Characterising exoplanetary systems with space-based Bracewell interferometers ARC meeting Denis 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/FKSIExozodiacal discsSuper-EarthConclusions Probing the inner region of planetary systems Observationnal constraints: - high angular resolution - high dynamic (1/10 6 to 1/10 10 )

Motivations Pegase/FKSIExozodiacal discsSuper-EarthConclusions 1-zodi disc 300 times brighter than Earth Implications for life-finding nulling interferometry missions:

Pegase/FKSIExozodiacal discsSuper-EarthConclusions Pegase/FKSI space-based precursors to Darwin/TPF

Mission overview Pegase/FKSIExozodiacal discsSuper-EarthConclusions 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 specificationsPeg.FKSI Telescope diameter [m] Wavelength [µm]1.5 – Baseline length [m] Spectral resolution6020 Instrument temperature [K]9065 RMS temp. fluctuations [K]0.1 RMS OPD error [nm]22 RMS pointing error [mas]1520 Pegase/FKSIExozodiacal discsSuper-EarthConclusions

Mission overview Pegase/FKSIExozodiacal discsSuper-EarthConclusions Common science objectives: - Spectroscopy of hot extrasolar giant planets - Circumstellar discs - Brown dwarfs - Active galactic nuclei

Detection principle Subtracting starlight by destructive interference Pegase/FKSIExozodiacal discsSuper-EarthConclusions

Detection principle Exo-planetary system Pegase/FKSIExozodiacal discsSuper-EarthConclusions

Exo-planetary system Nulling interferometer Transmission map Detection principle Pegase/FKSIExozodiacal discsSuper-EarthConclusions

Exo-planetary system Nulling interferometer Transmission map Detection principle Pegase/FKSIExozodiacal discsSuper-EarthConclusions

Exo-planetary system Nulling interferometer Transmission map Local zodiacal cloud Detection principle Pegase/FKSIExozodiacal discsSuper-EarthConclusions

Exo-planetary system Nulling interferometer Transmission map Local zodiacal cloud Exozodiacal cloud Detection principle Pegase/FKSIExozodiacal discsSuper-EarthConclusions

Pegase/FKSIExozodiacal discsSuper-EarthConclusions 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/FKSIExozodiacal discsSuper-EarthConclusions

Comparison with ground-based sites GENIE-UTALADDINPEGASEFKSI Diameter [m] Baseline [m] Wavelength [µm] SiteCerro ParanalDome CL2 Pegase/FKSIExozodiacal discsSuper-EarthConclusions

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/FKSIExozodiacal discsSuper-EarthConclusions

Prospects for Super-Earth detection Pegase/FKSIExozodiacal discsSuper-EarthConclusions

“Super-Earth” extrasolar planets 1. 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: HD40307bHD40307cHD40307dHD285968b Planet mass [M  ] Planet s-major axis [au] Stellar spectral typeK2.5V M2.5V Stellar distance [pc] ReferenceMayor et al Forveille et al Pegase/FKSIExozodiacal discsSuper-EarthConclusions

Detection of know Super-Earths Pegase/FKSIExozodiacal discsSuper-EarthConclusions FKSI not well suited for known Super-Earths (baseline too short)

Detection of know Super-Earths Pegase/FKSIExozodiacal discsSuper-EarthConclusions HD40307bHD40307cHD40307dHD285968b Planet mass [M  ] Planet s-major axis [au] Angular separation [mas] FKSI transmission (8 µm)> FKSI modulation efficiency>

Detection sensitivity Pegase/FKSIExozodiacal discsSuper-EarthConclusions FKSI not convenient for Super-Earths Could detect Neptune-sized planets (SNR increases as R p ²)

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/FKSIExozodiacal discsSuper-EarthConclusions

Pegase/FKSIExozodiacal discsSuper-EarthConclusions 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

Nulling interferometryPegaseDarwinConclusions Motivations Most detections by indirect techniques − Planetary photons not collected − Limited information on planets Direct detection difficult – High star/planet contrast (10 7 -IR and visible) – Small angular separation (0.1" for an Earth-Sun system located at 10pc) 5×10 9 7×10 6

Nulling interferometryPegaseDarwinConclusions Comparison with ground-based sites

Nulling interferometryPegaseDarwinConclusions Principles Subtracting starlight by destructive interference Transmission map b