Kavli Affiliate: Moritz Guenther
| First 5 Authors: Steven M. Silverberg, Scott J. Wolk, David A. Principe, P. Christian Schneider, Hans Moritz Guenther
| Summary:
HL Tau is one of the most well-studied Class I young stellar objects,
including frequent observations at near- and mid-infrared, (sub-) millimeter,
and X-ray wavelengths. We present the results of an X-ray variability
monitoring campaign with XMM-Newton in 2020 and X-ray gratings spectroscopy
from Chandra/HETGS in 2018. We find that the X-ray spectrum of HL Tau is
consistently hot (with characteristic plasma temperatures $T gtrsim 30$ MK)
over 31 epochs spanning 20 years, which is consistent in temperature with most
Class I YSOs. The high-resolution HETG spectrum indicates the presence of some
cooler plasma. We characterize the variability of the star across the 31
observations and find a subset of observations with significant variability on
a $sim$21-day timescale in the observed count rate and flux. We discuss the
possible origins of this variability, and identify further observations that
would better constrain the nature of the changes.
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