CURSA provides some limited facilities for accessing remote catalogues held on-line at various astronomical
data centres and archives around the world. You can select a subset from one of these catalogues and
save it as a catalogue on your local computer using either
catremote or the catalogue browser
(see Section 11).
xcatview provide the same functionality for accessing remote
xcatview is slightly more convenient to use. Currently the only sort of selection
which is permitted on remote catalogues is to select all the objects in the catalogue which lie within a
given angular distance from a given point on the celestial sphere (thus, the selection corresponds to
the ‘circular area’ or ‘cone search’ option of
catselect, see Section 16). The remote catalogues are
accessed via the Internet and obviously the option will only work when CURSA is being run on a
computer with suitable network connections. If you are using CURSA at a normal Starlink node then
remote access will usually be available. Conversely (and obviously) if you are using it
on a stand-alone Linux PC without network connections then remote access will not be
The remainder of this section refers to
catremote. However, all the material, apart from the specific
instructions for running
catremote, is equally applicable to accessing remote catalogues using
xcatview. Section 25.1 describes how to run
catremote and Section 25.3 how to configure it to
specify the list of remote catalogues which are accessible. Strictly speaking this information is all that
you need to know in order to use
catremote. However, it is useful if you understand various
peculiarities and shortcomings which are contingent on the way that the remote access operates;
subsequent sections provide the details.
Unlike most other CURSA applications
catremote is not an ADAM A-task (it is, in fact, a Perl script).
Usually this difference will not be important to you, but it does mean that
catremote behaves slightly
differently from the other applications when it is prompting for input values. In particular, it has no
default replies for prompts and the special replies described in Section 9 are not available. Nor does it
support either the normal options for copying textual information (see Section 10.1) or the quiet mode
(see Section 10.2).
| ||list the catalogues currently available|
| ||show details of a named catalogue|
| ||submit a query to a remote catalogue and retrieve the results|
| ||resolve an object name into coordinates|
| ||list the modes available|
The basic purpose of
catremote is to query remote astronomical catalogues and archives. In addition
to this basic query function it has a number of auxiliary functions, and each function corresponds to a
mode of the program. For completeness all the various modes are listed in Table 14, though the
modes that you are likely to use are:
These modes are described briefly below. Though incomplete, this description should be enough to
allow you to use
catremote. There is a comprehensive description in SSN/76.
catremote’s arguments can be specified on the command line, where they are identified by
position. The first command-line argument of
catremote is always the mode of operation, and is one
of the values listed in Table 14. The mode can only be specified on the command line. If it is omitted
help’ mode is assumed and the various modes are listed. The subsequent arguments required
depend on the mode chosen and are summarised in Table 15. These arguments may optionally be
omitted, starting at the right. Omitted arguments (other than the mode) will always be prompted
To obtain a list of all the remote catalogues which are currently accessible simply type:
A list of all the catalogues which are accessible will be displayed. This list will look something like the
extract shown in Table 16. Each line of the list refers to a different catalogue. The first item on each
line is the name of the catalogue. The second item is the type of the catalogue; the usual value is
catalog’, which corresponds to a simple catalogue, though other alternatives are possible. The
remainder of the line is a brief description of the catalogue. Thus, ‘
ppm@eso’ is the name of the
catalogue at ESO. You will give this name when you specify the catalogue to be queried. The catalogue
descriptions are usually quite brief and often contain acronyms.
By convention the names have the form catalogue
@institution where catalogue is an abbreviation for the
catalogue and institution an abbreviation for the institution where the on-line version is located. The
common values for institution are listed in Table 17.
| ||Canadian Astronomy Data Centre, Dominion Astrophysical Observatory|
| ||European Southern Observatory, Garching bei München|
| ||Department of Physics and Astronomy, University of Leicester|
| ||Royal Observatory Edinburgh|
To query a remote catalogue to find the objects which lie within a given angular distance of a central Right Ascension and Declination simply type:
The arguments can be omitted from the right and any that are omitted will be prompted for. The individual arguments are as follows.
:’) as the separator.
:’) as the separator. Southern Declinations are negative.
This description of the query mode is something of a simplification: for some catalogues it is possible to apply an additional condition which the objects satisfy as well as lying within a given circle of sky; see SSN/76 for details. If your coordinates for the central position are for some equinox other than J2000 then you can use the Starlink utility COCO (see SUN/56) to convert them to the required equinox.
catremote writes the extracted objects to a catalogue in your current directory. This catalogue is formatted as a
Tab-Separated Table (TST)21.
The name of the catalogue is generated automatically from the name of the remote catalogue and the
coordinates of the central position. For example, if the name of the remote catalogue was ‘
and the central position was Right Ascension
10:30:00 and Declination
20:40:00 then the name of
the local catalogue would be:
Note that the ‘
@’ in the remote catalogue name has been replaced with an underscore (‘
_’) and the
:’) have been removed from the coordinates. Also, for a negative Declination the minus sign
is replaced by an ‘
m’. These substitutions are made in order to ensure that the catalogue name consists
only of alphabetic characters, digits and underscores. This restriction is not really necessary
on Unix systems but may be useful if the catalogue is ever copied to another operating
catremote can be used to query a remote ‘name resolver’ to find the coordinates of a named object.
catremote namename-resolver object-name
If the name is recognised then the Right Ascension and Declination of the object are displayed (the Right Ascension is in sexagesimal hours, the Declination is in sexagesimal degrees and both are for epoch and equinox J2000). The technique only works if the name is recognised by the name resolver. The details of individual arguments are as follows.
simbad_ns@esoand probably will not be significant for other name resolvers.
catremote takes some input from Unix shell environment variables and these variables can be used to
control its behaviour. Some of the variables are optional, but others are mandatory and must be set
catremote is invoked. Default values are set when CURSA is started. All the environment
variables used are listed in Table 18, though the only ones that you are likely to need to change are
CATREM_MAXOBJ, which are described briefly below. For a complete description see
| ||Program to submit query|
| ||URL of configuration file|
| ||Maximum number of objects in results table|
| ||Echo URL sent to remote server?|
catremote. Specifying the configuration file is described in Section 25.3, below.
The list of all the remote catalogues which are currently accessible is defined in a so-called
configuration file. This file is not usually a file on your local computer (though in some cases it can be;
see below), but rather it is located on a remote machine. The remote catalogues which you can
access are not necessarily on the same remote machine as the configuration file, though
sometimes they will be.
catremote accesses the configuration file via the Hyper-Text Transfer
Protocol (HTTP) developed for the World Wide Web. You specify the configuration file to be
used by setting the Unix shell environment variable
CATREM_CONFIG to the URL (Uniform
Resource Locator) for the file. This process is exactly analogous to specifying the URL of
a Web page when using a Web browser. The default configuration file used by CURSA
To specify a given configuration file you simply set environment variable
CATREM_CONFIG to the
required URL prior to running
xcatview. For example, to specify a copy of the original
ESO configuration file type:
You can create your own configuration file. Such a file might contain, for example, only the catalogues which you use regularly. However, I recommend that you only try to create your own configuration file if you really understand what you are doing. Configuration files are documented in SSN/75.
This section outlines how the remote access mechanism works. It is not strictly necessary to follow it
in order to use
catremote, though it may help you to appreciate some of the reasons behind some of
catremote’s behaviour. The configuration file used by
catremote is no more than its name
implies. It simply defines a list of remote catalogues and provides some details for each:
its computer network address, the sorts of query that it will accept, a short description
For every remote catalogue listed in the configuration file there must be a server running on a remote
machine. This server will accept queries sent from
catremote, interrogate the relevant
catalogue to select the objects which satisfy the query and return the selected objects to
There is a standard protocol for both the queries and the returned results which allows
and the various servers to communicate. This protocol is a subset of a proposed general
format for exchanging information between remote astronomical information services
which is being developed at the Centre de Données astronomiques de Strasbourg (CDS)
and elsewhere. The proposal is described in the working document Astronomical Server
URL by M. Albrecht et al.. It is important to realise that this protocol is general,
and allows not just
catremote, but also various other clients, such as GAIA and
to communicate with various different servers for differing purposes. Thus, it is not optimised for
catremote, resulting in some peculiarities in the catalogues of selected objects written by
(see Section 25.5, below).
The Astronomical Server URL protocol, as its name implies, uses the Hyper-Text Transfer Protocol
(HTTP) developed for the World Wide Web. Thus, in order for
catremote to work successfully your
local computer must be configured for running Web clients (such as
netscape). Of course, most
Starlink nodes (and, indeed, most networked computers) will be so configured. One way of
catremote is that it is functioning as a very specialised Web browser. Similarly, the
remote servers are, strictly speaking, ‘gateways’ using the Common Gateway Interface
There are various types of remote servers: catalogues, name servers, data archives and image servers.
All are ‘catalogues’ in the sense of returning a table of values. A catalogue server returns traditional
columns such as position, magnitude, colours, spectral type etc. A name server primarily returns
columns containing celestial coordinates and alternative names for the object. A data archive will
return a normal catalogue of values but at least one column will list URLs pointing to images or
‘bulk data’ files for the objects tabulated. It is important to realise that though
can return these special columns CURSA contains no facilities for interpreting them. When
catremote displays the list of accessible catalogues it includes the type of each (catalogue,
data archive, name server or image server) immediately after the name and before the
You may notice the following peculiarities and shortcomings with selections extracted from remote catalogues.
This section considers whether it is better to access a given catalogue remotely or to obtain a copy of the complete catalogue (for example, as described in Section 2) and to access it on your local computer.
The advantages of remote access are that it is very quick and easy. Also the Right Ascension and Declination are automatically returned in a form which is fully compatible with CURSA. However, the catalogue may contain only some of the columns and most of the metadata (see Section 4) will be missing. Finally only ‘circular area’ selections are possible.
The advantages of local access are that the entire catalogue, including all its columns and metadata, is available and a variety of different sorts of selection can be made on it. The disadvantages are that more effort is involved in obtaining a copy and creating a version with coordinates which are fully compatible with CURSA.
As a rough guide, you should probably use remote access if you just want to make a quick ‘circular area’ selection and simply list or plot the results. However, if you are intending to make extensive use of a catalogue it is probably better to have a local copy.
xcatview is a ‘front-end’ graphical user interface which invokes
catremote to access the remote catalogue,
though as a user you will not normally be concerned with these details. Note, however, that the command line catalogue
catview, cannot access remote catalogues.
21Unlike other CURSA applications
catremote will only write catalogues in the TST format. This restriction is not
important because all the other CURSA applications can read catalogues in this format. If you want to convert the catalogue
to another format (for example, in order to input it into some other program) then simply use
catcopy, as described in