On the absence of wind bow-shocks around OB-runaway stars: Probing the physical conditions of the interstellar medium

F. Huthoff, L. Kaper*

*Corresponding author for this work

Research output: Contribution to journalArticleAcademicpeer-review

48 Citations (Scopus)

Abstract

High-resolution IRAS maps are used to search for the presence of stellar-wind bow-shocks around high-mass X-ray binaries (HMXBs). Their high space velocities, recently confirmed with Hipparcos observations, combined with their strong stellar winds should result in the formation of wind bow-shocks. Except for the already known bow-shock around Vela X-1 (Kaper et al. 1997), we do not find convincing evidence for a bow-shock around any of the other HMXBs. Also in the case of (supposedly single) OB-runaway stars, only a minority appears to be associated with a bow-shock (Van Buren et al. 1995). We investigate why wind bow-shocks are not detected for the majority of these OB-runaway systems: is this due to the IRAS sensitivity, the system's space velocity, the stellar-wind properties, or the height above the galactic plane? It turns out that none of these suggested causes can explain the low detection rate (∼40%). We propose that the conditions of the interstellar medium mainly determine whether a wind bow-shock is formed or not. In hot, tenuous media (like inside galactic superbubbles) the sound speed is high (∼100 km s-1), such that many runaways move at subsonic velocity through a low-density medium, thus preventing the formation of an observable bow-shock. Superbubbles are expected (and observed) around OB associations, where the OB-runaway stars were once born. Turning the argument around, we use the absence (or presence) of wind bow-shocks around OB runaways to probe the physical conditions of the interstellar medium in the solar neighbourhood.

Original languageEnglish
Pages (from-to)999-1010
Number of pages12
JournalAstronomy and Astrophysics
Volume383
Issue number3
DOIs
Publication statusPublished - Mar 2002
Externally publishedYes

Keywords

  • ISM: bubbles
  • ISM: structure
  • Stars: early-type
  • Stars: kinematics
  • Stars: mass loss
  • X-rays: binaries

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