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Short-period sub-Neptunes with substantial volatile envelopes are among the most common type of known exoplanets. However, recent studies of the Kepler population have suggested a dearth of sub-Neptunes on highly irradiated orbits, where they are vulnerable to atmospheric photoevaporation. Physically, we expect this "photoevaporation desert" to depend on the total lifetime X-ray and extreme ultraviolet flux, the main drivers of atmospheric escape. In this work, we study the demographics of sub-Neptunes as a function of lifetime exposure to high energy radiation and host star mass. We find that for a given present day insolation, planets orbiting a 0.3 $M_{sun}$ star experience $\sim$100 $\times$ more X-ray flux over their lifetimes versus a 1.2 $M_{sun}$ star. Defining the photoevaporation desert as a region consistent with zero occurrence at 2 $\sigma$, the onset of the desert happens for integrated X-ray fluxes greater than 1.43 $\times 10^{22}$ erg/cm$^2$ to 8.23 $\times 10^{20}$ erg/cm$^2$ as a function of planetary radii for 1.8 -- 4 $R_{\oplus}$. We also compare the location of the photoevaporation desert for different stellar types. We find much greater variability in the desert onset in bolometric flux space compared to integrated X-ray flux space, suggestive of photoevaporation driven by steady state stellar X-ray emissions as the dominant control on desert location. Finally, we report tentative evidence for the sub-Neptune valley, first seen around Sun-like stars, for M & K dwarfs. The discovery of additional planets around low-mass stars from surveys such as the TESS mission will enable detailed exploration of these trends., Comment: 22 pages, 15 figures

We present the confirmation of two new planets transiting the nearby mid-M dwarf LTT 3780 (TIC 36724087, TOI-732, $V=13.07$, $K_s=8.204$, $R_s$=0.374 R$_{\odot}$, $M_s$=0.401 M$_{\odot}$, d=22 pc). The two planet candidates are identified in a single TESS sector and are validated with reconnaissance spectroscopy, ground-based photometric follow-up, and high-resolution imaging. With measured orbital periods of $P_b=0.77$ days, $P_c=12.25$ days and sizes $r_{p,b}=1.33\pm 0.07$ R$_{\oplus}$, $r_{p,c}=2.30\pm 0.16$ R$_{\oplus}$, the two planets span the radius valley in period-radius space around low mass stars thus making the system a laboratory to test competing theories of the emergence of the radius valley in that stellar mass regime. By combining 63 precise radial-velocity measurements from HARPS and HARPS-N, we measure planet masses of $m_{p,b}=2.62^{+0.48}_{-0.46}$ M$_{\oplus}$ and $m_{p,c}=8.6^{+1.6}_{-1.3}$ M$_{\oplus}$, which indicates that LTT 3780b has a bulk composition consistent with being Earth-like, while LTT 3780c likely hosts an extended H/He envelope. We show that the recovered planetary masses are consistent with predictions from both photoevaporation and from core-powered mass loss models. The brightness and small size of LTT 3780, along with the measured planetary parameters, render LTT 3780b and c as accessible targets for atmospheric characterization of planets within the same planetary system and spanning the radius valley., Comment: Accepted to AJ. 8 figures, 6 tables. CSV file of the RV measurements (i.e. Table 2) are included in the source code

Understanding the anomalous radii of many transiting hot gas giant planets is a fundamental problem of planetary science. Recent detections of re-inflated warm Jupiters orbiting post-main-sequence stars and the re-inflation of hot Jupiters while their host stars evolve on the main-sequence may help constrain models for the anomalous radii of hot Jupiters. In this work, we present evolution models studying the re-inflation of gas giants to determine how varying the depth and intensity of deposited heating affects both main-sequence re-inflation of hot Jupiters and post-main-sequence re-inflation of warm Jupiters. We find that deeper heating is required to re-inflate hot Jupiters than is needed to suppress their cooling, and that the timescale of re-inflation decreases with increasing heating rate and depth. We find a strong degeneracy between heating rate and depth, with either strong shallow heating or weak deep heating providing an explanation for main-sequence re-inflation of hot Jupiters. This degeneracy between heating rate and depth can be broken in the case of post-main-sequence re-inflation of warm Jupiters, as the inflation must be rapid to occur within post-main-sequence evolution timescales. We also show that the dependence of heating rate on incident stellar flux inferred from the sample of hot Jupiters can explain re-inflation of both warm and hot Jupiters. TESS will obtain a large sample of warm Jupiters orbiting post-main-sequence stars, which will help to constrain the mechanism(s) causing the anomalous radii of gas giant planets., 15 pages, 13 figures, updated to reflect published version

All authors: Bluhm, P.; Luque, R.; Espinoza, N.; Pallé, E.; Caballero, J. A.; Dreizler, S.; Livingston, J. H.; Mathur, S.; Quirrenbach, A.; Stock, S.; Van Eylen, V.; Nowak, G.; López, E. D.; Csizmadia, Sz.; Zapatero Osorio, M. R.; Schöfer, P.; Lillo-Box, J.; Oshagh, M.; González-Álvarez, E.; Amado, P. J.; Barrado, D.; Béjar, V. J. S.; Cale, B.; Chaturvedi, P.; Cifuentes, C.; Cochran, W. D.; Collins, K. A.; Collins, K. I.; Cortés-Contreras, M.; Díez Alonso, E.; El Mufti, M.; Ercolino, A.; Fridlund, M.; Gaidos, E.; García, R. A.; Georgieva, I.; González-Cuesta, L.; Guerra, P.; Hatzes, A. P.; Henning, Th.; Herrero, E.; Hidalgo, D.; Isopi, G.; Jeffers, S. V.; Jenkins, J. M.; Jensen, E. L. N.; Kábath, P.; Kaminski, A.; Kemmer, J.; Korth, J.; Kossakowski, D.; Kürster, M.; Lafarga, M.; Mallia, F.; Montes, D.; Morales, J. C.; Morales-Calderón, M.; Murgas, F.; Narita, N.; Passegger, V. M.; Pedraz, S.; Persson, C. M.; Plavchan, P.; Rauer, H.; Redfield, S.; Reffert, S.; Reiners, A.; Ribas, I.; Ricker, G. R.; Rodríguez-López, C.; Santos, A. R. G.; Seager, S.; Schlecker, M.; Schweitzer, A.; Shan, Y.; Soto, M. G.; Subjak, J.; Tal-Or, L.; Trifonov, T.; Vanaverbeke, S.; Vanderspek, R.; Wittrock, J.; Zechmeister, M.; Zohrabi, F., We report the confirmation of a transiting planet around the bright weakly active M0.5 V star TOI-1235 (TYC 4384-1735-1, V ≈ 11.5 mag), whose transit signal was detected in the photometric time series of sectors 14, 20, and 21 of the TESS space mission. We confirm the planetary nature of the transit signal, which has a period of 3.44 d, by using precise RV measurements with the CARMENES, HARPS-N, and iSHELL spectrographs, supplemented by high-resolution imaging and ground-based photometry. A comparison of the properties derived for TOI-1235 b with theoretical models reveals that the planet has a rocky composition, with a bulk density slightly higher than that of Earth. In particular, we measure a mass of Mp = 5.9 ± 0.6 M⊕ and a radius of Rp = 1.69 ± 0.08 R⊕ , which together result in a density of ρp = 6.7- 1.1+ 1.3 g cm-3. When compared with other well-characterized exoplanetary systems, the particular combination of planetary radius and mass places our discovery in the radius gap, which is a transition region between rocky planets and planets with significant atmospheric envelopes. A few examples of planets occupying the radius gap are known to date. While the exact location of the radius gap for M dwarfs is still a matter of debate, our results constrain it to be located at around 1.7 R⊕ or larger at the insolation levels received by TOI-1235 b (~60 S⊕ ). This makes it an extremely interesting object for further studies of planet formation and atmospheric evolution. © ESO 2020., CARMENES is an instrument for the Centro Astronomico Hispano-Aleman de Calar Alto (CAHA, Almeria, Spain). CARMENES is funded by the German Max-Planck-Gesellschaft (MPG), the Spanish Consejo Superior de Investigaciones Cientificas (CSIC), the European Union through FEDER/ERF FICTS-2011-02 funds, and the members of the CARMENES Consortium (Max-Planck-Institut fur Astronomie, Instituto de Astrofisica de Andalucia, Landessternwarte Konigstuhl, Institut de Ciencies de l'Espai, Institut fur Astrophysik Gottingen, Universidad Complutense de Madrid, Thuringer Landessternwarte Tautenburg, Instituto de Astrofisica de Canarias, Hamburger Sternwarte, Centro de Astrobiologia and Centro Astronomico Hispano-Aleman), with additional contributions by the Spanish Ministry of Economy, the German Science Foundation through the Major Research Instrumentation Programme and DFG Research Unit FOR2544 "Blue Planets around Red Stars", the Klaus Tschira Stiftung, the states of Baden-Wurttemberg and Niedersachsen, and by the Junta de Andalucia. We acknowledge the use of public TESS Alert data from pipelines at the TESS Science Office and at the TESS Science Processing Operations Center. This research has made use of the Exoplanet Follow-up Observation Program website, which is operated by the California Institute of Technology, under contract with the National Aeronautics and Space Administration under the Exoplanet Exploration Program. Resources supporting this work were provided by the NASA High-End Computing (HEC) Program through the NASA Advanced Supercomputing (NAS) Division at Ames Research Center for the production of the SPOC data products. We acknowledge financial support from the European Research Council under the Horizon 2020 Framework Program via the ERC Advanced Grant Origins 83 24 28, the Deutsche Forschungsgemeinschaft through projects RE 281/32-1, RE 1664/14-1, RE 2694/4-1, and RA714/14-1, PA525/18-1, PA525/19-1 within the Schwerpunkt SPP 1992, the Agencia Estatal de Investigacion of the Ministerio de Ciencia, Innovacion y Universidades and the European FEDER/ERF funds through projects PGC2018-098153-B-C31, ESP2016-80435-C2-1-R, ESP2016-80435-C2-2-R, AYA2016-79425-C3-1/2/3P, AYA2015-69350-C3-2-P, RYC-2015-17697, and BES-2017-082610, the Centre of Excellence "Severo Ochoa" and "Maria de Maeztu" awards to the Instituto de Astrofisica de Canarias (SEV-2015-0548), Instituto de Astrofisica de Andalucia (SEV-2017-0709), and Centro de Astrobiologia (MDM-2017-0737), the European Union's Horizon 2020 research and innovation program under the Marie Sklodowska-Curie grant 713673, the Centre national d'etudes spatiales through grants PLATO and GOLF, the Czech Academy of Sciences through grant LTT20015, NASA through grants NNX17AF27G and NNX17AG24G, JSPS KAKENHI through grants JP18H01265 and JP18H05439, JST PRESTO through grant JPMJPR1775, the Fundacion Bancaria "la Caixa" through grant INPhINIT LCF/BQ/IN17/11620033, and the Generalitat de Catalunya/CERCA programme. NESSI was funded by the NASA Exoplanet Exploration Program and the NASA Ames Research Center and built at the Ames Research Center. The authors are honored to be permitted to conduct observations on Iolkam Du'ag (Kitt Peak), a mountain within the Tohono O'odham Nation with particular significance to the Tohono O'odham people. This work made use of observations from the LCOGT network and the following software: astrasens, AstroImageJ, Banzai, batman, caracal, emcee, juliet, serval, TESS Transit Finder, tpfplotter, Yabi, and the python packages astropy, lightkurve, matplotlib, and numpy. We thank the SuperWASP team and J. Sanz-Forcada for sharing unpublished information with us. Special thanks to Ismael Pessa for all their support through this work.

We present $Spitzer$ 4.5$��$m observations of the transit of TOI-700 d, a habitable zone Earth-sized planet in a multiplanet system transiting a nearby M-dwarf star (TIC 150428135, 2MASS J06282325-6534456). TOI-700 d has a radius of $1.144^{+0.062}_{-0.061}R_\oplus$ and orbits within its host star's conservative habitable zone with a period of 37.42 days ($T_\mathrm{eq} \sim 269$K). TOI-700 also hosts two small inner planets (R$_b$=$1.037^{+0.065}_{-0.064}R_\oplus$ & R$_c$=$2.65^{+0.16}_{-0.15}R_\oplus$) with periods of 9.98 and 16.05 days, respectively. Our $Spitzer$ observations confirm the TESS detection of TOI-700 d and remove any remaining doubt that it is a genuine planet. We analyze the $Spitzer$ light curve combined with the 11 sectors of TESS observations and a transit of TOI-700 c from the LCOGT network to determine the full system parameters. Although studying the atmosphere of TOI-700 d is not likely feasible with upcoming facilities, it may be possible to measure the mass of TOI-700 d using state-of-the-art radial velocity instruments (expected RV semi-amplitude of $\sim$70 cm/s)., 14 Pages, 5 Figures, 2 Tables, Accepted to AJ

Measures of exoplanet bulk densities indicate that small exoplanets with radius less than 3 Earth radii ($R_\oplus$) range from low-density sub-Neptunes containing volatile elements to higher density rocky planets with Earth-like or iron-rich (Mercury-like) compositions. Such astonishing diversity in observed small exoplanet compositions may be the product of different initial conditions of the planet-formation process and/or different evolutionary paths that altered the planetary properties after formation. Planet evolution may be especially affected by either photoevaporative mass loss induced by high stellar X-ray and extreme ultraviolet (XUV) flux or giant impacts. Although there is some evidence for the former, there are no unambiguous findings so far about the occurrence of giant impacts in an exoplanet system. Here, we characterize the two innermost planets of the compact and near-resonant system Kepler-107. We show that they have nearly identical radii (about $1.5-1.6~R_\oplus$), but the outer planet Kepler-107c is more than twice as dense (about $12.6~\rm g\,cm^{-3}$) as the innermost Kepler-107b (about $5.3~\rm g\,cm^{-3}$). In consequence, Kepler-107c must have a larger iron core fraction than Kepler-107b. This imbalance cannot be explained by the stellar XUV irradiation, which would conversely make the more-irradiated and less-massive planet Kepler-107b denser than Kepler-107c. Instead, the dissimilar densities are consistent with a giant impact event on Kepler-107c that would have stripped off part of its silicate mantle. This hypothesis is supported by theoretical predictions from collisional mantle stripping, which match the mass and radius of Kepler-107c., Comment: Published in Nature Astronomy on 4 February 2019, 35 pages including Supplementary Information material

Super-Earths belong to a class of planet not found in the Solar System, but which appear common in the Galaxy. Given that some super-Earths are rocky, while others retain substantial atmospheres, their study can provide clues as to the formation of both rocky planets and gaseous planets, and - in particular - they can help to constrain the role of photo-evaporation in sculpting the exoplanet population. GJ 9827 is a system already known to host 3 super-Earths with orbital periods of 1.2, 3.6 and 6.2 days. Here we use new HARPS-N radial velocity measurements, together with previously published radial velocities, to better constrain the properties of the GJ 9827 planets. Our analysis can't place a strong constraint on the mass of GJ 9827 c, but does indicate that GJ 9827 b is rocky with a composition that is probably similar to that of the Earth, while GJ 9827 d almost certainly retains a volatile envelope. Therefore, GJ 9827 hosts planets on either side of the radius gap that appears to divide super-Earths into pre-dominantly rocky ones that have radii below $\sim 1.5 R_\oplus$, and ones that still retain a substantial atmosphere and/or volatile components, and have radii above $\sim 2 R_\oplus$. That the less heavily irradiated of the 3 planets still retains an atmosphere, may indicate that photoevaporation has played a key role in the evolution of the planets in this system., 16 pages, 9 figures, accepted for publication in Monthly Notices of the Royal Astronomical Society

Stellar multiplicity is believed to influence planetary formation and evolution, although the precise nature and extent of this role remain ambiguous. We present a study aimed at testing the role of stellar multiplicity in the formation and/or evolution of the most massive, close-in planetary and substellar companions. Using direct imaging observations, as well as the Gaia DR2 catalogue, we searched for wide binary companions to 38 stars hosting massive giant planets or brown dwarfs (M > 7 MJup) on orbits shorter than ~1 AU. We report the discovery of a new component in the WASP-14 system, and present an independent confirmation of a comoving companion to WASP-18. From a robust Bayesian statistical analysis, we derived a binary fraction of 79.0+13.2-14.7% between 20-10,000 AU for our sample, twice as high as for field stars with a 3-{\sigma} significance. This binary frequency was found to be larger than for lower-mass planets on similar orbits, and we observed a marginally higher binary rate for inner companions with periods shorter than 10 days. These results demonstrate that stellar companions greatly influence the formation and/or evolution of these systems, suggesting that the role played by binary companions becomes more important for higher-mass planets, and that this trend may be enhanced for systems with tighter orbits. Our analysis also revealed a peak in binary separation at 250 AU, highlighting a shortfall of close binaries among our sample. This indicates that the mechanisms affecting planet and brown dwarf formation or evolution in binaries must operate from wide separations, although we found that the Kozai-Lidov mechanism is unlikely to be the dominant underlying process. We conclude that binarity plays a crucial role in the existence of very massive short-period giant planets and brown dwarf desert inhabitants, which are almost exclusively observed in multiple systems., Comment: Accepted for publication in MNRAS. 30 pages, 20 figures. Updated to include proof corrections

Small planets on close-in orbits tend to exhibit envelope mass fractions of either effectively zero or up to a few percent depending on their size and orbital period. Models of thermally-driven atmospheric mass loss and of terrestrial planet formation in a gas-poor environment make distinct predictions regarding the location of this rocky/non-rocky transition in period-radius space. Here we present the confirmation of TOI-1235 b ($P=3.44$ days, $r_p=1.738^{+0.087}_{-0.076}$ R$_{\oplus}$), a planet whose size and period are intermediate between the competing model predictions thus making the system an important test case for emergence models of the rocky/non-rocky transition around early M dwarfs ($R_s=0.630\pm 0.015$ R$_{\odot}$, $M_s=0.640\pm 0.016$ M$_{\odot}$). We confirm the TESS planet discovery using reconnaissance spectroscopy, ground-based photometry, high-resolution imaging, and a set of 38 precise radial-velocities from HARPS-N and HIRES. We measure a planet mass of $6.91^{+0.75}_{-0.85}$ M$_{\oplus}$, which implies an iron core mass fraction of $20^{+15}_{-12}$% in the absence of a gaseous envelope. The bulk composition of TOI-1235 b is therefore consistent with being Earth-like and we constrain a H/He envelope mass fraction to be $, Accepted to The Astronomical Journal. 8 figures & 5 tables. Table 2 is provided in the arXiv source code

The Kepler mission revealed a class of planets known as ''super-puffs,'' with masses only a few times larger than Earth's but radii larger than Neptune, giving them very low mean densities. All three of the known planets orbiting the young solar-type star Kepler 51 are super-puffs. The Kepler 51 system thereby provides an opportunity for a comparative study of the structures and atmospheres of this mysterious class of planets, which may provide clues about their formation and evolution. We observed two transits each of Kepler 51b and 51d with the Wide Field Camera 3 (WFC3) on the Hubble Space Telescope. Combining new WFC3 transit times with re-analyzed Kepler data and updated stellar parameters, we confirmed that all three planets have densities lower than 0.1 g/cm$^{3}$. We measured the WFC3 transmission spectra to be featureless between 1.15 and 1.63 $\mu$m, ruling out any variations greater than 0.6 scale heights (assuming a H/He dominated atmosphere), thus showing no significant water absorption features. We interpreted the flat spectra as the result of a high-altitude aerosol layer (pressure $, Comment: 29 pages, 16 figures, Re-submitted to AJ

We present the confirmation of a small, moderately-irradiated (F = 155 +/- 7 Fearth) Neptune with a substantial gas envelope in a P=11.8728787+/-0.0000085-day orbit about a quiet, Sun-like G0V star Kepler-1655. Based on our analysis of the Kepler light curve, we determined Kepler-1655b's radius to be 2.213+/-0.082 Rearth. We acquired 95 high-resolution spectra with TNG/HARPS-N, enabling us to characterize the host star and determine an accurate mass for Kepler-1655b of 5.0+3.1/-2.8 Mearth via Gaussian-process regression. Our mass determination excludes an Earth-like composition with 98\% confidence. Kepler-1655b falls on the upper edge of the evaporation valley, in the relatively sparsely occupied transition region between rocky and gas-rich planets. It is therefore part of a population of planets that we should actively seek to characterize further., 21 pages, 14 figures, 4 tables; accepted for publication in the Astronomical Journal

M-dwarf stars are promising targets for identifying and characterizing potentially habitable planets. K2-3 is a nearby (45 pc), early-type M dwarf hosting three small transiting planets, the outermost of which orbits close to the inner edge of the stellar (optimistic) habitable zone. The K2-3 system is well suited for follow-up characterization studies aimed at determining accurate masses and bulk densities of the three planets. Using a total of 329 radial velocity measurements collected over 2.5 years with the HARPS-N and HARPS spectrographs and a proper treatment of the stellar activity signal, we aim to improve measurements of the masses and bulk densities of the K2-3 planets. We use our results to investigate the physical structure of the planets. We analyse radial velocity time series extracted with two independent pipelines by using Gaussian process regression. We adopt a quasi-periodic kernel to model the stellar magnetic activity jointly with the planetary signals. We use Monte Carlo simulations to investigate the robustness of our mass measurements of K2-3\,c and K2-3\,d, and to explore how additional high-cadence radial velocity observations might improve them. Despite the stellar activity component being the strongest signal present in the radial velocity time series, we are able to derive masses for both planet b ($M_{\rm b}=6.6\pm1.1$ $M_{\rm \oplus}$) and planet c ($M_{\rm c}=3.1^{+1.3}_{-1.2}$ $M_{\rm \oplus}$). The Doppler signal due to K2-3\,d remains undetected, likely because of its low amplitude compared to the radial velocity signal induced by the stellar activity. The closeness of the orbital period of K2-3\,d to the stellar rotation period could also make the detection of the planetary signal complicated. [...], 14 pages, 15 figures, accepted for publication in A&A

The relative abundance of deuterium and hydrogen is a potent tracer of planet formation and evolution. Jupiter and Saturn have protosolar atmospheric D/H ratios, a relic of substantial gas accretion from the nebula, while the atmospheres of Neptune and Uranus are enhanced in D by accretion of ices into their envelopes. For terrestrial planets, D/H ratios are used to determine the mechanisms of volatile delivery and subsequent atmosphere loss over the lifetime of the planet. Planets and brown dwarfs more massive than 13 M_J quickly fuse their initial D reservoir. Here, we simulate spectra for giant exoplanets and brown dwarfs (2 M_Neptune to ~10 M_Jupiter) from Teff=200--1800 K including both CH3D and HDO to determine the observability of these dominant deuterium isotopologues in mid-infrared thermal emission spectra. Colder objects have stronger molecular features in their spectra, due to the temperature-dependence of molecular cross sections. CH3D is easier to observe than HDO at all temperatures considered, due to the strength of its absorption bands and locations of features at wavelengths with few other strong absorption features. We predict that for nearby cool brown dwarfs, the CH3D abundance can be measured at high signal-to-noise with the James Webb Space Telescope; for objects from 200--800 K closer than 10 pc, a protosolar D/H ratio would be readily observable in 2.5 hours. Moderately young Jupiter-mass planets (100--300 Myr) and young Neptunes (10 Myr) may be discovered with JWST and provide the best targets for detecting deuterium on an exoplanet in the coming decade. Future telescope designs should consider the importance of isotopes for understanding the formation and evolution of planetary atmospheres., Comment: 10 pages, 5 figures, published in ApJ Letters

Ultra-short period (USP) planets are a class of low mass planets with periods shorter than one day. Their origin is still unknown, with photo-evaporation of mini-Neptunes and in-situ formation being the most credited hypotheses. Formation scenarios differ radically in the predicted composition of USP planets, it is therefore extremely important to increase the still limited sample of USP planets with precise and accurate mass and density measurements. We report here the characterization of an USP planet with a period of 0.28 days around K2-141 (EPIC 246393474), and the validation of an outer planet with a period of 7.7 days in a grazing transit configuration. We derived the radii of the planets from the K2 light curve and used high-precision radial velocities gathered with the HARPS-N spectrograph for mass measurements. For K2-141b we thus inferred a radius of $1.51\pm0.05~R_\oplus$ and a mass of $5.08\pm0.41~M_\oplus$, consistent with a rocky composition and lack of a thick atmosphere. K2-141c is likely a Neptune-like planet, although due to the grazing transits and the non-detection in the RV dataset, we were not able to put a strong constraint on its density. We also report the detection of secondary eclipses and phase curve variations for K2-141b. The phase variation can be modeled either by a planet with a geometric albedo of $0.30 \pm 0.06$ in the Kepler bandpass, or by thermal emission from the surface of the planet at $\sim$3000K. Only follow-up observations at longer wavelengths will allow us to distinguish between these two scenarios., Comment: 16 pages, 10 figures., accepted for publication in AJ

We present precise radial velocity observations of WASP-47, a star known to host a hot Jupiter, a distant Jovian companion, and, uniquely, two additional transiting planets in short-period orbits: a super-Earth in a ~19 hour orbit, and a Neptune in a ~9 day orbit. We analyze our observations from the HARPS-N spectrograph along with previously published data to measure the most precise planet masses yet for this system. When combined with new stellar parameters and reanalyzed transit photometry, our mass measurements place strong constraints on the compositions of the two small planets. We find unlike most other ultra-short-period planets, the inner planet, WASP-47 e, has a mass (6.83 +/- 0.66 Me) and radius (1.810 +/- 0.027 Re) inconsistent with an Earth-like composition. Instead, WASP-47 e likely has a volatile-rich envelope surrounding an Earth-like core and mantle. We also perform a dynamical analysis to constrain the orbital inclination of WASP-47 c, the outer Jovian planet. This planet likely orbits close to the plane of the inner three planets, suggesting a quiet dynamical history for the system. Our dynamical constraints also imply that WASP-47 c is much more likely to transit than a geometric calculation would suggest. We calculate a transit probability for WASP-47 c of about 10%, more than an order of magnitude larger than the geometric transit probability of 0.6%., 15 pages, 3 figures, 3 tables. Accepted in AJ

We report a detailed characterization of the Kepler-19 system. This star was previously known to host a transiting planet with a period of 9.29 days, a radius of 2.2 R$_\oplus$ and an upper limit on the mass of 20 M$_\oplus$. The presence of a second, non-transiting planet was inferred from the transit time variations (TTVs) of Kepler-19b, over 8 quarters of Kepler photometry, although neither mass nor period could be determined. By combining new TTVs measurements from all the Kepler quarters and 91 high-precision radial velocities obtained with the HARPS-N spectrograph, we measured through dynamical simulations a mass of $8.4 \pm 1.6$ M$_\oplus$ for Kepler-19b. From the same data, assuming system coplanarity, we determined an orbital period of 28.7 days and a mass of $13.1 \pm 2.7$ M$_\oplus$ for Kepler-19c and discovered a Neptune-like planet with a mass of $20.3 \pm 3.4$ M$_\oplus$ on a 63 days orbit. By comparing dynamical simulations with non-interacting Keplerian orbits, we concluded that neglecting interactions between planets may lead to systematic errors that could hamper the precision in the orbital parameters when the dataset spans several years. With a density of $4.32 \pm 0.87$ g cm$^{-3}$ ($0.78 \pm 0.16$ $\rho_\oplus$) Kepler-19b belongs to the group of planets with a rocky core and a significant fraction of volatiles, in opposition to low-density planets characterized by transit-time variations only and the increasing number of rocky planets with Earth-like density. Kepler-19 joins the small number of systems that reconcile transit timing variation and radial velocity measurements., Comment: Accepted by AJ, 15 pages, 10 figures, 6 tables. Mass-Radius diagram for Exoplanets and code available at https://github.com/LucaMalavolta and https://github.com/lucaborsato

Strongly irradiated giant planets are observed to have radii larger than thermal evolution models predict. Although these inflated planets have been known for over fifteen years, it is unclear whether their inflation is caused by deposition of energy from the host star, or inhibited cooling of the planet. These processes can be distinguished if the planet becomes highly irradiated only when the host star evolves onto the red giant branch. We report the discovery of K2-97b, a 1.31 $\pm$ 0.11 R$_\mathrm{J}$, 1.10 $\pm$ 0.11 M$_\mathrm{J}$ planet orbiting a 4.20 $\pm$ 0.14 R$_\odot$, 1.16 $\pm$ 0.12 M$_\odot$ red giant star with an orbital period of 8.4 days. We precisely constrained stellar and planetary parameters by combining asteroseismology, spectroscopy, and granulation noise modeling along with transit and radial velocity measurements. The uncertainty in planet radius is dominated by systematic differences in transit depth, which we measure to be up to 30% between different lightcurve reduction methods. Our calculations indicate the incident flux on this planet was 170$^{+140}_{-60}$ times the incident flux on Earth while the star was on the main sequence. Previous studies suggest that this incident flux is insufficient to delay planetary cooling enough to explain the present planet radius. This system thus provides the first evidence that planets may be inflated directly by incident stellar radiation rather than by delayed loss of heat from formation. Further studies of planets around red giant branch stars will confirm or contradict this hypothesis, and may reveal a new class of re-inflated planets., Comment: 13 pages, 11 figures, published in AJ 12/2016

Exoplanet discoveries of recent years have provided a great deal of new data for studying the bulk compositions of giant planets. Here we identify 47 transiting giant planets ($20 M_\oplus < M < 20 M_{\mathrm{J}}$) whose stellar insolation is low enough ($F_* < 2\times10^8\; \text{erg}\; \text{s}^{-1}\; \text{cm}^{-2}$, or roughly $T_\text{eff} < 1000$) that they are not affected by the hot Jupiter radius inflation mechanism(s). We compute a set of new thermal and structural evolution models and use these models in comparison with properties of the 47 transiting planets (mass, radius, age) to determine their heavy element masses. A clear correlation emerges between the planetary heavy element mass $M_z$ and the total planet mass, approximately of the form $M_z \propto \sqrt{M}$. This finding is consistent with the core accretion model of planet formation. We also study how stellar metallicity [Fe/H] affects planetary metal-enrichment and find a weaker correlation than has been previously reported from studies with smaller sample sizes. We confirm a strong relationship between the planetary metal-enrichment relative to the parent star $Z_{\rm planet}/Z_{\rm star}$ and the planetary mass, but see no relation in $Z_{\rm planet}/Z_{\rm star}$ with planet orbital properties or stellar mass. The large heavy element masses of many planets ($>50$ $M_{\oplus}$) suggest significant amounts of heavy elements in H/He envelopes, rather than cores, such that metal-enriched giant planet atmospheres should be the rule. We also discuss a model of core-accretion planet formation in a one-dimensional disk and show that it agrees well with our derived relation between mass and $Z_{\rm planet}/Z_{\rm star}$., Accepted to The Astrophysical Journal. This revision adds a substantial amount of discussion; the results are the same

Kepler has discovered hundreds of systems with multiple transiting exoplanets which hold tremendous potential both individually and collectively for understanding the formation and evolution of planetary systems. Many of these systems consist of multiple small planets with periods less than ~50 days known as Systems with Tightly-spaced Inner Planets, or STIPs. One especially intriguing STIP, Kepler-80 (KOI-500), contains five transiting planets: f, d, e, b, and c with periods of 1.0, 3.1, 4.6, 7.1, 9.5 days, respectively. We provide measurements of transit times and a transit timing variation (TTV) dynamical analysis. We find that TTVs cannot reliably detect eccentricities for this system, though mass estimates are not affected. Restricting the eccentricity to a reasonable range, we infer masses for the outer four planets (d, e, b, and c) to be $6.75^{+0.69}_{-0.51}$, $4.13^{+0.81}_{-0.95}$, $6.93^{+1.05}_{-0.70}$, and $6.74^{+1.23}_{-0.86}$ Earth masses, respectively. The similar masses but different radii are consistent with terrestrial compositions for d and e and $\sim$2% H/He envelopes for b and c. We confirm that the outer four planets are in a rare dynamical configuration with four interconnected three-body resonances that are librating with few degree amplitudes. We present a formation model that can reproduce the observed configuration by starting with a multi-resonant chain and introducing dissipation. Overall, the information-rich Kepler-80 planets provide an important perspective into exoplanetary systems., Accepted to AJ. 19 pages, 7 figures. Additional animations available here[http://mmacdonald.altervista.org/kepler-80.html]

Kepler-20 is a solar-type star (V = 12.5) hosting a compact system of five transiting planets, all packed within the orbital distance of Mercury in our own Solar System. A transition from rocky to gaseous planets with a planetary transition radius of ~1.6 REarth has recently been proposed by several publications in the literature (Rogers 2015;Weiss & Marcy 2014). Kepler-20b (Rp ~ 1.9 REarth) has a size beyond this transition radius, however previous mass measurements were not sufficiently precise to allow definite conclusions to be drawn regarding its composition. We present new mass measurements of three of the planets in the Kepler-20 system facilitated by 104 radial velocity measurements from the HARPS-N spectrograph and 30 archival Keck/HIRES observations, as well as an updated photometric analysis of the Kepler data and an asteroseismic analysis of the host star (MStar = 0.948+-0.051 Msun and Rstar = 0.964+-0.018 Rsun). Kepler-20b is a 1.868+0.066-0.034 REarth planet in a 3.7 day period with a mass of 9.70+1.41-1.44 MEarth resulting in a mean density of 8.2+1.5-1.3 g/cc indicating a rocky composition with an iron to silicate ratio consistent with that of the Earth. This makes Kepler-20b the most massive planet with a rocky composition found to date. Furthermore, we report the discovery of an additional non-transiting planet with a minimum mass of 19.96+3.08-3.61 MEarth and an orbital period of ~34 days in the gap between Kepler-20f (P ~ 11 days) and Kepler-20d (P ~ 78 days)., 33 pages, 8 figures. Accepted for publication in AJ

HD 179070, aka Kepler-21, is a V = 8.25 F6IV star and the brightest exoplanet host discovered by Kepler. An early detailed analysis by Howell et al. (2012) of the first thirteen months (Q0 - Q5) of Kepler light curves revealed transits of a planetary companion, Kepler-21b, with a radius of about 1.60 +/- 0.04 R_earth and an orbital period of about 2.7857 days. However, they could not determine the mass of the planet from the initial radial velocity observations with Keck-HIRES, and were only able to impose a 2-sigma upper limit of 10 M_earth. Here we present results from the analysis of 82 new radial velocity observations of this system obtained with HARPS-N, together with the existing 14 HIRES data points. We detect the Doppler signal of Kepler-21b with a radial velocity semi-amplitude K = 2.00 +/- 0.65 m/s, which corresponds to a planetary mass of 5.1 +/- 1.7 M_earth. We also measure an improved radius for the planet of 1.639 (+0.019, -0.015) R_earth, in agreement with the radius reported by Howell et al. (2012). We conclude that Kepler-21b, with a density of 6.4 +/- 2.1 g/cm^3, belongs to the population of terrestrial planets with iron, magnesium silicate interiors, which have lost the majority of their envelope volatiles via stellar winds or gravitational escape. The radial velocity analysis presented in this paper serves as example of the type of analysis that will be necessary to confirm the masses of TESS small planet candidates.

Kepler-454 (KOI-273) is a relatively bright (V = 11.69 mag), Sun-like starthat hosts a transiting planet candidate in a 10.6 d orbit. From spectroscopy, we estimate the stellar temperature to be 5687 +/- 50 K, its metallicity to be [m/H] = 0.32 +/- 0.08, and the projected rotational velocity to be v sin i 10 years and mass >12.1M_J . The twelve exoplanets with radii, 40 pages, 13 figures, 6 pages; ApJ in press

We present here the detection of a system of four low-mass planets around the bright (V=5.5) and close-by (6.5 pc) star HD219134. This is the first result of the Rocky Planet Search program with HARPS-N on the TNG in La Palma. The inner planet orbits the star in 3.0937 +/-0.0004 days, on a quasi-circular orbit with a semi-major axis of 0.0382 +/- 0.0003 AU. Spitzer observations allowed us to detect the transit of the planet in front of the star making HD219134b the nearest known transiting planet to date. From the amplitude of the radial-velocity variation (2.33 +/- 0.24 m/s) and observed depth of the transit (359 +/- 38 ppm), the planet mass and radius are estimated to be 4.46 +/- 0.47 M_{\oplus} and 1.606 +/- 0.086 R_{\oplus} leading to a mean density of 5.89 +/- 1.17 g/cc, suggesting a rocky composition. One additional planet with minimum mass of 2.67 +/- 0.59 M_{\oplus} moves on a close-in, quasi-circular orbit with a period of 6.765 +/- 0.005 days. The third planet in the system has a period of 46.78 +/- 0.16 days and a minimum mass of 8.7 +/- 1.1 M{\oplus}, at 0.234 +/- 0.002 AU from the star. Its eccentricity is 0.32 +/- 0.14. The period of this planet is close to the rotational period of the star estimated from variations of activity indicators (42.3 +/- 0.1 days). The planetary origin of the signal is, however, the preferred solution as no indication of variation at the corresponding frequency is observed for activity-sensitive parameters. Finally, a fourth additional longer-period planet of mass of 62 +/- 6 M_{\oplus} orbits the star in 1190 days, on an eccentric orbit (e=0.27 +/- 0.11) at a distance of 2.14 +/- 0.27 AU., Comment: Accepted for publication in A&A

TRAPPIST-1 is a nearby ultra-cool dwarf that is host to a remarkable planetary system consisting of seven transiting planets. The orbital properties and radii of the planets have been well-constrained, and recently the masses of the inner six planets have been measured with additional ground and space-based photometric observations. Large uncertainties in these mass measurements have prevented a robust analysis of the planetary compositions. Here we perform many thousands of N-body dynamical simulations with planet properties perturbed from the observed values and identify those that are stable for millions of years. This allows us to identify self-consistent orbital solutions that can be used in future studies. From our range of dynamical masses, we find that most of the planets are consistent with an Earth-like composition, where TRAPPIST-1f is likely to have a volatile-rich envelope., Comment: 4 pages, 2 figure, 3 tables, accepted to ApJL; Changes made due to first review including modification and addition of figures

The Kepler-11 planetary system contains six transiting planets ranging in size from 1.8 to 4.2 times the radius of Earth. Five of these planets orbit in a tightly-packed configuration with periods between 10 and 47 days. We perform a dynamical analysis of the system based upon transit timing variations observed in more than three years of \ik photometric data. Stellar parameters are derived using a combination of spectral classification and constraints on the star's density derived from transit profiles together with planetary eccentricity vectors provided by our dynamical study. Combining masses of the planets relative to the star from our dynamical study and radii of the planets relative to the star from transit depths together with deduced stellar properties yields measurements of the radii of all six planets, masses of the five inner planets, and an upper bound to the mass of the outermost planet, whose orbital period is 118 days. We find mass-radius combinations for all six planets that imply that substantial fractions of their volumes are occupied by constituents that are less dense than rock. The Kepler-11 system contains the lowest mass exoplanets for which both mass and radius have been measured., 39 pages, 10 figures

NASA's Kepler Mission has revealed two transiting planets orbiting Kepler-68. Follow-up Doppler measurements have established the mass of the innermost planet and revealed a third jovian-mass planet orbiting beyond the two transiting planets. Kepler-68b, in a 5.4 day orbit has mass 8.3 +/- 2.3 Earth, radius 2.31 +/- 0.07 Earth radii, and a density of 3.32 +/- 0.92 (cgs), giving Kepler-68b a density intermediate between that of the ice giants and Earth. Kepler-68c is Earth-sized with a radius of 0.953 Earth and transits on a 9.6 day orbit; validation of Kepler-68c posed unique challenges. Kepler-68d has an orbital period of 580 +/- 15 days and minimum mass of Msin(i) = 0.947 Jupiter. Power spectra of the Kepler photometry at 1-minute cadence exhibit a rich and strong set of asteroseismic pulsation modes enabling detailed analysis of the stellar interior. Spectroscopy of the star coupled with asteroseismic modeling of the multiple pulsation modes yield precise measurements of stellar properties, notably Teff = 5793 +/- 74 K, M = 1.079 +/- 0.051 Msun, R = 1.243 +/- 0.019 Rsun, and density 0.7903 +/- 0.0054 (cgs), all measured with fractional uncertainties of only a few percent. Models of Kepler-68b suggest it is likely composed of rock and water, or has a H and He envelope to yield its density of about 3 (cgs)., Comment: 32 pages, 13 figures, Accepted to ApJ

We use models of coupled thermal evolution and photo-evaporative mass loss to understand the formation and evolution of the Kepler-36 system. We show that the large contrast in mean planetary density observed by Carter et al. (2012) can be explained as a natural consequence of photo-evaporation from planets that formed with similar initial compositions. However, rather than being due to differences in XUV irradiation between the planets, we find that this contrast is due to the difference in the masses of the planets' rock/iron cores and the impact that this has on mass loss evolution. We explore in detail how our coupled models depend on irradiation, mass, age, composition, and the efficiency of mass loss. Based on fits to large numbers of coupled evolution and mass loss runs, we provide analytic fits to understand threshold XUV fluxes for significant atmospheric loss, as a function of core mass and mass loss efficiency. Finally we discuss these results in the context of recent studies of the radius distribution of Kepler candidates. Using our parameter study, we make testable predictions for the frequency of sub-Neptune sized planets. We show that 1.8-4.0 R_earth planets should become significantly less common on orbits within 10 days and discuss the possibility of a narrow "occurrence valley" in the radius-flux distribution. Moreover, we describe how photo-evaporation provides a natural explanation for the recent observations of Ciardi et al. (2013) that inner planets are preferentially smaller within the systems., Comment: 12 pages, 9 figures, resubmitted to ApJ

Transiting planet surveys like Kepler have provided a wealth of information on the distribution of planetary radii, particularly for the new populations of super-Earth and sub-Neptune sized planets. In order to aid in the physical interpretation of these radii, we compute model radii for low-mass rocky planets with hydrogen-helium envelopes. We provide model radii for planets 1-20 Earth masses, with envelope fractions from 0.01-20%, levels of irradiation 0.1-1000x Earth's, and ages from 100 Myr to 10 Gyr. In addition we provide simple analytic fits that summarize how radius depends on each of these parameters. Most importantly, we show that at fixed composition, radii show little dependence on mass for planets with more than ~1% of their mass in their envelope. Consequently, planetary radius is to first order a proxy for planetary composition for Neptune and sub-Neptune sized planets. We recast the observed mass-radius relationship as a mass-composition relationship and discuss it in light of traditional core accretion theory. We discuss the transition from rocky super-Earths to sub-Neptune planets with large volatile envelopes. We suggest 1.75 Earth radii as a physically motivated dividing line between these two populations of planets. Finally, we discuss these results in light of the observed radius occurrence distribution found by Kepler., Comment: 17 pages, 9 figures, 7 tables, submitted to ApJ

We report the discovery and confirmation of two sub-Saturn planets orbiting a bright (V = 11.3), metal-rich ([Fe/H] = 0.42 $\pm$ 0.04 dex) G3 dwarf in the K2 Campaign 2 field. The planets are 5.68 $\pm$ 0.56 Earth-radii and 7.82 $\pm$ 0.72 Earth-radii and have orbital periods of 20.8851 $\pm$ 0.0003 d and 42.3633$\pm$0.0006 d, near to the 2:1 mean-motion resonance. We obtained 32 radial velocities (RVs) with Keck/HIRES and detected the reflex motion due to EPIC-203771098b and c. These planets have masses of 21.0 $\pm$ 5.4 Earth-masses and 27.0 $\pm$ 6.9 Earth-masses, respectively. With low densities of 0.63 $\pm$ 0.25 g/cc and 0.31 $\pm$ 0.12 g/cc, respectively, the planets require thick envelopes of H/He to explain their large sizes and low masses. Interior structure models predict that the planets have fairly massive cores of 17.6 $\pm$ 4.3 Earth-masses and 16.1 $\pm$ 4.2 Earth-masses, respectively. They may have formed exterior to their present locations, accreted their H/He envelopes at large orbital distances, and migrated in as a resonant pair. The proximity to resonance, large transit depths, and host star brightness offer rich opportunities for TTV follow-up. Finally, the low surface gravities of the EPIC-203771098 planets make them favorable targets for transmission spectroscopy by HST, Spitzer, and JWST., 12 pages, 6 figures, 3 tables, published in ApJ. v2: text updated to ApJ version, replaced EPIC-2037 with K2-24

We use models of thermal evolution and XUV-driven mass loss to explore the composition and history of low-mass low-density transiting planets. We investigate the Kepler-11 system in detail and provide estimates of both the current and past planetary compositions. We find that a H/He atmosphere on Kepler-11b is highly vulnerable to mass loss. By comparing to formation models, we show that in situ formation of the system is unlikely. Instead we propose that it is a water-rich system of sub-Neptunes that migrated from beyond the snow line. For the broader population of observed planets, we show that there is a threshold in bulk planet density and incident flux above which no low-mass transiting planets have been observed. We suggest that this threshold is due to the instability of H/He atmospheres to XUV-driven mass loss. Importantly, we find that this flux-density threshold is well reproduced by our thermal evolution/contraction models that incorporate a standard mass loss prescription. Treating the planets' contraction history is essential because the planets have significantly larger radii during the early era of high XUV fluxes. Over time low mass planets with H/He envelopes can be transformed into water-dominated worlds with steam atmospheres or rocky super-Earths. Finally, we use this threshold to provide likely minimum masses and radial velocity amplitudes for the general population of Kepler candidates. Likewise, we use this threshold to provide constraints on the maximum radii of low-mass planets found by radial velocity surveys., Comment: 17 pages, 7 figures. Accepted for publication in ApJ. Compared to the submitted version we made modest modifications to our mass loss model including reducing our default mass loss efficiency. However, the central conclusions of the paper are unchanged

(abridged) In the last decade, the advent of enormous galaxy surveys has motivated the development of automated morphological classification schemes to deal with large data volumes. Existing automated schemes can successfully distinguish between early and late type galaxies and identify merger candidates, but are inadequate for studying detailed morphologies of red sequence galaxies. To fill this need, we present a new automated classification scheme that focuses on making finer distinctions between early types roughly corresponding to Hubble types E, S0, and Sa. We visually classify a sample of 984 non-starforming SDSS galaxies with apparent sizes >14". We then develop an automated method to closely reproduce the visual classifications, which both provides a check on the visual results and makes it possible to extend morphological analysis to much larger samples. We visually classify the galaxies into three bulge classes (BC) by the shape of the light profile in the outer regions: discs have sharp edges and bulges do not, while some galaxies are intermediate. We separately identify galaxies with features: spiral arms, bars, clumps, rings, and dust. We find general agreement between BC and the bulge fraction B/T measured by the galaxy modeling package GIM2D, but many visual discs have B/T>0.5. Three additional automated parameters -- smoothness, axis ratio, and concentration -- can identify many of these high-B/T discs to yield automated classifications that agree ~70% with the visual classifications (>90% within one BC). Both methods are used to study the bulge vs. disc frequency as a function of four measures of galaxy 'size': luminosity, stellar mass, velocity dispersion, and radius. All size indicators show a fall in disc fraction and a rise in bulge fraction among larger galaxies.

When an extrasolar planet passes in front of its star (transits), its radius can be measured from the decrease in starlight and its orbital period from the time between transits. Multiple planets transiting the same star reveal more: period ratios determine stability and dynamics, mutual gravitational interactions reflect planet masses and orbital shapes, and the fraction of transiting planets observed as multiples has implications for the planarity of planetary systems. But few stars have more than one known transiting planet, and none has more than three. Here we report Kepler spacecraft observations of a single Sun-like star that reveal six transiting planets, five with orbital periods between 10 and 47 days plus a sixth one with a longer period. The five inner planets are among the smallest whose masses and sizes have both been measured, and these measurements imply substantial envelopes of light gases. The degree of coplanarity and proximity of the planetary orbits imply energy dissipation near the end of planet formation., Comment: published in Nature

The Kepler Mission has found thousands of planetary candidates with radii between 1 and 4 . These planets have no analogues in our own solar system, providing an unprecedented opportunity to understand the range and distribution of planetary compositions allowed by planet formation and evolution. A precise mass measurement is usually required to constrain the possible composition of an individual super-Earth-sized planet, but these measurements are difficult and expensive to make for the majority of Kepler planet candidates (PCs). Fortunately, adopting a statistical approach helps us to address this question without them. In particular, we apply hierarchical Bayesian modeling to a subsample of Kepler PCs that is complete for days and and draw upon interior structure models that yield radii largely independent of mass by accounting for the thermal evolution of a gaseous envelope around a rocky core. Assuming the envelope is dominated by hydrogen and helium, we present the current-day composition distribution of the sub-Neptune-sized planet population and find that H+He envelopes are most likely to be ∼1% of these planets’ total masses with an intrinsic scatter of ±0.5 dex. We address the gaseous/rocky transition and illustrate how our results do not result in a one-to-one relationship between mass and radius for this sub-Neptune population; accordingly, dynamical studies that wish to use Kepler data must adopt a probabilistic approach to accurately represent the range of possible masses at a given radius.

K2-55b is a Neptune-sized planet orbiting a K7 dwarf with a radius of $0.715^{+0.043}_{-0.040}R_\odot$, a mass of $0.688\pm0.069 M_\odot$, and an effective temperature of $4300^{+107}_{-100}$K. Having characterized the host star using near-infrared spectra obtained at IRTF/SpeX, we observed a transit of K2-55b with Spitzer/IRAC and confirmed the accuracy of the original K2 ephemeris for future follow-up transit observations. Performing a joint fit to the Spitzer/IRAC and K2 photometry, we found a planet radius of $4.41^{+0.32}_{-0.28} R_\oplus$, an orbital period of $2.84927265_{-6.42\times10^{-6}}^{+6.87\times10^{-6}}$ days, and an equilibrium temperature of roughly 900K. We then measured the planet mass by acquiring twelve radial velocity (RV) measurements of the system using HIRES on the 10m Keck I Telescope. Our RV data set precisely constrains the mass of K2-55b to $43.13^{+5.98}_{-5.80} M_\oplus$, indicating that K2-55b has a bulk density of $2.8_{-0.6}^{+0.8}$ g cm$^{-3}$ and can be modeled as a rocky planet capped by a modest H/He envelope ($M_{\rm envelope} = 12\pm3\% M_p$). K2-55b is denser than most similarly sized planets, raising the question of whether the high planetary bulk density of K2-55b could be attributed to the high metallicity of K2-55. The absence of a substantial volatile envelope despite the large mass of K2-55b poses a challenge to current theories of gas giant formation. We posit that K2-55b may have escaped runaway accretion by migration, late formation, or inefficient core accretion or that K2-55b was stripped of its envelope by a late giant impact., 22 pages, 7 figures, 4 tables. Accepted to the Astronomical Journal on June 25, 2018

We present results from a Keck/HIRES radial velocity campaign to study four sub-Saturn-sized planets, K2-27b, K2-32b, K2-39b, and K2-108b, with the goal of understanding their masses, orbits, and heavy element enrichment. The planets have similar sizes $(R_P = 4.5-5.5~R_E)$, but have dissimilar masses $(M_P = 16-60~M_E)$, implying a diversity in their core and envelope masses. K2-32b is the least massive $(M_P = 16.5 \pm 2.7~M_E)$ and orbits in close proximity to two sub-Neptunes near a 3:2:1 period commensurability. K2-27b and K2-39b are significantly more massive at $M_P = 30.9 \pm 4.6~M_E$ and $M_P = 39.8 \pm 4.4~M_E$, respectively, and show no signs of additional planets. K2-108b is the most massive at $M_P = 59.4 \pm 4.4~M_E$, implying a large reservoir of heavy elements of about $\approx50~M_E$. Sub-Saturns as a population have a large diversity in planet mass at a given size. They exhibit remarkably little correlation between mass and size; sub-Saturns range from $\approx 6-60~M_E$, regardless of size. We find a strong correlation between planet mass and host star metallicity, suggesting that metal-rich disks form more massive planet cores. The most massive sub-Saturns tend to lack detected companions and have moderately eccentric orbits, perhaps as a result of a previous epoch of dynamical instability. Finally, we observe only a weak correlation between the planet envelope fraction and present-day equilibrium temperature, suggesting that photo-evaporation does not play a dominant role in determining the amount of gas sub-Saturns accrete from their protoplanetary disks., 25 pages, 15 figures, accepted for publication in AJ

We report the detection of a transiting hot Neptune exoplanet orbiting TOI-824 (SCR J1448-5735), a nearby (d = 64 pc) K4V star, using data from the \textit{Transiting Exoplanet Survey Satellite} (TESS). The newly discovered planet has a radius, $R_{\rm{p}}$ = 2.93 $\pm$ 0.20 R$_{\oplus}$, and an orbital period of 1.393 days. Radial velocity measurements using the Planet Finder Spectrograph (PFS) and the High Accuracy Radial velocity Planet Searcher (HARPS) spectrograph confirm the existence of the planet and we estimate its mass to be $M_{\rm{p}}$ = 18.47 $\pm$ 1.84 M$_{\oplus}$. The planet's mean density is $\rho_{\rm{p}}$ = 4.03$^{+0.98}_{-0.78}$ g cm$^{-3}$ making it more than twice as dense as Neptune. TOI-824 b's high equilibrium temperature makes the planet likely to have a cloud free atmosphere, and thus an excellent candidate for follow up atmospheric studies. The detectability of TOI-824 b's atmosphere from both ground and space is promising and could lead to the detailed characterization of the most irradiated, small planet at the edge of the hot Neptune desert that has retained its atmosphere to date., Comment: 22 pages, 10 figures. Accepted for publication in the Astronomical Journal