IPHAS - Observing Manual

v3.1

21.June.2007

News

The observing scripts now check that the dome has reached the correct position before starting the integration.
The field selection does not select fields closer than 30 degrees to the moon.
A more automatic standard star observing script.

Opening up
1. See the WFC observing manual for general instructions.
2. To improve the dome seeing you should open the south doors (if weather conditions permit) and the dome (point away from the sun !) about 1-2 hours before sunset.
3. Make sure the IPHAS standard star catalogue is included in the TCS. To include the catalogue give the command
  USER>incl iphas_stds
4. You need to provide the coordinate of the moon to the field selection program. Before starting observing you should get the coordinates from the TCS with the command
  USER>moon
  Put the topocentric coordinates of the moon into the file /home/intobs/ha_survey/moon.pos.
5. You can use the following coordinates as input to staralt to see which IPHAS regions you can observe when during the night. These coordinates refer to the first field in each region. A catalogue with field centres generated by Janet Drew can be found here.
6. Change to the IPHAS survey directory in the system window
  SYS> /home/intobs/ha_survey/
7. Important:Make sure the autoguider is off. If the autoguider is running you will get additional noise !
  Important:Make sure the CCD is in FAST readout mode. Never use SLOW mode !!!
8. If you want to know the seeing during the night as measured from the survey images you should start the seeing monitor program before starting flats. Open a terminal on intdrpc as user intguest (this is the default) and do
```
DR> cd ~/IPHAS/Seeing
DR> ./get_seeing.perl
```
  This will measure the seeing for every target frame and save the data in a file named seeing_<obsdate>.dat. If you stop the script and restart it then it will continue at the last file where it stopped. As the measurement takes time you want to start this early in the night (before the standards ?). Otherwise the script will take a while to catch up with the current observation.
Evening twilight sky flats
Important:Make sure the autoguider is off and the CCD is in FAST readout mode. Never use SLOW mode !!!
Order of filters: Ha, r, i
Try to get at least 3 flat field exposures (20000-40000 ADU) for each filter.
Focusing
Use the r filter to focus. Once the correct focus position is found (the nominal focus is 43.55) then change the value used by the focus command in the /home/intobs/ha_survey/filter_wrap.csh script to the focus value used for the night.
Standard star observations
These are really only necessary if the night is photometric. But as the pipeline needs the observation of standard stars to figure out if the observing was done in cloudy or dusty conditions, they should be taken every night.
Standard star exposures in the evening are taken in twilight when the sky is getting dark and the telescope has been focused. Try to take 2-3 standard stars in each filter distributed in airmass.
There is a new script that tries to automate the standard star observations.
SYS> /home/intobs/ha_survey/stdobs.csh
The arguments to the script are the standards that you want to observe. A list of IPHAS standard stars can be found here
Note: The exposure time information is kept in the file standard.info.
While observing the standards you might also update the position of the moon (see above).
Survey observations
Important:Make sure the autoguider is off and the CCD is in FAST readout mode. Never use SLOW mode !!!
The fields that should be observed are read from the file fields.todo in the /home/intobs/ha_survey directory. The already observed fields are listed in the file fields.done in the same directory.
1. Copy the correct fields.todo.??? file to fields.todo
2. SYS> /home/intobs/ha_survey/survey_noguide_err.csh
3. If you want to change the observed sky region, change the fields.todo file while the Ha or r exposure is being taken or read out.
4. To stop the script (after all 3 exposures of a field have been taken), copy the file empty.dat to fields.todo .
5. If you stop the script or change region please make sure that you do this after the offset field has been observed.
One standard star should be taken in all filters every 2 hours during the nights observing. To get a real time display of the frames as they are coming in, use the command iphas_rtd in IRAF on the data reduction computer.
Note: If this does not seem to work it is most likely because IRAF was started in the wrong directory. Exit IRAF (cl>logout), change into the home directory (csh>cd) and start IRAF again (csh>ecl).
Important
If the seeing is good (<1.7 arcsec) and there are no clouds then the priority for observing regions is as follows:
1. Re-observations of Cat1 fields (Seeing>2.0, ell>0.2, Sky>2000, bad data)
2. Not yet observed fields
3. Re-observation of Cat2 fields (Seeing>1.85)
4. Re-observation of Cat3 fields (Seeing>1.7)
Concentrate on getting Cat1 and not observed fields done in all regions before starting on Cat2 and Cat3.
Note:Sky value on raw frames is roughly ADU-1900(Bias level).
The fields.todo files are sorted by priority, with not yet observed fields having highest priority. To find out what the distribution of to be observed fields per region in the different categories is, run the "region_status.perl" script.
SYS> /home/intobs/ha_survey/region_status.perl
Observed region status information is available at the regions status page.
Try to observe with the following constraints:
Standard star observations
Standard star exposures in the morning are taken in twilight when the sky is starting to get bright and the observing of IPHAS fields has stopped. Try to take 2-3 standard stars in each filter distributed in airmass.
Bias
While you wait for morning twilight to come this is a good oportunity to take some bias frames. Put the Halpha filter in (to prevent light leaking through the shutter) and take a maximum of 5 bias exposures. If you are in danger of loosing morning twilight flats then forget about the bias frames - flats are more important.
Morning twilight sky flats
Order of filters: i, r, Ha
Try to get at least 3 flat field exposures (20000-40000 ADU) for each filter.
Closing down
See the WFC observing manual