Aims: In this work, we discuss a way to combine High Dispersion Spectroscopy and High Contrast Imaging (HDS+HCI). For a planet located at a resolvable angular distance from its host star, the starlight can be reduced up to several orders of magnitude
using adaptive optics and/or coronography. In addition, the remaining starlight can be filtered out using high-dispersion spectroscopy, utilizing the significantly different (or Doppler shifted) high-dispersion spectra of the planet and star. In this way, HDS+HCI can in principle reach contrast limits of ~1e-5 x 1e-5, although in practice this will be limited by photon noise and/or sky-background. Methods: We present simulations of HDS+HCI observations with the E-ELT, both probing thermal emission from a planet at infrared wavelengths, and starlight reflected off a planet atmosphere at optical wavelengths. For the infrared simulations we use the baseline parameters of the E-ELT and METIS instrument, with the latter combining extreme adaptive optics with an R=100,000 IFS. We include realistic models of the adaptive optics performance and atmospheric transmission and emission. For the optical simulation we also assume R=100,000 IFS with adaptive optics capabilities at the E-ELT. Results: One night of HDS+HCI observations with the E-ELT at 4.8 um (d_lambda = 0.07 um) can detect a planet orbiting alpha Cen A with a radius of R=1.5 R_earth and a twin-Earth thermal spectrum of T_eq=300 K at a signal-to-noise (S/N) of 5. In the optical, with a Strehl ratio performance of 0.3, reflected light from an Earth-size planet in the habitable zone of Proxima Centauri can be detected at a S/N of 10 in the same time frame. Recently, first HDS+HCI observations have shown the potential of this technique by determining the spin-rotation of the young massive exoplanet beta Pictoris b. [abridged]
[Abridged] Recently, there have been a series of detections of molecules in the atmospheres of extrasolar planets using high spectral resolution (R~100,000) observations, mostly using the CRyogenic high-resolution InfraRed Echelle Spectrograph (CRIRE
S) on the Very Large Telescope. These measurements are able to resolve molecular bands into individual absorption lines. Observing many lines simultaneously as their Doppler shift changes with time allows the detection of specific molecules in the atmosphere of the exoplanet. We performed simulations of high-resolution CRIRES observations of a planets thermal emission and transit between 1-5 micron and performed a cross-correlation analysis on these results to assess how well the planet signal can be extracted. We also simulated day-side and night-side spectra at high spectral resolution for planets with and without a day-side temperature inversion, based on the cases of HD 189733b and HD 209458b. Several small wavelength regions in the L-band promise to yield cross-correlation signals from the thermal emission of hot Jupiters that can exceed those of the current detections by up to a factor of 2-3 for the same integration time. For transit observations, the H-band is also attractive, with the H, K, and L-band giving cross-correlation signals of similar strength. High-resolution night-side spectra of hot Jupiters can give cross-correlation signals as high as the day-side, or even higher. We show that there are many new possibilities for high-resolution observations of exoplanet atmospheres that have expected planet signals at least as high as those already detected. Hence, high-resolution observations at well-chosen wavelengths and at different phases can improve our knowledge about hot Jupiter atmospheres significantly, already with currently available instrumentation.
