4 Search Results

ABSTRACT We report the spectroscopic confirmation and fundamental properties of TOI$$-$$757 b, a mini$$-$$Neptune on a 17.5$$-$$d orbit transiting a bright star ($$V\, =\, 9.7$$ mag) discovered by the TESS mission. We acquired high$$-$$precision radial velocity measurements with the HARPS, ESPRESSO, and PFS spectrographs to confirm the planet detection and determine its mass. We also acquired space$$-$$borne transit photometry with the CHEOPS space telescope to place stronger constraints on the planet radius, supported with ground$$-$$based LCOGT photometry. WASP and KELT photometry were used to help constrain the stellar rotation period. We also determined the fundamental parameters of the host star. Wemore » find that TOI$$-$$757 b has a radius of $$R_{\mathrm{p}} = 2.5 \pm 0.1 R_{\oplus }$$ and a mass of $$M_{\mathrm{p}} = 10.5^{+2.2}_{-2.1} M_{\oplus }$$, implying a bulk density of $$\rho _{\text{p}} = 3.6 \pm 0.8$$ g cm$$^{-3}$$. Our internal composition modelling was unable to constrain the composition of TOI$$-$$757 b, highlighting the importance of atmospheric observations for the system. We also find the planet to be highly eccentric with e = 0.39$$^{+0.08}_{-0.07}$$, making it one of the very few highly eccentric planets among precisely characterized mini$$-$$Neptunes. Based on comparisons to other similar eccentric systems, we find a likely scenario for TOI$$-$$757 b’s formation to be high eccentricity migration due to a distant outer companion. We additionally propose the possibility of a more intrinsic explanation for the high eccentricity due to star$$-$$star interactions during the earlier epoch of the Galactic disc formation, given the low metallicity and older age of TOI$$-$$757.« less

Neptunes represent one of the main types of exoplanets and have chemical-physical characteristics halfway between rocky and gas giant planets. Therefore, their characterization is important for understanding and constraining both the formation mechanisms and the evolution patterns of planets. We investigate the exoplanet candidate TOI-1422 b, which was discovered by the TESS space telescope around the high proper-motion G2 V star TOI-1422 (V = 10.6 mag), 155 pc away, with the primary goal of confirming its planetary nature and characterising its properties. We monitored TOI-1422 with the HARPS-N spectrograph for 1.5 yr to precisely quantify its radial velocity (RV) variation.more » We analyse these RV measurements jointly with TESS photometry and check for blended companions through high-spatial resolution images using the AstraLux instrument. We estimate that the parent star has a radius of R$$_\star$$ = 1.019_-0.013^+0.014 R_⊙, and a mass of M$$_\star$$ = 1.019_-0.013^+0.014 M_⊙. Our analysis confirms the planetary nature of TOI-1422 b and also suggests the presence of a Neptune-mass planet on a more distant orbit, the candidate TOI-1422 c, which is not detected in TESS light curves. The inner planet, TOI-1422 b, orbits on a period of P_b = 12.9972 ± 0.0006 days and has an equilibrium temperature of T_eq,b = 867 ± 17 K. With a radius of R_b = 3.96_-0.11^+0.13 R_⊕, a mass of M_b = 9.0_-2.0^+2.3 M_⊕ and, consequently, a density of ρ_b = 0.795_-0.235^+0.290g cm^-3, it can be considered a warm Neptune-sized planet. Compared to other exoplanets of a similar mass range, TOI-1422 b is among the most inflated, and we expect this planet to have an extensive gaseous envelope that surrounds a core with a mass fraction around 10% – 25% of the total mass of the planet. The outer non-transiting planet candidate, TOI-1422 c, has an orbital period of P_c = 29.29_-0.20^+0.21 days, a minimum mass, M_csin i, of 11.1_-2.3^+2.6 M_⊕, an equilibrium temperature of T_eq,c = 661 ± 13 K and, therefore, if confirmed, could be considered as another warm Neptune.« less

ABSTRACT We present a precise characterization of the TOI-561 planetary system obtained by combining previously published data with TESS and CHEOPS photometry, and a new set of 62 HARPS-N radial velocities (RVs). Our joint analysis confirms the presence of four transiting planets, namely TOI-561 b (P = 0.45 d, R = 1.42 R⊕, M = 2.0 M⊕), c (P = 10.78 d, R = 2.91 R⊕, M = 5.4 M⊕), d (P = 25.7 d, R = 2.82 R⊕, M = 13.2 M⊕), and e (P = 77 d, R = 2.55 R⊕, M = 12.6 R⊕). Moreover, we identify an additional, long-period signal (>450 d) in the RVs, which could be duemore » to either an external planetary companion or to stellar magnetic activity. The precise masses and radii obtained for the four planets allowed us to conduct interior structure and atmospheric escape modelling. TOI-561 b is confirmed to be the lowest density (ρb = 3.8 ± 0.5 g cm−3) ultra-short period (USP) planet known to date, and the low metallicity of the host star makes it consistent with the general bulk density-stellar metallicity trend. According to our interior structure modelling, planet b has basically no gas envelope, and it could host a certain amount of water. In contrast, TOI-561 c, d, and e likely retained an H/He envelope, in addition to a possibly large water layer. The inferred planetary compositions suggest different atmospheric evolutionary paths, with planets b and c having experienced significant gas loss, and planets d and e showing an atmospheric content consistent with the original one. The uniqueness of the USP planet, the presence of the long-period planet TOI-561 e, and the complex architecture make this system an appealing target for follow-up studies.« less

ABSTRACT In this paper, we report the discovery of TOI-220 b, a new sub-Neptune detected by the Transiting Exoplanet Survey Satellite (TESS) and confirmed by radial velocity follow-up observations with the HARPS spectrograph. Based on the combined analysis of TESS transit photometry and high precision radial velocity measurements, we estimate a planetary mass of 13.8 ± 1.0 M⊕ and radius of 3.03 ± 0.15 R⊕, implying a bulk density of 2.73 ± 0.47 $$\rm {g\,cm}^{-3}$$. TOI-220 b orbits a relative bright (V= 10.4) and old (10.1 ± 1.4 Gyr) K dwarf star with a period of ∼10.69 d. Thus, TOI-220 b is a new warm sub-Neptune with very precise mass and radius determinations. A Bayesian analysismore » of the TOI-220 b internal structure indicates that due to the strong irradiation it receives, the low density of this planet could be explained with a steam atmosphere in radiative–convective equilibrium and a supercritical water layer on top of a differentiated interior made of a silicate mantle and a small iron core.« less