A・一般) ＣＣＳゼーマン効果と理論計算を連携させた星形成における磁場の

NRO UM
July 26, 2012
Magnetic Fields of
Prestellar Cores From CCS
Zeeman Observations
Fumitaka Nakamura (NAOJ)
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Collaborators
基 盤 研 究 A( 一 般 ) H24-28 「CCSゼーマン 効 果 と 理 論 計 算 を 連 携
させた 星 形 成 における 磁 場 の 役 割 の 研 究 」
Munetaka Momose (Ibaragi Univ.)
Satoshi Yamamoto (Univ. of Tokyo)
Daisuke Iono, Ryohei Kawabe, Tomoya Hirota (NAOJ)
Nario Kuno, Shuro Takano (NRO)
Kazuhito Dobashi (Tokyo Gakugei Univ.)
Tomoaki Matsumoto (Hosei)
Hideo Ogawa, Toshikazu Onishi, Hiroyuki Maezawa,
Kimihiro Kimura, Kazuki Tokuda, Tomohiro Tanaka
(Osaka Pref. Univ.)
Seiji Kameno, Izumi Mizuno (Kagoshima)
Hiroko Shinnaga (Hawaii)
2

Purpose of this study
measure the strengths of magnetic
fields associated with prestellar cores
by CCS (J N =4 3 -3 2 ) Zeeman
observations, and constrain the role of
magnetic fields in star formation
process.
develop a new 45 GHz receiver for the
NRO 45m telescope (see Ogawaʼ’s
talk)
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Role of Magnetic Fields in Star Formation
Critical Mass below which magnetic field can support the cloud against
gravity
magnetically subcritical
magnetically supercritical
M cr ~10M , R~0.05 pc
→ B cr ~ 170 G
The evolution of dense cores is
determined by the magnetic field.
However, the role of magnetic fields in star formation is
a matter of debate because of the difficulty of magnetic
field measurements.

Observations of Magnetic Fields
in Star Forming Regions
linear polarization
background star light (optical and near IR)
dust thermal emission
difficult to measure field strength
plane of the sky component
Zeeman observations
direct measurement of magnetic field strength
line of sight component
Sugitani, FN, et al. (in prep)

E
M
E
0
MB
M J, J -1, J - 2, ,
eh
9.310
4m c
e
21
- J 1, - J
(erg/G)
selection rule for transition
m 1,0,
1
molecular lines having large magnetic
moments
Molecule
freq
(GHz)
HI 1.420 2.8
OH 1.665 GHz 1.665 3.27
OH 1.667 GHz 1.667 1.96
CCS (43-32) 45.379 0.63
CN 113.5 2.18
Zeeman Effect
Splitting freq. per
1 G (Hz/G)
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circular polarization
これまでアレシボ 望 遠 鏡 305mを 用 いたHI,
OH 分 子 の 左 右 円 偏 波 の 差 により 検 出 されてき
た
低 周 波 ( 例 OH→1.6GHz)
→ 分 解 能 悪 い
Zeeman Effect
臨 界 密 度 が 低 く、 低 密 度 領 域 の 磁 場
from Shinnaga (2000)
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Previous Zeeman Measurements toward
Prestellar Cores
NRO45m CCS (J N =4 3 -3 2 )
Shinnaga et al.
no clear detection
other examples
CCS (J N =3 2 -2 1 ) DSN Levin et al. (2001)
C4H GBT Turner & Heiles (2001)
SO (J N = 1 2 -1 1 )
Effelsberg Uchida et al. (2001)
CN
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Target Core Pilot Survey
To successfully detect the Zeeman splitting, sample
selection is extremely important.
strong CCS emission + narrow line widths
pilot observations
OTF observations with S40+AC
Hirota et al. (2009,2011)
position switch observations
observations done by Tanaka
41 0
K km/s
0.7
0.6
L1495B
T peak ~ 2.5 K
V ~ 0.25 km/s
0.5
DEC (1950)
40 0
39 0
0.4
0.3
0.2
T A
*
(K)
28 38 0
0.1
12m40s 12m35s 12m30s 4h12m25s
RA (1950)
0.0
V LSR (km/s)
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Summary
The role of magnetic fields in star formation
is a matter of debate.
To shed light on the issue of magnetic field
problem, we plan CCS Zeeman observations
towards prestellar cores by developing a new
45GHz receiver for NRO 45m.
The target line is CCS(J N =4 3 -3 2 ) 45.379GHz.
The main goal is to clearly detect the Zeeman
splitting towards prestellar cores and
estimate the magnetic field strengths.
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