The Apache Point Observatory Catalog of Optical Diffuse Interstellar
  Bands
  Aiming for a new and more comprehensive DIB catalog between 4,000 and
9,000{\AA}, we revisited the Atlas Catalog based on the observations of HD
183143 and HD 204827 (Hobbs et al. 2008 and 2009). Twenty-five medium-to-highly
reddened sight lines were selected, sampling a variety of spectral types of the
background star and the interstellar environments. The median SNR of these
spectra is ~ 1,300 around 6,400{\AA}. Compared to the Atlas Catalog, 22 new
DIBs were found, and the boundaries of 27 (sets) of DIBs were adjusted,
resulting in an updated catalog containing 559 DIBs that we refer to as the
Apache Point Observatory Catalog of Optical Diffuse Interstellar Bands.
Measurements were then made based on this catalog. We found our survey most
sensitive between 5,500 and 7,000{\AA} due largely to the local SNR of the
spectra, the relative absence of interfering stellar lines, and the weakness of
telluric residuals. For our data sample, the number of DIBs detected in a given
sight line is mostly dependent on EB-V and less on the spectral type of the
background star. Some dependence on fH2 is observed, but less well-determined
due to the limited size of the data sample. The variations of the wavelengths
of each DIB in different sight lines are generally larger than those of the
known interstellar lines CH+, CH, and K I. Those variations could be due to the
inherent error in the measurement, or to differences in the velocity components
among sight lines.
