2009/01/20 by J. Robrade, J. H. M. M. Schmitt · 16 citations
Physics and Astronomy · #Astronomy #Astrophysics #Astrophysics and Star Formation Studies #Luminosity #Physics #Solar and Space Plasma Dynamics #Stars #Stellar, planetary, and galactic studies #astro-ph.SR
paper · pdf · doi:10.1051/0004-6361/200811224
published in Astronomy and Astrophysics 496(1), 229-233 (EDP Sciences) · accepted by A&A, 6 pages, 3 figures
arxiv created 2009/01/20 · openalex publication_date 2009/01/30 · arxiv updated 2009/12/01 · openalex created_date 2022/10/01 · openalex updated_date 2026/07/31
<i>Aims. <i/>X-ray emission is an important diagnostic for studying magnetic activity in presumably fully convective, very low-mass stars with virtually neutral photospheres.<i>Methods. <i/>We analyse an XMM-Newton observation of 1RXS J115928.5-524717, an ultracool dwarf with spectral type M9, and compare its X-ray properties to those of other similar very late-type stars.<i>Results. <i/>We clearly detected 1RXS J115928.5-524717 at soft X-ray energies in all EPIC detectors. Only minor variability was present during the observation and we attribute the X-ray emission to quasi-quiescent activity. The coronal plasma is described well by a two-temperature model at solar metallicity with temperatures of 2 MK and 6 MK and an X-ray luminosity of about 10<sup>26<sup/> erg/s in the 0.2-2.0 keV band. The corresponding activity level of log <i>L<i/><sub>X<sub/>/ points to a moderately active star. Altogether, X-ray activity from very low-mass stars shows similar trends as more massive stars, despite their different interior structure.<i>Conclusions. <i/>The nearby star 1RXS J115928.5-524717 is, after LHS 2065, the second ultracool M9 dwarf that emits X-rays at detectable levels in quasi-quiescence. While faint in absolute numbers, both stars are relatively X-ray active, implying an efficient dynamo mechanism that is capable of creating magnetic activity and coronal X-ray emission.