JWST NIRCam Defocused Imaging: Photometric Stability Performance and How it Can Sense Mirror Tilts

Understand

We use JWST NIRCam short wavelength photometry to capture a transit lightcurve of the exoplanet HAT-P-14 b to assess performance as part of instrument commissioning.

• The short wavelength precision is 152 ppm per 27 second integration as measured over the full time series compared to a theoretical limit of 107 ppm, after corrections to spatially correlated 1/f noise.
• Persistence effects from charge trapping are well fit by an exponential function with short characteristic timescales, settling on the order of 5-15 minutes.
• The short wavelength defocused photometry is also uniquely well suited to measure the realtime wavefront error of JWST.