RAPID mode was used relatively rarely, but it had some unique capabilities. There are also some unique problems that arise in treating the resultant data.
Proposal 5745 was a calibration test designed to map out the central portion of the PSF as presented to the GHRS apertures by COSTAR. This particular test made use of a spatial scan to map out the PSF while collecting data in RAPID mode.
35.7.1 The Exposure Logsheet
An abridged version of the Phase II Proposal for 5745 is shown in Figure 35.18. Here are some notes to go with individual lines of the Exposure Logsheet:
- Line 10: Sk-65º21 was acquired with an ONBOARD ACQ using -MIRROR-N1.
- Line 15: A confirmation IMAGE was taken as a sanity check for this program. In general, an IMAGE was unnecessary.
Figure 35.18: Exposure Logsheet for Program 5745
------------------------------------------------------------------------------------------------------------------------------------EXPOSURE LOGSHEET ID = 5745 [ 4]
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1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 |10 | 11 | 12 |13 |14| 15
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Line | Seq | Target |Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | S/N |Flx|Pr| Special
Number | Name | Name |Config| Mode |or FOV |Element |Waveln.| Parameters |Exp| |Rel. Time|Ref| | Requirements
------------------------------------------------------------------------------------------------------------------------------------
10 SK-65D21 HRS ACQ 2.0 MIRROR-N1 SEARCH-SIZE=5 1 25S 1 ONBOARD ACQ FOR 15
Comments: STEPTIME=1.0S EXPECT APPROX.
2800 COUNTS/S TARGET IS IN CVZ
------------------------------------------------------------------------------------------------------------------------------------
15 SK-65D21 HRS IMAGE 2.0 MIRROR-N1 NX=16 1 256S 1
------------------------------------------------------------------------------------------------------------------------------------
20 SK-65D21 HRS ACQ/ 0.25 MIRROR-N1 SEARCH-SIZE=5 1 25S 1 ONBOARD ACQ FOR 25
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25 SK-65D21 HRS ACQ/ 0.25 MIRROR-N1 SEARCH-SIZE=5 1 25S 1 ONBOARD ACQ FOR 40
------------------------------------------------------------------------------------------------------------------------------------
40 SK-65D21 HRS RAPID 0.25 G140L 1400 SAMPLE-TIME=1.0 1 112.5M 1 SPATIAL SCAN
Comments: 15X15 GRID WITH 0.053 ARC SEC
------------------------------------------------------------------------------------------------------------------------------------
Scan Paramters Form Proposal ID: 5745 [ 5]
------------------------------------------------------------------------------------------------------------------------------------
FGS Scan: DWELL Dwell Only: dwell points/line: 15 Seconds per dwell: 30.00
Scan width (arc-secs): 0.7420 Scan length (arc-secs): 0.7420 Angle between sides (degrees) 270.00
Number of lines: 15 Scan rate (arc-sec/sec): 0.0000 PA of first scan line (degrees) 90.000
Scan frame (CEL or S/C): S/C Length Offset (arc-sec): 0.3710 Width Offset (arc-sec): 0.3710
- The geometry of the spatial scan is shown in Figure 35.19. The splot display shows the relative orientations of the GHRS x, y and HST V2-V3 coordinate systems. Data points are delta distances in units of arcseconds.
Figure 35.19: Geometry of a Spatial Scan
- Line 20: Sk-65º21 was moved to the SSA using an ACQ/PEAKUP. The STEP-TIME was increased to compensate for the reduced throughput of the SSA relative to the LSA and to increase the signal-to-noise for the PEAKUP algorithm.
- Line 25: Another ACQ/PEAKUP. Again this is an exception rather than the rule for SSA ACQ/PEAKUPs (except when using MIRROR-A1).
- Line 40: This is the line where the spectra were obtained. A RAPID of 112.5 minute duration with a SAMPLE-TIME of 1.0 seconds was specified. We expected to get about 6750 individual spectra from this observation.
- Spatial Scan: The spatial scan specified a dwell scan that was 15 dwell points by 15 dwell points in extent. The spacing between dwell points was 0.053 arc seconds (about two deflection steps). The time spent at each dwell point was 30 seconds. Note that the total number of spectra was 30 one-second exposures, times 15 dwell points, times another 15 dwell points in the other direction, for a total of 6750.
35.7.2 Examining the RAPID Data
First let's look to see how many individual spectra we have:
cl> imhead ../data/z2i3010at.d0h,../data/z2i3010at.c1h l-The imheader task shows that we have many more spectra than expected. Further investigation turned up the fact that ten seconds was allocated for the slew from dwell point to dwell point. So we ended up having an extra ten seconds for each slew. Not all of these extra spectra are useful since the telescope was actually moving, but we ended up getting about 35 seconds per dwell point instead of the anticipated 30 seconds. The imheader output also shows that there are three less spectra in the calibrated output than in the raw data. Keep in mind that since there is no substepping or FP-SPLITs possible when using RAPID mode, that a single raw spectrum maps to a single calibrated spectrum. (Contrast this with a standard ACCUM with the default STEP-PATT: the raw data would contain six individual spectra-four substeps and two background spectra-which would be merged into a single calibrated spectrum.) In the case of RAPID mode, the first two readouts were generated during a hysteresis sequence that preceded every observation, and the last readout was produced by a final pass deflection made at the end of every observation. These readouts contain no useful science data and are not included in the calibrated data.
../data/z2i3010at.d0h[1/9024][500][real]: Z2I3010AT[1/9024]
../data/z2i3010at.c1h[1/9021][500][real]: Z2I3010AT[1/9021]
Manipulating a very large image can be difficult. For demonstration purposes, let's examine an arbitrary subsection of the original raw image in Figure 35.20. The gcopy task was used to extract a subset of groups from the original multi-group image. gstat computed the statistics for the new image.
Examining RAPID data as a two-dimensional image can be instructive. A simple way to convert the multi-group subset.hhh into a two-dimensional image is to use the gftoxdim task.
cl> gftoxdim subset.hhh subset_d2.hhhThe new image is now two-dimensional: the first dimension runs from diode 1 to 500 while the second dimension marks time.
cl> imhead subset_d2.hhh l-
subset_2d.hhh[500,41][real]: SUBSET_2D[1/1]
cl> display subset_d2.hhh 1 z1=0 z2=40 zr- zs-
Figure 35.20: Manipulating a Large Image
cl> gcopy ../data/z2i3010at.d0h subset.hhh groups=4604-4644
../data/z2i3010at.d0h -> subset.hhh
cl> gstat subset.hhh groups=*
# Image Statistics for subset.hhh
# GROUP NPIX MEAN MIDPT STDDEV MIN MAX
1 500 10.048 9.00849 5.7949 0. 28.
2 500 9.68 9.87606 5.31584 0. 24.
3 500 10. 9.12097 5.48161 0. 27.
4 500 10.334 9.88548 5.68217 0. 27.
5 500 10.174 9.94917 5.75412 0. 28.
6 500 10.166 9.00516 5.83254 0. 28.
7 500 10.014 9.06106 5.56919 0. 25.
8 500 10.04 9.8603 5.64465 0. 29.
9 500 9.792 9.00807 5.29384 0. 28.
10 500 9.886 9.92473 5.40587 0. 26.
11 500 9.818 8.99274 5.39881 0. 28.
12 500 10.072 9.82091 5.79603 0. 27.
13 500 10.092 9.89125 5.59913 0. 25.
14 500 9.856 9.10092 5.50562 0. 29.
15 500 10.004 9.05718 5.64195 0. 29.
16 500 9.822 9.01055 5.71381 0. 35.
17 500 9.952 9.88586 5.57313 0. 24.
18 500 10.054 9.94277 5.68822 0. 30.
19 500 9.856 9.01978 5.35805 0. 25.
20 500 9.958 8.97168 5.75312 0. 28.
21 500 9.916 8.98258 5.69824 0. 26.
22 500 10.07 9.86902 5.49741 0. 23.
23 500 9.834 9.90083 5.55231 0. 25.
24 500 10.206 9.83871 5.75446 0. 32.
25 500 10.122 9.00645 5.72859 0. 28.
26 500 10.148 10.128 5.65137 0. 31.
27 500 10.286 10.0233 5.7052 0. 28.
28 500 9.76 9.03122 5.41859 0. 25.
29 500 10.068 9.04799 5.69493 0. 25.
30 500 10.12 10.0108 5.52473 0. 28.
31 500 9.908 8.98854 5.53071 0. 26.
32 500 9.856 9.09568 5.40905 0. 29.
33 500 10.076 9.90533 5.61045 0. 25.
34 500 9.942 9.84996 5.42379 0. 27.
35 500 9.822 9.88937 5.39598 0. 25.
36 500 9.832 9.87903 5.58553 0. 25.
37 500 10.206 9.8606 5.54952 0. 27.
38 500 10.05 9.8626 5.61128 0. 26.
39 500 10.102 9.97581 5.49509 0. 25.
40 500 10.304 9.91161 5.80646 0. 27.
41 500 9.926 8.99917 5.49809 0. 32.
We can sum the two-dimensional image in each dimension for further -inspection:
cl> blkavg subset_2d.hhh subset_sum_y.hhh b1=1 b2=41 option=sumFigure 35.21 shows plots of three images. At the top is a greyscale plot of the extracted two-dimensional image, in the middle is a plot of the sum of the 500 diodes as a function of time, and at the bottom is a summed plot of the spectra over time.
cl> blkavg subset_2d.hhh subset_sum_x.hhh b1=500 b2=1 option=sum
cl> imhead subset_sum_?.hhh l-
subset_sum_x.hhh[500,1][real]: SUBSET_SUM_X[1/1]
subset_sum_y.hhh[1,41][real]: SUBSET_SUM_Y[1/1]
Figure 35.21: RAPID Data Displays
Copyright © 1997, Association of Universities for Research in Astronomy. All rights reserved.
Last updated: 01/14/98 15:45:39