4 New features in PHT observing modes

4.1 Telescope nodding

Telescope nodding using the raster mode with a raster leg separation dN = 0 arcsec. Applicable in AOTs PHT03, PHT22, and PHT40.

+ long detector stabilisation times since nodding can be regarded as a very slow chopping

+ continuous exposure

+ observer can select "his own optimal" chopping frequency by setting the integration time per raster point

+ 2 FCS measurements at beginning and end, no interrupt of sky-source sequence

+ no chopping avoidance area, if raster oriented relative to sky

0 yet to be tested

0 time efficiency can be adjusted:

2 background positions: sec on-source ( raster) yields 1500 sec
only 1/3 of raster time is on-source:

bck1 - src - bck2 - bck2 - src - bck1 - bck1 - src - ...

1 background position: sec on-source ( raster) yields 1150 sec
1/2 of time on-source:

bck1 - src - src - bck1 - bck1 - src - src - bck1

- arrays will be tilted with respect to chop direction if raster orientation relative to sky is chosen. But spacecraft y-axis orientation can also be chosen, thereby loosing free selection of sky orientation.

4.2 Reduction of minimum raster step size

• C-arrays: 15 arcsec
• PHT-P & PHT-S: on-target flag (OTF) threshold + 3''
  currently OTF threshold = 10 arsec -implies 13''
  near future OTF threshold = 2 arcsec -implies 5''(to be confirmed)