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1. Divergence beneath the Brillouin sphere and the phenomenology of prediction error in spherical harmonic series approximations of the gravitational field

   https://doi.org/10.1088/1361-6633/ad44d5  

   Bevis, M; Ogle, C; Costin, O; Jekeli, C; Costin, R D; Guo, J; Fowler, J; Dunne, G V; Shum, C K; Snow, K (June 2024, Reports on Progress in Physics)

   The Brillouin sphere is defined as the smallest sphere, centered at the origin of the geocentric coordinate system, that incorporates all the condensed matter composing the planet. The Brillouin sphere touches the Earth at a single point, and the radial line that begins at the origin and passes through that point is called the singular radial line. For about 60 years there has been a persistent anxiety about whether or not a spherical harmonic (SH) expansion of the external gravitational potential,V, will converge beneath the Brillouin sphere. Recently, it was proven that the probability of such convergence is zero. One of these proofs provided an asymptotic relation, called Costin’s formula, for the upper bound,E_N, on the absolute value of the prediction error,e_N, of a SH series model, $V_N(\theta ,\lambda ,r)$, truncated at some maximum degree, $N=n_{max}$. When the SH series is restricted to (or projected onto) a particular radial line, it reduces to a Taylor series (TS) in $1/r$. Costin’s formula is $E_N\simeq B{N}^{-b}(R/r{)}^N$, whereRis the radius of the Brillouin sphere. This formula depends on two positive parameters:b, which controls the decay of error amplitude as a function ofNwhenris fixed, and a scale factorB. We show here that Costin’s formula derives from a similar asymptotic relation for the upper bound,A_non the absolute value of the TS coefficients,a_n, for the same radial line. This formula, $A_n\simeq K{n}^{-k}$, depends on degree,n, and two positive parameters,kandK, that are analogous tobandB. We use synthetic planets, for which we can compute the potential,V, and also the radial component of gravitational acceleration, $g_r=\partial V/\partial r$, to hundreds of significant digits, to validate both of these asymptotic formulas. Let superscriptVrefer to asymptotic parameters associated with the coefficients and prediction errors for gravitational potential, and superscriptgto the coefficients and predictions errors associated withg_r. For polyhedral planets of uniform density we show that $b^V=k^V=7/2$and $b^g=k^g=5/2$almost everywhere. We show that the frequency of oscillation (around zero) of the TS coefficients and the series prediction errors, for a given radial line, is controlled by the geocentric angle,α, between that radial line and the singular radial line. We also derive useful identities connecting $K^V,B^V,K^g$, andB^g. These identities are expressed in terms of quotients of the various scale factors. The only other quantities involved in these identities areαandR. The phenomenology of ‘series divergence’ and prediction error (whenr < R) can be described as a function of the truncation degree,N, or the depth,d, beneath the Brillouin sphere. For a fixed $r\text{⩽}R$, asNincreases from very low values, the upper error boundE_Nshrinks until it reaches its minimum (best) value whenNreaches some particular or optimum value, $N_{\mathrm{opt}}$. When $N>N_{\mathrm{opt}}$, prediction error grows asNcontinues to increase. Eventually, when $N\gg N_{\mathrm{opt}}$, prediction errors increase exponentially with risingN. If we fix the value ofNand allow $R/r$to vary, then we find that prediction error in free space beneath the Brillouin sphere increases exponentially with depth,d, beneath the Brillouin sphere. Because $b^g=b^V-1$everywhere, divergence driven prediction error intensifies more rapidly forg_rthan forV, both in terms of its dependence onNandd. If we fix bothNandd, and focus on the ‘lateral’ variations in prediction error, we observe that divergence and prediction error tend to increase (as doesB) as we approach high-amplitude topography. 

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2. The Cosmic Ultraviolet Baryon Survey (CUBS). VII. On the Warm-hot Circumgalactic Medium Probed by O vi and Ne viii at 0.4 ≲ z ≲ 0.7

   https://doi.org/10.3847/1538-4357/ad410b  

   Qu, Zhijie; Chen, Hsiao-Wen; Johnson, Sean D; Rudie, Gwen C; Zahedy, Fakhri S; DePalma, David; Schaye, Joop; Boettcher, Erin T; Cantalupo, Sebastiano; Chen, Mandy C; et al (June 2024, The Astrophysical Journal)

   Abstract This paper presents a newly established sample of 103 unique galaxies or galaxy groups at 0.4 ≲z≲ 0.7 from the Cosmic Ultraviolet Baryon Survey (CUBS) for studying the warm-hot circumgalactic medium (CGM) probed by both Oviand Neviiiabsorption. The galaxies and associated neighbors are identified at <1 physical Mpc from the sightlines toward 15 CUBS QSOs atz_QSO≳ 0.8. A total of 30 galaxies or galaxy groups exhibit associated Oviλλ1031, 1037 doublet absorption within a line-of-sight velocity interval of ±250 km s⁻¹, while the rest show no trace of Ovito a detection limit of $\log N_{\mathrm{OVI}}/{\mathrm{cm}}^{-2}\approx 13.7$. Meanwhile, only five galaxies or galaxy groups exhibit the Neviiiλλ770, 780 doublet absorption, down to a limiting column density of $\log N_{\mathrm{NeVIII}}/{\mathrm{cm}}^{-2}\approx 14.0$. These Ovi- and Neviii-bearing halos reside in different galaxy environments with stellar masses ranging from $\log M_{\mathrm{star}}/M_{\odot }\approx 8$to ≈11.5. The warm-hot CGM around galaxies of different stellar masses and star formation rates exhibits different spatial profiles and kinematics. In particular, star-forming galaxies with $\log M_{\mathrm{star}}/M_{\odot }\approx 9–11$show a significant concentration of metal-enriched warm-hot CGM within the virial radius, while massive quiescent galaxies exhibit flatter radial profiles of both column densities and covering fractions. In addition, the velocity dispersion of Oviabsorption is broad withσ_υ> 40 km s⁻¹for galaxies of $\log M_{\mathrm{star}}/M_{\odot }>9$within the virial radius, suggesting a more dynamic warm-hot halo around these galaxies. Finally, the warm-hot CGM probed by Oviand Neviiiis suggested to be the dominant phase in sub-L* galaxies with $\log M_{\mathrm{star}}/M_{\odot }\approx 9–10$based on their high ionization fractions in the CGM. 

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3. 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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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. Experimental investigation of circumnutation-inspired penetration in sand

   https://doi.org/10.1088/1748-3190/ad8c89  

   Anilkumar, Riya; Martinez, Alejandro (November 2024, Bioinspiration & Biomimetics)

   Probes that penetrate soil are used in fields such as geotechnical engineering, agriculture, and ecology to classify soils and characterize their propertiesin situ. Conventional tools such as the Cone Penetration Test (CPT) often face challenges due to the lack of reaction force needed to penetrate stiff or dense soil layers, necessitating the use of large drill rigs. This paper investigates more efficient means of penetrating soil by taking inspiration from a plant-root motion known as circumnutation. Experimental penetration tests on sands are performed with circumnutation-inspired (CI) probes that advance at a constant vertical velocity ( $v$) while simultaneously rotating at a constant angular velocity ( $\omega$). These probes have bent tips with a given bent angle ( $\alpha$) and bent length ( $L_1$). The variation of the mobilized vertical force ( $F_z$), torque ( $T_z$.), and the mechanical work components with the ratio of tangential to vertical velocity (ωR/ν, whereRis the distance of the tip of the probe from the vertical axis of rotation) is investigated along with the effects of probe geometry, vertical velocity, and soil relative density ( $D_R$). The results show that the soil penetration resistance does not vary with $v$, but it increases as $\alpha$, $L_1$, and $D_R$are increased. $F_z$decays exponentially with increasing $\omega R/v$, $T_z$initially increases and then plateaus, while total work ( $W_T$) shows little magnitude changes initially but later increases monotonically. The mechanisms leading to these trends are identified as the changes in the probe projected areas and mobilized normal stresses due to differences in probe geometry and the effects of $\omega R/v$on the resultant force direction and soil disturbance. The results show that CI penetration within a specific range of $\omega R/v$leads to small increases in $W_T$(i.e., $\text{⩽}$25%), yet mobilizes $F_z$magnitudes that are 50%–80% lower than that mobilized during non-rotational penetration (i.e., CPT). This indicates that CI penetration can be adopted forin situcharacterization or sensor placement with smaller vertical forces, allowing for use of lighter rigs. 

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