Data-driven Discovery of Diffuse Interstellar Bands with APOGEE Spectra

TL;DR

This paper develops a data-driven model using APOGEE spectra to identify and characterize diffuse interstellar bands, improving understanding of interstellar medium features and aiding chemical tagging in Galactic studies.

Contribution

The study introduces a polynomial modeling approach to detect and analyze DIBs in APOGEE spectra, revealing new features and refining contamination removal methods.

Findings

Identified 84 interstellar absorption features, including all known DIBs in the range.

Many residual features are due to Earth's atmosphere and interstellar medium contamination.

Enhanced the accuracy of stellar spectra analysis for Galactic ISM research.

Abstract

Data-driven models of stellar spectra are useful tools to study non-stellar information, such as the Diffuse Interstellar Bands (DIBs) caused by intervening interstellar material. Using $\sim 55000$ spectra of $\sim 17000$ red clump stars from the APOGEE DR16 dataset, we create 2nd order polynomial models of the continuum-normalized flux as a function of stellar parameters ($T_{eff}$, $\log g$, [Fe/H], [$\alpha$/Fe], and Age). The model and data show good agreement within uncertainties across the APOGEE wavelength range, although many regions reveal residuals that are not in the stellar rest-frame. We show that many of these residual features -- having average extrema at the level of $\sim3\%$ in stellar flux on average -- can be attributed to incompletely-removed spectral lines from the Earth's atmosphere and DIBs from the interstellar medium (ISM). After removing most of the remaining contamination from the Earth's sky, we identify 84 absorption features not seen in unreddened sightlights that have $<50\%$ probability of being noise artifacts -- with 25 of these features having $<5\%$ probability of being noise artifacts -- including all 10 previously-known DIBs in the APOGEE wavelength range. Because many of these features occur in the wavelength windows that APOGEE uses to measure chemical abundances, characterization and removal of this non-stellar contamination is an important step in reaching the precision required for chemical tagging experiments. Proper characterization of these features will benefit Galactic ISM science and the currently-ongoing Milky Way Mapper program of SDSS-V, which relies on the APOGEE spectrograph.