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Alain Lecavelier des EtangsInstitut d’Astrophysique de Paris
Spectroscopy of extrasolar planets
atmosphere
VLST Workshop STScI Feb. 26-27, 2004
Alain Lecavelier des EtangsInstitut d’Astrophysique de Paris
Alfred Vidal-MadjarJean-Michel Désert
Roger FerletGuillaume Hébrard
(IAP, Paris)
VLST Workshop STScI Feb. 26-27, 2004
• 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
Spectroscopy of extrasolar planets atmosphere
VLST Workshop STScI Feb. 26-27, 2004
• What has been done (HST): (description of the present)
4 UV detections of the bottom and upper atmosphere of HD 209458bin 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
Spectroscopy of extrasolar planets atmosphere
VLST Workshop STScI Feb. 26-27, 2004
Transits: a powerful and sensitive method
VLST Workshop STScI Feb. 26-27, 2004
Transit of HD 209458(Charbonneau et al. 2000)
Radial velocity + Occultation depthRadial velocity + Occultation depth
Period = 3.524738 daysPeriod = 3.524738 days
Mass = 0.69 ±0.05 MMass = 0.69 ±0.05 MJupiterJupiter
Radius = 1.35 ±0.04 RRadius = 1.35 ±0.04 RJupiterJupiter
DensityDensity = 0.35 ±0.05 g/cm= 0.35 ±0.05 g/cm33
HD 209458bHD 209458b(Mazeh et al. 2000)
~0.01% accuracy
VLST Workshop STScI Feb. 26-27, 2004
HD 209458b: Detection of the atmosphere in NaI
(Charbonneau et al. 2002)
0.0232 ± 0.0057 %
VLST Workshop STScI Feb. 26-27, 2004
Search for HI Lyman (1216 Å)
1214 1215 1216 1217
Wavelength (Å)
Y (
slit
ape
rtur
e)
VLST Workshop STScI Feb. 26-27, 2004
VLST Workshop STScI Feb. 26-27, 2004
15 ±4%
Flu
x R
atio
Time (hours)
Beg
in o
f tr
ansi
t
End
of
tran
sit
• 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 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
15 ±4%
Time (hours)
Flu
x r
atio
-100 0 100 (km s-1) | | |
Wavelength (A)
Beforetransit
Duringtransit
VLST Workshop STScI Feb. 26-27, 2004
Escape rate estimateHow much for 15% absorption?
Escape rate > 1010 g/s
VLST Workshop STScI Feb. 26-27, 2004
An extended upper atmospherearound 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. 26-27, 2004
HST G140L ObservationsOct-Nov 2003
• Fig 1
VLST Workshop STScI Feb. 26-27, 2004
Terrestrial airglow
SiIII O IH I Lyman C II
Stellar spectrum
Stellar continuum
VLST Workshop STScI Feb. 26-27, 2004
Confirmation of the HI absorption
• Fig 2a
Wavelength (Å)
Out of transitIn transit
Si III
HI Lyman
~5 %
VLST Workshop STScI Feb. 26-27, 2004
Vidal-Madjar et al. 2004 (astro-ph/0401457)
Detection of Carbon and Oxygen
Wavelength (Å)
Out of TransitIn Transit
O I
C II
~13 %±4.5 %
~8 %±3.5 %
VLST Workshop STScI Feb. 26-27, 2004
ConsequenceVidal-Madjar et al. (2004 astro-ph/0401457)
• Oxygen and carbon are also present in the upper atmosphere of HD 209458b
• They are carried out by the hydrogen flow: HYDRODYNAMICAL ESCAPE (« BLOW-OFF »)
VLST Workshop STScI Feb. 26-27, 2004
• Last observations must be confirmed (2.5• Other species are likely detectable with HST
Cycle 13 proposal…
More can be done
Planets to be discovered
10m/s(present)1m/s(2003HARPS)
10-5
0.0001
0.001
0.01
0.1
1
10
100
0.01 0.1 1 10 100
SS
msini (Jup)
pulsar
m sin i
a (au)
Today ~120 planets know
COROT (2006)COROT (2006)
KEPLERKEPLER(2007/8)(2007/8)
Rad.Vel.< 2003Harps2003
VLST Workshop STScI Feb. 26-27, 2004
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. 26-27, 2004
Planets with Earth-like orbital distances
For d=1AU, Probability Transit R*/a=0.5%
~30% of known planets within 0.5-1.5 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. 26-27, 2004
Summary of detection capabilities on V≤8 stars
HST VLST Height species
FUV 4% 0.4% 10,000 km H, C, O, CO, O2
NUV 1% 0.1% 2,500 km Fe, Mg, et al.; CO, NO
Bands <0.1% <0.01% <250 km O3
Opt. 0.01% 0.001% 25 km Na, K, Li, OH (3090A)
NUV-Opt Time scan
VLST Workshop STScI Feb. 26-27, 2004
Time-scan
• HST observations used a total of ~100-200 minutes exposures during transits.
VLST gives diagnostics in few minutes exposure
• Tingress=80 (Rp/RJup) (a/1AU) ½ minutesTHD209458= 22 minutes
• Scan of the planets “weather” during the partial occultation phases (ingress, egress):
VLST Workshop STScI Feb. 26-27, 2004
Temperate Uranus(Ocean-planets)
(A. Leger 2003)
• Scale height: H = 250 (T/300K) (Rp/REarth)2 (Mp/MEarth)-1 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. 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. 26-27, 2004
This picture shows also the Earth atmosphere with emission from hydrogen and oxygen at high (HST) altitudewhere the C/O is obviously very low.
Terrestrial airglow
SiIII O IH I Lyman C II
Stellar spectrum
Stellar continuum
VLST Workshop STScI Feb. 26-27, 2004
• END
END