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1. 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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2. The Metallicity and Carbon-to-oxygen Ratio of the Ultrahot Jupiter WASP-76b from Gemini-S/IGRINS

   https://doi.org/10.3847/1538-3881/ad4a5f  

   Weiner_Mansfield, Megan; Line, Michael R; Wardenier, Joost P; Brogi, Matteo; Bean, Jacob L; Beltz, Hayley; Smith, Peter; Zalesky, Joseph A; Batalha, Natasha; Kempton, Eliza M-R; et al (June 2024, The Astronomical Journal)

   Abstract Measurements of the carbon-to-oxygen (C/O) ratios of exoplanet atmospheres can reveal details about their formation and evolution. Recently, high-resolution cross-correlation analysis has emerged as a method of precisely constraining the C/O ratios of hot Jupiter atmospheres. We present two transits of the ultrahot Jupiter WASP-76b observed between 1.4 and 2.4μm with the high-resolution Immersion GRating INfrared Spectrometer on the Gemini-S telescope. We detected the presence of H₂O, CO, and OH at signal-to-noise ratios of 6.93, 6.47, and 3.90, respectively. We performed two retrievals on this data set. A free retrieval for abundances of these three species retrieved a volatile metallicity of $\left(\frac{\mathrm{C}+\mathrm{O}}{\mathrm{H}}\right)=-{0.70}_{-0.93}^{+1.27}$, consistent with the stellar value, and a supersolar carbon-to-oxygen ratio of C/O $={0.80}_{-0.11}^{+0.07}$. We also ran a chemically self-consistent grid retrieval, which agreed with the free retrieval within 1σbut favored a slightly more substellar metallicity and solar C/O ratio ( $\left(\frac{\mathrm{C}+\mathrm{O}}{\mathrm{H}}\right)=-{0.74}_{-0.17}^{+0.23}$and C/O $={0.59}_{-0.14}^{+0.13}$). A variety of formation pathways may explain the composition of WASP-76b. Additionally, we found systemic (V_sys) and Keplerian (K_p) velocity offsets which were broadly consistent with expectations from 3D general circulation models of WASP-76b, with the exception of a redshiftedV_sysfor H₂O. Future observations to measure the phase-dependent velocity offsets and limb differences at high resolution on WASP-76b will be necessary to understand the H₂O velocity shift. Finally, we find that the population of exoplanets with precisely constrained C/O ratios generally trends toward super-solar C/O ratios. More results from high-resolution observations or JWST will serve to further elucidate any population-level trends. 

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3. The Scale of Stellar Yields: Implications of the Measured Mean Iron Yield of Core Collapse Supernovae

   https://doi.org/10.3847/1538-4357/ad6313  

   Weinberg, David_H; Griffith, Emily_J; Johnson, James_W; Thompson, Todd_A (September 2024, The Astrophysical Journal)

   Abstract The scale ofα-element yields is difficult to predict from theory because of uncertainties in massive star evolution, supernova physics, and black hole formation, and it is difficult to constrain empirically because the impact of higher yields can be compensated by greater metal loss in galactic winds. We use a recent measurement of the mean iron yield of core collapse supernovae (CCSN) by Rodriguez et al., ${\overline{y}}_{\mathrm{Fe}}^{\mathrm{cc}}=0.058\pm 0.007M_{\odot }$, to infer the scale ofα-element yields by assuming that the plateau of [α/Fe] abundance ratios observed in low-metallicity stars represents the yield ratio of CCSN. For a plateau at [α/Fe]_cc= 0.45, we find that the population-averaged yields of O and Mg are about equal to the solar abundance of these elements, $\log y_{\mathrm{O}}^{\mathrm{cc}}/Z_{\mathrm{O},\odot }=\log y_{\mathrm{Mg}}^{\mathrm{cc}}/Z_{\mathrm{Mg},\odot }=-0.01\pm 0.1$, where $y_{\mathrm{X}}^{\mathrm{cc}}$is the mass of element X produced by massive stars per unit mass of star formation. The inferred O and Fe yields agree with predictions of the Sukhbold et al. CCSN models assuming their Z9.6+N20 neutrino-driven engine, a scenario in which many progenitors withM< 40M_⊙implode to black holes rather than exploding. The yields are lower than assumed in many models of the galaxy mass–metallicity relation, reducing the level of outflows needed to match observed abundances. Our one-zone chemical evolution models with $\eta ={\dot{M}}_{\mathrm{out}}/{\dot{M}}_{*}\approx 0.6$evolve to solar metallicity at late times. By further requiring that models reach [α/Fe] ≈ 0 at late times, we infer a Hubble-time integrated Type Ia supernova rate of $1.1\times {10}^{-3}{M}_{\odot }^{-1}$, compatible with estimates from supernova surveys. 

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4. The Warm Neptune GJ 3470b Has a Polar Orbit

   https://doi.org/10.3847/2041-8213/ac6e3c  

   Stefànsson, Guđmundur; Mahadevan, Suvrath; Petrovich, Cristobal; Winn, Joshua N.; Kanodia, Shubham; Millholland, Sarah C.; Maney, Marissa; Cañas, Caleb I.; Wisniewski, John; Robertson, Paul; et al (May 2022, The Astrophysical Journal Letters)

   Abstract The warm Neptune GJ 3470b transits a nearby (d= 29 pc) bright slowly rotating M1.5-dwarf star. Using spectroscopic observations during two transits with the newly commissioned NEID spectrometer on the WIYN 3.5 m Telescope at Kitt Peak Observatory, we model the classical Rossiter–McLaughlin effect, yielding a sky-projected obliquity of $\lambda ={98}_{-12}^{+15◦}$and a $v\sin i={0.85}_{-0.33}^{+0.27}\mathrm{km}{\mathrm{s}}^{-1}$. Leveraging information about the rotation period and size of the host star, our analysis yields a true obliquity of $\psi ={95}_{-8}^{+9◦}$, revealing that GJ 3470b is on a polar orbit. Using radial velocities from HIRES, HARPS, and the Habitable-zone Planet Finder, we show that the data are compatible with a long-term radial velocity (RV) slope of $\dot{\gamma }=-0.0022\pm 0.0011\mathrm{m}{\mathrm{s}}^{-1}{\mathrm{day}}^{-1}$over a baseline of 12.9 yr. If the RV slope is due to acceleration from another companion in the system, we show that such a companion is capable of explaining the polar and mildly eccentric orbit of GJ 3470b using two different secular excitation models. The existence of an outer companion can be further constrained with additional RV observations, Gaia astrometry, and future high-contrast imaging observations. Lastly, we show that tidal heating from GJ 3470b’s mild eccentricity has most likely inflated the radius of GJ 3470b by a factor of ∼1.5–1.7, which could help account for its evaporating atmosphere. 

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5. IGRINS Observations of WASP-127 b: H ₂ O, CO, and Super-solar Atmospheric Metallicity in the Inflated Sub-Saturn

   https://doi.org/10.3847/1538-3881/ad72f3  

   Kanumalla, Krishna; Line, Michael R; Weiner_Mansfield, Megan; Welbanks, Luis; Smith, Peter_C B; Bean, Jacob L; Pino, Lorenzo; Brogi, Matteo; Panwar, Vatsal (October 2024, The Astronomical Journal)

   Abstract High-resolution spectroscopy of exoplanet atmospheres provides insights into their composition and dynamics from the resolved line shape and depth of thousands of spectral lines. WASP-127 b is an extremely inflated sub-Saturn (R_p= 1.311R_Jup,M_p= 0.16M_Jup) with previously reported detections of H₂O and CO₂. However, the seeming absence of the primary carbon reservoir expected at WASP-127 b temperatures (T_eq∼1400 K) from chemical equilibrium, CO, posed a mystery. In this manuscript, we present the analysis of high-resolution observations of WASP-127 b with the Immersion Grating Infrared Spectrometer on Gemini South. We confirm the presence of H₂O (8.67σ) and report the detection of CO (4.34σ). Additionally, we conduct a suite of Bayesian retrieval analyses covering a hierarchy of model complexity and self-consistency. When freely fitting for the molecular gas volume mixing ratios, we obtain super-solar metal enrichment for H₂O abundance of log₁₀X ${}_{{\mathrm{H}}_2\mathrm{O}}$= −1.23 ${}_{-0.49}^{+0.29}$and a lower limit on the CO abundance of log₁₀X_CO≥–2.20 at 2σconfidence. We also report tentative evidence of photochemistry in WASP-127 b based upon the indicative depletion of H₂S. This is also supported by the data preferring models with photochemistry over free-chemistry and thermochemistry. The overall analysis implies a super-solar (∼39× Solar; [M/H] = ${1.59}_{-0.30}^{+0.30}$) metallicity for the atmosphere of WASP-127 b and an upper limit on its atmospheric C/O ratio as < 0.68. 

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