Echelle spectra of the double-lined spectroscopic binary HD 204827 wereobtained on five nights, at a resolving power R = 38,000 and with a S/N ratio =750 near 6000 A in the final, combined spectrum. The stars show E(B-V) = 1.11and spectral types near O9.5V and B0.5III. A catalog is presented of 380diffuse interstellar bands (DIBs) measured between 3900 and 8100 A in thestars' spectrum. The central wavelengths, the widths (FWHM), and the equivalentwidths of nearly all of the bands are tabulated, along with the minimumuncertainties in the latter. The reliable removal of very weak stellar linesfrom the catalog, and of some stellar lines from the less severe blends withDIBs, is made generally easy by the highly variable radial velocities of bothstars. The principal result of this investigation is that the great majority ofthe bands in the catalog are very weak and relatively narrow. Typicalequivalent widths amount to a few mA, and the band widths (FWHM) are most oftennear 0.55 A. Therefore, most of these DIBs can be detected only in spectraobtained at a resolving power and a S/N ratio at least comparable to those usedhere. In addition, the anomalous interstellar reddening and the very high valueof the ratio N(C2)/E(B-V) seen toward HD 204827 indicate that the physicalconditions in one or more of the several interstellar clouds seen in thisdirection differ significantly from those found toward the prototypical DIBtarget HD 183143, for example. Probably primarily for these reasons, 113 of the380 bands, or 30%, were not detected in four previous, modern surveys of theDIBs seen in the spectra of stars other than HD 204827. Both the tabulated datafor the DIBs and a plot of our spectrum of HD 204827 are available online athttp://dibdata.org
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