期刊
ASTRONOMICAL JOURNAL
卷 137, 期 6, 页码 5012-5021出版社
IOP PUBLISHING LTD
DOI: 10.1088/0004-6256/137/6/5012
关键词
open clusters and associations: individual (sigma Orionis); stars: activity; X-rays: stars
资金
- Universidad Complutense de Madrid
- Comunidad Autonoma de Madrid
- Spanish Ministerio Educacion y Ciencia
- European Social Fund [AyA200502750, AyA2005-04286, AyA2005-24102-E, AyA2008-06423C03-03, AyA2008-00695, PRICITS-0505/ESP-0237, CSD2006-0070]
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 sigma Orionis cluster and a background galaxy. Five stars displayed unambiguous flares and had probabilities p(var) >> 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 sigma 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 sigma 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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