The GAPS Programme at TNG

Abstract

Context. The existence of hot Jupiters is still not well understood. Two main channels are thought to be responsible for their current location: a smooth planet migration through the proto-planetary disk or the circularization of an initial high eccentric orbit by tidal dissipation leading to a strong decrease of the semimajor axis. Different formation scenarios result in different observable effects, such as orbital parameters (obliquity/eccentricity), or frequency of planets at different stellar ages. Aims. In the context of the GAPS Young-Objects project, we are carrying out a radial velocity survey with the aim to search and characterize young hot-Jupiter planets. Our purpose is to put constraints on evolutionary models and establish statistical properties, such as the frequency of these planets from a homogeneous sample. Methods. Since young stars are in general magnetically very active, we performed multi-band (visible and near-infrared) spectroscopy with simultaneous GIANO-B + HARPS-N (GIARPS) observing mode at TNG. This helps to deal with stellar activity and distinguish the nature of radial velocity variations: stellar activity will introduce a wavelength-dependent radial velocity amplitude, whereas a Keplerian signal is achromatic. As a pilot study, we present here the cases of two already claimed hot Jupiters orbiting young stars: HD 285507 b and AD Leo b. Results. Our analysis of simultaneous high-precision GIARPS spectroscopic data confirms the Keplerian nature of HD285507's radial velocities variation and refines the orbital parameters of the hot Jupiter, obtaining an eccentricity consistent with a circular orbit. On the other hand, our analysis does not confirm the signal previously attributed to a planet orbiting AD Leo. This demonstrates the power of the multi-band spectroscopic technique when observing active stars.

Persistent Starspot Signals on M Dwarfs: Multiwavelength Doppler Observations with the Habitable-zone Planet Finder and Keck/HIRES

“…Further evidence that the RV rotation signal may not be entirely due to starspots is the 8 m s −1 NIR amplitude we observe with HPF. This amplitude is consistent with the prediction of Reiners et al (2013) and Carleo et al (2020) if the NIR variability is caused by Zeeman splitting rather than spotphotosphere contrast.…”

“…The RV signal at the rotation period is inconsistent between the optical and NIR RVs, and even between seasons for the HPF RVs-the HPF RVs exhibit a much higher rms scatter in the 2018 season (23 m s −1 ) than in 2019 (6.4 m s −1 ). This drop in variability from 2018 to 2019 is also observed by Carleo et al (2020) in visible-band HARPS-N RVs. In Figure 1, we show the 2019 HPF RVs, folded to the best-fit model at the rotation period, as identified by radvel (Fulton et al 2018).…”

“…We find that the joint HIRES+HARPS+HPF RV time series for AD Leo is incompatible with the presence of a giant exoplanet in spin-orbit resonance, in agreement with Carleo et al (2020). The starspot signal that caused Tuomi et al (2018) to propose a planet persisted throughout the 6 month observing season in 2006.…”

“…Walker et al (2012), which shows the photometric signal evolving over approximately two cycles. Carleo et al (2020) suggest that, instead of originating from dark starspots, the RV variations for AD Leo might be tied to inhibition of convection from the global magnetic field. In this hypothesis, the RV rotation signal will decay as the global field evolves, as observed by Lavail et al (2018), rather than with individual starspots.…”

Exploring the robustness of Keplerian signals to the removal of active and telluric features

“…Even fewer studies do rigorous analysis of wavelength dependence of a signal, which would ensure robustness of a planetary detection (e.g. Feng et al 2017a,c;Tuomi et al 2018;Carleo et al 2020). We quantify Keplerian signal robustness using this method with our active and telluric lines lists and further test on another active star HD 40979 with a different spectral type (Section 3.2).…”