Stellar X-ray variability and planetary evolution in the DS Tucanae system

TL;DR

This study analyzes X-ray variability in the DS Tucanae system, revealing stellar activity cycles and flaring behavior, and explores potential evolutionary paths for its exoplanet, emphasizing the need for further observations.

Contribution

It provides the first evidence of a possible stellar activity cycle in a very young star and models the potential long-term evolution of its exoplanet based on X-ray variability.

Findings

Detected X-ray flares and variability on hours to months timescales.

Observed a monotonic decline in stellar X-ray emission suggesting an activity cycle.

Predicted diverse evolutionary outcomes for the exoplanet, from Neptune-like to stripped super-Earth.

Abstract

We present an analysis of four Chandra observations of the 45 Myr old DS Tuc binary system. We observed X-ray variability of both stars on timescales from hours to months, including two strong X-ray flares from star A. The implied flaring rates are in agreement with past observations made with XMM-Newton, though these rates remain imprecise due to the relatively short total observation time. We find a clear, monotonic decline in the quiescent level of the star by a factor 1.8 across eight months, suggesting stellar variability that might be due to an activity cycle. If proven through future observations, DS Tuc A would be the youngest star for which a coronal activity cycle has been confirmed. The variation in our flux measurements across the four visits is also consistent with the scatter in empirical stellar X-ray relationships with Rossby number. In simulations of the possible evolution of the currently super-Neptune-sized planet DS Tuc Ab, we find a range of scenarios for the planet once it reaches a typical field age of 5 Gyr, from Neptune-size down to a completely stripped super-Earth. Improved constraints on the planet's mass in the future would significantly narrow these possibilities. We advocate for further Chandra observations to better constrain the variability of this important system.