VLBI observations of H 2 O masers towards the high-mass Young Stellar Objects in AFGL 5142

1. VLBI observations of H2O 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. Star Forming Regions GMC jet collapsingcore Angular momentum conservation Accretion disk jet 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) Theory: • 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 H2O;6.7 and 12 GHz CH3OH): permit to study the gas structure and kinematics nearby the YSO with a linear resolution of few AU

3. The case of AFGL 5142 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!!

4. 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. Observations Data reduction

5. 26 maser “features” over the four epochs • A final set of 12 distinct “features”, 7 out of these observed for more than one epoch 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.

6. Measured proper motions

7. Comparison of VLBI results with previous interferometric observations OVROoutflows (Hunter et al. 1999) Group I of VLBI masers 8.4 GHz continuum 88 Ghz continuum □ 1992 VLA H2O . 1998 VLA H2O Proper motions 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: 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!

9. Group I • 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?

10. Group I . . . . . Maser H2O Proper motions We tested the kinematics fitting two models: Keplerian disk and conical outflow. Only the keplerian disk model produces an acceptable solution! • The best fit disk: almost edge-onand (on the sky) parallel with the elongation axis • Disk radius:  800 AU (in agreement with expected values for massive stars) • MYSO= (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

11. Red shifted lobe Ambient gas Maser H2O Blue-shifted lobe • 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.

12. AFGL 5142 is a good example of a massive (proto)star, possibly associated with a keplerian disk and jet/outflow system • 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.

13. Final remarks • Only 5-7 antennae, out of the 11 presently available to observe at 22.2 GHz, took part in each runin 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 • 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)