Changes between Version 3 and Version 4 of GPC_BrightStarAstrometry_Issue
- Timestamp:
- Apr 1, 2011, 12:18:00 PM (15 years ago)
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GPC_BrightStarAstrometry_Issue
v3 v4 13 13 == 2mass comparison == 14 14 15 The SMF files for two exposures from the galactic plane (o5407g0385o and o5407g0385o) were matched against the 2mass catalog, and the shifts between the GPC1 and 2mass positions analysed as a function of magnitude. The following figures show dRA, dDEC, from the catalogs, along with these offsets transformed using the platescale and position angle into dx and dy coordinates. The flip in direction between OTA34 and OTA42 is due to the different orientations of the detectors. 15 The SMF files for two exposures from the galactic plane (o5407g0385o and o5407g0385o) were matched against the 2mass catalog, and the shifts between the GPC1 and 2mass positions analysed as a function of magnitude. The following figures show dRA, dDEC, from the catalogs, along with these offsets transformed using the platescale and position angle into dx and dy coordinates. The flip in direction between OTA34 and OTA42 is due to the different orientations of the detectors. The x-axis in all figures shows the instrumental magnitude of the star. 16 16 17 17 || || OTA34 || OTA42 || … … 39 39 || [[Image(o5407g0385o.ota24.dx.png)]] || [[Image(o5407g0385o.ota36.dx.png)]] || 40 40 41 42 41 Checking the differences in positions shows that in the raw cell coordinates, a bright source in GPC1 is at a smaller x position than the 2mass position. This means that an example object in cell00 has been shifted in the direction of cell01. The direction of the shift in cell coordinates is the same on all OTAs. There is some evidence of asymmetry in the raw images as well that supports this shift: 43 42 44 43 [[Image(asymmetry.png)]] 45 44 46 This effect starts around instrumental magnitude of -13. Using the SMF file to convert puts the peak flux for these stars around 5000 counts. The size of the shift is dependent on the brightness of the star, with the brightest objects having the largest shifts. 45 This effect starts around instrumental magnitude of -13. Using the SMF file to convert puts the peak flux for these stars around 5000 counts: 46 47 [[Image(peak.png)]]
