Abstract
Abstract During star formation, the accretion disk drives fast MHD winds, which usually contain two components, a collimated jet and a radially distributed wide-angle wind. These winds entrain the surrounding ambient gas producing molecular outflows. We report a recent observation of 12CO (2–1) emission of the HH 46/47 molecular outflow by the Atacama Large Millimeter/submillimeter Array, in which we identify multiple wide-angle outflowing shell structures in both the blueshifted and redshifted outflow lobes. These shells are highly coherent in position–position–velocity space, extending to ≳40–50 km s−1 in velocity and 104 au in space, with well-defined morphology and kinematics. We suggest these outflowing shells are the result of the entrainment of ambient gas by a series of outbursts from an intermittent wide-angle wind. Episodic outbursts in collimated jets are commonly observed, yet detection of a similar behavior in wide-angle winds has been elusive. Here we show clear evidence that the wide-angle component of the HH 46/47 protostellar outflows experiences variability similar to that seen in the collimated component.
Highlights
Outflows play an important role in star formation and the evolution of molecular clouds and cores, as they remove angular momentum from the accretion disk (e.g., Bjerkeli et al 2016; Hirota et al 2017; Lee et al 2017a; Zhang et al 2018), carve out cavities in their parent cores (e.g., Arce & Sargent 2006), and inject energy and momentum into the star-forming environments (e.g., Arce et al 2010; Plunkett et al 2013)
We report recent 12CO (2–1) observations of the HH 46/47 molecular outflow using the Atacama Large Millimeter/ submillimeter Array (ALMA) that reveal multiple wide-angle outflowing shells, which we argue were formed by an episodic wide-angle wind
We present ALMA 12CO (2–1) observation of the HH 46/ 47 molecular outflow, in which we have detected multiple wide-angle outflowing shell structures in both the blueshifted and redshifted lobes
Summary
Outflows play an important role in star formation and the evolution of molecular clouds and cores, as they remove angular momentum from the accretion disk (e.g., Bjerkeli et al 2016; Hirota et al 2017; Lee et al 2017a; Zhang et al 2018), carve out cavities in their parent cores (e.g., Arce & Sargent 2006), and inject energy and momentum into the star-forming environments (e.g., Arce et al 2010; Plunkett et al 2013). In more evolved pre-main sequence stars this component has been observed with optical atomic emission lines (e.g., Bacciotti et al 2000) Both jets and wide-angle winds can interact with the ambient molecular gas and entrain material to form slower, but much more massive outflows, which are typically observed in CO and other molecules and are generally referred to as molecular outflows. Sometimes are evenly spaced) along their axes (e.g., Lee et al 2007; Plunkett et al 2015) These knots often trace bow shocks that are formed by variations in the mass-loss rate or jet velocity, which in turn may be caused by variation in the accretion rate. Even in the redshifted side, the energy distribution shows that more energy is injected by the outflow at the base of the outflow cavity, which is consistent with a wide-angle wind entrainment scenario, rather than at the jet–bow-shock heads, as a jet-entrainment scenario would suggest
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