Exoplanet atmospheres

Abstract:

We investigate the properties of the interstellar medium, star formation, and the current-day stellar population in the strongly lensed star-forming galaxy H-ATLAS J091043.1-000321 (SDP.11), at z = 1.7830, using new Herschel and Atacama Large Millimeter/submillimeter Array (ALMA) observations of far-infrared fine-structure lines of carbon, oxygen, and nitrogen. We report detections of the [O iii] 52 μm, [N iii] 57 μm, and [O i] 63 μm lines from Herschel/PACS, and present high-resolution imaging of the [C ii] 158 μm line, and underlying continuum, using ALMA. We resolve the [C ii] line emission into two spatially offset Einstein rings, tracing the red and blue velocity components of the line, in the ALMA/Band 9 observations at 0farcs2 resolution. The values seen in the [C ii]/far-infrared (FIR) ratio map, as low as ~0.02% at the peak of the dust continuum, are similar to those of local ULIRGs, suggesting an intense starburst in this source. This is consistent with the high intrinsic FIR luminosity (~3 × 1012 L ⊙), ~16 Myr gas depletion timescale, and lesssim8 Myr timescale since the last starburst episode, estimated from the hardness of the UV radiation field. By applying gravitational lensing models to the visibilities in the uv-plane, we find that the lensing magnification factor varies by a factor of two across SDP.11, affecting the observed line profiles. After correcting for the effects of differential lensing, a symmetric line profile is recovered, suggesting that the starburst present here may not be the result of a major merger, as is the case for local ULIRGs, but instead could be powered by star formation activity spread across a 3–5 kpc rotating disk.

Abstract:

Phase curves are the best technique to probe the three-dimensional structure of exoplanets' atmospheres. In this chapter we first review current exoplanets' phase curve observations and the particular challenges they face. We then describe the different physical mechanisms shaping the atmospheric phase curves of highly irradiated tidally locked exoplanets. Finally, we discuss the potential for future missions to further advance our understanding of these new worlds.

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. This chapter focuses on high-resolution spectroscopy (HRS) (R = 25, 000–100, 000), which helps to disentangle and isolate the exoplanet’s spectrum. At high spectral resolution, molecular features are resolved 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. The lines in the exoplanet spectrum are detected by comparing them with high resolution spectra from atmospheric modelling codes; essentially a form of fingerprinting for exoplanet atmospheres. This measures the planet’s orbital velocity and helps define its true mass and orbital inclination. Consequently, HRS can detect both transiting and non-transiting planets. It also simultaneously characterizes the planet’s atmosphere, due to its sensitivity to the depth, shape, and position of the planet’s spectral lines. These are altered by the planet’s atmospheric composition, structure, clouds, and dynamics, including day-to-night winds and its rotation period. This chapter describes the HRS technique in detail, highlighting its successes in exoplanet detection and characterization, and concludes with the future prospects of using HRS to identify biomarkers on nearby rocky worlds and map features in the atmospheres of giant exoplanets.