Xcov 20 Observing Instructions
ZZ Ceti
Observing Instructions :
ZZ Ceti, also known as R548, is the second most stable optical clock
known. The pulsation spectrum consists
mainly of 2 doublets, one at 213 s and the other at 274 s. There are 3 objectives in observing R548 and they are outlined in the
Scientific Justification.
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Co-ordinates of ZZ Ceti
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RA (J2000) = 01 36 10
Dec (J2000) = -11 20 42
m_v = 14.16
Finder Charts are available at:
/finders/ZZCeti.html
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Time Check
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Please do a time check each night before taking data and
as often as possible during the run. Do all you can to ensure your time is correct. This is very critical in getting a good phase for this season as this
data set will be compared to previous data sets from the last 3 decades.
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Observing Logs
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Please send your observing logs along with the data.
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Run Start
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Please start your run on an integral multiple of ten seconds (XX:XX:00, 10, 20, 30, 40 or 50). Check the computer clock
just before the run start, and synchronize it to the master clock within 0.1s if possible. It is also a good idea to check
your clock at least once during the run and at the end of the run.
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Integration Time
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Use 5s integration time for PMT observations. Please communicate to HQ your integration time if you are using a CCD system. The
observers will be the best judge as to what a good integration time should be taking into account cycle time achievable with
each CCD system.
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Filters
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Do not use filters in any channel for PMT observations.
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Sky Calibration
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Observers with 3-channel photometers should record sky in all three channels near the beginning and possibly the end of
each run to permit accurate cross calibration. It you start before twilight ends, take sky points in twilight and again
after twilight ends. If you observe into twilight at the end of the night, take sky points before twilight and again in
twilight. Observers with 2 channel photometers should take sky by moving the telescope. We have sometimes in the past used
the channel 2 verniers to measure channel 2 sky (only) but we find this is not really reliable. Try to take sky as often as
needed, at least once per hour for 30s; more sky points are not needed and cause unwanted data gaps in the light
curve of the target star.
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Comarison/Guide Stars
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Please consult the finder chart and use one of the two stars marked there,
if possible. Also record your ch2
offsets and telescope plate scale so we can verify exactly which star was observed.
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Apertures
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Please use the smallest aperture consistent with getting data of good quality (e.g. no visible loss of light to the edge of
the aperture). A general rule of thumb is to use an aperture approximately 8-10 times the diameter of the seeing disk. (An
aperture too small can lead to light loss out the edges; one too large adds additional sky noise and possibly opens the
field up to nearby contaminating stars.) Record the size of the aperture (in arcsec) in your observing log.
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Problems and Questions
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If you have any questions or problems before/during/after the run, please contact Anjum or the HQ for a faster response.
wet.physics.iastate.edu
anjum@bullwinkle.as.utexas.edu