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Title page for ETD etd-03232012-215624


Type of Document Dissertation
Author Teets, William Kenneth
Author's Email Address william.k.teets@vanderbilt.edu
URN etd-03232012-215624
Title Evidence of Accretion-Generated X-rays in the Young, Erupting Stars V1647 Ori and EX Lupi
Degree PhD
Department Physics
Advisory Committee
Advisor Name Title
David Weintraub Committee Chair
Andreas Berlind Committee Member
David Jon Furbish Committee Member
Keivan Stassun Committee Member
Kelly Holley-Bockelmann Committee Member
Keywords
  • star formation
  • X-rays
  • pre-main sequence
  • T Tauri
  • accretion
Date of Defense 2012-03-02
Availability unrestricted
Abstract
We have observed two erupting, pre-main sequence stars, V1647 Ori and EX Lupi, with the Chandra X-ray Observatory during their 2008 optical eruptions. Our intensive X-ray monitoring of these objects affords the opportunity to investigate whether and how the intense X-ray emission is related to pre-main sequence accretion activity. All of our Chandra observations demonstrate that variations in the X- ray luminosity of both V1647 Ori and EX Lupi are correlated with similar changes in the optical/near-infrared brightness of this source during the eruptions, strongly supporting the hypothesis that accretion is the primary generation mechanism for these X-ray outbursts.

The Chandra monitoring demonstrates that the X-ray spectral properties of the 2008 eruption of V1647 Ori were strikingly similar to those of the 2003 eruption. We find that X-ray spectra obtained immediately following the second outburst are well modeled as a heavily absorbed (NH ~ 4 × 1022 cm−2), single-component plasma with characteristic temperatures (kTX ~ 2–6 keV) that are consistently too high to be generated via accretion shocks but are in the range expected for plasma heated by magnetic reconnection events. We also find that the X-ray absorbing column has not changed significantly throughout the observing campaign. Since the OIR and X-ray changes are correlated, we hypothesize that these reconnection events either occur in the accretion stream connecting the circumstellar disk to the star or in accretion- enhanced protostellar coronal activity.

From our models of the X-ray spectra of EX Lupi , we find strong evidence for a ~0.3 keV plasma component, which is that expected for accretion shock-generated plasma. During the optical outburst, we find the X-ray spectrum is best modeled with at least two plasma components, with temperatures of ≤1.0 and ≥2.0 keV. From 2008 March through October, the lower-temperature plasma component appears to fade as EX Lupi returns to its quiescent level in the optical, with this fading of the lower- temperature component being consistent with a decrease in accretion shock-generated plasma and the accompanying X-ray luminosity. These results contrast with results from X-ray observations of the erupting young star V1647 Ori during the 2003 and 2008 optical outbursts.

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