Abstract
ABSTRACT We report the results of wide field CO mapping in the region of IRAS 19312+1950. This Infrared Astronomical Satellite (IRAS) object exhibits SiO/H2O/OH maser emission, and is embedded in a chemically rich molecular component, the origin of which is still unknown. In order to reveal the entire structure and gas mass of the surrounding molecular component for the first time, we have mapped a wide region around IRAS 19312+1950 in the 12CO J = 1–0, 13CO J = 1–0 and C18O J = 1–0 lines using the Nobeyama 45 m telescope. In conjunction with archival CO maps, we investigated a region up to 20′ × 20′ in size around this IRAS object. We calculated the CO gas mass assuming local thermal equilibrium, the stellar velocity through the interstellar medium assuming an analytic model of bow shock, and the absolute luminosity, using the latest archival data and trigonometric parallax distance. The derived gas mass (225 M ⊙–478 M ⊙) of the molecular component and the relatively large luminosity (2.63 × 104 L ☉) suggest that the central SiO/H2O/OH maser source is a red supergiant rather than an asymptotic giant branch (AGB) star or post-AGB star.
Highlights
Exhibiting SiO maser emission is a typical characteristic of asymptotic giant branch (AGB) stars and red supergiant (RSG) (Genzel et al 1980; Jewell et al 1984; Barvainis & Clemens 1984; Nakashima et al 2000; Imai et al 2002b; Deguchi et al 2004; Nakashima & Deguchi 2006; Deguchi et al 2010; Fok et al 2012), a bipolar molecular jet traced in the H2O maser line (Nakashima et al 2011) is quite similar to that found in oxygenrich AGB/post-AGB stars (Imai et al 2002a; Yung et al 2011), and the intensity ratio of the OH maser satellite line to the main lines (> 1; Nakashima et al 2011) is consistent with that of mass-losing evolved stars with a cold dust envelope (Habing 1996; Yung et al 2013, 2014)
We revealed the entire structure of the CO emission of the molecular component of I19312 for the first time
For better understanding the situation, we obtain the following three values: (1) CO gas mass assuming the LTE condition, (2) a stellar velocity against to the interstellar medium assuming an analytic model of a bow shock, and (3) absolute luminosity using the latest archival photometric data and trigonometric parallax distance
Summary
An isolated mid-infrared source, IRAS 19312+1950 (I19312, hereafter) exhibits SiO, H2O and OH masers (Nakashima & Deguchi 2000, 2007; Nakashima et al 2011), and the properties of the masers of this IRAS object are quite reminiscent of a mass-losing evolved star, such as asymptotic giant branch (AGB) stars, a post-AGB stars, and red supergiants (RSGs) (Nakashima et al 2011). The mass-loss rate obtained by fitting dust radiative transfer models supports the AGB star status (Murakawa et al 2007), and the near-infrared morphology is reminiscent of that of post-AGB stars and proto-planetary nebulae (PPNe; Deguchi et al 2004; Murakawa et al 2007). Lumsden et al (2013) classified I19312 as a PPN, based on the properties of infrared spectra and images
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