A Catalog of Diffuse Interstellar Bands in the Spectrum of HD 204827

TL;DR

This study presents a detailed catalog of 380 diffuse interstellar bands in the spectrum of HD 204827, highlighting their properties and the conditions affecting their detection, with implications for understanding interstellar medium variability.

Contribution

The paper provides the first comprehensive catalog of DIBs in HD 204827, including measurements of wavelengths, widths, and strengths, and discusses the impact of unique interstellar conditions on DIB detection.

Findings

Most DIBs are very weak and narrow, requiring high-resolution spectra for detection.

Approximately 30% of the DIBs in this sightline were not previously detected in other surveys.

Interstellar conditions in HD 204827 differ significantly from typical DIB targets, affecting DIB visibility.

Abstract

Echelle spectra of the double-lined spectroscopic binary HD 204827 were obtained 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) = 1.11 and spectral types near O9.5V and B0.5III. A catalog is presented of 380 diffuse interstellar bands (DIBs) measured between 3900 and 8100 A in the stars' spectrum. The central wavelengths, the widths (FWHM), and the equivalent widths of nearly all of the bands are tabulated, along with the minimum uncertainties in the latter. The reliable removal of very weak stellar lines from the catalog, and of some stellar lines from the less severe blends with DIBs, is made generally easy by the highly variable radial velocities of both stars. The principal result of this investigation is that the great majority of the bands in the catalog are very weak and relatively narrow. Typical equivalent widths amount to a few mA, and the band widths (FWHM) are most often near 0.55 A. Therefore, most of these DIBs can be detected only in spectra obtained at a resolving power and a S/N ratio at least comparable to those used here. In addition, the anomalous interstellar reddening and the very high value of the ratio N(C2)/E(B-V) seen toward HD 204827 indicate that the physical conditions in one or more of the several interstellar clouds seen in this direction differ significantly from those found toward the prototypical DIB target HD 183143, for example. Probably primarily for these reasons, 113 of the 380 bands, or 30%, were not detected in four previous, modern surveys of the DIBs seen in the spectra of stars other than HD 204827. Both the tabulated data for the DIBs and a plot of our spectrum of HD 204827 are available online at http://dibdata.org