The ETC has not implemented any specific features for Solar System targets, but can be used to approximate reflected sunlight and thermal emission from them.
Main article: JWST Exposure Time Calculator Overview
Reflected light can be approximated using the Phoenix stellar model G2V template spectrum, and thermal emission can be approximated using the blackbody template. The user must determine the correct normalizations to apply to those template spectra in order to accurately represent the emission from their target on a given date. Targets expected to have both reflected-light and thermal emission components within the wavelength range of interest can be specified as two sources that coincide in the ETC scene.
Normalizing target spectra
The emission from a target has to be normalized in a way to represent the physics controlling the flux density of the spectrum as received at JWST. These factors include:
Point and extended sources
For targets too small to be resolved by JWST, the spectrum can be modeled using the ETC point-source target type.
Extended targets can also be specified in the ETC as elliptical shapes with brightness distributions that are flat, Gaussian, or Sersic profiles (the last is typically used for galaxies). An r-k power law for modeling comet comae is included starting in ETC v1.3.
For observers interested in Jupiter, Saturn, Mars, and highly-extended comets, capabilities of the web interface of the ETC limit the size of the scene to a few arc seconds across. This doesn't prevent estimates of SNR for a given observation, but does require observers to properly normalize the surface brightnesses of these sources, a feature available starting in ETC v1.2.
User supplied spectra
Main article: JWST ETC User Supplied Spectra
The ETC allows users to upload their own spectra for sources. ASCII and FITS format are supported, and the spectrum in either case consists of two vectors containing wavelength and flux density. Format and other requirements are described in the ETC documentation and help (see JWST ETC User Supplied Spectra).
Main article: JWST ETC Using the Sample Workbooks
The ETC contains a moving target sample workbook with two scenes specified:
See JWST Moving Target Useful References and Links for instructions on how to access the sample workbook. These workbooks are primarily focused on providing examples of how to construct an ETC scene useful for solar system observers. Details of how to specify ETC calculations (which equate to observations in APT) are given in detail in other workbooks that are specific to the instruments.
The ETC does not currently have:
One or more of these template spectra may be implemented instead as a library of spectra users can share external to the ETC, and then upload rather than residing within the ETC as true template spectra. As these materials are completed, observers can find additional information on this page, and should look for announcements on solar system community forums such as the DPS and PEN newsletters.
The engine driving ETC calculations, along with necessary throughput curves for imaging and spectral performance data and a library of monochromatic PSF models, are available to the community as the Pandeia Python package, which can be installed from here (Pontoppidan et al., 2016). As with template spectra, a community-based effort to develop an interface to Pandeia that can serve the needs of the solar system science community will be discussed at various community forums.
Pontoppidan, K. M., Pickering, T. E., Laidler, V. G. et al., 2016, Proc. SPIE9910, Observatory Operations: Strategies, Processes, and Systems VI, 991016