Config |Mode | Optional Parameters-------|-----------|------------------------------------------------------ NIC1 | ACCUM | NREAD = 1(default) - 25 NIC2 |-----------|------------------------------------------------------ NIC3 | MULTIACCUM| SAMP-TIMEi (i=01-25) = 0.215 - 8590.0 seconds
|-----------|------------------------------------------------------- | RAMP | NSAMP = 3(default) - 255 | | CR-ELIMINATION = CONTINUE(default), RETAIN, MARK, NONE |-----------|------------------------------------------------------- | ACCUM | READOUT = FAST(default), SLOW | MULTIACCUM| PATTERN = NONE(default), SPIRAL-DITH, STRIP-DITH, | RAMP | SQUARE-WAVE-DITH, ONE-CHOP, TWO-CHOP, | | FOUR-CHOP, EIGHT-CHOP, SPIRAL-DITH-CHOP | | NUM-DITH = 1 - 40 {upper limit TDB} | | DITH-SIZE = 0.0 - 40.0 arcsec {upper limit TDB} | | NUM-CHOP = 1 - 40 {upper limit TDB} | | CHOP-SIZE = 0.0 - 1800.0 arcsec | | OFFSET = SAM(default), SAM-NO-REACQ, SAM-NO-GYRO, FOM | | PATTERN-ORIENT = DETECTOR(default), 0.0 - 360.0 degrees | | FOMXPOS = 0.0(default) -26.0 to +26.0 arcsec | | FOMYPOS = 0.0(default) -26.0 to +26.0 arcsec | | | LAMP = NONE(default), FLAT1, FLAT2, FLAT3 | |-----------|------------------------------------------------------- | BRIGHTOBJ | -------|-----------|------------------------------------------------------- NIC2 | ACQ | -------|-----------|------------------------------------------------------- |NIC| | |ALIGN| | | FOCUS = 0(default), -4097 to +4097 steps| | | | XTILT = 0(default), -176 to +176 steps| | | | YTILT = 0(default), -176 to +176 steps| -------|-----------|------------------------------------------------------- | | Internal Calibration Targets -------|-----------|---------------------------------------- NIC1 | ACCUM | | DARK | NIC2 | MULTIACCUM| NIC3 | RAMP | -------|-----------|---------------------------------------- | | Apertures -------|-----------|---------------------------------------- NIC1 | ACCUM | NIC1, NIC1-FIX | MULTIACCUM| | RAMP | | BRIGHTOBJ | -------|-----------|---------------------------------------- NIC2 | ACCUM | NIC2, NIC2-FIX, NIC2-CORON
| MULTIACCUM| | RAMP | | BRIGHTOBJ | -------|-----------|---------------------------------------- NIC3 | ACCUM | NIC3, NIC3-FIX | MULTIACCUM| | RAMP | | BRIGHTOBJ | -------|-----------|---------------------------------------- NIC2 | ACQ | NIC2-ACQ -------|-----------|----------------------------------------
Items enclosed by | | are used for engineering purposes only
and are not available to GOs
Restrictions on Optional Parameters
1) SAMP-TIME01 thru SAMP-TIME25
a) Specified values must be sequential and monotonically increasing.
b) The interval between specified values must be long enough to allow for a readout of the full detector array which will depend on the value of the READOUT optional parameter. Currently, the minimum interval is 0.215 seconds if READOUT = FAST and 2.06 seconds if READOUT = SLOW.
2) The minimum RAMP mode sample time (exposure time/NSAMP) is 5 seconds. If two RAMP mode exposures are executing on different detectors in parallel, the minimum sample time is 10 seconds for both exposures. If three RAMP mode exposures are executing in parallel, the minimum sample time is 15 seconds for all three exposures.
Exposure Association for Calibration Pipeline Processing
Only those NICMOS exposures resulting from a single exposure logsheet line will be associated for the purposes of calibration pipeline processing and archive retrieval. Thus, all exposures resulting from the execution of a predefined pattern (including the NEXP multiple exposures at each offset) will be associated as will multiple exposures at single pointing when PATTERN = NONE and NEXP>1.
All other exposures resulting from multiple exposure lines in a proposal will be processed through the calibration pipeline and archived as single datasets. This includes exposures taken as part of a proposer defined background offset pattern using either the POS TARG special requirement or the FOMXPOS and FOMYPOS optional parameters.
NICMOS Apertures
Each camera will have two apertures defined near the center of the FOV. One aperture in each camera (NIC1, NIC2, NIC3) will be an optimal location near the center of the FOV considering detector efficiency and pixel quality which will be updated by the STScI as the detectors age on orbit. One aperture in each camera (NIC1-FIX, NIC2-FIX, NIC3-FIX) will correspond to a fixed pixel at or near the center of the detector array which will not change on orbit.
The aperture NIC2-CORON is the location of the coronographic spot in the NIC2 camera. It will be used by science exposures which have been preceeded by a target acquisition exposure using the NIC2-ACQ aperture. The acquisition aperture will be slightly offset from the coronographic aperture, but within the acquisition detector subarray.
NICMOS Science Modes
ACCUM - The detector array reset (i.e. setting the detector pixels to their bias levels) is followed by 1 - 25 (specified by the NREAD parameter) reads of the initial pixel values which are averaged onboard to define the initial signal level. After the exposure time has elapsed, the final pixels values are read NREAD times and averaged onboard. The data downlinked is the difference between the initial and final average signal levels for each pixel.
MULTIACCUM - The detector reset is followed by a single read of the initial pixel values. At the times specified by the SAMP-TIMEi parameters, the detector pixels are read out nondestructively. The last read of the detector array ends the exposure and thus the last SAMP-TIMEi must equal the total exposure time. All of the data from the initial and subsequent detector readouts is downlinked to the ground.
RAMP - As in the case of the MULTIACCUM mode, the initial detector readout is followed by a number of nondestructive readouts (specified by the NSAMP parameter). For the RAMP mode, the intermediate readouts are at equal intervals during the exposure and are not individually downlinked to the ground. Instead, the intermediate signals are used onboard to calculate the slope of the signal vs time for each pixel. The onboard calculation of the slope will also detect pixel saturation and (optionally) cosmic rays which will be flagged in the downlinked as well as the number of samples which were used in the slope calculation for each pixel.
BRIGHTOBJ - This readout mode must be used for very bright objects which would saturate the detector pixels in less time than it takes to read through the entire detector array. In this mode, each pixel is reset and then read twice in succession with the interval between the reads being the exposure time and the difference between the pixel values being the pixel intensity. This process is performed on each pixel in succession, however each quadrant of the detector can be operated in this mode simultaneously. Thus the observation time for such an exposure is 16384 (128x128) times the exposure time.
NICMOS Support Modes
ACQ - Acquisition mode exposures are used to locate the target in the NICMOS FOV for subsequent science exposures which are identified via the special requirements: EARLY ACQ FOR <exp IDs>, INTeractive ACQ FOR <exp IDs>, and ONBOARD ACQ FOR <exp IDs>. For the latter two cases, the HST is repositioned to place the target in the aperture specified for the subsequent science exposures. The target position and associated HST maneuver will be determined via ground or onboard software respectively.
ALIGN - An engineering mode which is used to move the NICMOS internal focus and tilt mechanisms via stored commanding for the purpose of on-orbit alignment of the aberration correction optics. ALIGN mode exposures do not acquire science data and must be interleaved with science mode exposures to obtain data with the alignment mechanisms at a variety of positions for the ground alignment process. The values of the optional parameters specify the positions of the three mechanisms in motor steps relative to a nominal zero position. The position corresponding to the stored commanding nominal zero is set via real-time command which allows the specification of a preplanned scan of a mechanism's position without knowledge of where in the mechanism range the scan will be executed.
NICMOS Optional Parameters
NREAD - Specifies the number of detector readouts to be used in determining the initial and final pixels values onboard for ACCUM mode exposures.
SAMP-TIME01 thru SAMP-TIME25 - Specifies the times from the start of the exposure at which the nondestructive readouts are performed in MULTIACCUM mode exposures. The number of samples downlinked will be one (for the initial readout) plus the number of non-zero sample times.
NSAMP - Specifies the number of intermediate nondestructive readouts for RAMP mode exposures.
CR-ELIMINATION - Specifies if the onboard algorithm for cosmic ray detection is to be used for RAMP mode exposures and if so what action should be taken upon detection:
NONE no cosmic ray detection is performed
CONTINUE the sample from a pixel in which a cosmic ray is detected is eliminated from the slope calculation and the slope calculation continues for subsequent samples of the pixel.
RETAIN the slope for a pixel prior to the sample in which a cosmic ray is detected is retained and subsequent samples of the pixel are not used.
MARK a pixel is marked as having been effected by a cosmic ray, but the slope calculation will include the effected sample.
READOUT - Specifies if the fast or slow detector readout rate is to be used.
PATTERN - Specifies the name of a predefined pattern of FOV offsets from the target position for purpose of background measurements. If PATTERN = NONE, the other background pattern related parameters have no meaning and may not be specified. Patterns are either a dither of the FOV starting at the target position, a chop of the FOV between the target position and background positions (returning to the target position after each background measurement) or a combination of the two (SPIRAL-DITH-CHOP). The number of positions in the pattern and the size of the FOV offsets must be specified by the proposer via NUM-DITH and DITH-SIZE for dither patterns and NUM-CHOP and CHOP-SIZE for chop patterns. For chop patterns, the pattern will be repeated until NUM-CHOP exposures have been taken. For the pattern SPIRAL-DITH-CHOP, the parameters NUM-DITH, DITH-SIZE and CHOP-SIZE must be specified and NUM-CHOP will have a fixed default value of 2.
A separate exposure as specified by the exposure logsheet line is taken at each of the FOV offset positions. If the number of exposure iterations on the logsheet line (NEXP) is greater than one, the exposure logsheet line will be executed NEXP times at each point in the background offset pattern. If PATTERN = NONE, the FOV is not moved and NEXP exposures are taken at the target position. Specifying NEXP>1 may be used for cosmic ray elimination in ground data processing.
The following are the eight pre-defined patterns as currently envisioned. The first exposure is always at the target position and the FOV offsets are all of equal size (specified by DITH-SIZE or CHOP-SIZE).
. North
SPIRAL-DITH 5--4--3 . /|\
| | . |
6 1--2 11 | PATTERN-ORIENT = 0
| | |
7--8--9--10 |
STRIP-DITH 1--2--3--4--5--6--7...
SQUARE-WAVE-DITH 2--3 6--7 10...
| | | | |
1 4--5 8--9
ONE-CHOP 1--2
TWO-CHOP 3--1--2
5
|
FOUR-CHOP 3--1--2
|
4
7 5 9
\|/
EIGHT-CHOP 3--1--2
/|\
8 4 6
SPIRAL-DITH-CHOP 9--7--5 10--8--6
| | | |
11 1--3 12 2--4
| |
13--15... 14--16...
OFFSET - Specifies if the background offset pattern is to be performed via a vehicle SAM or motion of the internal FOM (field offset mirror). The range of the FOM is +/- 26 arcsec in the X or Y detector coordinates which will limit the extent of the offset pattern in this mode. If OFFSET = FOM, the value of DITH-SIZE and CHOP-SIZE will be limited to 26 arcsec and any offsets in the resulting pattern that are more than 26 arcsec in X or Y from the target will not be executed.
If the default value of SAM is selected, pointings in the offset pattern that cannot be supported by the target quide stars will be executed under gyro control and any subsequent pointings within range of the target quide stars will require a guide star re-acquisition. If quide star reacquisitions after a drop to gyro control are not desired, the value SAM-NO-REACQ should be specified for the OFFSET parameter. If all of the exposures in the pattern are required to be performed under guide star control, SAM-NO-GYRO should be specified and multiple guide star pairs will will be selected (if possible) to support all of the pointings in the pattern. This mode of operation should be used only when necessary because it may reduce the ability to schedule the observation.
PATTERN-ORIENT - Specifies the orientation of the background pattern. If this parameter has its default value of DETECTOR (required if OFFSET = FOM), the FOV offsets will be performed in detector coordinates and thus the pattern will not have a fixed orientation on the sky. If the offsets are being performed via vehicle SAMs and a particular orientation on the sky is desired, PATTERN- ORIENT should be specified as a value between 0 and 360 degrees which specifies the position angle of the pattern with respect to the target position measured east of north. The scheduling system will translate this to target offsets in right ascension and declination on the sky, but will not restrict the telescope orientation. A fixed pattern orientation with respect to both detector and sky may be specified using the telescope ORIENT special requirement, however this may significantly restrict the ability to schedule the observation.
LAMP - Engineering parameter to specify the name of the internal NICMOS flat field lamp to be used for the exposure. The light from the lamp will be superimposed on the external FOV and thus exposures using the flat field lamps should be pointed to a dark position on the sky.
FOMXPOS - Specifies the offset of the NICMOS FOV using the NICMOS FOM in FOMYPOS - arcsec on the sky for the exposure line on which it is specified. These parameters allow the proposer to specify the pattern of FOM FOV offsets for a background filtering observation. They cannot be specified in conjunction with the BKG-OFFSET and BKG-SCALE parameters.
FOCUS - Engineering parameter to specify the relative position of the NICMOS focus mechanism in motor steps.
XTILT - Engineering parameter to specify the relative position of the NICMOS YTILT - X or Y tilt alignment mechanism in motor steps.