Changes
1.0m
,/* STE3/STE4 */
# Take a bias frame (run a single line module with Repeats=1, Image Type=Bias and Save=Yes) and '''check that it saves to
/data/40in/imag40/YYYY/MMDD on ltsp.
== Observing recipes: sky flats & dome flats ==
=== Sky flats ===
If sky conditions are photometric during morning/evening twilight, you will be able to take sky flats. See Section~\ref{sec-domeflats} if you need dome flats. Sky flats can be obtained in the following way:
# Follow the '''facility start-up''' procedure in Section~\ref{sec-facstartup}.
# Follow the appropriate '''instrument setup''' procedure (Section~\ref{sec-inststartup}).
# '''Slew the telescope to the zenith''', with the open dome shutter facing in the opposite direction to the rising/setting sun. Leave the drives in FAST mode (i.e. not tracking).
# On the TCS, move the '''guide mirror out of beam'''.
# On the instrument PC, '''select the required filter'''. If you need flats in a variety of filters, be sure to cycle through them in the correct order (e.g. UBVRI during evening twilight; IRVBU in the morning). This also applies if you need a range of prebin settings (i.e. start with low binning in the evening; high to low binning in the morning).
# '''With STE3/STE4''', click "Expose", create a module, select "Flat" for the image type, and "Sky" from the pulldown menu beside it. Keep the count rates between 20000 and 50000. Remember to select "Yes" under "Save to Disk". Snapshots can be used to gauge integration times and can be saved to disk if appropriate. Section~\ref{sec-SAAOskyflats} gives a recipe for taking sky flats. See Section~4 of "SAAO~CCD Camera Control Program, version 1.2", by J. W. Menzies, for more detailed instructions on setting up a module.
# Take a '''minimum of 15 flats in each filter/prebin setting''', keeping exposure times ≥1s with STE3/4 to allow the shutter time to open and close (SHOC has no shutter so does not have this limitation).
==== Sky flat recipe for the STE3/STE4: Modules ====
Since all exposures with the SAAO~CCD must be performed via a module (except for snapshots), it may seem challenging to set up and edit modules quickly enough to obtain sufficient sky flats during twilight. However, you can do this pretty quickly using the following example:
# '''Before twilight''', set up a module for your first filter and an exposure time of 1s (do not go below 1~s), with 1 repeat.
# For evening twilight, perform steps 1-4 of Section~\ref{sec-sky} to setup the telescope and facility prior to sunset.
# Click the small grey "On" button below the SAAO CCD image display.
# Shortly before (morning) or after (evening) sunrise/set ~10 minutes after sunset for B) click "Snapshot" → Exposure time = 1s. Click "Ready" to expose.
# Hover the cursor over the top portion of the image display as the image reads out, and read off the count level in the yellow "ADU" box below the image. Assess how the exposure time needs adjusting to maintain counts of 20000-50000 as the sky darkens/brightens.
# '''During readout''' click "Expose" → acknowledge the error message → "Select" module. Click on the desired module → "Edit". Adjust the exposure time in the box at the bottom → "Replace" → "Save" → "Continue".
# Enter number of modules = 1, Image Type = Flat → Sky. Save to disk = Yes.
# When the CCD finishes reading out, click "Ready".
# Repeat steps 5-8 until you have enough flats, or until the counts are too low in that filter.
# To move onto the next filter, repeat step 6, but edit the filter number as well as the exposure time.
# Continue steps 5-9 until you have sufficient flats in all your program filters.
With practice, you will easily be able to do this before the CCD finishes reading out in 2x2 binning.
== Dome flats ==
If poor weather conditions during twilight prevent you from obtaining sky flats, dome flats can be used instead. These can be obtained at any time by imaging a "uniformly" illuminated screen in the dome in the following way:
# Follow the facility start-up procedure in Section~\ref{sec-facstartup}, but there is no need to hook the outside doors open and '''do not open the dome'''. '''Remember to open the mirror covers.'''
# Follow the appropriate '''instrument setup''' procedure in Section~\ref{sec-inststartup}.
# '''Switch on the domeflat lamp''' by turning the dial on the wall between the North pier and the blue console.
# '''Rotate the dome''' to an azimuth of 180°, such that the lamp on the catwalk illuminates the round, white screen on the dome as uniformly as possible.
# '''Slew the telescope''' to HA = -3h 16m, Dec = -14° 37'
# '''Expose and save''' at least fifteen flats for each of the required combinations of filters and binning.
You may need to adjust the dial on the incandescent lamp between filters to achieve manageable exposure times. With STE3/4, keep exposure times ≥1s to allow the shutter time to open and close.
== Current known issues (last updated Nov 2013)==
