Near infrared diffuse interstellar bands toward the Cygnus OB2
  association
  We obtained the near-infrared (NIR) high-resolution
($R\equiv\lambda/\Delta\lambda\sim20,000$) spectra of the seven brightest
early-type stars in the Cygnus OB2 association for investigating the
environmental dependence of diffuse interstellar bands (DIBs). The WINERED
spectrograph mounted on the Araki 1.3m telescope in Japan was used to collect
data. All 20 of the known DIBs within the wavelength coverage of WINERED
($0.91<\lambda<1.36\mu$m) were clearly detected along all lines of sight
because of their high flux density in the NIR wavelength range and the large
extinction. The equivalent widths (EWs) of DIBs were not correlated with the
column densities of C$_2$ molecules, which trace the patchy dense component,
suggesting that the NIR DIB carriers are distributed mainly in the diffuse
component. On the basis of the correlations among the NIR DIBs both for stars
in Cyg OB2 and stars observed previously, $\lambda\lambda$10780, 10792, 11797,
12623, and 13175 are found to constitute a "family", in which the DIBs are
correlated well over the wide EW range. In contrast, the EW of $\lambda$10504
is found to remain almost constant over the stars in Cyg OB2. The extinction
estimated from the average EW of $\lambda$10504 ($A_V\sim3.6$mag) roughly
corresponds to the lower limit of the extinction distribution of OB stars in
Cyg OB2. This suggests that $\lambda$10504 is absorbed only by the foreground
clouds, implying that the carrier of $\lambda$10504 is completely destroyed in
Cyg OB2, probably by the strong UV radiation field. The different behaviors of
the DIBs may be caused by different properties of the DIB carriers.
