Transcript Transits WG

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 Questions
(1) 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)?
ELSA School - Leiden, 11/22/2007
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
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
Mimicking Planetary Transits
Eclipsing binaries:
- grazing
- low-mass companion
- multiple systems and blends
Typically, 95%-99% of detections…
The Mp-Rp Relation
Coreless??
Transiting planets
come in many flavors
What are their
actual interiors?
How did they form?
Very large core?
Roughly OK
Ljubljana University, 4/15/2008
Default models
have trouble!
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”
Ljubljana University, 4/15/2008
?
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, limbdarkening)!
Improving R*, M*, Rp , Mp
TrES-2
1<t<9 Gyr
[Fe/H] = -0.15
The uncertainty on R* is several times
smaller if a/R* is used instead of log(g)
By
1)
2)
3)
combining:
stellar properties,
spectroscopic mass function,
light-curve parameters
One obtains improved values for:
1) planet radius,
2) planet mass,
3) planet gravity
Sozzetti et al. (ApJ, 2007)
Ljubljana University, 4/15/2008
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
Transiting Systems Follow-up (2)
• Infrared Transits
–Temperature, reflectivity and
composition, rotation, winds
Burrows 2007
Knutson et al. 2007
Charbonneau et al. 2005
ELSA School - Leiden, 11/22/2007
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
Followup Decision Tree
• Very time-consuming
• For CoRoT & Kepler
(and all the more for
Plato) targets may not
even be feasible below
a certain radius size.
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?
• 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:
August 27, 2008
Exoplanets in Multi-Body Systems
Torun, Poland
Success: HST/FGS Follow-up
Benedict et al. 2002, 2006; McArthur et al. 2004; Bean et al. 2007
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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
August 27, 2008
Exoplanets in Multi-Body Systems
Torun, Poland
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
August 27, 2008
Exoplanets in Multi-Body Systems
Torun, Poland
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
August 27, 2008
Exoplanets in Multi-Body Systems
Torun, Poland
ESPRI Consortium
FSU A/B
Delay lines
?
AT
• 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)
August 27, 2008
Exoplanets in Multi-Body Systems
Torun, Poland
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
August 27, 2008
Exoplanets in Multi-Body Systems
Torun, Poland
Gaia Discovery Space (1)
Casertano, Lattanzi, Sozzetti et al. 2008
Gaia can measure accurately > 50%
of the present-day exoplanet sample
August 27, 2008
1) 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
Exoplanets in Multi-Body Systems
Torun, Poland
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
August 27, 2008
Exoplanets in Multi-Body Systems
Torun, Poland
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
August 27, 2008
104 stars per 0.1 MSun bin!
Exoplanets in Multi-Body Systems
Torun, Poland
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.
a) Interactions between a planet and the
gaseous/planetesimal disk?
b) Planet-planet resonant interactions?
c) Close encounters between planets?
d) Secular interactions with a companion star?
Thommes & Lissauer 2003
August 27, 2008
Exoplanets in Multi-Body Systems
Torun, Poland
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
August 27, 2008
Exoplanets in Multi-Body Systems
Torun, Poland
SIM DBT Campaign (1)
Planetary systems can be reliably detected and characterized,
with a relatively small number of false detections
August 27, 2008
Exoplanets in Multi-Body Systems
Torun, Poland
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
August 27, 2008
Exoplanets in Multi-Body Systems
Torun, Poland
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?
August 27, 2008
Exoplanets in Multi-Body Systems
Torun, Poland
Transits WG
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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])
August 27, 2008
Exoplanets in Multi-Body Systems
Torun, Poland
Astrometry WG
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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]
August 27, 2008
Exoplanets in Multi-Body Systems
Torun, Poland