-X-ray correlation in ultracool dwarfs, by nearly 4orders of magnitude. From the optical spectroscopy we find that the Balmer lineluminosity exceeds the X-ray luminosity by a factor of a few, suggesting that,unlike in early M dwarfs, chromospheric heating may not be due to coronal X-rayemission. More importantly, we detect a sinusoidal H-alpha light curve with aperiod of 2 hr, matching the rotation period of TVLM513-46546. This is thefirst known example of such Balmer line behavior, which points to a co-rotatingchromospheric hot spot or an extended magnetic structure, with a coveringfraction of about 50%. This feature may be transitory based on the apparentdecline in light curve peak during the four observed maxima. From the radiodata we infer a large scale steady magnetic field of ~100 G, in good agreementwith the value required for confinement of the X-ray emitting plasma. The radioflares, on the other hand, are produced in a component of the field with astrength of ~3 kG and a likely multi-polar configuration.



Autor: E. Berger, J.E. Gizis, M.S. Giampapa, R.E. Rutledge, J. Liebert, E. Martin, G. Basri, T.A. Fleming, C.M. Johns-Krull, N. Phan-Bao

Fuente: https://arxiv.org/







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