| dc.description.abstract | The goals of the research presented in this dissertation are to better understand the characteristics of the X-ray emitting plasmas of young stars and the physical mechanisms that produce the emission. We seek to achieve these goals through the analysis of X-ray observations of a sample of young stars, particularly T Tauri stars, obtained with the CXO. First, we present spatially-resolved X-ray observations of the binary T Tauri star system V710 Tau. Using Chandras Advanced CCD Imaging Spectrometer (ACIS), we imaged this 3.2 separation binary system, consisting of a classical T Tauri star, V710 Tau N, and a weak-lined T Tauri star, V710 Tau S. The Chandra images cleanly resolve the V710 Tau binary, demonstrating that both stars
emit X-rays and thereby enabling the first spectral/ temporal study of the individual
components of this mixed (classical and weak-lined) T Tauri star binary system. The
northern component, V710 Tau N, appears to have been in a flaring state during the first (2004 December) exposure. During this flare event, the X-ray flux of the classical T Tauri star hardened significantly. Single-component plasma models with plasma temperatures in the range kTx ~ 0.7 1.1 keV are adequate to fit the observed X-ray
spectra of V710 Tau S in 2004 December and both stars in 2005 April. The 2004 December flare-state observation of V710 Tau N requires a higher-temperature plasma component (kTx ~ 2.5 3.0 keV) in addition to the soft component (kTx ~ 0.5 keV) and is better fit by a model that includes a slightly enhanced Ne/Fe abundance ratio.
These results are generally consistent with statistical contrasts between the X-ray emission properties of classical (rapidly accreting) vs. weak-lined (weakly accreting or non-accreting) T Tauri stars.
Then, we present analysis of Chandra High Energy Transmission Grating Spectroscopy (HETGS) relatively long integration, high spectral resolution data for a sample of nine young stars, including classical, weak-lined, and post-T Tauri stars as well as a young main sequence star. For five of these nine stars we observed significant
flaring during the Chandra observing epochs. We extracted spectra for each observation, and for the observations with significant flaring, we extracted separate spectra for the flaring and quiescent epochs. From these spectra, we measured the line fluxes of the strongest emission lines, most notably the Hydrogen-like Lyman-alpha line
and the He-like triplet (forbidden, intercombination, and resonance) lines for Si, Mg,
and Ne as well as strong Fe lines. From these line flux measurements, we were able to infer densities and temperatures from line flux ratios sensitive to these properties.
In general, the quiescent state observations have higher densities (as inferred by the density-sensitive R ratio) than the flaring state observations. By measuring elemental abundance ratios, we find that all the observations of the stars in our sample have a high Ne/Fe ratio, but only one, TW Hya in quiescence, shows an enhanced Ne/O ratio. The X-ray emitting plasmas of the stars in our sample are therefore not likely
to be depleted of grain forming elements. | |
