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Subsections


3.10 ISOPHOT Modes of Operation

In this section summaries of the logic behind the ISOPHOT AOTs are given. Only those operations that may be relevant for data processing are mentioned. Details on the parameters to be entered by the observer are described in the ISOPHOT Observers' Manual by Klaas et al. 1994, [21]. For details on the filter wheel settings see Section A.1.


3.10.1 PHT-P: PHT03, PHT04, PHT05, PHT17/18/19


3.10.1.1 PHT03

PHT03 included the following operations:

  1. Pointing procedure, pointing:  
    PHT03 in single pointing mode:

    Repeat points 2 - 5 for all detector assemblies selected.

  2. In case of detectors P2 and P3, switch on heating and wait for heating stabilisation. Activate detector.

    Repeat points 3 - 4 for each filter using the activated detector:

  3. Rotate the filter and aperture wheels to the commanded configuration, optimised to instrument requirements. To minimize memory effects of the detectors the measurements with the different filter/aperture combinations were performed according to increasing power on the detector. A warning was given to the observer, if the ratio between the highest and the lowest flux on one detector for the selected filter/aperture combinations was higher than 1000. Such a flux combination within one AOT could lead to poor calibration. In order to minimize heating and cooling stabilisation times in multi-detector mode, the detectors were used in the order: 
    
        P3 -> P1 -> P2
    The heater for P2 was switched on before measuring with P1. The start with the P3 detector was also to avoid thermal disturbances by the P2 heater on the P3 measurement.
  4. Integrate on the source for the specified or calculated exposure time. A measurement was performed in staring mode or one of the three following chopped modes: 
    
          (i) RECTANGULAR
         (ii) SAWTOOTH
        (iii) TRIANGULAR
    In staring mode the observer had to provide an appropriate reference field measurement for background subtraction, which was not part of this AOT.
  5. The internal calibration was performed with the last filter/aperture combination used with the current detector. This meant that there was one FCS calibration per detector used. If the observation was in staring mode, a staring measurement on FCS1 was performed. If the sky was measured in any chopper mode, both FCS's were measured in rectangular chopped mode; FCS1 was tuned close to the [source+background] power, FCS2 close to the background power as calculated from the fluxes given by the user. After calibration, the FCSs were switched off.
  6. After the last integration the heaters were switched off, the detector assemblies were set to standby and the instrument was reconfigured to the default mechanical state which was the C200 serendipity mode configuration.

PHT03 in raster mode:

For raster mode measurements, only one detector could be chosen per AOT. Filters were not changed during the raster, but rather a complete map was performed per filter. If more than one filter was selected, the map measurements were sorted according to increasing power on detector. While PHT was measuring, the spacecraft independently performed a raster map giving no feedback to PHT on the pointing progress in the raster. To synchronize the spacecraft rastering and the instrument data collection, the AOT logic calculated the total time necessary to perform a complete raster including the microslews. After the elapse of that time the integration was stopped by a `pulse command' (a high priority interrupt to the PHT microprocessor) which also switched off all electronics including the detector heaters. After the pulse command a re-initialisation of the instrument was necessary, this was reflected in the AOT operations.

  1. Pointing on the first raster point.
  2. In case of a heated detector, switch on heating and wait for heating stabilisation. Activate detector.

    Repeat points 3 - 7 for each filter:

  3. Rotate the filter and aperture wheels to the commanded configuration.
  4. An internal calibration on FCS1 was performed in staring mode. After the calibration FCS1 was switched off.
  5. Set the instrument integration time such that it covered the time needed to perform a full raster map with the specified raster point integrations requested by the user. The spacecraft was commanded to perform a raster according to the requested parameters. PHT was collecting data during the raster slews. The raster point ID and the on-target flag were recorded to reconstruct where the spacecraft was pointing.
  6. After the raster had been completed the integration was halted by a pulse command. This pulse command also stopped the electronics. The detector was activated again and in case of a heated detector, a stabilisation heating time was included.
  7. An internal calibration on FCS1 was performed in staring mode. After the calibration FCS1 was switched off.
  8. From the last raster pointing the spacecraft moved back to the first raster pointing, in case the filter was not the last one in the selected sequence.
  9. After the last integration, the heaters were switched off, the detector assemblies were set to standby and the instrument was reconfigured to the default mechanical state which was the serendipity mode configuration.


3.10.1.2 PHT04

PHT04 included the following operations:

  1. Pointing procedure, pointing:
  2. In case of a heated detector, switch on heating and wait for heating stabilisation. Activate detector.
  3. Rotate filter wheel to the position of the required spectral bandpass.

    Repeat points 4 - 5 for each aperture:

  4. Rotate the aperture wheel to the respective aperture configuration. Measurements were ordered with increasing power on the detector, i.e. with increasing aperture size.
  5. Integrate on the source for the specified (or calculated) integration time. Measurement was performed in staring mode or one of the three following chopped modes: 
    
          (i) RECTANGULAR
         (ii) SAWTOOTH
        (iii) TRIANGULAR
  6. The internal calibration was performed with the last aperture used with the current detector. This meant that there was one FCS calibration per detector used. If the observation was in staring mode, a staring measurement on FCS1 was performed. If the sky was measured in any chopper mode, both FCSs were measured in rectangular chopped mode; FCS1 was tuned close to the [source+background] power, FCS2 close to the background power as calculated from the fluxes given by the user. After calibration, the FCSs were switched off.
  7. After the last integration, the heaters were switched off, the detector assemblies were set to standby and the instrument was reconfigured to the default state.


3.10.1.3 PHT05

For the absolute photometry AOT PHT05 only one filter and one aperture could be selected. Chopped and/or raster mode was not possible.

  1. Pointing on target.
  2. In case of heated detector, switch on heating and wait for heating stabilisation. Activate detector.
  3. If a dark measurement was requested then
  4. Rotate the filter and aperture wheels to the commanded configuration.
  5. If a cold FCS measurement was requested then
  6. Perform the sky measurement.
  7. Perform the calibration measurement in staring mode on the heated FCS1 with an measurement time equal to the sky measurement. After the calibration the FCS1 was switched off.
  8. The heaters were switched off, the detector assembly was set to standby and the instrument is reconfigured to default mode.

Note that the dark instrument configuration was different for the different P detectors in order to ensure that no (stray-)light could reach the detector, see Table 3.1 for the selected filter wheel settings. The mnemonics given in the table are explained in Appendix A.1.


Table 3.1: Filter wheel settings for dark measurements in AOTs.
Detector Wheel I Wheel II Wheel III
  mnemonic mnemonic mnemonic
P1 PHT_S 5_SEC P3_100_UM
P2 PHT_S 5_SEC P1_3P29_UM
P3 PHT_C_NO_POL 5_SEC P1_11P5_UM
C100 PHT_S C200_200_UM P3_100_UM
C200 PHT_S C100_50_UM P3_100_UM
SS/SL PHT_P_NO_POL 180_SEC P1_7P3_UM


3.10.1.4 PHT17/18/19

PHT17 initiated the following operations:

  1. Pointing on requested position.
  2. In case of heated detector, switch on heating and wait for heating stabilisation. Activate detector.

    Repeat points 3 - 4 for each filter using the selected detector:

  3. Rotate the filter and aperture wheels to the commanded configuration, optimised according to instrument requirements. To minimize memory effects of the detectors the measurements were sorted according to increasing power on the detector. The selected filters had to belong to the same detector.
  4. Integrate on the source for the specified (or calculated) integration time. Measurement was performed in staring mode.
  5. The internal calibration was performed in staring mode on FCS1 with the last filter of the selected detector. After the calibration, FCS1 was switched off.
  6. When moving to the next pointing of the sparse map, the detector remained switched-on.

PHT18 modules were optional for a sparse map execution (a minimum combination was PHT17 and PHT19). Up to 28 PHT18 modules could be inserted into a sparse map sequence. A sequence up to 30 positions in total was measured, which could be irregularly distributed, to create a sparse map.

PHT18 initiated the following operations:

  1. Pointing on requested position.

    Repeat points 2-3 for each filter using the activated detector:

  2. Rotate the filter (and aperture) wheel(s) to the commanded configuration, optimised according to instrument requirements. The measurements were sorted according to increasing power on the detector.
  3. Integrate on the source for the specified (or calculated) integration time.
  4. The detector was not switched off in this module.

PHT19 initiated the following operations:

  1. Pointing on requested position

    Repeat points 2-3 for each filter using the activated detector

  2. Rotate the filter (and aperture) wheel(s) to the commanded configuration, optimised according to instrument requirements.
  3. Integrate on the source for the specified (or calculated) integration time.
  4. At the end of the filter sequence a calibration measurement was performed in the last filter in staring mode on FCS1.
  5. The heater was switched off, detector assemblies were set to standby and the instrument was reset to the default configuration.

All measurements were performed in staring mode, thus the observer had to provide an appropriate reference field measurement for background subtraction, which was usually one or more measurements in the sequence.

Prior to PHT18, a PHT17 had to be performed in order to switch on the detector. After the last PHT18 had been done, a PHT19 was performed. Prior to a PHT19, a PHT17 had to be performed. During the whole sequence the detector remained activated, but measurements were only performed on the target positions.


3.10.2 PHT-C: PHT22, PHT25, PHT32, PHT37/38/39


3.10.2.1 PHT22

PHT22 initiated the following operations:

  1. Pointing procedure, pointing:

    PHT22 in single pointing mode:

    Repeat points 2 - 5 for all detector assemblies selected:

  2. Switch on heating and wait for heating stabilisation in case C100 was used. Activate detector.

    Repeat points 3 - 4 for each filter using the activated detector:

  3. Rotate the filter wheel to the commanded configuration, optimised according to instrument requirements. If filters of both C100 and C200 were requested, detectors were operated in the following order: 
    
        C200 -> C100
    To minimize memory effects of the detectors the measurements per detector were performed according to increasing power on the detector.
  4. Integrate on the source for the specified (or calculated) integration time. The measurement was performed in staring mode or chopped mode. If only filters of the C100 filter set were selected, one of the three following chopped modes was possible: 
    
          (i) RECTANGULAR
         (ii) SAWTOOTH
        (iii) TRIANGULAR
    If at least one filter of the C200 filter set was selected, the chopper mode was automatically restricted to RECTANGULAR chopping with 180$''$ throw. In staring mode the observer had to provide an appropriate reference field measurement for background subtraction which was not part of this AOT.
  5. The internal calibration was performed with the last filter used with the current detector. This meant that there was one FCS calibration per detector used. If the observation was in staring mode a staring measurement on FCS1 was performed. If the sky was measured in any chopper mode, both FCSs were measured in rectangular chopped mode; FCS1 was tuned close to the [source+background] power, FCS2 close to the background power as calculated from the fluxes given by the user. After calibration, the FCSs were switched off.
  6. After the last integration, the heater was switched off, the detector assemblies were set to standby and the instrument was reconfigured to the default configuration.

PHT22 in raster mode (restricted to filter sets belonging to either C100 or C200):

The procedure was identical to the raster logic presented for PHT03.


3.10.2.2 PHT25

See description of PHT05. The available detectors were C100 and C200 for which C100 needed heating. The cold FCS measurement time in the case of C200 was 128 s instead of 256 s.


3.10.2.3 PHT32

PHT32 initiated the following operations:

  1. Pointing on the first raster point
  2. Activate either PHT C100 or C200 depending on selection of filters and wait for stabilisation of the detector in case C100 had been selected.

    Repeat steps 3-7 for all filters:

  3. Rotate the filter wheel to the commanded filter position.
  4. An FCS1 calibration measurement was performed in staring mode.
  5. Set the instrument integration time such that it covered the time needed to perform a full raster map with the specified raster point integrations requested by the user. The spacecraft was commanded to perform a raster according to the requested parameters. On each raster position a number of chopper sweeps were performed. PHT was collecting data also during the raster slews.
  6. After the raster had been completed the integration was halted by a pulse command (see PHT03 raster description). This pulse command also switched off the electronics. The detector was activated again and in case of a heated detector, a stabilisation heating time was included.
  7. The map was concluded by a repetition of an FCS1 calibration measurement in the filter used for the preceding map at the last raster position.
  8. From the last raster pointing the spacecraft moved back to the first raster pointing, in case the filter was not the last one in the selected sequence.
  9. After the sequence in the last filter, the heater was switched off, detector assemblies were set to standby and the instrument was reconfigured to the default configuration.

Note: For AOT PHT32 the chopper was indirectly commanded depending on the detector (C100 or C200) chosen. In the case of C100 the chopper was commanded to perform in sawtooth mode 13 chopper steps with 15$''$ separation symmetrically with respect to the centre field of view. When C200 had been chosen, the chopper was commanded to perform in sawtooth mode 7 chopper steps with 30$''$ separation.


3.10.2.4 PHT37/38/39

The PHT37 AOT was the first AOT in the concatenated sequence PHT37, [PHT38], PHT39 which formed the PHT-C sparse map. It initiated the following

operations:

  1. Pointing on requested position.
  2. For C100 switch on heating and wait for heating stabilisation. Activate detector.

    Repeat points 3 - 4 for each filter using the activated detector:

  3. Rotate the filter wheel to the commanded configuration, optimised according to instrument requirements. To minimize memory effects of the detectors the measurements were sorted by increasing power on the detector.
  4. Integrate on source for the specified (or calculated) integration time. Measurement was performed in staring mode.
  5. Perform calibration in staring mode on FCS1 with the last filter of the selected detector. After the calibration, FCS1 was switched off.
  6. When moving to the next pointing of the sparse map, the detector remained switched on.

PHT38 initiated the following operations:

PHT38 modules were optional for a sparse map execution. Up to 28 PHT38 modules could be inserted into a sparse map sequence.

  1. Pointing on requested position.

    Repeat points 2-3 for each filter using the activated detector:

  2. Rotate the filter wheel to the commanded configuration, optimised according to instrument requirements. To minimize memory effects of the detectors the measurements were sorted by increasing power on the detector.
  3. Integrate on the source for the specified (or calculated) integration time.
  4. The detector was not switched off in this module.

PHT39 was the last AOT in the concatenated sequence PHT37, [PHT38], PHT39 which formed the sparse map. It initiated the following operations:

  1. Pointing on requested position:

    Repeat points 2-3 for each filter using the activated detector:

  2. Rotate the filter wheel to the commanded configuration, optimised according to instrument requirements. To minimize memory effects of the detectors the measurements were sorted by increasing power on the detector.
  3. Integrate on source for the specified (or calculated) integration time. Measurement was performed in the staring mode, thus the observer had to provide an appropriate reference field measurement for background subtraction, which was usually one or more positions in the sequence.
  4. Perform calibration measurement in staring mode on FCS1.
  5. Switch off heaters, switch detector assemblies to standby and reset instrument to default configuration.

The minimum number of sparse map modules was two: one PHT37 followed by one PHT39.


3.10.3 PHT-S: PHT40

PHT40 initiated the following operations:

PHT40 in single pointing mode:

  1. Pointing procedure, pointing:
  2. Activate detectors.
  3. Rotate wheels to configure DARK configuration for PHT-S (see Table 3.1).
  4. Integrate in dark position for the specified dark current measurement time of 32 s. Measurement was performed in staring mode.
  5. Rotate wheels to configure beam path to PHT-S.
  6. Integrate on the source for the specified (or calculated) integration time. Measurement was performed in staring mode or one of the three following chopped modes: 
    
          (i) RECTANGULAR
         (ii) SAWTOOTH
        (iii) TRIANGULAR
  7. After the integration the detector assemblies were set to standby and the instrument was reconfigured to the default mechanical set up.

PHT40 in raster mode:

Start with points 2- 6 at first raster position. Set the integration time such that it was longer than the time to perform the requested raster map. Perform point 6 in staring mode. After the raster had been completed the integration was halted by a pulse command (see PHT03 raster description). The instrument was measuring during micro-slews. Proceed with point 7.


3.10.4 Polarisation observations: PHT50, PHT51


3.10.4.1 PHT50

For PHT50 only the 25 $\mu $m filter could be used in combination with the 79$''$ aperture. The logic rounded the requested integration time per polariser to the nearest higher multiple of 128 s with a minimum of 256 s. A description of the CHW1 (change wheel I) positions is given in Section A.1.4. PHT50 initiated the following operations:

  1. Pointing on target.
  2. Switch on heating, wait for heating stabilisation, and activate P2.
  3. Rotate the filter wheel to P_25 and aperture wheel to $79''$.
    Repeat steps 4-6 to accumulate the requested integration time per polariser:
  4. Rotate CHW1 to PHT-P polariser 1 ($0^{\circ}$) and perform measurement of 128s.
  5. Rotate CHW1 to PHT-P polariser 2 ($120^{\circ}$) and perform measurement of 128s.
  6. Rotate CHW1 to PHT-P polariser 3 ($240^{\circ}$) and perform measurement of 128s.
  7. Rotate CHW1 to PHT-P polariser 1 ($0^{\circ}$) and perform measurement of 128s. This closed the polariser sequence with the start configuration allowing to assess long term detector drifts.
  8. Rotate CHW1 to PHT-P `no polariser' position and perform a sky measurement of 128s.
  9. Perform the calibration measurement in staring mode on the heated FCS1 with a measurement time of 128 s. After the calibration the FCS1 was switched off.
  10. The heater was switched off, the P2 assembly was set to standby and the instrument was reconfigured to default mechanical set-up.


3.10.4.2 PHT51

For PHT51 only the C200 detector array in the 170 $\mu $m filter set-up could be used. The logic rounded the requested integration time per polariser to the nearest higher multiple of 128 s with a minimum of 256 s. A description of the first filter wheel (CHW1) positions is given in Section A.1.4. PHT51 initiated the following operations:

  1. Pointing on target.
  2. Activate the C200 detector.
  3. Rotate the filterwheel 2 to C_160.
    repeat steps 4-6 to accumulate the requested integration time per polariser:
  4. Rotate CHW1 to PHT-C polariser 1 ($0^{\circ}$) and perform measurement of 128s.
  5. Rotate CHW1 to PHT-C polariser 2 ($120^{\circ}$) and perform measurement of 128s.
  6. Rotate CHW1 to PHT-C polariser 3 ($240^{\circ}$) and perform measurement of 128s.
  7. Rotate CHW1 to PHT-C `no polariser' position and perform a sky measurement of 128s.
  8. Perform the calibration measurement in staring mode on the heated FCS1 with a measurement time of 128s. After the calibration the FCS1 was switched off.
  9. The C200 assembly was set to standby and the instrument was reconfigured to default mechanical set-up.

In many cases the full sequence was repeated in a $2{\times}2$ raster map with 1 pixel displacement and the source centred on each pixel. This yielded a 4-fold redundancy for the central position of the resulting $3{\times}3$ raster map. This method gave the highest source-to-background contrast and provided a consistency check from the results of the 4 individual pixels.

next up previous contents index
Next: 4. Instrumental Characteristics Up: 3. Instrument Modes and Previous: 3.9 Serendipity Mode
ISO Handbook Volume IV (PHT), Version 2.0.1, SAI/1999-069/Dc