The Circumstellar Structure and Excitation Effects around the Massive Protostar Cepheus A HW 2

We report SMA 335 GHz continuum observations with angular resolution of ~0.3'', together with VLA ammonia observations with ~1'' resolution toward Cep A HW 2. We find that the flattened disk structure of the dust emission observed by Patel et al. is preserved at the 0.3'' scale, showing an elongated structure of ~0.6'' size (450 AU) peaking on HW 2. In addition, two ammonia cores are observed, one associated with a hot core previously reported and an elongated core with a double peak separated by ~1.3'', with signs of heating at the inner edges of the gas facing HW 2. The double-peaked ammonia structure, as well as the double-peaked CH3CN structure reported previously (and proposed to be two independent hot cores), surround both the dust emission as well as the double-peaked SO2 disk structure found by Jiménez-Serra et al. All these results argue against the interpretation of the elongated dust-gas structure as due to a chance superposition of different cores; instead, they imply that it is physically related to the central massive object within a "disk-protostar-jet " system.

[1]  C. Comito,et al.  A Photoevaporating Rotating Disk in the Cepheus A HW2 Star Cluster , 2007, 0704.3008.

[2]  U. Endesfelder,et al.  High-resolution study of a star-forming cluster in the Cepheus A HW2 region , 2007, 0704.1617.

[3]  E. Bergin,et al.  Dust and gas emission in the prototypical hot core G29.96-0.02 at sub-arcsecond resolution , 2007, 0704.0518.

[4]  J. Black,et al.  A computer program for fast non-LTE analysis of interstellar line spectra With diagnostic plots to interpret observed line intensity ratios , 2007, 0704.0155.

[5]  C. Brogan,et al.  Arcsecond-Scale Kinematic and Chemical Complexity in Cepheus A East , 2007, astro-ph/0703626.

[6]  N. Patel,et al.  Submillimeter Array Observations of 321 GHz Water Maser Emission in Cepheus A , 2007, Proceedings of the International Astronomical Union.

[7]  L. Testi,et al.  Infall of gas as the formation mechanism of stars up to 20 times more massive than the Sun , 2006, Nature.

[8]  G. Garay,et al.  Large Proper Motions in the Jet of the High-Mass YSO Cepheus A HW2 , 2006 .

[9]  Leiden,et al.  The magnetic field in the star-forming region Cepheus A. from H_2O maser polarization observations , 2005, astro-ph/0510452.

[10]  Qizhou Zhang,et al.  A disk of dust and molecular gas around a high-mass protostar , 2005, Nature.

[11]  Harvard-Smithsonian Center for Astrophysics,et al.  Observations and Modeling of the 2-25 μm Emission from High-Mass Protostellar Object Candidates , 2005 .

[12]  R. J. Cohen,et al.  Magnetic field in Cepheus A as deduced from OH maser polarimetric observations , 2005 .

[13]  Matthew R. Bate,et al.  Binary systems and stellar mergers in massive star formation , 2005 .

[14]  C. Thum,et al.  A New Intermediate-Mass Protostar in the Cepheus A HW2 Region , 2005, astro-ph/0506533.

[15]  P. Ho,et al.  The Submillimeter Array , 2004, Astronomical Telescopes and Instrumentation.

[16]  R. J. Cohen,et al.  Spatial and velocity coincidence of 4765‐ and 1720‐MHz OH masers in two star‐forming regions Cep A and W75N , 2004 .

[17]  J. Gallimore,et al.  Expansion of the R4 H2O Maser Arc near Cepheus A HW2 , 2002, astro-ph/0211462.

[18]  C. McKee,et al.  The Formation of Massive Stars from Turbulent Cores , 2002, astro-ph/0206037.

[19]  G. Garay,et al.  Discovery of Linear “Building Blocks” of Water Masers Shaping Linear/Arcuate Microstructures in Cepheus A , 2001 .

[20]  G. Garay,et al.  The distribution of the warm and dense molecular gas around Cepheus A HW 2 , 1999 .

[21]  G. Garay,et al.  Disk and Outflow in Cepheus A-HW2: Interferometric SiO and HCO+ Observations , 1999 .

[22]  G. Garay,et al.  The Nature of the Radio Sources within the Cepheus A Star-forming Region , 1996 .

[23]  G. Garay,et al.  The Thermal Radio Jet of Cepheus A HW2 and the Water Maser Distribution at 0.″08 Scale (60 AU) , 1996 .

[24]  G. Garay,et al.  Cepheus A HW2: A powerful thermal radio jet , 1994 .

[25]  D. Hollenbach,et al.  H2O masers in star-forming regions , 1989 .

[26]  F. Adams,et al.  Star Formation in Molecular Clouds: Observation and Theory , 1987 .

[27]  J. Wouterloot,et al.  The star-forming region in Cepheus A , 1984 .

[28]  I. Gatley,et al.  Far-infrared observations of the Cepheus OB3 molecular cloud , 1979 .

[29]  P. Goldsmith,et al.  Molecular cooling and thermal balance of dense interstellar clouds , 1978 .

[30]  N. Scoville,et al.  Infrared sources in molecular clouds. , 1976 .

[31]  H. L. Johnson,et al.  Photometric Distances of Galactic Clusters. , 1957 .