Imaging & Spectroscopy

Exoplanets Detection Limits Using Spectral Cross-correlation With Spectro-imaging. An Analytical Model Applied To The Case Of ELT-HARMONI

By Keith Cowing
Status Report
November 24, 2023
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Exoplanets Detection Limits Using Spectral Cross-correlation With Spectro-imaging. An Analytical Model Applied To The Case Of ELT-HARMONI
Evolution of the S/N (relative to its maximum) with the spectral resolution, for a fixed number of pixels (3300 pixels per spectrum here, corresponding to the case of HARMONI) and a correspondingly variable bandwidth. The largest spectral range is set to cover the H and K bands H (from 1 µm to 2.8 µm) for three different templates of planets signature. These maps include only the photon noise, not considering any wavelength-dependant instrumental transmission, which makes this result quite generic, informative of the planetary spectra properties and not of the instrument specificities. Three different planet temperatures are considered: 500 K (left), 1200 K (middle) and 1700 K (right). — astro-ph.IM

The combination of high-contrast imaging and medium to high spectral resolution spectroscopy offers new possibilities for the detection and characterization of exoplanets. The molecular mapping technique uses the difference between the planetary and stellar spectra.

While traditional post-processing techniques are quickly limited by speckle noise at short angular separation, it efficiently suppresses speckles. Its performance depends on multiple parameters such as the star magnitude, the adaptive optics residual halo, the companion spectrum, the telluric absorption, as well as the telescope and instrument properties. Exploring this parameter space through end-to-end simulations to predict potential science cases and to optimize future instrument designs is very time-consuming, making it difficult to draw conclusions.

We propose to define an efficient methodology for such an analysis. Explicit expressions of the estimates of signal and noise are derived, and they are validated through comparisons with end-to-end simulations. They provide an understanding of the instrumental dependencies, and help to discuss optimal instrumental choices with regard to the targets of interest. They are applied in the case of ELT/HARMONI, as a tool to predict the contrast performance in various observational cases. We confirm the potential of molecular mapping for high-contrast detections, especially for cool planets at short separations. We provide guidelines based on quantified estimates for design trade-offs of future instruments.

We discuss the planet detection performances of HARMONI observing modes. While they nicely cover the appropriate requirements for high detection capability of warm exoplanets, a transmission extended down to J band would be beneficial. A contrast of a few 1E-7 at 50mas should be within reach on bright targets in photon noise regime with molecular mapping.

Alexis Bidot, David Mouillet, Alexis Carlotti

Comments: 19 pages
Subjects: Instrumentation and Methods for Astrophysics (astro-ph.IM)
Cite as: arXiv:2311.13275 [astro-ph.IM] (or arXiv:2311.13275v1 [astro-ph.IM] for this version)
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Submission history
From: Alexis Carlotti
[v1] Wed, 22 Nov 2023 09:51:58 UTC (8,704 KB)

Explorers Club Fellow, ex-NASA Space Station Payload manager/space biologist, Away Teams, Journalist, Lapsed climber, Synaesthete, Na’Vi-Jedi-Freman-Buddhist-mix, ASL, Devon Island and Everest Base Camp veteran, (he/him) 🖖🏻