FAST search for circumstellar atomic hydrogen--I: the young planetary nebula IC 4997

TL;DR

This paper reports the detection of 21cm neutral atomic hydrogen absorption in the young planetary nebula IC 4997 using FAST, revealing details about its H I shell, mass, and the role of atomic hydrogen in the nebula's mass budget.

Contribution

First detection of H I absorption in IC 4997, providing insights into the nebula's atomic hydrogen content and its contribution to the overall mass.

Findings

H I shell mass of 1.46×10^{-2} M_sun

H I column density of 7.1×10^{20} cm^{-2}

Atomic-to-ionized hydrogen ratio of 0.6

Abstract

Using the Five-hundred-meter Aperture Spherical radio Telescope (FAST) in Guizhou, China, we detect the 21cm neutral atomic hydrogen absorption in the young planetary nebula IC 4997. The absorption arises from a shell also associated with Na I D lines. The H I shell has a mass of $1.46\times10^{-2}$ M$_\odot$ and a dynamic age of 990yr. The column density of H I is estimated to be $7.1\times10^{20}$ cm$^{-2}$, which can be well explained in terms of a photodissociation region around the ionized nebula, limited by self shielding of H$_2$. We find that the atomic-to-ionized hydrogen ratio is 0.6, suggesting that H I substantially contributes to overall nebular mass.