We obtained the near-infrared ( NIR ) high-resolution ( R \equiv \lambda / \Delta \lambda \sim 20 , 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 } \sim 3.6 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 .