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1. Theoretical Analysis of Critical Conditions for Crack Formation and Propagation, and Optimal Operation of SOECs

   https://doi.org/10.1149/1945-7111/ac5fee  

   Wang, Yudong; Virkar, Anil V.; Khonsari, M. M.; Zhou, Xiao-Dong (April 2022, Journal of The Electrochemical Society)

   A theoretical analysis on crack formation and propagation was performed based on the coupling between the electrochemical process, classical elasticity, and fracture mechanics. The chemical potential of oxygen, thus oxygen partial pressure, at the oxygen electrode-electrolyte interface ( ${\mu }_{O_2}^{\mathit{OE\mid El}}$) was investigated as a function of transport properties, electrolyte thickness and operating conditions (e.g., steam concentration, constant current, and constant voltage). Our analysis shows that: a lower ionic area specific resistance (ASR), $r_i^{OE},$and a higher electronic ASR ( $r_e^{OE}$) of the oxygen electrode/electrolyte interface are in favor of suppressing crack formation. The ${\mu }_{O_2}^{OE\mid El},$thus local pO₂, are sensitive towards the operating parameters under galvanostatic or potentiostatic electrolysis. Constant current density electrolysis provides better robustness, especially at a high current density with a high steam content. While constant voltage electrolysis leads to greater variations of ${\mu }_{O_2}^{OE\mid El}.$Constant current electrolysis, however, is not suitable for an unstable oxygen electrode because ${\mu }_{O_2}^{OE\mid El}$can reach a very high value with a gradually increased $r_i^{OE}.$A crack may only occur under certain conditions when $p_{O_2}^{TPB}>p_{cr}.$ 

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2. OGLE-2019-BLG-1180Lb: Discovery of a Wide-orbit Jupiter-mass Planet around a Late-type Star

   https://doi.org/10.3847/1538-3881/ad0723  

   Chung, Sun-Ju; Udalski, Andrzej; Yee, Jennifer C.; Gould, Andrew; Leading Authors; Albrow, Michael D.; Jung, Youn Kil; Hwang, Kyu-Ha; Han, Cheongho; Ryu, Yoon-Hyun; et al (November 2023, The Astronomical Journal)

   Abstract We report on the discovery and analysis of the planetary microlensing event OGLE-2019-BLG-1180 with a planet-to-star mass ratioq∼ 0.003. The event OGLE-2019-BLG-1180 has unambiguous cusp-passing and caustic-crossing anomalies, which were caused by a wide planetary caustic withs≃ 2, wheresis the star–planet separation in units of the angular Einstein radiusθ_E. Thanks to well-covered anomalies by the Korea Micorolensing Telescope Network (KMTNet), we measure both the angular Einstein radius and the microlens parallax in spite of a relatively short event timescale oft_E= 28 days. However, because of a weak constraint on the parallax, we conduct a Bayesian analysis to estimate the physical lens parameters. We find that the lens system is a super-Jupiter-mass planet of $M_{\mathrm{p}}={1.75}_{-0.51}^{+0.53}{M}_{\mathrm{J}}$orbiting a late-type star of $M_{\mathrm{h}}={0.55}_{-0.26}^{+0.27}{M}_{\odot }$at a distance $D_{\mathrm{L}}={6.1}_{-1.3}^{+0.9}\mathrm{kpc}$. The projected star–planet separation is $a_{\perp }={5.19}_{-1.23}^{+0.90}\mathrm{au}$, which means that the planet orbits at about four times the snow line of the host star. Considering the relative lens–source proper motion ofμ_rel= 6 mas yr⁻¹, the lens will be separated from the source by 60 mas in 2029. At that time one can measure the lens flux from adaptive optics imaging of Keck or a next-generation 30 m class telescope. OGLE-2019-BLG-1180Lb represents a growing population of wide-orbit planets detected by KMTNet, so we also present a general investigation into prospects for further expanding the sample of such planets. 

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3. Resolved Measurements of the CO-to-H ₂ Conversion Factor in 37 Nearby Galaxies

   https://doi.org/10.3847/1538-4357/ad23ed  

   Chiang 江, I-Da 宜達; Sandstrom, Karin M.; Chastenet, Jérémy; Bolatto, Alberto D.; Koch, Eric W.; Leroy, Adam K.; Sun 孙, Jiayi 嘉懿; Teng, Yu-Hsuan; Williams, Thomas G. (March 2024, The Astrophysical Journal)

   Abstract We measure the CO-to-H₂conversion factor (α_CO) in 37 galaxies at 2 kpc resolution, using the dust surface density inferred from far-infrared emission as a tracer of the gas surface density and assuming a constant dust-to-metal ratio. In total, we have ∼790 and ∼610 independent measurements ofα_COfor CO (2–1) and (1–0), respectively. The mean values forα_{CO (2–1)}andα_{CO (1–0)}are ${9.3}_{-5.4}^{+4.6}$and ${4.2}_{-2.0}^{+1.9}{M}_{\odot }{\mathrm{pc}}^{-2}{\left(\mathrm{K}\mathrm{km}{\mathrm{s}}^{-1}\right)}^{-1}$, respectively. The CO-intensity-weighted mean is 5.69 forα_{CO (2–1)}and 3.33 forα_{CO (1–0)}. We examine howα_COscales with several physical quantities, e.g., the star formation rate (SFR), stellar mass, and dust-mass-weighted average interstellar radiation field strength ( $\overline{U}$). Among them, $\overline{U}$, Σ_SFR, and the integrated CO intensity (W_CO) have the strongest anticorrelation with spatially resolvedα_CO. We provide linear regression results toα_COfor all quantities tested. At galaxy-integrated scales, we observe significant correlations betweenα_COandW_CO, metallicity, $\overline{U}$, and Σ_SFR. We also find thatα_COin each galaxy decreases with the stellar mass surface density (Σ_⋆) in high-surface-density regions (Σ_⋆≥ 100M_⊙pc⁻²), following the power-law relations ${\alpha }_{\mathrm{CO}(2–1)}\propto {\mathrm{\Sigma }}_{\star }^{-0.5}$and ${\alpha }_{\mathrm{CO}(1–0)}\propto {\mathrm{\Sigma }}_{\star }^{-0.2}$. The power-law index is insensitive to the assumed dust-to-metal ratio. We interpret the decrease inα_COwith increasing Σ_⋆as a result of higher velocity dispersion compared to isolated, self-gravitating clouds due to the additional gravitational force from stellar sources, which leads to the reduction inα_CO. The decrease inα_COat high Σ_⋆is important for accurately assessing molecular gas content and star formation efficiency in the centers of galaxies, which bridge “Milky Way–like” to “starburst-like” conversion factors. 

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4. TOI-5344 b: A Saturn-like Planet Orbiting a Super-solar Metallicity M0 Dwarf

   https://doi.org/10.3847/1538-3881/ad09c2  

   Han, Te; Robertson, Paul; Kanodia, Shubham; Cañas, Caleb; Lin, Andrea S. J.; Stefánsson, Gumundur; Libby-Roberts, Jessica E.; Larsen, Alexander; Kobulnicky, Henry A.; Mahadevan, Suvrath; et al (December 2023, The Astronomical Journal)

   Abstract We confirm the planetary nature of TOI-5344 b as a transiting giant exoplanet around an M0-dwarf star. TOI-5344 b was discovered with the Transiting Exoplanet Survey Satellite photometry and confirmed with ground-based photometry (the Red Buttes Observatory 0.6 m telescope), radial velocity (the Habitable-zone Planet Finder), and speckle imaging (the NN-Explore Exoplanet Stellar Speckle Imager). TOI-5344 b is a Saturn-like giant planet (ρ= 0.80 ${}_{-0.15}^{+0.17}$g cm⁻³) with a planetary radius of 9.7 ± 0.5R_⊕(0.87 ± 0.04R_Jup) and a planetary mass of ${135}_{-18}^{+17}{M}_{\oplus }$(0.42 ${}_{-0.06}^{+0.05}{M}_{\mathrm{Jup}}$). It has an orbital period of ${3.792622}_{-0.000010}^{+0.000010}$days and an orbital eccentricity of ${0.06}_{-0.04}^{+0.07}$. We measure a high metallicity for TOI-5344 of [Fe/H] = 0.48 ± 0.12, where the high metallicity is consistent with expectations from formation through core accretion. We compare the metallicity of the M-dwarf hosts of giant exoplanets to that of M-dwarf hosts of nongiants (≲8R_⊕). While the two populations appear to show different metallicity distributions, quantitative tests are prohibited by various sample caveats. 

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5. HSTPROMO Internal Proper-motion Kinematics of Dwarf Spheroidal Galaxies. I. Velocity Anisotropy and Dark Matter Cusp Slope of Draco

   https://doi.org/10.3847/1538-4357/ad571c  

   Vitral, Eduardo; van_der_Marel, Roeland_P; Sohn, Sangmo_Tony; Libralato, Mattia; del_Pino, Andrés; Watkins, Laura_L; Bellini, Andrea; Walker, Matthew_G; Besla, Gurtina; Pawlowski, Marcel_S; et al (July 2024, The Astrophysical Journal)

   Abstract We analyze four epochs of Hubble Space Telescope imaging over 18 yr for the Draco dwarf spheroidal galaxy. We measure precise proper motions for hundreds of stars and combine these with existing line-of-sight (LOS) velocities. This provides the first radially resolved 3D velocity dispersion profiles for any dwarf galaxy. These constrain the intrinsic velocity anisotropy and resolve the mass–anisotropy degeneracy. We solve the Jeans equations in oblate axisymmetric geometry to infer the mass profile. We find the velocity dispersion to be radially anisotropic along the symmetry axis and tangentially anisotropic in the equatorial plane, with a globally averaged value $\overline{{\beta }_{\mathrm{B}}}=-{0.20}_{-0.53}^{+0.28}$, (where 1 – ${\beta }_{\mathrm{B}}\equiv 〈v_{\tan }^2〉/〈v_{\mathrm{rad}}^2〉$in 3D). The logarithmic dark matter (DM) density slope over the observed radial range, Γ_dark, is $-{0.83}_{-0.37}^{+0.32}$, consistent with the inner cusp predicted in ΛCDM cosmology. As expected given Draco’s low mass and ancient star formation history, it does not appear to have been dissolved by baryonic processes. We rule out cores larger than 487, 717, and 942 pc at 1σ, 2σ, and 3σconfidence, respectively, thus imposing important constraints on the self-interacting DM cross section. Spherical models yield biased estimates for both the velocity anisotropy and the inferred slope. The circular velocity at our outermost data point (900 pc) is ${24.19}_{-2.97}^{+6.31}\mathrm{km}{\mathrm{s}}^{-1}$. We infer a dynamical distance of ${75.37}_{-4.00}^{+4.73}$kpc and show that Draco has a modest LOS rotation, with $\left(v/\sigma \right)=0.22\pm 0.09$. Our results provide a new stringent test of the so-called “cusp–core” problem that can be readily extended to other dwarfs. 

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