Stellar Activity on the Young Suns of Orion: COUP Observations of K5‐7 Pre–Main‐Sequence Stars

In January 2003, 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 1 Universe Division, Science Mission Directorate NASA Headquarters – 2 – 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 kT2 ≃ 2.1 × kT1. 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

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