Obscats

The obscat is a fits file containing event file names and other pertinent information about the files, such as on-time, datamode,..., gathered from keywords in the primary extension of the events files. The user can specify the items to be included in the obscat, and there are a set of built in defaults for each supported mission.

The data files must all be contained in the same directory, the data directory. The obscat is constructed by doing a directory listing on this directory, using a mission dependent regular expression for the file names. There is also the provision for user supplied regular expressions.

Although the catalogues are limited to the contents of one directory, the HK files can be kept in a separate directory.

Currently the MAKE OBSCAT command is designed primarily for the ASCA mission. It assumes the naming conventions of FRFREAD for the Event, HK and GTI files. However, the read command makes an obscat that can be SAVEd, LOADed and all the other functions the created catalogues admit.

If no observation catalogues are present, then one can be made by specifying the mission, the instrument, and the data directory ( and optionally the datamode), then issuing the MAKE OBSCAT command:

xsel > set mission ASCA
xsel:ASCA > set inst sis1
xsel:ASCA-SIS1 > set datamode BRIGHT
xsel:ASCA-SIS1-BRIGHT > set datadir ../../data/20019000
xsel:ASCA-SIS1-BRIGHT > make obscat

The first step is unnecessary if you always use the same mission, since Xselect stores a default mission that it loads at startup. To change this default, you can start up xselect with the command

% xselect default_mission=ROSAT

This will cause Xselect to load the ROSAT mission at startup, rather than ASCA which is the default Xselect is shipped with.

A catalogue will be made in the obscat directory (or the current working directory if no obscat directory is set) with the default name xsel_(instru).cat, where (instru) is s0, s1, g2, g3 for the ASCA mission. It is saved when the Xselect session is exited, regardless of whether the rest of the session is saved.

When a catalogue is made, it is automatically loaded into xselect and the contents displayed.

To view the contents of the catalogue again, use the command

xsel >  show obscat

Note that the plain SHOW OBSCAT command will usually only show you a subset of the parameters that are in the obscat. To see all the parameters, record by record, use the command:

xsel > show obscat list

Or, if you have a different list of parameters that you want to view in the column form, use the command

xsel > show obscat displist="@myparam.list"

where myparam.list is a list of the parameters you want to view.

If you have already made some catalogues, you can get a listing of them with the command

xsel > list obscat

This will list the catalogues in the current working directory (or obscat directory if one is set), and the data directory if one has been set.

You can load an already created catalogue with the command

xsel:ASCA > load obscat

You can either specify, by name, the obscat that you want to load, or if you give no arguments Xselect will display the catalogues present in the obscat directory and the data directory, and prompt you for a choice.

This command will also set the datadir, mission, instrument, and datamode (provided they are unique) from the catalogue, if you have not already done so.

To read data in from the catalogue, use the choose command. Choose works in two modes, you can say

xsel:ASCA >  choose 1-15

which will select the files 1-15 from the obscat. Or you can say

xsel:ASCA-SIS0 >  choose "datamode=='BRIGHT'"

which will select all the files from the obscat with BRIGHT datamode.

If you have a catalogue with the default name corresponding to the currently selected instrument, then choose and show will act on that catalogue automatically.

To apply selection criteria to the current catalogue to produce a new catalogue, rather than to just extract data from it, use the command

xsel >  select obscat  "datamode=='BRIGHT'"

This selection will not overwrite the previous catalogue, but it will rename it to move it out of the way. Since load obscat will give a brief description of each catalogue it finds, this should not be a problem, however if you want to save the current obscat with a name of your own choosing, you can do so with the command

xsel >  save obscat

Finally, the process of selection may result in many obscats that you don't want to keep. The CLEAR OBSCAT command will give you the same listing of the obscats as LIST and LOAD, and prompt you to remove those catalogues you no longer need.

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Last modified: Tuesday, 10-Jan-2023 11:03:02 EST

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