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Instrument Science Report ACS 2004-05

Results of UV Contamination Monitoring of the Advanced Camera for Surveys
F. R. Boffi, R. C. Bohlin, G. De Marchi April 8, 2004

ABSTRACT Proposals 9010, 9565 and 9655 (currently in progress) are devoted to the observation of the star cluster ngc 6681 to monitor the UV performance of the HRC and SBC detectors in ACS. Our results indicate that ACS does not suffer from UV contamination. The three HRC filters f220w, f250w and f330w, do not show sensitivity changes by more than 1%. Presently, for the SBC the only conclusion is that any change in sensitivity is less than 2%, because the precision of the current analysis is limited by the lack of an L-flat field.

1. Introduction
Monitoring ACS for UV contamination has been a major calibration program. Programs 9010 from SM3/ACS SMOV and 9565 are completed and program 9655 has been in progress since September 2003. The former programs have produced data with the HRC with a frequency of one filter every two weeks, then one filter every 11 days starting in May 2002 through July 2003. Program 9655 has had a frequency of one observation per month. In Table 1, a summary of all observations is provided. This document presents results of the UV contamination program including data through July 2003. In Section 2, all data sets are presented. In Section 3, the analysis procedure is outlined and results are given. In the last Section conclusions are drawn and recommendations for future Cycles are given.

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


Instrument Science Report ACS 2004-05

Table 1: Log of Observations for Proposals 9010, 9565 and 9655
Filename (_drz.fits[1]) j8c801011 j8c801021 j8c801031 j8c801mvq j8c801mwq j8c801mxq j8c801myq j8c801n0q j8c803011 j8c803021 j8c803031 j8c803htq j8c803huq j8c803hvq j8c803hwq j8c803hyq j8c804011 j8c804021 j8c804031 j8c804wmq j8c804wnq j8c804woq j8c804wpq j8c804wxq j8ep01011 j8ep01021 j8ep01031 j8ep01ufs j8ep01ugs j8ep01uhs Proposal ID 9010 9010 9010 9010 9010 9010 9010 9010 9010 9010 9010 9010 9010 9010 9010 9010 9010 9010 9010 9010 9010 9010 9010 9010 9565 9565 9565 9565 9565 9565 Obs. Date 2002-05-13 2002-05-13 2002-05-13 2002-05-13 2002-05-13 2002-05-13 2002-05-13 2002-05-13 2002-05-27 2002-05-27 2002-05-27 2002-05-27 2002-05-27 2002-05-27 2002-05-27 2002-05-27 2002-06-04 2002-06-04 2002-06-04 2002-06-04 2002-06-04 2002-06-04 2002-06-04 2002-06-04 2002-06-30 2002-06-30 2002-06-30 2002-06-30 2002-06-30 2002-06-30 Detector HRC HRC HRC SBC SBC SBC SBC SBC HRC HRC HRC SBC SBC SBC SBC SBC HRC HRC HRC SBC SBC SBC SBC SBC HRC HRC HRC SBC SBC SBC Filter F220W F250W F330W F115LP F125LP F140LP F150LP F165LP F220W F250W F330W F115LP F125LP F140LP F150LP F165LP F220W F250W F330W F115LP F125LP F140LP F150LP F165LP F220W F250W F330W F115LP F125LP F140LP Exp. Time 140.0 140.0 140.0 120.0 120.0 150.0 180.0 245.0 140.0 140.0 140.0 120.0 120.0 150.0 180.0 245.0 140.0 140.0 140.0 120.0 120.0 150.0 180.0 245.0 140.0 140.0 140.0 120.0 120.0 150.0

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Instrument Science Report ACS 2004-05 Table 1: Log of Observations for Proposals 9010, 9565 and 9655
Filename (_drz.fits[1]) j8ep01uis j8ep01ujs j8ep02011 j8ep02021 j8ep02031 j8ep02uxq j8ep02uyq j8ep02uzq j8ep02v0q j8ep02v1q j8ep03011 j8ep03021 j8ep03031 j8ep03gkq j8ep03glq j8ep03gmq j8ep03gnq j8ep03goq j8ep04011 j8ep04021 j8ep04031 j8ep04lsq j8ep04ltq j8ep04luq j8ep04lvq j8ep04lwq j8ep05011 j8ep05021 j8ep05031 j8ep05pnq j8ep05poq Proposal ID 9565 9565 9565 9565 9565 9565 9565 9565 9565 9565 9565 9565 9565 9565 9565 9565 9565 9565 9565 9565 9565 9565 9565 9565 9565 9565 9565 9565 9565 9565 9565 Obs. Date 2002-06-30 2002-06-30 2002-07-14 2002-07-14 2002-07-14 2002-07-14 2002-07-14 2002-07-14 2002-07-14 2002-07-14 2002-07-26 2002-07-26 2002-07-26 2002-07-26 2002-07-26 2002-07-26 2002-07-26 2002-07-26 2002-08-06 2002-08-06 2002-08-06 2002-08-06 2002-08-06 2002-08-06 2002-08-06 2002-08-06 2002-08-20 2002-08-20 2002-08-20 2002-08-20 2002-08-20 Detector SBC SBC HRC HRC HRC SBC SBC SBC SBC SBC HRC HRC HRC SBC SBC SBC SBC SBC HRC HRC HRC SBC SBC SBC SBC SBC HRC HRC HRC SBC SBC Filter F150LP F165LP F220W F250W F330W F115LP F125LP F140LP F150LP F165LP F220W F250W F330W F115LP F125LP F140LP F150LP F165LP F220W F250W F330W F115LP F125LP F140LP F150LP F165LP F220W F250W F330W F115LP F125LP Exp. Time 180.0 245.0 140.0 140.0 140.0 120.0 120.0 150.0 180.0 245.0 140.0 140.0 140.0 120.0 120.0 150.0 180.0 245.0 140.0 140.0 140.0 120.0 120.0 150.0 180.0 245.0 140.0 140.0 140.0 120.0 120.0

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Instrument Science Report ACS 2004-05 Table 1: Log of Observations for Proposals 9010, 9565 and 9655
Filename (_drz.fits[1]) j8ep05ppq j8ep05pqq j8ep05prq j8ep06011 j8ep06021 j8ep06031 j8ep06hpq j8ep06hqq j8ep06hrq j8ep06hsq j8ep06htq j8ep07011 j8ep07021 j8ep07031 j8ep07vgq j8ep07vhq j8ep07viq j8ep07vjq j8ep07vkq j8ep08011 j8ep08021 j8ep08031 j8ep08meq j8ep08mfq j8ep08mgq j8ep08mhq j8ep08miq j8hv01011 j8hv01021 j8hv01031 j8hv01m2q Proposal ID 9565 9565 9565 9565 9565 9565 9565 9565 9565 9565 9565 9565 9565 9565 9565 9565 9565 9565 9565 9565 9565 9565 9565 9565 9565 9565 9565 9655 9655 9655 9655 Obs. Date 2002-08-20 2002-08-20 2002-08-20 2002-08-30 2002-08-30 2002-08-30 2002-08-30 2002-08-30 2002-08-30 2002-08-30 2002-08-30 2002-09-11 2002-09-11 2002-09-11 2002-09-11 2002-09-11 2002-09-11 2002-09-11 2002-09-11 2002-09-27 2002-09-27 2002-09-27 2002-09-27 2002-09-27 2002-09-27 2002-09-27 2002-09-27 2002-10-15 2002-10-15 2002-10-15 2002-10-15 Detector SBC SBC SBC HRC HRC HRC SBC SBC SBC SBC SBC HRC HRC HRC SBC SBC SBC SBC SBC HRC HRC HRC SBC SBC SBC SBC SBC HRC HRC HRC SBC Filter F140LP F150LP F165LP F220W F250W F330W F115LP F125LP F140LP F150LP F165LP F220W F250W F330W F115LP F125LP F140LP F150LP F165LP F220W F250W F330W F115LP F125LP F140LP F150LP F165LP F220W F250W F330W F115LP Exp. Time 150.0 180.0 245.0 140.0 140.0 140.0 120.0 120.0 150.0 180.0 245.0 140.0 140.0 140.0 120.0 120.0 150.0 180.0 245.0 140.0 140.0 140.0 120.0 120.0 150.0 180.0 245.0 140.0 140.0 140.0 120.0

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Instrument Science Report ACS 2004-05 Table 1: Log of Observations for Proposals 9010, 9565 and 9655
Filename (_drz.fits[1]) j8hv01m3q j8hv01m4q j8hv01m5q j8hv01m6q j8hv02011 j8hv02021 j8hv02031 j8hv02eyq j8hv02ezq j8hv02f0q j8hv02f1q j8hv02f2q j8hv05011 j8hv05021 j8hv05031 j8hv05cuq j8hv05cvq j8hv05cwq j8hv05cxq j8hv05cyq j8hv06011 j8hv06021 j8hv06031 j8hv06qtq j8hv06quq j8hv06qvq j8hv06qwq j8hv06qxq j8hv07011 j8hv07021 j8hv07031 Proposal ID 9655 9655 9655 9655 9655 9655 9655 9655 9655 9655 9655 9655 9655 9655 9655 9655 9655 9655 9655 9655 9655 9655 9655 9655 9655 9655 9655 9655 9655 9655 9655 Obs. Date 2002-10-15 2002-10-15 2002-10-15 2002-10-15 2002-11-10 2002-11-10 2002-11-10 2002-11-10 2002-11-10 2002-11-10 2002-11-10 2002-11-10 2003-02-19 2003-02-19 2003-02-19 2003-02-19 2003-02-19 2003-02-19 2003-02-19 2003-02-19 2003-03-15 2003-03-15 2003-03-15 2003-03-15 2003-03-15 2003-03-15 2003-03-15 2003-03-15 2003-04-17 2003-04-17 2003-04-17 Detector SBC SBC SBC SBC HRC HRC HRC SBC SBC SBC SBC SBC HRC HRC HRC SBC SBC SBC SBC SBC HRC HRC HRC SBC SBC SBC SBC SBC HRC HRC HRC Filter F125LP F140LP F150LP F165LP F220W F250W F330W F115LP F125LP F140LP F150LP F165LP F220W F250W F330W F115LP F125LP F140LP F150LP F165LP F220W F250W F330W F115LP F125LP F140LP F150LP F165LP F220W F250W F330W Exp. Time 120.0 150.0 180.0 245.0 140.0 140.0 140.0 120.0 120.0 150.0 180.0 245.0 140.0 140.0 140.0 120.0 120.0 150.0 180.0 245.0 140.0 140.0 140.0 120.0 120.0 150.0 180.0 245.0 140.0 140.0 140.0

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Instrument Science Report ACS 2004-05 Table 1: Log of Observations for Proposals 9010, 9565 and 9655
Filename (_drz.fits[1]) j8hv07p4q j8hv07p5q j8hv07p6q j8hv07p7q j8hv07p8q j8hv08011 j8hv08021 j8hv08031 j8hv08sjq j8hv08skq j8hv08slq j8hv08smq j8hv08snq j8hv09011 j8hv09021 j8hv09031 j8hv09yxq j8hv09yyq j8hv09yzq j8hv09z0q j8hv09z1q j8hv10011 j8hv10021 j8hv10031 j8hv10ckq j8hv10clq j8hv10cmq j8hv10cnq j8hv10coq Proposal ID 9655 9655 9655 9655 9655 9655 9655 9655 9655 9655 9655 9655 9655 9655 9655 9655 9655 9655 9655 9655 9655 9655 9655 9655 9655 9655 9655 9655 9655 Obs. Date 2003-04-17 2003-04-17 2003-04-17 2003-04-17 2003-04-17 2003-05-14 2003-05-14 2003-05-14 2003-05-14 2003-05-14 2003-05-14 2003-05-14 2003-05-14 2003-06-12 2003-06-12 2003-06-12 003-06-12 003-06-12 003-06-12 003-06-12 003-06-12 2003-07-17 2003-07-17 2003-07-17 2003-07-18 2003-07-18 2003-07-18 2003-07-18 2003-07-18 Detector SBC SBC SBC SBC SBC HRC HRC HRC SBC SBC SBC SBC SBC HRC HRC HRC SBC SBC SBC SBC SBC HRC HRC HRC SBC SBC SBC SBC SBC Filter F115LP F125LP F140LP F150LP F165LP F220W F250W F330W F115LP F125LP F140LP F150LP F165LP F220W F250W F330W F115LP F125LP F140LP F150LP F165LP F220W F250W F330W F115LP F125LP F140LP F150LP F165LP Exp. Time 120.0 120.0 150.0 180.0 245.0 140.0 140.0 140.0 120.0 120.0 150.0 180.0 245.0 140.0 140.0 140.0 120.0 120.0 150.0 180.0 245.0 140.0 140.0 140.0 120.0 120.0 150.0 180.0 245.0

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Instrument Science Report ACS 2004-05

2. Data sets
The field observed by ACS is shown in Figure 1, where all standard stars are identified by the same letter used in STIS observations. We performed aperture photometry on all drizzled data sets by selecting an appropriate aperture. For the HRC data, we choose an 8.5 pixel radius aperture (0.23 arcsec radius) and for the SBC a 7.1 pixel (0.21 arcsec). Figure 1: Finding chart for NGC6681. This picture is a composite of a number of NUVMAMA F25SRF2 observations (Proffitt et al. STIS ISR 2003-01).

a

b

c

g k i j l m

2.1 HRC data Figures 2 through 4, refer to HRC observations (with filters F220W, F250W, and F330W) for all epochs. In each figure, each panel corresponds to a star labeled by its letter name, and for each epoch of observation the ratio of the star flux with the star flux at the initial epoch is plotted. The horizontal line indicates a flux ratio equal to one. There are no

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Instrument Science Report ACS 2004-05 sensitivity trends greater than 2% for any star. The larger scatter in the F220W is due to noisier data. Stars j at epochs 2002.63 and 2002.66 and star l at epochs 2002.56 and 2002.66 were affected, in all filters, by the presence of a bad column. These data points are not plotted in the figures and are not included when plotting the total flux ratios (Figure 5). For star g at epoch 2003.45 (2003-06-12) in both the F220W and the F250W filters, the photometry of the drizzled image is 16% less than at all other epochs and also differs from the photometry of the _flt files that are combined to produce the drizzled image. These two data points are excluded from all plots and from the statistical analysis. Figure 5 shows the trend with time of the total signal from all eight stars. The error bars are the Poisson statistics of the total number of counts at each epoch. The vertical ticks within the figure (bottom panel) indicate the epochs of the anneals and are derived from the appropriate proposals in Cycle 11 and in Cycle 12 (9031, 9566, 9650 and 10046). Unlike WFPC2, which has a cold window, contamination was not expected for ACS and no evidence has been seen. 2.2 SBC data A similar procedure was adopted for the SBC and similar results were obtained. Figures 6 through 11 are for the five filters and normalized total flux, as for the HRC. In the SBC observations, star a at epoch 2002.42 in filter F115LP was affected by a bad column, while star c at epoch 2003.37 both in filter F125LP and F140LP fell on the SBC repeller wire. For the SBC filters, no changes in sensitivity have been identified. However, the precision of the current analysis is limited by the lack of a L-flat field. Presently, the only conclusion is that Fig. 11 may suggest downward trends of ~5% per year. Stars a and j are much fainter than the other stars by a factor between 3 and 5.

3. Conclusions and recommendations
We have analyzed data from the UV contamination monitoring program for ACS from 2002 and 2003. We do not see any variation greater than 1% for the HRC. For the SBC, the lack of an L-flat limits the precision of the sensitivity trends. For Cycle 13, we recommend that UV contamination monitoring be continued at a rate which is half the frequency of observation in 2003 (proposal 9655). This means one orbit that includes both the HRC and the SBC filters every two months.

4. Acknowledgements:
F.R.B. would like to thank Cheryl Pavlovsky for her assistance with the many nuances of Framemaker. Thank you Cheryl!

4. References
Proffitt C. R., Brown T.R., Mobasher B., Davies J., 2003, STIS ISR 2003-01

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Instrument Science Report ACS 2004-05

Figure 2: HRC/F220W data for all eight stars in NGC6681

1.1

0.9

2002.4

2002.6

2002.8

2003.0

2003.2

2003.4

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Instrument Science Report ACS 2004-05 Figure 3: HRC/F250W data for all eight stars in NGC6681

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0.9 2002.4 2002.6 2002.8 2003.0 2003.2 2003.4

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Instrument Science Report ACS 2004-05 Figure 4: HRC/F330W data for all eight stars in NGC6681

1.1

0.9 2002.4 2002.6 2002.8 2003.0 2003.2 2003.4

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Instrument Science Report ACS 2004-05 Figure 5: Total Flux Ratios for the HRC

1.05

0.95

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Instrument Science Report ACS 2004-05 Figure 6: SBC/F115LP data for all eight stars in NGC6681

1.2

0.85

2002.4

2002.6

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Instrument Science Report ACS 2004-05 Figure 7: SBC/F125LP data for all eight stars in NGC6681

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Instrument Science Report ACS 2004-05 Figure 8: SBC/F140LP data for all eight stars in NGC6681

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0.85

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Instrument Science Report ACS 2004-05 Figure 9: SBC/F150LP data for all eight stars in NGC6681

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2002.4

2002.6

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Instrument Science Report ACS 2004-05 Figure 10: SBC/F165LP data for all eight stars in NGC6681

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Instrument Science Report ACS 2004-05 Figure 11: Total Flux Ratios for the SBC

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0.95 2002.4 2002.6 2002.8 2003.0 2003.2 2003.4

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