AD Leonis: Flares observed by XMM-Newton and Chandra

¹ SRON National Institute for Space Research, Sorbonnelaan 2, 3584 CA Utrecht, The Netherlands e-mail: A.J.J.Raassen@sron.nl;R.Mewe@sron.nl;R.L.J.van.der.Meer@sron.nl
² Department of Astrophysics, University of Nijmegen, PO Box 9010, 6500 GL Nijmegen, The Netherlands
³ Astronomical Institute “Anton Pannekoek", Kruislaan 403, 1098 SJ Amsterdam, The Netherlands
⁴ Paul Scherrer Institut, Würenlingen & Villigen, 5232 Villigen PSI, Switzerland e-mail: guedel@astro.phys.ethz.ch
⁵ Columbia Astrophysics Laboratory, Columbia University, 550 West 120th Street, New York, NY 10027, USA e-mail: audard@astro.columbia.edu

Corresponding author: E. J. M. van den Besselaar, besselaar@astro.kun.nl

Received: 3 February 2003
Accepted: 2 September 2003

Abstract

The M-dwarf AD Leonis has been observed with the Reflection Grating Spectrometers and the European Photon Imaging Camera aboard XMM-Newton and also with the Low Energy Transmission Grating Spectrometer aboard the Chandra X-ray Observatory. In the observation taken with XMM-Newton five large flares produced by AD Leo were identified and only one in the observation taken with Chandra. A quiescent level to the lightcurves is difficult to define, since several smaller flares mutually overlap each other. However, we defined a quasi-steady state outside of obvious flares or flare decays. The spectra from the flare state and the quasi-steady state are analysed separately. From these spectra the temperature structure was derived with a multi-temperature model and with a differential emission measure model. The multi-temperature model was also used to determine the relative abundances of , , , , , , , and . -like ions, such as and , produce line triplets which are used to determine or constrain the electron temperature and electron density of the corresponding ion. During the flare state a higher emission measure at the hottest temperature is found for both XMM-Newton and Chandra observations. The derived abundances suggest the presence of an inverse First Ionization Potential effect in the corona of AD Leo.