Magnetic field generated
by the extreme oxygenrich red supergiant
resides in HII region
Hiroko Shinnaga
新永 浩子
Kagoshima UniversityCollaborators: M. Claussen, S. Yamamoto,M. Shimojo
2017/12/21���星形成と銀河構造における磁場の役割

Outline•

We measured circumstellar magnetic field of anextreme red supergiant (RSG) VY CMa (25 Msun).

•Magnetic field is turned out to be very strong (up to150-650G, at least ~10G) within 20 — 80 R* from thestar••

Due to large expanded stellar envelope, RSGs wereexpected not to generate strong field.

At least for VY CMa, powerful dynamo processes must
be still active to generate intense magnetic field.
2017/12/21���星形成と銀河構造における磁場の役割

VY Canis Majoris The star
- Edge of huge (5 deg indiameter) HII region
Sharpless 310 (5Myr;open cluster).
CO- Still near the rim of theCloudparent cloud.
- Asymmetric nebula isfound at optical andinfrared.
- Complicated dust
structure surrounding theContours..CO; Grey scale..K bandsource.
2017/03/24��
ALMA恒星Workshop(Lada&Reid1973)

VY Canis Majoris•

M-type red supergiant (M5 Ib)•Distance of 1.14 kpc (Choi+’08 by VERA)•

M* ~ 25Msun•

L* ~ 5 x 105 Lsun•

R* ~ 1400 Rsun (~ 6.6AU)•T* ~ 3500 K-4•

Extremely high mass loss rate 3 x 10 Msun/yr•

Very complex dust features surrounding thestar
2017/12/21���星形成と銀河構造における磁場の役割

VY Canis Majoris

Sketch of dustfeatures(Smith et al. 2001)
1” ~ 1100AU

HST2017/12/21��
composite image(Smith�星形成と銀河構造における磁場の役割
et al. 2001)

VY Canis Majoris

2017/12/21��

wikipedia

�星形成と銀河構造における磁場の役割

Highly Excited SiO Transitions■ SiO rotational

7000K

transitions at different
vibrational states havebeen observed
towards the source■ Many of SiO
transitions are highlylinearly polarised.

3500K

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1750K

�星形成と銀河構造における磁場の役割

SiO v≧1 maser: Above radio photosphere•

SiO v≧1 rotationalemission traces
inner edge of thecircumstellar region•

Just above thephotosphere•

The pumping
mechanism still
remains unclear.

Schematic picture of stellar
atmosphere (Reid&Menten’97)

SiO v≧1 maser: Above radio photosphere•SiO v≧1 rotationalemission distributes
in irregular manner•

far different
from circular
distribution•

not mainly fromstellar radiation

SiO J=1-0(blue v=1/green v=2), 2-1(red) in v=1 withVLBA (Richter, Kemball, Jonas 2016)

VY Canis Majoris

SiO J=1-0, 2-1 in v=1,2with VLBA

(Richter, Kemball, Jonas 2016)

wikipedia

Nobeyama 45mTelescope© NRO/NAOJ/NINSSiO v=0 Observations•

Nobeyam 45m observation with Millimeter Polarimeter
revealed the high degree of linear polarization (Shinnaga+99).

•VLA imaging at v=0, J=1-0 transition has been made (Shinnagaet al. 2003).

•SiO v=0 maser revealed butterfly-shaped bipolar outflow
emanating from the star.

•SiO v=0 polarization follows the flow direction of theoutflow.

•Millimeter
Polarimeter
Indicate well-ordered strong
circumstellar
magnetic field.
(Shinnaga+’99)
2017/12/21��

(Shinnaga+’99)
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Very Large Array at NRAO

© NRAOSiO v=0 Observations

Knot-like structure
Butterfly-shape outflow(Shinnaga et al. ’03)

2017/12/21��

Polarized intensity(gray scale)
Shinnaga et al. ‘03
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SiO High J Maser Observations•

SiO high J maser transition (5-4, v=1) with SMA••3 Antennas••

215.596 GHz (1.39mm)

6.25 – 18.12 kλDec 2002.
•Δv = 0.5 km/s.

•Δf = 358 kHz

2017/12/21���星形成と銀河構造における磁場の役割

SiO High J Maser Observations■ Broad velocity range.
■ over > ~60km/s.

■ Main 7 components.
■ Spiky line profile.

■ Comp. 2 àprominent.

Most

Detection

Must be closest to.
the central star.

■Shinnaga+2004
2017/12/21���星形成と銀河構造における磁場の役割

Atacama Large Millimeter Array(ALMA)

2016/06/25

光のノスタルジアに寄せて17
Clem & Adri Bacri-Normier (wingsforscience.com)/ESO

Color scale:321GHzcontinuumContours:658GHz
continuumRichards+2014

SiO v=0 : inner CSE

Shinnaga et al. 20172017/12/21���星形成と銀河構造における磁場の役割

SiO v=0 : inner CSE
Highly linearly polarized features indicate thelarge-scale well-ordered magnetic field exists
in the CSE of the star.
Field strengths are predicted higher than 10G
according to theoretical models (e.g.
Western&Watron 94).
Shinnaga et al. 20172017/12/21���星形成と銀河構造における磁場の役割

Zeeman Effect

The only method to measure the LOS field strength
without assumption

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Shinnaga+ 2008

�星形成と銀河構造における磁場の役割

Zeeman Effect

CCS 32-21 in lab.

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Shinnaga&Yamamoto ‘00

�星形成と銀河構造における磁場の役割

Zeeman EffectShinnaga&Yamamoto ‘00

Zeeman splitting of SiO v=0 J=1-0 :2.3x10-4 Hz/uG(Honerjäger &Tischer’74)
2017/12/21���星形成と銀河構造における磁場の役割

SiO v=0 : inner CSE

Shinnaga et al. 20172017/12/21���星形成と銀河構造における磁場の役割

SiO v=0 : inner CSE

Shinnaga et al. 20172017/12/21���星形成と銀河構造における磁場の役割

SiO v=0 Strong Magnetic Field•

Zeeman shift wasdetected towards
three clumps•

Field strengths
ranging from 150 —650G•

within 500AU fromthe central star

Shinnaga et al.2017

2017/12/21���星形成と銀河構造における磁場の役割

SiO v=0 Strong Magnetic Field

SiO v=0 Strong Magnetic Field•

Assuming magnetic configuration to (r-1 ;toroidal), max of 50kG of stellar B isestimated.
•c.f 20kG was detected towards highmass (30Msun) star NGC1624-2 (Wade+’12)

Shinnaga et al.2017

2017/12/21���星形成と銀河構造における磁場の役割

SiO v=0 Strong Magnetic Field•

Supergiant has a convective shell around thehelium core, the convective shell may play a
critical role in generating the strong
magnetic field, with an extraordinarily highmass-loss rate (Shenoy et al. 2016).

Shinnaga et al.2017

2017/12/21���星形成と銀河構造における磁場の役割

Summary•

VY CMa has a intense magnetic field, evidenced byZeeman effect of SiO v=0 line (the first detection ever!)along with well-organized large-scale magnetic field.

•

Contrary to the expectation, magnetic field of RSG,
progenitor of core-collapse supernova, is turned out to bevery strong.

•At least for VY CMa, powerful dynamo processes must be
still active to generate intense magnetic field.
2017/12/21���星形成と銀河構造における磁場の役割