Sazuna/UAT_keywords huggingface dataset:
OrCAS: Origins, Compositions, and Atmospheres of Sub-Neptunes. I. Survey Definition. Sub-Neptunes—volatile-rich exoplanets smaller than Neptune—are intrinsically the most common type of planet known. However, the formation and nature of these objects, as well as the distinctions between subclasses (if any), remain unclear. Two powerful tools to tease out the secrets of these worlds are measurements of (i) atmospheric composition and structure revealed by transit and/or eclipse spectroscopy, and (ii) mass, radius, and density revealed by transit photometry and Doppler spectroscopy. Here, we present OrCAS, a survey to better elucidate the origins, compositions, and atmospheres of sub-Neptunes. This radial velocity survey uses a repeatable, quantifiable metric to select targets suitable for subsequent transmission spectroscopy and address key science themes about the atmospheric and internal compositions and architectures of these systems. Our survey targets 26 systems with transiting sub-Neptune planet candidates, with the overarching goal of increasing the sample of such planets suitable for subsequent atmospheric characterization. This paper lays out our survey's science goals, defines our target prioritization metric, and performs light-curve fits and statistical validation using existing TESS photometry and ground-based follow-up observations. Our survey serves to continue expanding the sample of small exoplanets with well-measured properties orbiting nearby bright stars, ensuring fruitful studies of these systems for many years to come.

Keywords: Exoplanet astronomy, Radial velocity, Transit photometry, Exoplanet atmospheres
Planetary Mass Determinations from a Simplified Photodynamical Model—Application to the Complete Kepler Dataset. We use PyDynamicaLC, a model using the least number of—and the least correlated—degrees of freedom needed to derive a photodynamical model, to describe some of the smallest—and lowest-transit-timing-variation-amplitude—of the Kepler planets. We successfully analyze 64 systems containing 218 planets, for 88 of which we were able to determine significant masses (to better than 3σ). We demonstrate consistency with literature results over 2 orders of magnitude in mass, and for the planets that already had literature mass estimations, we were able to reduce the relative mass error by ∼22% (median value). Of the planets with determined masses, 23 are new mass determinations, with no previous significant literature values, including a planet smaller and lighter than Earth (KOI-1977.02/Kepler-345 b). These results demonstrate the power of photodynamical modeling with the appropriately chosen degrees of freedom. This will become increasingly more important as smaller planets are detected, especially as the TESS mission gathers ever longer baseline light curves and for the analysis of the future PLATO mission data.

Keywords: Exoplanet astronomy, Exoplanet systems, Time series analysis
Eight New Candidate Multiplanet Systems among TESS Objects of Interest. We present a search of the TESS Object of Interest (TOI) Catalog for new multiplanet systems. We perform a Box Least Squares search on light curves prepared by the Quick-Look Pipeline to recover known candidates and perform a targeted search for additional candidates in each system. Following vetting and manual inspection, we present eight new planet candidates in multiplanet systems. Highlighted systems include TOI-2037 and TOI-6543, each displaying a nearness to a 2:1 orbital resonance. Four candidates in the TOI-5624 system, including our candidate TIC 53498154.02, have gained TOI status. If confirmed, the TOI-5624 system becomes the 29th known five-planet system. Our identification of candidate TIC 302305400.02 in the TOI-5487 system presents an interesting case study for the formation of hot Jupiter systems, potentially marking the first known system harboring a close-in giant outer companion to an existing hot Jupiter.

Keywords: Hot Jupiters, Exoplanets, Exoplanet systems, Orbital resonances, Transit photometry
Jitter Across 15 yr: Leveraging Precise Photometry from Kepler and TESS to Extract Exoplanets from Radial Velocity Time Series. Stellar activity contamination of radial velocity (RV) data is one of the top challenges plaguing the field of extreme-precision RV science. Previous work has shown that photometry can be very effective at removing such signals from RV data, especially stellar activity caused by rotating starspots and plage. The exact utility of photometry for removing RV activity contamination, and the best way to apply it, is not well known. We present a combination photometric and RV study of eight Kepler/K2 FGK stars with known stellar variability. We use NEID RVs acquired simultaneously with Transiting Exoplanet Survey Satellite (TESS) photometry, and we perform injection-recovery tests to quantify the efficacy of recent TESS photometry versus archival Kepler/K2 photometry for removing stellar variability from RVs. We additionally experiment with different TESS sectors when training our models in order to quantify the real benefit of simultaneously acquired RVs and photometry. We conclude that Kepler photometry typically performs better than TESS at removing noise from RV data when it is available, likely due to longer baseline and precision. In contrast, for targets with available K2 photometry, especially those most active, and with high-precision (σNEID &lt; 1 m s‑1) NEID RVs, TESS may be the more informative dataset. However, contrary to expectations, we have found that training on simultaneous photometry does not always achieve the best results.

Keywords: Antarctic observatories, Transits, Exoplanets, Stellar activity, Radial velocity
Analyses of Multiple Balmer Emission Lines from Accreting Brown Dwarfs and Very Low Mass Stars. A planetary growth rate, i.e., the mass accretion rate, is a fundamental parameter in planet formation, as it determines a planet's final mass. Planetary mass accretion rates have been estimated using hydrogen lines, based on the models originally developed for accreting stars, known as the accretion flow model. Recently, Aoyama et al. introduced the accretion shock model as an alternative mechanism for hydrogen line emission. However, it remains unclear which model is more appropriate for accreting planets and substellar objects. To address this, we applied both models to archival data consisting of 96 data points from 76 accreting brown dwarfs and very-low-mass stars, with masses ranging from approximately 0.02 to 0.1 M⊙, to test which model best explains their accreting properties. The results showed that the emission mechanisms of 15 data points are best explained by the shock model, while 55 data points are best explained by the flow model. For the 15 data points explained by the planetary shock model, the shock model estimates up to several times higher mass accretion rates than the flow model. As this trend is more pronounced for planetary-mass objects, it is crucial to determine which emission mechanism is dominant in individual planets. We also discuss the physical parameters that determine the emission mechanisms and the variability of line ratios.

Keywords: H I line emission
True Mass and Atmospheric Composition of the Nontransiting Hot Jupiter HD 143105 b. We present Keck/KPIC Phase II K-band observations of the nontransiting hot Jupiter HD 143105 b. Using a cross-correlation approach, we make the first detection of the planetary atmosphere at   km s‑1 and an inferior conjunction time 2.5 hr before the previously published ephemeris. The retrieved Kp value, in combination with the orbital period, mass of the host star, and lack of transit detection, give an orbital inclination of   and a true planet mass of 1.23 ± 0.10 MJ. While the equilibrium temperature of HD 143105 b is in the transition regime between noninverted and inverted atmospheres, our analysis strongly prefers a noninverted atmosphere. Retrieval analysis indicates the atmosphere of HD 143105 b is cloud free to approximately 1 bar and dominated by H2O absorption ( ), placing only an upper limit on the CO abundance (  at 95% confidence). We place no constraints on the abundances of Fe, Mg, or 13CO. From these abundances, we place an upper limit on the carbon-to-oxygen ratio for HD 143105 b, C/O &lt; 0.2 at 95% confidence, and find the atmospheric metallicity is approximately 0.1 × solar. The low metallicity may be responsible for the lack of a thermal inversion, which at the temperature of HD 143105 b would likely require significant opacity from TiO and/or VO. With these results, HD 143105 b joins the small number of nontransiting hot Jupiters with detected atmospheres.

Keywords: High resolution spectroscopy, Exoplanet atmospheric composition , Hot Jupiters, Exoplanet atmospheres
Diffuse Ionized Gas in the Anticenter of the Milky Way. Using data from the Large Area Multi-Object fiber Spectroscopic Telescope Medium-Resolution Spectroscopic Survey of Nebulae, we create a sample of 17,821 diffuse ionized gas spectra in the anticenter region of the Milky Way by excluding fibers in the directions of H II regions and supernova remnants. We then analyze the radial and vertical distributions of three line ratios ([N II]/Hα, [S II]/Hα, and [S II]/[N II]), as well as the oxygen abundance. [N II]/Hα and [S II]/Hα do not exhibit a consistent, monotonic decrease with increasing Galactocentric distance (Rgal). Instead, they show enhancement within the interarm region, positioned between the Local Arm and the Perseus Arm. [S II]/[N II] has a radial gradient of 0.1415 ± 0.0646 kpc‑1 for the inner disk (8.34 &lt; Rgal &lt; 9.65 kpc) and remains nearly flat for the outer disk (Rgal &gt; 9.65 kpc). In the vertical direction, [N II]/Hα, [S II]/Hα, and [S II]/[N II] increase with increasing Galactic disk height (∣z∣) in both southern and northern disks. Based on the N2S2Hα method, which combines [S II]/[N II] and [N II]/Hα, we estimate the oxygen abundance. The oxygen abundance exhibits a consistent radial gradient with Rgal, featuring a slope of ‑0.0559 ± 0.0209 dex kpc‑1 for the inner disk and a similar slope of ‑0.0429 ± 0.0599 dex kpc‑1 for the outer disk. A single linear fitting to the entire disk yields a slope of ‑0.0317 ± 0.0124 dex kpc‑1. In the vertical direction, the oxygen abundance decreases with increasing ∣z∣ in both southern and northern disks.

Keywords: Warm ionized medium, Interstellar line emission, Metallicity
Spectroscopically Resolved Partial Phase Curve of the Rapid Heating and Cooling of the Highly Eccentric Hot Jupiter HAT-P-2b with WFC3. The extreme environments of transiting close-in exoplanets in highly eccentric orbits are ideal for testing exoclimate physics. Spectroscopically resolved phase curves not only allow for the characterization of their thermal response to irradiation changes but also unveil phase-dependent atmospheric chemistry and dynamics. We observed a partial phase curve of the highly eccentric close-in giant planet HAT-P-2b (e = 0.51, M = 9MJup) with the Wide Field Camera 3 aboard the Hubble Space Telescope. Using these data, we updated the planet's orbital parameters and radius and retrieved high-frequency pulsations consistent with the planet-induced pulsations reported in Spitzer data. We found that the peak in planetary flux occurred at 6.7 ± 0.6 hr after periastron, with heating and cooling timescales of   hr and   hr, respectively. We compare the light curve to various 1D and 3D forward models, varying the planet's chemical composition. The strong contrast in flux increase and decrease timescales before and after periapse indicates an opacity term that emerges during the planet's heating phase, potentially due to more H‑ than expected from chemical equilibrium models. The phase-resolved spectra are largely featureless, which we interpret as indicative of an inhomogeneous dayside. However, we identified an anomalously high flux in the spectroscopic bin coinciding with the hydrogen Paβ line, and that is likely connected to the planet's orbit. We interpret this as due to shock heating of the upper atmosphere given the short timescale involved, or evidence for other star‑planet interactions.

Keywords: Exoplanet atmospheric composition , Exoplanets, Exoplanet atmospheric dynamics, Extrasolar gaseous planets, Extrasolar gaseous giant planets, Exoplanet atmospheres, Exoplanet atmospheric structure
Effects of Planetary Mass Uncertainties on the Interpretation of the Reflectance Spectra of Earth-like Exoplanets. Atmospheric characterization of Earth-like exoplanets through reflected light spectroscopy is a key goal for upcoming direct imaging missions. A critical challenge in this endeavor is the accurate determination of planetary mass, which may influence the measurement of atmospheric compositions and the identification of potential biosignatures. In this study, we used the Bayesian retrieval framework EXORELℜ to investigate the impact of planetary mass uncertainties on the atmospheric characterization of terrestrial exoplanets observed in reflected light. Our results indicate that precise prior knowledge of the planetary mass can be crucial for accurate atmospheric retrievals if clouds are present in the atmosphere. When the planetary mass is known within 10% uncertainty, our retrievals successfully identified the background atmospheric gas and accurately constrained atmospheric parameters together with clouds. However, with less constrained or unknown planetary mass, we observed significant biases, particularly in the misidentification of the dominant atmospheric gas. For instance, the dominant gas was incorrectly identified as oxygen for a modern Earthlike planet or carbon dioxide for an Archean Earth–like planet, potentially leading to erroneous assessments of planetary habitability and biosignatures. These biases arise because the uncertainties in planetary mass affect the determination of surface gravity and atmospheric scale height, leading the retrieval algorithm to compensate by adjusting the atmospheric composition. Our findings emphasize the importance of achieving precise mass measurements—ideally within 10% uncertainty—through methods such as extreme precision radial velocity or astrometry, especially for future missions like the Habitable Worlds Observatory.

Keywords: Exoplanet atmospheric composition , Direct imaging, Bayesian statistics, Spectroscopy
An In-depth Investigation of the Primordial Cluster Pair ASCC 19 and ASCC 21. Utilizing Gaia data from the literature, we report a new young (∼8.9 Myr) cluster pair, ASCC 19 and ASCC 21, located near the Orion star-forming complex. The clusters are separated by a 3D distance of 27.00 ± 7.51 pc. Both clusters share a common age (Log(age) = 6.95 ± 0.05), similar radial velocities (RV = 21.34 ± 4.47 km s‑1 for ASCC 19 and RV = 20.05 ± 3.86 km s‑1 for ASCC 21), and comparable metallicities ([Fe/H] = ‑0.14 ± 0.25 dex for ASCC 19 and [Fe/H] = ‑0.12 ± 0.04 dex for ASCC 21, from LAMOST-DR11). These similarities suggest that the clusters likely originated from the fragmentation of the same molecular cloud, forming a primordial cluster pair. Furthermore, the formation of the two clusters is attributed to the coalescence of multiple subclusters, as inferred from the distribution analysis between metal abundances and distances to clusters' centers. Neither cluster shows significant mass segregation. Their members with RVs exceeding 100 km s‑1 are young variables. Additionally, a tidal interaction between the clusters is observed. Comparisons of the Roche radius with tidal radii, as well as velocity difference with orbital velocity, suggest that the pair is an unbound system, that is, a double cluster. Finally, orbital motion simulations show that the clusters will not merge into a single system.

Keywords: Open star clusters, Young star clusters
A First Taste of MEAD (Measuring Extinction and Abundances of Dust). I. Diffuse Milky Way Interstellar Dust Extinction Features in JWST Infrared Spectra. We present the initial results of the Measuring Extinction and Abundances of Dust project, with a focus on the dust extinction features observed in our JWST near- and mid-infrared spectra of nine diffuse Milky Way sightlines (1.2 ≤ A(V) ≤ 2.5). For the first time, we find strong correlations between the 10 μm silicate feature strength and the column densities of Mg, Fe, and O in dust. This is consistent with the well-established theory that Mg- and Fe-rich silicates are responsible for this feature. We obtain an average stoichiometry of the silicate grains in our sample of Mg:Fe:O = 1.1:1:11.2, constraining the grain composition. We find variations in the feature properties, indicating that different sightlines contain different types of silicates. In the average spectrum of our sample, we tentatively detect features around 3.4 and 6.2 μm, which are likely caused by aliphatic and aromatic/olefinic hydrocarbons, respectively. If real, to the best of our knowledge, this is the first detection of hydrocarbons in purely diffuse sightlines with A(V) ≤ 2.5, confirming the presence of these grains in diffuse environments. We detected a 3 μm feature toward HD073882 and tentatively in the sample average, likely caused by water ice (or solid-state water trapped on silicate grains). If confirmed, to the best of our knowledge, this is the first detection of ice in purely diffuse sightlines with A(V) ≤ 2.5, supporting previous findings that these molecules can exist in the diffuse interstellar medium.

Keywords: Interstellar dust, Dust composition, Silicate grains, Interstellar abundances, Interstellar dust extinction, Extinction, Carbonaceous grains
New Ultracool Companions to Nearby White Dwarfs. We conducted a search for new ultracool companions to nearby white dwarfs using multiple methods, including the analysis of colors and examination of images in both the optical and the infrared. Through this process, we identified 51 previously unrecognized systems with candidate ultracool companions. 31 of these systems are resolved in at least one catalog, and all but six are confirmed as comoving companions via common proper motion and consistent parallax measurements (when available). We have followed up four comoving companions with near-infrared spectroscopy and confirm their ultracool nature. The remaining twenty candidates are unresolved, but show clear signs of infrared excess which is most likely due to the presence of a cold, low-mass companion or a dusty circumstellar disk. Three of these unresolved systems have existing optical spectra that clearly show the presence of a cool stellar companion to the white dwarf primary via spectral decomposition. These new discoveries, along with our age estimates for the primary white dwarfs, will serve as valuable benchmark systems for future characterization of ultracool dwarfs.

Keywords: White dwarf stars, Brown dwarfs, Binary stars, Low mass stars
A Measurement of the Water Abundance in the Atmosphere of the Hot Jupiter WASP-43b with High-resolution Cross-correlation Spectroscopy. Measuring the abundances of carbon- and oxygen-bearing molecules has been a primary focus in studying the atmospheres of hot Jupiters, as doing so can help constrain the carbon-to-oxygen (C/O) ratio. The C/O ratio can help reveal the evolution and formation pathways of hot Jupiters and provide a strong understanding of the atmospheric composition. In the last decade, high-resolution spectral analyses have become increasingly useful in measuring precise abundances of several carbon- and oxygen-bearing molecules. This allows for a more precise constraint of the C/O ratio. We present four transits of the hot Jupiter WASP-43b observed between 1.45 and 2.45 μm with the high-resolution Immersion GRating InfraRed Spectrometer on the Gemini-S telescope. We detected H2O at a signal-to-noise ratio of 3.51. We tested for the presence of CH4, CO, and CO2, but we did not detect these carbon-bearing species. We ran a retrieval for all four molecules and obtained a water abundance of  . We obtained an upper limit on the C/O ratio of C/O &lt; 0.95. These findings are consistent with previous observations from the Hubble Space Telescope and the James Webb Space Telescope.

Keywords: High resolution spectroscopy, Exoplanet atmospheric composition , Hot Jupiters, Extrasolar gaseous planets, Exoplanet atmospheres
Infrared Compositional Measurements in Comet C/2017 K2 (Pan-STARRS) at Heliocentric Distances Beyond 2.3 au. Comet C/2017 K2 (Pan-STARRS) provided a rare opportunity to investigate the evolution of coma composition and outgassing patterns over a transitional heliocentric distance (Rh) range where activity drivers in comets are thought to change from "hypervolatile" (CO, CH4, C2H6, and/or CO2)-dominated to H2O-dominated. We performed high-resolution ( /  ≈ 25,000–42,000), cross-dispersed, near-infrared spectroscopy of C/2017 K2 with iSHELL at the NASA Infrared Telescope Facility and NIRSPEC at the W. M. Keck II Observatory. We report gas rotational temperatures (Trot) and molecular production rates (Q; molecules per second) or upper limits for the "hypervolatile" species CH4, CO, and C2H6, together with less volatile ices (CH3OH, H2O, HCN, C2H2, NH3, and OCS) over a range of pre-perihelion distances, Rh = 3.15–2.35 au. We also report (or stringently constrain) abundance ratios (mixing ratios) of the targeted species with respect to CO, C2H6, and (when detected) H2O. All volatiles were enriched relative to water in C/2017 K2 when compared to their mean values among Oort Cloud comets, whereas abundances relative to C2H6 were consistent with their average values from other long-period comets.

Keywords: Long period comets, Comet volatiles , Comae
Excess Ultraviolet Emission at High Galactic Latitudes: A New Horizons View. We present new observations of the cosmic ultraviolet background (CUVB) at high Galactic latitudes (∣b∣ &gt; 40∘), made using the Alice UV spectrograph on board the New Horizons spacecraft. These observations were taken at about 57 au from the Sun, outside much of the foreground emission affecting previous missions, and allowed a new determination of the spectrum of the CUVB between 912─1100 Å and 1400─1800 Å. We found a linear correlation between the CUVB and the Planck E(B − V) with offsets at zero-reddening of 221 ± 11 photon units at 1000 Å and 264 ± 24 photon units at 1500 Å (4.4 ± 0.2 nW m−2 sr−1 at 1000 Å and 5.3 ± 0.5 nW m−2 sr−1 at 1500 Å). The former is the first firm detection of the offset in the range 912─1100 Å while the latter result confirms previous results from the Galaxy Evolution Explorer, showing that there is little emission from the solar system from 1400 to 1800 Å. About half of the offset may be explained by known sources (the integrated light of unresolved galaxies, unresolved stars, emission from ionized gas, and two-photon emission from warm hydrogen in the halo) with the source of the remaining emission as yet unidentified. There is no detectable emission below the Lyman limit with an upper limit of 3.2 ± 3.0 photon units.

Keywords: Ultraviolet sources, Extrasolar radiation, Diffuse radiation, Ultraviolet spectroscopy, Ultraviolet astronomy, Cosmic background radiation