Supported MULTIACCUM Sequences

Transcription

1 Instrument Science Report NICMOS-017 Supported MULTIACCUM s John W. MacKenty and Luis Colina November 21, 1996 ABSTRACT In this ISR we define a specific set of MULTIACCUM mode exposure time sequences. The selected sequences are flexible and cover the great majority of MULTIACCUM options from linear to logarithmic stepping, and from short fast exposures to long exposures covering a full orbit. We also define a modification to the RPS2 Proposal Editor (PED) which greatly simplifies the input of these MULTIACCUM exposure time sequences during phase II proposal implementation. These MULTIACCUM sequences will be calibrated preferentially by STScI and their use will avoid the interpolation of the darks during the reduction process. We strongly encourage observers to use these recommended sequences whenever practical. 1. Introduction Ground testing of NICMOS has led the NICMOS IDT to recommend that interpolation of dark current calibration exposures be avoided whenever possible. While STScI has previously defined a specific set of ACCUM mode exposure times, this has not yet been done for MULTIACCUM mode exposure times. Due to clocking constraints, NICMOS MUL- TIACCUM exposure times have values that need a lot of significant figures, but a large number of times are possible. In order to simplify the phase II proposal implementation, and to avoid any undesirable interpolation of dark current calibration exposures, we present in this ISR a set of 16 MULTIACCUM sequences which should cover the great majority of users observations. 2. s of s In consultation with Marcia Rieke and Glenn Schneider of the NICMOS IDT, we have defined the MULTIACCUM exposure time sequences listed in Table 1. As discussed in Section 3, these sequences may be truncated by observers to achieve their desired maximum exposure time. Three flavors of sequence are defined: 1

2 s with rapid readouts which obtain the densest temporal sampling operating either a single camera (SCAMRR), or two or three cameras in parallel (MCAMRR). s with linear step sizes. These sequences are valid for single and parallel observations with any of the cameras. The sequences each include 3 readouts during the first second to permit the (possible) compensation for non-linear effects, and the subsequent stepping is 1 second (STEP1), or 2 seconds (STEP2). Additional sequences consist of 2 readouts during the first second, and a subsequent linear stepping of 64 seconds (SPARS64), or 256 seconds (SPARS256). s which combine logarithmic and linear step sizes. These sequences are valid for single and parallel observations with any of the cameras. Each sequence includes 3 readouts during the first second to permit the (possible) compensation for non-linear effects. Subsequent steppings are logarithmic up to 8 secs (STEP8), 16 secs (STEP16), 32 secs (STEP32), 64 secs (STEP64), 128 secs (STEP128), or 256 secs (STEP256) and then linear in intervals of 8 secs (STEP8), 16 secs (STEP16), 32 secs (STEP32), 64 secs (STEP64), 128 secs (STEP128), or 256 secs (STEP256). s with 9 rapid readouts at both their start and end points to combine the readnoise reduction of the ACCUM MIF (i.e. ACCUM with Multiple Initial and Final readouts, NREAD>1) strategy with the dynamic range benefits of multiple samples during the integration. These sequences are valid for single and parallel observations with any of the cameras. These sequences extend up to 512 seconds (MIF512), 1024 secs (MIF1024), 2048 secs (MIF2048), and 3072 seconds (MIF3072). Table 1: MULTIACCUM Exposure Time s SCAMRR Single Camera Rapid Readout MCAMRR Multiple Cameras Rapid Readout STEP1 Linear 1 seconds step

3 Table 1: MULTIACCUM Exposure Time s STEP2 Linear 2 seconds step STEP8 Log /8 seconds linear STEP16 Log/16 seconds linear STEP32 Log/32 seconds linear STEP64 Log/64 seconds linear

4 Table 1: MULTIACCUM Exposure Time s STEP128 Log/128 seconds linear STEP256 Log/256 seconds linear MIF512 MIF 512 seconds MIF1024 MIF 1024 seconds MIF2048 MIF 2048 seconds

5 Table 1: MULTIACCUM Exposure Time s MIF3072 MIF 3072 seconds SPARS64 Linear 64 seconds step SPARS256 Linear 256 seconds step Implementation for Phase II Proposal Writing Since the entry of lengthly sequences of MULTIACCUM SAMP-TIMES into phase II proposal logsheets is both tedious for our observers and prone to errors, RPS2 will have an optional parameter to simplify the use of these predefined MULTIACCUM sequences. This way, the sequences indicated in Table 1 are available to GOs using PED or standard editors for phase II proposal preparation. The new optional parameter is called SAMP- SEQ and can be given any of the names indicated in Table 1 above. 5

6 If SAMP-SEQ is used, the number of readouts in the sequence can be truncated by specifying the number of SAMP-TIMES with the new optional parameter NSAMP (= 1-25). For example, if you want a STEP8 sequence with a maximum time of 120 seconds, you would choose SAMP-SEQ= STEP8 and NSAMP= 20, and the actual translation of the sequence into SAMP-TIMEs will be done by Transformation (the feasibility section of RPS2), and therefore will be transparent. The number of readouts will be NSAMP plus one for the initial readout, giving a maximum of 26 readouts for a single execution of a MULTIACCUM exposure. Also note that if SAMP-SEQ is used, the SAMP-TIMEnn optional parameters are illegal, and vice versa. This makes it easy to specify a predefined sequence, and there is no chance of changing some of the SAMP-TIMEs in the sequences listed in Table 1. 6