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Joshua N. Winn

Publications and source records attributed to Joshua N. Winn.

At least 253 records · Page 14Linked to original sources

Speckle Observations of TESS Exoplanet Host Stars: Understanding the Binary Exoplanet Host Star Orbital Period Distribution

We present high-resolution speckle interferometric imaging observations of TESS exoplanet host stars using the NN-EXPLORE NESSI instrument the at the 3.5-m WIYN telescope. Eight TOIs, that were originally discovered by Kepler, were previously observed using the Differential Speckle Survey Instrument (DSSI). Speckle observations of 186 TESS stars were carried out and 45 (24%) likely bound companions were detected. This is approximately the number of companions we would expect to observe given the established 46% binarity rate in exoplanet host stars. For the detected binaries, the distribution of stellar mass ratio is consistent with that of the standard Raghavan distribution and may show a decrease in high-q systems as the binary separation increases. The distribution of binary orbital periods, however, is not consistent with the standard Ragahavan model and our observations support the premise that exoplanet-hosting stars with binary companions have, in general, wider orbital separations than field binaries. We find that exoplanet-hosting binary star systems show a distribution peaking near 100 au, higher than the 40-50 au peak that is observed for field binaries. This fact led to earlier suggestions that planet formation is suppressed in close binaries.

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TIC 168789840: A Sextuply-Eclipsing Sextuple Star System

We report the discovery of a sextuply-eclipsing sextuple star system from TESS data, TIC 168789840, also known as TYC 7037-89-1, the first known sextuple system consisting of three eclipsing binaries. The target was observed in Sectors 4 and 5 during Cycle 1, with lightcurves extracted from TESS Full Frame Image data. It was also previously observed by the WASP survey and ASAS-SN. The system consists of three gravitationally-bound eclipsing binaries in a hierarchical structure of an inner quadruple system with an outer binary subsystem. Follow-up observations from several different observatories were conducted as a means of determining additional parameters. The system was resolved by speckle interferometry with a 0."42 separation between the inner quadruple and outer binary, inferring an estimated outer period of ~2 kyr. It was determined that the fainter of the two resolved components is an 8.217 day eclipsing binary, which orbits the inner quadruple that contains two eclipsing binaries with periods of 1.570 days and 1.306 days. MCMC analysis of the stellar parameters has shown that the three binaries of TIC 168789840 are "triplets", as each binary is quite similar to the others in terms of mass, radius, and Teff. As a consequence of its rare composition, structure, and orientation, this object can provide important new insight into the formation, dynamics, and evolution of multiple star systems. Future observations could reveal if the intermediate and outer orbital planes are all aligned with the planes of the three inner eclipsing binaries.

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TESS discovery of a super-Earth and three sub-Neptunes hosted by the bright, Sun-like star HD 108236

We report the discovery and validation of four extrasolar planets hosted by the nearby, bright, Sun-like (G3V) star HD~108236 using data from the Transiting Exoplanet Survey Satellite (TESS). We present transit photometry, reconnaissance and precise Doppler spectroscopy as well as high-resolution imaging, to validate the planetary nature of the objects transiting HD~108236, also known as the TESS Object of Interest (TOI) 1233. The innermost planet is a possibly-rocky super-Earth with a period of $3.79523_{-0.00044}^{+0.00047}$ days and has a radius of $1.586\pm0.098$ $R_\oplus$. The outer planets are sub-Neptunes, with potential gaseous envelopes, having radii of $2.068_{-0.091}^{+0.10}$ $R_\oplus$, $2.72\pm0.11$ $R_\oplus$, and $3.12_{-0.12}^{+0.13}$ $R_\oplus$ and periods of $6.20370_{-0.00052}^{+0.00064}$ days, $14.17555_{-0.0011}^{+0.00099}$ days, and $19.5917_{-0.0020}^{+0.0022}$ days, respectively. With V and K$_{\rm s}$ magnitudes of 9.2 and 7.6, respectively, the bright host star makes the transiting planets favorable targets for mass measurements and, potentially, for atmospheric characterization via transmission spectroscopy. HD~108236 is the brightest Sun-like star in the visual (V) band known to host four or more transiting exoplanets. The discovered planets span a broad range of planetary radii and equilibrium temperatures, and share a common history of insolation from a Sun-like star ($R_\star = 0.888 \pm 0.017$ R$_\odot$, $T_{\rm eff} = 5730 \pm 50$ K), making HD 108236 an exciting, opportune cosmic laboratory for testing models of planet formation and evolution.

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TESS observations of the WASP-121 b phase curve

We study the red-optical photometry of the ultra-hot Jupiter WASP-121 b as observed by the Transiting Exoplanet Survey Satellite (TESS) and model its atmosphere through a radiative transfer simulation. Given its short orbital period of $\sim1.275$ days, inflated state and bright host star, WASP-121 b is exceptionally favorable for detailed atmospheric characterization. Towards this purpose, we use \texttt{allesfitter} to characterize its full red-optical phase curve, including the planetary phase modulation and the secondary eclipse. We measure the day and nightside brightness temperatures in the TESS passband as $3012\substack{+40 \\ -42}$ K and $2022\substack{+254 \\ -602}$ K, respectively, and do not find a statistically significant phase shift between the brightest and substellar points. This is consistent with an inefficient heat recirculation on the planet. We then perform an atmospheric retrieval analysis to infer the dayside atmospheric properties of WASP-121 b such as its bulk composition, albedo and heat recirculation. We confirm the temperature inversion in the atmosphere and suggest H$^-$, TiO and VO as potential causes of the inversion, absorbing heat at optical wavelengths at low pressures. Future HST and JWST observations of WASP-121 b will benefit from its first full phase curve measured by TESS.

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TOI-954 b and K2-329 b: Short-Period Saturn-Mass Planets that Test whether Irradiation Leads to Inflation

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.

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Early Time Light Curves of Type Ia Supernovae Observed with TESS

We present early time light curves of Type Ia supernovae observed in the first six sectors of TESS data. Ten of these supernovae were discovered by ASAS-SN, seven by ATLAS, six by ZTF, and one by \textit{Gaia}. For nine SNe with sufficient dynamic range ($>$3.0 mag from detection to peak), we fit power law models and search for signatures of companion stars. We find a diversity of early time light curve shapes, although most of our sources are consistent with fireball models where the flux increases $\propto t^2$. Three SN display a flatter rise with flux $\propto t$. We do not find any evidence for additional structure such as multiple power law components in the early rising light curves. For assumptions about the SN properties and the observer viewing angle, and further assuming that companion stars would be in Roche-lobe overflow, we place limits on the radii of companions for six SNe with complete coverage of the early time light curves. The upper limits are $\lesssim$\,32 R$_\odot$ for these six supernovae, $\lesssim$\,20 R$_\odot$ for five of these six, and $\lesssim$\,4 R$_\odot$ for two of these six. The small sample size does not constrain occurrence rates of single degenerate Type Ia SN progenitors, but we expect that TESS observed enough SNe in its primary mission (26 sectors) to inform this measurement. We also show that TESS is capable of detecting emission from a 1 \rsun\ companion for a Type Ia SN within 50 Mpc, and may do so after about six years.

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The TESS-Keck Survey II: An Ultra-Short Period Rocky Planet and its Siblings Transiting the Galactic Thick-Disk Star TOI-561

We report the discovery of TOI-561, a multi-planet system in the galactic thick disk that contains a rocky, ultra-short period planet (USP). This bright ($V=10.2$) star hosts three small transiting planets identified in photometry from the NASA TESS mission: TOI-561 b (TOI-561.02, P=0.44 days, $R_b = 1.45\pm0.11\,R_\oplus$), c (TOI-561.01, P=10.8 days, $R_c=2.90\pm0.13\,R_\oplus$), and d (TOI-561.03, P=16.3 days, $R_d=2.32\pm0.16\,R_\oplus$). The star is chemically ([Fe/H]$=-0.41\pm0.05$, [$α$/H]$=+0.23\pm0.05$) and kinematically consistent with the galactic thick disk population, making TOI-561 one of the oldest ($10\pm3\,$Gyr) and most metal-poor planetary systems discovered yet. We dynamically confirm planets b and c with radial velocities from the W. M. Keck Observatory High Resolution Echelle Spectrometer. Planet b has a mass and density of $3.2\pm0.8\,M_\oplus$ and $5.5^{+2.0}_{-1.6}\,$g$\,$cm$^{-3}$, consistent with a rocky composition. Its lower-than-average density is consistent with an iron-poor composition, although an Earth-like iron-to-silicates ratio is not ruled out. Planet c is $7.0\pm2.3\,M_\oplus$ and $1.6\pm0.6\,$g$\,$cm$^{-3}$, consistent with an interior rocky core overlaid with a low-mass volatile envelope. Several attributes of the photometry for planet d (which we did not detect dynamically) complicate the analysis, but we vet the planet with high-contrast imaging, ground-based photometric follow-up and radial velocities. TOI-561 b is the first rocky world around a galactic thick-disk star confirmed with radial velocities and one of the best rocky planets for thermal emission studies.

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Hot Stars With Kepler Planets Have High Obliquities

It has been known for a decade that hot stars with hot Jupiters tend to have high obliquities. Less is known about the degree of spin-orbit alignment for hot stars with other kinds of planets. Here, we re-assess the obliquities of hot Kepler stars with transiting planets smaller than Neptune, based on spectroscopic measurements of their projected rotation velocities (vsini). The basis of the method is that a lower obliquity -- all other things being equal -- causes sini to be closer to unity and increases the value of vsini. We sought evidence for this effect using a sample of 150 Kepler stars with effective temperatures between 5950 and 6550K and a control sample of 101 stars with matching spectroscopic properties and random orientations. The planet hosts have systematically higher values of vsini than the control stars, but not by enough to be compatible with perfect spin-orbit alignment. The mean value of sini is 0.856 +/- 0.036, which is 4-sigma away from unity (perfect alignment), and 2-sigma away from pi/4 (random orientations). There is also evidence that the hottest stars have a broader obliquity distribution: when modeled separately, the stars cooler than 6250K have = 0.928 +/- 0.042, while the hotter stars are consistent with random orientations. This is similar to the pattern previously noted for stars with hot Jupiters. Based on these results, obliquity excitation for early-G and late-F stars appears to be a general outcome of star and planet formation, rather than being exclusively linked to hot Jupiter formation.

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The multi-planet system TOI-421 -- A warm Neptune and a super puffy mini-Neptune transiting a G9 V star in a visual binary

We report the discovery of a warm Neptune and a hot sub-Neptune transiting TOI-421 (BD-14 1137, TIC 94986319), a bright (V=9.9) G9 dwarf star in a visual binary system observed by the TESS space mission in Sectors 5 and 6. We performed ground-based follow-up observations -- comprised of LCOGT transit photometry, NIRC2 adaptive optics imaging, and FIES, CORALIE, HARPS, HIRES, and PFS high-precision Doppler measurements -- and confirmed the planetary nature of the 16-day transiting candidate announced by the TESS team. We discovered an additional radial velocity signal with a period of 5 days induced by the presence of a second planet in the system, which we also found to transit its host star. We found that the inner mini-Neptune, TOI-421b, has an orbital period of Pb =5.19672 +- 0.00049 days, a mass of Mb = 7.17 +- 0.66 Mearth and a radius of Rb = 2.68+0.19-0.18 Rearth, whereas the outer warm Neptune, TOI-421 c, has a period of Pc =16.06819 +- 0.00035 days, a mass of Mc = 16.42+1.06-1.04 Mearth, a radius of Rc = 5.09+0.16-0.15 Rearth and a density of rho_c =0.685+0.080-0.072 g cm-3 . With its characteristics the inner planet (rho_b=2.05+0.52-0.41 g cm-3) is placed in the intriguing class of the super-puffy mini-Neptunes. TOI-421b and TOI-421c are found to be well suitable for atmospheric characterization. Our atmospheric simulations predict significant Ly-alpha transit absorption, due to strong hydrogen escape in both planets, and the presence of detectable CH_4 in the atmosphere of TOI-421c if equilibrium chemistry is assumed.

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Two young planetary systems around field stars with ages between 20-320 Myr from TESS

Planets around young stars trace the early evolution of planetary systems. We report the discovery and validation of two planetary systems with ages $\lesssim 300$ Myr from observations by the Transiting Exoplanet Survey Satellite. TOI-251 is a 40-320 Myr old G star hosting a 2.74 +0.18/-0.18 REarth mini-Neptune with a 4.94 day period. TOI-942 is a 20-160 Myr old K star hosting a system of inflated Neptune-sized planets, with TOI-942b orbiting with a period of 4.32 days, with a radius of 4.81 +0.20/-0.20 REarth, and TOI-942c orbiting in a period of 10.16 days with a radius of 5.79 +0.19/-0.18 REarth. Though we cannot place either host star into a known stellar association or cluster, we can estimate their ages via their photometric and spectroscopic properties. Both stars exhibit significant photometric variability due to spot modulation, with measured rotation periods of $\sim 3.5$ days. These stars also exhibit significant chromospheric activity, with age estimates from the chromospheric calcium emission lines and X-ray fluxes matching that estimated from gyrochronology. Both stars also exhibit significant lithium absorption, similar in equivalent width to well-characterized young cluster members. TESS has the potential to deliver a population of young planet-bearing field stars, contributing significantly to tracing the properties of planets as a function of their age.

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Vetting of 384 TESS Objects of Interest with TRICERATOPS and Statistical Validation of 12 Planet Candidates

We present TRICERATOPS, a new Bayesian tool that can be used to vet and validate TESS Objects of Interest (TOIs). We test the tool on 68 TOIs that have been previously confirmed as planets or rejected as astrophysical false positives. By looking in the false positive probability (FPP) -- nearby false positive probability (NFPP) plane, we define criteria that TOIs must meet to be classified as validated planets (FPP < 0.015 and NFPP < 10^-3), likely planets (FPP < 0.5 and NFPP < 10^-3), and likely nearby false positives (NFPP > 10^-1). We apply this procedure on 384 unclassified TOIs and statistically validate 12, classify 125 as likely planets, and classify 52 as likely nearby false positives. Of the 12 statistically validated planets, 9 are newly validated. TRICERATOPS is currently the only TESS vetting and validation tool that models transits from nearby contaminant stars in addition to the target star. We therefore encourage use of this tool to prioritize follow-up observations that confirm bona fide planets and identify false positives originating from nearby stars.

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Science Extraction from TESS Observations of Known Exoplanet Hosts

The transit method of exoplanet discovery and characterization has enabled numerous breakthroughs in exoplanetary science. These include measurements of planetary radii, mass-radius relationships, stellar obliquities, bulk density constraints on interior models, and transmission spectroscopy as a means to study planetary atmospheres. The Transiting Exoplanet Survey Satellite (TESS) has added to the exoplanet inventory by observing a significant fraction of the celestial sphere, including many stars already known to host exoplanets. Here we describe the science extraction from TESS observations of known exoplanet hosts during the primary mission. These include transit detection of known exoplanets, discovery of additional exoplanets, detection of phase signatures and secondary eclipses, transit ephemeris refinement, and asteroseismology as a means to improve stellar and planetary parameters. We provide the statistics of TESS known host observations during Cycle 1 & 2, and present several examples of TESS photometry for known host stars observed with a long baseline. We outline the major discoveries from observations of known hosts during the primary mission. Finally, we describe the case for further observations of known exoplanet hosts during the TESS extended mission and the expected science yield.

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The K2 and TESS Synergy. I. Updated Ephemerides and Parameters for K2-114, K2-167, K2-237, and K2-261

Although the Transiting Exoplanet Survey Satellite (TESS) primary mission observed the northern and southern ecliptic hemispheres, generally avoiding the ecliptic, and the Kepler space telescope during the K2 mission could only observe near the ecliptic, many of the K2 fields extend far enough from the ecliptic plane that sections overlap with TESS fields. Using photometric observations from both K2 and TESS, combined with archival spectroscopic observations, we globally modeled four known planetary systems discovered by K2 that were observed in the first year of the primary TESS mission. Specifically, we provide updated ephemerides and system parameters for K2-114 b, K2-167 b, K2-237 b, and K2-261 b. These were some of the first K2 planets to be observed by TESS in the first year and include three Jovian sized planets and a sub-Neptune with orbital periods less than 12 days. In each case, the updated ephemeris significantly reduces the uncertainty in prediction of future times of transit, which is valuable for planning observations with the James Webb Space Telescope and other future facilities. The TESS extended mission is expected to observe about half of the K2 fields, providing the opportunity to perform this type of analysis on a larger number of systems.

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TOI 122b and TOI 237b, two small warm planets orbiting inactive M dwarfs, found by \textit{TESS}

We report the discovery and validation of TOI 122b and TOI 237b, two warm planets transiting inactive M dwarfs observed by \textit{TESS}. Our analysis shows TOI 122b has a radius of 2.72$\pm$0.18 R$_\rm{e}$ and receives 8.8$\pm$1.0$\times$ Earth's bolometric insolation, and TOI 237b has a radius of 1.44$\pm$0.12 R$_\rm{e}$ and receives 3.7$\pm$0.5$\times$ Earth insolation, straddling the 6.7$\times$ Earth insolation that Mercury receives from the sun. This makes these two of the cooler planets yet discovered by \textit{TESS}, even on their 5.08-day and 5.43-day orbits. Together, they span the small-planet radius valley, providing useful laboratories for exploring volatile evolution around M dwarfs. Their relatively nearby distances (62.23$\pm$0.21 pc and 38.11$\pm$0.23 pc, respectively) make them potentially feasible targets for future radial velocity follow-up and atmospheric characterization, although such observations may require substantial investments of time on large telescopes.

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Spitzer Reveals Evidence of Molecular Absorption in the Atmosphere of the Hot Neptune LTT 9979b

Non-rocky sub-jovian exoplanets in high irradiation environments are rare. LTT 9979b, also known as TESS Object of Interest (TOI) 193.01, is one of the few such planets discovered to date, and the first example of an ultra-hot Neptune. The planet's bulk density indicates that it has a substantial atmosphere, so to investigate its atmospheric composition and shed further light on its origin, we obtained {\it Spitzer} IRAC secondary eclipse observations of LTT 9979b at 3.6 and 4.5 $μ$m. We combined the {\it Spitzer} observations with a measurement of the secondary eclipse in the {\it TESS} bandpass. The resulting secondary eclipse spectrum strongly prefers a model that includes CO absorption over a blackbody spectrum, incidentally making LTT 9979b the first {\it TESS} exoplanet (and the first ultra-hot Neptune) with evidence of a spectral feature in its atmosphere. We did not find evidence of a thermal inversion, at odds with expectations based on the atmospheres of similarly-irradiated hot Jupiters. We also report a nominal dayside brightness temperature of 2305 $\pm$ 141 K (based on the 3.6 $μ$m secondary eclipse measurement), and we constrained the planet's orbital eccentricity to $e < 0.01$ at the 99.7 \% confidence level. Together with our analysis of LTT 9979b's thermal phase curves reported in a companion paper, our results set the stage for similar investigations of a larger sample of exoplanets discovered in the hot Neptune desert, investigations which are key to uncovering the origin of this population.

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TESS Hunt for Young and Maturing Exoplanets (THYME) III: a two-planet system in the 400 Myr Ursa Major Group

Exoplanets can evolve significantly between birth and maturity, as their atmospheres, orbits, and structures are shaped by their environment. Young planets ($<$1 Gyr) offer an opportunity to probe the critical early stages of this evolution, where planets evolve the fastest. However, most of the known young planets orbit prohibitively faint stars. We present the discovery of two planets transiting HD 63433 (TOI 1726, TIC 130181866), a young Sun-like ($M_*=0.99\pm0.03$) star. Through kinematics, lithium abundance, and rotation, we confirm that HD 63433 is a member of the Ursa Major moving group ($τ=414\pm23$ Myr). Based on the TESS light curve and updated stellar parameters, we estimate the planet radii are $2.15\pm0.10R_\oplus$ and $2.67\pm0.12R_\oplus$, the orbital periods are 7.11 and 20.55 days, and the orbital eccentricities are lower than about 0.2. Using HARPS-N velocities, we measure the Rossiter-McLaughlin signal of the inner planet, demonstrating that the orbit is prograde. Since the host star is bright (V=6.9), both planets are amenable to transmission spectroscopy, radial velocity measurements of their masses, and more precise determination of the stellar obliquity. This system is therefore poised to play an important role in our understanding of planetary system evolution in the first billion years after formation.

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The TESS Phase Curve of KELT-1b Suggests a High Dayside Albedo

We measured the optical phase curve of the transiting brown dwarf KELT-1b (TOI 1476, Siverd et al. 2012) using data from the TESS spacecraft. We found that KELT-1b shows significant phase variation in the TESS bandpass, with a relatively large phase amplitude of $234^{+43}_{-44}$ ppm and a secondary eclipse depth of $371^{+47}_{-49}$ ppm. We also measured a marginal eastward offset in the dayside hotspot of $18.3^\circ\pm7.4^\circ$ relative to the substellar point. We detected a strong phase curve signal attributed to ellipsoidal distortion of the host star, with an amplitude of $399\pm19$ ppm. Our results are roughly consistent with the Spitzer phase curves of KELT-1b (Beatty et al. 2019), but the TESS eclipse depth is deeper than expected. Our cloud-free 1D models of KELT-1b's dayside emission are unable to fit the full combined eclipse spectrum. Instead, the large TESS eclipse depth suggests that KELT-1b may have a significant dayside geometric albedo of $\mathrm{A}_\mathrm{g}\sim0.5$ in the TESS bandpass, which would agree with the tentative trend between equilibrium temperature and geometric albedo recently suggested by Wong et al. 2020. We posit that if KELT-1b has a high dayside albedo, it is likely due to silicate clouds (Gao et al. 2020) that form on KELT-1b's nightside (Beatty et al. 2019, Keating et al. 2019) and are subsequently transported onto the western side of KELT-1b's dayside hemisphere before breaking up.

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A Highly Eccentric Warm Jupiter Orbiting TIC 237913194

The orbital parameters of warm Jupiters serve as a record of their formation history, providing constraints on formation scenarios for giant planets on close and intermediate orbits. Here, we report the discovery of TIC 237913194b, detected in full frame images from Sectors 1 and 2 of TESS, ground-based photometry (CHAT, LCOGT), and FEROS radial velocity time series. We constrain its mass to $M_\mathrm{P} = 1.942_{-0.091}^{+0.091}\,{\rm M_{J}} $, and its radius to $R_\mathrm{P} = 1.117_{-0.047}^{+0.054}\,{\rm R_J}$, implying a bulk density similar to Neptune's. It orbits a G-type star (${\rm M}_{\star} = 1.026_{-0.055}^{+0.057}\,{\rm M}_{\odot}$, $V = 12.1$ mag) with a period of $15.17\,$d on one of the most eccentric orbits of all known warm giants ($e \approx 0.58$). This extreme dynamical state points to a past interaction with an additional, undetected massive companion. A tidal evolution analysis showed a large tidal dissipation timescale, suggesting that the planet is not a progenitor for a hot Jupiter caught during its high-eccentricity migration. TIC 237913194b further represents an attractive opportunity to study the energy deposition and redistribution in the atmosphere of a warm Jupiter with high eccentricity.

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