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POL_EXTENDED reduces such data using both regions of each band
to determine a modal sky level. It samples at each waveplate angle
before jittering the telescope position. There are two ways to make
a flat: either combine all waveplate angles (recipe SKY_FLAT_POL),
or if preferred (for, e.g., extremely high polarisation accuracy),
make flats for each waveplate angle separately (SKY_FLAT_POL_ANGLE).
K-band Fabry-Perot Imaging with UFTI
The simplest Fabry-Perot recipe is FP. It expects a sequence of
frames as tabulated on page 7.In the next level of complexity, the
above sequence is repeated for at least three jittered spatial positions
(recipe FP_JITTER). As you can see from the picture of OMC-1 below,
this can
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create pleasing results for extended sources. However, this can
be a lengthy observation since forty frames in all are required.
For compact sources with essentially zero signal in the background
sky, it is more efficient to use recipe FP_JITTER_NO_SKY, as this
only takes four frames per jitter position, excluding the off-source
frames from the table on page 7. It again differences successive
frames and flat fields. The above recipes need a flat, created by
recipe SKY_FLAT_FP. There is also a C-shell script (alignfp) available
for aligning the Fabry-Perot etalon prior to an observing run.
See Recipes
for further details of these and all the imaging recipes.
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Special data-reduction demands
Many observers seem unaware that most ORAC recipes have options
which they can tune to suit their data. For example, you can choose
the statistic by which pixels are combined to make a mosaic. What
often happens, however, is that a request is made for an existing
feature after the observing run in an observer's report, which is
a tad late. Another common occurrence is that while making a science
program with the Observation Tool shortly before the run, the observer
realises that there is no suitable recipe for the target data about
to be taken. While I have conjured new recipes in time, this cannot
always be guaranteed. Thus I urge you to think about your observations
ahead of time. Let your support scientist know of your requirements.
Given reasonable notice we can often write and test new recipes
for you.
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Primary Mirror Chills Out
Andy Adamson,
Tim Chuter,
Tim Hawarden & Erik Starman
Joint Astronomy Centre, Hilo, Hawaii
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The thermal inertia of UKIRT’s thin primary mirror is such
that a temperature significantly above that of the dome can be maintained
after sunset (the mirror’s thermal time constant is 30 hours).
The final stage in the UKIRT telescope upgrades programme is
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