Toy On-Orbit SNAP Spectrophotometric Calibration Scheme

Update:

Stuart Mufson, Nick Mostek

Indiana University

We have done extensive computations of the transfer of calibration from the fundamental to the primary calibrators.

The scheme is outlined in calibration scheme

Below we give some preliminary results. We will provide a more detailed account of these computations in the next week when we figure out how to present them.

First of all, we corrected some errors in the computation of the errors in the fundamental calibrator.

In our simple calibration scheme, we transfer calibration to primary calibrators by observing them with the SNAP spectrometer and then observing these stars photometrically. The spectroscopic errors are computed as they are for the fundamental calibrator. The photometric errors require a consideration of filter errors, both manufacturing and with respect to angle of incidence. We used filter files generated by Chuck Bower, and we investigated errors in the outer annulus of the SNAP focal plane. An example of one of these filter files is shown below:

The weighting function for angles of incidence is taken from Alex Kim's (no, not the pro tennis player that lost his first round match at the US Open) talk at the March collaboration meeting:

Some preliminary results. If we assume we calibrate filters to 5% accuracy, but angle of incidence is calibrated exactly, the errors for an m=16 K0III primary calibrator

The same computation for an m=19 K0III with filters calibrated to 5% accuracy

If we calibrate the filters to 1% acxcuracy

If we calibrate the angle of incidence to 0.25 degree