WFC3/IR Time Variable Background (TVB)

Here are brief descriptions of WFC3 Notebooks for WFC3/IR TVB:

WFC3/IR IMA Visualization Tools with an Example of Time Variable Background

We present tools to familiarize users with the structure of the WFC3/IR IMA files, to visualize individual reads and the difference between reads, and to plot the cumulative signal and count rate throughout the MULTIACCUM exposure. These visualization tools may be used to identify issues with the data, for example, a guidestar (GS) failure, a satellite trail in a specific read, or time variable background, which may take the form of scattered light or He I 10830 A airglow line emission.

Manual Recalibration of Images using calwf3: Turning off the WFC3/IR Linear Ramp Fit

We present calwf3 reprocessing examples to improve calibrated WFC3/IR images affected by TVB. The notebook shows how to diagnose images with poor-quality ramp fits and rerun calwf3 with the ‘CRCORR’ step turned off. This method is described as the ‘Last-minus-first’ technique WFC3 ISR 2016-16. See Section 3.5.2 of the WFC3 Data Handbook for more information.

Correcting for Helium Line Emission Background in WFC3/IR Exposures using the “Flatten-Ramp” Technique

We present different ways to identify IR exposures with time variable Helium (1.083 micron) line emission background, and how to correct for it using the “flatten-ramp” technique described in WFC3 ISR 2016-16. This method can be used to correct images affected by a sky background that does not vary across the field of view.

Correcting for Scattered Light in WFC3/IR Exposures: Manually Subtracting Bad Reads

We present a method to correct for TVB due to scattered light from observing close to the Earth’s limb. This method illustrates how to manually subtract any bad reads from the final exposure read of the WFC3/IR IMA data.

Please note that the FLT products in this notebook are really ‘corrected IMA’ files and therefore do not include the ‘ramp fitting’ step in calwf3. The final images will therefore still contain cosmic rays, and these artifacts may be removed using software such as AstroDrizzle when combining multiple exposures.

Correcting for Scattered Light in WFC3/IR Exposures: Using calwf3 to Mask Bad Reads

We present a method to correct for TVB due to scattered light from observing close to the Earth’s limb. This method illustrates how to mask bad reads in the RAW image and then reprocess with calwf3, and it may be used for rejecting anomalous reads occurring either at the beginning or at the end of an exposure.