European Workshop on Astronomical MoleculesZwolle, the Netherlands in 19 February 2004

The Kinematics, Physical Condition and Magnetic Field of the W3 IRS5 Region

Hiroshi Imai (Joint Institute for VLBI in Europe)

Anuj P. Sarma (Eastern Kentucky University)

European Workshop on Astronomical MoleculesZwolle, the Netherlands in 19 February 2004

The Kinematics, Physical Condition and Magnetic Field of the W3 IRS5 Region

Hiroshi Imai (Kagoshima University, Japan)

Anuj P. Sarma (Eastern Kentucky University)

Diagnostics of early phase of star formation with water masers• About W3 IRS5• Water maser kinematics:– Finding driving sources of the outflows

• Magnetic field– Zeeman splitting (B//)– Linear polarization (B⊥)

• Physical condition– Turbulence in the outflows/ambient gas

• Conclusions– How has W3 IRS5 been understood?

About W3 IRS5: bright sum-mm source• Bight Far-IR and sub-mm source in W3 Main • Earliest phase of star formation

Cited from Ladd et al. (1993)

About W3 IRS5: a molecular cloud core• M~1400 Msun (Hayashi et al. 1989)

C18O (contour) and 21 cmcontinuum emission in W3 Main(Tieftrunk et al. 1995; Colley 1980)

W3 Main

About W3 IRS5: polarimetry• Magnetic field in W3 Main

(Roberts et al. 1993; Greaves et al. 1994, 2003)– Spatial gradient in NE--SW direction– Weakening at the location of W3 IRS5

A molecular outflow (Mitchell et al. 1993)

About W3 IRS5: a high-mass star cluster

• Hyper compact HII regions?

• Or blobs of ionized gas in one outflow?

• Where is the high-mass YSOs (outflow driving

sources)?• How old is this star-for

ming region?

Water masers and 15-GHz continuum emission sources (Claussen et al. 1994)

6000 AU at 1.8 kpc

VLBA observations of the W3 IRS5 water masers

• Observations – Proper motion measurement M

arch 1997, October 1997 and January 1998– Polarimetry (Linear polarization, with the VLA) N

ovember 1998– Polarimetry (Zeeman effect measurement)

January 2000

VLBA observations of the W3 IRS5 water masers

• Publications– Imai et al. 2000, ApJ 538, 751– Sarma et al. 2001, ApJ 554, L217– Imai, Deguchi & Sasao 2002, ApJ 567, 971– Watson, Sarma & Singleton 2002, ApJ 570, L37– Imai et al. 2003, ApJ 595, 285

Water maser kinematics(Imai et al. 2000)

• Distance to W3 IRS5: ~1.8 kpc• c.f. .... – 2.3 kpc (kinematic distance) (Georgel

in & Georgelin 1972)– 2.2 kpc (Cas OB6, spectroscopic)

(Humphreys 1978)– 2.4 kpc (IC1805, spectroscopic) (Guetter

et al. 1989)– 1.8 kpc (IC1795, spectroscopic) (Og

ura & Ishida 1976)– Wait for annual parallax measureme

nts. (W3 OH, Hachisuka et al. 2004)

Water maser kinematics(Imai et al. 2000)

• Two distinct outflows from sources a and d1/d2

>>> almost same evolutionary stage (Δτ≦ 105 years)

• Outflow velocities: ~30 km/s

• Accelerated up to ~60 km/s

Water maser kinematics(Imai et al. 2000)

• Improved partially by continuum proper motions

(Wilson et al. 2003)– Fixed relative positions between

sources b and d1/d2>>> at least 2

early B-stars – Proper motions of sources

a and f with velocities ~130 km/s

– Sources c and e disappeared.

Water maser polarimetry:Tracing magnetic field of

the interior of a molecular cloud core

• Magnetic field on a tiny scale (< 1000 AU)– Regions very close to outflow origins and protostars– Sites of the earliest phase of star formation

• Really tracing magnetic field of molecular core?– Relation to the magnetic field on a larger scale– Local effects in maser phenomenon?

Water maser polarimetry (Sarma et al. 2001, 2002)

• Velocity resolution better than 0.1 km/s i

s necessary.

• Similar values of magnetic field strengths in four maser features:

B//~ -30 mG

Proper motions v.s. Electric Vector PAs (Imai et al. 2003)

The magnetic field model in W3 IRS5

Uniform B vector in the maser region

B⊥ PA in the maser region:~75 deg.

B// inclinationw.r.t. LOS45--60 deg.

0.5 pc at 1.8 kpc

The magnetic field model in W3 IRS5

An hourglassmodel (Roberts et al. 1993)

Pinch center at the east of the maser region(Sub-mm emission peak,Ladd et al. 1993)

Pinch ratio:A:B~1:7

0.5 pc at 1.8 kpc

• Empirical B-n relation of magnetic field (Clutcher 1999)

• ~25μG >>> ~1 mG pinch ratio ~7 >>> Enhanced by a factor ~50

• Enhanced by a factor ~20 in maser clumps Bcritic

al =(8πρmaserv2maser)1/2~ 250 mG < Bobserved >>

> The magnetic field cannot control the outflows.

Magnetic field between on large and small scales

€

B∝ nH2

0.47 (nH2≤107 cm-1)

Microstructures in water masers(Imai et al. 2002)

How to create such structures?

Two-point correlation functions(Imai et al. 2002)

Fractal fashion in the outflow and maser gas clumps. (c.f. Gwinn 1994; Strelniski et al. 1999; A.Richards’s talk)Flatter slop created more energetic flow and crating more intense maser emission.

Velocity difference in maser clumps(Imai et al. 2002)

Kolmogorov-type turbulence in a maser cloudCommon among water maser sources

Turbulence enhanced only on the outflow scale

How has W3 IRS5 been understood?Improved from Imai et al. (2000)

Conclusions

• Water maser kinematics for successfully finding driving sources in a cluster of newly-formed massive-stars.•Cluster formation on a very short time scale (105 yr)•Synchrotron emission blobs in stellar winds

• Water maser polarimetry for successfully elucidating 3D magnetic field at the center of a molecular cloud core.•Magnetically supercritical collapse of a core•Outflows dominated by stellar winds

• Common turbulence at interior and exterior of maser clumps

•Turbulence is excited only at exterior of maser clumps by outflows/stellar winds.