This page is a quick
introduction to Querator, its aim and capabilities.
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What is it?
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Querator is an advanced multi-archive search engine built to
address the needs of astronomers looking for multicolour imaging
data. Querator returns sets of images of a given astronomical
object or search region. A set contains exposures in a number of
different wave bands. The user constraints the number of desired
wave bands by selecting from a set of instruments, filters or by
specifying actual physical units.
Querator is very different from other tools. First, Querator is
the only tool to enable users to put constraints on the number of
colours (that is on the number of filters). This has proven to be
of great interest to astronomers interested, for instance, in
photometric redshift determination of just 'simple' multicolour
photometry.
Another interesting feature is Querator's ability to cross
correlate such catalogues as LEDA with supported image archives.
In this way, choosing the external server (e.g. LEDA) search
option, users can look for astronomical images simply specifying
physical constraints.
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How do I use it?
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To get started, from Querator home page,
choose which kind of search you are interested in. Options are:
object name search: you
just specify an object name (which will be resolved by SIMBAD),
along with constraints on each observation (e.g. exposure time),
minimum number of distinct filters that your object must have
been observed in, filter characteristics (wavelength coverage,
type of filter). Constraints on other parameters can be included
as well (e.g. seeing). You'll be asked to enter a search radius.
All images observed within the search radius from the center of
the object you selected will be examined as well. For each HTML
form field, 'default' values are given. Instead of object name,
it is possible to use object coordinates (either equatorial or
galactic) as search parameters.
sky box search: you just
specify a region of the sky along with constraints on each
observation (e.g. exposure time), minimum number of distinct
filters that each object must have been observed in, filter
characteristics (wavelength coverage, type of filter).
Constraints on other parameters can be included as well (e.g.
seeing). In this case, you need to enter a clustering radius
value. This value will define clusters (i.e. groups) of
observations. A cluster is defined as a group of observations
whose pointings are closer to each other than a clustering
radius. This concept is closely related to that of 'ECF
associations' for WFPC2 images. For each HTML form field,
'default' values are given.
external server (e.g. LEDA)
search: the same as object name search, with the
difference that you are interested in a list of objects. This
list is obtained querying a catalogue (such as the LEDA database)
making use of physical constraints.
user file upload the same as object name search,
with the difference that you are interested in a list of objects.
You can upload the list as an ascii file listing object names or
coordinates.
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| Querator Output |
Query Results are displayed in table format, one table for each cluster (see definition above) of results.
The same results are stored to a file in ASCII format.
With this format, any single ASCII table can be fed in SKYCAT. It means that if you have multiple tables in
your file, you have to split it using the [EOD] as separator before using SKYCAT, otherwhise only the first table
will be used.
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Further reading
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