Extinction of Taurus, Orion, Perseus and California Molecular Clouds Based on the LAMOST, 2MASS, and Gaia Surveys II: The Extinction Law

TL;DR

This study determines the extinction law from UV to IR for nearby molecular clouds using multi-survey data, revealing consistent optical extinction ratios and IR law, with UV and dense region variations linked to observational limits and ice absorption.

Contribution

It provides a comprehensive analysis of the extinction law across multiple wavelengths for various molecular clouds, utilizing extensive survey data and the blue-edge method.

Findings

Optical extinction ratio $R_{G_{BP}}$ is consistent across clouds.

IR extinction law aligns with previous studies.

UV extinction law is affected by observational depth and ice water absorption.

Abstract

The extinction law from ultraviolet (UV) to infrared (IR) (0.2-24 $\mu$m) is determined by relying on the blue-edge method and color excess ratios for some nearby molecular clouds, from low mass star forming region to massive star forming region. The observational data are collected from nine photometric surveys, along with stellar parameters from the APOGEE and LAMOST spectroscopic surveys. Within the uncertainties, the optical ratio of selective to total extinction ($R_{G_{BP}}$) does not vary substantially across the clouds, irrespective of the density, specifically $R_{G_{BP}} =2.302\pm0.027$, where $R_{G_{BP}} \equiv A_{G_{BP}}/E_{G_{BP},G_{RP}}$. The IR extinction law is consistent with \citet{Wang19_law}. The extinction law in the UV band is compromised by the shallow depth with $A_{V} \leq 2$ mag and is hard to describe by one parameter $R$. In addition, the extinction in the WISE/W1 band is significantly larger than in the Spitzer/IRAC1 band in the dense regions, which is attributed to the ice water absorption.