A photo-ionised canopy for the shock-excited Criss-Cross nebula^*

¹ Institut für Astro- und Teilchenphysik, Technikerstraße 25, 6020 Innsbruck, Austria e-mail: [Giovanna.Temporin;Ronald.Weinberger]@uibk.ac.at
² AIM – Unité Mixte de Recherche CEA – CNRS – Université Paris 7 – UMR 7158, DSM/DAPNIA/Service d'Astrophysique, CEA Saclay, Bât. 709, Orme des Merisiers, 91191 Gif-sur-Yvette Cedex, France
³ Thüringer Landessternwarte Tautenburg, Sternwarte 5, 07778 Tautenburg, Germany e-mail: stecklum@tls-tautenburg.de

Received: 19 December 2006
Accepted: 7 February 2007

Abstract

Aims.We study a new broad, well-defined arc of optical nebulosity close to the cloud-shock interacting Criss-Cross nebula, derive the basic physical properties of the nebulosity, and revise those of the nebula, and compare both objects to simulations of cloud-shock interactions from the literature.

Methods.Deep optical, partly wide-field images were used to reveal the intricate morphology and overall extent of the nebulosities. Optical spectroscopy enabled us to uncover their nature.

Results.The two nebulosities are obviously physically linked, but are of different types; the Criss-Cross nebula is, as was also shown in an earlier paper, excited via a slow shock from the expanding Orion-Eridanus bubble, but the broad arc is definitely photo-ionised. The source for ionising photons appears to be hot gas in this bubble. Some results of simulations of interactions of SNRs with interstellar clouds available from the literature bear a striking resemblance to our nebulae, which appear to represent an example – unrivalled in closeness and clarity – of an early-to-medium stage in the destruction of an isolated cloud over-run by a highly evolved SNR. Thereby the Criss-Cross nebula is, when seen from the SNR, the rear disrupted part of the original, small cloud, whereas the arc is probably its still rather intact front part.