Quiescent X-ray emission from the M9 dwarf LHS 2065

Abstract

Aims: X-ray emission is an important diagnostics to study magnetic activity in very low mass stars that are presumably fully convective and have an effectively neutral photosphere.
Methods: We investigate an archival XMM-Newton observation of LHS 2065, an ultracool dwarf with spectral type M9.
Results: We clearly detect LHS 2065 at soft X-ray energies in less than 1 h effective exposure time above the 3σ level with the PN and MOS1 detector. No flare signatures are present and we attribute the X-ray detection to quasi-quiescent activity. From the PN data we derived an X-ray luminosity of L_X = 2.2 ± 0.7 × 10²⁶ erg/s in the 0.3-0.8 keV band, the corresponding activity level of log L_X/L_bol≈ -3.7 points to a rather active star. Indications for minor variability and possible accompanying spectral changes are present, however the short exposure time and poor data quality prevents a more detailed analysis.
Conclusions: LHS 2065 is one of the coolest and least massive stars that emits X-rays at detectable levels in quasi-quiescence, implying the existence of a corona.