The diffuse interstellar band around 8620 {\AA} I. Methods and application to the GIBS data set

TL;DR

This paper presents an automated method for detecting and measuring the Gaia DIB at 8620 Å across diverse stellar spectra, validating it on GIBS data, and deriving its relation to interstellar reddening with consistent results.

Contribution

The authors developed a novel automated Gaussian fitting method for the Gaia DIB applicable to various stellar types, validated on GIBS data, and established its relation to reddening and precise wavelength.

Findings

Successfully extracted DIB measurements from ~5000 spectra.

Derived a consistent EW-reddening relation with literature.

Determined the Gaia DIB's rest wavelength as 8620.55 Å.

Abstract

We developed a set of procedures to automatically detect and measure the DIB around 8620 {\AA} (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 $E(J\,{-}\,K_{\rm S})$ relation is derived as $E(J\,{-}\,K_{\rm S})\,{=}\,1.875\,({\pm}\,0.152)\,{\times}\,{\rm EW}\,{-}\,0.011\,({\pm}\,0.048)$, according to $E(B\,{-}\,V)/{\rm EW}\,{=}\,2.721$, 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, $E(J\,{-}\,K_{\rm S})/{\rm EW}\,{=}\,1.884\,{\pm}\,0.225$, 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 {\AA}. A Gaussian profile is proved to be a proper and stable assumption for the Gaia DIB as no intrinsic asymmetry is found.