Absolute Flux Calibrated Spectrum of Vega

An absolute flux calibrated reference spectrum of Vega, the primary calibration standard in the optical, is presented. The spectrum covers the entire 0.12 to 2.6 microns wavelength. The ultraviolet spectrum is based on IUE measurements. The optical and near-infrared up to 1.05 microns consists of Hayes (1985) average spectrum. A model spectrum normalized to Hayes (1985) Johnson V flux covers the rest of the near-infrared interval up to 2.6 microns. The uncertainty on the absolute flux of the reference spectrum over the optical and nearinfrared range up to 1.05 microns is about 1.5%. For the 1.05 to 2.6 micron range the model predicts JHK fluxes 5% to 6% lower than the absolute measurements. In the ultraviolet, the uncertainty of the IUE average spectrum is about 5%. Model spectra based on ATLAS9 and ATLAS12 Kurucz’s codes and normalized to Hayes absolute scale are also presented. The model spectra agree with the optical and ultraviolet continuum measurements to 2% and 10%, respectively. Differences from 10% to 20% are obtained in the cores of the optical and near-infrared absorption lines, when the model and the observed spectra are compared. The absolute flux calibrated spectrum of Vega presented here is used to compute the average fluxes of Vega in Johnson’s UBVRI system and, subsequently, the zero-points fluxes of the photometric system. No reliable near-infrared spectrophotometric measurements of Vega exist to date. The calibrated ATLAS9 and ATLAS12 model spectra predict near-infrared JHK fluxes about 5%-6% lower than the measurements. Therefore the zero-point flux of the JHK bands cannot be determined from the flux of Vega in the same way described for the B and V bands by Colina & Bohlin (1994). Instrument Science Report CAL/SCS-008