arXiv subjects

H. Diamond-Lowe

Publications and source records attributed to H. Diamond-Lowe.

4 recordsLinked to original sources

arXiv2026

Enhancing the performance and capabilities of the MIRI instrument on JWST

MIRI, the Mid-Infrared Instrument on the James Webb Space Telescope, is the only instrument sensitive to wavelengths longward of 5 um on the observatory. In this regime, MIRI brings order-of-magnitude improvements over past instruments and missions in a wavelength range that is challenging or impossible to access from the ground. As such, MIRI occupies a unique parameter space, offering unparalleled capabilities in all areas of astrophysics, from the Solar System to the most distant galaxies in the Universe. We continue to make operational improvements to MIRI, four years into its operational lifetime, to create new observing opportunities, improve performance, and enhance its scientific return. In this paper we will describe several such improvements, and their anticipated impact on MIRI and JWST science.

astro-ph.IM↗

arXiv2026

Atmospheric constraints on GJ 1214 b from CRIRES+ and prospects for characterisation with ANDES

In this study, we aim to constrain the atmospheric composition of GJ 1214 b using all available transits observed with the upgraded CRIRES+ spectrograph at the VLT by searching for the signatures of water vapour, methane, and carbon dioxide. We analysed eight CRIRES+ transit datasets covering the K band (1.90-2.45 microns) at a resolving power of R ~ 100,000. We used the SysRem algorithm to correct for telluric and stellar contributions and employed the cross-correlation technique with templates from petitRADTRANS to search for H2O, CH4, and CO2. Injection-recovery tests across a grid of metallicities (Z) and cloud-deck pressures (pc) were performed to quantify detection limits. We also generated predictions for ANDES observations using end-to-end simulated datasets with EXoPLORE. We detect no significant H2O, CH4, or CO2 signatures. Injection-recovery tests show that such non-detections exclude atmospheres with low-altitude clouds and moderate or low metallicities. CH4 yields the tightest empirical limits, with CO2 unexpectedly ruling out intermediate metallicities (~ 100xsolar) with clouds deeper due to its rapidly rising opacity in compressed, high-Z atmospheres. Our constraints are in line with either a high-Z or a high-altitude aerosol layer, in agreement with recent JWST inferences. The combined analysis of eight CRIRES+ datasets provides the most stringent high-resolution constraints on the atmospheric properties of GJ 1214 b to date. Simulations of a single transit observed with ANDES on the ELT predict modest improvements for H2O, a substantially expanded detectable region for CH4, and the strongest gains for CO2, making the latter a particularly effective tracer for characterising high-metallicity atmospheres in sub-Neptunes.

astro-ph.EP↗

arXiv2025

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

Terrestrial exoplanets orbiting nearby small, cool stars known as M dwarfs are well suited for atmospheric characterisation. Given the strong XUV irradiation from M dwarf host stars, orbiting exoplanets are thought to be unable to retain primordial H/He-dominated atmospheres. However, the survivability of heavier secondary atmospheres is currently unknown. The aim of the Hot Rocks Survey programme is to determine if exoplanets can retain secondary atmospheres in the presence of M dwarf hosts. Among the sample of 9 exoplanets in the programme, here 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 $μ$m. TOI-1468 b's occultation was observed three times. We compare our observations to atmospheric models including varying amounts of CO$_{2}$ and H$_{2}$O. The observed occultation depth for the individual visits are 239$\pm$52 ppm, 341$\pm$53 ppm and 357$\pm$52 ppm. A joint fit yields an occultation depth of 311$\pm$31 ppm. The thermal emission is mostly consistent with no atmosphere and zero Bond albedo at 1.65-$σ$ confidence level or a blackbody at a brightness temperature of 1024$\pm$78 K. A pure CO$_{2}$ or H$_{2}$O atmosphere with a surface pressure above 1 bar is ruled out over 3-$σ$. Surprisingly, TOI-1468 b presents a surface marginally hotter than expected, hinting at an additional source of energy on the planet. It could originate from a temperature inversion, induction heating or be an instrumental artifact. 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 on M dwarfs recently approved by the STScI.

astro-ph.EP↗

arXiv2024

High-energy spectra of LTT 1445A and GJ 486 reveal flares and activity

The high-energy radiative output, from the X-ray to the ultraviolet, of exoplanet host stars drives photochemical reactions and mass loss in the upper regions of planetary atmospheres. In order to place constraints on the atmospheric properties of the three closest terrestrial exoplanets transiting M dwarfs, we observe the high-energy spectra of the host stars LTT1445A and GJ486 in the X-ray with XMM-Newton and Chandra and in the ultraviolet with HST/COS and STIS. We combine these observations with estimates of extreme ultraviolet flux, reconstructions of the Ly-a lines, and stellar models at optical and infrared wavelengths to produce panchromatic spectra from 1A--20um for each star. While LTT1445Ab, LTT1445Ac, and GJ486b do not possess primordial hydrogen-dominated atmospheres, we calculate that they are able to retain pure CO2 atmospheres if starting with 10, 15, and 50% of Earth's total CO2 budget, respectively, in the presence of their host stars' stellar wind. We use age-activity relationships to place lower limits of 2.2 and 6.6 Gyr on the ages of the host stars LTT1445A and GJ486. Despite both LTT1445A and GJ486 appearing inactive at optical wavelengths, we detect flares at ultraviolet and X-ray wavelengths for both stars. In particular, GJ486 exhibits two flares with absolute energies of 10^29.5 and 10^30.1 erg (equivalent durations of 4357+/-96 and 19724+/-169 s) occurring three hours apart, captured with HST/COS G130M. Based on the timing of the observations, we suggest that these high-energy flares are related and indicative of heightened flaring activity that lasts for a period of days, but our interpretations are limited by sparse time-sampling. Consistent high-energy monitoring is needed to determine the duration and extent of high-energy activity on individual M dwarfs, as well as the population as a whole.

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