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4.5 AOT 7


The purpose of AOT 7 is to make Fabry-Pérot  observations. If requested, Short Wave grating observations may be made in parallel. AOT 7 is achieved by using combinations of ICS's  9 and 4. After the instrument has been set up ICS 9 is used to make a dark-current measurement . Another ICS 9 is then used to start the FP. While the FP is operating ICS 4 is used to make SW grating scans, if any are requested. More than one of these may be uplinked while the FP scan is continuing. To observe more lines with the FP more ICS 9's are uplinked. Again ICS 4's could be uplinked to observe with the SW grating section. After all observations have concluded a final ICS 9 is used to make a dark measurement.

For the FP the stepsize is always two FP units, about 1/4 of an FP wavelength resolution . Reset intervals  are 1 or 2 seconds, with the dwell time equal to the reset time. The number of scans is greater than, or equal to, three, and only ``up'' grating scans are commanded.

If any SW grating observations are requested they are carried out in an identical manner to those of an SWS06 measurement. Users should read section 4.4 for a description of that.

Due to a slight internal misalignment of the Long Wave FP there are problems merging FP observations with grating observations when observing through aperture 3 . The `effective' aperture of the FP is displaced from the center of the grating aperture by approximately 10 arcseconds, causing an approximately 40% drop in throughput of the FP when pointing is determined by the grating. The solution decided on was to define a fourth `effective' aperture , centered on the FP aperture, and carry out all observations through this. This means the SW grating now loses approximately 40% of its throughput. Therefore LW FP observations (26 - 44 tex2html_wrap_inline6866 ) and SW grating observations (7.0 - 13.16 tex2html_wrap_inline6866 ) through aperture 3 will not be merged. If any aperture 3 grating observations are requested they will be done after the FP observations. This change was considered acceptable as the main purpose of AOT 7 is FP observations. Merging is still carried out when observations are made using apertures 1 or 2  .

However, some early AOT 7 observations were carried out before this change was implemented. Observers may therefore receive FP data merged with SW grating observations in the range 7 to 13.16 tex2html_wrap_inline6866 .

Note that band 2C  ends at 13.16 tex2html_wrap_inline6866 for AOT SWS07 - see table 3.1.

Figure 4.16 shows ERD, SPD and aperture data for part of an AOT 7. The ERD is shown as signal in bit values against time (ITK), and the SPD as signal (in tex2html_wrap_inline6860 ) against time (seconds). While the line is hard to see in the ERD, it can easily be seen in the SPD.

Figure 4.17 shows the LW grating position, the FP position and the resulting wavelength of light falling on detector during the part of an AOT 7.

Figure 4.18 shows SPD signal (in tex2html_wrap_inline6860 ) and AAR flux (in Jy), both against wavelength, for the same period of the example AOT 7. Note the wavelength shift in the location of the peak between the SPD and AAR. This is because the SPD wavelength scale is `ISOcentric', whereas the AAR is corrected to be heliocentric.

Figure 4.16: ERD, SPD and aperture data for part of an AOT 7

Figure 4.17: LW grating position, FP position and resulting wavelength for part of an AOT 7

Figure 4.18: SPD and AAR data for AOT 7

next up previous contents index
Next: 4.6 AOT behaviour Up: 4 AOT overview Previous: 4.4 AOT 6

K. Leech with contributions from
the SWS Instrument Dedicated Team (SIDT)
and the SWS Instrument Support Team (SIST)