Magnetic activity and hot Jupiters of young Suns: the weak-line T Tauri stars V819 Tau and V830 Tau

Abstract

We report results of a spectropolarimetric and photometric monitoring of the weak-line T Tauri stars (wTTSs) V819 Tau and V830 Tau within the MaTYSSE programme, involving the ESPaDOnS spectropolarimeter at the Canada-France-Hawaii Telescope. At ≃3 Myr, both stars dissipated their discs recently and are interesting objects for probing star and planet formation. Profile distortions and Zeeman signatures are detected in the unpolarized and circularly-polarized lines, whose rotational modulation we modelled using tomographic imaging, yielding brightness and magnetic maps for both stars.We find that the large-scale magnetic fields of V819 Tau and V830 Tau are mostly poloidal and can be approximated at large radii by 350-400 G dipoles tilted at ≃30 • to the rotation axis. They are significantly weaker than the field of GQ Lup, an accreting classical T Tauri star (cTTS) with similar mass and age which can be used to compare the magnetic properties of wTTSs and cTTSs. The reconstructed brightness maps of both stars include cool spots and warm plages. Surface differential rotation is small, typically ≃4.4× smaller than on the Sun, in agreement with previous results on wTTSs.Using our Doppler images to model the activity jitter and filter it out from the radial velocity (RV) curves, we obtain RV residuals with dispersions of 0.033 and 0.104 km s −1 for V819 Tau and V830 Tau respectively. RV residuals suggest that a hot Jupiter may be orbiting V830 Tau, though additional data are needed to confirm this preliminary result. We find no evidence for close-in giant planet around V819 Tau.

Magnetic topologies of young suns: the weak-line T Tauri stars TWA 6 and TWA 8A

“…The data are fit to an aim χ 2 , with the optimal fit determined using the maximumentropy routine of Skilling & Bryan (1984), and where the chosen map is that which contains least information (where entropy is maximized) required to fit the data. For further details about the specific application of our code to wTTSs, we refer the reader to previous papers in the series (e.g., Donati et al 2010Donati et al , 2014Donati et al , 2015.…”

“…The level of surface differential rotation of TWA 6 was determined in a similar manner as that carried out for other wTTSs (e.g., Skelly et al 2008Skelly et al , 2010Donati et al 2014Donati et al , 2015. Assuming that the rotation rate at the surface of the star varies with latitude θ as Ω eq − dΩ sin 2 θ (where Ω eq is the rotation rate at the equator and dΩ is the difference in rotation rate between the equator and the pole), we reconstruct brightness and magnetic maps at a fixed information content for many pairs of Ω eq and dΩ and determine the corresponding reduced chi-squared χ 2 r of our fit to the observations.…”

Magnetic field, activity, and companions of V410 Tau

“…The discrepancy with the value found in the previous paragraph indicates the presence of dark spots on the photosphere even when the star is the brightest. If we assume a spot coverage at maximum brightness of ∼25 %, typical of active stars, (like it was done in Donati et al 2014Donati et al , 2015Yu et al 2017), then the unspotted absolute magnitude would be 3.61 ± 0.32, which corresponds to an inclination 2 of 77 ± 22 • . However, the models best fitting our spectra have an inclination of 50 ± 10 • (see Sec 4), which would require the spot coverage at maximum brightness to actually be ∼50 %.…”

A hot Jupiter orbiting a 2-million-year-old solar-mass T Tauri star

“…Detecting hot Jupiters around T Tauri stars through velocimetry or photometry is thus quite challenging and requires efficient tools for filtering out the dominant jitter that activity induces in the spectra and light curves of young stars. We recently proposed a new method to achieve this goal 11 , whose first applications to non-accreting (weak-line) T Tauri stars proved promising though inconclusive 12 .…”

“…Technically speaking, Doppler imaging follows the principles of maximum-entropy image reconstruction, and iteratively looks for the image with lowest information content that fits the data at a given χ 2 level. For more details on the imaging process, our previous MaTYSSE studies 11,12 give a detailed account of all modelling steps. In this Letter, we carried out Doppler imaging modelling using either unpolarized (Stokes I) spectra only, or both unpolarized and circularly polarized (Stokes V) spectra simultaneously, with identical results regarding filtering performances and the extraction of radial velocity signals.…”