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  • Eleven New Transiting Brown Dwarfs and Very-low-mass Stars from TESS
    We present the discovery of 11 new transiting brown dwarfs (BDs) and low-mass M dwarfs from NASA’s Transiting Exoplanet Survey Satellite (TESS) mission: TOI-2844, TOI-3122, TOI-3577, TOI-3755, TOI-4462, TOI-4635, TOI-4737, TOI-4759, TOI-5240, TOI-5467, and TOI-5882. They consist of five BD companions and six very-low-mass stellar companions ranging in mass from 25 MJ to 128 MJ. We used a combination of photometric time-series, spectroscopic, and high-resolution imaging follow-up as a part of the TESS Follow-up Observing Program (or TFOP) to characterize each system. With over 50 transiting BDs confirmed, we now have a large enough sample to directly test different formation and evolutionary scenarios. We provide a renewed perspective on the transiting “brown dwarf desert” and its role in differentiating between planetary and stellar formation mechanisms. Our analysis of the eccentricity distribution for the transiting BD sample does not support previous claims of a transition between planetary and stellar formation at ∼42 MJ. We also contribute a first look into the metallicity distribution of transiting companions in the range 7–150 MJ, showing that this does not support a ∼42 MJ transition too. Finally, we also detect a significant lithium absorption feature in one of the BD hosts (TOI-5882). However, we determine that the host star is likely old based on rotation, kinematic, and photometric mdeasurements. We therefore claim that TOI-5882 may be a candidate for planetary engulfment.

  • StarFlow: Leveraging Normalizing Flows for Stellar Age Estimation in SDSS-V DR19
    Understanding the ages of stars is crucial for unraveling the formation history and evolution of our Galaxy. Traditional methods for estimating stellar ages from spectroscopic data often struggle with providing appropriate uncertainty estimations and are severely constrained by the parameter space. In this work, we introduce a new approach using normalizing flows—a type of deep generative model—to estimate stellar ages for evolved stars with improved accuracy and robust uncertainty characterization. The model is trained on stellar masses for evolved stars derived from asteroseismology and predicts the relationship between the carbon and nitrogen abundances of a given star and its age. Unlike standard neural network techniques, normalizing flows enable the recovery of full likelihood distributions for individual stellar ages, offering a richer and more informative perspective on uncertainties. Our method yields age estimations for 378,720 evolved stars and achieves a typical absolute age uncertainty of approximately 2 Gyr. By intrinsically accounting for the coverage and density of the training data, our model ensures that the resulting uncertainties reflect both the inherent noise in the data and the completeness of the sampled parameter space. Applying this method to data from the fifth-generation Sloan Digital Sky Survey Milky Way Mapper, we have produced the largest stellar age catalog for evolved stars to date.

  • The JDISC Survey: Linking the Physics and Chemistry of Inner and Outer Protoplanetary Disk Zones
    Mid-infrared spectroscopy of protoplanetary disks provides a chemical inventory of gas within a few astronomical unit, where planets are readily detected around older stars. With the James Webb Space Telescope (JWST) Disk Infrared Spectral Chemistry Survey, we explore demographic trends among 31 disks observed with MIRI (MRS) and with previous Atacama Large Millimeter/submillimeter Array millimeter continuum imaging at high angular resolution (5–10 au). With these signal-to-noise ratio of ∼200–450 spectra, we report emission from H2O, OH, CO, C2H2, HCN, CO2, [Ne ii], [Ne iii], and [Ar ii]. Emission from H2O, OH, and CO is nearly ubiquitous for low-mass stars, and detection rates of all molecules are higher than for similar disks observed with Spitzer-IRS. Slab model fits to the molecular emission lines demonstrate that emission from C2H2, HCN, and possibly CO2 is optically thin; thus since column densities and emitting radii are degenerate, observations are actually sensitive to the total molecular mass. C2H2 and HCN emission also typically originate in a hotter region ( , K, respectively) than CO2 ( K). The HCN to cold H2O luminosity ratios are generally smaller in smooth disks, consistent with more efficient water delivery via icy pebbles in the absence of large dust substructures. The molecular emission-line luminosities are also correlated with mass accretion rates and infrared spectral indices, similar to trends reported from Spitzer-IRS surveys. This work demonstrates the power of combining multiwavelength observations to explore inner disk chemistry as a function of outer disk and stellar properties, which will continue to grow as the sample of observed Class II systems expands in the coming JWST observation cycles.

  • Updated Mass, Eccentricity, and Tidal Heating Constraints for the Earth-sized Planet LP 791-18 d
    LP 791-18 d is a temperate Earth-sized planet (RP = 1.03 R⊕, P = 2.76 days) orbiting a late M dwarf, with an interior super-Earth (LP 791-18 b, RP = 1.2 R⊕, P = 0.95 days) and an exterior sub-Neptune (LP 791-18 c, RP = 2.5 R⊕, P = 4.99 days). Dynamical interactions between LP 791-18 d and c produce transit timing variations (TTVs) that can be used to constrain the planet masses and eccentricities. These interactions can also force a non-zero eccentricity for LP 791-18 d, which raises its internal temperature through tidal heating and could drive volcanic outgassing. We present three new transit observations of LP 791-18 c with Palomar/WIRC, including the most precise TTV measurements (<6 s uncertainty) of this planet to date. We fit these times with a TTV model to obtain updated constraints on the mass, eccentricity, and tidal heat flux of LP 791-18 d. We reduce the mass uncertainty by more than a factor of two (Md = 0.91 ±0.19 M⊕). We perform an updated fit assuming tidally damped free eccentricities and find and ec = 0.0001 ± 0.0001, consistent with circular orbits. We find that the observed TTVs are not sensitive to e ≤ ∼0.01. Without a tidally damped eccentricity prior, , much higher than the eccentricity predicted by n-body simulations incorporating the effects of dynamical excitation and tidal damping. We predict the timing offset relative to the prediction for a circular orbit of upcoming JWST secondary eclipse observations for LP 791-18 d ( minutes and minutes for the damped and undamped eccentricity cases, respectively), which could tightly constrain the eccentricity and tidal quality factor of this Earth-sized exoplanet.

  • ELemental Abundances of Planets and Brown Dwarfs Imaged around Stars (ELPIS). II. The Jupiter-like Inhomogeneous Atmosphere of the First Directly Imaged Planetary-mass Companion 2MASS 1207 b
    2MASS 1207 b, the first directly imaged planetary-mass companion, has been instrumental in advancing our understanding of exoplanets and brown dwarfs over the past 20 yr. We have performed extensive atmospheric retrieval analyses of 2MASS 1207 b’s JWST/NIRSpec spectrum using petitRADTRANS and a new atmospheric inhomogeneity framework, which characterizes homogeneous atmospheres, patchy clouds, cloud-free hot spots, or the combination of patchy clouds and spots. Among 24 retrieval runs with various assumptions, the most statistically preferred model corresponds to the patchy cloud scheme, with K, dex, and RJup, along with near-solar atmospheric compositions of [M/H] = −0.05 ± 0.03 dex and C/O = 0.440 ± 0.012. This model suggests ∼9% of 2MASS 1207 b’s atmosphere is covered by thin iron and silicate clouds, producing L-dwarf-like spectra, while the remaining 91% consists of thick iron and silicate clouds, emitting blackbody-like spectra. These thin-cloud patches and thick-cloud regions resemble Jupiter’s belts and zones, respectively, and this scenario is consistently supported by other retrieval runs incorporating inhomogeneous atmospheres. We demonstrate that the weak CO absorption of 2MASS 1207 b can be explained by the veiling effects of patchy thick clouds; the absence of 3.3 μm CH4 absorption is attributed to its hot thermal structure, which naturally leads to a CO-dominant, CH4-deficient atmosphere. The retrieved atmospheric models also match the observed variability amplitudes of 2MASS 1207 b. Our analysis reveals that the inferred atmospheric properties show significant scatter in less statistically preferred retrieval runs but converge to consistent values among the preferred ones. This underscores the importance of exploring diverse assumptions in retrievals to avoid biased interpretations of atmospheric properties and formation pathways.