PLAnetary Transits and Oscillations of stars

Thierry Appourchauxfor the PLATO Consortium

http://www.oact.inaf.it/plato/PPLC/Home.html

- Science Objectives- Instrumental Concept - Expected Performances- Conclusion

Outline

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

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

Science Objectives (2/2)

- 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

Why a seismic analysis of planet host stars?

-

Wagner et al. 2009, also: Valencia et al. 2007

5%

10%

10%

5%

maximum acceptable error bars

PLATO error bar (with seismology + Gaia)

standard error bar (no seismology)

We want to compare exoplanet characteristics to model predictions with various compositions and structures

PLATO target samples

> 20,000 bright (~ mV≤11)

cool dwarfs/subgiants (>F5V&IV):

exoplanet transits AND

seismic analysis of their host starsAND

ultra-high precision RV follow-up

noise < 2.7 10-5 in 1hr for 3 years

> 250,000 cool dwarfs/subgiants (~ mV≤13)

exoplanet transits + RV follow-up

>1,000 very bright

(mV≤8)

cool dwarfs/subgiantsfor 3 years

>3,000 very bright

(mV≤8)

cool dwarfs/subgiantsfor >5 months

exoplanets

around bright and nearby stars

Main focus of PLATO:

Bright and nearby stars !!

PLATO…is watching you !

noise < 8.10-5 in 1hr for 3 years

> 5,000 (3 years) + 5,000 (5 months) nearby M-dwarfs

(mV≤15-16) noise < 8. 10-4 in 1hr

Noise requirements: transit search

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

simulation: 1 R planet transiting a solar-like star at 1 AU - mean of 3 transits

transit well characterized

transit detectable

Noise requirements: seismic analysis≤ 2.7 x 10-5 in 1 hr

frequency (Hz)

pow

er (

ppm

2 /H

z)

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

Instrumental Concept

New design- 32 « normal » cameras : cadence 25 sec- 2 « fast » cameras : cadence 2.5 sec- pupil 120 mm- huge dynamical range: 4 ≤ mV ≤ 16 !!

Very wide field + large collecting area :multi-instrument approach

FPA

356 mm

S-FPL51

N-KzFS11 CaF2(Lithotec)

S-FPL53

L-PHL1

KzFSN5

164.

6 m

m

optics

fully dioptric, 6 lenses

Orbit around L2 Lagrangian point, 6-year nominal lifetime+ possible extension

optical field 37°

4 CCDs: 45102 18m « normal »

focal planes

« normal » FPA « fast » FPA

Concept of overlapping line of sight

4 groups of 8 cameras with offset lines of sightbaseline offset = 0.35 x field diameter (k=0.35)

8 8

8 8

16

16

16 16

2424

2424

32

Optimization of number of stars at given noise level AND of number of stars at given magnitude

37°

50°

>50% of the sky !

0°

30°

60°

90°

120°

150°

180°

210°

240°

270°

300°

330°

0h2h4h6h8h10h12h14h16h18h20h22h

CoRoT CoRoT

KeplerPLATO

PLATO

Observation strategy:1. two long pointings : 3 years + 2 years or 2 years + 2 years2. « step&stare » phase (1 or 2 years) : N fields 2-5 months each

Sky coverage

Expected noise level

jitter/PRNU

jitter/confusion + background

photon noise

photon noise dominant

noise calculated for 32 camerasno

ise

in 1

hr

(ppm

)

Performances of the long pointing phasesas a function of noise level

as a function of magnitude

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 25,000 13.6

1,290 8 30 8

58,490 11 1,300 11

spec 20,000

spec 250,000

spec 1,000

maximum noise level for seismic analysis of solar-like stars&earth-like planet transit measurement

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.

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

Orbit semi-major axis in units of habitable zone

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 planetsin 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