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2025

1. Protopapa, S., Wong, I., Lellouch, E., Johnson, P., Grundy, W., Glein, C., Muller, T., Kiss, C., Emery, J., Brunetto, R., Holler, B., Parker, A., Stansberry, J., Hammel, H., Milam, S., Guilbert-Lepoutre, A., Santos-Sanz, P., Pinilla-Alonso, N., 2025, ApJL, 991, L34, JWST Detection of Hydrocarbon Ices and Methane Gas on Makemake
   Abstract

   JWST/NIRSpec observations of Makemake reveal a chemically complex surface and evidence of gaseous CH₄. Our spectral modeling indicates a surface composition consisting of CH₄, CH₃D, and possibly CH₃OH, combined with aggregates of C₂H₂ and C₂H₆. The presence of C₂H₄ is also considered given its expected photochemical origin. Both areal and layered configurations reproduce the observed spectrum, with the latter being preferred. This composition confirms earlier hydrocarbon detections and suggests that CH₄ photolysis is either ongoing or occurred recently. The detection of CH₃D yields a D/H ratio in CH₄ ice of (3.98 0.34) 10⁴, consistent within 2 with previous estimates. We report the first detection of CH₄ fluorescence from Makemake, establishing it as only the second trans-Neptunian objectafter Plutowith confirmed volatile release. We explore two scenarios consistent with the observed CH₄ emission, though neither fully reproduces the data: an expanding coma, yielding production rates of (0.21.6) 10²⁸ molecules s¹ and a rovibrational temperature of 35 K, possibly originating from a localized plume, and a gravitationally bound atmosphere, which, if adopted, implies gas kinetic temperatures near 40 K and surface pressures of 10 pbarvalues consistent with stellar occultation constraints and an atmosphere in equilibrium with surface CH₄ ice. Discriminating between these scenarios will require higher spectral resolution and improved signal-to-noise observations. Together, the gas-phase CH₄, intermediate D/H ratio between that in water and CH₄ in comets, and complex surface composition challenge the traditional view of Makemake as a quiescent, frozen body.

2. Crawford, C., Li, Y., Huber, D., Yu, J., Bedding, T., Martell, S., Montet, B., Stello, D., Isaacson, H., Howard, A., Fulton, B., Zhang, J., Polanski, A., Weiss, L., 2025, MNRAS, 542, 3289, The highest mass Kepler red giants II. Spectroscopic parameters, the amplitudeactivity relation, and unexpected halo orbits
   Abstract

   The high-mass (M$\,>\,$2 $\text{M}_{\odot }$) Kepler red giant stars are less well-studied than their lower mass counterparts. In the previous article, we presented a sample of 48 high-mass Kepler red giants and measured their asteroseismic parameters. This article presents spectroscopic measurements from the same sample, using high-resolution Keck/HIRES spectra to determine $T_\text{eff}$, [Fe/H], $\log g$, and $v \sin i$. We refined our previous estimates of the stellar masses and radii based on the new $T_\text{eff}$. We also examined spectral features that could indicate binary activity, such as the Li line and [C/N] ratios. We found no Li-rich stars or clear [C/N] anomalies, but we observed a correlation between [C/N] and [Fe/H]. We measured chromospheric activity using the S-index of the Ca II H & K lines and found no correlation with internal magnetic fields. However, we confirmed an anticorrelation between surface chromospheric activity and radial mode oscillation amplitudes, which indicates that strong surface magnetic fields weaken stellar oscillations. Finally, we used the Gaia DR3 astrometric data to show that our sample of stars have orbits consistent with all three Galactic kinematic regions. Although these stars are quite young, their orbits carry them into the thick disc and even the halo, raising questions about the accuracy and viability of kinematics in unravelling Galactic history. In future work, we plan to use the spectroscopic parameters measured here to provide better constraints for boutique frequency modelling, which will allow us to test the asteroseismic scaling relations at the high-mass regime.

2 publications and 0 citations in 2025.

2 publications and 0 citations total.