Studies of the Diffuse Interstellar Bands. III. HD 183143
  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.
