Conclusion The angles of the HEG and MEG spectra on the ACIS-S detector were measured using the 15 A lines seen in the observations of Capella, ObsIDs 1099 and 1235. The new angle values are:
Analysis The angles were measured as the slope of the line connecting the centers of the plus and minus first-order images of the 15 A line; see the IDL script meas_line_angle.pro.
The "oa_AX, oa_AY" event arrays are returned by obs_anal.pro when the /EXPORT option is set. For the measurements here, the AX,AY arrays are the CXCDS Level 1 X,Y values with Y-sign flipped and rotated about zero-order by -1*average(aspect_ROLL) to align the X,Y to detector corrdinates. This alignment is verified by the narrow 1-D projection of the zero-order "streak" events.
Plots of the events and "center" locations as well are text output are available below:
meas_line_angle.pro output:
OBSID 1099
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HEG 15.010 A line, acisf1099_000N001_evt1.fits
Plus-side: 2688.91 -247.836
Minus-side: -2687.82 244.779
Angle: -5.23482
MEG 15.010 A line, acisf1099_000N001_evt1.fits
Plus-side: 1345.40 109.378
Minus-side: -1344.70 -112.955
Angle: 4.72468
OBSID 1235
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HEG 15.010 A line, acis_f1235_000N002_g02346_evt1a.fits
Plus-side: 2688.93 -247.056
Minus-side: -2687.73 245.617
Angle: -5.23551
MEG 15.010 A line, acis_f1235_000N002_g02346_evt1a.fits
Plus-side: 1345.39 110.168
Minus-side: -1344.67 -112.212
Angle: 4.72574
Please send any comments to
Dan Dewey at dd@space.mit.edu.