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Selecting a spectral database

The first step to analyze our spectra is to select a spectral line database. Weeds can access both the JPL database for molecular spectroscopy and the Cologne Database for Molecular Spectroscopy (CDMS). To select a database, type dbselect, followed by the name of the database. For example:

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LAS90> dbselect jpl
I-DATABASE, jpl database selected (online).

or:

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LAS90> dbselect cdms 
I-DATABASE, cdms database selected (online).

By default, the CDMS database is selected.

As mentioned already, Weeds makes online queries to the molecular databases. However, it is sometime helpful to make offline searches in a database, for example if you are on travel with no (or a slow) internet connection. Weeds allow us to download a part of - or even the entire - spectral catalog from a database. This catalog is stored in a cache file, and can be used later for offline searches. Caching the CDMS database between 80 and 130 GHz is done as follows:

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LAS90> dbcache cdms /lower 80e3 /upper 130e3 
I-DBCACHE, Caching cdms database...
Downloading lines:      100% |########################################################| Time: 00:00:18 
Downloading part.func.: 100% |########################################################| Time: 00:00:54 
I-DBCACHE, Done.
I-DBCACHE, cdms database selected (cached).

Depending on the speed of your internet connection and the frequency range you have selected, caching a database may take from a few seconds to a few tens of minutes, so please be patient! In particular, caching the JPL database may take a while, because of technical limitations with this database; caching the CDMS database is much faster.

Once you have cached a database, you may select it with the /cache option of the dbselect command2:

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LAS90> dbselect cdms /cache
I-DBSELECT, cdms database selected (cached).

A final note on caching a database: every time the same database is cached, the older cache file is overwritten; there is no update of an old cache file. However, caches of different databases are stored in different files, so caching the JPL database will not overwrite an older cache of the CDMS.


next up previous
Next: Identifying lines on a Up: weeds Previous: Getting started
Gildas manager 2011-09-07