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Astron. Astrophys. 327, 388-391 (1997)

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2. Observations and data reduction

The low-resolution spectra we present in this paper have been obtained during different observing runs between 1993 and 1996 (Table 1).

[TABLE]

Table 1. Observational characteristics of the NEAs.

The observations have been performed at the European Southern Observatory (ESO, La Silla, Chile) and at the Asiago Observatory (Italy). At La Silla we used the 1.5 m telescope equipped with a Boller & Chivens spectrograph and a type Ford CCD (2048 [FORMULA] 2048 pixels) detector. The grating used was a 225 gr/mm with a dispersion of 330 Å/mm in the first order. The CCD has a 15 [FORMULA] m square pixel, yielding a dispersion of 5 Å/pixel in the wavelength direction. The spectral range covered is about 0.5 [FORMULA] 1 [FORMULA] m with an instrumental FWHM of 10 Å.

At the Asiago Observatory we used the 1.82 m telescope equipped with a Boller & Chivens spectrograph and a Thomson CCD (430 [FORMULA] 600 pixels) as detector. The grating was a 150 gr/mm with a dispersion of 340 Å/mm in the first order. The CCD has 23 [FORMULA] m square pixels giving a dispersion of about 7.8 Å/pixel in the wavelength direction. The spectral coverage is about 0.5 [FORMULA] 1 [FORMULA] m with an instrumental FWHM of 15.6 Å.

The reduction of the spectra has been performed using standard procedures of data reduction using the softwares MIDAS, IRAF and IDL. In order to calibrate the observational data, bias, flat-field, calibration lamp, spectrophotometric standard star and solar analog (Hardorp, 1978) spectra were secured at different intervals throughout each night. After bias subtraction, flat-field correction, cosmic-rays removal, wavelength calibration, airmass correction, flux calibration, division by the solar analog spectrum, we obtained the reflectivity spectra of the objects. The standard stars and the solar analogs were observed at airmasses similar to those of the asteroids with differences less than 0.2 in each case. In Table 1 we report the circumstances of the observations.

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© European Southern Observatory (ESO) 1997

Online publication: April 8, 1998
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