Far Ultraviolet Spectroscopic Explorer observations of high-velocity gas associated with the Monoceros Loop SNR

¹ Experimental Astrophysics Group, Space Sciences Laboratory, UC Berkeley, Berkeley, CA 94720, USA
² Service d'Aéronomie du CNRS, 91371 Verrières-le-Buisson, France

Corresponding author: B. Y. Welsh, bwelsh@ssl.berkeley.edu

Received: 14 February 2001
Accepted: 2 April 2001

Abstract

We present Far Ultraviolet Spectroscopic Explorer () observations of high-velocity gas (V_LSR = +65 km s^-1) seen towards the star HD 47240 which lies just behind the Monoceros Loop Supernova Remnant at a distance of ~1800 pc. This high-velocity absorption feature is detected in the far ultraviolet lines of O I, Ar I, N I, C I, Fe II and P II, in addition to being detected at visible wavelengths in Na I and Ca II and at near ultraviolet wavelengths in Mg II, Mg I, S II, O I, Si II, C II*, Al II and Fe II. High-velocity interstellar gas has not been detected in the high-ionization (high-temperature) species of O VI, C IV and Si IV. Gas phase abundances relative to that of sulphur for this high velocity feature have been derived. The refractory elements of Fe, Si and Al are all less depleted than that normally found for cold disk gas in the interstellar medium, with a pattern of relative abundance more similar to that of warm interstellar disk gas. However, the elements of N, O, and Ar show an opposite pattern of relative depletion in which their apparent elemental deficiency may be attributed to ionization effects, as also found for high-velocity gas associated with the Vela SNR by Jenkins et al. ([CITE]). The lack of detection of high-ionization gas at high velocity suggests that the Monoceros Loop remnant is more evolved than other remnants such as the Vela SNR or Cygnus Loop, and that an age of 30 000-150 000 years seems appropriate.