Water Maser Bipolar Outflow in the Cepheus A
HW3d Star-forming Region*Chibueze, J. O., Imai, H., Tafoya, D., Omodaka, T., Kameya, O.,
Hirota, T., Torrelles, J. M., & Chong, S.
*Kagoshima University, Japan. (james@milkyway.sci.kagoshima-u.ac.jp)

Abstract/Summary

Cepheus A (Cep A) is a massive star-forming region at the distance of ~700 pc (Dzib et al. 2011). It is clear that HW2
harbors a massive young star (Rodrıguez et al. 1994; Patel et al. 2005), but unclear in the case of other HW objects. In fact,Garay et al. (1996), through multifrequency Very Large Array (VLA) radio continuum observations, argue that some of theHW objects are internally excited by a young stellar object (YSO), while others are externally shock-excited at the interface
between winds of other YSOs and molecular clumps in the region. We present the results of multi-epoch H2O maser
observations carried out with the VERA toward Cep A. We focused on the HW3d objects in Cep A. We measured for the firsttime the relative proper motions of 30 H2O maser features, whose spatio-kinematics trace (one or more) compact bipolar
outflow. This outflow is highly collimated, expanding through ~290 AU (400 mas) , and having a mean expansion velocity of~10km/s (~3 mas/yr). The dynamical time-scale of the outflow is estimated to be ~100 years, indicating that this object is in
a very early phase of star formation. We also have analyzed VLA archive data of 1.3 cm continuum emission in 1995 and2006 obtained towards Cepheus A. These results indicate possible distinct protostars around HW3d and/or strong variability
in its radio continuum emission.

Observations
The observations of the Cepheus A H 2O masers at~22 GHz with VERA were carried out in 9 epochs fromMay, 2006 to August, 2007. A position-reference source,
J2302+6405 was simultaneously observed with Cep A.

Comparing the VLA 1.3cm continuum map of 1995
and 2006, there is an unexpected shift in the peak positionof the HW3d continuum source relative to the HW2 source.
Our estimation of the proper motion yielded ~65 km/s.
Is this possible?

Results & HW3d Internal Exciting Source Evidence

We carried out a radial expansion model fitting analysis.

We obtained 30 maser proper motions, tracing a bipolar
outflow in HW3d of Cep A.

1.3cm continuum contour map of Cepheus A made from the 2006
observation. The beam size is 0.11 × 0.1 arcsec at the position angle of73.8 . Contour levels are 5, 5, 7, 9, 12, 15, 20, 30, 40, 50, 60, 70, 80, 100,
and 120 times the RMS noise (5.182 × 10-5Jy/beam) of the map. HW2,HW3d and HWc are shown in the map according to the naming system byHughes & Wouterloot (1984) (left panel). The plus signs on the HW2,HW3c, and HW3d objects indicate the peak position of the continuum
sources observed in 1995 (reported by Torrelles et al., 2011).

*Majorly negative expansion
velocities = high velocity infall?

oLeft Maser distribution of HW3d(east) (top) and HW3d(west)(bottom).
Right Distributions of the expansion velocities of the individual maser
features that were derived from the model fitting in HW3d (top panel),
HW3d(east) (middle panel) and HW3d(west) (bottom panel), respectively.
Properties HW2HW3dH2O dyn.
time-scale 3500yrs 100yrs
Protostars

42Continuum
emission 800 mas 400 mas
size
Left The distribution of the H2O masers aligned with the HW3d 1.3cm
continuum map. Right The proper motions of these maser features. Astrometricanalysis of the r07049 observation epoch enabled us to determine the absolute
position of a maser spot (-6.67 km/s component) at RA(J2000) =22h56m17.97745s & DEC(J2000)= +62o01′49.3784′′, which made the alignmentof the maps possible.

Table of model fitting results

We concluded the following;* HW3d is internally excited by a young protostar* There is high possibility of more than one exciting source in HW3d
* HW3d compared to HW2 is in an earlier phase of evolution