Extremely Large Telescope

Abstract:

The spectrum of an exoplanet reveals the physical, chemical, and biological processes that have shaped its history and govern its future. However, observations of exoplanet spectra are complicated by the overwhelming glare of their host stars. Here, we focus on high-resolution spectroscopy (HRS) (R∼5,000−140,000), which helps disentangle and isolate the exoplanet’s spectrum. HRS resolves molecular features into a dense forest of individual lines in a pattern that is unique for a given molecule. For close-in planets, the spectral lines undergo large Doppler shifts during the planet’s orbit, while the host star and Earth’s spectral features remain essentially stationary, enabling a velocity separation of the planet. For slower-moving, wide-orbit planets, HRS, aided by high contrast imaging, instead isolates their spectra using their spatial separation (high contrast spectroscopy; HCS). The planet’s spectral lines are compared with HRS model atmospheric spectra, typically using cross-correlation to sum their signals. It is essentially a form of fingerprinting for exoplanet atmospheres and works for both transiting and non-transiting planets. It measures their orbital velocity, true mass, and simultaneously characterizes their atmosphere. The unique sensitivity of HRS to the depth, shape, and position of the planet’s spectral lines allows it to measure atmospheric composition, structure, clouds, and dynamics, including day-to-night winds and equatorial jets, plus its rotation period and even its magnetic field. These are extracted using statistically robust log-likelihood frameworks and match space-based instruments in their precision. This chapter describes the HRS technique in detail and concludes with future prospects with Extremely Large Telescopes to identify biosignatures on nearby rocky worlds and map features in the atmospheres of giant exoplanets.

Abstract:

Time-delay cosmography leverages strongly lensed quasars to measure the Universe's current expansion rate, _ independently from other methods. The latest TDCOSMO milestone measurement primarily used quadruply lensed quasars for their mass profile constraints. However, doubly lensed quasars, being more abundant and offering precise time delays, could expand the sample by a factor of 5, significantly advancing towards a 1% precision measurement of We present the first TDCOSMO analysis of a doubly imaged source, ̋Eonze, including the measurement of the four necessary ingredients. First, by combining 17 years of data from the SMARTS, Euler, and WFI telescopes, we measured a time delay of 176.3 +11.4 -10.3 days. Second, using MUSE data, we extracted stellar velocity dispersion measurements in three radial bins with 5% to 13% precision. Third, employing F160W HST imaging for lens modelling and marginalising over various modelling choices, we measured the Fermat potential difference between the images. Fourth, using wide-field imaging, we measured the convergence added by objects not included in the lens modelling. By combining these four ingredients, we measured the time delay distance and the angular diameter distance to the deflector, favouring a power-law mass model over a baryonic and dark matter composite model. The measurement was performed blindly to prevent experimenter bias and resulted in a Hubble constant of hc = 64.2^ +5.8 _ -5.0 times łint ̨msmpc, where łint is the internal mass sheet degeneracy parameter. This is in agreement with the TDCOSMO-2025 milestone and its precision for łint=1 is comparable to that obtained with the best-observed quadruply lensed quasars (4-6%). This work is a stepping stone towards a precise measurement of using a large sample of doubly lensed quasars, supplementing the current sample. The next TDCOSMO milestone paper will include this system in its hierarchical analysis, constraining łint and jointly with multiple lenses.