Analysis and modeling of high temporal resolution spectroscopic observations of flares on AD Leonis

¹ Departamento de Astrofísica, Facultad de Ciencias Físicas, Universidad Complutense de Madrid, 28040 Madrid, Spain e-mail: icc@astrax.fis.ucm.es
² Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138, USA
³ Armagh Observatory, College Hill, Armagh BT61 9DG, Northern Ireland
⁴ Osservatorio Astronomico di Palermo, Piazza del Parlamento 1, 90134 Palermo, Italy
⁵ Research Division, ESA Space Science Department, ESTEC/SCI-R, PO Box 299, 2200 AG Noordwijk, The Netherlands

Received: 10 June 2005
Accepted: 1 February 2006

Abstract

We report the results of a high temporal resolution spectroscopic monitoring of the flare star AD Leo. During 4 nights, more than 600 spectra were taken in the optical range using the Isaac Newton Telescope (INT) and the Intermediate Dispersion Spectrograph (IDS). We observed a large number of short and weak flares occurring very frequently (flare activity > 0.71 h^-1). This is consistent with the very important role that flares can play in stellar coronal heating. The detected flares are non white-light flares and, although most solar flares are of this kind, very few such events have been observed previously in stars. The behaviour of different chromospheric lines (Balmer series from Hα to H₁₁, H & K, D₁ and D₂, 4026 Å and D₃) was studied in detail for a total of 14 flares. We estimated the physical parameters of the flaring plasma by using a procedure that assumes a simplified slab model of flares. All the obtained physical parameters are consistent with previously derived values for stellar flares, and the areas – less than 2.3% of the stellar surface – are comparable with the size inferred for other solar and stellar flares. We studied the relationships between the physical parameters and the area, duration, maximum flux and energy released during the detected flares.