Imaging & Spectroscopy

Direct Detection And Characterization Of Exoplanets Using Imaging Fourier Transform Spectroscopy

By Keith Cowing
Status Report
October 30, 2023
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Direct Detection And Characterization Of Exoplanets Using Imaging Fourier Transform Spectroscopy
Examples of simulation result for an Earth twin at 10 pc in a visible (710-800 nm, R=140, top) and NIR bandpass (1050-1250 nm, R = 70, bottom). (a)&(d): simulated interferogram of a two-port iFTS, with a Boxcar apodization function. Red points are the difference of intensity at two outputs at each scanning step, with error bars from photon noise and detector noise. (b)&(e) present simulated spectra for an iFTS (red) and an IFS (blue). (c)&(f) present the analytical and numerical signal-to-noise ratios of an iFTS (red) and an IFS (blue). Here, we use a 6 m sized telescope with dark current of 0.77 e−/hr/pix for the visible camera and readout noise of 5.9 e−/frame/pix for the NIR camera with a frame time of 1000s. The SNRs are computed for a 500 hrs exposure time analytically and numerically. Other instrument parameters see in Table 2. — astro-ph.EP

Space-based direct imaging provides prospects for detection and spectral characterization of exoplanets at optical and near-infrared wavelengths. Integral field spectrographs (IFS) have been historically baselined for these mission concepts.

However, multiple studies have revealed that detector noise is a serious obstacle for such instruments when observing extremely faint targets such as Earth-like planets. Imaging Fourier transform spectrographs (iFTS) are generally less sensitive to detector noise, and have several other compelling features such as simultaneous imaging and spectroscopy, smaller-format detector requirements, and variable spectral resolution. To date, they have not been studied as options for such missions.

In this work, we compare the capabilities of integral field spectrographs and imaging Fourier transform spectrographs to directly obtain spectra from an Earth-like planet using analytic and numerical models. Specifically, we compare the required exposure time to achieve the same signal-to-noise ratio of the two architectures over a range of detector and optical system parameters. We find that for a 6-meter telescope, an IFS outperforms an iFTS at optical wavelengths.

In the near-IR, the relative efficiency of an IFS and iFTS depends on the instrument design and detector noise. An iFTS will be more efficient than an IFS if the readout noise of near-IR detector is above 2-3 e-/pix/frame (t_frame=1000s), which correspond to half to one-third of detector noise of the state-of-art. However, if the readout noise is further reduced to below this threshold, the performance of an IFS will experience a substantial improvement and become more efficient. These results motivate consideration of an iFTS as an alternative option for future direct imaging space missions in the near-IR.

Jingwen Zhang, Michael Bottom, Eugene Serabyn

Comments: 26 pages, 13 pages, submitted to PASP
Subjects: Earth and Planetary Astrophysics (astro-ph.EP); Instrumentation and Methods for Astrophysics (astro-ph.IM)
Cite as: arXiv:2310.15231 [astro-ph.EP] (or arXiv:2310.15231v1 [astro-ph.EP] for this version)
Submission history
From: Jingwen Zhang
[v1] Mon, 23 Oct 2023 18:00:06 UTC (3,219 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) 🖖🏻