Hen 2–104: a close-up look at the Southern Crab^*

¹ Isaac Newton Group of Telescopes, Ap. de Correos 321, 38700 Sta. Cruz de la Palma, Spain e-mail: [msantander;rcorradi;mischa]@ing.iac.es
² Instituto de Astrofísica de Canarias, 38200 La Laguna, Tenerife, Spain e-mail: [miguelsg;amr]@iac.es
³ Instituto de Astronomía, Universidad Nacional Autónoma de México, México, D. F., México e-mail: morisset@astroscu.unam.mx
⁴ INAF Osservatorio Astronomico di Padova, via dell'Osservatorio 8, 36012 Asiago (VI), Italy e-mail: munari@pd.astro.it
⁵ Department of Astronomy, University of Washington, Seattle, Washington 98195-1580, USA e-mail: balick@astro.washington.edu
⁶ Space Telescope Science Institute (STScI), 3700 San Martin Drive, Baltimore, MD 21218, USA e-mail: mlivio@stsci.edu

Received: 7 December 2007
Accepted: 25 February 2008

Abstract

Aims. 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.

Methods. 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 enable a 3-D spatio-kinematical model of the nebula to be constructed, which, 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 [Sii]  671.7, 673.1 emission line doublet provide a density map of the inner lobes of the nebula, which with the distance estimation provide a measurement of its ionized mass.

Results. We measure densities ranging from to 1000 cm^-3 in the inner lobes, and from 300 to 500 cm^-3 in the outer lobes. We determine an expansion-parallax distance of  kpc to Hen 2–104, which implies an unexpectedly large ionized mass for the nebula of approximately one tenth of a solar mass.