1. Spectroscopy of extrasolar planets atmosphere
Alain Lecavelier des Etangs
Institut d’Astrophysique de Paris

2. Alfred Vidal-Madjar Jean-Michel Désert Roger Ferlet Guillaume Hébrard (IAP, Paris)
Alain Lecavelier des Etangs
Institut d’Astrophysique de Paris
VLST Workshop STScI Feb , 2004

3. Future is difficult to predict
Spectroscopy of extrasolar planets atmosphere
Future is difficult to predict
In 1994, “When will the first extrasolar planet detected ? ” answers: 2000, 2010…
1 year ago: detection of OI: “not within the current capabilities”
Prediction: Future is impossible to predict
VLST Workshop STScI Feb , 2004

4. With a VLST: (extrapolation to the future from the present)
Spectroscopy of extrasolar planets atmosphere
What has been done (HST): (description of the present) 4 UV detections of the bottom and upper atmosphere of HD b in space, in the UV-optical wavelength range.
With a VLST: (extrapolation to the future from the present)
Large sample of extrasolar planets
Detailed view of planets around nearby stars
Toward Earth and Ocean-like planets
VLST Workshop STScI Feb , 2004

5. VLST Workshop STScI Feb. 26-27, 2004
Transits: a powerful and sensitive method
VLST Workshop STScI Feb , 2004

6. Transit of HD 209458 (Charbonneau et al. 2000)
VLST Workshop STScI Feb , 2004

7. Radial velocity + Occultation depth
HD b
(Mazeh et al. 2000)
Period = days
Mass = 0.69 ±0.05 MJupiter
Radius = 1.35 ±0.04 RJupiter
Density = 0.35 ±0.05 g/cm3

8. ~0.01% accuracy

9. VLST Workshop STScI Feb. 26-27, 2004
HD b: Detection of the atmosphere in NaI (Charbonneau et al. 2002)
± %
VLST Workshop STScI Feb , 2004

10. Search for HI Lyman a (1216 Å)
Y (slit aperture)
1214
1215
1216
1217
Wavelength (Å)
VLST Workshop STScI Feb , 2004

11. VLST Workshop STScI Feb. 26-27, 2004

12. VLST Workshop STScI Feb. 26-27, 2004
15 ±4%
Flux Ratio
Time (hours)
Begin of transit
End of transit
VLST Workshop STScI Feb , 2004

13. The planet is evaporating
15 ±4%
Time (hours)
Flux ratio
(km s-1)
| | |
Wavelength (A)
Before transit
During transit
HD209458b (1.35 RJupiter = 96,500 km) → 1.6 % absorption
Roche Lobe (2.7 Rplanet = 3.6 RJupiter) → 10 % absorption
Hydrogen: 15 % absorption → Rplanet= 4.3 RJupiter = km
→ Beyond the Roche Lobe  Hydrogen is escaping
Absorption width: –130 km/s to 100 km/s
Vesc = 54 km/s
→ Beyond escape velocity  Hydrogen is escaping
The planet is evaporating

14. Escape rate estimate How much for 15% absorption?
VLST Workshop STScI Feb , 2004

15. Escape rate > 1010 g/s

16. An extended upper atmosphere around the extrasolar planet HD209458b
A. Vidal-Madjar (IAP)
A. Lecavelier des Étangs (IAP)
J.-M. Désert (IAP)
G. E. Ballester (Univ. Arizona)
R. Ferlet (IAP)
G. Hébrard (IAP)
M. Mayor (Obs. Genève)
Nature 422, 143 (2003)
VLST Workshop STScI Feb , 2004

17. HST G140L Observations Oct-Nov 2003
Fig 1
VLST Workshop STScI Feb , 2004

18. VLST Workshop STScI Feb. 26-27, 2004
Terrestrial airglow
Stellar spectrum
SiIII
H I Lyman a
O I
C II
Stellar continuum
VLST Workshop STScI Feb , 2004

19. Confirmation of the HI absorption
HI Lyman a
Fig 2a
Out of transit
In transit
Si III
~5 %
Wavelength (Å)
VLST Workshop STScI Feb , 2004

20. Detection of Carbon and Oxygen
Vidal-Madjar et al (astro-ph/ )
Detection of Carbon and Oxygen
Out of Transit
C II
In Transit
O I
~13 %
±4.5 %
~8 %
±3.5 %
Wavelength (Å)
VLST Workshop STScI Feb , 2004

21. Consequence Vidal-Madjar et al. (2004 astro-ph/0401457)
Oxygen and carbon are also present in the upper atmosphere of HD b
They are carried out by the hydrogen flow:  HYDRODYNAMICAL ESCAPE (« BLOW-OFF »)
VLST Workshop STScI Feb , 2004

22. VLST Workshop STScI Feb. 26-27, 2004
More can be done
Last observations must be confirmed (2.5s)
Other species are likely detectable with HST Cycle 13 proposal…
VLST Workshop STScI Feb , 2004

23. Planets to be discovered
Today ~120 planets know
Rad.Vel. < 2003
10m/s
(present)
1m/s
(2003
HARPS)
KEPLER (2007/8)
Harps 2003
COROT (2006)

24. A large number of targets for the VLST
≥7% planet / star
15% « Hot Jupiter » / planet  1% « Hot Jupiter » / star
10% transiting planet / « Hot Jupiter »  0.1% transit / star
10,000 G stars (V≤8)  10 « Hot Jupiter » transits on stars V≤8
85,000 G stars (V≤10)  85 transits on V≤10
300,000 G stars (V≤12)  300 transits on V≤12
VLST Workshop STScI Feb , 2004

25. Planets with Earth-like orbital distances
For d=1AU, Probability Transit  R*/a=0.5%
~30% of known planets within AU
0.15% 1AU-transiting planet per planetary system
~30 transiting planet on Earth-like orbit around a G-type star V≤12
(For giant planets only…)
IF 25% low-mass planet/star ~30 transiting low-mass planet on Earth-like orbit around a G-type star V≤10
VLST Workshop STScI Feb , 2004

26. Summary of detection capabilities on V≤8 stars
HST VLST Height species
FUV % % 10,000 km H, C, O, CO, O2
NUV % % 2,500 km Fe, Mg, et al.; CO, NO
Bands <0.1% <0.01% <250 km O3
Opt % % km Na, K, Li, OH (3090A)
NUV-Opt Time scan
VLST Workshop STScI Feb , 2004

27. VLST Workshop STScI Feb. 26-27, 2004
Time-scan
HST observations used a total of ~ minutes exposures during transits.
 VLST gives diagnostics in few minutes exposure
Tingress=80 (Rp/RJup) (a/1AU) ½ minutes THD209458= 22 minutes
Scan of the planets “weather” during the partial occultation phases (ingress, egress):
VLST Workshop STScI Feb , 2004

28. Temperate Uranus (Ocean-planets) (A. Leger 2003)
Scale height: H = 250 (T/300K) (Rp/REarth)2 (Mp/MEarth)-1 m km  HO2 =8 km on the Earth
Uranus parameter (Rp=4REarth , Mp=15MEarth)  same scale height: HO2 =8 km  Expected occultation depth ~0.001% … Likely detectable on broad-bands.
VLST Workshop STScI Feb , 2004

29. VLST Workshop STScI Feb. 26-27, 2004
Scientific goals
Structures of the atmosphere of extra-solar planets (composition, dust/clouds/haze content, “weather”).
Interaction between planets and stars
Evolution of planets atmosphere (escape, fate of remaining core..)
Probe of new kinds of planets
(temperate Uranus, evaporation-modified hot-Jupiters)
Life ? (improve our knowledge of habitable planets)
VLST Workshop STScI Feb , 2004

30. VLST Workshop STScI Feb. 26-27, 2004
This picture shows also the Earth atmosphere
with emission from hydrogen and oxygen at high (HST) altitude
where the C/O is obviously very low.
Terrestrial airglow
Stellar spectrum
SiIII
H I Lyman a
O I
C II
Stellar continuum
VLST Workshop STScI Feb , 2004

31. VLST Workshop STScI Feb. 26-27, 2004
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VLST Workshop STScI Feb , 2004