X-ray Study of Low-mass Young Stellar Objects in the ρ Ophiuchi ...

Chapter 9ConclusionWe summarize the main results of the systematic analysis of two Chandra observations of ρ Ophwith ≈100 ks exposure as follows;1. From the central ∼1 pc × 2 pc region of ρ Oph, we detect 195 X-ray sources. About 60 % ofthem (110) are identified with optical and/or infrared counterpart, including class I, II, andIII sources and some young brown dwarfs. The X-ray detection rate is surprisingly high of∼60 %, hence we suspect that virtually all YSOs in ρ Oph may emit X-rays.2. A total of 71 flares are detected. Most of the flares show the typical profile of the solar andstellar flares, while some bright flares have unusually long rise timescale.3. All the X-ray spectra are well fitted by a single temperature thin plasma model of 0.3 solarabundances except for some sources. The plasma temperature is 0.6–5 keV in the quiescentphase, then becomes systematically higher (1–10 keV) in the flare phase. Class I–II sourcesshow higher flare temperature than class III sources.4. We find positive correlations of N H vs A V , < L X > vs L bol , < L X > vs mass, and < L X >vs L R .5. There is a positive correlation between τ r and τ d , which is well explained by the standardmagnetic reconnection model. Shorter τ r and τ d are due to the smaller L and/or larger Bvalues.6. We find a negative correlation between < kT > and τ r , which indicates the same order of theflare loop length regardless of their classes. Larger < kT > values for class I and II sourcesare due to larger B values.117