HETGS "What if..." there were only BI CCDs...

I [Dave H] made ARFs (effective area tables) with mkgarf using OBsID 1235 for template headers. An aspect dither pattern was included. From the nominal S3 aim-point, I stepped the zero-order towards S2 by 1.0, 2.0, 2.5, and 3.0 arcminutes (the latter two aims put the zero-order onto S2; the gap is at about 2.0 arcminutes offset).

The following graphs show the HEG and MEG areas for combined plus and minus first orders along with their sum and the nominal FI+BI area (top panels). The bottom panels show the ratio of the BI-only to nominal FI+BI areas.

An offset of -2.5 arcmin closes the gap in the spectra and also maintains coverage of the astrophysically important O VII He-like lines at 21.6, 21.8, and 22.1 A.

Postscript file


dph@space.mit.edu