Studies of atmospheres of directly imaged extrasolar planets with high-resolution spectrographs have shown that their characterization
is predominantly limited by noise on the stellar halo at the location of the studied exoplanet. An instrumental combination of highcontrast imaging and high spectral resolution that suppresses this ...
Studies of atmospheres of directly imaged extrasolar planets with high-resolution spectrographs have shown that their characterization
is predominantly limited by noise on the stellar halo at the location of the studied exoplanet. An instrumental combination of highcontrast imaging and high spectral resolution that suppresses this noise and resolves the spectral lines can therefore yield higher quality
spectra. We study the performance of the proposed HiRISE fiber coupling between the direct imager SPHERE and the spectrograph
CRIRES+ at the Very Large Telescope for spectral characterization of directly imaged planets. Using end-to-end simulations of
HiRISE we determine the signal-to-noise ratio (S/N) of the detection of molecular species for known extrasolar planets in H and K
bands, and compare them to CRIRES+. We investigate the ultimate detection limits of HiRISE as a function of stellar magnitude, and
we quantify the impact of different coronagraphs and of the system transmission. We find that HiRISE largely outperforms CRIRES+
for companions around bright hosts like β Pictoris or 51 Eridani. For an H = 3.5 host, we observe a gain of a factor of up to 36 in
observing time with HiRISE to reach the same S/N on a companion at 200 mas. More generally, HiRISE provides better performance
than CRIRES+ in two-hour integration times between 50–400 mas for hosts with H < 8.5 and between 50–800 mas for H < 7. For
fainter hosts like PDS 70 and HIP 65426, no significant improvements are observed. We find that using no coronagraph yields the
best S/N when characterizing known exoplanets due to higher transmission and fiber-based starlight suppression. We demonstrate
that the overall transmission of the system is in fact the main driver of performance. Finally, we show that HiRISE outperforms the
best detection limits of SPHERE for bright stars, opening major possibilities for the characterization of future planetary companions
detected by other techniques
