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PLAnetary Transits
and Oscillations of stars
Thierry Appourchaux
for the PLATO Consortium
http://www.oact.inaf.it/plato/PPLC/Home.html
Outline
- Science Objectives
- Instrumental Concept
- Expected Performances
- Conclusion
Science Objectives (1/2)
• Understand formation and evolution of planetary
systems (= planets + host stars)
• Understand evolution toward habitability
• Complete statistical study of exoplanetary systems
• Identification and characterisation of planetary systems
- including planets of all masses and sizes on various orbits
- around stars of all types and ages
- including seismic characterization of planet host stars
- in particular rocky planets in habitable zone of solar-like stars
Science Objectives (2/2)
Goal: detect and characterise exoplanets
- measurement of radius and mass, hence of mean density
- estimate of age
Method: transit search AND seismic analysis on the same stars
- photometric transits : Rp/Rs (Rs known thanks to Gaia + seismology)
- radial velocity follow-up : Mp/Ms
- seismic analysis of host stars : Rs, Ms, age
Tool:
- ultra-high precision, long, uninterrupted CCD photometric
monitoring of very wide samples of bright stars: CoRoT - Kepler
heritage
Why a seismic analysis of planet host stars?
We want to compare exoplanet characteristics to model predictions with various compositions and structures
maximum acceptable error bars
standard error bar
(no seismology)
10%
PLATO error bar
(with seismology + Gaia)
5%
10%
-
5%
Wagner et al. 2009, also: Valencia et al. 2007
- seismically determined masses and radii of host stars are required to derive useful constraints on planetary interiors
- will give us the opportunity to study diversity of planets : planets with same radius and different masses
- seismically determined exoplanetary ages will be used to place exoplanets in an evolutionary context
PLATO target samples
Main focus of PLATO:
Bright and nearby
stars !!
> 20,000
bright
(~ mV≤11)
cool dwarfs/subgiants
(>F5V&IV):
PLATO…
is watching you !
exoplanet transits
AND
seismic analysis of their host stars
AND
ultra-high precision RV follow-up
>1,000 very
bright
noise < 2.7 10-5 in 1hr
for 3 years
(mV≤8)
cool dwarfs/subgiants
for 3 years
exoplanets
around bright and nearby stars
>3,000 very
(mV≤8)
cool dwarfs/subgiants
> 5,000 (3 years) + 5,000 (5 months) nearby M-dwarfs
(mV≤15-16)
noise < 8. 10-4 in 1hr
> 250,000 cool dwarfs/subgiants (~ mV≤13)
exoplanet transits + RV follow-up
noise < 8.10-5 in 1hr for 3 years
bright
for >5 months
Noise requirements: transit search
simulation: 1 R planet transiting a solar-like star at 1 AU - mean of 3 transits
transit
detectable
transit well
characterized
noise requirement
≤ 2.7 x 10-5 in 1 hr for high S/N transit measurement
for transit search :
≤ 8.0 x 10-5 in 1 hr for marginal transit detection
Noise requirements: seismic analysis
≤ 2.7 x 10-5 in 1 hr
power (ppm2/Hz)
CoRoT HD 49385 mV = 7.4 137 days PLATO equivalent mV = 9.6
same data noise 2.7 x 10-5 per hr PLATO equivalent mV = 11.1
oscillation spectrum
still distinguishable
although affected by
noise
frequency
(Hz)
Instrumental Concept
Very wide field + large collecting area :
multi-instrument approach
optics
356 mm
164.6 mm
S-FPL51
L-PHL1
N-KzFS11 CaF2 S-FPL53 KzFSN5
(Lithotec)
FPA
fully dioptric, 6 lenses
focal planes
optical field
37°
4 CCDs:
45102 18m
New design
- 32 « normal » cameras : cadence 25 sec
- 2 « fast » cameras : cadence 2.5 sec
- pupil 120 mm
- huge dynamical range: 4 ≤ mV ≤ 16 !!
« normal »
« normal » FPA
« fast » FPA
Orbit around L2 Lagrangian point, 6-year nominal lifetime
+ possible extension
Concept of overlapping line of sight
4 groups of 8 cameras with offset lines of sight
baseline offset = 0.35 x field diameter (k=0.35)
16
24
16
24
32
24
8
8
16
50°
37°
8
24
16
8
Optimization of number of stars at given noise level
AND of number of stars at given magnitude
Sky coverage
Observation strategy:
1. two long pointings : 3 years + 2 years or 2 years + 2 years
2. « step&stare » phase (1 or 2 years) : N fields 2-5 months each
12 0°
Kepler
PLATO
15 0°
90 °
18 0°
60 °
CoRoT
CoRoT
21 0°
22 h
20 h
18 h
16 h
14 h
12 h
10 h
8h
30 °
24 0°
0°
27 0°
33 0°
30 0°
>50% of the sky !
PLATO
6h
4h
2h
0h
Expected noise level
noise calculated for 32 cameras
noise in 1 hr (ppm)
jitter/confusion + background
photon noise dominant
photon noise
jitter/PRNU
Performances of the long pointing phases
as a function of noise level
PLATO (4360 deg2)
Kepler (100 deg2)
noise level
(ppm/√hr)
nb of cool dwarfs &
subgiants
mV
range
nb of cool dwarfs &
subgiants
mV
27
22,000
9.6 - 10.9
1,300
11.2
80
330,000
11.6 - 12.7
spec 250,000
25,000
13.6
8
30
8
11
1,300
11
spec 20,000
1,290
spec 1,000
58,490
maximum noise level for
seismic analysis of solar-like stars
&
earth-like planet transit measurement
as a function of magnitude
numbers of cool dwarfs and subgiants observable by PLATO and Kepler,
for various photometric noise levels and various magnitudes, during long monitoring sequences
Note that solar-like oscillations will be measurable for more then 20,000 dwarfs!
Scientific Impact
Expected number of detected transiting planets by PLATO and Kepler:
- each star has one and only one planet in each cell
- planet is detected if a transit signal AND a radial velocity signal are measured
- intrinsic stellar « noise » is taken into account
numbers in white are
expected numbers of
detections by PLATO and
Kepler in each cell: Kepler
contributions are
represented by the green
sectors.
Orbit semi-major axis in
units of habitable zone
The lower right corner (telluric planets in the HZ), not covered by Kepler because of the overwhelming
difficulty of FU observations, will be explored by PLATO thanks to its focus on bright stars.
Note that all planets detected by PLATO referred to in this diagram will have their host star fully
characterized by asteroseismology
Conclusion
Building on CoRoT and Kepler experience,
- PLATO is a next generation planet finder and characterizer
- its focus will be mainly on bright and nearby targets
- it will detect and characterize significant numbers of telluric planets
in the habitable zone
- PLATO will provide seismic analysis of planet host stars and of a very
large sample of stars of all types and ages
- PLATO will represent a major step forward after the pioneering CoRoT
and Kepler missions