Southern spectrophotometric standards.

We have obtained new observations of both secondary and tertiary spectrophotometric standards with the RC spectrographs and CCD cameras on the 1.5-m and 4-m telescopes at CTIO in the wavelength range of 3300-7550 angstroms, as well as UBV(RI)KC photometry for these stars. We have modified the monochromatic fluxes of the secondary spectrophotometric standards published by Taylor (1984) according to the new calibration of Vega provided by Hayes (1985). We have also uned the zero-point of the energy distribution of these stars by matching their V synthetic magnitudes to the observed magnitudes. We use these adjusted spectrophotometric standards in order to calculate ne fluxes for the tertiary standards of Stone and Baldwin (1983), as well as for three stars of the northern hemisphere from Stone (1977). We find that the synthetic magnitudes calculated from our spectra through the B and V bands agree extremely well with our photometry, to better than 1% on average. For the monochromatic fluxes, we find an internal precision better than 0.01 mag at all wavelengths, and a fair agreement with previous measurements of the tertiary standards. We present also a fine grid of averaged monochromatic fluxes (at continuous steps of 16 angstroms) for the ten secondary standards selected for our program, to be used in the flux calibration of high dispersion spectra.