Studies of the Diffuse Interstellar Bands. III. HD 183143

TL;DR

This study catalogs 414 diffuse interstellar bands in the spectrum of HD 183143, revealing most are weak and narrow, with no clear molecular pattern, and compares these features to those in other stars to infer differences in interstellar conditions.

Contribution

It provides a comprehensive catalog of DIBs in HD 183143, including 135 newly reported bands, and analyzes their properties and differences from other sightlines.

Findings

Most DIBs are weak and narrow with typical widths near 0.7 Å.

No preferred wavenumber spacings among the DIBs were found.

DIBs toward HD 183143 are redder, broader, and stronger than those toward HD 204827.

Abstract

Echelle spectra of HD 183143 [B7Iae, E(B-V) = 1.27] were obtained on three nights, at a resolving power R = 38,000 and with a signal-to-noise ratio ~1000 at 6400 A in the final, combined spectrum. A catalog is presented of 414 diffuse interstellar bands (DIBs) measured between 3900 and 8100 A in this 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. Among the 414 bands, 135 (or 33%) were not reported in four previous, modern surveys of the DIBs in the spectra of various stars, including HD 183143. The principal result of this study is that the great majority of the bands in the catalog are very weak and fairly narrow. Typical equivalent widths amount to a few mA, and the bandwidths (FWHM) are most often near 0.7 A. No preferred wavenumber spacings among the 414 bands are identified which could provide clues to the identities of the large molecules thought to cause the DIBs. At generally comparable detection limits in both spectra, the population of DIBs observed toward HD 183143 is systematically redder, broader, and stronger than that seen toward HD 204827 (Paper II). In addition, interstellar lines of C2 molecules have not been detected toward HD 183143, while a very high value of N(C2)/E(B-V) is observed toward HD 204827. Therefore, either the abundances of the large molecules presumed to give rise to the DIBs, or the physical conditions in the absorbing clouds, or both, must differ significantly between the two cases.