SIMBAD references

The flux-density scale of Perley & Butler is extended downward to ∼50 MHz by utilizing recent observations with the Karl G. Jansky Very Large Array (VLA) of 20 sources between 220 MHz and 48.1 GHz, and legacy VLA observations at 73.8 MHz. The derived spectral flux densities are placed on an absolute scale by utilizing the Baars et al. values for Cygnus A (3C405) for frequencies below 2 GHz, and the Mars-based polynomials for 3C286, 3C295, and 3C196 from Perley & Butler above 2 GHz. Polynomial expressions are presented for all 20 sources, with accuracy limited by the primary standards to 3%-5% over the entire frequency range. Corrections to the scales proposed by Perley & Butler, and by Scaife & Heald are given.