* Astronomy

Title: Hen 2-104: A close-up look at the Southern Crab
Authors: M. Santander-Garcia, R. L. M. Corradi, A. Mampaso, C. Morisset, U. Munari, M. Schirmer, B. Balick, M. Livio

The kinematics, shaping, density distribution, expansion distance, and ionised 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 ionised 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 ±
0.9 kpc to Hen 2-104, implying an unexpectedly large ionised mass for the nebula of the order of one tenth of a solar mass.

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