The Kinematics, Physical Condition and

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European Workshop on Astronomical Molecules

Zwolle, 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 Molecules

Zwolle, 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 M
sun

(Hayashi et al. 1989)

C
18
O (contour) and 21 cm

continuum 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
-
forming 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





March 1997, October 1997 and January 1998


Polarimetry (Linear polarization, with the
VLA)


November 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)


(Georgelin & Georgelin 1972)


2.2 kpc
(Cas OB6, spectroscopic)




(Humphreys 1978)


2.4 kpc
(IC1805, spectroscopic)
(Guetter et al. 1989)


1.8 kpc
(IC1795, spectroscopic)

(Ogura & Ishida 1976)


Wait for annual parallax
measurements.



(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


10
5

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 is




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 楮⁴桥h
浡獥爠牥杩潮g

~75 deg.


B
//

inclination

w.r.t. LOS

45
--
60 deg.

0.5 pc at 1.8 kpc

The magnetic field model in W3 IRS5

An hourglass

model

(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
B
critical

=(
8πρ
maser
v
2
maser
)
1/2
~ 250 mG < B
observed


>>> The magnetic field






cannot control the outflows.

Magnetic field between on

large and small scales


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 cloud

Common 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 (10
5

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.