ROME (Radio Observations of Magnetized Exoplanets). II. HD 189733 Does Not Accrete Significant Material from its Exoplanet like a T Tauri Star from A Disk

TL;DR

This study investigates whether HD 189733 accretes material from its exoplanet like a T Tauri star, finding no evidence of accretion shocks or hotspots and suggesting observed activity is due to stellar magnetism.

Contribution

The paper provides a comprehensive analysis showing that HD 189733 does not exhibit typical accretion signatures, challenging previous claims and offering alternative explanations for observed activity.

Findings

No accretion shocks or hotspots detected in photometric data.

Accretion rate estimated at 10^9 to 10^11 g/s, similar to cometary absorption events.

Observed emissions are consistent with stellar magnetic activity, not accretion.

Abstract

It has been asserted that the primary star in the HD 189733 system steadily accretes evaporated exospheric gases from its ``hot Jupiter'' companion, rather like a T Tauri star accreting from a disk. We conduct statistical and periodogram analyses of the photometric time series of the primary, as acquired by the automated photoelectric telescope (APT), Microvariability and Oscillations of Stars (MOST), and Wise Observatory, to investigate this claim with the goal of revealing the presence of accretion shocks or photospheric accretion hotspots as are found in T Tauri systems such as AA Tau. None of the anticipated features were found. We re-analyze existing radio, optical, ultraviolet, and X-ray data within the framework of accreting T Tauri systems to determine physical quantities such as plasma density and temperature, accretion rate, and flare lengths. We find that with an accretion rate of $\dot{M}\sim10^{9}$ to 10$^{11}$ g s$^{-1}$, the star is more similar to a system that intermittently absorbs gas from sungrazing comets in outburst than classical T Tauri systems, which have accretion rates at least two orders of magnitude larger. If such accretion exists, it would result in undetectably low activity at all wavelengths. Alternatively, all of the emission properties observed thus far are in agreement with stellar activity from a magnetically active star.