Near-infrared diffuse interstellar bands in 0.91-1.32 micron

TL;DR

This study surveys near-infrared diffuse interstellar bands using high-resolution spectra, discovering new DIBs, analyzing their correlations with optical DIBs and reddening, and suggesting their carriers are likely cation molecules influenced by interstellar conditions.

Contribution

It provides the first comprehensive NIR DIB survey with 15 new detections and analyzes their physical and chemical connections to optical DIBs and interstellar environment.

Findings

15 new NIR DIBs identified, expanding known spectral features.

NIR DIBs show weaker correlation with reddening than optical DIBs.

Certain NIR DIBs are correlated with optical DIB 5780.5, indicating similar carrier properties.

Abstract

We present a comprehensive survey of diffuse interstellar bands (DIBs) in $0.91-1.32\mu$m with a newly-developed near-infrared (NIR) spectrograph, WINERED, mounted on the Araki 1.3 m Telescope in Japan. We obtained high-resolution ($R=28,300$) spectra of 25 early-type stars with color excesses of $0.07<E(B-V)<3.4$. In addition to the five DIBs previously detected in this wavelength range, we identified 15 new DIBs, 7 of which were reported as DIB "candidates" by Cox. We analyze the correlations among NIR DIBs, strong optical DIBs, and the reddening of the stars. Consequently, we found that all NIR DIBs show weaker correlations with the reddening rather than the optical DIBs, suggesting that the equivalent widths of NIR DIBs depend on some physical conditions of the interstellar clouds, such as UV flux. Three NIR DIBs, $\lambda\lambda$10780, 10792, and 11797, are found to be classifiable as a "family," in which the DIBs are well correlated with each other, suggesting that the carriers of these DIBs are connected with some chemical reactions and/or have similar physical properties such as ionization potential. We also found that three strongest NIR DIBs $\lambda\lambda10780, 11797, 13175$ are well correlated with the optical DIB $\lambda 5780.5$, whose carrier is proposed to be a cation molecule with high ionization potential, indicating that the carriers of the NIR DIBs could be cation molecules.