Exoplanets and Stellar Physics

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JWST reveals cosmic ray dominated chemistry in the local ULIRG IRAS 07251$-$0248

(2025)

Authors:

G Speranza, M Pereira-Santaella, M Agúndez, E González-Alfonso, I García-Bernete, JR Goicoechea, M Imanishi, D Rigopoulou, MG Santa-Maria, N Thatte

Accelerating Long-period Exoplanet Discovery by Combining Deep Learning and Citizen Science

Astronomical Journal American Astronomical Society 170:1 (2025) 39

Authors:

Shreshth A Malik, Nora L Eisner, Ian R Mason, Sofia Platymesi, Suzanne Aigrain, Stephen J Roberts, Yarin Gal, Chris J Lintott

Abstract:

Automated planetary transit detection has become vital to identify and prioritize candidates for expert analysis and verification given the scale of modern telescopic surveys. Current methods for short-period exoplanet detection work effectively due to periodicity in the transit signals, but a robust approach for detecting single-transit events is lacking. However, volunteer-labeled transits collected by the Planet Hunters TESS (PHT) project now provide an unprecedented opportunity to investigate a data-driven approach to long-period exoplanet detection. In this work, we train a 1D convolutional neural network to classify planetary transits using PHT volunteer scores as training data. We find that this model recovers planet candidates (TESS objects of interest; TOIs) at a precision and recall rate exceeding those of volunteers, with a 20% improvement in the area under the precision-recall curve and 10% more TOIs identified in the top 500 predictions on average per sector. Importantly, the model also recovers almost all planet candidates found by volunteers but missed by current automated methods (PHT community TOIs). Finally we retrospectively utilise the model to simulate live deployment in PHT to reprioritize candidates for analysis. We also find that multiple promising planet candidates, originally missed by PHT, would have been found using our approach, showing promise for upcoming real-world deployment.

From Pretransit to Posteclipse: Investigating the Impact of 3D Temperature, Chemistry, and Dynamics on High-resolution Emission Spectra of the Ultrahot Jupiter WASP-76b

The Astrophysical Journal American Astronomical Society 986:1 (2025) 63-63

Authors:

Joost P Wardenier, Vivien Parmentier, Elspeth KH Lee, Michael R Line

Abstract:

Abstract High-resolution spectroscopy has provided a wealth of information about the climate and composition of ultrahot Jupiters (UHJs). However, the 3D structure of their atmospheres makes observations more challenging to interpret, necessitating 3D forward-modeling studies. In this work, we model phase-dependent thermal emission spectra of the archetype UHJ WASP-76b to understand how the line strengths and Doppler shifts of Fe, CO, H2O, and OH evolve throughout the orbit. We postprocess outputs of the SPARC/MITgcm global circulation model with the 3D Monte Carlo radiative transfer code gCMCRT to simulate emission spectra at 36 orbital phases. We then cross correlate the spectra with different templates to obtain cross-correlation function and K p–V sys maps. For each species, our models produce consistently negative K p offsets in pre- and posteclipse, which are driven by planet rotation. The size of these offsets is similar to the equatorial rotation velocity of the planet. Furthermore, we demonstrate how the weak vertical temperature gradient on the nightside of UHJs mutes the absorption features of CO and H2O, which significantly hampers their detectability in pre- and posttransit. We also show that the K p and V sys offsets in pre- and posttransit are not always a measure of the line-of-sight velocities in the atmosphere. This is because the cross-correlation signal is a blend of dayside emission and nightside absorption features. Finally, we highlight that the observational uncertainty in the known orbital velocity of UHJs can be multiple kilometers per second, which makes it hard for certain targets to meaningfully report absolute K p offsets.

Hot Rocks Survey II. The thermal emission of TOI-1468 b reveals a bare hot rock

Astronomy & Astrophysics 698:A68 (2025) 18

Authors:

E. A. Meier Valdés, B.-O. Demory, H. Diamond-Lowe, J. M. Mendonça, P. C. August, M. Fortune, N. H. Allen, D. Kitzmann, A. Gressier, M. Hooton, K. D. Jones, L. A. Buchhave, N. Espinoza, C. E. Fisher, N. P. Gibson, K. Heng, J. Hoeijmakers, B. Prinoth, A. D. Rathcke and J. D. Eastman

Abstract:

Terrestrial exoplanets orbiting nearby small cool stars, known as M dwarfs, are well suited for an atmospheric characterisation. Because the intense X-ray and UV (XUV) irradiation from M dwarf host stars is strong, orbiting exoplanets are thought to be unable to retain primordial hydrogen- or helium-dominated atmospheres. However, it is currently unknown whether heavier secondary atmospheres can survive.
The aim of the Hot Rocks Survey programme is to determine whether exoplanets can retain secondary atmospheres in the presence of M dwarf hosts. In the sample of nine exoplanets in the programme, we aim to determine whether TOI-1468 b has a substantial atmosphere or is consistent with a low-albedo bare rock.
The James Webb Space Telescope provides an opportunity to characterise the thermal emission with MIRI at 15 μm. The occultation of TOI-1468 b was observed three times. We compared our observations to atmospheric models that include varying amounts of CO2 and H2O.
The observed occultation depths for the individual visits are 239±52 ppm, 341±53 ppm, and 357±52 ppm. A joint fit yields an occultation depth of 311±31 ppm. The thermal emission is mostly consistent with no atmosphere and a zero Bond albedo at a confidence level of 1.65σ, or a blackbody at a brightness temperature of 1024 ± 78 K. A pure CO2 or H2O atmosphere with a surface pressure above 1 bar is ruled out at higher than 3σ.
Surprisingly, the surface of TOI-1468 b is marginally hotter than expected. This indicates an additional source of energy on the planet. This source might originate from a temperature inversion or induction heating, or it might be an instrumental artefact. The results within the Hot Rocks Survey build on the legacy of studying the atmospheres of exoplanets around M dwarfs. The outcome of this survey will prove useful to the large-scale survey of M dwarfs that was recently approved by the STScI.

JWST NIRISS transmission spectroscopy of the super-Earth GJ 357b, a favourable target for atmospheric retention

Monthly Notices of the Royal Astronomical Society Oxford University Press 540:4 (2025) 3677-3692

Authors:

Jake Taylor, Michael Radica, Richard D Chatterjee, Mark Hammond, Tobias Meier, Suzanne Aigrain, Ryan J MacDonald, Loic Albert, Björn Benneke, Louis-Philippe Coulombe, Nicolas B Cowan, Lisa Dang, René Doyon, Laura Flagg, Doug Johnstone, Lisa Kaltenegger, David Lafrenière, Stefan Pelletier, Caroline Piaulet-Ghorayeb, Jason F Rowe, Pierre-Alexis Roy

Abstract:

We present a JWST Near Infrared Imager and Slitless Spectrograph/Single Object Slitless Spectroscopy transmission spectrum of the super-Earth GJ 357 b: the first atmospheric observation of this exoplanet. Despite missing the first 40 per cent of the transit due to using an out-of-date ephemeris, we still recover a transmission spectrum that does not display any clear signs of atmospheric features. We perform a search for Gaussian-shaped absorption features within the data but find that this analysis yields comparable fits to the observations as a flat line. We compare the transmission spectrum to a grid of atmosphere models and reject, to 3 confidence, atmospheres with metallicities solar (4 g mol−1) with clouds at pressures down to 0.01 bar. We analyse how the retention of a secondary atmosphere on GJ 357 b may be possible due to its higher escape velocity compared to an Earth-sized planet and the exceptional inactivity of its host star relative to other M2.5V stars. The star’s XUV luminosity decays below the threshold for rapid atmospheric escape early enough that the volcanic revival of an atmosphere of several bars of CO is plausible, though subject to considerable uncertainty. Finally, we model the feasibility of detecting an atmosphere on GJ 357 b with MIRI/LRS, MIRI photometry, and NIRSpec/G395H. We find that, with two eclipses, it would be possible to detect features indicative of an atmosphere or surface. Further to this, with three to four transits, it would be possible to detect a 1 bar nitrogen-rich atmosphere with 1000 ppm of CO.