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THE CIRCUMSTELLAR MEDIUM OF AGB STARS: A study of scattered stellar light and molecular radio line emission. PART I : A study of episodic mass loss: The detached shells of some AGB stars seen in scattered stellar light. PART II : Modelling of radio line emission

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THE CIRCUMSTELLAR MEDIUM OF AGB STARS:

A study of scattered stellar light and

molecular radio line emission

PART I : A study of episodic mass loss:

The detached shells of some AGB stars

seen in scattered stellar light

PART II : Modelling of radio line emission

from circumstellar molecules in a sample of

M-type AGB-variables

Thesis Presentation

Stockholm, 04-03-03


SETTING A BACKGROUND:

A schematic view of an AGB star


Observations of Scattered Stellar Light

* Spectroscopy

Gustafsson et.al.,1997

Paper I

F77 filter

R Scl KI line

Paper II

Stokes U

* Direct imaging

* Imaging polarimetry


Direct Imaging

Observations

- Telescopes:

ESO 3.6m

NOT

- Cameras:

EFOSC1

EFOSC2

ALFOSC

- Coronographic mask

- Filters: F59, F77

- Lyot stop

Image reduction

- Templates stars

- Data Calibration



CO maps:

CO 10

The Targets

  • - Carbon stars with detached gas shells:

  • R Scl, U Ant, TT Cyg, S Sct, U Cam

  • AGB stars with detached dust shells:

  • U Hya, R Hya, X Tra, VX Sgr

CO line profiles:


Achievements

* Feasibility of this type of observations

* The circumstellar medium of R Scl

* The circumstellar medium of U Ant


Outlook

- New data:

U Ant

S Sct

- New observations with VLT, HST


SETTING A BACKGROUND:

A schematic view of an AGB star


Circumstellar Molecules

- In all type of Circumstellar Envelopes

H2

- In Oxigen-rich Circumstellar Envelopes

CO

SiO

OH

H2O

- In Carbon-rich Circumstellar Envelopes

CO

HCN


Original sample:

1442 SRVs

Subsample:

SRVs

IRVs

Miras

S60 ≥ 2 Jy

S60 ≥ 5 Jy

IRAS [12] - [25] > 1.2

91 objects

33 objects

12 objects

47 detected in CO

22 detected in CO

12 detected in CO

12 detected in SiO

28 detected in SiO

8 detected in SiO

The Sample & Detection Rate


Goal:

CO

SiO

Mass loss rates

Gas expansion velocities

Abundances

Standard CSE envelope:

- Density law: r -2 (constant M and vexp)

- CSE inner radius: 1.0x1014 cm (~3R*)

- Turbulent velocity: 0.5 km/s

  • Radiation field: A central blackbody

    • CMB radiation at 2.7K

  • Cooling processes: Adiabatic expansion

  • Line cooling (CO,H2O,H2 )

  • Heating processes: Dust drift through gas

  • Photoelectric heating

h-parameter

The Model

Code: Montecarlo code by F. Schöier


Mass loss rates

12

0

-8.5

-5.5

IRVs

SRVs

Gas expansion velocities

25

0

20

SiO abundances

IRVs

SRVs

10-4

10-7

10-8

10-4

Achievements


Observations:

- Small sample:

Interferometric maps

- Large sample:

Multi-line spectra

Sources in the M range 10-6- 10-5 M/yr

Outlook

Models:

- CO :

Photodissociation models

Turbulent velocity

- SiO :

Dust modelling

Cooling in the inner envelope

Accelaration

Envelope size


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