VLT/MUSE discovers a jet from the evolved B[e] star MWC 137

Abstract

Aims. Not all stars exhibiting the optical spectral characteristics of B [e] stars are in the same evolutionary stage. The Galactic B[e] star MWC 137 is a prime example of an object with uncertain classification, where previous work has suggested either a pre-or a postmain sequence classification. Our goal is to settle this debate and provide a reliable evolutionary classification. Methods. Integral field spectrograph observations with the Very Large Telescope Multi Unit Spectroscopic Explorer (VLT MUSE) of the cluster SH 2-266 are used to analyze the nature of MWC 137. Results. A collimated outflow is discovered that is geometrically centered on MWC 137. The central position of MWC 137 in the cluster SH 2-266 within the larger nebula suggests strongly that it is a member of this cluster and that it is the origin of both the nebula and the newly discovered jet. Comparison of the color-magnitude diagram of the brightest cluster stars with stellar evolutionary models results in a distance of about 5.2 ± 1.4 kpc. We estimate that the cluster is at least 3 Myr old. The jet emanates from MWC 137 at a position angle of 18-20• . The jet extends over 66 (1.7 pc) projected on the plane of the sky, shows several knots, and has electron densities of about 10 3 cm −1 and projected velocities of up to ±450 km s −1 . From the Balmer emission line decrement of the diffuse intracluster nebulosity, we determine E(B-V) = 1.4 mag for the inner 1 cluster region. The spectral energy distribution of the brightest cluster stars yields a slightly lower extinction of E(B-V) ∼ 1.2 mag for the inner region and E(B-V) ∼ 0.4-0.8 mag for the outer region. The extinction toward MWC 137 is estimated to be E(B-V) ∼ 1.8 mag (A V ∼ 5.6 mag). Conclusions. Our analysis of the optical and near-infrared color-magnitude and color-color diagrams suggests a post-main sequence stage for MWC 137. The existence of a jet in this object implies the presence of an accretion disk. Several possibilities for MWC 137's nature and the origin of its jet are discussed: e.g., the presence of a companion and a merger event.

Resolving the kinematics of the discs around Galactic B[e] supergiants

“…MWC 137 is embedded into a rich CSE . Although its nature has been debated, observations favor a post-main sequence scenario (Mehner et al 2016), especially with the detection of both 12 CO and 13 CO emission features Muratore et al 2015). In Fig.…”

“…As these velocities are smaller than that of the CO ring, their corresponding rings are located further away from the CO ring (with no other emitting region closer to the star). Using a stellar mass estimate of 10-15 M ⊙ (Mehner et al 2016) we can calculate the ring radii for the CO and the four [OI] rings (see Table 3).…”

“…Regarding Hα, there are additional spectra from 1986/1988 (Zickgraf 2003) and from 2011/2013 ) that do not show significant changes. It is interesting to note that Mehner et al (2016) discovered a jet (better traced in [N ii] λ6583). They argue that the central position of MWC 137 in the nebula and the jet suggests that it is the origin of both, which is not confirmed by a more detailed analysis of the kinematics of the nebula around MWC 137 .…”

Near-infrared Spectra of a Sample of Galactic Unclassified B[e] Stars

“…Nevertheless, our findings of possible multiple rings centered at various velocities is in agreement with what was reported for other B[e] stars in binary systems (see, e.g., Maravelias et al 2018). Alternatively, the blue wings of the [N II] and [Ni II] lines might suggest high-velocity outflows of ionized gas, maybe in the form of a jet or knots, as is seen in the B[e] star MWC 137 (Mehner et al 2016;Kraus et al 2017).…”

The Luminous Blue Variable RMC 127 as Seen with ALMA and ATCA

“…We do not have evidence of a dense disk in our data (although Schulte-Ladbeck et al 1993 andDavies et al 2005 suggested the presence of a disk at a few stellar radii), but we also do know that RMC 127 is a fast rotator (with a projected rotational velocity of 105 km s 1 -; Agliozzo et al 2017b). A collimated outflow was discovered from the evolved B[e] star MWC 137 (Mehner et al 2016).…”