High Resolution Spectroscopy and High Contrast Imaging with the ELT : looking for O$_2$ in Proxima b

Abstract: We research the requirements of High Contrast Imaging when combined with the cross correlation (CC) of high resolution spectra with known spectroscopic templates for detecting and characterising exoplanets in reflected light. We simulate applying the technique to a potentially habitable Proxima b-like planet and show that the O$2$ A-band spectral feature could feasibly be detected on nearby rocky exoplanets using future instruments on the ELT . The technique is then more widely analysed showing that detections of planets and O$_2$ with signal to noise in the CC function (SNR${CC}$) > 3 can be obtained when the signal to noise of the simulated planet spectrum (SNR$_{spec}$) is from 0.25 to 1.2. We place constraints on the spectral resolution, instrument contrast, point spread function (PSF), exposure times and systematic error in stellar light subtraction for making such detections. We find that accurate stellar light subtraction (with 99.99% removal) and PSFs with high spatial resolutions are key to making detections. Lastly a further investigation suggests the ELT could potentially discover and characterise planets of all sizes around different spectral type stars, as well as detecting O$_2$ on Super-Earths with habitable zone orbits around nearby M stars.