UVES spectroscopy of T Chamaeleontis: line variability, mass accretion rate, and spectro-astrometric analysis
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 disc object T Chamaeleontis 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. Hα and [O I] λ 6300, the most prominent lines, were analysed using spectro-astrometry. Hα being a direct accretion tracer is the target for the T Cha b detection, while [O I] λ 6300 is considered to be an indirect tracer of accretion. [O I] λ 6300 is classified as a broad low-velocity component (BC LVC). \dot{M}_acc was derived for all epochs using new [O I] λ 6300 LVC relationships and the Hα line luminosity. It is shown that a wind is the likely origin of the [O I] λ 6300 line and that the [O I] λ 6300 line serves as a better accretion tracer than Hα in this case. From the comparison between \dot{M}_acc({[O I]}) and \dot{M}_acc(Hα) it is concluded that T Cha is not an intrinsically weak accretor but rather that a significant proportion of the Hα 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 a limit on the strength of the Hα emission from accreting planetary companions, and thus can have an important input into the planning of high-angular resolution observations.
- Publication:
-
Monthly Notices of the Royal Astronomical Society
- Pub Date:
- April 2019
- DOI:
- 10.1093/mnras/stz280
- arXiv:
- arXiv:1902.01170
- Bibcode:
- 2019MNRAS.484.4315C
- Keywords:
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- techniques: high angular resolution;
- techniques: spectroscopic;
- planets and satellites: individual: T Cha;
- stars: pre-main-sequence;
- Astrophysics - Solar and Stellar Astrophysics
- E-Print:
- doi:10.1093/mnras/stz280