Science Use Case: High Contrast Imaging with MIRI Coronagraphy - OLD

Science Proposal: Directly Image GJ 758 B

We wish to observe the brown dwarf companion GJ 758 B using all 3 of MIRI’s FQPM coronagraphs. Because the companion is moving closer to the star in projected separation, with an expected separation in 2019 of 1” = ~2 lambda/D at 15 microns, we will use the Small Grid Dither technique and KLIP algorithm to build an optimal PSF reference our observations. JWST’s superb sensitivity allows short exposure times: The ETC predicts SNR > 50 in both F1065C and F1150 in only 270 s exposure time (Groups=100, Ints=11 with FAST readout of the coronagraphic subarrays). In F1550C with higher thermal background, using 730 s exposure (Groups=200, Ints=15) we achieve SNR ~ 10. In each coronagraphic filter we observe the target twice, with a relative roll of 10 ± 4 deg between the observations, plus a PSF calibrator (HD 190360). An absolute position angle constraint will be used to position the companion near 45º relative to the FQPM masks, away from the quadrant boundaries. For the PSF calibrator, we will use the 9 point small grid dither to build a PSF reference library with robustness to relative offsets between science target and calibrator relative to the coronagraph masks. The PSF calibrator is 0.5 mag brighter than the science target so the individual exposure times per filter are reduced accordingly, but the 9 point dither then increases the total time.  Total time reported in APT for this program is 2.01 hours science, 7.26 hours total. 

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