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

Abstract

Echelle spectra of the double-lined spectroscopic binary HD 204827 were obtained on five nights, at a resolving power R ¼ 38;000 and with a S/N ¼ 750 near 6000 8 in the final, combined spectrum. The stars show E(B À V ) ¼ 1:11 and spectral types near O9.5 V and B0.5 III. A catalog is presented of 380 diffuse interstellar bands (DIBs) measured between 3900 and 8100 8 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 m8, and the bandwidths (FWHM ) are most often near 0.55 8. Therefore, most of these DIBs can be detected only in spectra obtained at a resolving power and a S/ N at least comparable to those used here. In addition, the anomalous interstellar reddening and the very high value of the ratio N(C 2 )/E(B À 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 (30%) were not detected in four previous modern surveys of the DIBs seen in the spectra of stars other than HD 204827. No preferred wavenumber spacings among the 380 bands are reliably identified which could provide clues to the identities of the large molecules thought to cause the DIBs.

Using Machine Learning to classify the diffuse interstellar bands

“…Our reference list of DIBs includes 197 lines which we compile using the catalogs of Jenniskens & Desert (1994), Jenniskens et al (1996), Krelowski, Sneden & Hittgen (1995), Hobbs et al (2008) and Jenniskens et al (1996).…”

VISIBLE ABSORPTIONS OF POTENTIAL DIFFUSE ISM HYDROCARBONS: C9H9 AND C9H5 RADICALS

“…Band positions, widths, and intensities are given in Table 3. The strongest band at 5719.46 Å (FWHM=0.99 Å) matches a weak DIB in HD183143 (5719.63 Å; W=21.7 mÅ; FWHM=0.92 Å; Hobbs et al 2009) and HD204827 (5719.48 Å; W=16.7 mÅ; FWHM=0.69 Å; Hobbs et al 2008). The first band of the observed progression at 5904.39 Å (FWHM=1.17 Å) is three times weaker than the strongest one.…”

“…These features remain underdetermined until further experiments are performed, e.g., hole burning or use of specific precursors. Table 2 compares the five strongest bands of the recorded C 9 H 9 spectrum with tabulated DIB data from HD204827 and HD183143 (Hobbs et al 2008(Hobbs et al , 2009). The positions of the laboratory bands at 6182 and 6085 Å are within 0.2 Å of two very weak DIBs (equivalent width W<10 mÅ).…”

On the rotational energy distributions of reactive, non-polar species in the interstellar medium

“…Additionally, the optimum detectability of C 2 + may be in more diffuse lines of sight, where the E B-V may be less than 0.5, which is at the limit of good absorption line measurements (Hobbs et al 2008). …”