Distribution and Kinematics of H I through Raman He II Spectroscopy of NGC 6302

Abstract

The young planetary nebula NGC 6302 is known to exhibit Raman-scattered He II features at 6545 and 4851 Angstrom. These features are formed through inelastic scattering of He II$\lambda \lambda$ 1025 and 972 with hydrogen atoms in the ground state, for which the cross sections are $1.2\times 10^{-21}$ and $1.4\times 10^{-22}\mathrm{c}{\mathrm{m}}^2$, respectively. We investigate the spectrum of NGC 6302 archived in the ESO Science Portal. Our Gaussian line fitting analysis shows that the Raman-scattered He II features are broader and more redshifted than the hypothetical model Raman features that would be formed in a cold static H I medium. We adopt a simple scattering geometry consisting of a compact He II emission region surrounded by a H I medium to perform Monte Carlo simulations using the radiative transfer code $STaRS$. Our simulations show that the H I region is characterized by the H I column density $N_{\mathrm{HI}}=3\times 10^{21}\mathrm{c}{\mathrm{m}}^{-2}$ with the random speed component $v_{\mathrm{ran}}=10\mathrm{km}{\mathrm{s}}^{-1}$ expanding with a speed $v_{\exp }=13\mathrm{km}{\mathrm{s}}^{-1}$ from the He II emission region. Based on our best fit parameters, we estimate the H I mass of the neutral medium $M_{\mathrm{HI}}\simeq 1.0\times 10^{-2}{\mathrm{M}}_{\odot }$, pointing out the usefulness of Raman He II spectroscopy as a tool to trace H I components.

12 pages, 8 figures, accepted for publication in ApJ

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