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  • The Local Ultraviolet to Infrared Treasury. II. Refining Star Formation Histories of 10 Metal-poor Dwarf Galaxies with Simultaneous UV-optical Two-CMD Fitting
    We present the star formation histories (SFHs) of 10 metal-poor (≲12% Z⊙), star-forming dwarf galaxies from the Local Ultraviolet to Infrared Treasury survey. The derived SFHs exhibit significant variability, consistent with the irregular star formation expected for dwarf galaxies. Using synthetic near-ultraviolet (UV) and optical color–magnitude diagrams (CMDs) with various yet targeted configurations for dust and input SFHs, we quantitatively demonstrate that simultaneous modeling of the UV and optical CMDs (“UVopt” case) improves the precision of SFH measurements in recent time bins up to ∼1 Gyr, compared to the classical single optical CMD modeling (“Opt-only” case). The UVopt case reduces uncertainties relative to the Opt-only case by ∼4%–8% over the past 10 Myr, ∼8%–20% over 100 Myr, and ∼8%–14% over 1 Gyr, across various dust configurations and input SFHs. Additionally, we demonstrate discrepancies in stellar models for blue core helium-burning (BHeB) stars at the low-metallicity regime. This discrepancy can artificially inflate star formation rate (SFR) estimates in younger age bins by misinterpreting the evolved BHeB stars as reddened upper main-sequence (MS) stars. Incorporating UV data improves BHeB-MS separation and mitigates the limitations of current low-metallicity stellar models. Comparisons of the UVopt SFHs with Hα and far-UV (FUV)-based SFRs reconfirm that Hα is an unreliable tracer over its nominal 10 Myr timescale for low-SFR galaxies, while FUV provides a more reliable tracer but yields SFRFUV values up to twice those of CMD-based 〈SFR〉100 Myr. Our findings underscore the importance of UV data in refining recent SFHs in low-metallicity environments.

  • Many Elements Matter: Detailed Abundance Patterns Reveal Star Formation and Enrichment Differences among Milky Way Structural Components
    Many nucleosynthetic channels create the elements, but two-parameter models characterized by α and Fe nonetheless predict stellar abundances in the Galactic disk to accuracies of 0.02–0.05 dex for most measured elements, near the level of current abundance uncertainties. It is difficult to make individual measurements more precise than this to investigate lower-amplitude nucleosynthetic effects, but population studies of mean abundance patterns can reveal more subtle abundance differences. Here, we look at the detailed abundances for 67,315 stars from the Apache Point Observatory Galactic Evolution Experiment (or APOGEE) Data Release 17, but in abundance residuals away from a best-fit two-parameter, data-driven nucleosynthetic model. We find that these residuals show complex structures with respect to age, guiding radius, and vertical action that are not random and are also not strongly correlated with sources of systematic error such as , Teff, and radial velocity. The residual patterns, especially in Na, C+N, Mn, and Ce, trace kinematic structures in the Milky Way, such as the inner disk, thick disk, and flared outer disk. A principal component analysis suggests that most of the observed structure is low-dimensional and can be explained by a few eigenvectors. We find that some, but not all, of the effects in the low-α disk can be explained by dilution with fresh gas, so that the abundance ratios resemble those of stars with higher metallicity. The patterns and maps we provide can be combined with accurate forward models of nucleosynthesis, star formation, and gas infall to provide a more detailed picture of star and element formation in different Milky Way components.

  • A Moderate Albedo from Reflecting Aerosols on the Dayside of WASP-80 b Revealed by JWST/NIRISS Eclipse Spectroscopy
    Secondary eclipse observations of exoplanets at near-infrared wavelengths enable the detection of thermal emission and reflected stellar light, providing insights into the thermal structure and aerosol composition of their atmospheres. These properties are intertwined as aerosols influence the energy budget of the planet. WASP-80 b is a warm gas giant with an equilibrium temperature of 825 K orbiting a bright late-K/early-M dwarf, and for which the presence of aerosols in its atmosphere has been suggested from previous Hubble Space Telescope and Spitzer observations. We present an eclipse spectrum of WASP-80 b obtained with JWST NIRISS/SOSS, spanning 0.68–2.83 μm, which includes the first eclipse measurements below 1.1 μm for this exoplanet, extending our ability to probe light reflected by its atmosphere. When a reflected light geometric albedo is included in the atmospheric retrieval, our eclipse spectrum is best explained by a reflected light contribution of ∼30 ppm at short wavelengths, although further observations are needed to statistically confirm this preference. We measure a dayside brightness temperature of K and constrain the reflected light geometric albedo across the SOSS wavelength range to , allowing us to estimate a 1σ range for the Bond albedo of 0.148 ≲ AB ≲ 0.383. By comparing our spectrum with aerosol models, we find that manganese sulfide and silicate clouds are disfavored, while cloud species with weak-to-moderate near-infrared reflectance, along with soots or low formation-rate tholin hazes, are consistent with our eclipse spectrum.

  • Solar, Dust, and Tidal Effects on Martian Dayside Exospheric Temperature: An Empirical Model Based on a Decadal MAVEN/IUVS Data Set
    The Martian exospheric temperature, Texo, is a fundamental parameter that regulates atmospheric escape from Mars to space. Previous studies have shown that this parameter varies significantly in response to both solar forcing and atmospheric dynamics. Accurately quantifying and modeling exospheric temperature is essential for understanding Mars’ long-term climate evolution. Using a decadal data set of Lyα airglow emission observed by the Imaging Ultraviolet Spectrograph on the Mars Atmosphere and Volatile EvolutioN mission, we derived the Martian dayside exospheric temperature under varying solar and atmospheric conditions during 2014–2023. Our analysis indicates that the Martian dayside exospheric temperature varies from ∼140 to 300 K over the past decade. Long-term variations are primarily driven by solar forcing, with a sensitivity of ∼45 K mW−1 m2 to the solar Lyα flux measured at Mars. Short-term variations are influenced by dust activity and atmospheric tides. On average, the Martian dayside exospheric temperature is enhanced by ∼20.1 K during large-scale dust storms, and atmospheric tides lead to longitudinal variations with magnitudes of ∼10–15 K and ∼10–30 K near aphelion and perihelion, respectively. We developed an empirical model of the Martian dayside exospheric temperature through multidimensional least-squares fitting, which is capable of capturing the combined effects of solar, dust, and tidal forces. This model offers a valuable tool for estimating the Martian exospheric variability under diverse conditions.

  • The Lyα Sky as Observed by New Horizons at 57 au
    During 2023 September the Alice ultraviolet spectrograph on the New Horizons (NH) spacecraft was used to map diffuse Lyα emission over most of the sky, at a range of ∼56.9 au from the Sun. At that distance, models predict that the interplanetary medium Lyα emissions result from comparable amounts of resonant backscattering of the solar Lyα line by interstellar hydrogen atoms (H i) passing through the solar system, in addition to an approximately isotropic background of ∼50 ± 20 R from the local interstellar medium (LISM). The NH observations show no strong correlations with nearby cloud structures of the LISM or with expected structures of the heliosphere, such as a hydrogen wall associated with the heliopause. To explain the relatively bright and uniform Lyα of the LISM, we propose that hot, young stars within the Local Hot Bubble shine on its interior walls, photoionizing H i atoms there. Recombination of these ions can account for the observed ∼50 R Lyα background, after amplification of the diffuse Lyα by resonant scattering, although sophisticated (i.e., 3D) radiative transfer models should be used to confirm this conjecture. Future observations of the diffuse Lyα, with instruments capable of resolving the line profile, could provide a new window on H i populations in the LISM and heliosphere. The NH Alice all-sky Lyα observations presented here may be repeated at some point in the future, if resources allow, and the two maps could be combined to provide a significant increase in angular resolution.