Evaporation of Hot Jupiters
Observations & Models
Alfred Vidal-Madjar
Jean-Michel Désert
Guillaume Hébrard
Alain Lecavelier
(IAP, Paris)
Roger Ferlet
Institut
d’Astrophysique
Alain Lecavelier
des Etangsde Paris
Institut d’Astrophysique de Paris
Evaporation of Hot-Jupiters
Evaporation of Hot-Jupiters
HD 209458b transit
(Charbonneau et al. 2000)
Evaporation of Hot-Jupiters
Osiris
Period = 3.524738 jours
Mass = 0.69 ± 0.05 MJupiter
Occultation = 1.58 %
Radius = 1.35 ± 0.04 RJupiter
Density = 0.35 ± 0.05 g/cm3
Evaporation of Hot-Jupiters
Evaporation of Hot-Jupiters
HD 209458b:
Detection of the atmosphere in NaI
(Charbonneau et al. 2002)
0.0232 ± 0.0057 %
Evaporation of Hot-Jupiters
-100 0 100 (km s-1)
|
|
|
HI Lyman α
Flux (erg cm-2 s-1 Å-1)
Before
transit
During
transit
Wavelength (Å)
Evaporation of Hot-Jupiters
End of transit
Begin of transit
Flux Ratio
15 ±4%
(~ 4 σ)
Time (hours)
Evaporation of Hot-Jupiters
Flux ratio
2 constraints:
15
±4%
-100
|
0
|
100 (km s-1)
|
Before
transit
Vidal-Madjar et al.
Nature, 2003, 422
143
During
transit
Time (hours)
Wavelength (A)
• HD209458b (1.35 RJupiter = 96,500 km)
→ 1.6 % absorption
Roche lobe (2.7 Rplanet = 3.6 RJupiter)
→ 10 % absorption
Hydrogen: 15 % absorption → 3.2 Rplanet= 4.3 RJupiter = 300 000 km
→ Beyond the Roche lobe Î Hydrogen is escaping
• Absorption width: Vred ≤ –100 km/s
Vesc = 54 km/s
→ Beyond escape velocity Î Hydrogen is escaping
ÎThe planet is evaporating
Escape rate estimate
How much for 15% absorption?
Particle simulation
• Radiation pressure: β = 0.7
• Star and planet gravity are taken into account
• Free parameters:
– HI volume density at the exobase:
(at r ~ 0.5xRRoche : 2 x 105 cm-3)
– Life time of HI: few hours (~ 6 h)
→ Escape rate > 1010 g/s
Evaporation of Hot-Jupiters
Escape rate estimate
How much for 15% absorption?
Evaporation of Hot-Jupiters
Flux Ratio
Escape rate > 1010 g/s
Nature,
=> Taux
d’évaporation
> 1010 g s-1
Nature, 2003, 422, 143
Time (hours)
Evaporation of Hot-Jupiters
STIS G140L, low resolution observations
Oct-Nov 2003
• Fig Lyman
1
α
Evaporation of Hot-Jupiters
Terrestrial airglow
SiIII
H I Lyman α
OI
C II
Confirmation of the HI absorption
HI Lyman α
Out of transit
• Fig 2a
In transit
Si III
~5%
Wavelength (Å)
Evaporation of Hot-Jupiters
Detection of Carbon and Oxygen
Out of Transit
In Transit
C II
OI
Vidal-Madjar et al. 2004 (astro-ph/0401457)
~ 13 %
~8%
± 4.5 %
± 3.5 %
Wavelength (Å)
Evaporation of Hot-Jupiters
Consequences
(Vidal-Madjar et al. 2004 ApJ 604, L69)
•
Oxygen and carbon are also present in the upper
atmosphere of HD 209458b
•
They are carried away by the hydrogen flow
at least with a velocity of about V > 10 km/s
(~ sound speed)
Î HYDRODYNAMIC ESCAPE
(« BLOW-OFF »)
Evaporation of Hot-Jupiters
Other consequences
• Presence of OI*, OI** Î n ≈ 106 cm -3 at RRoche
• n = τ/(σ.L) (L~3 105 km) Î n ≈ 106 cm -3 at RRoche
• Escape rate:
~ n.S.V
where S is the surface of the Roche lobe (RRoche= 3.6 RJup)
V is the H, O and C atoms velocity at the Roche lobe level (V > 10 km/s)
Escape rate > 1.3 x 1010 g/s !!!
Evaporation of Hot-Jupiters
Models of the atmospheric
escape
Two important hypothesis:
• Temperature of the upper atmosphere: Tup ≠ Teff
Note that Tup(Jupiter) ~1000 K is not explained…
• Tidal forces from the close-by parent star
NB: Burrows & Lunine, Nature 378, 333 (1995)
ÎEscape(H2+,H+,HI) = 1010 g s-1
Evaporation of Hot-Jupiters
Le Roche
Lobe de
Roche
Lobe
• Lobe de Roche 1D
Evaporation of Hot-Jupiters
Escape through the exobase
Evaporation of Hot-Jupiters
Escape rate
(Lecavelier et al., 2004, A&A, 418, L1)
-1
-1))
Log
escape
rate
(g
s
Log10
escape
rate
(g
s
10
W
Evaporation > 1010 g s-1
Evaporation of Hot-Jupiters
ces
r
o
f
l
a
ith tid
et
n
a
l
p
d
Isolate
Temperature
of the upper atmosphere
Hypothesis:
Heating = UV (Lyα) + EUV
Cooling
= Thermal Conduction
+ Collisional excitation of HI levels
+ Collisional ionisation
+ Escape
Evaporation ofDistance
Hot-Jupiters
Orbital
(AU)
Log10 escape rate (g s-1)
Escape Rate
c es
r
o
f
l
a
id
t
h
t
i
W
et
n
a
l
p
d
Isolate
Evaporation of Hot-Jupiters
Planets‘ Life Time (log10 t/years)
Planet Mass (M Jupiter)
« Evaporation-modified » planets.
Evaporation
of Hot-Jupiters(AU)
Orbital
Distance