AAS 207th Meeting, 8-12 January 2006
Session 74 Planets in Binary Star Systems, Young Stars and Jets
Poster, Tuesday, 9:20am-6:30pm, January 10, 2006, Exhibit Hall

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[74.12] The 2005 Accretion Outburst in V1118 Ori: Evidence for A Spectral Change in X-rays

M. Audard (Columbia Astrophysics Laboratory), M. Güdel (Paul Scherrer Institut), S.L. Skinner (CASA/Univ. of Colorado), K.R. Briggs (Paul Scherrer Institut), F.M. Walter (Stony Brook University), G. Stringfellow (CASA/Univ. of Colorado), R.T. Hamilton, E.F. Guinan (Villanova University)

We present results from our X-ray monitoring campaign of the 2005 accretion outburst in the young low-mass star V1118 Ori. Optical and near-infrared photometry are presented as well. The X-ray data from early 2005 indicate that the X-ray flux and luminosity varied within a factor of two only, and were similar to the pre-outburst values measured in a serendipitous observation in 2002. Similarly, the hydrogen column density showed no evidence for significant excursions from the pre-outburst value of a few times 1021 cm-2. However, we observed a spectral change from a dominant hot plasma (~25 MK) in 2002 and in January 2005 to a cooler plasma (~8 MK) in February and March 2005. We argue that the closing in of the accretion disk during the outburst disrupted the hot magnetic loops high in the corona, whereas the lower cooler loops were less affected and became the dominant coronal component.

We acknowledge support by NASA through Chandra award DD5-6029X and through XMM-Newton award NNG05GI96G to Columbia University. The Chandra X-ray Observatory Center is operated by the Smithsonian Astrophysical Observatory for and on behalf of the NASA under contract NAS8-03060. Based on observations obtained with XMM-Newton, an ESA science mission with instruments and contributions directly funded by ESA Member States and NASA. The PSI group acknowledges support from the Swiss National Science Foundation (grants 20-58827.99 and 20-66875.01). Stony Brook's participation in SMARTS is made possible by support from the offices of the Provost and the Vice President for Research. We thank J. Allyn Smith, P. McGehee, J. Espinoza, and D. Gonzalez for doing the observations with the SMARTS telescopes. We also thank H. Tannanbaum, N. Schartel, and the VLA TOO panel for granting time to observe V1118 Ori.

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