Water Absorption from Gas Very Near the Massive Protostar AFGL 2136 IRS 1

TL;DR

This study uses near-infrared water vapor absorption lines to analyze the physical conditions of warm, dense gas close to the massive protostar AFGL 2136 IRS 1, providing new insights into its environment.

Contribution

First extensive use of near-infrared water vapor absorption lines to determine physical parameters near a massive protostar.

Findings

Gas temperature ~506 K

Very dense gas with n(H2)>5*10^9 cm^-3

Water column density ~1.02*10^19 cm^-2

Abstract

We present ground-based observations of the nu_1 and nu_3 fundamental bands of H2O toward the massive protostar AFGL 2136 IRS 1, identifying absorption features due to 47 different ro-vibrational transitions between 2.468 micron and 2.561 micron. Analysis of these features indicates the absorption arises in warm (T=506+-25 K), very dense (n(H2)>5*10^9 cm^-3) gas, suggesting an origin close to the central protostar. The total column density of warm water is estimated to be N(H2O)=(1.02+-0.02)*10^19 cm^-2, giving a relative abundance of N(H2O)/N(H2)~10^-4. Our study represents the first extensive use of water vapor absorption lines in the near infrared, and demonstrates the utility of such observations in deriving physical parameters.