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ϵ Canis Majoris and the Ionization of the Local Cloud

Published online by Cambridge University Press:  12 April 2016

J.V. Vallerga  and
B.Y. Welsh
J.V. Vallerga
Affiliation:
Eureka Scientific, 2452 Delmer St., Oakland, CA 94602, USA
B.Y. Welsh
Affiliation:
Eureka Scientific, 2452 Delmer St., Oakland, CA 94602, USA

Abstract

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Using the EUV (70 – 730 Å) spectrum of the brightest EUV source, ϵ CMa taken with the Extreme Ultraviolet Explorer Satellite (EUVE) and simple models that extrapolate this spectrum to the Lyman edge at 912 Å, we have determined the local interstellar hydrogen photoionization parameter, Г, solely from this B2 II star to be 1.1 × 10−15 s−1. This figure is a factor of 7 greater than previous estimates of Г calculated for all nearby stars combined (Bruhweiler & Cheng 1988). Using measured values of the density and temperature of neutral interstellar hydrogen gas in the Local Cloud, we derive a particle density of ionized hydrogen, n(H+), and electrons, ne, of 0.015 – 0.019 cm−3 assuming ionization equilibrium and a helium ionization fraction of less than 20%. These values correspond to a hydrogen ionization fraction, XH from 19% to 15%, respectively.

Type
V. The Interstellar Medium and Diffuse Background
Information
International Astronomical Union Colloquium , Volume 152: Astrophysics in the Extreme Ultraviolet , 1996 , pp. 277 - 282
Copyright
Copyright © Kluwer 1996

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