Dynamics in atmospheres and outflows of evolved stars Elvire De - - PowerPoint PPT Presentation

Dynamics in atmospheres and outflows of evolved stars

Elvire De Beck Wouter Vlemmings, Theo Khouri, Matthias Maercker, Hans Olofsson Department of Space, Earth and Environment, Chalmers University of Technology Onsala Space Observatory

The Dynamical Universe for All Lund Observatory, 5th - 6th February 2018

Quick intro

Surface temperature Luminosity compared to the sun

• Evolved stars in this talk


= Post-Main-Sequence Giants


• < 8 Msun


AGB: asymptotic giant branch stars

• >8 Msun


RSG: red supergiant stars


• Cool surface ~ 3000K
• Luminous ~ 100 - 100,000 Lsun
• Mass loss ~ 10-8-10-3 Msun/yr

Dynamics of AGB stars

Review: Mass loss of stars on the asymptotic giant branch Mechanisms, models and measurements Hoefner & Olofsson, 2018, A&ARv 26:1

Evolution and appearance on AGB strongly affected by range of dynamical processes

• large-scale convective flows 


>> transport of newly formed chemical elements to the surface

• stellar pulsations

>> trigger shock waves in extended stellar atmosphere


• dust grain formation in upper atmosphere 


>> acceleration through scattering/absorption and collisions with gas


• massive outflows of gas and dust

These lead to

• enrichment of ISM
• evolution from giant


to white dwarf

Dynamics of AGB stars

Observations of asymmetries and inhomogeneities

• short-lived & small-scale: photosphere and dust-forming layers
• long-lived & large-scale: circumstellar envelope

High-angular resolution observations give information on e.g. dust condensation

• location
• chemical composition
• size


“These are essential constraints for building realistic models

• f wind acceleration and

developing a predictive theory of mass loss for AGB stars, which is a crucial ingredient of stellar and galactic chemical evolution models.”

Review: Mass loss of stars on the asymptotic giant branch Mechanisms, models and measurements Hoefner & Olofsson, 2018, A&ARv 26:1

Observations: large scales

Large scales = circumstellar envelope (CSE)
 >> spherical

• entire outflow
• shells

Olofsson et al. (2000) CO (J=1-0), PdBI TT Cyg, detached shell Castro Carrizo et al. (2010) CO (J=2-1), PdBI IK Tau, normal mass loss

~17”

(~0.02pc)

Observations: large scales

Large scales = circumstellar envelope (CSE)
 >> spherical

• entire outflow
• shells

De Beck & Olofsson (2018) APEX spectral survey at 0.8-1.9 mm R Dor, normal mass loss

• main, smooth, spherical component
• up to 4 extra components in the outflow
• one at velocities >> wind expansion velocity
• shells / rings / spiral / … ?
• 20
• 10

10 20 Velocity [km s

• 1]

SiO, v=1(4-3) SiO, v=1(5-4) SiO, v=1(7-6) SiO, v=2(4-3) SiO, v=2(6-5) SiO, v=2(7-6) SiO, v=3(4-3)

• 20
• 10

10 20 Velocity [km s

• 1]

Normalised intensity

2-1 3-2 4-3 2-1 3-2 4-3

• 20 -15 -10 -5
• 20
• 10

10 20 Velocity [km s

• 1]

4-3 5-4 6-5 7-6 8-7 4-3 5-4 6-5 7-6 8-7

• 15
• 10
• 5
• 20
• 10

10 20 Velocity [km s

• 1]

Normalised intensity

65-54 67-56 55-44 56-45 54-43 44-33 45-34 65-54 67-56 55-44 56-45 54-43 44-33 45-34

5 10 15 20

• 37
• 35.5
• 34
• 32.5
• 31
• 29.5
• 28
• 26.5
• 25
• 23.5
• 22
• Dec. offset [arcsec]
• 20.5
• 19
• 17.5
• 16
• 14.5
• 13
• 11.5
• 10
• 8.5

0.5 1 1.5

• 7
• 20
• 10

10 20

• 20
• 10

10 20

• 5.5
• 4

R.A. offset [arcsec]

• 2.5
• 1

Observations: large scales

Large scales = circumstellar envelope (CSE)
 >> spherical

• entire outflow
• shells

>> not so spherical

• binary interaction

Maercker et al. (2012, 2014, 2016) R Scl, detached shell source CO(J=3-2), ALMA
 Dust-scattered stellar light, PolCor

• previously unknown binary companion


~60 AU separation

• from spiral windings:


information on changes in velocity and mass loss

• n evolutionary timescales
• Dust and gas dynamics comparable?

Observations: large scales

Large scales = circumstellar envelope (CSE)
 >> spherical

• entire outflow
• shells

>> not so spherical

• binary interaction

Maercker et al. (2012, 2014, 2016) R Scl, detached shell source CO(J=3-2), ALMA
 Dust-scattered stellar light, PolCor

• previously unknown binary companion


~60 AU separation

• from spiral windings:


information on changes in velocity and mass loss

• n evolutionary timescales
• Dust and gas dynamics comparable?

R.A. offset [arcsec]

• Dec. offset [arcsec]

−20 −10 10 20 −20 −15 −10 −5 5 10 15 20 0.2 0.4 0.6 0.8 1

• Dec. offset [arcsec]

− − − − − −

Observations: large scales

Large scales = circumstellar envelope (CSE)
 >> spherical

• entire outflow
• shells

>> not so spherical

• binary interaction
• disk

43.0 km/s

East Offset [arcsec] Offset [arcsec] 10 5 −5 −10 5 −5 Jy/beam

0.2 0.4 0.6 0.8 1 1.2 1.4 1.6

− − −

Ramstedt et al. (2014) Mira, 0.5” (~45 AU) binary separation CO(J=3-2), ALMA, “bubble” in the AGB wind Kervella et al. (2014, 2015, 2016) L2 Pup ALMA, VLT (NACO/SPHERE), edge-on disk

Observations: small scales

• Small scales
• upper atmospheric layers (warm molecular layer)


i.e. before wind acceleration

Khouri et al. (2016) CO(v=1, J=3-2), ALMA

• inverse P-Cygni profiles

indicate infall motion

• multiple epochs reflect

changes of the upper atmosphere

• temperature
• density
• motion

Observations: small scales

• Small scales
• upper atmospheric layers


i.e. before wind acceleration

• dust formation region

Khouri et al. (2016), SPHERE/ZIMPOL, R Dor

• Top


variable morphology in continuum
 = changing opacity of TiO in extended atmosphere


• Bottom


polarised light from ~annular region around central star.

• density profile steeper than constant-v wind
• upper limit for the d/g ~2×10-4 at 5.0 R,

consistent with minimum required by wind- driving models

Observations: small scales

• Small scales
• upper atmospheric layers


i.e. before wind acceleration

• dust formation region
• surface imaging

Paladini et al. (2018, Nature) π1 Gruis, VLTI/PIONIER surface granulation due to convection Vlemmings et al. (2017, Nature Astro.) W Hya, ALMA heating of the upper atmosphere due to shocks chromosphere?

Conclusions

Mass loss dominates appearance and evolution on AGB >> critical to have predictive description as input for models of

• stellar evolution
• galactic chemical evolution

>> strongly dependent on variety of dynamical processes Observations show

• asymmetries and inhomogeneities
• on large spatial scales & long timescales
• on small spatial scales & short timescales
• dust location, size, composition
• surface structure for stars other than our Sun (!)


constraining

• convection and pulsation motions
• dust growth
• wind acceleration
• mass-loss rates

and heading for a deeper understanding of the dynamics of evolved stars.

− − 5 −5

− − −

Theoretical models

surface granulation due to convection

• 600
• 400
• 200

200 400 600 y [RO

• ]

t= 0.0 d t= 28.9 d t= 57.9 d t= 86.8 d t= 112.9 d

• 600-400-200 0 200 400 600

x [RO

• ]
• 600
• 400
• 200

200 400 600 y [RO

• ]

t= 141.8 d

• 600-400-200 0 200 400 600

x [RO

• ]

t= 170.7 d

• 600-400-200 0 200 400 600

x [RO

• ]

t= 199.7 d

• 600-400-200 0 200 400 600

x [RO

• ]

t= 228.6 d

• 600-400-200 0 200 400 600

x [RO

• ]

t= 257.5 d

• 500

500 y [RO

• ]
• 500

500 y [RO

• ]
• 500

500 y [RO

• ]
• 500

500 y [RO

• ]
• 500

500 y [RO

• ]
• 500

500 x [RO

• ]
• 500

500 y [RO

• ]
• 500

500 x [RO

• ]

Freytag et al. (2017) star-in-a-box models

temperature density