Seminars at FGG
Identifying new hot Neptune-sized exoplanets ideal for high-resolution atmospheric spectroscopy follow-up
Speaker: Francesca Manni (INAF - Osservatorio Astronomico di Torino (Italy))
Date and time: 2025-03-05 12:00
The hot Neptune desert refers to a region in the exoplanet population where few sub-Neptunes and hot Neptunes are found, particularly those with short orbital periods and high irradiation, even though selection bias favors the detection of such planets. This suggests that short-period planets are intrinsically rare. Moreover, Kepler data has revealed a bimodal distribution of small planets, with a noticeable gap in sizes between roughly 1.5 - 2 R⊕, often called the radius gap. Planets on either side of the gap fall into two main categories: super-Earths, generally rocky with radii between 1.2 - 1.7 R⊕, an sub-Neptunes, larger planets with radii between 1.7 - 4 R⊕ rich in volatiles. Some super-Earths may be stripped cores of sub-Neptunes, highlighting the crucial role mass loss plays in the early evolution of exoplanets during the first few hundred million years. Strong irradiation typically leads to planets being either small and rocky, with masses below 10 M⊕ and radii less than 2 R⊕, or large gas giants with radii exceeding 1 Jupiter radius (RJ). Until recently, the hot Neptune desert was almost devoid of known planets, but recent discoveries have begun to populate this region. However, the number of planets found is still too small to determine the conditions that allow their existence. High-precision measurements of the radius and mass of these planets are essential to refine theoretical models and better understand their formation and evolution. We will present the analysis of TESS photometric data and new RV measurements, taken with the high-resolution spectrograph HARPS, to investigate an exoplanet candidate hosted by the G star TOI-5795 (V = 10.7 mag). The HARPS spectra were also used to determine the physical and atmospheric parameters of the parent star, which appears to have no signs of activity, and our global analysis confirmed the existence of TOI-5795b, which resulted to be a super-Neptune with a radius of 5.4 ± 0.2 R⊕, orbiting with a period of about 6.14 days, relegating it at the edge of the desert. With a mass of 16.4 ± 2 M⊕ and an equilibrium temperature of about 1110 K, its transmission spectroscopy metric is about 90, which makes it a good candidate for atmospheric follow-up with the JWST. This is the first planet discovered by the HOt-NEptune Initiative (HONEI), a novel program that targets several hot-Neptune candidates with both HARPS and HARPS-N spectrographs.