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2013/01/26 ALMA 時代の宇宙の構造形成理論 @ 北海道大学 - PowerPoint PPT Presentation


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2013/01/26 ALMA 時代の宇宙の構造形成理論 @ 北海道大学. Disk stability in low- metallicity star formation ~ 低金属量星形成における降着円盤の安定性 ~. K.Tanaka , K.Omukai (Kyoto-U). Primordial stars massive ~ 100Msun zero -metal . ? ? ?. Present-day stars low mass ~1Msun dusty (~1wt% ). Low metallicity stars.

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2013/01/26

ALMA時代の宇宙の構造形成理論

@北海道大学


Disk stability in low-metallicity star formation

~ 低金属量星形成における降着円盤の安定性 ~

K.Tanaka, K.Omukai (Kyoto-U)

Primordial stars

massive ~ 100Msun

zero-metal.

Present-day stars

low mass ~1Msun

dusty (~1wt%)


Low metallicity stars
Low metallicity stars

Low-metal. stars have crucial roles

for the evolution of universe!!

But we do not understand how they formed…

Primordial stars

massive

high-Mdot

zero-metal.

Present-day stars

low mass

low-Mdot

solar-metal.

What makes difference?

→ metal/dust cooling must be important.


Importance of dust c ooling

Free-Fall

(compression heating)

Importance of dust cooling

×

Omukai+05etc.

metal/dust cooling

Zero-metal.

low↑

Metallicity

high↓

Solar-metal.

Dust cooling makes Jeans-mass smaller!


Accretion through disk
Accretion through disk

Most material accretes onto stars through disks.

Dose the disks are gravitaitonally stable?


Main accretion phase in low metallicity star formation
Main accretion phasein low metallicity star formation

Since most material accretes onto a star through a disk,

the disk property is crucial for newborn stellar mass.

We study the disk structure and its stability

in low metallicity star formation.


Star formation model
Star formation model

We apply simple analytic model.

Step.1.

We construct

Infalling envelope models

at various metallicities

Step.2.

From the envelope models,

we evaluate disk structures

and its stability.


Infalling envelope structure
Infalling envelope structure

Accretion rate and disk size depend on infalling envelope

One-zone by Omukai05

R&M of envelope,

from ρ&T in one-zone model.

(Hosokawa&Omukai09b)

Acc. rate:

Radius:


Pre stellar core
Pre-stellar core

T decreases with metal.

・Mdot (~T3/2) decreases

・Rj increases

Core radius

We give Ω by hand

Ω=0.5xΩKep

Abel+02

Hosokawa+11

metal.

metal.

Acc. rate

From core model,

we estimate disk size & M.

Enclosed mass


Disk structure
Disk structure

Standard disk model

Local equilibrium : (Heating) = (Cooling)

Heating:Viscous heating

Cooling:H2line, Gas continuum, Dust collision

(Dust emission)

Parameters

Metallicity:Z=0-Zsun

Angular velocity:Ω=0.5xΩKep

Viscous parameter:α=1


Disk structure1
Disk structure

Disk temp. is relatively high.

zero-metal.

Toomre’s Q value

Unstable for Q<1

Kratter+10


Disk structure2
Disk structure

low-metal.

10-4Zsun

solar-metal.

zero-metal.

T[K]

100Msun

100Msun

1

0.1

0.1

10

100Msun

1

10

100Msun

Q

100Msun

1

10

0.1

0.1

100Msun

1

10

R[AU]

R[AU]

R[AU]

Metallicity affects disk structure


Disk stability
Disk stability

Low-metal. disk is very unstable!!


Why low metal disk is unstable
Why low-metal. disk is unstable?

infalla

Disk would be unstable

when infall rate exceeds its capacity.

accretion

Q-value also tells that

disk is unstable when Tdisk<Tcore.

Dust cooling efficient at disk

rather than envelope.


If disk is very unstable
If disk is very unstable…

Present-day massive star formation (Peters+10)

“Fragmentation-induced starvation”

Infalling material divided into multiple stars

→ Low-metal. stars form as compact clusters (?)


Conclusion sf in various metal via disk acc
ConclusionSF in various metal. via disk acc.

High-Mdot & High-T disk → ~stable

Single (or binary) massive star ~ 100Msun

mass is limited by photoionization feedback

(Hosokawa-san’s talk)

In zero-metal.

In solar-metal.

Low-Mdot & Low-T disk → ~stable

Single (or binary) low mass star ~1Msun

mass is limited by pre-stellar core mass


Conclusion sf in various metal via disk acc1
ConclusionSF in various metal. via disk acc.

High-Mdot & High-T disk → ~stable

Single (or binary) massive star ~ 100Msun

mass is limited by photoionization feedback

(Hosokawa-san’s talk)

In zero-metal.

In low-metal.

10-5~10-2Zsun

High-Mdot & Low-T disk → ~unstable

Low-mass stellar cluster

by disk fragmentation

In solar-metal.

Low-Mdot & Low-T disk → ~stable

Single (or binary) low mass star ~1Msun

mass is limited by pre-stellar core mass


Future work
Future work

Dynamical evolutions!!

Fragmentation, ejection, episodic accretion

Radiative hydro. simulation by Dr.Vorobyov (Vienan-U)

with our dust/metal cooling (Omukai+05)

Vorobyov&Basu10 etc.


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