Ben S. Lakeland

We present the discovery of the planetary system orbiting the bright ( V = 7.2), nearby (35 pc), Sun-like ( M _⋆ = 1.050 ± 0.044 M _⊙ , R _⋆ = 1.129 ± 0.013 R _⊙ ) star, HD 60779. We report two Transiting Exoplanet Survey Satellite transits and a subsequent Characterising Exoplanet Satellite transit of HD 60779 b, a sub-Neptune ( 3.24 6 − 0.097 + 0.100 R ⊕ ) planet on a 29.98617 5 − 0.000033 + 0.000030 day orbit. Additionally, 313 High Accuracy Radial velocity Planet Searcher for the Northern hemisphere radial velocity (RV) measurements reveal the mass of planet b ( 14.1 9 − 0.96 + 0.97 M ⊕ ) and the presence of an outer planet, HD 60779 c ( P _orb = 104.79 ± 0.23 days, M p sin i = 28.3 ± 1.5 M ⊕ ). Both of these planets’ orbits are consistent with being circular, suggesting that they have a dynamically quiet history. The data are not sufficient to determine whether planet c transits. HD 60779’s uniquely high systemic RV (129.75 ± 0.12 km s ⁻¹ ) allows its Ly α emission to avoid absorption by the interstellar medium, making it a prime candidate for probing atmospheric escape from HD 60779 b. HD 60779 is also the third brightest host of a P _orb > 25 day sub-Neptune with a measured mass and radius, distinguishing it in terms of accessibility to spectroscopic characterization.

The measurement of exoplanet masses using the radial velocity (RV) technique is currently limited by stellar activity, which introduces quasiperiodic variability signals that must be modeled and removed to enhance the sensitivity of the RV measurements to exoplanet signals. Neural networks have previously been demonstrated effective in modeling stellar activity signals in HARPS-N solar data using white light cross correlation functions (CCFs). Building on this work, we train a neural network on 6 yr of HARPS-N solar data with additional parameters commonly associated to stellar activity, including chromatic CCFs, line shape metrics, spectral activity indicators, total solar irradiance (TSI) light curves from SORCE and TSIS-1, and TSI time derivatives. Our results show that parameters such as the bisector inverse slope and Na D equivalent widths (EWs) do not significantly improve the neural network’s ability to predict activity-induced RV variations compared to using the white light CCFs alone. However, parameters such as unsigned magnetic flux, the TSI and its time derivative, S-index, H α EW, chromatic CCFs, contrast, and FWHM do improve the neural network's ability to predict RV scatter. Our new model reduces the RV scatter in a held-out test set from 147.1 cm s ⁻¹ to 93.3 cm s ⁻¹ , consistent with supergranulation noise levels reported in previous studies. These results suggest that finding effective tracers for (super)granulation will be critical to train models capable of further mitigating RV jitter, and necessary for characterizing Earth analogs.

Over the past decade, ALMA has uncovered a range of substructures within exoKuiper belts, pointing to a population of undetected planets. With JWST's sensitivity, we now have the opportunity to identify these planets thought to be responsible for the observed substructures in debris discs. We present Cycle 1 JWST/MIRI 11.4 μm coronagraphic observations of three exoKuiper belts that exhibit gaps in their radial structures: HD 92945, HD 107146, and HD 206893, to determine whether planets are responsible for carving these structures, as seen in our Solar System with the gas giants. We reduce the JWST/MIRI data using spaceKLIP, and introduce new routines to mitigate the Brighter-Fatter effect and persistence. We do not detect any planet candidates, and all detected objects in the field-of-view are consistent with background stars or galaxies. However, by combining JWST mass limits, archival observational constraints, and astrometric accelerations, we rule out a significant portion of planet parameter space, placing tight constraints on the planets possibly responsible for these gaps. To interpret these results, we explore multiple gap-carving scenarios in discs, either massless or with non-zero mass, including clearing by in-situ planet(s), as well as shaping by inner planets through mean-motion or secular apsidal resonances. Finally, we conclude that the planets causing the proper motion anomaly in these systems must reside within the inner 20 au.

Over the past decade, ALMA has uncovered a range of substructures within exoKuiper belts, pointing to a population of undetected planets. With James Webb Space Telescope (JWST)’s sensitivity, we now have the opportunity to identify these planets thought to be responsible for the observed substructures in debris discs. We present Cycle 1 JWST/MIRI $11.4~\mu$m coronagraphic observations of three exoKuiper belts that exhibit gaps in their radial structures: HD 92945, HD 107146, and HD 206893, to determine whether planets are responsible for carving these structures, as seen in our Solar system with the gas giants. We reduce the JWST/MIRI data using spaceklip, and introduce new routines to mitigate the Brighter-Fatter effect and persistence. We do not detect any planet candidates, and all detected objects in the field of view are consistent with background stars or galaxies. However, by combining JWST mass limits, archival observational constraints, and astrometric accelerations, we rule out a significant portion of planet parameter space, placing tight constraints on the planets possibly responsible for these gaps. To interpret these results, we explore multiple gap-carving scenarios in discs, either massless or with non-zero mass, including clearing by in situ planet(s), as well as shaping by inner planets through mean-motion or secular apsidal resonances. Finally, we conclude that the planets causing the proper-motion anomaly in these systems must reside within the inner 20 au.

We present the discovery of the planetary system orbiting the bright (V = 7.2), nearby (35 pc), Sun-like star HD 60779, which has a mass of 1.050 +/- 0.044 solar masses and a radius of 1.129 +/- 0.013 solar radii. We report two TESS transits and a subsequent CHEOPS transit of HD 60779 b, a sub-Neptune with a radius of 3.250 (+0.100 / -0.098) Earth radii on a 29.986175 (+0.000030 / -0.000033) day orbit. Additionally, 286 HARPS-N radial velocity measurements reveal the mass of planet b (14.7 +1.1 / -1.0 Earth masses) and the presence of an outer planet, HD 60779 c, with an orbital period of 104.25 (+0.30 / -0.29) days and a minimum mass (m sin i) of 27.7 +/- 1.6 Earth masses. Both planets' orbits are consistent with being circular, suggesting that they have a dynamically quiet history. The data are not sufficient to determine whether planet c transits. HD 60779's uniquely high systemic radial velocity (129.75 +/- 0.12 km/s) allows its Lyman-alpha emission to avoid absorption by the interstellar medium, making it a prime candidate for probing atmospheric escape from HD 60779 b. HD 60779 is also the third-brightest host of a sub-Neptune with orbital period greater than 25 days and with both mass and radius measured, distinguishing it in terms of accessibility to spectroscopic characterization.

In recent years, supergranulation has emerged as one of the biggest challenges for the detection of Earth-twins in radial velocity planet searches. We used eight years of Sun-as-a-star radial velocity observations from HARPS-N to measure the quiet-Sun’s granulation and supergranulation properties of most of its 11-yr activity cycle, after correcting for the effects of magnetically active regions using two independent methods. In both cases, we observe a clear, order of magnitude variation in the time-scale of the supergranulation component, which is largest at activity minimum and is strongly anticorrelated with the relative Sunspot number. We also explored a range of observational strategies which could be employed to characterize supergranulation in stars other than the Sun, showing that a comparatively long observing campaign of at least 23 nights is required, but that up to 10 stars can be monitored simultaneously in the process. We conclude by discussing plausible explanations for the ‘supergranulation’ cycle.