Crescent-shaped Molecular Outflow from the Intermediate-mass Protostar DK Cha Revealed by ALMA

Abstract

We report on an Atacama Large Millimeter/submillimeter Array study of the Class I or II intermediate-mass protostar DK Cha in the Chamaeleon II region. The 12CO(J = 2–1) images have an angular resolution of ∼1″ (∼250 au) and show high-velocity blueshifted (≳70 km s−1) and redshifted (≳50 km s−1) emissions, which have 3000 au scale crescent-shaped structures around the protostellar disk traced in the 1.3 mm continuum. Because the high-velocity components of the CO emission are associated with the protostar, we concluded that the emission traces the pole-on outflow. The blueshifted outflow lobe has a clear layered velocity gradient with a higher-velocity component located on the inner side of the crescent shape, which can be explained by a model of an outflow with a higher velocity in the inner radii. Based on the directly driven outflow scenario, we estimated the driving radii from the observed outflow velocities and found that the driving region extends over 2 orders of magnitude. The 13CO emission traces a complex envelope structure with arc-like substructures with lengths of ∼1000 au. We identified the arc-like structures as streamers because they appear to be connected to a rotating infalling envelope. DK Cha is useful for understanding characteristics that are visible by looking at nearly face-on configurations of young protostellar systems, providing an alternative perspective for studying the star formation process.

ALMA Survey of Orion Planck Galactic Cold Clumps (ALMASOP): A Forming Quadruple System with Continuum “Ribbons” and Intricate Outflows

“…The formulae used and more details for these calculations are described in Appendix C. The total outflow mass and mass-loss rate are 3.1 × 10 −3 M e and 2.5 × 10 −6 M e yr −1 , respectively. These results are similar to outflow parameters detected in the Orion A cloud (Harada et al 2023). Note, however, that we adopt the maximum projected length of each lobe as the outflow length (λ out ).…”

“…The outflow lobes are highly fragmented with strip and knot-like substructures. The overall morphology in G206.93-16.61E2 is reminiscent of the crescent-shaped structure of the pole-on outflow surrounding the protostar DK Cha (Harada et al 2023). Given this, the complicated arc-like outflow structures in G206.93-16.61E2 may also indicate a nearly pole-on outflow cavity.…”

“…Recent studies have indicated that the outflows of multiple systems can have a great impact on the evolution of their member protostars (Jørgensen et al 2022;Harada et al 2023). In G206.93-16.61E2, the high-velocity 12 CO J = 2−1 line emission reveals an outflow structure spanning 24″ (∼9600 au) and consisting of two asymmetric, intricate, arc-like structures around the protostellar system, as shown in Figure 2.…”

An ALMA-resolved View of 7000 au Protostellar Gas Ring around the Class I Source CrA-IRS 2 as a Possible Sign of Magnetic Flux Advection

“…In the IRS 2 system, the SO component connected to the protostar is observed only around the systemic velocity (see Figure 2). This characteristic differs from other potential streamers characterized by their velocity structure, which exhibits an accelerating velocity toward the protostar vicinities (e.g., Harada et al 2023;Kido et al 2023). In summary, the rings found in this IRS 2 system do not resemble structures or phenomena well known from previous observations of protostellar envelopes and are either newly discovered features or have not been discussed in depth.…”

“…Fernández-López et al (2020) andHarada et al (2023) have identified ring-or crescent-shaped molecular outflows that a pole-on configuration can explain. Sai et al…”