Transits What questions to ask? What are the observables? Constraints on precision? Model interpretation? Ground-based? Space-borne? All-sky vs. pointed

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?

10 Big Questions10 Big Questions

(1)(1) Where are the earthlike planets, and what is their frequency?Where are the earthlike planets, and what is their frequency?

(2) What is the preferred method of gas giant planet formation? (2) What is the preferred method of gas giant planet formation?

(3) Under which conditions does migration occur and stop? (3) Under which conditions does migration occur and stop?

(4) What is the origin of the large planetary eccentricities? (4) What is the origin of the large planetary eccentricities?

(5) Are multiple-planet orbits coplanar?(5) Are multiple-planet orbits coplanar?

(6) How many families of planetary systems can be identified from a dynamical viewpoint? (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(7) What are the atmospheres, inner structure, and evolutionary properties of gasgiant planets, neptunes, and telluric planets? giant planets, neptunes, and telluric planets?

(8) Do stars with circumstellar dust disks actually shelter planets? (8) Do stars with circumstellar dust disks actually shelter planets?

(9) What are the actual mass and orbital element distributions of planetary systems? (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 (10) How do planet properties and frequencies depend on the characteristics of the parent stars (spectral type, age, metallicity, and binarity/multiplicity)?stars (spectral type, age, metallicity, and binarity/multiplicity)?

ELSA School - Leiden, 11/22/2007ELSA School - Leiden, 11/22/2007

Transit PhotometryTransit Photometry

* Observable: decrease of stellar brightness,* Observable: decrease of stellar brightness,when planet moves across the stellar diskwhen planet moves across the stellar disk

* Condition of observability: planetary orbit* Condition of observability: planetary orbitmust be (almost) perpendicular to the planemust be (almost) perpendicular to the planeof the skyof the sky

* The method allows a determination* The method allows a determinationof parameters that are not accessible with of parameters that are not accessible with Doppler spectroscopy, e.g. ratio of radii,Doppler spectroscopy, e.g. ratio of radii,orbital inclination, limb darkening of the starorbital inclination, limb darkening of the star

Probability of Eclipses:Probability of Eclipses:

It is easier to detect an eclipseIt is easier to detect an eclipseby a planet on a tight orbitby a planet on a tight orbit


Must combine with RV in order to derive mass and radius of the planetMust combine with RV in order to derive mass and radius of the planet

Transit Depth and DurationTransit Depth and Duration


Warning!Warning!Prone to a variety of Prone to a variety of

astrophysical false alarmsastrophysical false alarms

52 Transiting systems are known to-date

Mimicking Planetary Mimicking Planetary TransitsTransits

Eclipsing binaries:Eclipsing binaries:

- grazing- grazing

- low-mass companion- low-mass companion

- multiple systems and blends- multiple systems and blends

Typically, 95%-99% of detections…

Ljubljana University, 4/15/2008Ljubljana University, 4/15/2008

The MThe Mpp-R-Rpp Relation Relation

Roughly OKRoughly OKVery large core?Very large core?

Coreless??Coreless??

Default models Default models have trouble!have trouble!

Transiting planetsTransiting planetscome in many flavorscome in many flavors

What are theirWhat are theiractual interiors?actual interiors?

How did they form?How did they form?


The MThe Mcc – [Fe/H] Connection – [Fe/H] Connection

??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”

??

Do inferred exoplanets core masses depend on metallicity?Do inferred exoplanets core masses depend on metallicity?

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)!


Improving RImproving R*, *, MM*, *, RRp p , M, Mpp

Sozzetti et al. (ApJ, 2007)Sozzetti et al. (ApJ, 2007)

1<1<tt<9 Gyr<9 Gyr[Fe/H] = -0.15[Fe/H] = -0.15

The uncertainty on RThe uncertainty on R** is several is several times times smaller if a/Rsmaller if a/R** is used instead of is used instead of log(g)log(g)

By combining:By combining:1)1) stellar properties, stellar properties, 2)2) spectroscopic mass function, spectroscopic mass function, 3)3) light-curve parameters light-curve parameters

One obtains improved values for:One obtains improved values for:1)1) planet radius, planet radius, 2)2) planet mass, planet mass, 3)3) planet gravity planet gravity

TrES-2

Transiting Systems Follow-up Transiting Systems Follow-up (1)(1)

Visible Transits: Visible Transits: - radius, density, composition, radius, density, composition, moons or other planets, moons or other planets, spin-spin-orbit alignmentorbit alignment


Winn et al. 2007

Holman et al. 2005

Transiting Systems Follow-up Transiting Systems Follow-up (2)(2)

• • Infrared TransitsInfrared Transits

––Temperature, reflectivity and Temperature, reflectivity and

composition, rotation, windscomposition, rotation, winds


Knutson et al. 2007Burrows 2007Charbonneau et al. 2005

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!)

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

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.

Plato

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.

Followup Decision Tree

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?

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

Success: HST/FGS Follow-upSuccess: HST/FGS Follow-up

• A mass for GJ 876cA mass for GJ 876c• A mass for A mass for εε Eri b Eri b• A mass for the Neptune-sized A mass for the Neptune-sized ρρ11 Cnc d (if Cnc d (if

coplanar)coplanar)• Not a planet but an M dwarf: HD 33636 bNot a planet but an M dwarf: HD 33636 b

Benedict et al. 2002, 2006; McArthur et al. 2004; Bean et al. 2007

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 Secular changes in the target motion (perspective accelerations), relativistic corrections due to a) (perspective accelerations), relativistic corrections due to a) the observer’s motion (aberration) and b) the gravitational the observer’s motion (aberration) and b) the gravitational fields in the observer’s vicinity (light deflection)fields in the observer’s vicinity (light deflection)

• Astrophysical ‘noise’: astrometric ‘jitter’ intrinsic to the target: strometric ‘jitter’ intrinsic to the target: spots, faculae, flares, etc., astrometric ‘jitter’ due to spots, faculae, flares, etc., astrometric ‘jitter’ due to environment: disks, stellar companionsenvironment: disks, stellar companions

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 Expected to reach the atmospheric limiting precision of ~10-20 μμasas

ESPRI Consortium

AT

?

FSU A/B

Delay lines

• Instrument getting close to commissioningInstrument getting close to commissioning• The Consortium will carry out a two-fold program (astrometry of known systems, The Consortium will carry out a two-fold program (astrometry of known systems, planet search around stars of various spectral types and ages)planet search around stars of various spectral types and ages)

Adaptive Optics/CoronagraphyAdaptive Optics/Coronagraphy

•See next talk and poster by Helminiak & Konacki

AO + symmetrization of the reference frame AO + symmetrization of the reference frame to remove low-f components of the image motion to remove low-f components of the image motion spectrum and improve image centroid.spectrum and improve image centroid.

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

V=15, t=10 min

Gaia Discovery Space Gaia Discovery Space (1)(1)

Gaia can measure accurately > 50% Gaia can measure accurately > 50% of the present-day exoplanet sampleof the present-day exoplanet sample

1)1) Massive planets (>2-3 MMassive planets (>2-3 MJJ) at 2<a<4 AU are ) at 2<a<4 AU are detectable out to ~200 pc around solar analogsdetectable out to ~200 pc around solar analogs2) Saturn-sized planets with 1<a<4 AU are 2) Saturn-sized planets with 1<a<4 AU are measurable around nearby (<25 pc) M dwarfsmeasurable around nearby (<25 pc) M dwarfs

Casertano, Lattanzi, Sozzetti et al. 2008Casertano, Lattanzi, Sozzetti et al. 2008

Gaia Discovery Space Gaia Discovery Space (2)(2)

How Many Planets will Gaia find?How Many Planets will Gaia find?

How Many Multiple-Planet Systems will Gaia find?How Many Multiple-Planet Systems will Gaia find?

Star counts (V<13), Star counts (V<13), FFpp(M(Mpp,P),,P),Gaia completeness Gaia completeness limitlimit

Star counts (V<13),Star counts (V<13),FFp,multp,mult,,Gaia detection Gaia detection limitlimit


The Gaia Legacy The Gaia Legacy (1)(1)

How do Planet Properties and Frequencies How do Planet Properties and Frequencies Depend Upon the Characteristics of the Parent Depend Upon the Characteristics of the Parent Stars (also, What is the Preferred Mechanism of Stars (also, What is the Preferred Mechanism of Gas Giant Planet Formation?)?Gas Giant Planet Formation?)?

Gaia will test the fine structure of giant Gaia will test the fine structure of giant planet parameters distributions and planet parameters distributions and frequencies, and investigate their frequencies, and investigate their possible changes as a function of stellar possible changes as a function of stellar mass, metallicity, and age with mass, metallicity, and age with unprecedented resolutionunprecedented resolution 101044 stars per 0.1 M stars per 0.1 MSunSun bin! bin!

Johnson 2007Johnson 2007

Casertano et al. 2008Casertano et al. 2008??Sozzetti et al. 2008Sozzetti et al. 2008

The Gaia Legacy (2)The Gaia Legacy (2)How Do Dynamical Interactions Affect the Architecture of How Do Dynamical Interactions Affect the Architecture of Planetary Systems?Planetary Systems?

E.g., coplanarity tests will allow to determine E.g., coplanarity tests will allow to determine the relative importance of many proposed the relative importance of many proposed mechanisms for eccentricity excitation in a mechanisms for eccentricity excitation in a statistical sense, not just on a star-by-star basis.statistical sense, not just on a star-by-star basis.

Thommes & Lissauer 2003Thommes & Lissauer 2003

a)a) Interactions between a planet and the Interactions between a planet and the gaseous/planetesimal disk? gaseous/planetesimal disk?

b)b) Planet-planet resonant interactions? Planet-planet resonant interactions?

c)c) Close encounters between planets? Close encounters between planets?

d) Secular interactions with a companion star?d) Secular interactions with a companion star?

A word of Caution…A word of Caution…

If the single-measurement precision degrades significantly,If the single-measurement precision degrades significantly,exoplanets could disappear from the Gaia science caseexoplanets could disappear from the Gaia science case


SIM DBT Campaign (1)

Planetary systems can be reliably detected and characterized, Planetary systems can be reliably detected and characterized, with a relatively small number of false detectionswith a relatively small number of false detections

SIM DBT Campaign (2) All detectable planets (above a SNR~6 All detectable planets (above a SNR~6

threshold) were in fact detectedthreshold) were in fact detected

Terrestrial planets orbits can be characterized Terrestrial planets orbits can be characterized even in presence of gas giantseven in presence of gas giants

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?

Transits WG

• Cristina Afonso ([email protected]) • Roi Alonso ([email protected]) • David Blank ([email protected]) • Claude Catala' ([email protected]) • Hans Deeg ([email protected]), reserve • Coel Hellier ([email protected]) • David W. Latham ([email protected]) Dante

Minniti ([email protected]) • Frederic Pont ([email protected], to be

updated) • Heike Rauer ([email protected])

mailto:[email protected]










Astrometry WG

• Fabien Malbet, [email protected] • Petro Lazorenko, [email protected]• Sabine Reffert, [email protected]• Alessandro Sozzetti, [email protected] • Nick Elias, [email protected] • Ralf Launhardt, [email protected] • Matthew Muterspaugh, [email protected]• Gerard van Belle, [email protected] • Andreas Quirrenbach,

[email protected] • Francoise Delplanck, [email protected]





Documents

Transits What questions to ask? What are the observables? Constraints on precision? Model interpretation? Ground-based? Space-borne? All-sky vs. pointed