NIRISS Exploration of the Atmospheric diversity of Transiting exoplanets (NEAT) program is a GTO program designed to study exoplanet atmospheric composition, energy budget, and dynamics. The main science goal is to obtain NIRISS single object slitless spectroscopy (SOSS) transit observations of a sample of 14 exoplanets. These targets span a temperature range from 300 – 3000 K and mass range from 1 Earth to 2 Jupiter masses. By spanning a range of both temperatures and masses, the NEAT program will consider a large span of planet formation and evolution regimes.
The NIRISS SOSS mode is designed to obtain spectra in the 0.6 – 2.8 μm wavelength range for a single source on the NIRISS detector. SOSS disperses the light both spectroscopically and spatially—to optimize for bright object time series observations—using the GR700XD grism coupled with a cylindrical lens. Because SOSS requires all TSO observations to be taken on the same pixels for maximum reproducibility over the lifetime of the mission, a target acquisition is required for all SOSS observations observed with a subarray (and strongly encouraged in full frame readout mode) to accurately position the source on the detector.
NIRISS SOSS is the only JWST observing mode that permits slitless spectroscopy between 0.6 and 2.8 μm and is thus well-suited to characterize exoplanet atmospheres. Five molecules of interest in exoplanet atmospheres (water, carbon monoxide, hydrogen cyanide, methane, and ammonia) are expected to show significant spectral features in the SOSS wavelength range—depending on atmospheric pressure and temperature. The spectroscopic resolution (R ~ 700 at 1.25 μm) and large cross-dispersion (which minimizes systematic errors) make SOSS optimal for exoplanet observations because the signal-to-noise ratios (SNR) of the host stars is greatest at lower wavelengths, enabling better precision in the measurement of exoplanet atmospheres.
The Step-by-Step ETC Guide walks the user through navigating the JWST Exposure Time Calculator (ETC) to determine exposure parameters appropriate for the science goals for this program, providing a conservative average SNR estimate.
The Step-by-Step PandExo Guide provides a more robust spectroscopic SNR estimate, using the same calculation engine as ETC (Pandeia).
The Astronomer Proposal Tool (APT) is used to submit JWST proposals. The Step-by-Step APT Guide provides instructions for filling out the APT observation templates. The exposure parameters determined by the ETC are specified in the APT observation template.
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