91̽»¨

Abstract:

LTT-9779,b is an inhabitant of the hot-Neptune desert and one of only a few planets with a measured high albedo. Characterising the atmosphere of this world is the key to understanding the processes that dominate in reducing the number of short-period intermediate-mass planets that create the hot-Neptune desert. We aim to characterise the reflected light of LTT-9779,b at high spectral resolution to break the degeneracy between clouds and atmospheric metallicity. This is key to interpreting its mass-loss history, which might illuminate how it kept its place in the desert. We used the high-resolution cross-correlation spectroscopy technique on four half-nights of ESPRESSO observations in 4-UT mode (16.4 m effective mirror) to constrain the reflected-light spectrum of Å‚ttb. We did not detect the reflected-light spectrum of Å‚ttb, although these data had the expected sensitivity at the level 100 ppm. Injection tests of the post-eclipse data indicated that TiO should have been detected for a range of different equilibrium chemistry models. Therefore, this non-detection suggests TiO depletion in the western hemisphere, but this conclusion is sensitive to temperature, which affects the chemistry in the upper atmosphere and the reliability of the line list. Additionally, we were able to constrain the top of the western cloud deck to P_ top, western bar and the top of the eastern cloud deck to P_ top, eastern bar, which is consistent with the predicted altitude of MgSiO_3 and Mg_2SiO_4 clouds from JWST NIRISS/SOSS. While we did not detect the reflected-light spectrum of Å‚ttb, we verified that this technique can be used in practice to characterise the reflected light of exoplanets at high spectral resolution when their spectra contain a sufficient number of deep spectral lines. Therefore, this technique may become an important cornerstone of exoplanet characterisation with the ELT and beyond.

Abstract:

Substellar companions such as exoplanets and brown dwarfs exhibit changes in brightness arising from top-of-atmosphere inhomogeneities, providing insights into their atmospheric structure and dynamics. This variability can be measured in the light curves of high-contrast companions from the ground by combining differential spectrophotometric monitoring techniques with high-contrast imaging. However, ground-based observations are sensitive to the effects of turbulence in Earth’s atmosphere, and while adaptive optics (AO) systems and bespoke data processing techniques help to mitigate these, residual systematics can limit photometric precision. Here, we inject artificial companions to data obtained with an AO system and a vector Apodizing Phase Plate coronagraph to test the level to which telluric and other systematics contaminate such light curves, and thus how well their known variability signals can be recovered. We find that varying companions are distinguishable from non-varying companions, but that variability amplitudes and periods cannot be accurately recovered when observations cover only a small number of periods. Residual systematics remain above the photon noise in the light curves but have not yet reached a noise floor. We also simulate observations to assess how specific systematic sources, such as non-common path aberrations and AO residuals, can impact aperture photometry as a companion moves through pupil-stabilized data. We show that only the lowest order aberrations are likely to affect flux measurements, but that thermal background noise is the dominant source of scatter in raw companion photometry. Predictive control and focal-plane wavefront sensing techniques will help to further reduce systematics in data of this type.

Abstract:

We reanalyzed spectra that were taken as part of the SL2S lens galaxy survey with the goal to obtain the stellar velocity dispersion with a precision and accuracy sufficient for time-delay cosmography. In order to achieve this goal, we imposed stringent cuts on the signal-to-noise ratio (S/N), and employed recently developed methods to mitigate and quantify residual systematic errors that are transferred from template libraries and fitting process. We also quantified the covariance across the sample. For galaxy spectra with S/N $>20/$Ã…, our new measurements have an average random uncertainty of 3-4%, an average systematic uncertainty of 2%, and a covariance across the sample of 1%. We find a negligible covariance between spectra taken with different instruments. The systematic uncertainty and covariance need to be included when the sample is used as an external dataset in time-delay cosmography. We revisited empirical scaling relations of lens galaxies based on the improved kinematics. We show that the SL2S sample, the TDCOSMO time-delay lens sample, and the lower-redshift SLACS sample follow the same correlation of the effective radius, stellar velocity dispersion, and lensing mass, known as the lensing-mass fundamental plane, as the previously derived correlation that assumed isothermal mass profiles for the deflectors. We also derived for the first time the lensing-mass fundamental plane assuming free power-law mass density profiles, and we show that the three samples also follow the same correlation. This is consistent with a scenario in which massive galaxies evolve by growing their radii and mass, but stay within the plane.