SWAS Spectrum Server Users' Guide


SWAS Data Products

SWAS was a NASA Small Explorer Project (SMEX) launched in December 1998 to study the chemical composition of interstellar gas clouds. The SWAS spacecraft made detailed far-infrared spectroscopic maps of interstellar clouds on scales of approximately 1 square degree. The positional coverage varied widely from cloud to cloud: most clouds were measured at only a few positions, but a few, such as DR 21, were measured at over 50 positions. The instrument measured the following spectral lines:


Frequency (GHz)

Molecular oxygen (O2)


Water (H2O)


Neutral carbon (CI)


Isotopic carbon monoxide (13CO)


Isotopic water (H218O)


Typically, multiple spectra were measured for each line at each discrete position, and co-addition of these spectra yielded the highest quality spectrum.

The SWAS Science Operations Center at SAO released spectral data in two formats: CLASS and FITS. The FITS files contain the grand co-additions of individual spectral lines for each position in a cloud, while the corresponding CLASS files contain all the spectra for a given cloud. Details of the products are given at the NSSDC SWAS page at https://lambda.gsfc.nasa.gov/product/swas/data_r_data_p.cfm. (Quick-look images of the co-added spectra of the central position of each source, which are available through the IRSA site, are also available at https://lambda.gsfc.nasa.gov/product/swas/s_sw.cfm).


The IRSA SWAS Spectrum Server

The service allows users to:

Using the IRSA SWAS Image Server

The main page provides two ways of accessing SWAS spectra:

For selecting, click either the "From Sky Map" or "From Table of Sources" links on the main page. For searching enter the location and submit. Special Note: We employ the source names used by SWAS, some of which are not resolved by the NED or SIMBAD name resolvers. This service therefore uses a dedicated SWAS name resolver that is called before NED and SIMBAD. The SWAS names can be seen by hitting the "From Table of Sources" link.

For the searching option, the service will bring up a second page showing:

The inventory page allows users to select spectral lines and download either individual ASCII tables, a script that will retrieve all tables, FITS files of co-added data, or CLASS files of all data.

Moving Objects

Spectra of a small sample of solar system objects are available by clicking on "From Moving Target List" on the main page. Since an ensemble co-add would be misleading in most cases, the full data are only available in the CLASS format.