Chandra and XMM-Newton X-ray Observations of the Hyperactive T Tauri Star RY Tau

TL;DR

This study uses Chandra and XMM-Newton X-ray observations to analyze the physical mechanisms behind the bright X-ray emission of the T Tauri star RY Tau, revealing hot plasma dominated emission with complex variability.

Contribution

First detailed high-resolution X-ray spectral analysis of RY Tau, identifying the dominance of hot plasma and magnetic origins of flares and variability.

Findings

X-ray emission dominated by very hot plasma at ~50 MK

Presence of short-duration superhot flares and complex variability

Weak contribution from cool plasma possibly related to accretion shocks

Abstract

We present results of pointed X-ray observations of the accreting jet-driving T Tauri star RY Tau using Chandra and XMM-Newton. We obtained high-resolution grating spectra and excellent-quality CCD spectra and light curves with the objective of identifying the physical mechanisms underlying RY Tau's bright X-ray emission. Grating spectra reveal numerous emission lines spanning a broad range of temperature superimposed on a hot continuum. The X-ray emission measure distribution is dominated by very hot plasma at T_hot ~ 50 MK but higher temperatures were present during flares. A weaker cool plasma component is also present as revealed by low-temperature lines such as O VIII. X-ray light curves show complex variability consisting of short-duration (~hours) superhot flares accompanied by fluorescent Fe emission at 6.4 keV superimposed on a slowly-varying (~one day) component that may be tied to stellar rotation. The hot flaring component is undoubtedly of magnetic (e.g. coronal) origin. Soft and hard-band light curves undergo similar slow variability implying that at least some of the cool plasma shares a common magnetic origin with the hot plasma. Any contribution to the X-ray emission from cool shocked plasma is small compared to the dominant hot component but production of individual low-temperature lines such as O VIII in an accretion shock is not ruled out.