The search for and characterization of exoplanets are among the most active and rapidly advancing fields in modern astrophysics. The initial caution after the first bewildering discoveries has given way to a succession of discoveries with neck-breaking pace. To date, more than 4000 exoplanets have been detected, spanning wide ranges in physical, orbital and stellar parameters, and with a great variety of system architectures. The observed exoplanet diversity has revolutionized our view of planetary system formation and evolution, for which the Solar System is no longer the paradigm. Understanding the causes of exoplanet diversity and variety is an objective of the next-generation of ESA/NASA missions.
My scientific goal is to answer outstanding questions such as:
1. What is the bulk composition of exoplanets?
2. How does it relate with the other observable parameters (e.g., host star abundances, ages, stellar and planetary masses, radii, orbital parameters)?
3. How did exoplanet systems form and evolve?
To answer these questions, I make use of state-of-the-art techniques that enable spectroscopic observations of the exoplanet atmospheres, providing information on their chemical composition, thermal state and dynamics.
Transit/eclipse/phase-curve spectroscopy rely on measurements of the combined star+exoplanet flux as a function of the orbital phase. Transits are revealed by a few percent periodic decrement in flux as the planet occults part of the stellar disk, leading to measurements of the exoplanet size, along with estimates of the orbital parameters and stellar mean density. Eclipses can provide a direct measure of the emergent flux from the planet’s dayside as the star occults the planet. Phase-curve observations give the planetary flux with varying viewing angle.
Transmission and emission spectra of dozens of exoplanet atmospheres have been obtained from measurements of transit and eclipse depths, respectively, at multiple wavelengths. These spectra have enabled detection of chemical species, clouds and haze in exoplanet atmospheres, together with constraints on their vertical temperature and density profiles. Thermal phase-curves have informed us about the atmospheric circulation and transport processes in a dozen planets.
The scientific inferences are mostly limited by the low signal-to-noise ratio, the poor wavelength coverage and low spectral resolution (R <200), the potential bias arising from the imperfect removal of instrumental systematic effects and/or other astrophysical signals.
I have extensive experience in the analysis of transit, eclipse and phase-curve data obtained from many space observatories, including the development of specialized data detrending pipelines for the removal of instrument systematics (Morello, 2015; Morello et al., 2014, 2015, 2016, 2019; Damiano et al., 2017) and high-precision stellar modeling (Morello et al., 2017; Morello, 2018; Howarth & Morello, 2017). Recently, I contributed to the creation of the largest catalog of exoplanet atmospheres (Tsiaras et al. 2018), containing the transmission spectra of thirty gaseous planets observed with HST/WFC3 at 1.1-1.7 μm. We revealed the presence of water vapour in all of the statistically detectable atmospheres, and the signature of TiO/VO absorption in the atmospheres of WASP-76 b (4 σ) and WASP-121 b (hints). We also detected for the first time gaseous absorption in a super-Earth atmosphere (Tsiaras et al. 2016).
High-resolution Doppler spectroscopy from ground-based telescopes is now emerging as a powerful complementary method. It relies on phase-resolved spectra of the star-planet system with resolution 
. These spectra are routinely used to measure the radial velocity variations of the parent star due to the gravitational pull exerted by the planet, which provide constraints on the planet’s mass and orbital parameters. Many algorithms have been adopted to remove the stellar and telluric spectra and the best practices are still being improved. The spectral lines from the planet undergo orders-of-magnitude larger Doppler shifts than telluric and stellar lines, making them easier to disentangle. The planetary signal can be enhanced by cross-correlation with template spectra containing the expected chemical species, taking into account the Doppler shifts due to the varying radial velocity of the planet. A high-significance peak in the cross-correlation denotes detection of species in the template spectrum along with the planet’s radial velocity.