Stable Coronal X-Ray Emission Over Twenty Years of XZ Tau

TL;DR

This study shows that the coronal X-ray emission of the binary YSO XZ Tau AB remains stable over twenty years, with variability mainly due to flares, and suggests that observed scatter in stellar X-ray properties partly results from intrinsic variability.

Contribution

It provides long-term high-resolution X-ray observations of XZ Tau AB, demonstrating stable coronal emission and linking stellar variability to ensemble scatter in X-ray properties.

Findings

Coronal X-ray spectrum remains consistent over twenty years outside flares.

Flares cause short-term variability but do not alter long-term emission levels.

Intrinsic variability contributes to scatter in stellar X-ray properties in clusters.

Abstract

XZ Tau AB is a frequently observed binary YSO in the Taurus Molecular Cloud; XZ Tau B has been classified as an EXOr object. We present new Chandra/HETG-ACIS-S observations of XZ Tau AB, complemented with variability monitoring of the system with XMM-Newton, to constrain the variability of this system and identify high-resolution line diagnostics to better understand the underlying mechanisms that produce the X-rays. We observe two flares with XMM-Newton, but find that outside of these flares the coronal X-ray spectrum of XZ Tau AB is consistent over twenty years of observations. We compare the ensemble of XZ Tau X-ray observations over time with the scatter across stars observed in point-in-time observations of the Orion Nebula Cluster and find that both overlap in terms of plasma properties, i.e., some of the scatter observed in the X-ray properties of stellar ensembles stems from intrinsic source variability.