# Interstellar extinction in Orion. Variation of the strength of the UV bump across the complex

## TL;DR

This study investigates how the UV bump feature varies across different regions in the Orion molecular cloud, revealing a decrease in UV bump strength in denser and UV-irradiated areas, indicating dust grain evolution.

## Contribution

It applies a novel technique to Orion, confirming the UV bump's variation with density and radiation, extending previous methods from Taurus to Orion.

## Key findings

- UV bump decreases in dense cores and UV-irradiated regions
- Dust grain size distribution becomes shallower with density
- Results extend to the Rosette cloud with uncertain conclusions

## Abstract

There is growing observational evidence of dust coagulation in the dense filaments within molecular clouds. Infrared observations show that the dust grains size distribution gets shallower and the relative fraction of small to large dust grains decreases as the local density increases. Ultraviolet (UV) observations show that the strength of the 2175 {\AA} feature, the so-called UV bump, also decreases with cloud density. In this work, we apply the technique developed for the Taurus study to the Orion molecular cloud and confirm that the UV bump decreases over the densest cores of the cloud as well as in the heavily UV irradiated {\lambda} Orionis shell. The study has been extended to the Rosette cloud with uncertain results given the distance (1.3 kpc).