Data Set Overview : The Small Solar System Objects Spectroscopic Survey (S3OS2) was performed between November 1996 and May 2001 at the European Southern Observatory. The 1.52m telescope was equipped with a Boller and Chivens spectrograph and a 2048x2048 pixels CCD. A low-resolution grating (225gr/mm) was used with the spectrograph, with a dispersion of 330 Angstroms/mm in the first order. All observations were done with a 5-arcsec slit oriented in the east-west direction. This configuration resulted in an useful spectral range of 4900 to 9200 Angstroms. 70% of the asteroids have been observed more than once, and 53% of them, on two different, and quasi-consecutive nights. However, only the spectrum with the smallest noise in the region between 6000 and 6500 Angstroms is made public in this database.  The spectral reduction was done using tasks of the Image Reduction and Analysis Facility (IRAF), using the classical procedure with averaged bias and dome flat-fields. Wavelength calibration was achieved by using a He-Ar lamp, which spectrum was obtained several times during each night. The spectra were corrected for airmass by using the mean extinction curve of La Silla (Tug, Messenger, vol. 11, p. 7-8, 1977). At least two solar analogs (Hardorp, A&A 63, 383-390,1978) were observed in each night in order to compute reflectivities. They were reduced by using the same procedures used for the asteroids. Finally, each spectrum of an asteroid was divided by that of the solar analog star, yielding the reflectance of the asteroid. Tests made using different solar analog stars produced differences in the reflectance spectra smaller than 1%/1000 Angstroms. The solar analogs HD44594 and HD144585 were the most adopted in the survey.

Confidence Level Overview : The observations were made as near as possible to the local meridian of the asteroid, at airmasses between 1 and 2.11, with a median value of 1.13. Compositional differences on an asteroid's surface can exist and this may produce distinct spectra of the same object. The spectra presented here represent the surface reflectance of the area visible at the moment of the observation. The user is referred to the paper of Lazzaro et al. Icarus 172, 179-220, 2004 for a more complete description of the data, instruments and observational circumnstances.