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Detection of a Cool, Accretion-Shock-Generated X-Ray Plasma in EX Lupi During the 2008 Optical EruptionEX Lupi is the prototype for a class of young, pre-main-sequence stars which are observed to undergo irregular, presumably accretion-generated, optical outbursts that result in a several magnitude rise of the optical flux. EX Lupi was observed to optically erupt in 2008 January, triggering Chandra ACIS Target of Opportunity observations shortly thereafter. We find very strong evidence that most of the X-ray emission in the first few months after the optical outburst is generated by accretion of circumstellar material onto the stellar photosphere. Specifically, we find a strong correlation between the decreasing optical and X-ray fluxes following the peak of the outburst in the optical, which suggests that these observed declines in both the optical and X-ray fluxes are the result of declining accretion rate. In addition, in our models of the X-ray spectrum, we find strong evidence for an approx 0.4 keV plasma component, as expected for accretion shocks on low-mass, pre-main-sequence stars. From 2008 March through October, this cool plasma component appeared to fade as EX Lupi returned to its quiescent level in the optical, consistent with a decrease in the overall emission measure of accretion-shock-generated plasma. The overall small increase of the X-ray flux during the optical outburst of EX Lupi is similar to what was observed in previous X-ray observations of the 2005 optical outburst of the EX Lupi-type star V1118 Ori but contrasts with the large increase of the X-ray flux from the erupting young star V1647 Ori during its 2003 and 2008 optical outbursts.
Document ID
20130012785
Acquisition Source
Goddard Space Flight Center
Document Type
Reprint (Version printed in journal)
External Source(s)
doi:10.1088/0004-637X/760/1/89
Authors
Teets, William K. (NASA Goddard Space Flight Center Greenbelt, MD, United States)
Weintraub, David A. (NASA Goddard Space Flight Center Greenbelt, MD, United States)
Kastner, Joel H. (Rochester Inst. of Tech. Rochester, NY, United States)
Grosso, Nicholas (Strasbourg Univ. France)
Hamaguchi, Kenji (NASA Goddard Space Flight Center Greenbelt, MD, United States)
Richmond, Michael (Rochester Inst. of Tech. Rochester, NY, United States)
Date Acquired
August 27, 2013
Publication Date
November 20, 2012
Publication Information
Publication: The Astrophysical Journal
Volume: 760
Issue: 1
Subject Category
Astronomy
Report/Patent Number
GSFC-E-DAA-TN7968
Funding Number(s)
CONTRACT_GRANT: NNG06EO90A
Distribution Limits
Public
Copyright
Public Use Permitted.

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