# UVES Spectroscopy of T Chamaeleontis: Line Variability, Mass Accretion Rate and Spectro-astrometric Analysis

## TL;DR

This study uses spectro-astrometry on T Chamaeleontis to analyze line variability and accretion rates, assessing the potential to detect its protoplanet T Cha b and constraining the star's properties.

## Contribution

It demonstrates the application and limitations of spectro-astrometry in detecting protoplanets and measuring accretion in transitional disk objects.

## Key findings

- [O I] 6300 line is a better accretion tracer than Hα for T Cha.
- T Cha is not an intrinsically weak accretor; Hα emission is partly obscured.
- Spectro-astrometry can set limits on planetary companion emissions.

## Abstract

Although advances in exoplanet detection techniques have seen an increase in discoveries, observing a planet in the earliest stages of formation still remains a difficult task. Here four epochs of spectra of the transitional disk object T Cha are analysed to determine whether spectro-astrometry can be used to detect a signal from its proposed protoplanet, T Cha b. The unique properties of T Cha are also further constrained. H{\alpha} and [O I]{\lambda} 6300, the most prominent lines, were analysed using spectro-astrometry. H{\alpha} being a direct accretion tracer is the target for the T Cha b detection while [O I]{\lambda} 6300 is considered to be an indirect tracer of accretion. [O I]{\lambda} 6300 is classified as a broad low velocity component (BC LVC). The mass accretion rate was derived for all epochs using new [O I]{\lambda} 6300 LVC relationships and the H{\alpha} line luminosity. It is shown that a wind is the likely origin of the [O I]{\lambda} 6300 line and that the [O I]{\lambda} 6300 line serves as a better accretion tracer than H{\alpha} in this case. From the comparison between M acc([OI]) and M acc(H{\alpha}) it is concluded that T Cha is not an intrinsically weak accretor but rather that a significant proportion of the H{\alpha} emission tracing accretion is obscured. T Cha b is not detected in the spectro-astrometric analysis yet a detection limit of 0.5 mas is derived. The analysis in this case was hampered by spectro-astrometric artefacts and by the unique properties of T Cha. While it seems that spectro-astrometry as a means of detecting exoplanets in TDs can be challenging it can be used to put an limit on the strength of the H{\alpha} emission from accreting planetary companions and thus can have an important input into the planning of high angular resolution observations.