Sample Spectral Atlas for Sirius

We present a sample spectral atlas of Sirius for the region 354 to 440 nm in which we show a photographic spectrum that resolves the line profiles and has a small-scale signal to noise better than 300. The atlas also shows a calculated spectrum that demonstrates our capabilities in spectrum synthesis. We are able to compute a spectrum, broaden it with microturbulence and rotation, transmit it through the atmosphere, convolve it with the instrumental profile, plot it together with the observed spectrum, and label each line. This approach to analyzing stellar spectra has a number of advantages over working with lists of line identifications or equivalent widths or individual line profiles: (1) The reader gets an immediate impression of the quality of the data and of blending, and many lines that appear to be single are shown to be blends. (2) The reader can much better estimate the continuum level and the total blocking to check model atmosphere predictions and assess the reliability of an abundance determined from any given line. (3) Determinations of stellar parameters and abundances can be based on all the data, not just on a small sample. (4) The reader gets an intuitive "feel" for the data and for the properties of the star, which is missing in other approaches. (5) All the data are presented and the reader who disagrees with our treatment can reanalyze them. Our programs can be used to analyze existing and future ground-based, balloon, rocket, and satellite observations of the sun and stars. For Sirius we plot a roughly photometric spectrum at 10 nm/panel, then at 5 nm/panel with a comparison rotationally broadened calculated spectrum, then at 0.8 nm/panel with comparison unbroadened and rotationally broadened calculated spectra and line identifications. No attempt has yet been made to fit the calculated spectra to the observed spectrum. The observed spectrum has been only roughly normalized to the calculated spectrum to make it photometric. From the sample spectrum it is clear that Sirius is strongly underabundant in Ca, contrary to earlier studies, and that its abundances are roughly consistant with other metallic line stars although not extreme. There is no region of the spectrum shown here that is not produced by overlapping lines.