The document summarizes observations and modeling of HI in circumstellar envelopes around asymptotic giant branch (AGB) stars. It discusses using HI observations to study the stellar winds and surrounding material due to HI's high velocity resolution and abundance. As a case study, it examines observations of the AGB star Y CVn using CO lines, dust continuum, and HI to determine properties of its circumstellar shell like expansion velocity and distance from the star. Modeling is then used to fit the observational data and learn about the shell.

1. HI in circumstellar envelopes around AGB stars:
Observations and modelling
Libert Y.1 , Le Bertre T.1 , G´rard E.2
e
1 LERMA, Observatoire de Paris
2 GEPI, Observatoire de Paris
December 14, 2007
Libert Y.1 , Le Bertre T.1 , G´rard E.2 ( 1 LERMA, Observatoire de Paris 2 GEPI, Observatoire 14, Paris )
e CfA R & G Lunch Talk December de 2007 1 / 24

2. Introduction
1
HR diagram
The mass-loss process
HI observations
1
The key aspects
Why HI ?
A favorable case: Y CVn
2
Properties of Y CVn
Observations
3
CO observations
dust continuum observations
Neutral Hydrogen observations
results
4
Direct results
Modelling
Conclusions & Prospects
5
Libert Y.1 , Le Bertre T.1 , G´rard E.2 ( 1 LERMA, Observatoire de Paris 2 GEPI, Observatoire 14, Paris )
e CfA R & G Lunch Talk December de 2007 2 / 24

3. AGB in HR diagram
Libert Y.1 , Le Bertre T.1 , G´rard E.2 ( 1 LERMA, Observatoire de Paris 2 GEPI, Observatoire 14, Paris )
e CfA R & G Lunch Talk December de 2007 3 / 24

4. The mass-loss process
So considerable that it can govern the evolution of the star
∼ 1-5 M → ∼ 0.6-0.8 M
Produces C, O, He, ... + s-elements (neutron capture)
Important contribution to the Galactic composition
⇒ Important clues for stellar & interstellar physics
Libert Y.1 , Le Bertre T.1 , G´rard E.2 ( 1 LERMA, Observatoire de Paris 2 GEPI, Observatoire 14, Paris )
e CfA R & G Lunch Talk December de 2007 4 / 24

5. The mass-loss process
So considerable that it can govern the evolution of the star
∼ 1-5 M → ∼ 0.6-0.8 M
Produces C, O, He, ... + s-elements (neutron capture)
Important contribution to the Galactic composition
⇒ Important clues for stellar & interstellar physics
Libert Y.1 , Le Bertre T.1 , G´rard E.2 ( 1 LERMA, Observatoire de Paris 2 GEPI, Observatoire 14, Paris )
e CfA R & G Lunch Talk December de 2007 4 / 24

6. The mass-loss process
So considerable that it can govern the evolution of the star
∼ 1-5 M → ∼ 0.6-0.8 M
Produces C, O, He, ... + s-elements (neutron capture)
Important contribution to the Galactic composition
⇒ Important clues for stellar & interstellar physics
Libert Y.1 , Le Bertre T.1 , G´rard E.2 ( 1 LERMA, Observatoire de Paris 2 GEPI, Observatoire 14, Paris )
e CfA R & G Lunch Talk December de 2007 4 / 24

7. The mass-loss process
So considerable that it can govern the evolution of the star
∼ 1-5 M → ∼ 0.6-0.8 M
Produces C, O, He, ... + s-elements (neutron capture)
Important contribution to the Galactic composition
⇒ Important clues for stellar & interstellar physics
Libert Y.1 , Le Bertre T.1 , G´rard E.2 ( 1 LERMA, Observatoire de Paris 2 GEPI, Observatoire 14, Paris )
e CfA R & G Lunch Talk December de 2007 4 / 24

8. ibert Y.1 , Le Bertre T.1 , G´rard E.2 ( 1 LERMA, Observatoire de Paris 2 GEPI, Observatoire 14, Paris )
e CfA R & G Lunch Talk December de 2007 5 / 24

9. The key aspects
Produce an accurate set of data for spectral and spatial information
Use a physical model to fit the line profile
Access to the properties of the stellar wind and the surrounding local
matter
Libert Y.1 , Le Bertre T.1 , G´rard E.2 ( 1 LERMA, Observatoire de Paris 2 GEPI, Observatoire 14, Paris )
e CfA R & G Lunch Talk December de 2007 6 / 24

10. Why HI observations ?
High velocity resolution (∼ 0.08 km.s−1 @ 21
cm)
70 % of the mass of the object
Molecules photodissociated near the centre (∼
1016 cm depending on the mass-loss rate)
For Teff > 2500 K : H mainly atomic
(Glassgold & Huggins 1983)
Flux ∝ Mass :
MHI = 2.37 10−7 × D 2 (pc) × Stot
Circumstellar HI shielded by interstellar HI
⇒ Probe the furthest part of a
Circumstellar Shell (CS)
Libert Y.1 , Le Bertre T.1 , G´rard E.2 ( 1 LERMA, Observatoire de Paris 2 GEPI, Observatoire 14, Paris )
e CfA R & G Lunch Talk December de 2007 7 / 24

11. The NRT beam shape
Libert Y.1 , Le Bertre T.1 , G´rard E.2 ( 1 LERMA, Observatoire de Paris 2 GEPI, Observatoire 14, Paris )
e CfA R & G Lunch Talk December de 2007 8 / 24

12. The NRT beam shape
4 in RA
FWHM = 0.88 λ =⇒
L
22 in Dec
Libert Y.1 , Le Bertre T.1 , G´rard E.2 ( 1 LERMA, Observatoire de Paris 2 GEPI, Observatoire 14, Paris )
e CfA R & G Lunch Talk December de 2007 8 / 24

13. A favorable case: Y CVn
Distance: ∼ 218±35 pc (Hipparcos parallax: 4.59±0.73 mas)
Galactic coordinates
Radial velocity: 21 km.s−1
Effective temperature: 2700 K
l=126◦
b=+72◦
Libert Y.1 , Le Bertre T.1 , G´rard E.2 ( 1 LERMA, Observatoire de Paris 2 GEPI, Observatoire 14, Paris )
e CfA R & G Lunch Talk December de 2007 9 / 24

14. A favorable case: Y CVn
Distance: ∼ 218±35 pc (Hipparcos parallax: 4.59±0.73 mas)
Galactic coordinates
Radial velocity: 21 km.s−1
Effective temperature: 2700 K
l=126◦
b=+72◦
Libert Y.1 , Le Bertre T.1 , G´rard E.2 ( 1 LERMA, Observatoire de Paris 2 GEPI, Observatoire 14, Paris )
e CfA R & G Lunch Talk December de 2007 9 / 24

15. A favorable case: Y CVn
Distance: ∼ 218±35 pc (Hipparcos parallax: 4.59±0.73 mas)
Galactic coordinates
Radial velocity: 21 km.s−1
Effective temperature: 2700 K
l=126◦
b=+72◦
Libert Y.1 , Le Bertre T.1 , G´rard E.2 ( 1 LERMA, Observatoire de Paris 2 GEPI, Observatoire 14, Paris )
e CfA R & G Lunch Talk December de 2007 9 / 24

16. A favorable case: Y CVn
Distance: ∼ 218±35 pc (Hipparcos parallax: 4.59±0.73 mas)
Galactic coordinates
Radial velocity: 21 km.s−1
Effective temperature: 2700 K
l=126◦
b=+72◦
Libert Y.1 , Le Bertre T.1 , G´rard E.2 ( 1 LERMA, Observatoire de Paris 2 GEPI, Observatoire 14, Paris )
e CfA R & G Lunch Talk December de 2007 9 / 24

17. Jy
ibert Y.1 , Le Bertre T.1 , G´rard E.2 ( 1 LERMA, Observatoire de Paris 2 GEPI, Observatoire de 2007 )
e CfA R & G Lunch Talk December 14, Paris 10 / 24

18. Observations in the CO lines
Plateau de Bure, 30m IRAM (CO 2→1 & CO 1→0)
CSO Mauna Kea, Hawaii (CO 2→1 & CO 3→2)
...
Models are used to deduce several properties of the CS, with several input
parameters such as:
The envelope expansion velocity
The distance of the star
The main beam temperature
The fractional CO abundance
˙ ∼ 1 10−7 M .yr−1 ; rCO ∼ 0.9 1017 cm ≡ 3 10−2 pc
⇒M
Libert Y.1 , Le Bertre T.1 , G´rard E.2 ( 1 LERMA, Observatoire de Paris 2 GEPI, Observatoire de 2007 )
e CfA R & G Lunch Talk December 14, Paris 11 / 24

19. Size ( ) Vexp VLSR Flux
(km.s−1 ) (km.s−1 )
() (Jy)
12 CO (1→0) 12.8 9.7 19.6 6.4
12 CO (2→1) 8.8 7.8 20.7 24.1
Libert Y.1 , Le Bertre T.1 , G´rard E.2 ( 1 LERMA, Observatoire de Paris 2 GEPI, Observatoire de 2007 )
e CfA R & G Lunch Talk December 14, Paris 12 / 24

20. Size ( ) Vexp VLSR Flux
(km.s−1 ) (km.s−1 )
() (Jy)
12 CO (1→0) 12.8 9.7 19.6 6.4
12 CO (2→1) 8.8 7.8 20.7 24.1
Neri et al. (1998 A&AS, 130,1)
ibert Y.1 , Le Bertre T.1 , G´rard E.2 ( 1 LERMA, Observatoire de Paris 2 GEPI, Observatoire de 2007 )
e CfA R & G Lunch Talk December 14, Paris 12 / 24

21. Observations in the dust continuum
IRAS results @ 60 and 100 µm (Young et al. 1993a & b)
ISO results @ 90 and 160 µm (Izumiura et al. 1996)
N↑ W
→
Y CVn @ 90 µm by ISOPHOT. The field is 8.3 ×34.8
Libert Y.1 , Le Bertre T.1 , G´rard E.2 ( 1 LERMA, Observatoire de Paris 2 GEPI, Observatoire de 2007 )
e CfA R & G Lunch Talk December 14, Paris 13 / 24

22. HI observations
Libert Y., Le Bertre T., G´rard E., 2007, MNRAS, 381, 1161
e
→ quasi-gaussian narrow component (comp. 1) centered at 20.5 km.s−1
FWHM : 3.8 km.s−1
→ Pedestal (comp.2) centered at 21.1 km.s−1 Half width : 7.8 km.s−1
Libert Y.1 , Le Bertre T.1 , G´rard E.2 ( 1 LERMA, Observatoire de Paris 2 GEPI, Observatoire de 2007 )
e CfA R & G Lunch Talk December 14, Paris 14 / 24

23. (CO spectrum: Knapp G.R., Young K., et al., 1998, ApJS, 117, 209)
Libert Y.1 , Le Bertre T.1 , G´rard E.2 ( 1 LERMA, Observatoire de Paris 2 GEPI, Observatoire de 2007 )
e CfA R & G Lunch Talk December 14, Paris 15 / 24

24. Step in RA:
1 beam (4 )
Step in Dec:
1/2 beam (11 )
ibert Y.1 , Le Bertre T.1 , G´rard E.2 ( 1 LERMA, Observatoire de Paris 2 GEPI, Observatoire de 2007 )
e CfA R & G Lunch Talk December 14, Paris 16 / 24

25. Direct results
Factor of 4 in velocity between Comp. 1 & Comp. 2
But: supersonic wind in the freely expanding zone
⇒ shock
From an adiabatic shock:
v1 1 3µmH 2
∼ and T1 ∼ v0 ∼ 1800K
v0 4 16k
But: from the HI profile:
FWHM(km.s −1 ) = 0.214 T (K )
⇒ Mean temperature 210 K
Empirical temperature profile (to be adjusted with the observations):
T r
log = a log
T1 r1
Libert Y.1 , Le Bertre T.1 , G´rard E.2 ( 1 LERMA, Observatoire de Paris 2 GEPI, Observatoire de 2007 )
e CfA R & G Lunch Talk December 14, Paris 17 / 24

26. Direct results
Factor of 4 in velocity between Comp. 1 & Comp. 2
But: supersonic wind in the freely expanding zone
⇒ shock
From an adiabatic shock:
v1 1 3µmH 2
∼ and T1 ∼ v0 ∼ 1800K
v0 4 16k
But: from the HI profile:
FWHM(km.s −1 ) = 0.214 T (K )
⇒ Mean temperature 210 K
Empirical temperature profile (to be adjusted with the observations):
T r
log = a log
T1 r1
Libert Y.1 , Le Bertre T.1 , G´rard E.2 ( 1 LERMA, Observatoire de Paris 2 GEPI, Observatoire de 2007 )
e CfA R & G Lunch Talk December 14, Paris 17 / 24

27. Direct results
Factor of 4 in velocity between Comp. 1 & Comp. 2
But: supersonic wind in the freely expanding zone
⇒ shock
From an adiabatic shock:
v1 1 3µmH 2
∼ and T1 ∼ v0 ∼ 1800K
v0 4 16k
But: from the HI profile:
FWHM(km.s −1 ) = 0.214 T (K )
⇒ Mean temperature 210 K
Empirical temperature profile (to be adjusted with the observations):
T r
log = a log
T1 r1
Libert Y.1 , Le Bertre T.1 , G´rard E.2 ( 1 LERMA, Observatoire de Paris 2 GEPI, Observatoire de 2007 )
e CfA R & G Lunch Talk December 14, Paris 17 / 24

28. Direct results
Factor of 4 in velocity between Comp. 1 & Comp. 2
But: supersonic wind in the freely expanding zone
⇒ shock
From an adiabatic shock:
v1 1 3µmH 2
∼ and T1 ∼ v0 ∼ 1800K
v0 4 16k
But: from the HI profile:
FWHM(km.s −1 ) = 0.214 T (K )
⇒ Mean temperature 210 K
Empirical temperature profile (to be adjusted with the observations):
T r
log = a log
T1 r1
Libert Y.1 , Le Bertre T.1 , G´rard E.2 ( 1 LERMA, Observatoire de Paris 2 GEPI, Observatoire de 2007 )
e CfA R & G Lunch Talk December 14, Paris 17 / 24

29. Direct results
Factor of 4 in velocity between Comp. 1 & Comp. 2
But: supersonic wind in the freely expanding zone
⇒ shock
From an adiabatic shock:
v1 1 3µmH 2
∼ and T1 ∼ v0 ∼ 1800K
v0 4 16k
But: from the HI profile:
FWHM(km.s −1 ) = 0.214 T (K )
⇒ Mean temperature 210 K
Empirical temperature profile (to be adjusted with the observations):
T r
log = a log
T1 r1
ibert Y.1 , Le Bertre T.1 , G´rard E.2 ( 1 LERMA, Observatoire de Paris 2 GEPI, Observatoire de 2007 )
e CfA R & G Lunch Talk December 14, Paris 17 / 24

30. Modelling HI emission
Constant mass-loss rate
Spherical symmetry
Ideal gas
Stationary
Constant velocity in the free expanding zone ( → r1 )
∼ 8 km.s−1
Libert Y.1 , Le Bertre T.1 , G´rard E.2 ( 1 LERMA, Observatoire de Paris 2 GEPI, Observatoire de 2007 )
e CfA R & G Lunch Talk December 14, Paris 18 / 24

31. Results
∼ 1 km.s−1 redshift between modeled pedestal and that from the
observations
→ Motion of the star with respect to the surrounding matter
Possibly related to the East-West asymmetry
Libert Y.1 , Le Bertre T.1 , G´rard E.2 ( 1 LERMA, Observatoire de Paris 2 GEPI, Observatoire de 2007 )
e CfA R & G Lunch Talk December 14, Paris 19 / 24

32. Results (Cont I)
Libert Y.1 , Le Bertre T.1 , G´rard E.2 ( 1 LERMA, Observatoire de Paris 2 GEPI, Observatoire de 2007 )
e CfA R & G Lunch Talk December 14, Paris 20 / 24

33. Results (Cont II)
Libert Y.1 , Le Bertre T.1 , G´rard E.2 ( 1 LERMA, Observatoire de Paris 2 GEPI, Observatoire de 2007 )
e CfA R & G Lunch Talk December 14, Paris 21 / 24

34. Results (Cont III)
Constant mass-loss rate:
∼ 1 10−7 M yr−1
Age: ∼ 4.5 105 yr
Libert Y.1 , Le Bertre T.1 , G´rard E.2 ( 1 LERMA, Observatoire de Paris 2 GEPI, Observatoire de 2007 )
e CfA R & G Lunch Talk December 14, Paris 22 / 24

35. Conclusions & Prospects
Mass-loss rate constant over 5 105 years
Velocity profile does not correspond to a brief and intense mass-loss
event
Feature dominated by the narrow component
Ideal tools for studying ISM with different physical conditions and in
different sites using tenth of other red giants
High spatial and spectral resolution needed (wind slow and slowed
down)
⇒ Observations obtained with the VLA (4 other objects) with Lynn
D. Matthews & Mark J. Reid (work in progress)
Libert Y.1 , Le Bertre T.1 , G´rard E.2 ( 1 LERMA, Observatoire de Paris 2 GEPI, Observatoire de 2007 )
e CfA R & G Lunch Talk December 14, Paris 23 / 24

36. Conclusions & Prospects
Mass-loss rate constant over 5 105 years
Velocity profile does not correspond to a brief and intense mass-loss
event
Feature dominated by the narrow component
Ideal tools for studying ISM with different physical conditions and in
different sites using tenth of other red giants
High spatial and spectral resolution needed (wind slow and slowed
down)
⇒ Observations obtained with the VLA (4 other objects) with Lynn
D. Matthews & Mark J. Reid (work in progress)
Libert Y.1 , Le Bertre T.1 , G´rard E.2 ( 1 LERMA, Observatoire de Paris 2 GEPI, Observatoire de 2007 )
e CfA R & G Lunch Talk December 14, Paris 23 / 24

37. Conclusions & Prospects
Mass-loss rate constant over 5 105 years
Velocity profile does not correspond to a brief and intense mass-loss
event
Feature dominated by the narrow component
Ideal tools for studying ISM with different physical conditions and in
different sites using tenth of other red giants
High spatial and spectral resolution needed (wind slow and slowed
down)
⇒ Observations obtained with the VLA (4 other objects) with Lynn
D. Matthews & Mark J. Reid (work in progress)
Libert Y.1 , Le Bertre T.1 , G´rard E.2 ( 1 LERMA, Observatoire de Paris 2 GEPI, Observatoire de 2007 )
e CfA R & G Lunch Talk December 14, Paris 23 / 24

38. Conclusions & Prospects
Mass-loss rate constant over 5 105 years
Velocity profile does not correspond to a brief and intense mass-loss
event
Feature dominated by the narrow component
Ideal tools for studying ISM with different physical conditions and in
different sites using tenth of other red giants
High spatial and spectral resolution needed (wind slow and slowed
down)
⇒ Observations obtained with the VLA (4 other objects) with Lynn
D. Matthews & Mark J. Reid (work in progress)
Libert Y.1 , Le Bertre T.1 , G´rard E.2 ( 1 LERMA, Observatoire de Paris 2 GEPI, Observatoire de 2007 )
e CfA R & G Lunch Talk December 14, Paris 23 / 24

39. Conclusions & Prospects
Mass-loss rate constant over 5 105 years
Velocity profile does not correspond to a brief and intense mass-loss
event
Feature dominated by the narrow component
Ideal tools for studying ISM with different physical conditions and in
different sites using tenth of other red giants
High spatial and spectral resolution needed (wind slow and slowed
down)
⇒ Observations obtained with the VLA (4 other objects) with Lynn
D. Matthews & Mark J. Reid (work in progress)
Libert Y.1 , Le Bertre T.1 , G´rard E.2 ( 1 LERMA, Observatoire de Paris 2 GEPI, Observatoire de 2007 )
e CfA R & G Lunch Talk December 14, Paris 23 / 24

40. Conclusions & Prospects
Mass-loss rate constant over 5 105 years
Velocity profile does not correspond to a brief and intense mass-loss
event
Feature dominated by the narrow component
Ideal tools for studying ISM with different physical conditions and in
different sites using tenth of other red giants
High spatial and spectral resolution needed (wind slow and slowed
down)
⇒ Observations obtained with the VLA (4 other objects) with Lynn
D. Matthews & Mark J. Reid (work in progress)
Libert Y.1 , Le Bertre T.1 , G´rard E.2 ( 1 LERMA, Observatoire de Paris 2 GEPI, Observatoire de 2007 )
e CfA R & G Lunch Talk December 14, Paris 23 / 24

41. Merci !