An Atlas of Spectrophotometric Landolt Standard Stars

We present CCD observations of 102 Landolt standard stars obtained with the Ritchey‐Chrétien spectrograph on the Cerro Tololo Inter‐American Observatory 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 Å to 1.1 μm. Mean differences between UBVRI spectrophotometry computed using Bessell’s standard passbands and Landolt’s published photometry were determined 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, will 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.