The Structure of Winds in AGB Stars

Moshe Elitzur (Kentucky)

Željko Ivezić (Princeton)

Dejan Vinković (Kentucky)

MNRAS 327, 403 (2001)

Once the sonic point is crossed…

• Radiation pressure decouples the outflow from the wind origin

• Same grains same wind structure however grains were formed!

gravityP

~dragP

~P radrad

wy

dyPQ

22

21

Wind Problem

• Radiation pressure

• Gas drag

• Gravity

tcosA2

1)y()y(

y

P

dy

dw2

22

wln)(

)w()(

)w)((

w)1(4wy1

11P

3

2/12/12

21

2/32/33122

2

11

Physical Domain

FcL

vM

<>F = (Q*/QV) V (1 + V)-0.36

Q* = <Q>B(T*)

cL

vM

Fudge factor –task for full models

Scaling

Away from boundaries, wind structure fully controlled by

Velocity Profile

Scale of v set by

222

22d

H

d cm10nn

k

r'r

1vv

V < 1: k = 2/3 (drift)

V > 1: k 0.4 (reddening)

K. Young 1995:

• v independent of L

• Mv 3.3

Drift!

Miras, low :M

Radiation pressure:

• v L1/2

• v independent of M

5.1v

3 )1(MAv

Drift Effect on Outflow

L/M 3/4V

222A

Same ndd/nH for C- and O-stars!

Drift+Reddening effect on v

• Lower – decoupling; v

• Higher – quenching; v

M

M

14/14max

14/34

6max

kmsL20v

yrML102)v(M

v = 18

• Shape V

• Flux level

SED Analysis

Zubko & Elitzur ’00

v = 0.83

Solutions by DUSTY http://www.pa.uky.edu/~moshe/dusty/

+ distance L

• L + v , 22M

W Hya

Thermal H2O Lines

• W Hya (ZE ‘00):

21 lines fitted H2O abundances

• VY CMa (Harwit & Bergin ‘02):

Same line ratios!

Hofmann et al ‘01

Vinković ‘02

Conclusions

• The “standard model” works

• Single variable –

• Dust drift – major ingredient

• Minimal = ?

22 ~ 1; why?

M

dFF1

dFF

Fc1

dFc1

dtdv

F

F

steady state: dt = (1/v)dr

F

F2

c12

dcL

dvM

drFrvdvr