1. 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 Walter Alef: Max-Planck-Institut für Radioastronomie (Bonn) Jan Brand: IRA-CNR, Istituto di Radioastronomia di Bologna

2. High resolution observations at radio, millimetre and FIR wavelengths:  Thermal line observations by mm and radio connected interferometers (e.g., OVRO, VLA): linear resolutions of  1000 AU, insufficient to resolve the disk structure and to study the ``root'' of the jet  VLBI observations of maser lines (e.g., 22 GHz H 2 O; 6.7 and 12 GHz CH 3 OH): permit to study the gas structure and kinematics nearby the YSO with a linear resolution of few AU Star Forming Regions jet Accretion disk jet Angular momentum conservation collapsing core GMCTheory:Observations 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)

3. 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  ). Hunter et al. (1995): VLA 8.4 GHz thermal continuum source (interpreted as free-free emission from an ionized wind); CO bipolar outflow; H 2 NIR emission jet. VLBI water maser observations are needed!! The case of AFGL 5142 Previous observations stronlgy suggest the presence of an high-mass YSO: Zhang et al. (2002): VLA NH 3 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.

4. Observations 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) Data reduction 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.

5. Identification of maser features Identification of maser features Every channel map has been searched for emission above a conservative detection threshold (in the range 5-10  ) The detected maser spots have been fitted with two-dimensional elliptical Gaussians (intensities in the range: 0.3-17 Jy beam -1 ) A maser “feature” is considered real if it is detected in at least three contiguous channels (spectral FWHM > 0.3 km/s), with a position shift of the intensity peak from channel to channel smaller than the FWHM size.  26 maser “features” over the four epochs  A final set of 12 distinct “features”, 7 out of these observed for more than one epoch

6. Measured proper motions Measured proper motions

7. Comparison of VLBI results with previous interferometric observations 8.4 GHz continuum 88 Ghz continuum □ 1992 VLA H 2 O. 1998 VLA H 2 O  Proper motions OVRO outflows (Hunter et al. 1999) Group I of VLBI masers Group II of VLBI masers

8. Kinematics of the masing gas Simple interpretation: The detected maser features are tracing the flow motion in the innermost portion of the molecular outflow BUT: 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'' Large scale outflow 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!

9.  It is found closer (~ 500-1000 AU) to the expected location of the massive YSO, where an accretion disk and/or the base of the jet should be found  It has an elongated spatial distribution (close to that of proper motion orientation): edge-on rotating disk or outflow motion along the elongation axis? Group I

10. The best fit disk: almost edge-on and (on the sky) parallel with the elongation axis Disk radius:  800 AU (in agreement with expected values for massive stars) M YSO = (38  20) M   the central object is a massive YSO, compatible with previous core (Hunter et al 1999) and disk (Zhang et al 2001) mass estimates Group I We tested the kinematics fitting two models: Keplerian disk and conical outflow. Only the keplerian disk model produces an acceptable solution!.... Proper motions H 2 O Maser H 2 O

11. Group II  There are too few observables to test meaningfully a kinematical model.  Group II might be associated with a distinct (as yet undetected) YSO.  The positions and the LOF velocities of these features are in agreement with the blue-shifted lobe of the (SiO and HCO + ) molecular outflow. Their emission is excited by the interaction of the gas outflowing from the YSO with the ambient gas of the progenitor molecular core. Maser H 2 O Ambient gas Red shifted lobe Blue-shifted lobe

12. Conclusions  Using the EVN we have observed water masers towards the massive SFR AFGL 5142 for four epochs (Oct 1996 – Nov 1997)  We have identified the water maser emission centers and calculated the proper motions for persistent features.  Group I features could arise on the surface of a nearly edge-on keplerian disk  Maser features of Group II might be excited by the interaction of the gas outflowing from the YSO with the ambient gas. AFGL 5142 is a good example of a massive (proto)star, possibly associated with a keplerian disk and jet/outflow system

13. Future work We have proposed and obtained four epochs of 22 GHz VLBA observations Advantages: shorter time separation (~1 month vs 3-4 months of EVN) between two consecutive epochs higher sensitivity (10 antennas vs 5-7 of our EVN epochs) Final remarks Only 5-7 antennae, out of the 11 presently available to observe at 22.2 GHz, took part in each run in 1996-1997 Our EVN observations were able to measure the proper motions of strong (  0.3 Jy/beam) and long-living (~1 yr) water maser features