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 ====== Scientific Research ======
+Accretion Disks surrounding O-type Protostars
+Ciriaco Goddi (goddi@jive.nl)
+High-mass stars are prominent in the ecology of the interstellar medium and the evolution of Galaxies.
+Though much needed, there is no general theory of high-mass star formation.
+The main issue for models is that the intense stellar radiation pressure
+and the thermal pressure from the surrounding ionized material,
+may reverse the accretion flow and prevent matter from reaching the star.
+Recent theoretical studies  have however demonstrated that radiation pressure can be overcome
+ if accretion occurs through a circumstellar disk.
+ Despite the theoretical evidence, we have not yet conclusively identified a single high-mass protostar
+ in the Galaxy surrounded by an accretion disk.
+We observed NGC7538-IRS1 (at 2.7 kpc) with the European VLBI Newtwork (EVN) in the 6.7 GHz maser line of methanol,
+ which is a typical signpost of high-mass star formation.
+ Four observing epochs spanning eight years were used to measure positions, proper motions, line-of-sight velocities and accelerations of methanol masers.
+These measurements provided 3D kinematics and dynamics of circumstellar gas on scales from tens to a thousand AU.
+We find compelling evidence that NGC7538-IRS1 is forming a multiple system of
+high-mass young-stars surrounded by disks.
+Data modeling enabled us to identify quasi-Keplerian rotation around a 25 solar mass star
+and a thick disk containing 16 solar masses around a nearby protostar.
+These measurements are critical to test theoretical models of accretion for massive stars.
+The results will be published in the following issue of A&A.
+Figure 1: The NGC7538 Star Forming Region (2.7 kpc).
+(Left) Three color IRAC image in the mid-infrared from the Spitzer Space Observatory.
+(Right) 6.7 GHz methanol maser emission spots (filled circles) observed with the EVN
+overlaid on the the 22 GHz continuum map imaged with the VLA (black image and white contours).
+Colors denote line-of-sight velocities, with blue indicating blue-shifted emission and red indicating red-shifted emission.
+The sizes of the circles scale with the flux density. The ellipses represent the disk planes surrounding the two young stars IRS1a and IRS1b,
+resolved by the EVN, with the solid lines indicating the near-side and the dashed lines the far-side of the disks.
+{{:2013:ngc7538_ir_maser.jpg?200|}}
+Massive Star Forming Regions and Magnetic Fields
+Gabriele Surcis, Huib Jan van Langevelde, and Ciriaco Goddi together with colleagues from Sweden, Spain, Mexico,
+and South Korea observed the polarized emission of 22 GHz water masers around the massive young stellar objects (YSOs)
+W75N-VLA2 and W75N-VLA1. The two massive YSOs are separated by just 1300 astronomical units and are at two
+different evolutionary stages, i.e., VLA1 is the most evolved and VLA2 the least evolved. The interferometric
+observations showed at 1~au scale that while the water masers distribution and the magnetic field around VLA1 have
+not changed since 2005, the shell structure of the masers around VLA2 is still expanding and increasing its
+ellipticity. Furthermore, the magnetic field around VLA2 has changed its orientation according to the new
+direction of the major-axis of the shell-like structure and it is now aligned with the magnetic field in VLA1.
+This confirm that the water masers around VLA2 are tracing the evolution from a non-collimated to a collimated
+outflow.
+Gabriele Surcis and Huib Jan van Langevelde together with Wouter Vlemmings (Chalmers University of Technology),
+Busaba Hutawarakorn Kramer (MPIfR), and Anna Bartkiewicz (Nicolaus Copernicus University)
+continued their work on measuring magnetic fields morphology close to massive YSOs (au scale) by using 6.7 GHz
+methanol masers. The group measured the magnetic field morphology towards eight new massive YSOs. These sources
+are part of a large sample of massive YSOs, the so-called flux-limited sample, that is composed of 31 sources.
+A preliminary statistical analysis of the results obtained from the first 19 sources reveals evidences that the
+magnetic fields around massive YSOs are preferentially oriented along the molecular outflow.
+Furthermore, the group together with Luca Moscadelli (Osservatorio Astronomico di Arcetri) have determined the
+morphology of the magnetic field at au scale around the massive YSO IRAS20126+4104 by observing the polarized
+emission of the 22 GHz water masers and the 6.7 GHz methanol masers. The orientation of the magnetic field
+derived from the masers agrees with the S-shaped morphology on larger scale by using the dust-polarized emission
+at 350~\mu~m.
+---------------------------
+Figures captures.
+figure_1a.eps, figure_1b.eps: A close-up view of the 22 GHz water masers detected around the VLA1 (left panel)
+and VLA2 (right panel). The reference position is $\alpha_{2000}=20^{\rm{h}}38^{\rm{m}}36^{\rm{s}}\!.435$ and
+$\delta_{2000}=42^{\circ}37'34''\!\!.84$. The octagonal symbols are the identified masers scaled logarithmically
+according to their peak flux density. The linear polarization vectors, scaled logarithmically according to
+polarization fraction, are overplotted. In the bottom-right corner of both panels the error-weighted orientation
+of the magnetic field ($\Phi_{\rm{B}}$) is also reported; the two dashed segments indicate the uncertainties. The
+ellipse drawn in the right panel is the result of the best fit of the water masers. The estimated values of the
+magnetic field strength are also shown in both panels next to the corresponding water maser.
+figure_2a.eps, figure_2b.eps: Left panel: The black bars represent the magnetic field direction determined from
+the polarized dust emission at 350~$\mu$m, whose continuum emission is in the background. The white box indicates
+the position of the right panel.
+Right panel: methanol (triangles), OH (squares), and water (octagons) masers in IRAS20126+4104. The gold asterisk
+ represents the B0.5 protostar ($\alpha_{2000}=20^{\rm{h}}14^{\rm{m}}26^{\rm{s}}\!.0498$ and
+$\delta_{2000}=41^{\circ}13'32''\!\!.443$, MCR11), while the dotted line represents the Keplerian disk of
+$\sim$1000~au ($\rm{PA_{disk}}=53^{\circ}\pm7$\d. The red and blue lines indicate the red- and blue-shifted lobes
+of the jet, respectively. The thick green segments represent the magnetic field direction determined from the
+polarized methanol and water maser emissions. The green dashed segments represent the magnetic field direction
+determined from the linearly polarized emission of OH masers (Edris et al. 2005, A&A, 434, 213).
+{{:2013:figure_1a.jpg?200|}}
+{{:2013:figure_1b.jpg?200|}}
+{{:2013:figure_2a.jpg?200|}}
+{{:2013:figure_2b.jpg?200|}}