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--- 2013:reasearch [2014/01/21 14:18] – created poll
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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|}}