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2025

1. Kroft, M., Beatty, T., Crossfield, I., Livesey, J., Becker, J., Luhn, J., Robertson, P., Bieryla, A., Ciardi, D., Clark, C., Goliguzova, M., Howell, S., Lissauer, J., Littlefield, C., Lund, M., Safonov, B., Murphy, J., Batalha, N., Bossett, M., Brande, J., Daylan, T., Dressing, C., Gagnebin, A., Huber, D., Isaacson, H., Kane, S., Kreidberg, L., Latham, D., Luque, R., Polanski, A., Premnath, P., Rhem, M., Rogers, C., Turtelboom, E., 2025, AJ, 170, 150, A Pair of Dynamically Interacting Sub-Neptunes around TOI-6054
   Abstract

   We confirm the planetary nature of a pair of transiting sub-Neptune exoplanets orbiting the bright F-type subgiant star TOI-6054 (V = 8.02, K = 6.673) as a part of the OrCAS radial velocity survey using WIYN/NEID observations. We find that TOI-6054b and TOI-6054c have radii of 2.64 0.15R and 2.82 0.17R, respectively, and masses of 12.5 1.7M and 9.3 1.9M. The planets have zero-albedo equilibrium temperatures of 1360 32 K and 1143 28 K. The host star has expanded and will evolve off of the main sequence within the next 500 Myr, and the resulting increase in stellar luminosity has more than doubled the stellar flux the two planets receive compared to the start of the host star's main-sequence phase. Consequently, TOI-6054b may be losing some of its primordial hydrogen/helium atmosphereif it has one. Based on dynamical simulations performed using the orbital parameters of the two planets, TOI-6054b, and TOI-6054c are very likely in a 5:3 mean motion resonance. The TOI-6054 system thus has the potential to be an excellent candidate for future atmospheric follow-up observations, with two similarly sized sub-Neptunes around a bright star. We also estimate that if TOI-6054b is currently losing its H/He atmosphere, this should be observable from space and from the ground.

2. Barat, S., Desert, J., Mukherjee, S., Goyal, J., Xue, Q., Kawashima, Y., Vazan, A., Misener, W., Schlichting, H., Fortney, J., Bean, J., Avarsekar, S., Henry, G., Baeyens, R., Line, M., Livingston, J., David, T., Petigura, E., Sikora, J., Shivkumar, H., Feinstein, A., Oklopcic, A., 2025, AJ, 170, 165, A Metal-poor Atmosphere with a Hot Interior for a Young Sub-Neptune Progenitor: JWST/NIRSpec Transmission Spectrum of V1298 Tau b
   Abstract

   We present the JWST/NIRSpec G395H transmission spectrum of the young (1030 Myr) transiting planet V1298 Tau b (9.85 0.35 R, T_eq = 670 K). Combined Hubble Space Telescope and JWST observations reveal a haze-free, H/He-dominated atmosphere with a large scale height (1500 km), allowing detection of CO₂ (35), H₂O (30), CO (10), CH₄ (6), SO₂ (4), and OCS (3.5). Our observations probe several scale heights (4.4 in the CO₂ 4.3 m band and 3 in the 2.7 m water band). The planet's mass, inferred from atmospheric scale height using free retrieval and grid modeling, is 12 1 M and 15 1.7 M, respectively, which is significantly lower than previous radial velocity estimates and confirms it as "gas-dwarf" sub-Neptune progenitor. We find an atmospheric metallicity (log Z = 0.6 0.6+0.4 solar) and subsolar C/O ratio (0.22 0.05+0.06 ). The atmospheric metallicity is low compared to mature sub-Neptunes by an order of magnitude. The CH₄ abundance ([CH₄] = 6.2 0.5+0.3 ]) is 7 lower than the equilibrium chemistry prediction. To adjust for the low methane abundance, the self-consistent grids favor a high internal temperature (500 K) and vertical mixing (K_zz 10⁷10⁸ cm² s¹). These internal temperatures are inconsistent with predictions from evolutionary models, which expect 100200 K at the current system age. We estimate a gas-to-core mass fraction between 0.1% and 8%, with a core mass of 1112 M, consistent with in-situ gas-dwarf formation. A deep atmospheric metallicity gradient may explain both the high internal temperature and low observable metallicity. Over time, mass loss from such an atmosphere could enhance its metallicity, potentially reconciling V1298 Tau b with mature sub-Neptunes.

2 publications and 1 citations in 2025.

2 publications and 1 citations total.