arXiv subjects

David Charbonneau

Publications and source records attributed to David Charbonneau.

At least 91 records · Page 5Linked to original sources

arXiv2022

A Possible Alignment Between the Orbits of Planetary Systems and their Visual Binary Companions

Astronomers do not have a complete picture of the effects of wide-binary companions (semimajor axes greater than 100 AU) on the formation and evolution of exoplanets. We investigate these effects using new data from Gaia EDR3 and the TESS mission to characterize wide-binary systems with transiting exoplanets. We identify a sample of 67 systems of transiting exoplanet candidates (with well-determined, edge-on orbital inclinations) that reside in wide visual binary systems. We derive limits on orbital parameters for the wide-binary systems and measure the minimum difference in orbital inclination between the binary and planet orbits. We determine that there is statistically significant difference in the inclination distribution of wide-binary systems with transiting planets compared to a control sample, with the probability that the two distributions are the same being 0.0037. This implies that there is an overabundance of planets in binary systems whose orbits are aligned with those of the binary. The overabundance of aligned systems appears to primarily have semimajor axes less than 700 AU. We investigate some effects that could cause the alignment and conclude that a torque caused by a misaligned binary companion on the protoplanetary disk is the most promising explanation.

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arXiv2021

TOI-2285b: A 1.7 Earth-radius Planet Near the Habitable Zone around a Nearby M Dwarf

We report the discovery of TOI-2285b, a sub-Neptune-sized planet transiting a nearby (42 pc) M dwarf with a period of 27.3 days. We identified the transit signal from the Transiting Exoplanet Survey Satellite photometric data, which we confirmed with ground-based photometric observations using the multiband imagers MuSCAT2 and MuSCAT3. Combining these data with other follow-up observations including high resolution spectroscopy with the Tillinghast Reflector Echelle Spectrograph, high resolution imaging with the SPeckle Polarimeter, and radial velocity (RV) measurements with the InfraRed Doppler instrument, we find that the planet has a radius of 1.74 $\pm$ 0.08 $R_\oplus$, a mass of $<$ 19.5 $M_\oplus$ (95\% c.l.), and an insolation flux of 1.54 $\pm$ 0.14 times that of the Earth. Although the planet resides just outside the habitable zone for a rocky planet, if the planet harbors an H$_2$O layer under a hydrogen-rich atmosphere, then liquid water could exist on the surface of the H$_2$O layer depending on the planetary mass and water mass fraction. The bright host star in the near infrared ($K_s=9.0$) makes this planet an excellent target for further RV and atmospheric observations to improve our understanding on the composition, formation, and habitability of sub-Neptune-sized planets.

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arXiv2021

GJ 367b: A dense ultra-short period sub-Earth planet transiting a nearby red dwarf star

Ultra-short-period (USP) exoplanets have orbital periods shorter than one day. Precise masses and radii of USPs could provide constraints on their unknown formation and evolution processes. We report the detection and characterization of the USP planet GJ 367b using high precision photometry and radial velocity observations. GJ 367b orbits a bright (V-band magnitude = 10.2), nearby, red (M-type) dwarf star every 7.7 hours. GJ 367b has a radius of $0.718 \pm 0.054$ Earth-radii, a mass of $0.546 \pm 0.078$ Earth-masses, making it a sub-Earth. The corresponding bulk density is $8.106 \pm 2.165$ g cm$^-3$, close to that of iron. An interior structure model predicts the planet has an iron core radius fraction of $86 \pm 5\%$, similar to Mercury's interior.

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arXiv2021

K2-79b and K2-222b: Mass measurements of two small exoplanets with periods beyond 10 days that overlap with periodic magnetic activity signals

We present mass and radius measurements of K2-79b and K2-222b, two transiting exoplanets orbiting active G-type stars. Their respective 10.99d and 15.39d orbital periods fall near periods of signals induced by stellar magnetic activity. The two signals might therefore interfere and lead to an inaccurate estimate of exoplanet mass. We present a method to mitigate these effects when radial velocity and activity indicator observations are available over multiple observing seasons and the orbital period of the exoplanet is known. We perform correlation and periodogram analyses on sub-sets composed of each target's two observing seasons, in addition to the full data sets. For both targets, these analyses reveal an optimal season with little to no interference at the orbital period of the known exoplanet. We make a confident mass detection of each exoplanet by confirming agreement between fits to the full radial velocity set and the optimal season. For K2-79b, we measure a mass of 11.8 $\pm$ 3.6 $M_{Earth}$ and a radius of 4.09 $\pm$ 0.17 $R_{Earth}$. For K2-222b, we measure a mass of 8.0 $\pm$ 1.8 $M_{Earth}$ and a radius of 2.35 $\pm$ 0.08 $R_{Earth}$. According to model predictions, K2-79b is a highly irradiated Uranus-analog and K2-222b hosts significant amounts of water ice. We also present an RV solution for a candidate second companion orbiting K2-222 at 147.5d.

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arXiv2021

TOI-712: a system of adolescent mini-Neptunes extending to the habitable zone

As an all-sky survey, NASA's $TESS$ mission is able to detect the brightest and rarest types of transiting planetary systems, including young planets that enable study of the evolutionary processes that occur within the first billion years. Here, we report the discovery of a young, multi-planet system orbiting the bright K4.5V star, TOI-712 ($V = 10.838$, $M_\star = 0.733_{-0.025}^{+0.026} M_\odot$, $R_\star = 0.674\pm0.016 R_\odot$, $T_{\rm eff} = 4622_{-60}^{+61}$ K). From the $TESS$ light curve, we measure a rotation period of 12.48 days, and derive an age between about $500$ Myr and 1.1 Gyr. The photometric observations reveal three transiting mini-Neptunes ($R_b = 2.049^{+0.12}_{-0.080} R_\oplus$, $R_c = 2.701^{+0.092}_{-0.082} R_\oplus$, $R_d = 2.474^{+0.090}_{-0.082} R_\oplus $), with orbital periods of $P_b = 9.531$ days, $P_c = 51.699$ days, and $P_d = 84.839$ days. After modeling the three-planet system, an additional Earth-sized candidate is identified, TOI-712.05 ($P = 4.32$ days, $R_P = 0.81 \pm 0.11 R_\oplus$). We calculate that the habitable zone falls between 0.339 and 0.844 au (82.7 and 325.3 days), placing TOI-712 d near its inner edge. Among planetary systems harboring temperate planets, TOI-712 ($T = 9.9$) stands out as a relatively young star bright enough to motivate further characterization.

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arXiv2021

TOI-530b: A giant planet transiting an M dwarf detected by TESS

We report the discovery of TOI-530b, a transiting giant planet around an M0.5V dwarf, delivered by the Transiting Exoplanet Survey Satellite (TESS). The host star is located at a distance of $147.7\pm0.6$ pc with a radius of $R_{\ast}=0.54\pm0.03\ R_{\odot}$ and a mass of $M_{\ast}=0.53\pm0.02\ M_{\odot}$. We verify the planetary nature of the transit signals by combining ground-based multi-wavelength photometry, high resolution spectroscopy from SPIRou as well as high-angular-resolution imaging. With $V=15.4$ mag, TOI-530b is orbiting one of the faintest stars accessible by ground-based spectroscopy. Our model reveals that TOI-530b has a radius of $0.83\pm0.05\ R_{J}$ and a mass of $0.4\pm0.1\ M_{J}$ on a 6.39-d orbit. TOI-530b is the sixth transiting giant planet hosted by an M-type star, which is predicted to be infrequent according to core accretion theory, making it a valuable object to further study the formation and migration history of similar planets. We discuss the potential formation channel of such systems.

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arXiv2021

A Lyman-alpha transit left undetected: the environment and atmospheric behavior of K2-25b

K2-25b is a Neptune-sized exoplanet (3.45 Earth radii) that orbits its M4.5 host with a period of 3.48 days. Due to its membership in the Hyades Cluster, the system has a known age (727 +/- 75 Myr). K2-25b's youth and its similarities with Gl 436b suggested that K2-25b could be undergoing strong atmospheric escape. We observed two transits of K2-25b at Lyman-alpha using HST/STIS in order to search for escaping neutral hydrogen. We were unable to detect an exospheric signature, but placed an upper limit of (R_p/R_s) < 0.56 at 95% confidence by fitting the light curve of the Lyman-alpha red-wing, or < 1.20 in the blue-wing. We reconstructed the intrinsic Lyman-alpha profile of K2-25 to determine its Lyman-alpha flux, and analyzed XMM-Newton observations to determined its X-ray flux. Based on the total X-ray and extreme ultraviolet irradiation of the planet (8763 +/- 1049 erg/s/cm^2), we estimated the maximum energy-limited mass loss rate of K2-25b to be 10.6 x 10^10 g/s (0.56 Earth masses per 1 Gyr), five times larger than the similarly estimated mass loss rate of Gl 436b (2.2 x 10^10 g/s). The photoionization time is about 3 hours, significantly shorter than Gl 436b's 14 hours. A non-detection of a Lyman-alpha transit could suggest K2-25b is not significantly losing its atmosphere, or factors of the system are resulting in the mass loss being unobservable (e.g., atmosphere composition or the system's large high energy flux). Further observations could provide more stringent constraints.

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arXiv2021

The TESS Mission Target Selection Procedure

We describe the target selection procedure by which stars are selected for 2-minute and 20-second observations by TESS. We first list the technical requirements of the TESS instrument and ground systems processing that limit the total number of target slots. We then describe algorithms used by the TESS Payload Operation Center (POC) to merge candidate targets requested by the various TESS mission elements (the Target Selection Working Group, TESS Asteroseismic Science Consortium, and Guest Investigator office). Lastly, we summarize the properties of the observed TESS targets over the two-year primary TESS mission. We find that the POC target selection algorithm results in 2.1 to 3.4 times as many observed targets as target slots allocated for each mission element. We also find that the sky distribution of observed targets is different from the sky distributions of candidate targets due to technical constraints that require a relatively even distribution of targets across the TESS fields of view. We caution researchers exploring statistical analyses of TESS planet-host stars that the population of observed targets cannot be characterized by any simple set of criteria applied to the properties of the input Candidate Target Lists.

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arXiv2021

The Magellan-TESS Survey I: Survey Description and Mid-Survey Results

$Kepler$ revealed that roughly one-third of Sun-like stars host planets orbiting within 100 days and between the size of Earth and Neptune. How do these planets form, what are they made of, and do they represent a continuous population or multiple populations? To help address these questions, we began the Magellan-TESS Survey (MTS), which uses Magellan II/PFS to obtain radial velocity (RV) masses of 30 TESS-detected exoplanets and develops an analysis framework that connects observed planet distributions to underlying populations. In the past, small planet RV measurements have been challenging to obtain due to host star faintness and low RV semi-amplitudes, and challenging to interpret due to the potential biases in target selection and observation planning decisions. The MTS attempts to minimize these biases by focusing on bright TESS targets and employing a quantitative selection function and observing strategy. In this paper, we (1) describe our motivation and survey strategy, (2) present our first catalog of planet density constraints for 27 TESS Objects of Interest (TOIs; 22 in our population analysis sample, 12 that are members of the same systems), and (3) employ a hierarchical Bayesian model to produce preliminary constraints on the mass-radius (M-R) relation. We find that the biases causing previous M-R relations to predict fairly high masses at $1~R_\oplus$ have been reduced. This work can inform more detailed studies of individual systems and offer a framework that can be applied to future RV surveys with the goal of population inferences.

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arXiv2021

A More Precise Mass for GJ 1214 b and the Frequency of Multi-Planet Systems Around Mid-M Dwarfs

We present an intensive effort to refine the mass and orbit of the enveloped terrestrial planet GJ 1214 b using 165 radial velocity (RV) measurements taken with the HARPS spectrograph over a period of ten years. We conduct a joint analysis of the RVs with archival Spitzer/IRAC transits and measure a planetary mass and radius of $8.17\pm 0.43 M_{\oplus}$ and $2.742^{+0.050}_{-0.053} R_{\oplus}$. Assuming GJ 1214 b is an Earth-like core surrounded by a H/He envelope, we measure an envelope mass fraction of $X_{\rm env}= 5.24^{+0.30}_{-0.29}$%. GJ 1214 b remains a prime target for secondary eclipse observations of an enveloped terrestrial, the scheduling of which benefits from our tight constraint on the orbital eccentricity of $<0.063$ at 95% confidence, which narrows the secondary eclipse window to 2.8 hours. By combining GJ 1214 with other mid-M dwarf transiting systems with intensive RV follow-up, we calculate the frequency of mid-M dwarf planetary systems with multiple small planets and find that $90^{+5}_{-21}$% of mid-M dwarfs with a known planet with mass $\in [1,10] M_{\oplus}$ and orbital period $\in [0.5,50]$ days, will host at least one additional planet. We rule out additional planets around GJ 1214 down to $3 M_{\oplus}$ within 10 days such that GJ 1214 is a single-planet system within these limits, a result that has a $44^{+9}_{-5}$% probability given the prevalence of multi-planet systems around mid-M dwarfs. We also investigate mid-M dwarf RV systems and show that the probability that all reported RV planet candidates are real planets is $<12$% at 99% confidence, although this statistical argument is unable to identify the probable false positives.

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arXiv2021

Populating the brown dwarf and stellar boundary: Five stars with transiting companions near the hydrogen-burning mass limit

We report the discovery of five transiting companions near the hydrogen-burning mass limit in close orbits around main sequence stars originally identified by the Transiting Exoplanet Survey Satellite (TESS) as TESS Objects of Interest (TOIs): TOI-148, TOI-587, TOI-681, TOI-746, and TOI-1213. Using TESS and ground-based photometry as well as radial velocities from the CORALIE, CHIRON, TRES, and FEROS spectrographs, we found the companions have orbital periods between 4.8 and 27.2 days, masses between 77 and 98 $\mathrm{M_{Jup}}$, and radii between 0.81 and 1.66 $\mathrm{R_{Jup}}$. These targets have masses near the uncertain lower limit of hydrogen core fusion ($\sim$73-96 $\mathrm{M_{Jup}}$), which separates brown dwarfs and low-mass stars. We constrained young ages for TOI-587 (0.2 $\pm$ 0.1 Gyr) and TOI-681 (0.17 $\pm$ 0.03 Gyr) and found them to have relatively larger radii compared to other transiting companions of a similar mass. Conversely we estimated older ages for TOI-148 and TOI-746 and found them to have relatively smaller companion radii. With an effective temperature of 9800 $\pm$ 200 K, TOI-587 is the hottest known main-sequence star to host a transiting brown dwarf or very low-mass star. We found evidence of spin-orbit synchronization for TOI-148 and TOI-746 as well as tidal circularization for TOI-148. These companions add to the population of brown dwarfs and very low-mass stars with well measured parameters ideal to test formation models of these rare objects, the origin of the brown dwarf desert, and the distinction between brown dwarfs and hydrogen-burning main sequence stars.

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arXiv2021

High-contrast observations of brown dwarf companion HR 2562 B with the vector Apodizing Phase Plate coronagraph

The vector Apodizing Phase Plate (vAPP) is a class of pupil plane coronagraph that enables high-contrast imaging by modifying the Point Spread Function (PSF) to create a dark hole of deep flux suppression adjacent to the PSF core. Here, we recover the known brown dwarf HR 2562 B using a vAPP coronagraph, in conjunction with the Magellan Adaptive Optics (MagAO) system, at a signal-to-noise of S/N = 3.04 in the lesser studied L-band regime. The data contained a mix of field and pupil-stabilised observations, hence we explored three different processing techniques to extract the companion, including Flipped Differential Imaging (FDI), a newly devised Principal Component Analysis (PCA)-based method for vAPP data. Despite the partial field-stabilisation, the companion is recovered sufficiently to measure a 3.94 $μ$m narrow-band contrast of (3.05$\pm$1.00) $\times$ 10$^{-4}$ ($Δ$m$_{3.94 μm}$ = 8.79$\pm$0.36 mag). Combined with archival GPI and SPHERE observations, our atmospheric modelling indicates a spectral type at the L/T transition with mass M = 29$\pm$15 M$_{\text{Jup}}$, consistent with literature results. However, effective temperature and surface gravity vary significantly depending on the wavebands considered (1200$\leq$T$_{\text{eff}}$(K)$\leq$1700 and 4.0$\leq$log(g)(dex)$\leq$5.0), reflecting the challenges of modelling objects at the L/T transition. Observations between 2.4-3.2 $μ$m will be more effective in distinguishing cooler brown dwarfs due to the onset of absorption bands in this region. We explain that instrumental scattered light and wind-driven halo can be detrimental to FDI+PCA and thus must be sufficiently mitigated to use this processing technique. We thus demonstrate the potential of vAPP coronagraphs in the characterisation of high-contrast substellar companions, even in sub-optimal conditions, and provide new, complementary photometry of HR 2562 B.

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arXiv2021

The high-energy spectrum of the nearby planet-hosting inactive mid-M dwarf LHS 3844

To fully characterize the atmospheres, or lack thereof, of terrestrial exoplanets we must include the high-energy environments provided by their host stars. The nearby mid-M dwarf LHS 3844 hosts a terrestrial world which lacks a substantial atmosphere. We present a time series UV spectrum of LHS 3844 from 1131-3215A captured by HST/COS. We detect one flare in the FUV, which has an absolute energy of 8.96+/-0.79e28 erg and an equivalent duration of 355+/-31 s. We extract the flare and quiescent UV spectra separately. For each spectrum we estimate the Ly-alpha flux using correlations between UV line strengths. We use Swift-XRT to place an upper limit on the soft X-ray flux and construct a differential emission model (DEM) to estimate flux that is obscured by the interstellar medium. We compare the DEM flux estimates in the XUV to other methods that rely on scaling from the Ly-alpha, Si IV, and N V lines in the UV. The XUV, FUV, and NUV flux of LHS 3844 relative to its bolometric luminosity is log10(Lband/LBol) = -3.65, -4.16, and -4.56, respectively, for the quiescent state. These values agree with trends in high-energy flux as a function of stellar effective temperature found by the MUSCLES survey for a sample of early-M dwarfs. Many of the most spectroscopically accessible terrestrial exoplanets orbit inactive mid- to late-M dwarfs like LHS 3844. Measurements of M dwarf high-energy spectra are preferable for exoplanet characterization, but are not always possible. The spectrum of LHS 3844 is a useful proxy for the current radiation environment for these worlds.

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arXiv2021

TOI-1231 b: A Temperate, Neptune-Sized Planet Transiting the Nearby M3 Dwarf NLTT 24399

We report the discovery of a transiting, temperate, Neptune-sized exoplanet orbiting the nearby ($d$ = 27.5 pc), M3V star TOI-1231 (NLTT 24399, L 248-27, 2MASS J10265947-5228099). The planet was detected using photometric data from the Transiting Exoplanet Survey Satellite and followed up with observations from the Las Cumbres Observatory and the Antarctica Search for Transiting ExoPlanets program. Combining the photometric data sets, we find that the newly discovered planet has a radius of 3.65$^{+0.16}_{-0.15}$ R$_{\oplus}$, and an orbital period of 24.246 days. Radial velocity measurements obtained with the Planet Finder Spectrograph on the Magellan Clay telescope confirm the existence of the planet and lead to a mass measurement of 15.5$\pm$3.3 M$_{\oplus}$. With an equilibrium temperature of just 330K TOI-1231 b is one of the coolest small planets accessible for atmospheric studies thus far, and its host star's bright NIR brightness (J=8.88, K$_{s}$=8.07) make it an exciting target for HST and JWST. Future atmospheric observations would enable the first comparative planetology efforts in the 250-350 K temperature regime via comparisons with K2-18 b. Furthermore, TOI-1231's high systemic radial velocity (70.5 k\ms) may allow for the detection of low-velocity hydrogen atoms escaping the planet by Doppler shifting the H I Ly-alpha stellar emission away from the geocoronal and ISM absorption features.

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arXiv2021

The Featureless HST/WFC3 Transmission Spectrum of the Rocky Exoplanet GJ 1132b: No Evidence For A Cloud-Free Primordial Atmosphere and Constraints on Starspot Contamination

Orbiting a M dwarf 12 pc away, the transiting exoplanet GJ 1132b is a prime target for transmission spectroscopy. With a mass of 1.7 Earth masses and radius of 1.1 Earth radii, GJ 1132b's bulk density indicates that this planet is rocky. Yet with an equilibrium temperature of 580 K, GJ 1132b may still retain some semblance of an atmosphere. Understanding whether this atmosphere exists and its composition will be vital for understanding how the atmospheres of terrestrial planets orbiting M dwarfs evolve. We observe five transits of GJ 1132b with the Wide Field Camera 3 (WFC3) on the Hubble Space Telescope (HST). We find a featureless transmission spectrum from 1.1--1.7 microns, ruling out cloud-free atmospheres with metallicities <300x Solar with >4.8$σ$ confidence. We combine our WFC3 results with transit depths from TESS and archival broadband and spectroscopic observations to find a featureless spectrum from 0.7--4.5 microns. GJ 1132b has a high mean molecular weight atmosphere, possesses a high-altitude aerosol layer, or has effectively no atmosphere. Higher precision observations are required to differentiate between these possibilities. We explore the impact of hot and cold starspots on the observed transmission spectrum GJ 1132b, quantifying the amplitude of spot-induced transit depth features. Using a simple Poisson model we estimate spot temperature contrasts, spot covering fractions, and spot sizes for GJ 1132. These limits, and the modeling framework, may be useful for future observations of GJ 1132b or other planets transiting similarly inactive M dwarfs.

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arXiv2021

The TESS Objects of Interest Catalog from the TESS Prime Mission

We present 2,241 exoplanet candidates identified with data from the Transiting Exoplanet Survey Satellite (TESS) during its two-year prime mission. We list these candidates in the TESS Objects of Interest (TOI) Catalog, which includes both new planet candidates found by TESS and previously-known planets recovered by TESS observations. We describe the process used to identify TOIs and investigate the characteristics of the new planet candidates, and discuss some notable TESS planet discoveries. The TOI Catalog includes an unprecedented number of small planet candidates around nearby bright stars, which are well-suited for detailed follow-up observations. The TESS data products for the Prime Mission (Sectors 1-26), including the TOI Catalog, light curves, full-frame images, and target pixel files, are publicly available on the Mikulski Archive for Space Telescopes.

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arXiv2021

Precise transit and radial-velocity characterization of a resonant pair: a warm Jupiter TOI-216c and eccentric warm Neptune TOI-216b

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

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arXiv2021

TOI-811b and TOI-852b: New transiting brown dwarfs with similar masses and very different radii and ages from the TESS mission

We report the discovery of two transiting brown dwarfs (BDs), TOI-811b and TOI-852b, from NASA's Transiting Exoplanet Survey Satellite mission. These two transiting BDs have similar masses, but very different radii and ages. Their host stars have similar masses, effective temperatures, and metallicities. The younger and larger transiting BD is TOI-811b at a mass of $M_b = 55.3 \pm 3.2{\rm M_J}$ and radius of $R_b = 1.35 \pm 0.09{\rm R_J}$ and it orbits its host star in a period of $P = 25.16551 \pm 0.00004$ days. Its age of $93^{+61}_{-29}$ Myr, which we derive from an application of gyrochronology to its host star, is why this BD's radius is relatively large, not heating from its host star since this BD orbits at a longer orbital period than most known transiting BDs. This constraint on the youth of TOI-811b allows us to test substellar mass-radius isochrones where the radius of BDs changes rapidly with age. TOI-852b is a much older (4.0 Gyr from stellar isochrone models of the host star) and smaller transiting BD at a mass of $M_b = 53.7 \pm 1.3{\rm M_J}$, a radius of $R_b = 0.75 \pm 0.03{\rm R_J}$, and an orbital period of $P = 4.94561 \pm 0.00008$ days. TOI-852b joins the likes of other old transiting BDs that trace out the oldest substellar mass-radius isochrones where contraction of the BD's radius asymptotically slows. Both host stars have a mass of $M_\star = 1.32{\rm M_\odot}\pm0.05$ and differ in their radii, $T_{\rm eff}$, and [Fe/H] with TOI-811 having $R_\star=1.27\pm0.09{\rm R_\odot}$, $T_{\rm eff} = 6107 \pm 77$K, and $\rm [Fe/H] = +0.40 \pm 0.09$ and TOI-852 having $R_\star=1.71\pm0.04{\rm R_\odot}$, $T_{\rm eff} = 5768 \pm 84$K, and $\rm [Fe/H] = +0.33 \pm 0.09$. We take this opportunity to examine how TOI-811b and TOI-852b serve as test points for young and old substellar isochrones, respectively.

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