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Mapping Magnetic Field
Structure in Star-forming
Regions
賴詩萍
Oct 4, 2006, NTHU Phys Colloquium
康德-拉普拉斯 星雲假說
康德(1755年) - 原始星雲是由大小不等
的固體微粒組成的﹐“天體在吸引最強
的地方開始形成”﹐萬有引力使得微粒
相互接近。
拉普拉斯(1796年) - 形成太陽系的雲是
一團巨大的﹑灼熱的﹑轉動著的氣體﹐
大致呈球狀。由於冷卻﹐星雲逐漸收縮,
星雲的中心部分凝聚成太陽 。
Star formation standard model
Shu et al. 1987
Shu et al. (1987)
Star formation standard model
P. Andre
Starless Cores – Barnard 68
Simplest Star Formation Theory
Thermal pressure support - Jeans Mass (1928)
Thermal
Pressure
Gravitation
Why B is important in star
formation?

Regulating star formation efficiency

Observed star formation efficiency is low


B provides support in



Theoritical 200 M/year >> Observed 3 M/year
Static fields
MHD waves (turbulence)
Facilitating gravitational collapse


Angular momentum problem – magnetic braking
Magnetic flux problem - ambipolar diffusion
Morphology Evolution
Magnetic support theories
MHD simulations (Ostriker, Gammie, & Stone 1999)
2
cs
 2
VA
large -> random morphology
How to measure B?
Zeeman Effect – Too Difficult!!
Polarization of Dust Emission: PBp
Polarized Molecular Line Emission
(the Goldreich-Kylafis Effect): PBp or PBp
B
V
Polarization Observations with
Berkeley-Illinois-Maryland Array
(BIMA)
Dust Polarization observations with BIMA
Magnetic Field Morphology – W51 e1/e2
JCMT   14” at 850 m
Chrysostomou et al. (2002)
BIMA   2” at 1.3 mm
Lai et al. (2001)
NGC 2024
JCMT   14” at 850 m
Matthews et al. (2002)
BIMA   2” at 1.3 mm
Lai et al. (2002)
DR21(OH) –
JCMT vs. BIMA
(B map)
Lai et al. (2003)
NGC1333 IRAS4A
NGC1333 IRAS4A
NGC1333 IRAS4A
Twisted hourglass geometry
BIMA   2” at 1.3 mm
Lai (2002)
SMA   1” at 850 m
Girart, Rao, Marrone (2006)
Physical quantities
Dispersion of Polarization Angle ()
1.
Field Strengths (the Chandrasekhar-Fermi Method)
2.
Mass-to-magnetic-flux Ratios
3.
Turbulent-to-magnetic-energy Ratios
Chandrasekhar-Fermi Method
Dispersion of Polarization Angle ()
⇒ Field Strengths in the plane of sky
•
Uniform fields perturbed by MHD turbulence -    B
•
Incompressible fluid -  invariant
•
Small perturbation -
•
Isotropic turbulence -  p   los
4 
 
B
B
Ostriker, Stone, & Gammie 2001
 ⇒ Bp, M/ΦB,p, turb
Results

Bp ~ 0.8 – 3.5 mG

M/ΦB,p ~ 0.1 – 4.9 critical mass-to-flux ratio

 turb ~ 0.03 – 0.4
Future Work – More observations!!
Current/Future instruments
SMA (the only working interferometer for now)
 CARMA = BIMA + OVRO (?)
 ALMA!! (wait at least 7 years)

3D Magnetic Field Structure

Zeeman measurements
High density (106 cm-3) - CN
 Young Cores – CCS


Line polarization
ALMA in 7 years
廣告時間
“Star and Planet formation” Journal Club
時間 : 隔週週二中午 12:10-1:00 pm
 地點 : 502A
 目的

輪流報告最新的研究結果
 培養學生對這個研究主題的興趣


參與老師: 江瑛貴, 陳惠茹, 呂聖元, 賴詩萍