Impact of Multi-Planet Systems on Exoplanet Searches

Transcription

1 Impact of Multi-Planet Systems on Exoplanet Searches Eric B. Ford University of Florida Towards Other Earths: Perspectives and Limitations in the ELT Era Porto, Portugal October 21, 2009

2 Multi-Planet Systems are Common a (AU) Wright et al. (2008)

3 Semi-major Axis Distribution Wright et al. (2008)

4 Architecture of Multi-Planet Systems Multiple Planet Systems: ~34 (+3 in Porto) Hierarchical (No Significant Interactions) Secular Evolution (Insignificant short-term interactions) History of eccentricity & inclination excitation If one is tidal evolving, can probe planet structure Mean Motion Resonances (short & long-term interactions) Evidence for convergent migration Abundance of different MMRs can probe: Migration rates Eccentricity at time of migration Significant of turbulence Relative importance of migration via gas disk versus planetessimal disk

5 What Determines Final Orbits? 11 GLS Difference in architectures of systems with: Giant planets only? Low-mass planets only? Both giant & low-mass planets? Illustration by E. Chiang

6 Architecture of Low-mass Systems? If formation of multiple low-mass planets and slow, smooth migration are common, then many planets enter MMRs Cresswell & Nelson 2006

7 Direct Imaging Good: Count the Planets (if sufficiently distant & high contrast) Fabrycky & Murray-Clay 2009 Bad: Precise orbits will require patience Stability can provide useful orbital constraints (e.g., HR 8799 Fabrycky & Murray-Clay 2009; Gozdziewski & Migaszewski 2009) But be cautious for young systems (e.g., Scharf & Menou 2009; Veras & Ford 2009; Dodson-Robinson et al. 2009) HR 8799 b, c & d Marois et al. 2009

8 Microlensing Good: Sensitivity to low-mass planets Signal from each planet temporally compact Bad: Limited orbital information May miss planets essential for understanding architecture of the system (either due to time coverage or geometry) OGLE 2006-BLG-109L b & c Gaudi et al. 2008

9 Good: Dynamical Detections: Doppler, Astrometry & Timing Precise orbital constraints Bad: Low-mass planets challenging Long-period planets challenging Signal complexity increases with more planets (especially if densely packed system) When to stop adding planets? Bayesian model comparison (Ford & Gregory 2007)

10 Good: Dynamical Detections: Doppler, Astrometry & Timing Precise orbital constraints Bad: Low-mass planets challenging Long-period planets challenging Signal complexity increases with more planets (especially if densely packed system) When to stop adding planets? Ups And b, c & d Butler et al Figures from exoplanets.org

11 Good: Dynamical Detections: Doppler, Astrometry & Timing Precise orbital constraints Bad: Low-mass planets challenging Long-period planets challenging Signal complexity increases with more planets (especially if densely packed system) When to stop adding planets? HD Fig. from Lovis et al. 2006; see also Alibert et al. 2005, 2006; Payne et al. 2009

12 Good: Dynamical Detections: Doppler, Astrometry & Timing Precise orbital constraints Bad: Low-mass planets challenging Long-period planets challenging Signal complexity increases with more planets (especially if densely packed system) When to stop adding planets? CoRoT-7 b & c Queloz et al Orbital Phase

13 Dynamical Detections: Doppler, Astrometry & Timing Good: Precise orbits (esp. SIM-Lite) Complete set of mass & orbits Bad: Masses, Relative inclinations Greatly improves capabilities for studying orbital dynamics Sensitivity depends on distance Long-period planets challenging Signal complexity increases with more planets When to stop adding planets? Simulated HD 12661b&c Sozzetti et al. 2003

14 Double-Blind Study of RV+SIM-Lite (Phase II) Preliminary Results Type of measure Score Completeness In HZ 95% (21/22) For TP 81% (35/43) For TP in HZ 94% (17/18) Overall 87% (61/70) Reliability In HZ 100% (20/20) For TP 97% (38/39) For TP in HZ 100% (16/16) Mass (Earths) Overall 91% (63/69) Period (yr) Completeness = # detections / # detectable Traub et al. in prep Reliability = # correct detections / # total detections See also Sozzetti et al. 2003, Table adapted from Catanzarite & Traub Ford 2006, Casertano et al. 2008

15 Challenge of Long-Period Orbits HD b & c Wright et al. (2008)

16 Challenge of Systems Near 2:1 Mean Motion Resonance Difficult to distinguish between models from RVs or astrometry alone Potential to detect planetplanet interactions (e.g., GJ 876 bc), but requires many high S/N observations Easy to distinguish if one planet transits from TTVs Figure RV vs time: Black: One eccentric planet Red: Two planets in 2:1 MMR Anglada-Escude et al. 2008

17 Transit Timing Variations of Hot-Jupiter + Earth-mass Planet RMS of Transit Times Veras & Ford in prep

18 Systems of Multiple Transiting Good: Planets Precise orbital constraints Transit information helps interpret dynamical observations Bad: Precise period and phase Minimum number of planets Long-period planets rarely transit Often requires extensive follow-up of (challenging) host stars

19 Multi-Planet System with Transits HAT P 13 b & c Inner planet transits Outer planet dominates RV signal Opportunity to characterize planetary interior HAT-P-13 b & c Batygin et al Bakos et al. 2009

20 Transit Time Variations >20s 9s 6s 3s HAT-P-13 b & c HAT-P-13 b Payne, Veras, Ford in prep Bakos et al. 2009

21 Conclusions Multiple planet systems are common Sensitivity to low-mass planets is expected to result in more (known) planets per system Architecture and orbital dynamics of multi-planet systems is powerful probe of formation & evolution Potential differences with planet mass Doppler, Astrometry and/or Timing can effectively characterize multi-planet systems If many observations & long time span of observations Systems with both dynamical & transit observations are particularly powerful due to precise constraints