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A Comparison of the X-Ray Properties of FU Ori-type Stars to Generic Young Stellar Objects

Kuhn, Michael A. and Hillenbrand, Lynne A. (2019) A Comparison of the X-Ray Properties of FU Ori-type Stars to Generic Young Stellar Objects. Astrophysical Journal, 883 (2). Art. No. 117. ISSN 1538-4357. doi:10.3847/1538-4357/ab3a3f.

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Like other young stellar objects (YSOs), FU Ori-type stars have been detected as strong X-ray emitters. However, little is known about how the outbursts of these stars affect their X-ray properties. We assemble available X-ray data from XMM-Newton and Chandra observations of 16 FU Ori stars, including a new XMM-Newton observation of Gaia 17bpi during its optical rise phase. Of these stars, six were detected at least once, while 10 were non-detections, for which we calculate upper limits on intrinsic X-ray luminosity (L_X) as a function of plasma temperature (kT) and column density (N_H). The detected FU Ori stars tend to be more X-ray luminous than is typical for non-outbursting YSOs, based on comparison to a sample of low-mass stars in the Orion Nebula Cluster. FU Ori stars with high L X have been observed both at the onset of their outbursts and decades later. We use the Kaplan–Meier estimator to investigate whether the higher X-ray luminosities for FU Ori stars are characteristic or a result of selection effects, and we find the difference to be statistically significant (p < 0.01) even when non-detections are taken into account. The additional X-ray luminosity of FU Ori stars relative to non-outbursting YSOs cannot be explained by accretion shocks, given the high observed plasma temperatures. This suggests that, for many FU Ori stars, either (1) the outburst leads to a restructuring of the magnetosphere in a way that enhances X-ray emission, or (2) FU Ori outbursts are more likely to occur among YSOs with the highest quiescent X-ray luminosity.

Item Type:Article
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URLURL TypeDescription Paper
Kuhn, Michael A.0000-0002-0631-7514
Additional Information:© 2019 The American Astronomical Society. Received 2019 May 10; revised 2019 July 31; accepted 2019 August 9; published 2019 September 26. We thank the XMM-Newton team for approving Gaia 17bpi as an unanticipated TOO. We would like to thank Hannah Earnshaw for advice on reducing the XMM-Newton data, Matthew Povich for useful discussions about star-forming regions, and the anonymous referee for suggestions that improved the manuscript. Facilities: XMM-Newton - , Chandra X-ray Observatory. - Software: CIAO (Fruscione et al. 2006), HEASOFT (HEASARC 2014), PIMMS (Mukai 1993), R (R Core Team 2018), SAS (SAS Development Team 2014), survival (Therneau & Grambsch 2000), TOPCAT (Taylor 2005), XSPEC (Arnaud 1996).
Group:Astronomy Department
Issue or Number:2
Record Number:CaltechAUTHORS:20190927-091850997
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Official Citation:Michael A. Kuhn and Lynne A. Hillenbrand 2019 ApJ 883 117
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:98900
Deposited By: Tony Diaz
Deposited On:27 Sep 2019 18:02
Last Modified:16 Nov 2021 17:42

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