The diffuse interstellar band around 8620 Å I. Methods and application to the GIBS data set

Abstract

We developed a set of procedures to automatically detect and measure the DIB around 8620 Å (the Gaia DIB) for a wide range of temperatures. The DIB profile is fit with a Gaussian function. Specifically, the DIB feature is extracted from the spectra of late-type stars by subtracting the corresponding synthetic spectra. For early-type stars we applied a specific model based on the Gaussian process that needs no prior knowledge of the stellar parameters. The method was tested on $\sim$5000 spectra from the Giraffe Inner Bulge Survey (GIBS). After validation, we obtained 4194 reasonable fitting results from the GIBS database. An EW versus $E(J-K_{\mathrm{S}})$ relation is derived as $E(J-K_{\mathrm{S}})=1.875(\pm 0.152)\times \mathrm{EW}-0.011(\pm 0.048)$, according to $E(B-V)/\mathrm{EW}=2.721$, which is highly consistent with previous results toward similar sightlines. After a correction based on the VVV database for both EW and reddening, the coefficient derived from individual GIBS fields, $E(J-K_{\mathrm{S}})/\mathrm{EW}=1.884\pm 0.225$, is also in perfect agreement with literature values. Based on a subsample of 1015 stars toward the Galactic center within $-3^{\circ }<b<3^{\circ }$ and $-6^{\circ }<l<3^{\circ }$, we determined a rest-frame wavelength of the Gaia DIB as 8620.55 Å. A Gaussian profile is proved to be a proper and stable assumption for the Gaia DIB as no intrinsic asymmetry is found.

17 pages, 16 figures

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