Stellar activity on the young suns of Orion: COUP observations of K5-7 pre-main-sequence stars

被引:180
作者
Wolk, SJ
Harnden, FR
Flaccomio, E
Micela, G
Favata, F
Shang, H
Feigelson, ED
机构
[1] Harvard Smithsonian Ctr Astrophys, Cambridge, MA 02138 USA
[2] INAF, Osservatorio Astron GS Vaiana, I-90134 Palermo, Italy
[3] European Space Technol Ctr, European Space Agcy, Res & Space Sci Support Dept, Div Astrophys, NL-2200 AG Noordwijk, Netherlands
[4] Acad Sinica, Inst Astron & Astrophys, Taipei, Taiwan
[5] Penn State Univ, Dept Astron & Astrophys, University Pk, PA 16802 USA
关键词
meteors; meteoroids; open clusters and associations : individual (Orion Nebula Cluster); stars : activity; stars : pre-main-sequence; Sun : activity; X-rays : stars;
D O I
10.1086/432099
中图分类号
P1 [天文学];
学科分类号
0704 ;
摘要
In 2003 January, the Chandra Orion Ultradeep Project ( COUP) detected about 1400 young stars during a 13.2 day observation of the Orion Nebula Cluster ( ONC). This paper is a study of the X-ray properties of a well-defined sample of 28 solar-mass ONC stars based on COUP data. Our goals are to characterize the magnetic activity of analogs of the young Sun and thereby to improve understanding of the effects of solar X-rays on the solar nebula during the era of planet formation. Given the length of the COUP observation we are able to clearly distinguish characteristic and flare periods for all stars. We find that active young suns spend 70% of their time in a characteristic state with relatively constant flux and magnetically confined plasma with temperatures kT(2) similar or equal to 2.1 x kT(1). During characteristic periods, the 0.5 - 8 keV X-ray luminosity is about 0.03% of the bolometric luminosity. One or two powerful flares per week with peak luminosities log L-X similar to 30 32 ergs s(-1) are typically superposed on this characteristic emission accompanied by heating of the hot plasma component from similar or equal to 2.4 to similar or equal to 7 keVat the flare peak. The energy distribution of flares superposed on the characteristic emission level follows the relationship dN/dE proportional to E-1.7. The flare rates are consistent with the production of sufficiently energetic protons to spawn a spallogenic origin of some important short-lived radionuclides found in ancient meteorites. The X-rays can ionize gas in the circumstellar disk at a rate of 6 x 10(-9) ionizations per second at 1 AU from the central star, orders of magnitude above cosmic-ray ionization rates. The estimated energetic particle fluences are sufficient to account for many isotopic anomalies observed in meteoritic inclusions.
引用
收藏
页码:423 / 449
页数:27
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