Space Telescope Science Institute   9.6.2 Example 2: SBC Objective Prism Spectrum of a UV Spectrophotometric Standard Star  9.6.4 Example 4: SBC imaging of Jupiter's Aurora at Lyman-alpha

9.6.3 Example 3: WFC VIS Polarimetry of the Jet of M87


What signal to noise ratio is reached in three one orbit exposures (~2400 seconds each) for M87, when using the WFC, F555W for one orbit each in the three VIS polarizers? Gain is 2, box size is 5 x 5 pixels, CR-SPLIT=2, and average sky.

If the M87 jet region has µ= 17 magnitudes/arcseconds2, using the ETC with a flat continuum spectral distribution and an exposure time of 2400 seconds (CR-SPLIT=2), gives S/N = 131.6 for an observation with each VIS polarizer filter (which is an average of the polarizer at the 3 available position angles 0º, 60º, and 120º). If the polarization P is 20%, then P*S/N = 26.3, so using

from Chapter 6, P/P  = 0.031, or = 6.2x10-3, which is the error on the fractional polarization. The error on the position angle should be ~1.0ºusing the formula, again from Chapter 6, of


 9.6.2 Example 2: SBC Objective Prism Spectrum of a UV Spectrophotometric Standard Star  9.6.4 Example 4: SBC imaging of Jupiter's Aurora at Lyman-alpha
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