Collected Links for Preparing OmegaCAM Observations
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Technical
description of the instrument:
OmegaCAM is a wide-field blue-optimized CCD camera, which will be the
sole instrument on the 2.6m ESO-Paranal VLT Survey Telescope currently
under
construction. It has a 1x1 square degree field of view, tiled with 32
closely
packed low-noise thinned E2V CCDs.
Each image contains some 16400x16400 0.21 arcsec pixels. The design of
VST and OmegaCAM ensures that image quality should be uniformly good
all
over the field.
An atmospheric dispersion corrector is available for work at high
airmasses, but cannot be used in u band.
Cosmetic quality of the CCDs is good but not perfect, so some
dithering is required. The layout of the focal plane (including four
auxiliary CCDs for guiding and image quality measurement, and the
globular cluster omega Cen for your pleasure) is as follows:
Geographical information
on VST:
altitude 2635.43 m
latitude -24 deg 37 min 33.117 sec (UT1)
longitude 70 deg 24 min 11.642 sec (UT1)
See Paranal web page for
details and in particular
General Observing Conditions and Data for Paranal
Observing modes:
We distinguish the following observing modes:
- Dither,
with large pointing offsets (nominally 5 pointings) of the order of 1-2
arcminutes optimised to the largest gaps between the CCDs (~400
pixels). This will lead to a full sky coverage but with a rather
complex weight map. At least 5 pointings are necessary to obtain a
sampling over the whole field that is uniform within a factor of 2 (see
colour-coding of image on the right, showing relative exposure times
after a fairly optimal 5-point dither).
- Jitter,
with pointing offsets matching the smallest gaps between CCDs ~ 5
pixels, will lead to output images with incomplete sky-coverage but
with a very homogeneous sampling on the sky. The variation of noise
will be minimal over the whole field of view. It is the mode that
optimises homogeneity and will be used during observations for which
the wide CCD gaps are not critical
(see image on the right).
- SSO is the mode for observing Solar System Objects. It has non-sideral tracking and the auto guiding is switched off.
Observing strategies:
An observing strategy employs one or a combination of the basic
observing modes. It also defines a number of additional instructions
for the scheduling of the observations. The observing strategy will be
recorded in the FITS header of the observations. Optionally, the header
information can be used in data reduction pipelines, in particular
those operated by the Consortium when addressing the combination (e.g.
stacking) of images.
We discriminate among the following strategies:
-Standard which consists of a single observation (observation
block);
-Deep which does deep integrations, possibly taken at selected
atmospheric conditions over several nights;
-Freq which frequently visits (monitors) the same field on
timescales ranging from minutes to months and has overriding priority
on the telescope schedule;
-Mosaic maps area of the sky larger than 1 square degree, which
is essentially an item for the scheduling, as the pipeline has to
produce
uniform quality data anyway. The combination of various field centers
into
one image is not considered a standard pipeline task.
OmegaCAM Exposure
Time Estimator:
There is currently no Exposure Time Estimator for OmegaCAM but one can
use the following table as a guide.
These numbers assume dark skies, and were
computed with the proper filter profiles of OmegaCAM.
10-sigma AB magnitudes (point source, dark time, 3 arcsec aperture); Halpha in
erg/cm2/s
Integration time | u' | g' | r' | i' | z' | B | V | Halpha |
---|---|---|---|---|---|---|---|---|
100 s | 22.4 | 23.1 | 22.6 | 22.0 | 20.8 | |
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1.2E-15 |
1000 s | 23.9 | 24.5 | 23.9 | 23.3 | 22.1 | |
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2.8E-16 |
10000 s | 25.2 | 25.7 | 25.1 | 24.6 | 23.3 | |
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8.4E-17 |
Integration time | u' | g' | r' | i' | z' | B | V | Halpha |
---|---|---|---|---|---|---|---|---|
100 s | 21.5 | 22.7 | 22.4 | 22.0 | 20.7 | |
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1000 s | 22.9 | 24.0 | 23.7 | 23.2 | 22.0 | |
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10000 s | 24.1 | 25.3 | 25.0 | 24.5 | 23.2 | |
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Integration time | u' | g' | r' | i' | z' | B | V | Halpha |
---|---|---|---|---|---|---|---|---|
100 s | 22.8 | 23.6 | 23.0 | 22.5 | 21.2 | |
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1000 s | 24.3 | 24.9 | 24.3 | 23.8 | 22.5 | |
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10000 s | 25.6 | 26.2 | 25.5 | 25.0 | 23.8 | |
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Integration time | u' | g' | r' | i' | z' | B | V | Halpha |
---|---|---|---|---|---|---|---|---|
100 s | 22.0 | 23.1 | 22.8 | 22.4 | 21.1 | |
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1000 s | 23.3 | 24.4 | 24.1 | 23.7 | 22.4 | |
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10000 s | 24.5 | 25.7 | 25.4 | 24.9 | 23.7 | |
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A page of S/N vs exposure time plots,
including some of the other narrow-band filters,
is here.
Experience with the ESO/MPG 2.2m WFI is a useful guide, but note that
WFI and OmegaCAM filters are different.
Mode of operation:
All data are taken in service mode by ESO. Some facility for quick-look
data reduction in Chile may be possible, but otherwise it may take 2-3
weeks between the time the data are taken, and availability of the
data.
Data reduction:
OmegaCAM data will be ingested into the ASTRO-WISE system, operated
at
the OmegaCEN data center in Groningen. This means that reduced images
(astrometrically and photometrically calibrated, co-added) will be
available, as well as source lists (based on SExtractor). The data can
be worked on remotely, including extensive datamining facilities on the
source lists and images, or exported.
References:
OmegaCAM: the 16k × 16k CCD Camera for the VLT Survey Telecope,
in .pdf format, as
published
in ESO Messenger 110. .
OmegaCAM: The 16k × 16k Survey Camera for the VLT Survey
Telescope
Article by E. Deul, K. Kuijken and E. Valentijn, in ps or pdf format.
Click here for March 2003
PowerPoint Presentation