characterising exoplanetary systems with space-based bracewell interferometers arc meeting denis...
TRANSCRIPT
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. FKSI
Telescope 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
.
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-Earths
Pegase/FKSI Exozodiacal discs Super-Earth Conclusions
• FKSI not well suited for known Super-Earths (baseline too short)
Detection of know Super-Earths
Pegase/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 sensitivity
Pegase/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 coverage
Pegase/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