Astrometric and photometric characterization of $\eta$ Tel B combining two decades of observations

TL;DR

This study combines two decades of observations to precisely characterize the orbit, mass, and environment of the brown dwarf companion $ au$ Tel B, achieving unprecedented astrometric accuracy and constraining potential satellites or disks.

Contribution

It provides the first detailed orbital and photometric analysis of $ au$ Tel B using new high-contrast imaging data and Gaia-Hipparcos astrometry, refining its orbital parameters and mass.

Findings

$ au$ Tel B has a low-eccentricity orbit with semi-major axis of 218 au.

Astrometric measurements achieved the smallest uncertainties to date.

No satellites or disks were detected around $ au$ Tel B within detection limits.

Abstract

$\eta$ Tel is an 18 Myr system with a 2.09 M$_{\odot}$ A-type star and an M7-M8 brown dwarf companion, $\eta$ Tel B, separated by 4.2'' (208 au). High-contrast imaging campaigns over 20 years have enabled orbital and photometric characterization. $\eta$ Tel B, bright and on a wide orbit, is ideal for detailed examination. We analyzed three new SPHERE/IRDIS coronagraphic observations to explore $\eta$ Tel B's orbital parameters, contrast, and surroundings, aiming to detect a circumplanetary disk or close companion. Reduced IRDIS data achieved a contrast of 1.0$\times 10^{-5}$, enabling astrometric measurements with uncertainties of 4 mas in separation and 0.2 degrees in position angle, the smallest so far. With a contrast of 6.8 magnitudes in the H band, $\eta$ Tel B's separation and position angle were measured as 4.218'' and 167.3 degrees, respectively. Orbital analysis using Orvara code, considering Gaia-Hipparcos acceleration, revealed a low eccentric orbit (e $\sim$ 0.34), inclination of 81.9 degrees, and semi-major axis of 218 au. $\eta$ Tel B's mass was determined to be 48 \MJup, consistent with previous calculations. No significant residual indicating a satellite or disk around $\eta$ Tel B was detected. Detection limits ruled out massive objects around $\eta$ Tel B with masses down to 1.6 \MJup at a separation of 33 au.