Hen 2-104: A close-up look at the Southern Crab

TL;DR

This study combines high-resolution imaging and spectroscopy to model the 3D structure and dynamics of the nebula Hen 2-104, estimating its distance and ionized mass with improved precision.

Contribution

It provides a detailed 3D kinematic model of Hen 2-104 using multi-epoch imaging and integral field spectroscopy, including a new distance and mass estimate.

Findings

Distance to Hen 2-104 is 3.3±0.9 kpc.

Inner lobes have densities of 500-1000 cm$^{-3}$.

Ionized mass is approximately 0.1 solar masses.

Abstract

The kinematics, shaping, density distribution, expansion distance, and ionized mass of the nebula Hen 2-104, and the nature of its symbiotic Mira are investigated. A combination of multi-epoch HST images and VLT integral field high-resolution spectroscopy is used to study the nebular dynamics both along the line of sight and in the plane of the sky. These observations allow us to construct a 3-D spatio-kinematical model of the nebula, which together with the measurement of its apparent expansion in the plane of the sky over a period of 4 years, provides the expansion parallax for the nebula. The integral field data featuring the [S{\sc ii}] $\lambda\lambda$671.7,673.1 emission line doublet provide us with a density map of the inner lobes of the nebula, which together with the distance estimation allow us to estimate its ionized mass. We find densities ranging from n$_e$=500 to 1000 cm$^{-3}$ in the inner lobes and from 300 to 500cm$^{-3}$ in the outer lobes. We determine an expansion parallax distance of 3.3$\pm$0.9 kpc to Hen 2-104, implying an unexpectedly large ionized mass for the nebula of the order of one tenth of a solar mass.