High-resolution X-ray spectra of high-mass stars and low-mass T-Tauri stars obtained during the first year of the Chandra mission are providing important clues about the mechanisms which produce X-rays on very young stars .
For \zeta Pup ( O4 If ) and \zeta Ori ( O9.5 I ) , the broad , blue-shifted line profiles , line ratios , and derived temperature distribution suggest that the X-rays are produced throughout the wind via instability-driven wind shocks .
For some less luminous OB stars , like \theta ^ { 1 } Ori C ( O7 V ) and \tau Sco ( B0 V ) , the line profiles are symmetric and narrower .
The presence of time-variable emission and very high-temperature lines in \theta ^ { 1 } Ori C and \tau Sco suggest that magnetically confined wind shocks may be at work .
The grating spectrum of the classical T-Tauri star TW Hya is remarkable because the forbidden-line emission of He-like Ne IX and O VII is very weak , implying that the X-ray emitting region is very dense , n _ { e } \approx 6 \times 10 ^ { 12 } { ~ { } cm } ^ { -3 } , or that the X-rays are produced very close to the ultraviolet hotspot at the base of an accretion funnel .
ACIS light curves and spectra of flares and low-mass and high-mass young stellar objects in Orion and \rho Ophiuchus further suggest that extreme magnetic activity is a general property of many very young stars .