IRC −10414: a bow-shock-producing red supergiant star★

Abstract

Most runaway OB stars, like the majority of massive stars residing in their\nparent clusters, go through the red supergiant (RSG) phase during their\nlifetimes. Nonetheless, although many dozens of massive runaways were found to\nbe associated with bow shocks, only two RSG bow-shock-producing stars,\nBetelgeuse and \\mu Cep, are known to date. In this paper, we report the\ndiscovery of an arc-like nebula around the late M-type star IRC-10414 using the\nSuperCOSMOS H-alpha Survey. Our spectroscopic follow-up of IRC-10414 with the\nSouthern African Large Telescope (SALT) showed that it is a M7 supergiant,\nwhich supports previous claims on the RSG nature of this star based on\nobservations of its maser emission. This was reinforced by our new radio- and\n(sub)millimeter-wavelength molecular line observations made with the Atacama\nPathfinder Experiment (APEX) 12 meter telescope and the Effelsberg 100 m radio\ntelescope, respectively. The SALT spectrum of the nebula indicates that its\nemission is the result of shock excitation. This finding along with the\narc-like shape of the nebula and an estimate of the space velocity of IRC-10414\n(\\approx 70\\pm20 km/s) imply the bow shock interpretation for the nebula. Thus,\nIRC-10414 represents the third case of a bow-shock-producing RSG and the first\none with a bow shock visible at optical wavelengths. We discuss the smooth\nappearance of the bow shocks around IRC-10414 and Betelgeuse and propose that\none of the necessary conditions for stability of bow shocks generated by RSGs\nis the ionization of the stellar wind. Possible ionisation sources of the wind\nof IRC-10414 are proposed and discussed.\n