Alain Lecavelier des Etangs Institut d’Astrophysique de Paris

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)


• 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


• 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


Transits: a powerful and sensitive method


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


HD 209458b: Detection of the atmosphere in NaI

(Charbonneau et al. 2002)

0.0232 ± 0.0057 %


Search for HI Lyman (1216 Å)

1214 1215 1216 1217

Wavelength (Å)

Y (s

lit a

pertu

re)



15 ±4%

Flux

Rat

io

Time (hours)

Beg

in o

f tra

nsit

End

of tr

ansi

t

• 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)

Flux

ra

tio-100 0 100 (km s-1) | | |

Wavelength (A)

Beforetransit

Duringtransit


Escape rate estimateHow much for 15% absorption?

Escape rate > 1010 g/s


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)


HST G140L ObservationsOct-Nov 2003

• Fig 1


Terrestrial airglow

SiIII O IH I Lyman C II

Stellar spectrum

Stellar continuum


Confirmation of the HI absorption

• Fig 2a

Wavelength (Å)

Out of transitIn transit

Si III

HI Lyman

~5 %


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 %


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 »)


• 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


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


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


Summary of detection capabilities on V≤8 stars

HST VLST Height speciesFUV 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


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 minutes

THD209458= 22 minutes• Scan of the planets “weather” during the partial

occultation phases (ingress, egress):


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.


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)


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


• END

END

Documents

Alain Lecavelier des Etangs Institut d’Astrophysique de Paris