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Instrument Science Report STIS 2004-03

Full-Field Sensitivity of STIS CCD Imaging and its Temporal Dependence
Bahram Mobasher, James Davies and Paul Goudfrooij May 26, 2004

ABSTRACT Using calibration data obtained during 1997-2002, a study of the full-field sensitivity of the STIS CCD in clear (50CCD) imaging mode is carried out. Throughputs measured for several stars in deep exposures of a sparse field in the globular cluster Cen (= NGC 5139) show a negligible temporal variation of the order of 1% in sensitivity over the past five years. This does not depend on the brightness of the stars considered here, nor on their color (within the range covered, 0.5 < B - V < 0.9). Also, no significant changes in the CCD throughput were found after the switch to Side-2 electronics in July 2001. We do find a dependence of the count rate on exposure time at recent epochs which increases for fainter stars. The magnitude of this effect is consistent with being caused by Charge Transfer Inefficiency (CTI) of the STIS CCD. Finally, the variation of throughput across the field of view of the CCD is studied and found to be a < 3 effect.

Introduction
This report presents a study of the sensitivity of the STIS CCD in imaging mode, across its full field of view. Calibration data accumulated during Cycles 7-10 were used for this report. Given the time covered by the calibration data, a study of the temporal variation of the full-field sensitivity can be performed. Changes in the throughput as a function of position on the detector are also investigated. Allowing for temporal variation of the sensitivity, the dependence of the full-field sensitivity on the brightness and color of stars will

Copyright© 1999 The Association of Universities for Research in Astronomy, Inc. All Rights Reserved.


Instrument Science Report STIS 2004-03 be explored. Furthermore, behavior of the full-field sensitivity after the switch of STIS to the side-2 electronics in May 2001 will be studied.

Observations
The calibration programs 7639, 8416, 8847 and 8912 (cycles 7-10) were executed by observing a sparse photometric standard star field in the outskirts of the globular cluster Omega Cen (NGC 5139) located at RA=13h25m37.04s, DEC=-47d35'38.3" (see Figure 1). The exposures used the clear aperture (50CCD mode) to monitor the CCD sensitivity over the whole field of view. This is a star field known from WFPC2 photometric observations. The STIS observations were repeated roughly every six months, so that the spacecraft orientation changed by approximately 180 degrees between different epochs. Details of the observations are presented in Table 1. A CCD gain setting of 4 e-/DN was used for all observations. The data were reduced using the STIS pipeline (CALSTIS). A total of 12 stars were selected at different locations on the detector as labelled in Figure 1, covering a wide range in magnitudes (16.5 < mST < 20.5; where mST is magnitude in the STMAG system). The color range covered is 0.5 < B - V < 0.9 (in the Johnson system). The X,Y positions of the stars at different epochs are presented in Table 2. Aperture photometry was then carried out on these stars using the PHOT task in the APPHOT package within IRAF. To explore the effect of aperture size (and background noise) on the results, different aperture diameters corresponding to 3, 5, 10 and 15 pixels were used. The photometry results are listed in Table 3. Temporal variation of the sensitivity For each star, the mean of the magnitudes from all the exposures were calculated. The difference between the mean and observed magnitude at any given epoch (m - ) was then plotted as a function of the time of observation (solid circles in Figure 2). Larger m - values correspond to fainter magnitudes. Different panels in Figure 2 show the temporal dependence of m - for stars of different luminosities. Since year 2001, observations were also carried out with shorter exposure times and different read-out amplifiers to study the effect of imperfect Charge Transfer Efficiency (CTE). As CTE is lower for lower signal levels (e.g., Goudfrooij & Kimble 2002), a comparison of long and short exposures of the same field yields a measure of CTE. (The data with short exposure times are not used in the analysis of temporal behavior of the CCD detailed upon below.) Least-square fits are performed to the long-exposure data depicted in Figure 2 (filled circles). The results are listed in Table 4. No significant trend with time is observed, i.e., the deviation in the luminosities of individual stars from the mean luminosity over time is relatively constant with time (< 1% over 5 years). Furthermore, for stars with mST < 20, the relation is flat and does not depend on luminosity or color of the star (in the color

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Instrument Science Report STIS 2004-03 range covered by these stars). However, lower-luminosity stars (e.g., star `g' with mST = 20.51) do show a hint of becoming fainter by 2% in latter years. The sensitivity of this result to the aperture size and the background correction is depicted in Figure 3 which presents the relation between the mean magnitude of the stars measured inside different apertures, as mentioned above, and their rms scatter around the mean. For stars with mST < 20, no increase in rms scatter is found towards fainter magnitudes. Within the errors, this is also independent on the aperture size used. However, for stars with mST > 20, the rms scatter corresponding to larger apertures increases to 0.03. This is consistent with a prediction based on Poisson statistics (see solid line in Fig. 3), indicating the increase in rms at fainter magnitudes to be mostly due to statistical noise. This also confirms that there is no significant dependence of the photometric repeatability for the stars considered here. The vertical dotted line in Figure 2 indicates the time at which STIS had to switch to its side-2 electronics after the side-1 electronics failed (July 2001). Comparing the STIS/ CCD data from before and after this event, we find no significant change in the sensitivity of the detector. Charge Transfer Efficiency Since calendar year 2001, observations were taken with both long and short exposure times to evaluate the effect of imperfect CTE. The photometry of the short-exposure data is overplotted in Figure 2; they are the solid circles with the highest m- value at a given epoch. It can be seen that at any given epoch, the difference between magnitudes measured from long vs. short exposures increases for fainter stars. At year 2001.2, the change is from 0.01 (at m=16.93) to 0.07 (at m=20.56). To test whether this difference is due to the effect of imperfect CTE, we corrected the counts in Figure 2 for this effect, using the algorithm published by Goudfrooij & Kimble (2002), which was derived from more extensive monitoring of stellar photometry. The open symbols in Figure 2 depict our photometry after corrected for imperfect CTE. This correction renders the short-exposure photometry to be consistent with that of the long-exposure one, and further reduces any temporal variation that was apparent from the non-corrected photometry discussed before. Full-Field sensitivity of 50CCD Since we have shown that there is negligible temporal dependence of the measured brightness of stars in the magnitude and color ranges studied, we combined the data for a given star, taken at different times (separated by four years), without correcting the magnitudes for time dependence. The dependence of sensitivity on the location on the detector is then measured by calculating the mean magnitude of individual stars over the last four years, located at different locations on the detector. Deviations of the magnitudes of each star

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Instrument Science Report STIS 2004-03 from the mean are then measured. These deviations, corresponding to 1, 2 and 3 sigma from the mean, are shown in Fig. 4 using different sizes at the star's position on the detector. These correspond to small (1 sigma), medium (2 sigma) and large (3 sigma) circles. Each of the panels in Figure 4 shows the full-field sensitivity corresponding to a given star. As is clear from Figure 4, there is no evidence for any significant dependence of sensitivity on position on the detector and no deterioration of sensitivity at a given position (i.e. no accumulation of large circles in a given area of the diagrams).

Summary
The full-field sensitivity calibration of the STIS CCD imaging mode was carried out in the period 1997-2000. We find a negligible temporal variation once the photometry is corrected for imperfect CTE. This is found to be independent of the luminosity and color of the stars involved. The throughput at different locations on the detector is measured and found to be a < 3 effect.

Recommendation
Given the negligible variation of clear (50CCD) imaging throughput with time and and position on the CCD (at least for stars with B - V redder than about 0.5), we can safely reduce the frequency of the full-field sensitivity calibration program for CCD imaging. However, the effect of imperfect CTE is found to be non-negligible and should remain closely monitored in the future.

References
Goudfrooij, P., & Kimble, R. A., 2002, "Correcting STIS CCD Photometry for CTE loss", in 2002 HST Calibration Workshop, eds. S. Arribas, A. Koekemoer, & B. Whitmore, p. 105.

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Instrument Science Report STIS 2004-03

Figure 1: STIS/CCD image of cluster NGC5139 with selected stars (of different luminosities and colors) marked.

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Figure 2: Temporal variation of STIS/CCD. Each panel corresponds to a given star of a given magnitude and color (filled symbols). Stars observed using two different exposure times are also included. The first five data points are from 15 sec exposures, next two are 50 sec and final three epochs are taken using both 10 and 60 sec exposures. The data, corrected for CTI effect, are also shown (open symbols). The vertical dotted line corresponds to the time of safing of STIS in May 2001.

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Instrument Science Report STIS 2004-03

Figure 3: Changes in the mean magnitude of individual stars with the rms around the mean. The panels show the relation using different apertures (5, 10, 15 pixels). The lines show the relation due to Poisson noise.

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Figure 4: Full-field sensitivity of detector. Each panel corresponds to a given star. Symbol sizes indicate 1 sigma (small), 2 sigma (medium) and 3 sigma (large) deviations from the mean. The mean magnitude and 1 sigma deviation for each star are also shown on each panel.

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Instrument Science Report STIS 2004-03 Table 1. List of the observations of star cluster at different epochs.
prog dataset 7639 o4go02010 o4go03010 o4go04010 o4go05010 o4go01010 8416 o5ir01010 o5ir02010 8847 o69902010 o69902020 o69902030 o69902040 8912 o6ib01010 o6ib01020 o6ib02010 o6ib02020 o6ib02030 o6ib02040 1 Sep 2001 1 Sep 2001 15 Feb 2002 15 Feb 2002 15 Feb 2002 15 Feb 2002 D D D D B B 4 4 4 4 4 4 5 2 5 2 5 2 10.0 60.0 10.0 60.0 10.0 60.0 3 Feb 2001 3 Feb 2001 3 Feb 2001 3 Feb 2001 D D B B 4 4 4 4 5 2 5 2 10.0 60.0 10.0 60.0 2 Jul 1999 26 Mar 2000 D D 4 4 5 5 50.0 50.0 16 Dec 1997 26 Feb 1998 1 Jun 1998 10 Dec 1998 7 Feb 1999 D D D D D 4 4 4 4 4 5 5 5 5 5 15.0 15.0 15.0 15.0 15.0 date amp gain cr-split exptime (s)

Table 2. Selected stars for the present study with their corresponding X,Y positions at each epoch.
star a b c d e f g epoch 1997.95 1997.95 1997.95 1997.95 1997.95 1997.95 1997.95 dataset o4go02010 o4go02010 o4go02010 o4go02010 o4go02010 o4go02010 o4go02010 x 138.000 210.210 348.670 214.400 292.310 409.490 845.450 y 259.230 297.260 366.720 528.070 652.420 913.170 874.220

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Instrument Science Report STIS 2004-03
star h i j k l a b c d e f g i j k l a b c d e f g h i j k l a b c d e f g h i j k l a b epoch 1997.95 1997.95 1997.95 1997.95 1997.95 1998.16 1998.16 1998.16 1998.16 1998.16 1998.16 1998.16 1998.16 1998.16 1998.16 1998.16 1998.50 1998.50 1998.50 1998.50 1998.50 1998.50 1998.50 1998.50 1998.50 1998.50 1998.50 1998.50 1998.93 1998.93 1998.93 1998.93 1998.93 1998.93 1998.93 1998.93 1998.93 1998.93 1998.93 1998.93 1999.10 1999.10 dataset o4go02010 o4go02010 o4go02010 o4go02010 o4go02010 o4go03010 o4go03010 o4go03010 o4go03010 o4go03010 o4go03010 o4go03010 o4go03010 o4go03010 o4go03010 o4go03010 o4go04010 o4go04010 o4go04010 o4go04010 o4go04010 o4go04010 o4go04010 o4go04010 o4go04010 o4go04010 o4go04010 o4go04010 o4go05010 o4go05010 o4go05010 o4go05010 o4go05010 o4go05010 o4go05010 o4go05010 o4go05010 o4go05010 o4go05010 o4go05010 o4go01010 o4go01010 x 995.580 752.870 639.540 869.040 604.140 55.3200 136.170 289.250 274.440 410.200 657.350 988.850 756.190 580.940 683.020 334.920 869.910 801.220 669.150 816.660 749.840 656.470 219.140 67.9500 286.950 387.450 146.360 390.950 188.900 254.570 380.980 224.170 282.560 359.510 796.370 947.030 744.970 654.330 902.650 674.960 55.5100 136.590 y 857.140 604.340 461.570 317.150 88.7200 521.310 510.050 485.700 694.990 750.550 893.910 608.450 442.940 393.060 142.050 110.740 815.760 771.680 690.560 541.670 411.110 141.490 141.550 145.350 418.780 570.950 695.150 945.780 215.580 263.910 353.300 492.720 627.190 902.410 928.900 934.430 648.330 490.370 381.910 116.650 511.290 502.000

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Instrument Science Report STIS 2004-03
star c d e f g i j k l a b c d e f g h i j k l a c e g i k l a b c d e f g i j k a b c d epoch 1999.10 1999.10 1999.10 1999.10 1999.10 1999.10 1999.10 1999.10 1999.10 1999.50 1999.50 1999.50 1999.50 1999.50 1999.50 1999.50 1999.50 1999.50 1999.50 1999.50 1999.50 2000.23 2000.23 2000.23 2000.23 2000.23 2000.23 2000.23 2001.09 2001.09 2001.09 2001.09 2001.09 2001.09 2001.09 2001.09 2001.09 2001.09 2001.09 2001.09 2001.09 2001.09 dataset o4go01010 o4go01010 o4go01010 o4go01010 o4go01010 o4go01010 o4go01010 o4go01010 o4go01010 o5ir01010 o5ir01010 o5ir01010 o5ir01010 o5ir01010 o5ir01010 o5ir01010 o5ir01010 o5ir01010 o5ir01010 o5ir01010 o5ir01010 o5ir02010 o5ir02010 o5ir02010 o5ir02010 o5ir02010 o5ir02010 o5ir02010 o69902010 o69902010 o69902010 o69902010 o69902010 o69902010 o69902010 o69902010 o69902010 o69902010 o69902020 o69902020 o69902020 o69902020 x 290.210 270.310 404.640 648.180 986.460 757.790 584.000 692.150 345.010 903.090 829.590 688.540 816.870 734.600 608.990 174.730 25.2700 276.090 394.390 170.230 443.600 238.690 356.740 639.160 890.070 615.070 334.560 92.03 57.33 136.43 285.78 294.24 435.23 696.53 994.45 744.72 565.47 639.14 57.26 136.36 285.70 294.16 y 481.450 690.210 749.080 898.350 621.110 450.040 395.900 147.560 107.760 773.780 738.460 673.980 508.210 386.640 130.430 183.880 206.090 450.830 589.550 742.310 961.280 892.420 687.440 758.350 218.280 296.320 165.230 418.02 555.48 535.36 494.33 703.83 744.16 859.16 539.14 400.34 370.09 109.42 555.50 535.40 494.35 703.82

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Instrument Science Report STIS 2004-03
star e f g i j k a b c d e f g i j k a b c d e f g i j k a b c d e f g i j k a b c d e f epoch 2001.09 2001.09 2001.09 2001.09 2001.09 2001.09 2001.67 2001.67 2001.67 2001.67 2001.67 2001.67 2001.67 2001.67 2001.67 2001.67 2001.67 2001.67 2001.67 2001.67 2001.67 2001.67 2001.67 2001.67 2001.67 2001.67 2002.15 2002.15 2002.15 2002.15 2002.15 2002.15 2002.15 2002.15 2002.15 2002.15 2002.15 2002.15 2002.15 2002.15 2002.15 2002.15 dataset o69902020 o69902020 o69902020 o69902020 o69902020 o69902020 o6ib01010 o6ib01010 o6ib01010 o6ib01010 o6ib01010 o6ib01010 o6ib01010 o6ib01010 o6ib01010 o6ib01010 o6ib01020 o6ib01020 o6ib01020 o6ib01020 o6ib01020 o6ib01020 o6ib01020 o6ib01020 o6ib01020 o6ib01020 o6ib02010 o6ib02010 o6ib02010 o6ib02010 o6ib02010 o6ib02010 o6ib02010 o6ib02010 o6ib02010 o6ib02010 o6ib02020 o6ib02020 o6ib02020 o6ib02020 o6ib02020 o6ib02020 x 435.17 696.48 994.44 744.64 565.41 639.07 958.58 881.48 735.89 710.08 566.36 296.64 25.96 286.47 467.80 416.81 958.65 881.51 735.94 710.13 566.41 296.66 26.01 286.49 467.84 416.88 57.48 136.51 285.94 294.37 435.36 696.65 994.56 744.74 565.55 639.23 57.45 136.48 285.90 294.34 435.37 696.61 y 744.16 859.19 539.20 400.37 370.12 109.42 411.43 438.04 491.42 283.54 255.14 161.91 506.13 623.71 638.77 905.00 411.45 438.07 491.44 283.52 255.16 161.94 506.18 623.71 638.77 905.00 546.29 526.16 485.14 694.63 734.91 849.90 529.85 391.15 360.79 100.13 546.33 526.23 485.16 694.65 734.96 849.95

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Instrument Science Report STIS 2004-03
star g i j k epoch 2002.15 2002.15 2002.15 2002.15 dataset o6ib02020 o6ib02020 o6ib02020 o6ib02020 x 994.54 744.71 565.52 639.23 y 529.94 391.18 360.89 100.16

Table 3. Photometry of stars at different epochs. Magnitudes corresponding to different apertures (3,5,10 and 15 pixels) are presented.
star a b c d e f g h i j k l a b c d e f g i j k l a b c d e f g h i epoch 1997.95 1997.95 1997.95 1997.95 1997.95 1997.95 1997.95 1997.95 1997.95 1997.95 1997.95 1997.95 1998.16 1998.16 1998.16 1998.16 1998.16 1998.16 1998.16 1998.16 1998.16 1998.16 1998.16 1998.50 1998.50 1998.50 1998.50 1998.50 1998.50 1998.50 1998.50 1998.50 mST (r=3) 19.1540 19.7620 18.5360 16.9230 20.5480 20.1710 20.5490 16.6030 18.8230 20.7610 17.8860 20.7720 19.1270 19.7800 18.5250 16.9260 20.5610 20.2120 20.5440 18.8270 20.7380 17.8670 20.7730 19.1820 19.7700 18.5320 16.9310 20.5700 20.1980 20.5370 16.5720 18.8360 mST(r=5) 19.0810 19.6880 18.4560 16.8510 20.4540 20.0920 20.4380 16.5160 18.7450 20.6860 17.8070 20.6690 19.0560 19.7090 18.4500 16.8560 20.4760 20.1260 20.4730 18.7480 20.6780 17.7890 20.7280 19.1070 19.6810 18.4520 16.8540 20.4650 20.0800 20.4610 16.4950 18.7540 mST(r=10) 19.0390 19.6430 18.4250 16.8250 20.3950 20.0840 20.4160 16.4840 18.7180 20.6670 17.7780 20.6000 19.0290 19.6740 18.4180 16.8290 20.4440 20.1030 20.4440 18.7230 20.6190 17.7670 20.7130 19.0690 19.6300 18.4200 16.8260 20.4360 20.0320 20.3960 16.4640 18.7140 mST(r=15) 19.0250 19.6290 18.4050 16.8080 20.3830 20.0970 20.3870 16.4650 18.7050 20.6100 17.7600 20.6350 19.0050 19.6300 18.3930 16.8100 20.4350 20.1270 20.4440 18.7130 20.5760 17.7560 20.7390 19.0440 19.6180 18.4040 16.8080 20.3830 19.9960 20.3530 16.4440 18.6930

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Instrument Science Report STIS 2004-03
star j k l a b c d e f g h i j k l a b c d e f g i j k l a b c d e f g h i j k l a c e g epoch 1998.50 1998.50 1998.50 1998.93 1998.93 1998.93 1998.93 1998.93 1998.93 1998.93 1998.93 1998.93 1998.93 1998.93 1998.93 1999.10 1999.10 1999.10 1999.10 1999.10 1999.10 1999.10 1999.10 1999.10 1999.10 1999.10 1999.50 1999.50 1999.50 1999.50 1999.50 1999.50 1999.50 1999.50 1999.50 1999.50 1999.50 1999.50 2000.23 2000.23 2000.23 2000.23 mST (r=3) 20.7390 17.8810 20.7230 19.1740 19.8010 18.5240 16.9260 20.5550 20.2090 20.5280 16.5990 18.8370 20.7430 17.8740 20.8010 19.1480 19.7740 18.5310 16.9350 20.5630 20.2230 20.5440 18.8440 20.7400 17.8740 20.8000 19.1720 19.7760 18.5340 16.9350 20.5600 20.2160 20.5610 16.5610 18.8240 20.7190 17.8750 20.7770 19.1640 18.5340 20.5630 20.5770 mST(r=5) 20.6670 17.8130 20.7000 19.0860 19.7150 18.4450 16.8590 20.4690 20.1420 20.4660 16.5180 18.7600 20.6600 17.8040 20.6710 19.0720 19.6910 18.4570 16.8660 20.4970 20.1440 20.4830 18.7590 20.6290 17.8010 20.7500 19.0880 19.6890 18.4520 16.8550 20.4690 20.1170 20.4780 16.4910 18.7480 20.6380 17.8070 20.6810 19.0920 18.4620 20.4880 20.4960 mST(r=10) 20.6380 17.7870 20.6950 19.0420 19.6630 18.4200 16.8330 20.4480 20.1070 20.4530 16.4850 18.7280 20.6370 17.7750 20.6560 19.0350 19.6420 18.4250 16.8380 20.4680 20.1370 20.4540 18.7290 20.5740 17.7720 20.7190 19.0550 19.6540 18.4250 16.8270 20.4340 20.0950 20.4400 16.4650 18.7170 20.5940 17.7800 20.6530 19.0640 18.4360 20.4690 20.4730 mST(r=15) 20.5890 17.7710 20.7580 18.9990 19.6330 18.4000 16.8140 20.4000 20.1230 20.4550 16.4680 18.7150 20.6270 17.7590 20.6090 19.0080 19.6150 18.4040 16.8200 20.4840 20.1410 20.4580 18.7120 20.5370 17.7530 20.7070 19.0360 19.6180 18.4020 16.8070 20.4070 20.0720 20.4160 16.4490 18.6990 20.5530 17.7610 20.6270 19.0440 18.4190 20.4630 20.4520

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Instrument Science Report STIS 2004-03
star i k l a b c d e f g i j k a b c d e f g i j k a b c d e f g i j k a b c d e f g i j epoch 2000.23 2000.23 2000.23 2001.09 2001.09 2001.09 2001.09 2001.09 2001.09 2001.09 2001.09 2001.09 2001.09 2001.09 2001.09 2001.09 2001.09 2001.09 2001.09 2001.09 2001.09 2001.09 2001.09 2001.67 2001.67 2001.67 2001.67 2001.67 2001.67 2001.67 2001.67 2001.67 2001.67 2001.67 2001.67 2001.67 2001.67 2001.67 2001.67 2001.67 2001.67 2001.67 mST (r=3) 18.8260 17.8770 20.909 19.341 19.959 18.693 17.065 20.699 20.352 20.765 18.990 20.904 17.998 19.286 19.916 18.671 17.055 20.685 20.315 20.643 18.947 20.856 17.967 19.336 19.948 18.687 17.062 20.719 20.404 20.723 18.977 20.877 17.995 19.302 19.913 18.677 17.059 20.675 20.335 20.639 18.948 20.847 mST(r=5) 18.7500 17.8090 20.790 19.183 19.811 18.559 16.944 20.566 20.239 20.616 18.871 20.820 17.891 19.134 19.767 18.537 16.936 20.563 20.208 20.532 18.830 20.745 17.862 19.216 19.832 18.575 16.950 20.588 20.280 20.592 18.864 20.761 17.890 19.177 19.800 18.563 16.946 20.567 20.218 20.517 18.836 20.736 mST(r=10) 18.7170 17.7800 20.731 19.094 19.741 18.485 16.877 20.469 20.192 20.540 18.789 20.765 17.816 19.060 19.690 18.466 16.869 20.493 20.140 20.461 18.757 20.666 17.791 19.119 19.743 18.492 16.873 20.487 20.153 20.568 18.783 20.704 17.822 19.093 19.712 18.481 16.869 20.483 20.136 20.458 18.763 20.647 mST(r=15) 18.7010 17.7620 20.711 19.065 19.682 18.452 16.850 20.458 20.122 20.473 18.763 20.694 17.787 19.027 19.648 18.438 16.843 20.468 20.114 20.431 18.728 20.624 17.764 19.070 19.702 18.472 16.844 20.367 20.121 20.555 18.743 20.616 17.798 19.061 19.673 18.452 16.840 20.422 20.103 20.441 18.732 20.597

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Instrument Science Report STIS 2004-03
star k a b c d e f g i j k a b c d e f g i j k epoch 2001.67 2002.15 2002.15 2002.15 2002.15 2002.15 2002.15 2002.15 2002.15 2002.15 2002.15 2002.15 2002.15 2002.15 2002.15 2002.15 2002.15 2002.15 2002.15 2002.15 2002.15 mST (r=3) 18.008 19.348 20.005 18.713 17.069 20.716 20.312 20.748 18.990 20.931 18.004 19.295 19.916 18.674 17.053 20.671 20.323 20.658 18.952 20.858 17.967 mST(r=5) 17.904 19.196 19.858 18.572 16.948 20.609 20.208 20.643 18.867 20.807 17.891 19.146 19.774 18.539 16.936 20.560 20.222 20.560 18.836 20.753 17.860 mST(r=10) 17.833 19.129 19.811 18.508 16.883 20.544 20.150 20.544 18.793 20.771 17.816 19.081 19.720 18.472 16.870 20.530 20.182 20.520 18.768 20.714 17.792 mST(r=15) 17.806 19.117 19.775 18.494 16.857 20.543 20.143 20.554 18.766 20.823 17.789 19.066 19.699 18.455 16.846 20.574 20.213 20.558 18.750 20.747 17.768

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