Landolt Spectrophotometric Standards
We present CCD observations of 102 Landolt standard stars obtained with the
R-C spectrograph on the CTIO 1.5 m telescope. Using stellar atmosphere
models we have extended the flux points to our six spectrophotometric
secondary standards, in both the blue and the red, allowing us to produce
flux-calibrated spectra that span a wavelength range from 3050 Ang to 1.1 um.
We find mean differences between UBVRI spectrophotometry computed using
Bessell's standard passbands and Landolt's published photometry to be 1% or
less. Observers in both hemispheres will find these spectra useful for
flux-calibrating spectra and through the use of accurately constructed
instrumental passbands be able to compute accurate corrections to bring
instrumental magnitudes to any desired standard photometric system
(S-corrections). In addition, by combining empirical and modeled spectra
of the Sun, Sirius and Vega, we calculate and compare synthetic photometry
to observed photometry taken from the literature for these three stars.