An Atlas of Spectrophotometric Landolt Standard Stars

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