Local clouds: Ionization, temperatures, electron densities and interfaces, from GHRS and IMAPS spectra of Canis Majoris^*

¹ ISO Data Center, ESA Astrophysics Division, PO Box 50727, 28080 Madrid, Spain
² Laboratoire d'Astronomie Spatiale, BP 8, 13376 Marseille Cedex 12, France
³ Princeton University Observatory, Princeton, NJ 08544-1001, USA e-mail: ebj@astro.princeton.edu

Corresponding author: C. Gry, cgry@iso.vilspa.esa.es

Received: 20 September 2000
Accepted: 5 December 2000

Abstract

The composition and physical properties of several local clouds, including the Local Interstellar Cloud (LIC) in which the Sun is embedded, are derived from absorption features in the UV spectrum of the star ϵ CMa. We derive temperatures and densities for three components by combining our interpretations of the ionization balance of magnesium and the relative population of C ii in an excited fine-structure level. We find that for the LIC n_e = cm^-3 and K. We derive the ionization fractions of hydrogen and discuss the ionizing processes. In particular the hydrogen and helium ionizations in the LIC are compatible with photoionization by the local EUV radiation fields from the hot stars and the cloud interface with the hot gas. We confirm the detection of high ionization species: Si iii is detected in all clouds and C iv in two of them, including the LIC, suggesting the presence of ionized interfaces around the local clouds.