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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. Validation of Elemental and Isotopic Abundances in Late-M Spectral Types with the Benchmark HIP 55507 AB System

   https://doi.org/10.3847/1538-4357/ad1243  

   Xuan, Jerry W.; Wang, Jason; Finnerty, Luke; Horstman, Katelyn; Grimm, Simon; Peck, Anne E.; Nielsen, Eric; Knutson, Heather A.; Mawet, Dimitri; Isaacson, Howard; et al (February 2024, The Astrophysical Journal)

   Abstract M dwarfs are common host stars to exoplanets but often lack atmospheric abundance measurements. Late-M dwarfs are also good analogs to the youngest substellar companions, which share similarT_eff∼ 2300–2800 K. We present atmospheric analyses for the M7.5 companion HIP 55507 B and its K6V primary star with Keck/KPIC high-resolution (R∼ 35,000)K-band spectroscopy. First, by including KPIC relative radial velocities between the primary and secondary in the orbit fit, we improve the dynamical mass precision by 60% and find $M_B={88.0}_{-3.2}^{+3.4}{M}_{\mathrm{Jup}}$, putting HIP 55507 B above the stellar–substellar boundary. We also find that HIP 55507 B orbits its K6V primary star with $a={38}_{-3}^{+4}$au ande= 0.40 ± 0.04. From atmospheric retrievals of HIP 55507 B, we measure [C/H] = 0.24 ± 0.13, [O/H] = 0.15 ± 0.13, and C/O = 0.67 ± 0.04. Moreover, we strongly detect¹³CO (7.8σsignificance) and tentatively detect ${\mathrm{H}}_2^{18}\mathrm{O}$(3.7σsignificance) in the companion’s atmosphere and measure ${}^{12}\mathrm{CO}{/}^{13}\mathrm{CO}={98}_{-22}^{+28}$and ${\mathrm{H}}_2^{16}\mathrm{O}/{\mathrm{H}}_2^{18}\mathrm{O}={240}_{-80}^{+145}$after accounting for systematic errors. From a simplified retrieval analysis of HIP 55507 A, we measure ${}^{12}\mathrm{CO}{/}^{13}\mathrm{CO}={79}_{-16}^{+21}$and ${\mathrm{C}}^{16}\mathrm{O}/{\mathrm{C}}^{18}\mathrm{O}={288}_{-70}^{+125}$for the primary star. These results demonstrate that HIP 55507 A and B have consistent¹²C/¹³C and¹⁶O/¹⁸O to the <1σlevel, as expected for a chemically homogeneous binary system. Given the similar flux ratios and separations between HIP 55507 AB and systems with young substellar companions, our results open the door to systematically measuring¹³CO and ${\mathrm{H}}_2^{18}\mathrm{O}$abundances in the atmospheres of substellar or even planetary-mass companions with similar spectral types. 

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3. Detection and Bulk Properties of the HR 8799 Planets with High-resolution Spectroscopy

   https://doi.org/10.3847/1538-3881/ac1349  

   Wang 王, Jason J. 劲飞; Ruffio, Jean-Baptiste; Morris, Evan; Delorme, Jacques-Robert; Jovanovic, Nemanja; Pezzato, Jacklyn; Echeverri, Daniel; Finnerty, Luke; Hood, Callie; Zanazzi, J. J.; et al (September 2021, The Astronomical Journal)

   Abstract Using the Keck Planet Imager and Characterizer, we obtained high-resolution (R∼ 35,000)K-band spectra of the four planets orbiting HR 8799. We clearly detected H₂O and CO in the atmospheres of HR 8799 c, d, and e, and tentatively detected a combination of CO and H₂O in b. These are the most challenging directly imaged exoplanets that have been observed at high spectral resolution to date when considering both their angular separations and flux ratios. We developed a forward-modeling framework that allows us to jointly fit the spectra of the planets and the diffracted starlight simultaneously in a likelihood-based approach and obtained posterior probabilities on their effective temperatures, surface gravities, radial velocities, and spins. We measured $v\sin \left(i\right)$values of ${10.1}_{-2.7}^{+2.8}\mathrm{km}{\mathrm{s}}^{-1}$for HR 8799 d and ${15.0}_{-2.6}^{+2.3}\mathrm{km}{\mathrm{s}}^{-1}$for HR 8799 e, and placed an upper limit of <14 km s⁻¹of HR 8799 c. Under two different assumptions of their obliquities, we found tentative evidence that rotation velocity is anticorrelated with companion mass, which could indicate that magnetic braking with a circumplanetary disk at early times is less efficient at spinning down lower-mass planets. 

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4. Keck Planet Imager and Characterizer Emission Spectroscopy of WASP-33b

   https://doi.org/10.3847/1538-3881/acda91  

   Finnerty, Luke; Schofield, Tobias; Sappey, Ben; Xuan, Jerry W.; Ruffio, Jean-Baptiste; Wang, Jason J.; Delorme, Jacques-Robert; Blake, Geoffrey A.; Buzard, Cam; Fitzgerald, Michael P.; et al (June 2023, The Astronomical Journal)

   Abstract We present Keck Planet Imager and Characterizer (KPIC) high-resolution (R∼35,000)K-band thermal emission spectroscopy of the ultrahot Jupiter WASP-33b. The use of KPIC’s single-mode fibers greatly improves both blaze and line-spread stabilities relative to slit spectrographs, enhancing the cross-correlation detection strength. We retrieve the dayside emission spectrum with a nested-sampling pipeline, which fits for orbital parameters, the atmospheric pressure–temperature profile, and the molecular abundances. We strongly detect the thermally inverted dayside and measure mass-mixing ratios for CO ( ${\mathrm{logCO}}_{\mathrm{MMR}}=-{1.1}_{-0.6}^{+0.4}$), H₂O ( ${\mathrm{logH}}_2{\mathrm{O}}_{\mathrm{MMR}}=-{4.1}_{-0.9}^{+0.7}$), and OH ( ${\mathrm{logOH}}_{\mathrm{MMR}}=-{2.1}_{-1.1}^{+0.5}$), suggesting near-complete dayside photodissociation of H₂O. The retrieved abundances suggest a carbon- and possibly metal-enriched atmosphere, with a gas-phase C/O ratio of ${0.8}_{-0.2}^{+0.1}$, consistent with the accretion of high-metallicity gas near the CO₂snow line and post-disk migration or with accretion between the soot and H₂O snow lines. We also find tentative evidence for¹²CO/¹³CO ∼ 50, consistent with values expected in protoplanetary disks, as well as tentative evidence for a metal-enriched atmosphere (2–15 × solar). These observations demonstrate KPIC’s ability to characterize close-in planets and the utility of KPIC’s improved instrumental stability for cross-correlation techniques. 

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5. Discovery of Super-enriched Gas ∼1 Gyr after the Big Bang

   https://doi.org/10.3847/2041-8213/aceefe  

   Huyan 呼延, Jianghao 江豪; Kulkarni, Varsha P.; Poudel, Suraj; Tejos, Nicolas; Péroux, Celine; Lopez, Sebastian (August 2023, The Astrophysical Journal Letters)

   Abstract Abundances of chemical elements in the interstellar and circumgalactic media of high-redshift galaxies offer important constraints on the nucleosynthesis by early generations of stars. Damped Lyαabsorbers (DLAs) in spectra of high-redshift background quasars are excellent sites for obtaining robust measurements of element abundances in distant galaxies. Past studies of DLAs at redshiftsz> 4 have measured abundances of ≲0.01 solar. Here we report the discovery of a DLA atz= 4.7372 with an exceptionally high degree of chemical enrichment. We estimate the Hicolumn density in this absorber to be log (N_{H I}/cm⁻²) = 20.48 ± 0.15. Our analysis shows unusually high abundances of carbon and oxygen ([C/H] = 0.88 ± 0.17, [O/H] = 0.71 ± 0.16). Such a high level of enrichment a mere 1.2 Gyr after the Big Bang is surprising because of insufficient time for the required amount of star formation. To our knowledge, this is the first supersolar absorber found atz> 4.5. We find the abundances of Si and Mg to be [Si/H] = $-{0.56}_{-0.35}^{+0.40}$and [Mg/H] = ${0.59}_{-0.50}^{+0.27}$, confirming the metal-rich nature of this absorber. By contrast, Fe shows a much lower abundance ([Fe/H] = $-{1.53}_{-0.15}^{+0.15}$). We discuss implications of our results for galactic chemical evolution models. The metallicity of this absorber is higher than that of any other known DLA and is >2 orders of magnitude above predictions of chemical evolution models and theN_{H I}-weighted mean metallicity from previous studies atz> 4.5. The relative abundances (e.g., [O/Fe] = 2.29 ± 0.05, [C/Fe] = 2.46 ± 0.08) are also highly unusual compared to predictions for enrichment by early stars. 

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