Spectroscopic Coronagraphy for Planetary Radial Velocimetry of Exoplanets

Abstract

We propose the application of coronagraphic techniques to the spectroscopic direct detection of exoplanets via the Doppler shift of planetary molecular lines. Even for an unresolved close-in planetary system, we show that the combination of a visible nuller and an extreme adaptive optics system can reduce the photon noise of a main star and increase the total signal-to-noise ratio (S/N) of the molecular absorption of the exoplanetary atmosphere: it works as a spectroscopic coronagraph. Assuming a 30 m telescope, we demonstrate the benefit of these high-contrast instruments for nearby close-in planets that mimic 55 Cnc b ($0.6\lambda /D$ of the angular separation in the K band). We find that the tip-tilt error is the most crucial factor; however, low-order speckles also contribute to the noise. Assuming relatively conservative estimates for future wavefront control techniques, the spectroscopic coronagraph can increase the contrast to $\sim 50-130$ times and enable us to obtain $\sim 3-6$ times larger S/N for warm Jupiters and Neptunes at 10 pc those without it. If the tip-tilt error can be reduced to $\lesssim 0.3$ mas (rms), it gains $\sim 10-30$ times larger S/N and enables us to detect warm super-Earths with an extremely large telescope. This paper demonstrates the concept of spectroscopic coronagraphy for future spectroscopic direct detection. Further studies of the selection of coronagraphs and tip-tilt sensors will extend the range of application of the spectroscopic direct detection beyond the photon collecting area limit.

9 pages, 7 figures, accepted for publication in ApJS, minor changes to match the proof

References in corpus (2)

• Weighing The Non-Transiting Hot Jupiter Tau BOO b
• The Spin Effect on Planetary Radial Velocimetry of Exoplanets

Cited by in corpus (12)

• Combining high-dispersion spectroscopy (HDS) with high contrast imaging (HCI): Probing rocky planets around our nearest neighbors
• Theoretical Emission Spectra of Atmospheres of Hot Rocky Super-Earths
• Enhancing stellar spectroscopy with extreme adaptive optics and photonics
• The composition of hot Jupiter atmospheres assembled within chemically evolved protoplanetary discs
• The Pale Green Dot: A Method to Characterize Proxima Centauri b using Exo-Aurorae
• Direct characterization of young giant exoplanets at high spectral resolution by coupling SPHERE and CRIRES+
• Auto-Differentiable Spectrum Model for High-Dispersion Characterization of Exoplanets and Brown Dwarfs
• Synergies between Venus & Exoplanetary Observations
• Detecting Proxima b's atmosphere with JWST targeting CO2 at 15 micron using a high-pass spectral filtering technique
• Spectral unmixing for exoplanet direct detection in hyperspectral data
• High-contrast Demonstration of an Apodized Vortex Coronagraph
• Exoplanets Sciences with Nulling Interferometers and a Single-Mode Fiber-Fed Spectrograph