Instrument Science Report NICMOS 2005-005 NICMOS Cycles 13 and 14 Calibration s Santiago Arribas, Eddie Bergeron, Roelof de Jong, Sangeeta Malhotra, Bahram Mobasher, Keith Noll, Al Schultz, Tommy Wiklind, Chun Xu. November 17, 2005 ABSTRACT This document summarizes the NICMOS Calibration s for Cycles 13 and 14. These plans complement the SMOV3b, the Cycle 10 (interim), and the Cycles 11 and 12 (regular) calibration programs executed after the installation of the NICMOS Cooling System (NCS).. These previous programs have shown that the instrument is very stable, which has motivated a further reduction in the frequency of the monitoring programs for Cycle 13. In addition, for Cycle 14 some of these programs were slightly modified to account for 2 Gyro HST operations. The special calibrations on Cycle 13 were focussed on a follow up of the spectroscopic recalibration initiated in Cycle 12. This program led to the discovery of a possible count rate non-linearity, which has triggered a special program for Cycle 13 and a number of subsequent tests and calibrations during Cycle 14. At the time of writing this is a very active area of research. We also briefly comment on other calibrations defined to address other specific issues like: the autoreset test, the SPAR sequences tests, and the low-frequency flat residual for NIC1. The calibration programs for the 2-Gyro campaigns are not included here, since they have been described somewhere else. Further details and updates on specific programs can be found via the NICMOS web site. Introduction Since the installation of the NICMOS Cooling System (NCS) during the Servicing Mission 3b, NICMOS has shown a very stable behavior as a consequence of its well controlled operating temperature (Wiklind & Wheeler, 2006; Bergeron 2006), which has facilitated greatly its calibration. This stable behavior has had an important impact on the Copyright 1999 The Association of Universities for Research in Astronomy, Inc. All Rights Reserved.
calibration plans, which have evolved into three main directions. First, the frequency of some of the monitoring programs have been gradually reduced. Second, due to the higher instrument s stability, the systematic errors in the calibration have become relatively more important. Consequently a reduction in the systematic errors in zero points and grism sensitivity curves has been pursued. Third, we have also studied the behavior of the instrument at extreme count rate regimes (e.g. UDF, very high S/N spectrophotometry). Apart from these generic lines, other calibrations to address specific problems (e.g. autoreset, new multi-accum sequences, etc.) have been also implemented. In the following paragraphs we will briefly comment on each of these categories, pointing out the most relevant aspects of the Cycles 13 and 14 Calibration s. 1- Monitor programs: As a consequence of the stable behavior shown by the instrument, the frequency of the different monitoring programs, which track the stability of key properties of the instrument (i.e.darks, flats, focus, photometry), have been gradually reduced between Cycles 10 and 13. Although it was discussed the possibility of reducing the frequency of some programs even further by combining their information (i.e. photometric stability could, in principle, be checked using the photometric monitoring data), it was considered important to maintain homogeneity in the programs across cycles. During Cycle 13 the major reductions affected to the flat and focus programs, whose frequency were cut by factors of 2 and 1.5, respectively. During Cycle 14 we maintain the same frequency as in Cycle 13 for all monitor programs. However, the change to a 2 Gyro operating mode for HST has reduced the visibility period of some of the objects traditionally used for some of these programs, like the photometric and focus monitor. Consequently we have added new objects to these programs (G191B2B as new photometric standard and 47Tuc as a new focussing cluster). 2- Photometric and Spectrophotometric recalibrations: The more stable behavior of the detectors has made the systematic errors to have a relatively more important role in limiting the actual accuracy of standard observations. Consequently we launched in Cycle 12 two programs (photometric and spectrophotometric re-calibrations) aimed at improving the systematic errors associated with the photometric zero-points and sensitivity curves with respect to those achieved during Cycle 7 and 7N. The photometric re-calibration expanded the number and type of stars used for obtaining the zero points for all filters. Similarly, the spectroscopic recalibration allowed a reanalysis of the sensitivity curves for the three grisms using a larger number and variety of stars. Several of the selected objects were common for the two proposals. Therefore, these data allowed a spectro-photometric recalibration by cross-checking results obtained independently from these modes (i.e. imaging/filters and spectroscopy/grism). 2
This program (which included new faint calibrating stars) has led to the discovery of a possible count rate non-linearity. This effect, the so called Bohlin effect, is described in detail in Bohlin, Lindler, & Riess (2005). As a response to this effect, a special calibration program was implemented in Cycle 13, and several tests and calibrations have followed during Cycle 14. Since this effect is more significant at a very low count rate regime, it will be briefly commented in the following section. The new data obtained with the photometric re-calibration program (as well as the larger set of data collected with the photometric monitoring programs) also suggested the possibility of some systematic residual associated to the position of the object in the field of view. During Cycles 7 and 7N the possible variation of the response (after flat-fielding) as a function of the position in the field of view was estimated to be small compared with the actual uncertainties in the photometry. However, with the current higher precision data this is unclear, and a study to analyze the low frequency flat residuals has been implemented in the Cycle 14 Calibration. This will be done initially for camera 1 since the intra-pixel sensitivity effect on the photometry is smaller. Depending on the results of this program it could be also implemented in cameras 2 and 3 (which require extensive dithering to average out this effect; Xu & Mobasher, 2003). 3- Calibrating the extremes: From the very high S/N regime to the UDF During Cycles 12-14 the behavior of NICMOS at extreme count rate regimes has been investigated. On one hand a Cycle 12 calibration proposal lead by R. Gilliland was aimed at investigating the relative spectrophotometric accuracy of the instrument at very high S/ N regime. It was found that NICMOS can reach a relative precision of around 10-4 or even higher in time series observations (Gilliland and Arribas, 2003). Further details can be found in Gilliland (2006). On the other extreme, the Hubble Ultra Deep Field observations imposed new calibration challenges. Details on these particular calibrations are discussed in Mobasher & Riess (2005) and Thompson (2006). Provided that objects in the UDF are observed at extremely low count rates, their calibration may be affected by the Bohlin effect mentioned above. In order to understand better the origin of this reported non-linearity, a program which includes several tests has been implemented in the Cycle 14 Calibration. These tests include: i) the measurement of the wavelength dependence of the persistence decay after an exposure of a bright star in a series of multiaccum dark frames, ii) the measure of the non-linearity dependence on the count rate by observing a field of stars in a sequence of lamp off/on, and so artificially increasing the background level (this will be done in imaging and grism modes), and iii) the photometric measurements of the faint standard stars SNAP-2 and WD1657+343, (on which the NIC- MOS non-linearity was originally discovered using grism observations) will be repeated to obtain higher S/N. All these observations should clarify the origin of the non-linearity effect, and its possible relation with the UDF calibrations (de Jong 2006) 3
4- Specific calibrations: Some programs implemented in the calibration plans just addressed very specific issues like: i) Delta-T program: The goal of this program was to study the effects of the detector temperature on the darks. (This was a Cycle 12 calibration program implemented to late to be included in the standard calibration plan for this cycle). ii) Autoreset test: This Cycle 13 calibration program is aimed at testing the short term temperature ripples in the NICMOS dewar. iii) New SPARS sequences: This Cycle 14 program had the goal of testing the darks of the newly implemented SPARS multiaccum sequences. Further details on the individual proposals may be found in the tables and text below, and via the standard HST and NICMOS web sites. The reader may also want to check the proceedings of the Calibration Workshop held at the STScI in October 26-28 (Eds. A. Koekemoer, Dressel, L., Goudfrooij, 2006). References Bergeron, E. 2006, The 2005 HST Calibration Workshop. Eds. A. Koekemoer, L. Dressel, P. Goudfrooij (in press Bohlin, R., Lindler, R., & Riess, A. 2005, NICMOS-ISR-2005-002 Gilliland, R., and Arribas, S. 2003, NICMOS-ISR-2005-001 Gilliland, R. 2006, The 2005 HST Calibration Workshop. Eds. A. Koekemoer, L. Dressel, P. Goudfrooij (in press). de Jong, R. 2006, The 2005 HST Calibration Workshop. Eds. A. Koekemoer, L. Dressel, P. Goudfrooij (in press). Mobasher, B., and Riess, A. 2005 NICMOS-ISR-2005-003 Thompson, R. 2006, The 2005 HST Calibration Workshop. Eds. A. Koekemoer, L. Dressel, P. Goudfrooij (in press) Wiklind, T, and Wheeler, T. 2006, The 2005 HST Calibration Workshop. Eds. A. Koekemoer, L. Dressel, P. Goudfrooij (in press). Xu, C., and Mobasher, B. 2003 NICMOS-ISR_2003-009 4
NICMOS Cycle 13 Calibration ID Proposal Title Frequency Estimated Time (orbits) Scheduling External Internal Required Required (FTE) Products Accuracy Required Notes Routine Monitoring Programs 10380 Multiaccum Darks monthly 36 0.2 CDBS 4-5% Same as in Cycle 12 10382 Focus Stability NIC1 and NIC2 every 3 months 9 0.3 ISR 1mm Same as in Cycle 12, but NIC1 or NIC2 every 45 days (instead of monthly) 1 NIC3 execution. 10381 Photometry Stability bi-monthly 12 0.5 CDBS 2% Same as in Cycle 12 10379 Flats Stability quarterly 3 0.2 IR / ISR 0.5% Same as in Cycle 12, but quarterly (instead of bi-monthly) Special Calibration Programs 10383 Grism Recalibration: follow up once 2 0.3 ISR 1% Observations of BD+17 4708 10454 Extreme count rates linearity test once 12 0.5 ISR 1% Response to the discovery of a possible non-linearity effect 10465 NICMOS Autoreset Test once 2 0.3 ISR 1% Test of the short term temperature ripples in the NICMOS dewar TOTAL TIME (including all executions) 38 38 2.3
Proposal ID 10380: NICMOS Cycle 13: MA DarksProposal ID 10454: Purpose The purpose of this proposal is to monitor the dark current, read noise, and shading profile for all three NICMOS detectors throughout the duration of Cycle 12. This proposal is a continuation of PID 9321 and 9636 which cover the period between the end of SMOV3B and the end of Cycle 11. For SPARS64, NSAMP has been changed from 19 to 23, in order to provide Superdarks for proposal 9803 (UDF). Description Each iteration of this proposal consists of ten dark exposures of 1088s (sample sequence of SPARS64 and NSAMP=23) for all 3 cameras. In addition, a set of 3 SCAMRR, NSAMP=25 sequences for each camera will be obtained in order to set an accurate estimate of the read noise. Finally, in order to characterize the shading profile of the NICMOS detectors, a set of 5 STEP256, NSAMP=12 sequences for each camera will be taken. These contain all commonly used NICMOS Delta-times, except the shortest one (0.2s) which is covered by the SCAMRR sequences. As an additional benefit, the dark exposures will allow us to estimate the cosmic ray rates outside the SAA. This sequence will be repeated once a month for 12 months to allow the monitoring of NICMOS detector behavior as a function of time and temperature throughout Cycle 12. FractionGO- 100% Supported R: Observation Each monthly visit will require 3 internal orbits. Therefore 36 orbits are required to cover the cycle : 0.3 FTE Analysis Products Darks for all readout sequences. Direct superdarks for SPARS64 (NSAMP=23) Accuracy Goals Scheduling Requirements 4-5 % per visit for the linear component of the dark current. In principle S/N ~ 50, but degradation due to CR lower this figure. S/N ~ 35 (12) for the amplifier glow at the corner (center). Monthly. SAA free orbits 6
Proposal ID 10382: NICMOS Cycle 13: Focus Stability Purpose The purpose of this activity is to check the focus for the three cameras Description Steps: a) Use refined target field positions as determined in cycle 7 b) Use MULTIACCUM sequences of sufficient dynamic range to account for defocus c) Do a 17-point focus sweep, +/- 8mm about the PAM mechanical zeropoint for each cameras 1 and 2, in 1mm steps. (10-point focus sweep from -0.5 to -9.5 for camera 3). d) Use PAM X/Y tilt and OTA offset slew compensations refined from previous focus monitoring/optical aligment activities. e) Use phase retreval algorithms to establish PAM focuss for each camera. Fraction 100% Programs Supported Observation Analysis Every visit will require 1 external orbit. (if only NIC1 or NIC2 are checked) or 2 orbits is NIC3 is also done. NIC1 and NIC2 will be executed 4 times during the cycle (every 3 months), and NIC3 once. NIC1 or NIC2 will be checked every 45 days. A total of 9 orbits are needed to cover the cycle. 0.3 FTE Products ISR, Update of focus as needed Accuracy The best focus should be known within 1 mm Goals Scheduling& Every ~ 45 days NIC1 or NIC2 (alternate their executions). Special One NIC3 execution Requirements 7
Proposal ID 10381: NICMOS Cycle 13: Photometric Stability Purpose To verify the stability of the NICMOS photometric calibration over a broad range of wavelengths. Description Observations of a standard star (P330E) through the following subset of filters: F090M, F110W, F160W and F190N for NIC1; F110W, F160W, F190N, F222M for NIC2 and F110W, F160W, and F222M for NIC3. All observations are done using a spiral dither pattern, with 4 dither points for NIC1 and NIC2, and 7 dithers for NIC3 (to help reduce intrapixel sensitivity effects on the photometry). The integration times are set to achieve S/N =~ 200-350 in the standard photometry apertures for each exposure, while keeping peak pixel counts to < 66% of saturation level. The NIC1/F190N observation has somewhat lower S/N (~110) per exposure. NIC3/F110W may come slightly closer to saturation (~73% according to the ETC). Fraction 100% Programs Supported Observation Analysis Each bi-monthly visit will require 2 external orbits. Therefore, 12 orbits are required for the complete period. 0.30 FTE Products Internal Report or ISR. Updated zero pionts for CDBS Accuracy 2-1% Goals Scheduling& SAA free orbits preferred. Special Requirements 8
Proposal ID 10379: NICMOS Cycle 13: Flats Stability Purpose A series of camera 1, 2, & 3 flat fields will be obtained to monitor the health of the cameras. Description Each 1-orbit visit will obtain pointed flat fields in each camera (NIC1 filters F110M, F110W, F160W; NIC2 filters F110W, F160W, F222M; NIC3 filters F110W, F160W, F222M). Some filters will be rotated through the sequence so that many filters will be used during a year. A four point dither pattern will be used to allow removal of background objects. At each dithered position, observations will be obtained with the lamp off and followed by lamp on observations. Every four months well exposure observations will be taken to study the non-linearity corrections. The Cameras 1 and 2 will be used in parallel. For almost all the exposures, Lamp 1 (High Intensity) will be used. Fraction 100% Programs Supported Observation Analysis Each quarterly visit will require one orbit. Therefore, 3 orbits are needed for the complete Cycle. 0.2 FTE Products Depending on the results an internal report or an ISR. Accuracy 1-2 % Goals Scheduling& SAA free orbits. Special Requirements 9
Proposal ID 10383: NICMOS Cycle 13: Grism Recalibration: follow up Purpose All cycle 12 data for the spectroscopic recalibration (ID 9998) were successfully acquired. One problem is that the repeatability as measured by the comparison of the cycle 11 to the cycle 12 observations of P330E is only 2%. The goal and expectation is for repeatability to better than 1%. The somewhat poorer results may be attributed to flat field differences between the Thompson dither strategy during Cycle 11 and that used in during Cycle 12 (ID 9998); or perhaps, there is some synoptic change in the system throughput. In order distinguish these possibilities and hopefully recover a repeatability of 1%, the observations of one star must be repeated as early as possible in Cycle 13, using the same dither strategy as 9998. Description Observations of the bright sloan standard BD+17d4708 with G096, G141, and G206 using the same dither strategy as in 9998. This star has been previously observed on 04Jan10. P330E would be a good choice, except that it was previously observed too recently on 04Jun19 to measure any sensitivity change back to 04 Jan; and the scheduling would be rushed to get it before going into solar avoidance in October. Fraction ~ 8% of the programs will have a direct benefit of the spectroscopic recalibration. However, this recalibrationl (togather with the photometric recalibration) will provide a robust basis for the NICMOS absolute calibration, which has a broader interest Req.: Obs. 2 orbits are required Re. Analysis 0.30 FTE Products ISR, CDBS Acc. Goals 1% Scheduling& Spe. Requi. Ideally,to minimize the effect of any synoptic sensitivity change, the observations should be made in September, before P330E goes into the solar avoidance zone in mid-october. SAA free orbits 10
Proposal ID 10465: NICMOS Cycle 13: Autoreset test Purpose Test of the short term temperature ripples in the NICMOS dewar. Description The test consists of running the NICMOS detectors with and without the AUTORESET mode on. Orbits free of NICMOS science observations are to be used and each mode (ON/OFF) will run for approximately 24 hours. The long duration is on order to allow the temperature in the dewar to stabilize. Normal telemetry data will be sufficient for the temperature monitoring. SAA passages are handled as usual when NICMOS observations are scheduled: the NICMOS detectors are turned off and after the SAA passage, two post-saa darks are done and the NICMOS detectors are left in an ON mode. The remaining time will be divided into 2 different parts, each one lasting approximately 24 hours: Visits 11, 12, 13, 21, 22, 23, 31, 32, 33, 41, 42, 43, 51, 52, 53, 61 will cover ~24 hours with AUTOFLUSH mode OFF. These visits are grouped together. Visits 15, 16, 17, 25, 26, 27, 35, 36, 37, 45, 46, 47, 55, 56, 57, 65 will cover ~24 hours with AUTOFLUSH mode ON. These visits are grouped together. Each set of visits should be done over a 24 hour time period without interuption, with normal HST activities. The two sets (AUTOFLUSH ON and OFF) do not have to be done back-to-back, but should be scheduled as close to each other in time as practical. Fraction 100 % Req.: Obs. 2 internal orbits are required Re. Analysis 0.30 FTE Products Technical report Acc. Goals 1% Scheduling& See program Spe. Requi. 11
Proposal ID 10454: NICMOS Cycle 13: Extreme count rates linearity test Purpose To test the linearity of the detectors at count rates falling at the low and high extremes of what is feasible.this program is a response to the discovery that grism observations obtained with NIC3 show a systematic offset from spectra taken with STIS and ACS in the 0.8-1.0 micron overlap region. The observations are consistent with a NIC3 sensitivity that depends on incident flux, i.e. count rate. Description By observing one bright star (BD+17D4708, the Sloan Digital SkySurvey absolute standard) and two faint stars (SNAP-2, a solar analog star;wd1657+343, a white dwarf) in a number of filters we will check whether this is an intrinsic feature of the all NICMOS detectors, something intrinsic to NIC3, or a result of a not understood effect of the grism observations. We will furthermore be able to test whether the effect has a wavelength dependence.photometric observations will be done for all three NICMOS cameras, using a subset of filters for each. The filters to be used were selected to overlap maximally with the existing standard star observations of intermediate brightness. In addition, we will obtain extra spectroscopic data on WD1657+343, the faintest and best modeled white dwarf of the stars on which the original discovery of the non-linearity was made. This will reduce the errors in this spectrum from 5% to 2% and will allow a better estimate of the effect. Fraction ~ 100% of the programs will benefit of this calibration Req.: Obs. 12 orbits are required Re. Analysis 0.50 FTE Products ISR, CDBS Acc. Goals 1% Scheduling& Spe. Requi. In order to ease scheduling, there are no time constraints specified in the proposal. However, because of the potentially important implications of this effect, it is very important that these orbits bescheduled as soon as possible. They could be critical for the proper calibration of NICMOS The targets have visibility 1) BD+17D4708: 16 Apr - 17 Jan 2) SNAP-2: 3 Feb-1 Mar 3) WD1657+343: 3 Feb-26 FebThere are no SAA requirements on this proposal, although SAA-free orbits are always prefered if possible. 12
NICMOS Cycle 14 Calibration ID Proposal Title Frequency Estimated Time (orbits) Scheduling External Internal Required Required (FTE) Products Accuracy Required Notes Routine Monitoring Programs 10723 Multiaccum Darks monthly 24 0.2 CDBS 4-5% Same as in Cycle 13 10724 Focus Stability NIC1 or NIC2 every 45 days 13 10 0.3 ISR 1mm Similar to Cycle 13 (4 NIC1, 4 NIC2, and 2 NIC3 executions) New field (47Tuc), for 2Gy operations 10725 Photometry Stability bi-monthly 12 0.3 CDBS 2% Same as in Cycle 13, but new object (G191B2B) for 2Gy operations 10728 Flats Stability every 3 4 0.2 IR / ISR 0.5% Same as in Cycle 13 months Special Calibration Programs 10726 Non-linearity tests once 12 1 ISR 1% Several tests to analyse the count rate dependent non-linearity seen in NIC- MOS spectro-photometric observations 10727 Low-frequency flat residuals for NIC1 10721 Test for newly implemented SPARS sequences once 2 0.5 ISR/ CDBS 1% To better characterize the flatfielding errors seen for camera 1 in the photometric monitoring data once 12 0.2 IR 4-5% To measure the dark currents for the new multiaccum sequences for all three NICMOS detectors. TOTAL TIME (including all executions) 40 36 2.5
Proposal ID 10723: NICMOS Cycle 14: MA Darks Purpose The purpose of this proposal is to monitor the dark current of the three NICMOS detectors throughout the duration of Cycle 14. This proposal is a continuation of PID 9321, 9636 and 9993 which cover the period between the end of SMOV3B and the end of Cycle 13. Description Each iteration of this proposal consists of ten dark exposures of 1344s (sample sequence of SPARS64 and NSAMP=23) for all 3 cameras. The dark exposures will also allow us to estimate the cosmic ray rates outside the SAA. This sequence will be repeated once a month for 12 months to allow the monitoring of NICMOS detector behavior as a function of time and temperature throughout Cycle 14. Since 2000 the (linear) darks for all 3 detectors have been stable (using data from proposals: PID 9321,9636,10064,9803 [UDF],9993,10380). Occasionally high darks are obtained due to persistance after observations of extremely bright objects (e.g. Mars). FractionGO- 100% Supported R: Observation Each monthly visit will require 2 internal orbits. Therefore 24 orbits are required to cover the cycle : 0.3 FTE Analysis Products Darks for all readout sequences. Accuracy 4-5 % per visit for the linear component of the dark current. Goals Scheduling Monthly. SAA free orbits Requirements 14
Proposal ID 10724: NICMOS Cycle 14: Focus Stability Purpose Check the focus for the three cameras Description Steps:a) Use new target field positions (47Tuc) to account for 2Gy operations b) Use MULTIACCUM sequences of sufficient dynamic range to account for defocus c) Do a 17-point focus sweep, +/- 8mm about the PAM mechanical zeropoint for each cameras 1 and 2, in 1mm steps. (10-point focus sweep from -0.5 to -9.5 for camera 3). d) Use PAM X/Y tilt and OTA offset slew compensations refined from previous focus monitoring/optical aligments. e) Phase retreval algorithms (and encircled energy) to establish PAM focuss for each camera. Fraction 100% Programs Supported Observation Analysis Every visit will require 1 external orbit. (if only NIC1 or NIC2 are checked) or 2 orbits is NIC3 is also done. NIC1 and NIC2 will be executed 4 times during the cycle (every 3 months), and NIC3 twice. NIC1 or NIC2 will be checked every 45 days. A total of 10 orbits are needed to cover the cycle. 0.3 FTE Products ISR, Update of focus as needed Accuracy The best focus should be known within 1 mm Goals Scheduling& Every ~ 45 days NIC1 or NIC2 (alternate their executions). Special Two NIC3 executions Requirements 15
Proposal ID 10725 : NICMOS Cycle 14: Photometric Stability Purpose To verify the stability of the NICMOS photometric calibration over a broad range of wavelengths. Description Observations of the standard stars (P330E and G191B2B) through the following subset of filters: F090M, F110W, F160W and F190N for NIC1; F110W, F160W, F190N, F222M for NIC2 and F110W, F160W, and F222M for NIC3. All observations are done using a spiral dither pattern, with 4 dither points for NIC1 and NIC2, and 7 dithers for NIC3 (to help reduce intrapixel sensitivity effects on the photometry). The integration times are set to achieve S/N =~ 200-350 in the standard photometry apertures for each exposure, while keeping peak pixel counts to < 66% of saturation level. The NIC1/F190N observation has somewhat lower S/N (~110) per exposure. NIC3/ F110W may come slightly closer to saturation (~73% according to the ETC). Fraction 100% Programs Supported Observation Analysis Each bi-monthly visit will require 2 external orbits. Therefore, 12 orbits are required for the complete period. 0.30 FTE Products Internal Report or ISR. Updated zero pionts for CDBS Accuracy 2-1% Goals Scheduling& Special Requirements The two selected targets should cover the whole Cycle under 2Gy operations, but one month. SAA free orbits preferred. 16
Proposal ID 10728: NICMOS Cycle 14: Flats Stability Purpose A series of camera 1, 2, & 3 flat fields will be obtained to monitor the health of the cameras. Description Each 1-orbit visit will obtain pointed flat fields in each camera (NIC1 filters F110M, F110W, F160W; NIC2 filters F110W, F160W, F222M; NIC3 filters F110W, F160W, F222M). Some filters will be rotated through the sequence so that many filters will be used during a year. A four point dither pattern will be used to allow removal of background objects. At each dithered position, observations will be obtained with the lamp off and followed by lamp on observations. Every three months well exposure observations will be taken to study the non-linearity corrections. The Cameras 1 and 2 will be used in parallel. After the last full well exposed image darks will be taken in the occulted part of the orbit to measure persistence due to charge trapping. Fraction 100% Programs Supported Observation Analysis Each visit will require one orbit. Therefore, 4 orbits are needed for the complete Cycle. 0.2 FTE Products Depending on the results an internal report or an ISR. Accuracy 1-2 % Goals Scheduling& SAA free orbits. Special Requirements 17
Proposal ID 10726: NICMOS Cycle 14: Non-linearity tests Purpose This program incorporates a number of tests to analyse the count rate dependent non-linearity seen in NICMOS spectrophotometric observations. Description It will consists of five visits. In visit 1 we will observe a few fields with stars of a range in luminosity in NGC1850 with NIC- MOS in NIC1 in F090M, F110W and F160W and NIC2 F110W, F160W, and F180W. We will repeat the observations with flatfield lamp on, creating artificially high count-rates, allowing tests of NICMOS linearity as function of count rate. To access the effect of charge trapping and persistence, we first take darks (so there is not too much charge already trapped), than take exposures with the lamp off, exposures with the lamp on, and repeat at the end with lamp off. Finally, we continue with taking darks during occultation. In visit 2 we will observe spectro-photometric standard P041C using the G096 and G141 grisms in NIC3, and repeat the lamp off/on/off test to artificially create a high background. In visits 3&4 we repeat photometry measurements of faint standard stars SNAP-2 and WD1657+343, on which the NICMOS non- linearity was originally discovered using grism observations. These measurements are repeated, because previous photometry was obtained with too short exposure times, hence substantially affected by charge trapping non-linearity. Measurements will be made with NIC1: Visit 5 forms the persistence test of the program. The bright star GL-390 (used in a previous persistence test) will iluminate the 3 NICMOS detectors in turn for a fixed time, saturating the center many times, after which a series of darks will be taken to measure the persistence (i.e. trapped electrons and the decay time of the traps). To determine the wavelength dependence of the trap chance, exposures of the bright star in different filters will be taken, as well as one in the G096 grism with NIC3. Fraction 100% Req.: Obs. For external orbits for the persistence test and 4 external orbits for the lamp off/on test, for a total of 8 orbits. Re. Analysis 0.5 FTE Products ISR, if necessary.refinement of pipeline Acc. Goals 1% Scheduling& SAA free orbits preferred Spe. Requi. 18
Proposal ID 10727: NICMOS Cycle 14: L-Flat residuals Purpose We will perform a low frequency flatfield investigation for NIC- MOS Camera 1 in order to better characterize the flatfielding errors seen for camera 1 in the photometric monitoring data. NGC1850 will be dithered in a 3x3 pattern in 4 filters: F090M, F110W, F160W, and F190N. Each exposure will last at least 100 s to mitigate charge trapping non-linearity effects. Please schedule this at the earliest opportunity, as the problems with the NIC1 flat field may be related to the NICMOS non-linearity currently being investigated. Description Fraction We will perform a low frequency flatfield investigation for NIC- MOS Camera 1 in order to better characterize the flatfielding errors seen for camera 1 in the photometric monitoring data. A spars stellar field near NGC1850 will be dithered in a 3x3 pattern in 4 filters: F090M, F110W, F160W, and F190N. Each exposure will last at least 100 s to mitigate charge trapping nonlinearity effects. We do the 9 points offset with 9 explicit pointings to get a celestial coordinate 3x3 pattern that matches the (somewhat linear) distribution of stars near the center of the cluster. 100% t Req.: Obs. 2 external orbits Re. Analysis 0.5 FTE Products Depending on the results, ISR, CDBS, pipeline improvement Acc. Goals 1% Scheduling& Early in the cycle, SAA free orbits Spe. Requi. 19
Proposal ID 10721: NICMOS Cycle 14: Dark current of new SPARS sequences Purpose On June 12, 2005, 4 new NICMOS multiaccum sequences (SPARS4, SPARS16, SPARS32, SPARS128) were implemented. The purpose of this observation is to measure the darkcurrent for these new multiaccum sequences for all three NICMOS detectors. Description 3 internal orbits are allocated to each of the 4 new SPARS sequences, in order to measure the dark currents for each detector (NIC1, NIC2 and NIC3). The 3 detectors are arranged to work in parallel. Each orbit consists of multiple copies of similar exposures, with NSAMP ranging from 22 to 25, in order to fully fill each orbit. Fraction 10% t Req.: Obs. 12 internall orbits Re. Analysis 0.2 FTE Products Internal report Acc. Goals 4-5% Scheduling& Spe. Requi. All visits should be scheduled in SAA-free orbits in order to avoid contamination by cosmic ray persistence. 20