2025/07/01 by Ouyang, Xu-Jia, Zhang, Yong, Zijlstra, Albert +4
#Astrophysics of Galaxies (astro-ph.GA) #FOS: Physical sciences #Solar and Stellar Astrophysics (astro-ph.SR)
paper · doi:10.48550/arxiv.2507.00414
The detection of circumstellar atomic hydrogen (\ionH1) via the 21 cm line remains a persistent challenge in planetary nebula (PN) studies, primarily due to contamination from ubiquitous interstellar \ionH1 21 cm emission. In this paper, we report the results of a \ionH1 survey of 12 high surface brightness PNe located at Galactic latitudes |b|≥10\arcdeg, performed with the Five-hundred-meter Aperture Spherical radio Telescope (FAST), which is currently the most sensitive telescope in the L band. Although the contamination from interstellar emission is still severe, we detect or tentatively detect circumstellar \ionH1 21 cm absorption associated with two PNe: NGC 6905 and NGC 7662. \ionH1 exhibits a comparatively high detection frequency in bipolar PNe. We estimate the \ionH1 masses of the two PNe to range from 0.01 to 0.14 M\sun, resulting in atomic-to-ionized hydrogen ratios of 0.02--0.3. The \ionH1 shells have dynamical ages of 2100--2400 years. Our measurements confirm previous findings that the optical depth of \ionH1 decreases with increasing linear radius of the nebula. The mass loss rates traced by the \ionH1 absorption are larger than 10-5 M_\sun yr-1, indicating that they originate from the superwind phase at the tip of the asymptotic giant branch.