Jeffrey W Percival
|3.0||20-Sep-2001||Included SAAO Detector Subsystem Document|
|3.1||25-Sep-2001||Complete Merge of SAAO Detector Document|
|3.11||26-Sep-2001||Consistency and Typo Correction|
|4.0||01-Mar-2003||New State Descriptions|
|4.1||10-Mar-2003||Fixed sentence fragments in Overview|
|4.2||11-Mar-2003||Remove uninteresting mode tables near the end|
|4.3||20-Mar-2005||Remove etalon zero-point cals from procedures|
This document replaces version 3.11 of the PFIS OCDD. This document improves upon the PDR version by using a better "parameter space" of instrument configurations and readout modes.
We take care to relate the newly defined instrument states to the ones defined in the old OCDD.
PFIS is operationally complex. It produces a wide range of science data using various combinations of focal plane masks, polarizing elements, gratings, Fabry-Perot etalons, filters, an articulating camera that allows both imaging and spectroscopy, and a CCD subsystem that supports four readout modes.
To manage this operational complexity, we have designed a state-space representation of the operational modes of PFIS. This representation clearly shows which states are useful, and shows exactly what to do to move between states, and how long it will take.
The SAAO team's CCD OCDD (whew!) is here.
PFIS uses focal plane masks and slits in many of its observing modes.
Normal imaging uses the circular 8 arcminute field of view. An optional long slit is used for spectroscopy.
For high time resolution observations, the chips are masked off below the frame transfer boundary. An optional long slit supports spectroscopy. In frame transfer mode, the image or spectrum is exposed for some time, and then it is quickly shifted into the masked region. The unmasked upper portion begins collecting new photons while the lower masked portion is read out.
You can shorten the slit and shift fewer lines per transfer to increase the time resolution. For example, a 1 arcminute slit would allow a new spectrum to be transferred in a quarter of the time as a 4 arcminute slit. See the CCD Readout section for more details.
For polarimetric imaging or spectroscopy, only the central 4 arcminute portion of the focal plane is used. The beamsplitter optic sends the E beam to one side of the frame transfer boundary (say, the upper half of the chip) and the O beam to the other half of the chip. Frame Transfer operations are not possible with polarimetry, because the E and O beams use up space on both sides of the frame transfer boundary.
Multi-object spectroscopy requires the use of a carbon-fiber mask in the focal plane. The mask will be milled with a laser cutter and placed in a slitmask magazine designed to hold 20-30 masks (see related mask design study). User designed slitmasks will be cut and stored on site and labeled with a bar code to identify the mask and mask holder (frame) to be used with each mask.
Peakup holes are cut into the mask and correspond to the focal plane positions of reference stars. Peaking up the position of the slits on the sky requires several images taken at slightly different telescope pointings. The CCD control computer will sum and report the counts within pre-programmed sub-arrays on the chips, and the PFIS computer will command the telescope to the position that produced the highest throughput.
Managing the instrument configuration is simplified by identifying 6 basic opto-mechanical configurations.
There are 6 unique state transitions (hardware movements):
Here is how the states and transitions are related:
Despite having 6 configuration states, there are only 4 operational procedures (and 3 variants involving CCD charge-shuffle mode). For example, states S1 and S2 share the same operational mode: open the shutter, expose, close the shutter, and read out the CCD. States S1 and S4, however, differ in that state S4 generates multiple exposures, one for each waveplate setting.
|+T1, S2||+T3, S3||+T2, S4||+T1, S2||+T3, S3|
|-T1, S1||-T1, S1||-T2, S5||-T1, S1|
|s3||-T3, S1||-T3, S1||
|-T3, S1||-T3, S1||+T2, S6|
|s4||-T2, S1||-T2, S1||-T2, S1||
|+T1, S5||+T3, S6|
|s5||-T2, S2||-T2, S2||-T2, S2||-T1, S4||
|s6||-T2, S3||-T2, S3||-T2, S3||-T3, S4||-T3, S4||
Example: Suppose you are in state S5 (Spectropolarimetry), and you want to be in state S3 (Fabry-Perot Imaging) for the next observation.
Note that this state-space representation easily allows one to see the time required to move between two instrument configurations, indicates how the move is to be made, and specifies a central element of the PFIS control system software.
After configuring PFIS into some observational mode, the PFIS control software executes some procedure. The procedure runs on the server side, not the client. The client (MMI) asks for a procedure by name, and supplies the required parameters. The server runs the procedure, then responds to the client.
There are three polarimetric waveplate sequences: linear, circular, and all Stokes (produces both linear and circular measurements). The sequences are:
We can represent this a little differently. The basic quantum of rotation is 90/8 degrees, or 11.25 degrees. The next table gives the waveplate sequences in terms of multiples of the quantum of rotation.
Shuffle-mode procedures are the only ones that interact, in a closed-loop fashion, with some other subsystem. In this mode, photons are collected for some time, and then two things happen: the CCD charge is shuffled up or down on the CCD chip, but not read out, and some piece of hardware is moved to a new position. The move will involve exactly one other item:
This table presents the observing modes broken down into imaging and spectroscopy, and according to CCD readout mode.
This table relates the new state-space view of PFIS to the PDR OCDD modes.
|1||OIUN||Imaging||S1||N||Stromgren band imaging over 8 field; narrowband imaging over 8 field; imaging in preparation for multi-slit spectroscopic work.||Yes|
|2||MIUH||High Time Resolution Imaging||S1||H||Sub-second photometric observations using Stromgren or narrowband filters of transient objects: cataclysmic variables, compact objects with accretion disks, AGN, Gamma ray bursts.||No|
|21||OIUD||Drift Scan Imaging||S1||D||Deep uniform photometry of extended regions, surveys.||No|
|11||SGUN||Long Slit Spectroscopy||S2||N||Conventional single long slit spectroscopy over 7.5 fields at arbitrary position angles. Used with the SALT ADC, parallactic angle considerations do not restrict the position angle of the observation.||Yes|
|17||MGUN||Multi-slit Spectroscopy||S2||N||Multi-object spectroscopy in fields up to 6 diameter; redshift surveys; spectral surveys of stars and galaxies.||Yes|
|12||SGUH||High Time Resolution Long Slit Spectroscopy||S2||H||Time-resolved spectroscopy of cataclysmic variables, flares, eclipses, AGN variability, gamma ray burst optical transients.||Yes|
|18||MGUH||High Time Resolution Multi-slit Spectroscopy||S2||H||Multi-object spectroscopy in fields up to 4 diameter; redshift surveys; spectral surveys of stars and galaxies.||No|
|22||OGUD||Drift Scan Spectroscopy||S2||D||Shallow, wide-area spectroscopic surveys.||No|
|6||OFUN||Fabry-Perot Imaging||S3||N||High resolution imaging spectroscopy of multiple or extended objects; dynamical studies of HII regions, star clusters, and galaxy clusters.||Yes|
|8||SFUN||Fabry-Perot Imaging with Coronographic Mask||S3||H||Spectroscopic imaging of faint extended objects near bright sources.||No|
|3||MILN||Linear Polarimetric Imaging||S4||N||Stromgren or narrow band polarimetric surveys of interstellar polarization; intrinsic stellar polarization.||No|
|5||MICN||Circular Polarimetric Imaging||S4||N||Stromgren or narrow band circular polarimetric surveys of interstellar polarization; intrinsic stellar polarization; low-resolution (R=10) spectral polarimetry.||No|
|4||MILH||High Time Resolution Linear Polarimetric Imaging||S4||H||Stromgren or narrow band polarimetric studies of rapidly varying polarized stars and AGNs.||No||Not Possible|
|13||SGLN||Long Slit Linear Spectropolarimetry||S5||N||R=2000 to R=6000 long slit spectropolarimetric studies of cataclysmic variables, young stellar associations, stars with disks, AGNs, and interstellar absorption features.||Yes|
|15||SGCN||Long Slit Circular Spectropolarimetry||S5||N||R=2000 to R=6000 long slit circular spectropolarimetric studies of cataclysmic variables, young stellar associations, stars with disks, AGNs, and interstellar absorption features.||No|
|19||MGLN||Multi-slit Linear Spectropolarimetry||S5||N||Multi-object linear spectropolarimetry in fields up to 4 diameter; polarimetric surveys.||Yes|
|20||MGCN||Multi-slit Circular Spectropolarimetry||S5||N||Multi-object circular spectropolarimetry in fields up to 4 diameter; polarimetric surveys.||No|
|14||SGLH||High Time Resolution Long Slit Linear Spectriopolarimetry||S5||H||R=2000 to R=6000 long slit linear spectropolarimetric studies of cataclysmic variables, young stellar associations, stars with disks, AGNs, and interstellar absorption features.||No||Not Possible|
|16||SGCH||High Time Resolution Long Slit Circular Spectropolarimetry||S5||H||R=2000 to R=6000 long slit circular spectropolarimetric studies of cataclysmic variables, young stellar associations, stars with disks, AGNs, and interstellar absorption features.||No||Not Possible|
|7||OFUV||Shuffle Mode Fabry-Perot Imaging||S5||S||High resolution imaging spectroscopy of multiple or extended faint objects; dynamical studies of HII regions, star clusters, and galaxy clusters; provides good background subtraction.||No|
|9||MFLN||Linear Polarimetric Fabry-Perot Imaging||S6||N||R=500 to R=13000 imaging linear spectropolarimetric studies of extended objects such as HII regions, reflection nebulae, star clusters, young stellar associations, and galactic nuclei.||No|
|10||MFCN||Circular Polarimetric Fabry-Perot Imaging||S6||N||R=500 to R=13000 imaging circular spectropolarimetric studies of extended objects such as HII regions, reflection nebulae, star clusters, young stellar associations, and galactic nuclei.||No|