The spectra in the Low-Resolution Spectrometer (LRS) Catalog are divided into two bands (8-13 microns and 11-22 microns). The file LRS_HEADER.DAT lists only the wavelengths corresponding to each channel of the spectra (see Table 1 below). The file LRS_SPECTRA.DAT contains the spectra and associated header information (see Table 2). The spectra are in order of increasing right ascension of the corresponding point source. As described below, the spectra are identified by the name of the corresponding source in the Point Source Catalog. Both files have 80-character ASCII records.

Distance from Slit: ANGLE(100)

As described in detail in Chapter IX of the Explanatory Supplement, each sample in the spectrum corresponds to a certain in-scan distance of the source from the centerline of the spectrometer entrance aperture. ANGLE lists these angular distances.

Wavelength Calibration: LAMBDA1, LAMBDA2

There is a non-linear relation between the displacement of the source from the centerline of the spectrometer and the sampled wavelength. The wavelengths corresponding to each sample (or ANGLE) are given in LAMBDA1 and LAMBDA2 for the two wavelength bands. The beginning and end of each spectrum contain measurements that lie outside of the wavelength coverage of the instrument but which can be used for baseline determination. The wavelength values corresponding to these values of sample number (or ANGLE) are set to 0.

The entries starting at bytes 0 through 25 are identical to the items with the same names in the Point Source Catalog. This is also the case for the entries starting at bytes 71, 73, 75, and 960. Their explanations will not be duplicated here, but may be found in the description of the format of the PSC.

Number of Spectra: NSPECTRA, NACCEPT

NSPECTRA is the number of spectra observed for the source; NACCEPT is the number of 8-13 micron and the 11-22 micron spectrum halves ultimately averaged to make the entry in the catalog.

Characterization of the Spectrum: LRSCHAR

A description of the method of characterization is given in Section IX.D of the Explanatory Supplement. Table 3 lists the spectral classes used to characterize the spectrum.

Quality of the Spectrum Halves: SPQUAL

Depending on the signal-to-noise ratio of the 8-13 micron and 11-22 micron halves of the spectra, the number of accepted spectrum halves and the difference in level of the baselines on either side of the spectrum halves, a quality digit is assigned to each half of the spectrum: 1 indicates good quality, 2 moderate quality, and 3 barely acceptable.

Scale Factor for All Spectrum Flux Densities: SCALE

Multiplying the integers BASELINE, NOISE, and SPECTRUM by the factor SCALE converts the values into units of W m-2 micron-1.

Baseline of Spectrum Halves: BASELINE(4)

These four values are the averages of samples of 1 through 20 (short wavelength end) and 81 through 100 (long wavelength end) of both the 8-13 micron and 11-22 micron halves of the spectrum.

RMS Noise: NOISE

Using the twenty samples on the long wavelength end used for BASELINE, the RMS noise per spectrum half is determined.

Signal-to-Noise Ratio: SNR

The average value of the samples in the wavelength ranges 8-13 microns and 11-22 microns, respectively, are divided by the NOISE values determined.

Baseline Asymmetry: ASYMM

This value indicates by what fraction of the average signal the baselines on the short and long wavelength sides of the spectrum halves differ. A large baseline asymmetry indicates that a confusing source may have contaminated the spectrum. The baseline asymmetry is usually large near the Galactic plane.

LRS/Survey Flux Ratio: SRATIO

The ratio of the integrated flux (after convolution of the spectral flux densities with the 12 micron bandpass of the survey instrument) in the spectrum and the 12 micron survey flux is given in this item. Normally this value should be close to unity (section IX.C of the Explanatory Supplement). As the 11-22 micron part of the LRS spectrum hardly overlaps with the 25 micron survey band, a ratio of LRS/survey for this band is not significant.

The Spectrum: SPECTRUM(200)

The integer values of the spectrum; they must be multiplied by SCALE for conversion to W m-2 micron-1. The wavelengths corresponding to the 100 samples given for the 8-13 micron and the 11-22 micron halves of the spectrum are given in the catalog header file LRS_HEADER.DAT. Values for non-significant wavelengths are set to zero. For baseline interpolation, either the sample numbers or the ANGLE (distance in arcmin from the spectrometer center line) can be used.

• LRS catalog information
• Spectral Classification Scheme (in the Explanatory Supplement)