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About 1 out of 200 Sun-like stars has a planet with an orbital period shorter than one day: an ultrashort-period planet 1 , 2 . All of the previously known ultrashort-period planets are either hot Jupiters, with sizes above 10 Earth radii ( R ⊕ ), or apparently rocky planets smaller than 2  R ⊕ . Such lack of planets of intermediate size (the ‘hot Neptune desert’) has been interpreted as the inability of low-mass planets to retain any hydrogen/helium (H/He) envelope in the face of strong stellar irradiation. Here we report the discovery of an ultrashort-period planet with a radius of 4.6  R ⊕ and a mass of 29  M ⊕ , firmly in the hot Neptune desert. Data from the Transiting Exoplanet Survey Satellite 3 revealed transits of the bright Sun-like star LTT 9779 every 0.79 days. The planet’s mean density is similar to that of Neptune, and according to thermal evolution models, it has a H/He-rich envelope constituting 9.0 − 2.9 + 2.7 % of the total mass. With an equilibrium temperature around 2,000 K, it is unclear how this ‘ultrahot Neptune’ managed to retain such an envelope. Follow-up observations of the planet’s atmosphere to better understand its origin and physical nature will be facilitated by the star’s brightness ( V mag  = 9.8). LTT 9779 b is Neptune-sized planet rotating around its star with a period of 0.79 days and an equilibrium temperature of 2,000 K. It is not clear how it retained its atmospheric envelope, which contains ~10% of H/He, as it should have been photoevaporated by now.

An amendment to this paper has been published and can be accessed via a link at the top of the paper.

El objetivo principal de esta tesis es abordar el desafıo de detectar y caracterizar Jupiteres calientes alrededor de estrellas calientes. La elevada temperatura de las estrellas dificulta la confirmacion de exoplanetas debido a la rapida rotacion estelar, lo que resulta en una menor precision en las mediciones de velocidades radiales. Un metodo para caracterizar y confirmar planetas que orbitan este tipo de estrella es el de Tomografıa Doppler (TD). En este trabajo, se desarrollo un metodo de TD, en un marco bayesiano y se probo en seis sistemas. Se utilizaron datos publicados de tres de ellos (WASP-19b, KELT-7b y HAT-P-56b), obteniendo resultados visuales similares a los publicados. Para dos sistemas (HD2685 y TOI-812), se predijeron y observaron los transitos, pero no fue posible recuperar la se˜nal del planeta. Y un sistema que sera publicado prontamente (TOI-3362-b, Espinoza et al. in prep) que es consistente con la alineacion del sistema. Tambien se construyo un catalogo de siete estrellas (incluyendo HD2685b) interesantes para nuestro estudio. Este catalogo se contruyo a partir de una seleccion de estrellas calientes (hecha con datos de Gaia DR2) que poseıan altas se˜nales de transito en las curva de luz obtenidas de TESS. De esas siete estrellas, cuatro poseen planetas ya confirmados y tres candidatos a planeta, de especial interes debido a las caracterısticas unicas de cada sistema. Tambien se desarrollo un codigo capaz de predecir la observabilidad de la Tomografıa Doppler, considerando las caracterısticas de la estrella, el planeta y el instrumento utilizado para la observacion. Las conclusiones de este estudio indican que tanto el metodo de deconvolucion como el modelo de prediccion de Tomografıa Doppler son utiles y consistentes con trabajos previos. Sin embargo, es necesario desarrollar nuevas herramientas para cuantificar la precision de estos metodos.Las conclusiones de este estudio indican que tanto el metodo de deconvolucion como el modelo de prediccion de Tomografıa Doppler son utiles y consistentes con trabajos previos. Sin embargo, es necesario desarrollar nuevas herramientas para cuantificar la precision de estos metodos.

We report the discovery and orbital characterization of three new transiting warm giant planets. These systems were initially identified as presenting single transit events in the light curves generated from the full frame images of the Transiting Exoplanet Survey Satellite (TESS). Follow-up radial velocity measurements and additional light curves were used to determine the orbital periods and confirm the planetary nature of the candidates. The planets orbit slightly metal-rich late F- and early G-type stars. We find that TOI 4406b has a mass of \\(M_P\\)= 0.30 \\(\\pm\\) 0.04 \\(M_J\\) , a radius of \\(R_P\\)= 1.00 \\(\\pm\\) 0.02 \\(R_J\\) , and a low eccentricity orbit (e=0.15 \\(\\pm\\) 0.05) with a period of P= 30.08364 \\(\\pm\\) 0.00005 d . TOI 2338b has a mass of \\(M_P\\)= 5.98 \\(\\pm\\) 0.20 \\(M_J\\) , a radius of \\(R_P\\)= 1.00 \\(\\pm\\) 0.01 \\(R_J\\) , and a highly eccentric orbit (e= 0.676 \\(\\pm\\) 0.002 ) with a period of P= 22.65398 \\(\\pm\\) 0.00002 d . Finally, TOI 2589b has a mass of \\(M_P\\)= 3.50 \\(\\pm\\) 0.10 \\(M_J\\) , a radius of \\(R_P\\)= 1.08 \\(\\pm\\) 0.03 \\(R_J\\) , and an eccentric orbit (e = 0.522 \\(\\pm\\) 0.006 ) with a period of P= 61.6277 \\(\\pm\\) 0.0002 d . TOI 4406b and TOI 2338b are enriched in metals compared to their host stars, while the structure of TOI 2589b is consistent with having similar metal enrichment to its host star.

TOI-2202 b is a transiting warm Jovian-mass planet with an orbital period of P=11.91 days identified from the Full Frame Images data of five different sectors of the TESS mission. Ten TESS transits of TOI-2202 b combined with three follow-up light curves obtained with the CHAT robotic telescope show strong transit timing variations (TTVs) with an amplitude of about 1.2 hours. Radial velocity follow-up with FEROS, HARPS and PFS confirms the planetary nature of the transiting candidate (a\\(_{\\rm b}\\) = 0.096 \\(\\pm\\) 0.002 au, m\\(_{\\rm b}\\) = 0.98 \\(\\pm\\) 0.06 M\\(_{\\rm Jup}\\)), and dynamical analysis of RVs, transit data, and TTVs points to an outer Saturn-mass companion (a\\(_{\\rm c}\\) = 0.155 \\(\\pm\\) 0.003 au, m\\(_{\\rm c}\\)= \\(0.37 \\pm 0.10\\) M\\(_{\\rm Jup}\\)) near the 2:1 mean motion resonance. Our stellar modeling indicates that TOI-2202 is an early K-type star with a mass of 0.82 M\\(_\\odot\\), a radius of 0.79 R\\(_\\odot\\), and solar-like metallicity. The TOI-2202 system is very interesting because of the two warm Jovian-mass planets near the 2:1 MMR, which is a rare configuration, and their formation and dynamical evolution are still not well understood.

We report the discovery of a warm sub-Saturn, TOI-257b (HD 19916b), based on data from NASA's Transiting Exoplanet Survey Satellite (TESS). The transit signal was detected by TESS and confirmed to be of planetary origin based on radial velocity observations. An analysis of the TESS photometry, the Minerva-Australis, FEROS, and HARPS radial velocities, and the asteroseismic data of the stellar oscillations reveals that TOI-257b has a mass of \\(M_P=0.138\\pm0.023\\)\\,\\(\\rm{M_J}\\) (\\(43.9\\pm7.3\\)\\,\\(M_{\\rm \\oplus}\\)), a radius of \\(R_P=0.639\\pm0.013\\)\\,\\(\\rm{R_J}\\) (\\(7.16\\pm0.15\\)\\,\\(R_{\\rm \\oplus}\\)), bulk density of \\(0.65^{+0.12}_{-0.11}\\) (cgs), and period \\(18.38818^{+0.00085}_{-0.00084}\\)\\,\\(\\rm{days}\\). TOI-257b orbits a bright (\\(\\mathrm{V}=7.612\\)\\,mag) somewhat evolved late F-type star with \\(M_*=1.390\\pm0.046\\)\\,\\(\\rm{M_{\\odot}}\\), \\(R_*=1.888\\pm0.033\\)\\,\\(\\rm{R_{\\odot}}\\), \\(T_{\\rm eff}=6075\\pm90\\)\\,\\(\\rm{K}\\), and \\(v\\sin{i}=11.3\\pm0.5\\)\\,km\\,s\\(^{-1}\\). Additionally, we find hints for a second non-transiting sub-Saturn mass planet on a \\(\\sim71\\)\\,day orbit using the radial velocity data. This system joins the ranks of a small number of exoplanet host stars (\\(\\sim100\\)) that have been characterized with asteroseismology. Warm sub-Saturns are rare in the known sample of exoplanets, and thus the discovery of TOI-257b is important in the context of future work studying the formation and migration history of similar planetary systems.

We report the discovery of a transiting planet first identified as a candidate in Sector 1 of the Transiting Exoplanet Survey Satellite (TESS), and then confirmed with precision radial velocities. HD1397b has a mass of \\({\\rm M_P}\\) = \\(0.335_{-0.018}^{+0.018}\\) \\({\\rm M_J}\\), a radius of \\({\\rm R_P}\\) = \\(1.021_{-0.014}^{+0.015}\\) \\({\\rm M_J}\\), and orbits its bright host star (\\(V = 7.8\\) mag) with an orbital period of \\(11.53508 \\pm 0.00057 \\) d, on a moderately eccentric orbit (\\(e\\) = 0.210 \\(\\pm\\) 0.038). With a mass of \\({\\rm M}_{\\star}\\) = \\(1.284_{-0.016}^{+0.020}\\) \\({\\rm M}_{J}\\), a radius of \\({\\rm R}_{\\star}\\) = 2.314\\(_{-0.042}^{+0.049}\\) \\({\\rm R_J}\\), and an age of 4.7 \\(\\pm\\) 0.2 Gyr, the solar metallicity host star has already departed from the main sequence. We find evidence in the radial velocity measurements for a long term acceleration, and a \\(P \\approx 18\\) d periodic signal that we attribute to rotational modulation by stellar activity. The HD1397 system is among the brightest systems currently known to host a transiting planet, which will make it possible to perform detailed follow-up observations in order to characterize the properties of giant planets orbiting evolved stars.

TOI-216 hosts a pair of warm, large exoplanets discovered by the TESS Mission. These planets were found to be in or near the 2:1 resonance, and both of them exhibit transit timing variations (TTVs). Precise characterization of the planets' masses and radii, orbital properties, and resonant behavior can test theories for the origins of planets orbiting close to their stars. Previous characterization of the system using the first six sectors of TESS data suffered from a degeneracy between planet mass and orbital eccentricity. Radial velocity measurements using HARPS, FEROS, and PFS break that degeneracy, and an expanded TTV baseline from TESS and an ongoing ground-based transit observing campaign increase the precision of the mass and eccentricity measurements. We determine that TOI-216c is a warm Jupiter, TOI-216b is an eccentric warm Neptune, and that they librate in the 2:1 resonance with a moderate libration amplitude of 60 +/- 2 degrees; small but significant free eccentricity of 0.0222 +0.0005/-0.0003 for TOI-216b; and small but significant mutual inclination of 1.2-3.9 degrees (95% confidence interval). The libration amplitude, free eccentricity, and mutual inclination imply a disturbance of TOI-216b before or after resonance capture, perhaps by an undetected third planet.

We report the discovery of two short-period Saturn-mass planets, one transiting the G subgiant TOI-954 (TIC 44792534, \\( V = 10.343 \\), \\( T = 9.78 \\)) observed in TESS sectors 4 and 5, and one transiting the G dwarf K2-329 (EPIC 246193072, \\( V = 12.70 \\), \\( K = 10.67 \\)) observed in K2 campaigns 12 and 19. We confirm and characterize these two planets with a variety of ground-based archival and follow-up observations, including photometry, reconnaissance spectroscopy, precise radial velocity, and high-resolution imaging. Combining all available data, we find that TOI-954 b has a radius of \\(0.852_{-0.062}^{+0.053} \\, R_{\\mathrm{J}}\\) and a mass of \\(0.174_{-0.017}^{+0.018} \\, M_{\\mathrm{J}}\\) and is in a 3.68 day orbit, while K2-329 b has a radius of \\(0.774_{-0.024}^{+0.026} \\, R_{\\mathrm{J}}\\) and a mass of \\(0.260_{-0.022}^{+0.020} \\, M_{\\mathrm{J}}\\) and is in a 12.46 day orbit. As TOI-954 b is 30 times more irradiated than K2-329 b but more or less the same size, these two planets provide an opportunity to test whether irradiation leads to inflation of Saturn-mass planets and contribute to future comparative studies that explore Saturn-mass planets at contrasting points in their lifetimes.

We present the discovery of two new 10-day period giant planets from the Transiting Exoplanet Survey Satellite (\\(TESS\\)) mission, whose masses were precisely determined using a wide diversity of ground-based facilities. TOI-481 b and TOI-892 b have similar radii (\\(0.99\\pm0.01\\) \\(\\rm R_{J}\\) and \\(1.07\\pm0.02\\) \\(\\rm R_{J}\\), respectively), and orbital periods (10.3311 days and 10.6266 days, respectively), but significantly different masses (\\(1.53\\pm0.03\\) \\(\\rm M_{J}\\) versus \\(0.95\\pm0.07\\) \\(\\rm M_{J}\\), respectively). Both planets orbit metal-rich stars ([Fe/H]= \\(+0.26\\pm 0.05\\) dex and [Fe/H] = \\(+0.24 \\pm 0.05\\) dex, for TOI-481 and TOI-892, respectively) but at different evolutionary stages. TOI-481 is a \\(\\rm M_{\\star}\\) = \\(1.14\\pm0.02\\) \\(\\rm M_{\\odot}\\), \\(\\rm R_{\\star}\\) = \\(1.66\\pm0.02\\) \\(\\rm R_{\\odot}\\) G-type star (\\(T_{\\rm eff}\\) = \\(5735 \\pm 72\\) K), that with an age of 6.7 Gyr, is in the turn-off point of the main sequence. TOI-892, on the other hand, is a F-type dwarf star (\\(T_{\\rm eff}\\) = \\(6261 \\pm 80\\) K), which has a mass of \\(\\rm M_{\\star}\\) = \\(1.28\\pm0.03\\) \\(\\rm M_{\\odot}\\), and a radius of \\(\\rm R_{\\star}\\) = \\(1.39\\pm0.02\\) \\(\\rm R_{\\odot}\\). TOI-481 b and TOI-892 b join the scarcely populated region of transiting gas giants with orbital periods longer than 10 days, which is important to constrain theories of the formation and structure of hot Jupiters.