Exoplanet science with ground based ELTs

Transcription

1 Exoplanet science with ground based ELTs Markus Kasper, European Southern Observatory (ESO) 1

2 Outline Scaling laws and Adaptive Optics Observational properties of Exoplanets E-ELT CODEX METIS EPICS (high contrast imaging) 2

3 BGL imaging scaling laws With AO (diff.lim) Gain 40-m over 8-m Spatial resolution D x 5 Const. SNR D 2 x 25 (3.5 mag) D Seeing limited Time to reach SNR (efficiency) D 4 x 625 (1h -> 6s) D 2 Example: Broad band imaging Earth at 10 pc V Earth > 1 phot/m 2 /minute! Integration time needed for SNR 5: 1-m telescope, object photon noise only: ~ 25 minutes 1-m telescope (stellar halo at 1e-9): ~2 hours 40-m telescope with AO (stellar halo at 1e-6, Vis-NIR): ~2 hours 3

4 Sharpening images by Adaptive Optics AO in operation since ~10 years Many flavors: SCAO MCAO GLAO LGS AO LTAO MOAO XAO ( ) 4

5 Why Adaptive Optics? Spatial resolution Exoplanets at large (tens of AU) orbital distances are rare 1AU at 10 pc correspond to 0.1 SNR Small area of corrected PSF catches fewer BG photons Detectivity t(snr) D-4! ~mag 10 5

6 XAO lab demonstration HOT at ESO in collaboration with Arcetri and Durham Univ. Turbulence simulator, 32x32 MEMS DM, SHS, PWS, coronagraphy, NIR camera, 700 corrected modes H-band Strehl ratios ~90% in 0.5 seeing 6

7 LGSF at UT4 Collaboration ESO/MPE, commissioning with SINFONI and NACO early 2007 Typical commissioning performance S K ~20%, FWHM ~100 mas 7

8 Exoplanet Observational Parameters 8

9 Planet detection by radial velocity 1 AU : 28.4 m s -1 5 AU : 12.7 m s AU : 4.8 m s -1 1 AU : 1.5 m s -1 Super-Earth (5 M Ε 0.1 AU : 1.4 m s -1 Super-Earth (5 M Ε 1 AU : 0.45 m s -1 1 AU : 9 cm s -1 9

10 by astrometry Better mass sensitivity at larger distances!!! GAIA discovery space From ESO/ESA WG report 10

11 Observational parameters: Thermal Emission of Giant planets Brightness and spectra mainly a function of T eff, radii R J Spectral resolution ~100 for molecular bands (mostly H 2 0, CH 4, NH 3 ) ~1000 for atomic lines Spectra from Burrows et al., Myr 100 Myr 5 Gyr 1000 K 5 M J 12 M J 70 M J 500 K 1 M J 3.5 M J 30 M J 11

12 Thermal Emission: Contrast and Absolute Magnitude x 5 x 50 4mu limit, ELT, 1 hr H limit Ultra-cool objects are best observed in the near to thermal-ir. For T eff < ~300 K, thermal IR or reflected light 12

13 Planets in reflected light Albedo: Wavelength dependent Typically ~0.3 L d -2 V 1AU: 0.1AU: ~23.5 V 5AU: 1AU: 0.1AU:

14 Exoplanets spectra For ground-based observations, sky background must be considered 14

15 EELT basics 15

16 42-m E-ELT M5 42-m sgemented, 5-mirror design, Nasmyth focii Adaptive (integrated deformable mirror) Corrects for windshake and atmosphere. Multiple sodium LGS Construction proposal end of 2010, 1 st light 2018 M4 specifications 2.5 m flat, ~8000 act. 1 ms response Stroke 25-90μm Inter act: 2-3μm 16

17 Artists impressions 17

18 E-ELT focal stations Focal station selected by removable mirror MCAO METIS EPICS GLAO LTAO 2 GLAO Correctors 1 small (60 cm) Removable and Rotating Mirror 1 large (1.2 mt) Removable Mirror CODEX 18

19 CODEX High resolution spectrograph for radial velocity surveys 19

20 HARPS: stability at 1 m/s La Silla, 3.6-m telescope State-of-the-art Plenty of spectacular discoveries - Observatoire de Genève - Physikalisches Institut, Bern - Observatoire Haute-Provence - Service d Aéronomie, Paris - ESO 20

21 Two super-earth (5-7 MEarth) in a 4-planet system + a very light planet of 1.94 MEarth Gl 581, M3V star Mayor et al, in press Bonfils et al.2005 Udry et al.2007 P1=3.15d M1=1.94MEarth P2=5.37d M2=15.7MEarth P3=12.9 d M3=5.4MEarth P4= 66.8 d M4= 7.1 MEarth Udry et al.2007 revised in Mayor et al. 21

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23 Towards better instruments 10 yr survey at 10 m/s 10 yr survey at 1 m/s 10 yr survey at <0.1 m/s jovian planets hot Jupiters: Migration upper mass limit (a): stopping mechanisms giant planet frequency neptunian planets planetary desert depth: runaway accretion rates horizontal branch: conditions for runaway gas accretion (Mcrit), gap opening terrestrial planets failed cores frequency: solid surface density distribution close in terrestrial planets: type I migration rates 23

24 Sources of Noise Photon Noise Rule of thumb: S/N ratio of 5000/pixel for 2 cm s -1 at R= V~9 at ELT (42 m ) in 20 Minutes Intrinsic stellar noise Stellar Oscillations, Granulation, Magnetic activity Instrumental / Observational noise stability of wavelength reference and position of spectrum on detector 24

25 Intrinsic Stellar RV Variability What is noise for RV measurements, is signal for others: Stellar Oscillations, Granulation, Magnetic activity 25

26 Stellar Noise Stellar Activity Noise, Oscillations Noise : -> Bin (average) the data α Cen B simulations based on HARPS measurements (Udry 2009) 26

27 Instrument noise R & D Telescope Guiding: Errors can be mitigated by scrambling introduced by different types of fibres. Tests ongoing at ESO (G. Avila) Wavelength Calibration: Development of highly stable Laser Frequency Comb (LFC) Calibration System in collaboration with MPQ Detector Stability: Analysis and modeling of HARPS tests and development of super stable cryostat (FP7) to avoid motion introduced by differential thermal expansion and even thermal expansion of the detector itself 27

28 Fibres FRD & Scrambling Scrambling Gain = (d/d)/(f/fwhm) 1 cm s -1 requires Gain=2500 assuming 0.01 arcsec guiding error Gain increase with increasing losses VERY ENCOURAGING RESULTS 28

29 Calibration with LFC VTT tests (La Palma, 1.5 µ) March 08 Steinmetz et al. 2008, Science 321, 1335 Tests with HARPS January 09 (525 nm) 29

30 Detector and Cryostat Tests with HARPS 1. Super stable cryostat under study. 2. Negotiations started with CCD manufacturers on possible large format (9x9cm) CCDs 30

31 Conceptual design CODEX Approximative Dimensions vacuum vessel: 3000x2400x4200 (mm), 3 Optical Benches 31

32 METIS Thermal IR (3-14 micron) imager and spectrograph 32

33 Wavelength range of E-ELT instruments 33

34 Exoplanets in the mid-ir - why? => Detection of intrinsic emission (rather than reflected star light) 34

35 Thermal Emission: Contrast and Absolute Magnitude x 5 x 50 4mu limit, ELT, 1 hr H limit Ultra-cool objects are best observed in the near to thermal-ir. For T eff < ~300 K, intrinsic radiation on thermal IR only 35

36 Instrument Science requirements Wavelength range: 3 to 14 μm diffraction limited (Nyquist sampling) at 3.5 and 7 μm coronagraph Spectrograph: low-resolution (R 3000), long slit (LMN) visual NGS wavefront sensor, aim: Strehl ratio 90% in N-band on bright sources (V 13mag) Notes on contrast and image quality: *rightness ratio star / planet better in the thermal IR: *Strehl ratio increases with observing wavelength 36

37 Possible target samples Optimize detection limits with respect to planet apparent brightness and angular separation to star: 1. Very nearby (~5 pc) stars: 50 mas -> 0.25AU at 5pc 2. Nearby (~ 20 pc) intermediate age (< 1 Gyr) stars 37

38 Substellar companions to stars in the 6pc sample SCR Gl 229b SCR b has ~40 to 50 MJup (Biller et al. 2007) Eps Eps is suspected to house multiple giant planets Wolfgang Brandner (MPIA) ESO E-ELT Design Reference Mission (DRM & DRSP) workshop, Garching, May 2009 ε Indi B Eps Indi A has a binary brown dwarf as companion with a system mass ~120 MJup (Cardoso et al. 2009) 38

39 The 6 pc sample * 90 stars, dominated by K- and M-dwarfs * L- and T-dwarfs are preferentially companions to stars * number of systems vs. distance indicates incompleteness for dist 4 pc => up to 100(!) ultra-cool dwarfs missing? 39

40 Spectroscopic follow-up in MIR L-M-N band low-res spectra: CH 4, CO, NH 3, C 2 H 4, H2O... Leggett et al Leggett et al

41 Main challenges of METIS Cryogenics and vacuum (huge cryostat) Thermal background, baffling PSF suppression (coronagraphs) PSF calibration (differential techniques) 41

42 EPICS Vis - NIR high contrast imager and spectrograph 42

43 Exoplanets observations early 2009 ~ 300 Exoplanets detected, >80% by radial velocities, mostly gas giants, a dozen Neptunes and a handful of Super-Earths Constraints on Mass function, orbit distribution, metallicity Some spectral information from transiting planets HR 8799, Marois et al 2008 Beta Pic, Lagrange et al 2009 Alpbach Summer School, July Spectrum 09 of HD b 43 Richardson et al., Nature 445, 2007

44 (Some) open issues Planet formation (core accretion vs gravitational disk instability) Planet evolution (accretion shock vs spherical contraction / hot start ) Orbit architecture (Where do planets form?, role of migration and scattering) Abundance of low-mass and rocky planets Giant planet atmospheres 44

45 Object Class 1, young & self-lum Planet formation in star forming regions or young associations Requirements: High spat. resolution of ~30 mas (3 AU at 100 pc, snow line for G-star ) Moderate contrast ~

46 Object Class 2, within ~20 pc Orbit architecture, low-mass planet abundance ~500 stars from Paranal 30 deg, ~60-70% M-dwarfs Requirements High contrasts ~10-9 at 250 mas (Jupiter at 20pc) + spatial resolution ~10-8 at 40 mas (Gl 581d,~8 M ) 46

47 Object Class 3, already known ones Planet evolution and atmospheres discovered by RV, 8-m direct imaging (SPHERE, GPI) or astrometric methods (GAIA, PRIMA) From ESO/ESA WG report SPHERE discovery space GAIA discovery space 47

48 Contrast requirements summary 48

49 EPICS Concept 49

50 Concept: Achieve very high contrast Highest contrast observations require multiple correction stages to correct for 1. Atmospheric turbulence 2. Diffraction Pattern 3. Quasi-static instrumental aberrations XAO, S~90% XAO Diffraction + static aberration correction Visible diffraction suppression NIR diffraction suppression Speckle Calibration, Differential Methods Diff. Pol. Coherencebased concept? IFS Contrast ~ Contrast ~ 10-6 Contrast ~ 10-9 x 1000! 50

51 Main parameters (baseline) Serial SCAO M4 / internal WFS, XAO XAO: roof PWS at 825 nm, 3 khz 200x200 actuators (20 cm pupil spacing) RTC requirements: Efficient algorithms studied outside EPICS phase-a XAO concept 1e-6 1e-7 Numerical simulation, Visa Korkiakoski AO + coro 51

52 XAO with APL coronagraph 700K object next to K0 star Good agreement with SPHERE simulations Additional gain by quasi-static speckle calibration (SDI, ADI) 52

53 Correction of quasi-static WFE incl. segments piston DM cleans its control area from speckles Need: measure static aberrations some nm level at science wavelength through residual turbulence (PD or Speckle Nulling) Standard WFE specs ok for most optics (near pupil) Concept to be demonstrated FP7 funded exp. and HOT) 53

54 Residual PSF calibration Getting from systematic PSF residuals ( ) to Spectral Devonvolution (Sparks&Ford, Thatte et al.), Trade-off: spectral bandwidth vs inner working angle, IFS (baseline Y-H) Multi-band spectral or polarimetric differential imaging for smallest separation, needs planet feature (e.g. CH 4 band, or polarization) IFS and differential polarimeter ( nm) Coherence based methods (speckles interfere with Airy Pattern, a planet does not) Self-Coherent camera Angular Differential Imaging (ADI) All 54

55 Spectral Differential Imaging, SDI Lenzen paper Produce identical images, 1 with planet and 1 without Differential aberrations are the challenge Close et al., NACO SDI 55

56 Angular differential imaging (ADI) Keep telescope / instrument configuration (and hence quasi-static speckles) fixed, let field rotate NACO at Nasmyth of VLT (Alt-Az) -> pupil and field rotate at different speeds Standard: Rotate NACO to stabilize field PA New option: Rotate NACO to stabilize pupil (and diffraction pattern and quasi-static speckles) 56

57 Polarimetric Differential imaging Light reflected of an Exoplanet is polarized, typically by P~0.1 Stellar light is (nearly) unpolarized ZIMPOL and EPOL concept Convert polarization into intensity measured by identical CCD pixels No flat field issues No chromatic effect Challenge differential aberration, <1 nm rms measured 57

58 Spectral deconvolution PSF residuals move ~λ Planet s position fixed 58

59 Spectral Deconvolution 59

60 Speckle chromaticity and Fresnel SD needs smooth speckle spectrum -> near-pupil optics 20 nm rms in pupil plane 20 nm rms at 10x Talbot 60

61 Baseline Concept All optics near the pupil plane minimize amplitude errors and speckle irregular chromaticity 61

62 End-2-end analysis Apodizer only leads to improved final contrast APLC Apodizer 62

63 E-ELT WFE requirements Segment alignment (PTT) < 36 nm rms Segment figuring < 50 nm rms Segment high orders < 50 nm rms M2-5, f>50 cycles/pupil Roughness < 30 nm rms < 5 nm rms 63

64 EPICS Detection rates, MC simulation 64

65 Predicted Science Output MC simulations planet population with orbit and mass distribution from e.g. Mordasini (2008) Model planet brightness (thermal, reflected, albedo, phase angle, ) Match statistics with RV results Contrast model Analytical AO model incl. realistic error budget Spectral deconvolution No diffraction or static WFE Y-H, 10% throughput, 4h obs 65

66 Detection rates, nearby+young stars 0.5 Contrast requirements Mordasini population 66

67 Predicted EPICS output Target class 1. Young stars 2. Nearby stars 3. Stars w. planets # targets Selfluminous planets Giant planets Neptunes Rocky planets 688 ~100 (~100) Dozens Very few (?) 512 Dozen ~100 Dozens Dozen >100 Some >100 >Dozen >2 67

68 Summary ELTs can do plenty of Exoplanet science down to the rocky planet regime Earth analogs are at the ultimate limit Planet formation can be studies in star forming regions with EPICS Planetary system architecture can be measured at small (CODEX) and large (EPICS and METIS) angular separations Determination of masses (CODEX) and spectral properties (EPICS and METIS) will allow us to test exoplanet theory 68

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