On the Relation between Interstellar Spectral Features and Reddening
  It is well known that interstellar spectral features correlate with color
excess E(B$-$V). This suggests that measuring intensities of these features
allows one to estimate reddening of stars. The aim of this paper is to check
how tight intensities of interstellar diffuse bands (DIBs)are related to the
amount of extinction, measured using E(B$-$V). We have measured equivalent
widths of the strongest DIBs (centered at $\lambda\lambda$ 5780.6, 5797.0,
6196.0, 6379.3, 6613.5, and 8620.7 A), as well as of CH (near 4300.3 A) and
CH$^+$ (near 4232.5 A) in high resolution, high S/N ratio echelle spectra from
several spectrographs. The equivalent widths of the 8620 DIB in noisy spectra
were measured using a template, which was constructed using the high quality
spectrum of BD+40 4220. DIB relations with the color excess in the range
0.1--2.0 mag were examined. Our careful analysis demonstrates that all the
above mentioned interstellar spectral features (except, perhaps, 6379 DIB) do
correlate with E(B$-$V) relatively tightly (with the Pearson's correlation
coefficient of 0.8+). Moreover, the observed scatter is apparently not caused
by measurement errors but is of physical origin. We present several examples
where the strength ratios of a DIB/molecule to E(B$-$V) are different than the
average.
