A Preliminary Investigation of the Diffuse Interstellar Line at 8621 Å

Abstract

We have obtained high-resolution spectra at the Dominion AstrophysicalObservatory, the Calar Alto Observatory, and the European SouthernObservatory of hot stars in the near-infrared region to study thediffuse interstellar band (DIB) at 8621 {Å}. Field stars as well asselected members of the Perseus spiral arm, the {ρ} Ophiuchi complex,and the Cygnus OB2 association were observed and the equivalent widthsof the band measured, as well as interstellar K I absorption at 7699{Å}. In total we measure the equivalent width of the 8621 band in 64stars. In a series of figures we show the correlations of the DIB withreddening, polarization, K I, and strengths of other DIBs at 5780, 5797,and 6613 {Å}. The quality of the correlations are discussed by meansof the Spearman rank correlation test. Good correlations are found withreddening and, among the other DIBs, 8621 correlates best with 5780. Byexamining the three special regions mentioned above we confirm theweakness of the 8621 DIB in the hot stars of the {ρ} Oph star-formingregion. In the Perseus spiral arm region we find that the DIBs areformed largely in foreground clouds but not in the gas that appears tohave been blown away from the young massive stars of the Perseus arm. InCyg OB2 we find that the equivalent widths of the 8621 line lie abovethe linear correlation of equivalent width with E(B-V) and theirstrength does not vary as strongly with reddening. The heavily reddenedCyg OB2 star 12 is the most extreme example of the relativeinsensitivity of the 8621 equivalent width to reddening in the CygnusOB2 region.