Dissecting a supernova impostor’s circumstellar medium: MUSEing about the SHAPE of η Carinae’s outer ejecta ^⋆

¹ ESO – European Organisation for Astronomical Research in the Southern Hemisphere, Alonso de Cordova 3107, Vitacura, Santiago de Chile Chile
e-mail: amehner@eso.org
² Instituto de Astronomía, Universidad Nacional Autónoma de México, Apdo Postal 106, Ensenada 22800, Baja California, Mexico
³ School of Physics, Trinity College Dublin, Dublin 2, Ireland
⁴ ESO – European Organisation for Astronomical Research in the Southern Hemisphere, Karl-Schwarzschild-Straße 2, 85748 Garching, Germany
⁵ Department of Astronomy, University of Minnesota, Minneapolis, MN 55455, USA
⁶ School of Physics and Astronomy, The University of Leeds, Leeds, LS2 9JT, UK

Received: 22 April 2016
Accepted: 30 September 2016

Abstract

Aims. The role of episodic mass loss is one of the outstanding questions in massive star evolution. The structural inhomogeneities and kinematics of their nebulae are tracers of their mass-loss history. We conduct a three-dimensional morpho-kinematic analysis of the ejecta of η Car outside its famous Homunculus nebula.

Methods. We carried out the first large-scale integral field unit observations of η Car in the optical, covering a field of view of 1′× 1′ centered on the star. Observations with the Multi Unit Spectroscopic Explorer (MUSE) at the Very Large Telescope (VLT) reveal the detailed three-dimensional structure of η Car’s outer ejecta. Morpho-kinematic modeling of these ejecta is conducted with the code SHAPE.

Results. The largest coherent structure in η Car’s outer ejecta can be described as a bent cylinder with roughly the same symmetry axis as the Homunculus nebula. This large outer shell is interacting with the surrounding medium, creating soft X-ray emission. Doppler velocities of up to 3000 km s^-1 are observed. We establish the shape and extent of the ghost shell in front of the southern Homunculus lobe and confirm that the NN condensation can best be modeled as a bowshock in the orbital/equatorial plane.

Conclusions. The SHAPE modeling of the MUSE observations provides a significant gain in the study of the three-dimensional structure of η Car’s outer ejecta. Our SHAPE modeling indicates that the kinematics of the outer ejecta measured with MUSE can be described by a spatially coherent structure, and that this structure also correlates with the extended soft X-ray emission associated with the outer debris field. The ghost shell immediately outside the southern Homunculus lobe hints at a sequence of eruptions within the time frame of the Great Eruption from 1837–1858 or possibly a later shock/reverse shock velocity separation. Our 3D morpho-kinematic modeling and the MUSE observations constitute an invaluable dataset to be confronted with future radiation-hydrodynamics simulations. Such a comparison may shed light on the yet elusive physical mechanism responsible for η Car-like eruptions.