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Webb Office Hours Session 2:  February 22, 2024

Q&A's: 

Q1: Where are the Webb Office Hours procedures and guidelines?

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A2: Consider an integration with three groups up the ramp, each group combining four frames on board before downlink, i.e., 1 1 1 1 2 2 2 2 3 3 3 3. The time associated with each downlinked group consisting of a single frame. Assume the time to read all pixels in a single frame is 10 seconds. Photons are gathered for a total of 30 seconds, starting with the first pixel in the first frame and ending with the last pixel in the last frame. The first pixel is read at t=0, t=10, and t=20, so the effective integration time is only 20 seconds. The last pixel is read at t=10, t=20, and t=30, so the effective integration time is again only 20 seconds. To conserve downlink bandwidth, some detector readout patterns average measurements for a pixel from multiple frames. In this case, the effective time for a downlinked measurement of a pixel is the average of the measurement times of in the four individual frames that were combined , e.g., 1, 1, 1, 1. The total time spent gathering photons is 12 frame times. The effective integration time is the time interval between the first (1) and last group (3), which is only 8 frame times. To calculate flux, divide the on board. In this scenario, the effective integration time for a pixel is the time associated with the last group in an integration minus the time associated with the first group.  

Effective integration time is provided in the JWST Header keyword: EFFINTTM "Effective integration Time in units of seconds."