WARM, DENSE GAS NEAR THE MASSIVE PROTOSTAR AFGL 2136 IRS 1 AS REVEALED BY ABSORPTION FROM THE $\nu_1$, $\nu_2$, AND $\nu_3$ BANDS OF WATER
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Date
2013
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Ohio State University
Abstract
We have identified absorption features due to 47 different ro-vibrational transitions of the $\nu_1$ and $\nu_3$ fundamental and $\nu_2$ overtone bands of H$_2$O between 2.468~$\mu$m and 2.561~$\mu$m toward the massive protostar AFGL~2136~IRS~1, and determined column densities in each rotational level. Analysis of the relative level populations indicates the absorption arises in warm ($T\approx500$~K), very dense ($n_{\rm H}>10^{10}$~cm$^{-3}$) gas in local thermodynamic equilibrium, with a total water column density of $N({\rm H_{2}O})\approx10^{19}$~cm$^{-2}$. This gas must be very close to the central protostar, either in the inner envelope or a circumstellar disk/torus. Our findings are consistent with results inferred from 4.7~$\mu$m CO observations,. 1990, ApJ, 363, 554} 6~$\mu$m H$_2$O observations,, and our own 2.5~$\mu$m HF observations. This study represents the first extensive use of water vapor absorption lines in the near infrared, and we examine the possibility of using such observations to derive physical parameters in the gas surrounding other protostars. %Alternatively, the observed relative populations can be produced by radiative pumping if less-dense ($n_{\rm H}\sim10^{4}$~cm$^{-3}$) gas "sees'' a 700~K blackbody subtending 2$\pi$~sr. %The relative abundance of water with respect to hydrogen is $N({\rm H_{2}O})/N({\rm H}_2)\approx10^{-4}$, about half that reported for warm CO: $N({\rm CO})/N({\rm H}_2)\approx2\times10^{-4}$.. 1990, ApJ, 363, 554} %Our study represents the first extensive use of water vapor absorption lines in the near infrared, and we examine the possibility of using such observations to derive physical parameters in the gas surrounding other protostars.
Description
Author Institution: Department of Physics \& Astronomy, Johns Hopkins University, Baltimore, MD 21218; Department of Astronomy and Astrophysics, University of Chicago, Chicago, IL 60637; Department of Physics, University of California Davis, Davis, CA 95616