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VLBI observations of H 2 O masers towards the high-mass Young Stellar Objects in AFGL 5142. Ciriaco Goddi Università di Cagliari, INAF-Osservatorio Astronomico di Cagliari (Italy). Collaborators: Luca Moscadelli: INAF, Osservatorio Astronomico di Cagliari
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towards the high-mass Young Stellar Objects in AFGL 5142
Università di Cagliari, INAF-Osservatorio Astronomico di Cagliari (Italy)
Luca Moscadelli:INAF, Osservatorio Astronomico di Cagliari
Walter Alef:Max-Planck-Institut für Radioastronomie (Bonn)
Jan Brand:IRA-CNR, Istituto di Radioastronomia di Bologna
Angular momentum conservation
Low-mass YSOs: high angular resolution observations, from the millimeter to the optical (HST), have revealed the existence of disk/jet systems, confirming the theory
High-mass YSOs: On average more distant from the Sun (1 kpc) and during the ZAMS phase still enshrouded in dust and gas envelopes (optical and NIR observations impracticable)
permit to study the gas structure and kinematics nearby the YSO with a linear resolution of few AU
Previous observations stronlgy suggest the presence of an high-mass YSO:
Hunter et al. (1995):•VLA 8.4 GHz thermal continuum source (interpreted as
free-free emission from an ionized wind);
• CO bipolar outflow;
• H2 NIR emission jet.
Hunter et al. (1999): • OVRO SiO jet and HCO+ outflow;
• OVRO 88 GHz source (coincident with the 8.4 GHz source)
The radio flux and the bolometric luminosity of the source both indicate
the presence of a massive object (M 10 M).
Zhang et al. (2002): VLA NH3 compact structure (diameter 1800 AU), interpreted
as a rotating disk surrounding a high-mass young star.
Hunter et al. (1995; 1999): a cluster of VLA 22 GHz water masers
associated with the continuum sources.
The VLA angular resolution (~0.1 arcsec) is inadequate to determine the
detailed spatial distribution and the proper motions of the maser spots.
VLBI water maser observations are needed!!
Array: EVN (Medicina, Cambridge, Onsala, Effelsberg, Metsahovi, Noto, Jodrell and Shanghai)
Transition rest frequency = 22235.080 Mhz
Observational epochs: Oct 1996, and June,
Sept, Nov 1997
Integration time: 13 scans of 6.5 minutes
Bandwidth = 1 MHz
Spectral channels = 112
Velocity resolution = 0.12 km s-1
Polarizations = LCP & RCP
Correlator = MKIII (Bonn, Germany)
Reduction package: NRAO AIPS
Channel map sky area: 4''4''
Velocity range: [-10.5, 0.7] km s-1.
Clean beam FWHM: 2.1 1.1 mas.
RMS noise level: 0.02-0.27 Jy beam-1.
Identification of maser features
detection threshold (in the range 5-10 )
Gaussians (intensities in the range: 0.3-17 Jy beam-1)
channels (spectral FWHM > 0.3 km/s), with a position shift of the intensity
peak from channel to channel smaller than the FWHM size.
(Hunter et al. 1999)
Group I of VLBI masers
8.4 GHz continuum
88 Ghz continuum
□ 1992 VLA H2O
. 1998 VLA H2O
Group II of VLBI masers
The detected maser features are tracing the flow motion in the innermost portion of the molecular outflow
Large scale outflow
Diameter ~ 50'', vel. dispersion ~100 km s-1, (assuming a Hubble flow)
rate dispersion~2 km s-1 arcsec-1
vel. dispersion~8 km s-1, distance ~ 0.35''
vel. dispersion~1.7 km s-1, distance ~1''
VLBI Group I
VLBI Group II
The whole VLBI maser distribution can not be directly
associated with the large-scale molecular outflow.
The two groups are tracing a more complex structure!
where an accretion disk and/or the base of the jet should be found
edge-on rotating disk or outflow motion along the elongation axis?
. . .
We tested the kinematics fitting two models:
Keplerian disk and conical outflow.
Only the keplerian disk model produces an acceptable solution!
previous core (Hunter et al 1999) and disk (Zhang et al 2001) mass estimates
with the blue-shifted lobe of the (SiO and HCO+) molecular outflow.
associated with a keplerian disk and jet/outflow system
AFGL 5142 for four epochs (Oct 1996 – Nov 1997)
motions for persistent features.
outflowing from the YSO with the ambient gas.
took part in each runin 1996-1997
( 0.3 Jy/beam) and long-living (~1 yr) water maser features