Transits

1. Transits • What questions to ask? • What are the observables? Constraints on precision? Model interpretation? • Ground-based? • Space-borne? All-sky vs. pointed • Follow-up observations (confirmation) issues • What is already being done and what needs to be done? • What are the risks?

2. Where are the earthlike planets, and what is their frequency? • (2) What is the preferred method of gas giant planet formation? • (3) Under which conditions does migration occur and stop? • (4) What is the origin of the large planetary eccentricities? • (5) Are multiple-planet orbits coplanar? • (6) How many families of planetary systems can be identified from a dynamical viewpoint? • (7) What are the atmospheres, inner structure, and evolutionary properties of gas • giant planets, neptunes, and telluric planets? • (8) Do stars with circumstellar dust disks actually shelter planets? • (9) What are the actual mass and orbital element distributions of planetary systems? • (10) How do planet properties and frequencies depend on the characteristics of the parent stars (spectral type, age, metallicity, and binarity/multiplicity)? 10 Big Questions ELSA School - Leiden, 11/22/2007

3. Transit Photometry * Observable: decrease of stellar brightness, when planet moves across the stellar disk * Condition of observability: planetary orbit must be (almost) perpendicular to the plane of the sky * The method allows a determination of parameters that are not accessible with Doppler spectroscopy, e.g. ratio of radii, orbital inclination, limb darkening of the star Probability of Eclipses: It is easier to detect an eclipse by a planet on a tight orbit Must combine with RV in order to derive mass and radius of the planet ELSA School - Leiden, 11/22/2007

4. Transit Depth and Duration 52 Transiting systems are known to-date Warning! Prone to a variety of astrophysical false alarms ELSA School - Leiden, 11/22/2007

5. Mimicking Planetary Transits Eclipsing binaries: - grazing- low-mass companion- multiple systems and blends Typically, 95%-99% of detections…

6. The Mp-Rp Relation Coreless?? Transiting planets come in many flavors What are their actual interiors? How did they form? Roughly OK Very large core? Default models have trouble!

7. The Mc – [Fe/H] Connection Do inferred exoplanets core masses depend on metallicity? Burrows et al. (ApJ, 2007): “The core mass of transiting planets scales linearly (or more) with [Fe/H]” ? Guillot et al. (A&A, 2006): “The heavy element content of transiting extrasolar planets should be a steep function of stellar metallicity” ?

8. How well do we know the Hosts? • Main-stream approach: main-sequence stars astrophysics is a solved problem, for practical purposes • For transiting systems, the star is most of the time the limit (mass, radius, limb-darkening)!

9. Improving R*, M*, Rp , Mp The uncertainty on R* is several times smaller if a/R* is used instead of log(g) TrES-2 • By combining: • stellar properties, • spectroscopic mass function, • light-curve parameters 1<t<9 Gyr [Fe/H] = -0.15 • One obtains improved values for: • planet radius, • planet mass, • planet gravity Sozzetti et al. (ApJ, 2007)

10. Transiting Systems Follow-up (1) • Visible Transits: • radius, density, composition, moons or other planets, spin-orbit alignment Holman et al. 2005 Winn et al. 2007 ELSA School - Leiden, 11/22/2007

11. Transiting Systems Follow-up (2) • Infrared Transits –Temperature, reflectivity and composition, rotation, winds Knutson et al. 2007 Burrows 2007 Charbonneau et al. 2005 ELSA School - Leiden, 11/22/2007

12. Photometric Precision • 0.002-0.003 mag is achieved from the ground (high-cadence, meter-sized telescopes) • For Earth-sized companions / solar-type stars, need better than 0.0001 mag • The latter cannot be achieved from the ground (and again, the star is the likely limit!)

13. In addition… • Transit timing variations allow to infer the presence of additional components • If more than one transit, derive densities directly from photometry alone • Must achieve very high timing precision (1-10 sec typically). Difficult from the ground

14. At present… • CoRoT & Kepler, pointed, and possibly TESS, all-sky can provide much of the observational material of quality needed to address many issues • There is a time niche from the ground for M dwarfs transit searches.

15. Plato

16. Followup Decision Tree Confirmation observations • Very time-consuming • For CoRoT & Kepler (and all the more for Plato) targets may not even be feasible below a certain radius size.

17. Astrometry • What questions to ask? • What observables? What constraints on precision? Model interpretation? • Filled-aperture vs. diluted • From the ground? • From space? All-sky vs pointed. • What is already being done and what needs to be done? • What are the risks?

18. What about Astrometry? • Astrometry measures stellar positions and uses them to determine a binary orbit projected onto the plane of the sky • Astrometry measures all 7 parameters of the orbit, in multiple systems it derives the relative inclination angles between pairs of orbits, regardless of the actual geometry. Mass is derived given a guess for the primary’s. • In analysis, one has to take the proper motion and the stellar parallax into account • The measured amplitude of the orbital motion (in milli-arcsec) is: Exoplanets in Multi-Body Systems Torun, Poland

19. Success: HST/FGS Follow-up • A mass for GJ 876c • A mass for ε Eri b • A mass for the Neptune-sized ρ1 Cnc d (if coplanar) • Not a planet but an M dwarf: HD 33636 b Benedict et al. 2002, 2006; McArthur et al. 2004; Bean et al. 2007 Exoplanets in Multi-Body Systems Torun, Poland

20. μas Astrometry is needed • But it’s difficult! • From the ground: photon noise, instrumental noise, atmospheric noise (turbulence+DCR) • In space: more random/systematic noise sources: attitude errors (solar wind, micrometeorites, particle radiation, radiation pressure, thermal drifts and spacecraft jitter), CTI, and so on… • Astrophysical ‘effects’: Secular changes in the target motion (perspective accelerations), relativistic corrections due to a) the observer’s motion (aberration) and b) the gravitational fields in the observer’s vicinity (light deflection) • Astrophysical ‘noise’: astrometric ‘jitter’ intrinsic to the target: spots, faculae, flares, etc., astrometric ‘jitter’ due to environment: disks, stellar companions Exoplanets in Multi-Body Systems Torun, Poland

21. VLTI/PRIMA The recorded distance between white fringes of the reference and the object is given by the sum of four terms: (ΔS . B) the Angular separation (< 1 arcmin) times Baseline; + (Ф ) the Phase of Visibility of Object observed for many baselines; + (ΔA) the Optical Path Difference caused by Turbulence (supposed averaged at zero in case of long time integration); + (ΔC) the Optical Path Difference measured by Laser Metrology inside the VLTI. n.b. For astrometry both Objects are supposed to have the Phase of their complex visibility = zero (point source object) Expected to reach the atmospheric limiting precision of ~10-20 μas Exoplanets in Multi-Body Systems Torun, Poland

22. FSU A/B Delaylines ? AT ESPRI Consortium • Instrument getting close to commissioning • The Consortium will carry out a two-fold program (astrometry of known systems, • planet search around stars of various spectral types and ages) Exoplanets in Multi-Body Systems Torun, Poland

23. Adaptive Optics/Coronagraphy AO + symmetrization of the reference frame to remove low-f components of the image motion spectrum and improve image centroid. V=15, t=10 min Lazorenko 2004,2006 Predicting the star location with respect to the occulting spot from image centroid, instrument feedback, or PSF symmetry still results in mas precision at best Digby et al. 2006 • See next talk and poster by Helminiak & Konacki Exoplanets in Multi-Body Systems Torun, Poland

24. Gaia Discovery Space (1) Casertano, Lattanzi, Sozzetti et al. 2008 • Massive planets (>2-3 MJ) at 2<a<4 AU are • detectable out to ~200 pc around solar analogs • 2) Saturn-sized planets with 1<a<4 AU are • measurable around nearby (<25 pc) M dwarfs Gaia can measure accurately > 50% of the present-day exoplanet sample Exoplanets in Multi-Body Systems Torun, Poland

25. Gaia Discovery Space (2) How Many Planets will Gaia find? Star counts (V<13), Fp(Mp,P), Gaia completeness limit How Many Multiple-Planet Systems will Gaia find? Star counts (V<13), Fp,mult, Gaia detection limit Casertano, Lattanzi, Sozzetti et al. 2008 Exoplanets in Multi-Body Systems Torun, Poland

26. The Gaia Legacy (1) How do Planet Properties and Frequencies Depend Upon the Characteristics of the Parent Stars (also, What is the Preferred Mechanism of Gas Giant Planet Formation?)? Johnson 2007 Sozzetti et al. 2008 ? Casertano et al. 2008 Gaia will test the fine structure of giant planet parameters distributions and frequencies, and investigate their possible changes as a function of stellar mass, metallicity, and age with unprecedented resolution 104 stars per 0.1 MSun bin! Exoplanets in Multi-Body Systems Torun, Poland

27. The Gaia Legacy (2) How Do Dynamical Interactions Affect the Architecture of Planetary Systems? E.g., coplanarity tests will allow to determine the relative importance of many proposed mechanisms for eccentricity excitation in a statistical sense, not just on a star-by-star basis. • Interactions between a planet and the • gaseous/planetesimal disk? • Planet-planet resonant interactions? • Close encounters between planets? • d) Secular interactions with a companion star? Thommes & Lissauer 2003 Exoplanets in Multi-Body Systems Torun, Poland

28. A word of Caution… Casertano, Lattanzi, Sozzetti et al. 2008 If the single-measurement precision degrades significantly, exoplanets could disappear from the Gaia science case Exoplanets in Multi-Body Systems Torun, Poland

29. SIM DBT Campaign (1) Planetary systems can be reliably detected and characterized, with a relatively small number of false detections Exoplanets in Multi-Body Systems Torun, Poland

30. SIM DBT Campaign (2) All detectable planets (above a SNR~6 threshold) were in fact detected Terrestrial planets orbits can be characterized even in presence of gas giants Exoplanets in Multi-Body Systems Torun, Poland

31. Which directions? • Ground-based astrometry appears to have limited potential for detection, but can contribute significantly to better the knowledge of existing systems. • In Space, synergy Gaia/SIM (and/or TESS/Plato)? • If SIM won’t be there, what else? Exoplanets in Multi-Body Systems Torun, Poland

32. Transits WG • Cristina Afonso (afonso@mpia-hd.mpg.de) • Roi Alonso (roi.alonso@oamp.fr) • David Blank (david.blank@jcu.edu.au) • Claude Catala' (Claude.Catala@obspm.fr) • Hans Deeg (hdeeg@iac.es), reserve • Coel Hellier (ch@astro.keele.ac.uk) • David W. Latham (dlatham@cfa.harvard.edu) Dante Minniti (dante@astro.puc.cl) • Frederic Pont (frederic.pont@inscience.ch, to be updated) • Heike Rauer (Heike.Rauer@dlr.de) Exoplanets in Multi-Body Systems Torun, Poland

33. Astrometry WG • Fabien Malbet, Fabien.Malbet@obs.ujf-grenoble.fr • Petro Lazorenko, laz@MAO.Kiev.UA • Sabine Reffert, sreffert@lsw.uni-heidelberg.de • Alessandro Sozzetti, sozzetti@oato.inaf.it • Nick Elias, n.elias@lsw.uni-heidelberg.de • Ralf Launhardt, rl@mpia-hd.mpg.de • Matthew Muterspaugh, matthew1@ssl.berkeley.edu • Gerard van Belle, gerard.van.belle@eso.org • Andreas Quirrenbach, A.Quirrenbach@lsw.uniheidelberg.de • Francoise Delplanck, fdelplan@eso.org Exoplanets in Multi-Body Systems Torun, Poland