The GAPS Programme at TNG

Abstract

Context. Detecting and characterising exoworlds around very young stars (age ≤10 Myr) are key aspects of exoplanet demographic studies, especially for understanding the mechanisms and timescales of planet formation and migration. Any reliable theory for such physical phenomena requires a robust observational database to be tested. However, detection using the radial velocity method alone can be very challenging because the amplitude of the signals caused by the magnetic activity of such stars can be orders of magnitude larger than those induced even by massive planets. Aims. We observed the very young (~2 Myr) and very active star V830 Tau with the HARPS-N spectrograph between October 2017 and March 2020 to independently confirm and characterise the previously reported hot Jupiter V830 Tau b (Kb = 68 ± 11 m s−1; mb sin ib = 0.57 ± 0.10 MJup; Pb = 4.927 ± 0.008 d). Methods. Because of the observed ~1 km s−1 radial velocity scatter that can clearly be attributed to the magnetic activity of V830 Tau, we analysed radial velocities extracted with different pipelines and modelled them using several state-of-the-art tools. We devised injection-recovery simulations to support our results and characterise our detection limits. The analysis of the radial velocities was aided by a characterisation of the stellar activity using simultaneous photometric and spectroscopic diagnostics. Results. Despite the high quality of our HARPS-N data and the diversity of tests we performed, we were unable to detect the planet V830 Tau b in our data and cannot confirm its existence. Our simulations show that a statistically significant detection of the claimed planetary Doppler signal is very challenging. Conclusions. It is important to continue Doppler searches for planets around young stars, but utmost care must be taken in the attempt to overcome the technical difficulties to be faced in order to achieve their detection and characterisation. This point must be kept in mind when assessing their occurrence rate, formation mechanisms, and migration pathways, especially without evidence of their existence from photometric transits.

Cluster Difference Imaging Photometric Survey. II. TOI 837: A Young Validated Planet in IC 2602

“…RV surveys of highly active pre-main-sequence (PMS) stars in Taurus also led to the youngest hot Jupiters yet reported orbiting V830Tau, TAP26, and CITau (Donati et al 2016;Johns-Krull et al 2016;Yu et al 2017;Biddle et al 2018;Flagg et al 2019). The planetary nature of at least two of these signals has been debated (Damasso et al 2020;Donati et al 2020).…”

LRG-BEASTS: sodium absorption and Rayleigh scattering in the atmosphere of WASP-94A b using NTT/EFOSC2

“…Carter & Winn 2009;Csizmadia et al 2015;Aigrain et al 2016;Pepper et al 2017;Luger et al 2017;Santerne et al 2018;Lienhard et al 2020;Nowak et al 2020;Leleu et al 2021), in disentangling planetary signals from stellar activity in radial velocity signals (e.g. Haywood et al 2014;Rajpaul et al 2015Rajpaul et al , 2016Faria et al 2016;Suárez Mascareño et al 2018;Barragán et al 2019;Damasso et al 2020;Ahrer et al 2021) and in transmission spectroscopy (e.g. Gibson et al 2012aGibson et al ,b, 2013aEvans et al 2015;Hirano et al 2016;Evans et al 2016;Cartier et al 2016;Louden et al 2017;Kirk et al 2017Kirk et al , 2018Kirk et al , 2019Kirk et al , 2021.…”

A HARPS-N mass for the elusive Kepler-37d: a case study in disentangling stellar activity and planetary signals

“…For example, a subset of local RVs exhibiting periodicities known to be associated with the stellar rotation period could be excluded, or a clustering analysis might help identify chunks with similar properties and link problematic chunks with one another. We adopted a conservative version of a simple approach that has at least been tested on both synthetic and real spectra (Damasso et al 2020;Rajpaul et al 2020); specifically, we excluded all chunks exhibiting the following simple properties:…”

“…In the case of very strong stellar variability, it can well be the case (e.g. Damasso et al 2020) that even when combining local chunk RVs that all appear uncorrelated with activity indicators -due to low SNR -the resultant RVs nevertheless exhibit overwhelming correlations with activity indicators. On a related note, the traditional activity indicators we used are only imperfect proxies for activity signals in RVs.…”