IPHAS - Observing Manual

v2.5

9.October.2006

Opening up
See the WFC observing manual
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.
Make sure the IPHAS standard star catalogue is included in the TCS. To include the catalogue give the command
USER>incl iphas_stds
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.
Evening twilight sky flats
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 43.95) 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.
Survey observations
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: Although the quicklook pipeline is running during the IPHAS survey nights (eg. to determine the seeing) no data is copied back to the data reduction computer to reduce the network traffic.
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>0.4, Sky>2000)
2. Not yet observed fields
3. Re-observation of Cat2 fields (Seeing>1.85, ell>0.3, Sky>1000)
4. Re-observation of Cat3 fields (Seeing>1.7, ell>0.2, Sky>500)
Note:Sky value on raw frames is roughly ADU-1600(Bias).
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