132 research outputs found
Magnetic field measurements at milliarcsecond resolution around massive young stellar objects
Magnetic fields have only recently been included in theoretical simulations
of high-mass star formation. The simulations show that magnetic fields can play
a crucial role not only in the formation and dynamics of molecular outflows,
but also in the evolution of circumstellar disks. Therefore, new measurements
of magnetic fields at milliarcsecond resolution close to massive young stellar
objects (YSOs) are fundamental for providing new input for numerical
simulations and for understanding the formation process of massive stars. The
polarized emission of 6.7 GHz CH3OH masers allows us to investigate the
magnetic field close to the massive YSO where the outflows and disks are
formed. Recently, we have detected with the EVN CH3OH maser polarized emission
towards 10 massive YSOs. From a first statistical analysis we have found
evidence that magnetic fields are primarily oriented along the molecular
outflows. To improve our statistics we are carrying on a large observational
EVN campaign for a total of 19 sources, the preliminary results of the first
seven sources are presented in this contribution. Furthermore, we also describe
our efforts to estimate the Lande' g-factors of the CH3OH maser transition to
determine the magnetic field strength from our Zeeman-splitting measurements.Comment: Accepted for publication in the proceeding of the "12th European VLBI
Network Symposium and Users Meeting", eds Tarchi et al. PoS(EVN 2014)04
A new sample of OH/IR stars in the Galactic center
Wetensch. publicatieFaculteit der Wiskunde en Natuurwetenschappe
Stellar positions from SiO masers in the Galactic center
Wetensch. publicatieFaculteit der Wiskunde en Natuurwetenschappe
Circular polarization of circumstellar water masers around S Per
Wetensch. publicatieFaculteit der Wiskunde en Natuurwetenschappe
The nature of OH/IR stars in the galactic centre
Wetensch. publicatieFaculteit der Wiskunde en Natuurwetenschappe
Envelope structure on 700 AU scales and the molecular outows of low - mass young stellar objects
Wetensch. publicatieFaculteit der Wiskunde en Natuurwetenschappe
Anomalously excited OH and the competition between maser transitions toward Centaurus A
Wetensch. publicatieFaculteit der Wiskunde en Natuurwetenschappe
The magnetic field in the star-forming region Cepheus A. from H_2O maser polarization observations
Wetensch. publicatieFaculteit der Wiskunde en Natuurwetenschappe
SN 2007gr: a Normal Type Ic Supernova with a Mildly Relativistic Radio Jet?
A nearby type Ic supernova, SN 2007gr was observed with the EVN in two epochs 60 days apart (second observation also included the Green Bank Telescope). In both cases one of the EVN stations was the Westerbork Synthesis Radio Telescope (WSRT), which recorded the observational data not only in the VLBI mode, but also in its normal interferometric mode. Thus it provided an important reference observation. In the first epoch the fluxes measured by the VLBI network and the WSRT alone match well. However in the second epoch the peak brightness observed in the VLBI experiment is much lower than the total flux recorded by the WSRT. There could be multiple reasons for this discrepancy: a resolution effect, coherence losses in VLBI, or extended emission contaminating the WSRT measurement. With new WSRT observations we costrain the level of background emission and find that there is still a difference between the corrected total flux density and the VLBI peak brightness. If one assumes that this is dominated by resolution, this would correspond to an average apparent expansion speed of ~0.4c
Sub - arcsec imaging at 267 GHz of a young binary system: detection of a dust disk of radius less than 70 AU around T Tauri N
Wetensch. publicatieFaculteit der Wiskunde en Natuurwetenschappe
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