NIRISS SOSS Time-Series Observations of HAT-P-1
This goal of this example program is to observe the exoplanet transit of HAT-P-1b, and is based on the GTO program "NIRISS Exploration of the Atmospheric diversity of Transiting exoplanets (NEAT)". NEAT is designed to study exoplanet atmospheric composition, energy budget, and dynamics.
Example Science Program #31
This example program was constructed pre-launch, and details may be out of date with actual observatory performance. However, it still provides a useful example for training purposes.
Please refer to JWST Example Science Programs for more information.
On this page
See also: Step-by-Step ETC Guide for NIRISS SOSS Time-Series Observations of HAT-P-1, Step-by-Step APT Guide for NIRISS SOSS Time-Series Observations of HAT-P-1
Steps for creating observations
Step 1 - Determine the required wavelength coverage: near-infrared or mid-infrared
NIRCam Grism Time Series, NIRISS Single Object Slitless Spectroscopy, NIRSpec Bright Object Time-Series Spectroscopy,
MIRI Low Resolution Spectroscopy
Five molecules of interest in exoplanet atmospheres (water, carbon monoxide, hydrogen cyanide, methane, and ammonia) are expected to show significant spectral features at near-infrared wavelengths—depending on atmospheric pressure and temperature. The signal-to-noise ratios (SNR) of the host stars is greatest at lower wavelengths, enabling better precision in the measurement of exoplanet atmospheres. We thus omit MIRI low resolution spectroscopy from consideration, as well as NIRCam grism time series since that only provides coverage between 2.4–5.0 μm, at longer wavelengths than NIRISS single object slitless spectroscopy (SOSS) and NIRSpec bright object time-series spectroscopy.
Step 2- Select an instrument observing mode
See also: NIRISS SOSS Recommended Strategies
NIRISS SOSS simultaneously covers the wavelength range from 0.6–2.8 μm. NIRSpec bright object time-series spectroscopy would require 2 visits to achieve the same wavelength coverage. The SOSS slitless configuration avoids pointing-related flux variations, and combined with the cross-dispersed properties, minimizes flat field and intra-pixel gain variation issues. We thus chose the NIRISS SOSS observing mode for this program.
Step 3 - Determine the readout pattern and subarray configuration
See also: NIRISS Detector Readout Patterns, NIRISS Detector Subarrays
Words in bold are GUI menus/
panels or data software packages;
bold italics are buttons in GUI
tools or package parameters.
We chose the NISRAPID readout pattern (where there is 1 frame per group) which is the only permitted readout pattern when using a subarray in the SOSS mode.
Step 4 - Calculate required exposure configuration using the JWST Exposure Time Calculator (ETC)
See also: JWST Exposure Time Calculator Overview, JWST Time-Series Observations TSO Saturation
To determine the exposure parameters for this observation using the JWST Exposure Time Calculator (ETC), please see the article Step-by-Step ETC Guide for NIRISS SOSS Time-Series Observations of HAT-P-1. Note the ETC is useful for a conservative, average SNR estimate.
Step 5 - Use PandExo for more detailed modeling of spectroscopic exoplanet transits
Interested users are encouraged to use PandExo (Batalha et al. 2017) for detailed modeling of exoplanet transits and to optimize exposure configurations for their observing program.
Step 6 - Determine whether target acquisition is required and use the ETC to determine the appropriate strategy
See also: NIRISS Target Acquisition
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. The step-by-step ETC guide for this example science program details how to determine exposure parameters for a successful target acquisition for this program.
Step 7 - Complete the Astronomer's Proposal Tool (APT) template
For details filling out the Astronomer's Proposal Tool (APT) for this example science program, please see the article Step-by-Step APT Guide for NIRISS SOSS Time-Series Observations of HAT-P-1.
Batalha, N. E., Mandell, A., Pontoppidan, K., et al. 2017, PASP, 129, 064501 (ADS)
PandExo: A Community Tool for Transiting Exoplanet Science with JWST & HST