Characterising exoplanetary systems with space-based Bracewell

interferometers

ARC meetingDenis Defrère

Liege, 19 February 2009

Motivations

Extrasolar planetsExozodiacal discs

− Signal: formation, evolution and architecture of planetary systems− Noise: level of exozodiacal dust around nearby MS stars

?

Pegase/FKSI Exozodiacal discs Super-Earth Conclusions

• Probing the inner region of planetary systems

• Observationnal constraints:- high angular resolution - high dynamic (1/106 to 1/1010)

Motivations

Pegase/FKSI Exozodiacal discs Super-Earth Conclusions

• 1-zodi disc 300 times brighter than Earth

• Implications for life-finding nulling interferometry missions:

Pegase/FKSI Exozodiacal discs Super-Earth Conclusions

Pegase/FKSI space-based precursors to Darwin/TPF

Mission overviewPegase/FKSI Exozodiacal discs Super-Earth Conclusions

• Pegase- Proposed in 2004 to CNES- Free-flying demonstrator

• FKSI (Fourier-Kelvin Stellar Interfer.)- GSFC mission (NASA)- Studied at the phase A level

Mission overview Instrumental specifications Peg. FKSITelescope diameter [m] 0.4 0.5Wavelength [µm] 1.5 – 6.0 3.0-8.0Baseline length [m] 40-500 12.5Spectral resolution 60 20Instrument temperature [K] 90 65RMS temp. fluctuations [K] 0.1 0.1RMS OPD error [nm] 2 2RMS pointing error [mas] 15 20

Pegase/FKSI Exozodiacal discs Super-Earth Conclusions

Mission overviewPegase/FKSI Exozodiacal discs Super-Earth Conclusions

• Common science objectives:- Spectroscopy of hot extrasolar giant

planets- Circumstellar discs- Brown dwarfs- Active galactic nuclei

Detection principle

Subtracting starlight by destructive interference

Pegase/FKSI Exozodiacal discs Super-Earth Conclusions

Pegase/FKSI Exozodiacal discs Super-Earth Conclusions

Performance for exozodiacal

disc detection

• Adapting the GENIEsim software for space-based nulling interferometers

• Detectable exozodiacal density for 4 representative Darwin targets

• FKSI more sensitive in all cases

Performance for disc detection

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Pegase/FKSI Exozodiacal discs Super-Earth Conclusions

Comparison with ground-based sites

GENIE-UT ALADDIN PEGASE FKSI

Diameter [m] 8 2 0.4 0.5

Baseline [m] 47-130 4-30 40-500 12.5

Wavelength [µm] 3.5-4.1 3.1-4.1 1.5-6 3.0-8.0

Site Cerro Paranal Dome C L2 L2

Pegase/FKSI Exozodiacal discs Super-Earth Conclusions

Comparison with ground-based sites

• Space-based instruments outperform GENIE and ALADDIN:o Pegase: by a factor 2 to 15;o FKSI: by a factor 25 to 50.

• Main advantages:o Low thermal background;o Good OPD control.

•

Pegase/FKSI Exozodiacal discs Super-Earth Conclusions

Prospects for Super-Earth

detection

Pegase/FKSI Exozodiacal discs Super-Earth Conclusions

“Super-Earth” extrasolar planets1. Main characteristics:− Between 2 and 10 Earth masses− 14 detected so far by radial velocity, microlensing or pulsar timing:

• around low-mass stars• semi-major axes range between 0.02 and 2 au

− Found likely in multiplanetary systems (80% known candidates)

2. Favorable examples:

HD40307b HD40307c HD40307d HD285968b

Planet mass [M] 4.2 6.9 9.2 8.4

Planet s-major axis [au] 0.047 0.081 0.134 0.066

Stellar spectral type K2.5V K2.5V K2.5V M2.5V

Stellar distance [pc] 13 13 13 9.4

Reference Mayor et al. 2009 Mayor et al. 2009 Mayor et al. 2009 Forveille et al. 2008

Pegase/FKSI Exozodiacal discs Super-Earth Conclusions

Detection of know Super-EarthsPegase/FKSI Exozodiacal discs Super-Earth Conclusions

• FKSI not well suited for known Super-Earths (baseline too short)

Detection of know Super-EarthsPegase/FKSI Exozodiacal discs Super-Earth Conclusions

HD40307b HD40307c HD40307d HD285968b

Planet mass [M] 4.2 6.9 9.2 8.4

Planet s-major axis [au] 0.047 0.081 0.134 0.066

Angular separation [mas] 3.6 6.2 10.3 7.1

FKSI transmission (8 µm) >0.01 0.02 0.06 0.03

FKSI modulation efficiency >0.01 0.02 0.03 0.01

Detection sensitivityPegase/FKSI Exozodiacal discs Super-Earth Conclusions

• FKSI not convenient for Super-Earths• Could detect Neptune-sized planets (SNR increases as Rp²)

GENIE: 80%ALADDIN: 35%PEGASE: 50%FKSI: 30%

• 1354 target star in the Darwin/TPF catalogue

• ALADDIN and space-based instruments complementary

Sky coveragePegase/FKSI Exozodiacal discs Super-Earth Conclusions

Pegase/FKSI Exozodiacal discs Super-Earth Conclusions

Summary and conclusions• Performance study for exozodiacal disc detection

− Space-based instruments far more sensitive− Detection achieve very quickly− FKSI: 1-zodi level achievable for all Darwin/TPF targets− Pegase: shorter baseline configuration highly recommended

• Prospects for Super-Earth exoplanet detection− FKSI not convenient to observe Super-Earth exoplanets− Can do the job for some short period Super-Earths

• Sky coverage complementary with ALADDIN