# Updated extraction of the APOGEE 1.5273 {\mu}m diffuse interstellar band: a Planck view on the carrier depletion in dense cores

## TL;DR

This study uses APOGEE DR14 data to measure the 15,273 Å diffuse interstellar band, revealing its depletion in dense cloud cores and its correlation with dust extinction and optical depth, enhancing understanding of interstellar medium properties.

## Contribution

The paper introduces a new large catalog of DIB measurements and demonstrates the depletion of the DIB carrier in dense interstellar cloud cores using Planck data.

## Key findings

- DIB strength correlates linearly with dust extinction at low levels.
- Depletion of the DIB carrier occurs in dense cloud cores.
- The DIB-carrier depletion relates empirically to dust optical depth.

## Abstract

The latest SDSS/APOGEE data release DR14 has provided an increased number of stellar spectra in the H band and associated stellar models using an innovative algorithm known as The Cannon. We took advantage of these novelties to extract the 15 273 {\AA} near-infrared DIB and to study its link with dust extinction and emission. We modified our automated fitting methods dedicated to hot stars and used in earlier studies with some adaptations motivated by the change from early- or intermediate-type stars to red giants. A new method has also been developed to quantify the upper limits on DIB strengths. We compared our DIB measurements with the stellar extinctions Av from the Starhorse database. We then compared the resulting DIB-extinction ratio with the dust optical depth derived from Planck data, globally and also separately for nearby off-Plane cloud complexes. Our analysis has led to the production of a catalog containing 124 064 new measurements of the 15 273 {\AA} DIB, allowing us to revisit the correlation between DIB strength and dust reddening. The new data reveal clearly that the sky-averaged 15 273 {\AA} DIB strength is linearly correlated with Av over two orders as reported by earlier studies but leveling-off with respect to extinction for highly reddened lines-of-sight behind dense clouds. The comparison with Planck individual optical depths reveals in a conspicuous way this DIB depletion in the dense cores and shows it applies to all off-Plane dense clouds. APOGEE measurements confirm the ubiquity of the 15 273 {\AA} DIB carrier decrease with respect to dust grains in dense cloud cores, in a manner that can be empirically related to the dust optical depth reached in the cloud.