N.B. The new PNS controller software has a bug:

Everytime we press the OPEN button for the uniblitz we actually CLOSE it. And viceversa. Also the log on the control software is misleading. So, the CLOSE and OPEN buttons have the opposite meaning: CLOSE actually means OPEN THE UNIBLITZ... and OPEN means CLOSE THE UNIBLITZ.

Moreover, every time we EXPOSE on the PNS control software, the comand OPENS the shutter and CLOSES the uniblitz (even if in the log it is written that it has opened it). Every time that the exposure is completed.... the comand CLOSES the shutter and OPENS the uniblitz (even if in the log it is written that it has it)..

+++ CASE A
Ha images has a different exposure time of the L and R arms

  1. TO> EXPOSE 1800 "galaxy name"
    (this will start the integration on the PNSL and PNSR CCDs)
  2. PNS Laptop: EXPOSE 1800 (this will open the shutter and close (!) the uniblitz)
now... during the 1800 seconds we do several Halpha exposures:
  1. TO> run pnsHa "galaxy name"
    (this will start the integration on the PNSHa CCD)
  2. PNS Laptop: open the uniblitz by clicking the CLOSE button
  3. wait for
  4. PNS Laptop: close the uniblitz by clicking the OPEN button
repeat this several times, while the long 1800 secs exposure is ongoing...

N.B. you MUST close the uniblitz before the CCD reads out, so this procedure requires concentration and full-time monitoring of the terminals.

+++ CASE B
PNSL, PNSR and PNSHa have the same exposure time

  1. TO> EXPOSE_all 1800 "galaxy name"
    (this will start the integration on the PNSL, PNSR and PNSHa CCDs)
  2. PNS Laptop: EXPOSE 1800
    (this will open the shutter and close (!) the uniblitz)
  3. PNS Laptop: (as soon as the integration starts on Ha) open the uniblitz by clicking the CLOSE button
  4. at the end of the exposure, remember to close the uniblitz shutter

PNS MANUAL: Taking Science Exposures

Important note on Object Targetting

Because of the field distortion it is very desirable to put the object on the same place on the chip each time (except for arsec shifts for dithering). The co-ordinates do not guarantee this (pointing models can differ by 1 arc minute!). For each object, enter into the database the PROBE COORDINATES and the PIXEL COORDINATES on which you are guiding, e.g.

M94
PROBE   34000   102000
294.8   126.4

and use this to acquire the object the next time. Note by Juerg Rey on acquiring objects with WHT/PNS.

autoguider settings as of 2007:

NGC 4473: radial 32947 ; theta 170110

for other targets check header of previous observations.

About field centre:

When the filter is tilted at a non-zero angle, the passband depends on position over the field, so the target will typically need to be placed off-centre (in the y=spatial direction) in order to have the optimum bandpass for its velocity. This is accomplished using a programme called filtercutoff.c. The aim of this programme is to make sure that, over some range in y, 99% of the PNe are within the bandpass (i.e., the central velocity +/- 2.68 * the central velocity dispersion, assuming a radially constant velocity dispersion, which is very conservative for some galaxies). Reported is the number of Reff that are observable with this criterion.

Important note on Position Angle:

Combining data taken at different position angles is VERY complicated, even if the position angles differ by exactly 180 degrees (left arm and right arm swap role under a rotation of 180 deg, but the different cameras will have slightly different distortions). So if data are to be combined, ALWAYS use the same PA! The list of targets previously observed also mentions the PA that was used.

Set the PA of the telescope to be perpendicular to the axis you want the dispersion direction along. E.g., if you want the dispersion direction along a galaxy's minor axis, then PAtelescope=PAmin + 90°= PAmaj .
!!!!!!!! NOTE: THIS HAS NOW CHANGED. Currently (04/12/2007), one simply needs to set the telescope PA equal to the axis along which you want the dispersion. E.g.,
if you want the dispersion direction along a galaxy's minor axis, then PAtelescope=PAmin. !!!!!!!!

Remember that the x-pixel direction is the dispersion direction.

Diagrammes of the field layouts:

PA=0°:
PNSL:   

E      PNSR:    -- N



|
|

N --

E


PA=90°:
PNSL:    E --
     PNSR:    N



|
|



N

-- E

Important note on the Autoguider:

The telescope operators are not used to an instrument with large field of view at Cass and may select an object for guiding on which causes the guide probe to vignet part of the field. So ask the operator to choose an object with autoradial larger than 34000 if possible.

How to take on-sky science exposures

The PNS shutter is rather slow, and is controlled from the PNS PC which does not interact with the CCD controllers. This makes for a slightly messy procedure, which involves synchronizing by hand the start of the integrations and the opening of the shutter. The procedure described below uses a few scripts to make this as painless as possible.

Perform the following commands, in sequence:

  1. Once target acquisition is complete, make sure A&G mirror is OUT (check A&G mimic display). If it is not, issue AGMIRROR OUT on A&G console.
  2. Prepare two command lines without hitting return yet (where time is the desired exposure time in seconds):
    1. on DAS prepare expose time "title" - Note (i) that the ""s are necessary if the title contains blank spaces
      (this will start exposures of time+30 and time+70 secs on PNSL and PNSR respectively, to give the shutter time to open and close and to ensure consecutive readouts of the CCDs to avoid crosstalk);
    2. on PNS PC prepare expose time
      (this will open the shutter, count down time secs, close the shutter, and make a horrible noise.
  3. Now hit returns: first on DAS, and once both CCDs have started their integrations also on PNS console.
  4. At the end of the readout, the shutter closes automatically, the PC howls, and the CCDs read out, first PNSL and then PNSR. If all is well then the readout starts only after the shutter has closed, and the readouts are sequential.

About flexure:

Arclamp tests with telescope pointing at 90°, 70°, 50°, 30°, 10° elevation indicate the following spot position shifts per 5° elevation change (approx max expected in 1800sec exposure):

With cryostats in symmetric position:
PNSL: 0.17 pix (8 km/s) in x, 0.23 pix in y (see summed arc images to see what this shift looks like from 90° to 10°)

PNSR: 0.03 pix in x, 0.12 pix in y


With cryostats "vertical":
PNSL: 0.54 pix (25 km/s) in x, 0.27 pix in y
PNSR: 0.02 pix in x, 0.02 pix in y
About this Document

We need your input to keep these notes up-to-date. Please add to this document, or create new ones which can be linked from it. Send your input by email.
Last updated 9-12-2007 by EN and LC.


Documents of this background colour are part of a set linked from the manual