A Highly collimated Water Maser Bipolar Outflow in the Cepheus A HW3d Massive Young Stellar Object

Abstract

We present the results of multi-epoch very long baseline interferometry (VLBI) water (H2O) maser observations carried out with the VLBI Exploration of Radio Astrometry (VERA) toward the Cepheus A HW3d object. We measured for the first time relative proper motions of the H2O maser features, whose spatio-kinematics traces a compact bipolar outflow. This outflow looks highly collimated and expanding through ~ 280 AU (400 mas) at a mean velocity of ~ 21 km/s (~ 6 mas/yr) without taking into account the turbulent central maser cluster. The opening angle of the outflow is estimated to be ~ 30{\circ}. The dynamical time-scale of the outflow is estimated to be ~ 100 years. Our results provide strong support that HW3d harbors an internal massive young star, and the observed outflow could be tracing a very early phase of star formation. We also have analyzed Very Large Array (VLA) archive data of 1.3 cm continuum emission obtained in 1995 and 2006 toward Cepheus A. The comparative result of the HW3d continuum emission suggests the possibility of the existence of distinct young stellar objects (YSOs) in HW3d and/or strong variability in one of their radio continuum emission components.

34 pages, 4 figures, accepted for publication in ApJ

References in corpus (5)

• Theory of Star Formation
• Star formation through gravitational collapse and competitive accretion
• A Photoevaporating Rotating Disk in the Cepheus A HW2 Star Cluster
• VLBA determination of the distance to nearby star-forming regions VI. The distance to the young stellar object HW 9 in Cepheus A
• The Circumstellar Structure and Excitation Effects around the Massive Protostar Cepheus A HW 2

Cited by in corpus (12)

• The extraordinary outburst in the massive protostellar system NGC6334I-MM1: Flaring of the water masers in a north-south bipolar outflow driven by MM1B
• Evolution of the Water Maser Expanding Shell in W75N VLA 2
• Sun-Sized Water Vapor Masers in Cepheus A
• Multi-frequency VLBI observations of maser lines during the 6.7~GHz maser flare in the high-mass young stellar object G24.33$+$0.14}
• Formation and evolution of the water maser outflow event in AFGL 2591 VLA 3-N
• Interaction Between HII Region and AFGL333-Ridge: Implications to the Star Formation Scenario
• A very young, compact bipolar H${}_2$O maser outflow in the intermediate-mass star-forming LkH$\alpha$ 234 region
• The Extraordinary Outburst in the Massive Protostellar System NGC6334I-MM1: Spatio-kinematics of Water Masers during a Contemporaneous Flare Event
• Trigonometric Parallax of IRAS 22555+6213 with VERA: 3-Dimensional View of Sources Along the Same Line of Sight
• The methanol emission in the $J_1-J_0$ A${}^{-+}$ line series as a tracer of specific physical conditions in high-mass star-forming regions
• Multi-epoch VLBA H${}_2$O maser observations toward the massive YSOs AFGL 2591 VLA 2 and VLA 3
• Proper Motions of Water Masers in the Star-forming Region IRAS 23139+5939