A high-resolution H I study of the interstellar medium local to HD 193793

Abstract

A 2° field centered at the optical position of the Wolf-Rayet (WR) star HD 193793 (≡ WR 140) was surveyed in the H I 21 cm line and in the 1420 MHz radio continuum, using the Dominion Radio Astrophysical Observatory interferometer. The aim of this observations was to look for evidence of an interaction between the WR star and its local interstellar medium (ISM). Our H I data displays a large oval minimum at a velocity of V<SUB>sys</SUB> ≃ -12 km s<SUP>-1</SUP>, close to the optical position of HD 193793. We believe this H I void was created by WR 140 and its massive companion (HD 193793 is a member of a well-known binary system). The major axis of the H I void is ∼11.5 pc and its axial ratio, the ratio of major to minor axis, is ∼1.4. This structure is observable over a velocity range of around 11 km s<SUP>-1</SUP>. The H I minimum appears surrounded by a clumpy shell of H I in emission that has a total mass of neutral hydrogen of M<SUB>H I</SUB> ∼ 1300 solar masses. The kinematical distance corresponding to a local standard of rest velocity of -12 km s<SUP>-1</SUP> is approximately 5.4 kpc, which disagrees with the distance of HD 193793, namely, around 1 kpc. Therefore, it is concluded that the H I bubble was blown in an ISM having nonnegligible peculiar motions. <i>Hipparcos</i> proper-motion measurements indicate that HD 193793 has a tangential velocity of 28 ± 3 km s<SUP>-1</SUP> <i>along</i> the major axis of one of the H I minima detected in the interior of the main H I cavity. To reconcile this motion with the physical size of the H I structure blown by the winds of the binary system, it is concluded that such tangential velocity was acquired by the system a short while ago, namely, ∼1.3 × 10<SUP>5</SUP> yr. Maps from the <i>IRAS</i> database show a large-scale IR feature, with good spatial correlation with the H I shell surrounding the main H I void. We believe the emission from the IR shell arises from dust grains heated by the energetic stellar continuum photons emitted by the stellar objects.