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Title:
X-Ray Variability of σ Orionis Young Stars as Observed with ROSAT
Authors:
Caballero, J. A.; López-Santiago, J.; de Castro, E.; Cornide, M.
Affiliation:
AA(Investigador Juan de-la-Cierva at the UCM. ), AB(Departamento de Astrofísica y Ciencias de la Atmósfera, Facultad de Física, Universidad Complutense de Madrid, E-28040 Madrid, Spain ), AC(Departamento de Astrofísica y Ciencias de la Atmósfera, Facultad de Física, Universidad Complutense de Madrid, E-28040 Madrid, Spain ), AD(Departamento de Astrofísica y Ciencias de la Atmósfera, Facultad de Física, Universidad Complutense de Madrid, E-28040 Madrid, Spain )
Publication:
The Astronomical Journal, Volume 137, Issue 6, pp. 5012-5021 (2009). (AJ Homepage)
Publication Date:
06/2009
Origin:
IOP
AJ Keywords:
open clusters and associations: individual: sigma Orionis, stars: activity, X-rays: stars
DOI:
10.1088/0004-6256/137/6/5012
Bibliographic Code:
2009AJ....137.5012C

Abstract

We used the Aladin Virtual Observatory tool and High Resolution Imager ROSAT archival data to search for X-ray variability in scale of days in 23 young stars in the σ Orionis cluster and a background galaxy. Five stars displayed unambiguous flares and had probabilities p varGt 99% of being actual variables. Two of the detected flares were violent and long lasting, with maximum duration of six days and amplitude of eight times above the quiescent level. We classified another four stars as possible X-ray variables, including the binary system formed by the B2Vp star σ Ori E and its close late-type companion. This makes a minimum frequency of high-amplitude X-ray variability in excess of a day of 39% among σ Orionis stars. The incidence of this kind of X-ray variability seems to be lower among classical T Tauri stars with mid-infrared flux excesses than among fast-rotating, disk-less young stars.
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