arXiv subjects

Shreyas Vissapragada

Publications and source records attributed to Shreyas Vissapragada.

At least 37 records · Page 2Linked to original sources

arXiv2025

Validation of TESS Planet Candidates with Multi-Color Transit Photometry and TRICERATOPS+

We present an upgraded version of TRICERATOPS, a software package designed to calculate false positive probabilities for planet candidates identified by the Transiting Exoplanet Survey Satellite (TESS). This enhanced framework now incorporates ground-based light curves in separate bandpasses, which are routinely obtained as part of the candidate vetting process. We apply this upgraded framework to explore the planetary nature of 14 TESS planet candidates, combining primarily J band light curves acquired with the 200-inch Hale Telescope at Palomar Observatory with complementary archival observations from the Las Cumbres Observatory Global Telescope (LCOGT), the Fred Lawrence Whipple Observatory (FLWO), and the Teide Observatory, along with existing TESS data and contrast curves from high-resolution imaging. As a result of this analysis we statistically validate (False Positive Probability < 1.5% and Nearby False Positive Probability < 0.1%) six new planets in five systems: TOI-1346 b, TOI-1346 c, TOI-2719 b, TOI-4155 b, TOI-6000 b, and TOI-6324 b. For these systems, we provide updated estimates of their stellar and planetary properties derived from the TESS and ground-based observations. These new systems contain planets with radii between 0.9-6 Re and orbital periods between 0.3-5.5 days. Finally, we use our upgraded version of TRICERATOPS to quantify the relative importance of multi-wavelength transit photometry and high-resolution imaging for exoplanet candidate validation, and discuss which kinds of candidates typically benefit the most from ground-based multi-color transit observations.

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arXiv2025

Exoplanet Atmospheric Escape Observations with the Habitable Worlds Observatory

The Decadal Survey on Astronomy and Astrophysics 2020 highlights the importance of advancing research focused on discovering and characterizing habitable worlds. In line with this priority, our goal is to investigate how planetary systems evolve through atmospheric escape and to develop methods for identifying potentially Earth-like planets. By leveraging the ultraviolet (UV) capabilities of the Habitable Worlds Observatory (HWO), we can use transit spectroscopy to observe atmospheric escape in exoplanets and explore the processes that shape their evolution, assess the ability of small planets to retain their atmospheres, and search for signs of Earth-like atmospheres. To achieve this, we support the development of a UV spectrograph with moderate- to high-resolution capabilities for point-source observations, coverage of key spectral features in the 100-300 nm range, and detectors that can register high count rates reliably. This article is an adaptation of a science case document developed for the Characterizing Exoplanets Steering Committee within HWO's Solar Systems in Context Working Group.

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arXiv2025

Tidally Heated Sub-Neptunes, Refined Planetary Compositions, and Confirmation of a Third Planet in the TOI-1266 System

TOI-1266 is a benchmark system of two temperate ($<$ 450 K) sub-Neptune-sized planets orbiting a nearby M dwarf exhibiting a rare inverted architecture with a larger interior planet. In this study, we characterize transit timing variations (TTVs) in the TOI-1266 system using high-precision ground-based follow-up and new TESS data. We confirm the presence of a third exterior non-transiting planet, TOI-1266 d (P = 32.5 d, $M_d$ = 3.68$^{+1.05}_{-1.11} M_{\oplus}$), and combine the TTVs with archival radial velocity (RV) measurements to improve our knowledge of the planetary masses and radii. We find that, consistent with previous studies, TOI-1266 b ($R_b$ = 2.52 $\pm$ 0.08 $R_{\oplus}$, $M_b$ = 4.46 $\pm$ 0.69 $M_{\oplus}$) has a low bulk density requiring the presence of a hydrogen-rich envelope, while TOI-1266 c ($R_c$ = 1.98 $\pm$ 0.10 $R_{\oplus}$, $M_c$ = 3.17 $\pm$ 0.76 $M_{\oplus}$) has a higher bulk density that can be matched by either a hydrogen-rich or water-rich envelope. Our new dynamical model reveals that this system is arranged in a rare configuration with the inner and outer planets located near the 3:1 period ratio with a non-resonant planet in between them. Our dynamical fits indicate that the inner and outer planet have significantly nonzero eccentricities ($e_b + e_d = 0.076^{+0.029}_{-0.019}$), suggesting that TOI-1266 b may have an inflated envelope due to tidal heating. Finally, we explore the corresponding implications for the formation and long-term evolution of the system, which contains two of the most favorable cool ($<$ 500 K) sub-Neptunes for atmospheric characterization with JWST.

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arXiv2025

The Hottest Neptunes Orbit Metal-Rich Stars

The Neptune desert is no longer empty. A handful of close-in planets with masses between those of Neptune and Saturn have now been discovered, and their puzzling properties have inspired a number of interesting theories on the formation and evolution of desert-dwellers. While some studies suggest that Neptune desert planets form and evolve similarly to longer-period Neptunes, others argue that they are products of rare collisions between smaller planets, or that they are the exposed interiors of giant planets (i.e., ``hot Jupiters gone wrong''). These origin stories make different predictions for the metallicities of Neptune desert host stars. In this paper, we use the homogeneous catalog of stellar metallicities from Gaia Data Release 3 to investigate the origins of Neptune desert-dwellers. We find that planets in the Neptune desert orbit stars that are significantly more metal-rich than the hosts of longer-period Neptunes ($p = 0.0016$) and smaller planets ($p = 0.00014$). In contrast, Neptune desert host star metallicities are statistically indistinguishable from those of hot Jupiter host stars ($p = 0.55$). Therefore, we find it relatively unlikely that Neptune desert planets formed and evolved similarly to longer-period Neptunes, or that they resulted from collisions between smaller planets, at least without another metallicity-selective process involved. A more straightforward explanation for this result is that planets in the desert truly are the exposed interiors of larger planets. Atmospheric spectroscopy of Neptune desert worlds may therefore provide a rare glimpse into the interiors of giant exoplanets.

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arXiv2025

Atmospheric Mass Loss from TOI-1259 A b, a Gas Giant Planet With a White Dwarf Companion

The lack of close-in Neptune-mass exoplanets evident in transit surveys has largely been attributed either to photoevaporative mass loss or high-eccentricity migration. To distinguish between these two possibilities, we investigate the origins of TOI-1259 A b, a Saturn-mass (0.4 M$_J$, 1.0 R$_J$) exoplanet lying along the upper edge of the Neptune desert. TOI-1259 A b's close-in ($P$ = 3.48 days) orbit and low bulk density make the planet particularly vulnerable to photoevaporation. Using transits observed in the 1083 nm metastable helium line, we probe the upper atmosphere of TOI-1259 A b with the Hale Telescope at Palomar Observatory and the Near-Infrared Spectrograph on Keck II. We report an excess absorption of $0.395\pm{0.072}\%$ with Palomar and a blueshifted absorption of $2.4\pm0.52\%$ with Keck, consistent with an extended escaping atmosphere. Fitting this signal with a Parker wind model, we determine a corresponding atmospheric mass loss rate of log($\dot{M}$) = $10.33\pm 0.13$ g/s for a thermosphere temperature of $8400^{+1200}_{-1000}$ K based on the Palomar absorption and log($\dot{M}$) = $10.0\pm 0.1$ g/s for a thermosphere temperature of $8200^{+1000}_{-900}$ K based on the Keck absorption. This relatively low rate suggests that this planet would not have been significantly altered by mass loss even if it formed in-situ. However, the presence of a white dwarf companion, TOI-1259 B, hints that this planet may not have formed close-in, but rather migrated inward relatively late. Given the estimated parameters of the proto-white dwarf companion, we find that high-eccentricity migration is possible for the system.

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arXiv2024

A Fourth Planet in the Kepler-51 System Revealed by Transit Timing Variations

Kepler-51 is a $\lesssim 1\,\mathrm{Gyr}$-old Sun-like star hosting three transiting planets with radii $\approx 6$-$9\,R_\oplus$ and orbital periods $\approx 45$-$130\,\mathrm{days}$. Transit timing variations (TTVs) measured with past Kepler and Hubble Space Telescope (HST) observations have been successfully modeled by considering gravitational interactions between the three transiting planets, yielding low masses and low mean densities ($\lesssim 0.1\,\mathrm{g/cm^3}$) for all three planets. However, the transit time of the outermost transiting planet Kepler-51d recently measured by the James Webb Space Telescope (JWST) 10 years after the Kepler observations is significantly discrepant from the prediction made by the three-planet TTV model, which we confirmed with ground-based and follow-up HST observations. We show that the departure from the three-planet model is explained by including a fourth outer planet, Kepler-51e, in the TTV model. A wide range of masses ($\lesssim M_\mathrm{Jup}$) and orbital periods ($\lesssim 10\,\mathrm{yr}$) are possible for Kepler-51e. Nevertheless, all the coplanar solutions found from our brute-force search imply masses $\lesssim 10\,M_\oplus$ for the inner transiting planets. Thus their densities remain low, though with larger uncertainties than previously estimated. Unlike other possible solutions, the one in which Kepler-51e is around the $2:1$ mean motion resonance with Kepler-51d implies low orbital eccentricities ($\lesssim 0.05$) and comparable masses ($\sim 5\,M_\oplus$) for all four planets, as is seen in other compact multi-planet systems. This work demonstrates the importance of long-term follow-up of TTV systems for probing longer period planets in a system.

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arXiv2024

Exoplanet Aeronomy: A Case Study of WASP-69b's Variable Thermosphere

Aeronomy, the study of Earth's upper atmosphere and its interaction with the local space environment, has long traced changes in the thermospheres of Earth and other solar system planets to solar variability in the X-ray and extreme ultraviolet (collectively, "XUV") bands. Extending comparative aeronomy to the short-period extrasolar planets may illuminate whether stellar XUV irradiation powers atmospheric outflows that change planetary radii on astronomical timescales. In recent years, near-infrared transit spectroscopy of metastable HeI has been a prolific tracer of high-altitude planetary gas. We present a case study of exoplanet aeronomy using metastable HeI transit observations from Palomar/WIRC and follow-up high-energy data from the Neil Gehrels Swift Observatory that were taken within one month of the WASP-69 system, a K-type main sequence star with a well-studied hot Jupiter companion. Supplemented by archival data, we find that WASP-69's X-ray flux in 2023 was less than 50% of what was recorded in 2016 and that the metastable HeI absorption from WASP-69b was lower in 2023 versus past epochs from 2017-2019. Via atmospheric modeling, we show that this time-variable metastable HeI signal is in the expected direction given the observed change in stellar XUV, possibly stemming from WASP-69's magnetic activity cycle. Our results underscore the ability of multi-epoch, multi-wavelength observations to paint a cohesive picture of the interaction between an exoplanet's atmosphere and its host star.

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arXiv2024

Detection of an Atmospheric Outflow from the Young Hot Saturn TOI-1268b

Photoevaporative mass-loss rates are expected to be highest when planets are young and the host star is more active, but to date there have been relatively few measurements of mass-loss rates for young gas giant exoplanets. In this study we measure the present-day atmospheric mass-loss rate of TOI-1268b, a young (110 - 380 Myr) and low density (0.71$^{+0.17}_{-0.13}$~g~cm$^{-3}$) hot Saturn located near the upper edge of the Neptune desert. We use Palomar/WIRC to search for excess absorption in the 1083~nm helium triplet during two transits of TOI-1268b. We find that it has a larger transit depth ($0.285_{-0.050}^{+0.048}\%$ excess) in the helium bandpass than in the TESS observations, and convert this excess absorption into a mass-loss rate by modeling the outflow as a Parker wind. Our results indicate that this planet is losing mass at a rate of $\log \dot{M} = 10.2 \pm 0.3$~g~s$^{-1}$ and has a thermosphere temperature of 6900$^{+1800}_{-1200}$~K. This corresponds to a predicted atmospheric lifetime much larger than 10 Gyr. Our result suggests that photoevaporation is weak in gas giant exoplanets even at early ages.

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arXiv2024

Helium in the Extended Atmosphere of the Warm Super-Puff TOI-1420b

Super-puffs are planets with exceptionally low densities ($ρ\lesssim 0.1$~g~cm$^{-3}$) and core masses ($M_c \lesssim 5 M_\oplus$). Many lower-mass ($M_p\lesssim10M_\oplus$) super-puffs are expected to be unstable to catastrophic mass loss via photoevaporation and/or boil-off, whereas the larger gravitational potentials of higher-mass ($M_p\gtrsim10M_\oplus$) super-puffs should make them more stable to these processes. We test this expectation by studying atmospheric loss in the warm, higher-mass super-puff TOI-1420b ($M = 25.1M_\oplus$, $R = 11.9R_\oplus$, $ρ= 0.08$~g~cm$^{-3}$, $T_\mathrm{eq} = 960$~K). We observed one full transit and one partial transit of this planet using the metastable helium filter on Palomar/WIRC and found that the helium transits were $0.671\pm0.079\%$ (8.5$σ$) deeper than the TESS transits, indicating an outflowing atmosphere. We modeled the excess helium absorption using a self-consistent 1D hydrodynamics code to constrain the thermal structure of the outflow given different assumptions for the stellar XUV spectrum. These calculations then informed a 3D simulation which provided a good match to the observations with a modest planetary mass-loss rate of $10^{10.82}$~g~s$^{-1}$ ($M_p/\dot{M}\approx70$~Gyr). Super-puffs with $M_p\gtrsim10M_\oplus$, like TOI-1420b and WASP-107b, appear perfectly capable of retaining atmospheres over long timescales; therefore, these planets may have formed with the unusually large envelope mass fractions they appear to possess today. Alternatively, tidal circularization could have plausibly heated and inflated these planets, which would bring their envelope mass fractions into better agreement with expectations from core-nucleated accretion.

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arXiv2024

A High-Resolution Non-Detection of Escaping Helium In The Ultra-Hot Neptune LTT 9779b: Evidence for Weakened Evaporation

The recent discovery of ``ultra-hot'' ($P < 1$ day) Neptunes has come as a surprise: some of these planets have managed to retain gaseous envelopes despite being close enough to their host stars to trigger strong photoevaporation and/or Roche lobe overflow. Here, we investigate atmospheric escape in LTT 9779b, an ultra-hot Neptune with a volatile-rich envelope. We observed two transits of this planet using the newly-commissioned WINERED spectrograph ($R\sim68,000$) on the 6.5 m Clay/Magellan II Telescope, aiming to detect an extended upper atmosphere in the He 10830 A triplet. We found no detectable planetary absorption: in a 0.75 A passband centered on the triplet, we set a 2$σ$ upper limit of 0.12% ($δR_p/H < 14$) and a 3$σ$ upper limit of 0.20% ($δR_p/H < 22$). Using a H/He isothermal Parker wind model, we found corresponding 95% and 99.7% upper limits on the planetary mass-loss rate of $\dot{M} < 10^{10.03}$ g s$^{-1}$ and $\dot{M} < 10^{11.11}$ g s$^{-1}$ respectively, smaller than predicted by outflow models even considering the weak stellar XUV emission. The low evaporation rate is plausibly explained by a metal-rich envelope, which would decrease the atmospheric scale height and increase the cooling rate of the outflow. This hypothesis is imminently testable: if metals commonly weaken planetary outflows, then we expect that \textit{JWST} will find high atmospheric metallicities for small planets that have evaded detection in He 10830 A.

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arXiv2023

Masses, Revised Radii, and a Third Planet Candidate in the "Inverted" Planetary System Around TOI-1266

Is the population of close-in planets orbiting M dwarfs sculpted by thermally driven escape or is it a direct outcome of the planet formation process? A number of recent empirical results strongly suggest the latter. However, the unique architecture of the TOI-1266 system presents a challenge to models of planet formation and atmospheric escape given its seemingly "inverted" architecture of a large sub-Neptune ($P_b=10.9$ days, $R_{p,b}=2.62\pm 0.11\, \mathrm{R}_{\oplus}$) orbiting interior to that of the system's smaller planet ($P_c=18.8$ days, $R_{p,c}=2.13\pm 0.12\, \mathrm{R}_{\oplus}$). Here we present revised planetary radii based on new TESS and diffuser-assisted ground-based transit observations, and characterize both planetary masses using a set of 145 radial velocity measurements from HARPS-N ($M_{p,b}=4.23\pm 0.69\, \mathrm{M}_{\oplus}, M_{p,c}=2.88\pm 0.80\, \mathrm{M}_{\oplus}$). Our analysis also reveals a third planet candidate ($P_d=32.3$ days, $M_{p,d}\sin{i} = 4.59^{+0.96}_{-0.94}\, \mathrm{M}_{\oplus}$), which if real, would form a chain of near 5:3 period ratios, although the system is likely not in a mean motion resonance. Our results indicate that TOI-1266 b and c are among the lowest density sub-Neptunes around M dwarfs and likely exhibit distinct bulk compositions of a gas-enveloped terrestrial ($X_{\mathrm{env},b}=5.5\pm 0.7$%) and a water-rich world (WMF$_c=59\pm 14$%), which is supported by hydrodynamic escape models. If distinct bulk compositions are confirmed through atmospheric characterization, the system's unique architecture would represent an interesting test case of inside-out sub-Neptune formation at pebble traps.

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arXiv2023

TESS Spots a Super-Puff: The Remarkably Low Density of TOI-1420b

We present the discovery of TOI-1420b, an exceptionally low-density ($ρ= 0.08\pm0.02$ g cm$^{-3}$) transiting planet in a $P = 6.96$ day orbit around a late G dwarf star. Using transit observations from TESS, LCOGT, OPM, Whitin, Wendelstein, OAUV, Ca l'Ou, and KeplerCam along with radial velocity observations from HARPS-N and NEID, we find that the planet has a radius of $R_p$ = 11.9 $\pm$ 0.3 $R_\Earth$ and a mass of $M_p$ = 25.1 $\pm$ 3.8 $M_\Earth$. TOI-1420b is the largest-known planet with a mass less than $50M_\Earth$, indicating that it contains a sizeable envelope of hydrogen and helium. We determine TOI-1420b's envelope mass fraction to be $f_{env} = 82^{+7}_{-6}\%$, suggesting that runaway gas accretion occurred when its core was at most $4-5\times$ the mass of the Earth. TOI-1420b is similar to the planet WASP-107b in mass, radius, density, and orbital period, so a comparison of these two systems may help reveal the origins of close-in low-density planets. With an atmospheric scale height of 1950 km, a transmission spectroscopy metric of 580, and a predicted Rossiter-McLaughlin amplitude of about $17$ m s$^{-1}$, TOI-1420b is an excellent target for future atmospheric and dynamical characterization.

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arXiv2023

Transit Timing Variations in the three-planet system: TOI-270

We present ground and space-based photometric observations of TOI-270 (L231-32), a system of three transiting planets consisting of one super-Earth and two sub-Neptunes discovered by TESS around a bright (K-mag=8.25) M3V dwarf. The planets orbit near low-order mean-motion resonances (5:3 and 2:1), and are thus expected to exhibit large transit timing variations (TTVs). Following an extensive observing campaign using 8 different observatories between 2018 and 2020, we now report a clear detection of TTVs for planets c and d, with amplitudes of $\sim$10 minutes and a super-period of $\sim$3 years, as well as significantly refined estimates of the radii and mean orbital periods of all three planets. Dynamical modeling of the TTVs alone puts strong constraints on the mass ratio of planets c and d and on their eccentricities. When incorporating recently published constraints from radial velocity observations, we obtain masses of $M_{\mathrm{b}}=1.48\pm0.18\,M_\oplus$, $M_{c}=6.20\pm0.31\,M_\oplus$ and $M_{\mathrm{d}}=4.20\pm0.16\,M_\oplus$ for planets b, c and d, respectively. We also detect small, but significant eccentricities for all three planets : $e_\mathrm{b} =0.0167\pm0.0084$, $e_{c} =0.0044\pm0.0006$ and $e_{d} = 0.0066\pm0.0020$. Our findings imply an Earth-like rocky composition for the inner planet, and Earth-like cores with an additional He/H$_2$O atmosphere for the outer two. TOI-270 is now one of the best-constrained systems of small transiting planets, and it remains an excellent target for atmospheric characterization.

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arXiv2023

Transmission spectroscopy of the lowest-density gas giant: metals and a potential extended outflow in HAT-P-67b

Extremely low-density exoplanets are tantalizing targets for atmospheric characterization because of their promisingly large signals in transmission spectroscopy. We present the first analysis of the atmosphere of the lowest-density gas giant currently known, HAT-P-67 b. This inflated Saturn-mass exoplanet sits at the boundary between hot and ultrahot gas giants, where thermal dissociation of molecules begins to dominate atmospheric composition. We observed a transit of HAT-P-67 b at high spectral resolution with CARMENES and searched for atomic and molecular species using cross-correlation and likelihood mapping. Furthermore, we explored potential atmospheric escape by targeting H$α$ and the metastable helium line. We detect Ca II and Na I with significances of 13.2$σ$ and 4.6$σ$, respectively. Unlike in several ultrahot Jupiters, we do not measure a day-to-night wind. The large line depths of Ca II suggest that the upper atmosphere may be more ionized than models predict. We detect strong variability in H$α$ and the helium triplet during the observations. These signals suggest the possible presence of an extended planetary outflow that causes an early ingress and late egress. In the averaged transmission spectrum, we measure redshifted absorption at the $\sim 3.8\%$ and $\sim 4.5\%$ level in the H$α$ and He I triplet lines, respectively. From an isothermal Parker wind model, we derive a mass loss rate of $\dot{M} \sim 10^{13}~\rm{g/s}$ and an outflow temperature of $T \sim 9900~\rm{K}$. However, due to the lack of a longer out-of-transit baseline in our data, additional observations are needed to rule out stellar variability as the source of the H$α$ and He signals.

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arXiv2023

Observing atmospheric escape in sub-Jovian worlds with JWST

Hydrodynamic atmospheric escape is considered an important process that shapes the evolution of sub-Jovian exoplanets, particularly those with short orbital periods. The metastable He line in the near-infrared at $1.083$ $μ$m is a reliable tracer of atmospheric escape in hot exoplanets, with the advantage of being observable from the ground. However, observing escaping He in sub-Jovian planets has remained challenging due to the systematic effects and telluric contamination present in ground-based data. With the successful launch and operations of JWST, we now have access to extremely stable high-precision near-infrared spectrographs in space. Here we predict the observability of metastable He with JWST in two representative and previously well-studied warm Neptunes, GJ 436 b ($T_{\rm eq} = 687~{\rm K}$, $R_{\rm p} = 0.37~{\rm R_J}$) and GJ 1214 b ($T_{\rm eq} = 588~{\rm K}$, $R_{\rm p} = 0.25~{\rm R_J}$). Our simulated JWST observations for GJ 436 b demonstrate that a single transit with NIRSpec/G140H is sensitive to mass loss rates that are two orders of magnitude lower than what is detectable from the ground. Our exercise for GJ 1214 b show that the best configuration to observe the relatively weak outflows of warm Neptunes with JWST is with NIRSpec/G140H, and that NIRSpec/G140M and NIRISS/SOSS are less optimal. Since none of these instrument configurations can spectrally resolve the planetary absorption, we conclude that the 1D isothermal Parker-wind approximation may not be sufficient for interpreting such observations. More sophisticated models are critical for breaking the degeneracy between outflow temperature and mass-loss rate for JWST measurements of metastable He.

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arXiv2023

An unlikely survivor: a low-density hot Neptune orbiting a red giant star

Hot Neptunes, gaseous planets smaller than Saturn ($\sim$ 3-8 R$_\oplus$) with orbital periods less than 10 days, are rare. Models predict this is due to high-energy stellar irradiation stripping planetary atmospheres over time, often leaving behind only rocky planetary cores. We present the discovery of a 6.2 R$_\oplus$(0.55 R$_\mathrm{J}$), 19.2 M$_\oplus$(0.060 M$_\mathrm{J}$) planet transiting a red giant star every 4.21285 days. The old age and high equilibrium temperature yet remarkably low density of this planet suggests that its gaseous envelope should have been stripped by high-energy stellar irradiation billions of years ago. The present day planet mass and radius suggest atmospheric stripping was slower than predicted. Unexpectedly low stellar activity and/or late-stage planet inflation could be responsible for the observed properties of this system.

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arXiv2022

The Possible Tidal Demise of Kepler's First Planetary System

We present evidence of tidally-driven inspiral in the Kepler-1658 (KOI-4) system, which consists of a giant planet (1.1$R_\mathrm{J}$, 5.9$M_\mathrm{J}$) orbiting an evolved host star (2.9$R_\odot$, 1.5$M_\odot$). Using transit timing measurements from Kepler, Palomar/WIRC, and TESS, we show that the orbital period of Kepler-1658b appears to be decreasing at a rate $\dot{P} = 131_{-22}^{+20}$~ms~yr$^{-1}$, corresponding to an infall timescale $P/\dot{P}\approx2.5$~Myr. We consider other explanations for the data including line-of-sight acceleration and orbital precession, but find them to be implausible. The observed period derivative implies a tidal quality factor $Q_\star' = 2.50_{-0.62}^{+0.85}\times10^4$, in good agreement with theoretical predictions for inertial wave dissipation in subgiant stars. Additionally, while it probably cannot explain the entire inspiral rate, a small amount of planetary dissipation could naturally explain the deep optical eclipse observed for the planet via enhanced thermal emission. As the first evolved system with detected inspiral, Kepler-1658 is a new benchmark for understanding tidal physics at the end of the planetary life cycle.

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arXiv2022

TOI-1136 is a Young, Coplanar, Aligned Planetary System in a Pristine Resonant Chain

Convergent disk migration has long been suspected to be responsible for forming planetary systems with a chain of mean-motion resonances (MMR). Dynamical evolution over time could disrupt the delicate resonant configuration. We present TOI-1136, a 700-Myr-old G star hosting at least 6 transiting planets between $\sim$2 and 5 $R_\oplus$. The orbital period ratios deviate from exact commensurability by only $10^{-4}$, smaller than the $\sim$\,$10^{-2}$ deviations seen in typical Kepler near-resonant systems. A transit-timing analysis measured the masses of the planets (3-8$M_\oplus$) and demonstrated that the planets in TOI-1136 are in true resonances with librating resonant angles. Based on a Rossiter-McLaughlin measurement of planet d, the star's rotation appears to be aligned with the planetary orbital planes. The well-aligned planetary system and the lack of detected binary companion together suggest that TOI-1136's resonant chain formed in an isolated, quiescent disk with no stellar fly-by, disk warp, or significant axial asymmetry. With period ratios near 3:2, 2:1, 3:2, 7:5, and 3:2, TOI-1136 is the first known resonant chain involving a second-order MMR (7:5) between two first-order MMR. The formation of the delicate 7:5 resonance places strong constraints on the system's migration history. Short-scale (starting from $\sim$0.1 AU) Type-I migration with an inner disk edge is most consistent with the formation of TOI-1136. A low disk surface density ($Σ_{\rm 1AU}\lesssim10^3$g~cm$^{-2}$; lower than the minimum-mass solar nebula) and the resultant slower migration rate likely facilitated the formation of the 7:5 second-order MMR. TOI-1136's deep resonance suggests that it has not undergone much resonant repulsion during its 700-Myr lifetime. One can rule out rapid tidal dissipation within a rocky planet b or obliquity tides within the largest planets d and f.

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