Astronomy and Astrophysics – Astronomy
Scientific paper
Dec 1998
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1998apj...509..761s&link_type=abstract
The Astrophysical Journal, Volume 509, Issue 2, pp. 761-767.
Astronomy and Astrophysics
Astronomy
24
Ism: Individual (L1517), Stars: Coronae, Stars: Individual (Hd 282624 ), Stars: Individual ( Su Aur), Stars: Pre-Main-Sequence, X-Rays: Stars
Scientific paper
We present the results of a ~40 ks pointed ASCA observation of the L1517 star-forming region, centered on the X-ray-bright T Tauri star SU Aurigae. This star has the highest X-ray luminosity of any classical T Tauri star in the Taurus-Auriga region, and its optical spectra show evidence for both mass inflow and outflow. Strong X-ray emission was detected from SU Aur (L_x = 10^30.9 ergs s^-1) as well as weaker emission from five other pre-main-sequence stars. Although no large-amplitude flares were detected, the X-ray emission of SU Aur showed clear variability in the form of a slow decline in count rate during the 1.3 day observation. We provide the first direct comparison of the coronal differential emission measure (DEM) distribution of a classical T Tauri star with that of a young main-sequence star of similar spectral type. The DEM distributions of SU Aur (G2; age 3 Myr) and the young solar-like star EK Draconis (G0 V; age 70 Myr) are qualitatively similar, with both showing a bimodal temperature distribution characterized by a cool plasma component peaking at ~8-9 MK and a hot component peaking at ~20-21 MK. However, there is a striking difference in the relative proportion of plasma at high temperatures in the two stars, with hot plasma (>=20 MK) accounting for ~80% of the volume emission measure of SU Aur, compared to only ~40% in EK Dra. These results provide new insight into the changes that will occur in the corona of a T Tauri star as it descends onto the main sequence. A sharp decline in the fraction of coronal plasma at flarelike temperatures will occur during the late-T Tauri and post-T Tauri phases, and other recent X-ray studies have shown that this decline will continue after the young solar-like star reaches the main sequence.
Skinner Stephen Lee
Walter Frederick M.
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