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Roman Space Telescope

Anticipated Performance Tables for the Roman WFI

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These tables are provided in support of the Request for Information on the Roman Early Definition Astrophysics Survey Option.

The first set of tables gives the exposure time required to reach a fixed signal-to-noise ratio as a function of AB magnitude. Users can select the source size (point sources and exponential disks with half-light radius 0.2” and 0.3”), for four levels of zodiacal light. Tables are then available for various values of signal-to-noise and various size photometric apertures.


The second set of tables gives the imaging signal-to-noise expected as a function of AB magnitude for a single observation at 55, 75, or 106 second integration time, for the magnitude range 17 < AB < 25.


The next set of three tables gives exposure time requirements to reach fixed signal-to-noise per pixel for the slitless grism, again as a function of source AB magnitude. Here the columns correspond to specific wavelengths distributed over the spectrum to illustrate how the time to reach a given S/N varies with wavelength. The three tables are for half-light radii of 0, 0.2, and 0.3 arcseconds, and the signal-to-noise calculations assume an optimal weighted extraction of the spectrum.


The next set of three tables gives exposure time requirements to reach fixed signal-to-noise per pixel for the slitless prism, again as a function of source AB magnitude. Here the columns correspond to specific wavelengths distributed over the spectrum. Note that the prism dispersion is a strong function of wavelength and the widths of the pixels vary, being relatively narrow at the blue end and considerably wider at redder wavelengths. The three tables are for half-light radii of 0, 0.2, and 0.3 arcseconds, and the signal-to-noise calculations assume an optimal weighted extraction of the spectrum.


The last table gives the time for a point source to saturate, as a function of magnitude, which will be useful for exploring the bright end limits of Roman performance.



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IPAC/Caltech
Space Telescope Science Institute (STScI)


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