Prospects for the Detection of Protoplanets [Review]

Transcription

1 Prospects for the Detection of Protoplanets [Review] Sebastian Wolf Emmy Noether Research Group Evolution of Circumstellar Dust Disks to Planetary Systems Max Planck Institute for Astronomy discs06 Cambridge, UK [July 20, 2006]

2 Planet Formation in a Nutshell Theory Star Formation Process Circumstellar Disks Planets (sub)µm particles cm/dm grains Brownian Motion, Sedimentation, Drift Inelastic Collision => Coagulation Agglomeration; Fragmentation Planetesimales Gravitational Interaction: Oligarchic Growth Planets (cores) Gas Accretion (Waelkens 2001) Alternativ: Gravitational Instability Giant Planet

3 IRAS how to identify Grain Growth? SED: (sub)mm slope Shape of ~10μm silicate feature Scattered light polarization (e.g., spectro-polarimetry) HK Tau Multi-wavelength imaging + Radiative Transfer Modelling

4 The Butterfly Star in Taurus Wolf, Padgett, & Stapelfeldt (2003) IRAS HK Tau IRAS

5 The Butterfly Star in Taurus submm-sized grains in the disk midplane, IRAS instellar-like grain size in the circumstellar envelope HK Tau 600 AU ~ 4.3 IRAS Wolf, Padgett, & Stapelfeldt (2003)

6 Size Scales Solar System Angular diameter of the orbit of solar system planets in a distance of the Taurus star-forming region (140pc) Neptune mas Jupiter - 74 mas Earth - 14 mas

7 Mid-infrared interferometric spectroscopy - Dust processing in the innermost regions MIDI setup [Leinert et al. 2004]

8 Mid-infrared interferometric spectroscopy - Dust processing in the innermost regions Silicate Feature [Leinert et al. 2004] Effect also found in disks around TTauri Stars - (Schegerer & Wolf, in prep.)

9 Finding Planets In Disks?! Additional Problems (Dust...) UV (N)IR IR mm Young disks Scattering Thermal Reemission Extinction (Inclination-dependent) Dust parameters, T(r,θ,φ), ρ(r,θ,φ)

10 Response of a gaseous, viscous protoplanetary disk to an embedded planet Disk surface densities for planets with masses 1, 0.1, and 0.01M J orbiting a 1M sun star (Bate et al. 2003) [see also Bryden et al. 1999, Kley et al. 2001, Lubow et al. 1999, Ogilvie & Lubow 2002, D Angelo et al. 2003, Winters et al. 2003]

11 0.01 M J 0.03 M J 0.3 M J 1 M J (Bate et al. 2003)

12 Is this what we have to look for? [ G. Bryden ]

13 Jupiter in a 0.05 M sun disk around a solar-mass star as seen with ALMA d=140pc Baseline: 10km λ=700μm, t int =4h (Wolf et al. 2002)

14 inclination = 5 Scattered light images λ = 1.14μm Gap width (FWHM): ~ 1 AU. [7 AU 7 AU]. based on 2D density distributions resulting from hydrodynamics simulations inclination = 70 no gap gap [ no planet ] [ 2M J planet at 1 AU ] Log( Disk surface brightness) vertical structure is assumed to be Gaussian with a scale height that varies as a power law with radius (i.e., a flared disk) [Varniere et al. 2006]

15 2M J planet at 1 AU Azimuthally averaged optical surface brightness profiles for a disk with / without an embedded planet. Decrease in the surface brightness profile near the planet Bright bump in the profile at the outer edge of the gap [ Varniere et al ] Richling (in prep.): Observability of gaps depending on wavelength + viewing angle (based on irradiated α-disk models) Steinacker & Henning (2003): Analysis of the spectral appearance of gaps Wilner et al. 2004: Observations of the inner disk structure with the Square Kilometer Array (Science Case Study)

16 Small-scale spirals encircling the planet (detached from the global spiral) = Feature of a circumplanetary disk Gaps in young disks - In the vicinity of the planet Zoom in onto the planet: Disk surface densities for a planet with a mass of 0.5M J orbiting a 1M sun star. Plus signs: Lagrange points. Overplotted curve: Roche lobe. (D Angelo et al. 2002)

17 Is this what we have to look for? Density distribution in the midplane of the circumstellar disk with an embedded massive planet. Can we map young giant planets?

18 Close-up view: Planetary region Procedure Density Structure (2D Hydrosimulation) Stellar heating (3D Radiative transfer) Planetary heating (3D Radiative transfer) Prediction of Observations Wolf & D Angelo (2005)

19 Close-up view: Planetary region M planet / M star = 1M Jup / 0.5 M sun 50 pc Orbital radius: 5 AU Disk mass as in the circumstellar disk as around the Butterfly Star in Taurus Maximum baseline: 10km, 900GHz, t int =8h Wolf & D Angelo (2005) 100 pc Random pointing error during the observation: (max. 0.6 ) ; Amplitude error, Anomalous refraction; Continuous observations centered on the meridian transit; Zenith (opacity: 0.15); 30 o phase noise; Bandwidth: 8 GHz

20 Close-up view: Planetary region 50 pc 1. The resolution of the images to be obtained with ALMA will allow detection of the warm dust in the vicinity of the planet only if the object is at a distance of not more than about 100 pc. For larger distances, the contrast between the planetary region and the adjacent disk in all of the considered planet/star/disk configurations will be too low to be detectable. 2. Even at a distance of 50 pc, a sufficient resolution to allow a study of the circumplanetary region can be obtained only for those configurations with the planet on a Jupiter-like orbit but not when it is as close as 1 AU to the central star. 100 pc 3. The observation of the emission from the dust in the vicinity of the planet will be possible only in the case of the most massive, young circumstellar disks we analyzed. Wolf & D Angelo (2005)

21 Strong spiral shocks near the planet are able to decouple the larger particles (>0.1mm) from the gas => formation of an annular gap in the dust, even if there is no gap in the gas density (example: gap in 1mm grains opened by a 0.05M Jup planet) Gaps in young disks - two-fluid simulations PaardeKooper & Mellema (2004)

22 Imaging in the Mid-infrared (~10micron) Hot Accretion Region around the Planet 10μm surface brightness profile of a T Tauri disk with an embedded planet ( inner 40AUx40AU, distance: 140pc) [Wolf & Klahr, in prep.] i=0deg i=60deg Science Case Study for T-OWL: Thermal Infrared Camera for OWL (Lenzen et al. 2005) Justification of the Observability in the Mid-IR for nearby objects (d<100pc)

23 Wolf, Klahr, Egner, et al in Lenzen et al T-OWL Thermal Infrared Camera for OWL 5 AU 10 pc 30 pc 70 pc

24 MATISSE Multi AperTure Mid-Infrared SpectroScopic Experiment High-Resolution Multi-Band Image Reconstruction + Spectroscopy in the Mid-IR Proposed 2 nd Generation VLTI Instrument Specifications: L, M, N, Q band: ~ μm Spectral resolutions: 30 / / Simultaneous observations in 2 spectral bands What s new? Image reconstruction on size scales of 3 / 6 mas (L band) 10 / 20mas (N band) using ATs / UTs Multi-wavelength approach in the mid-infrared 3 new mid-ir observing windows for interferometry (L,M,Q) Improved Spectroscopic Capabilities

25 MATISSE MATISSE Precursor of Darwin in terms of image reconstruction; Experience (MIDI + AMBER)

26 What is the status of disk clearing in the inner few AU? Sublimation radius ~ 0.1-1AU (TTauri HAe/Be stars) but: Observations: Significant dust depletion >> Sublimation Radii TW Hydrae (10Myr): ~ 4 AU (Calvet et al. 2002) GM Aur: ~ 4 AU (Rice et al. 2003) CoKu Tau/4: ~10 AU (D Alessio et al. 2005, Quillen et al. 2004) 10μm image of a circumstellar disk with an inner hole, radius 4AU (inclination: 60deg; distance 140pc; inner 60AU x 60AU)

27 Constraints on a planetary origin for the gap in the protoplanetary disc of GM Aurigae increasing planetary mass Azimuthally averaged mid-plane density profiles for substellar objects (planets). The SED of GM Aur computed using azimuthally averaged density profiles. A ~ 2 M J planet, orbiting at 2.5 AU in a disk with mass M and radius 300 AU, provides a good match both to the SED and to CO observations which constrain the velocity field in the disc. A range of planet masses is allowed by current data, but could in principle be distinguished with further observations between 3 and 20 μm. Rice et al. (2003)

28 Imaging in the Nearinfrared 5AU Solar-type central star 2.2 micron (scattered stellar light) AB Aurigae - Spiral arm structure (Herbig Ae star; H band; Fukagawa, 2004)

29 Young disks Which disks to study? Inner disk (< a few AU) Clearly identified disks, well studied, but potentially planet-building sites well hidden AB Aurigae HD Very distant Etc.... Preparatory studies, concentrating on face-on disks Useful techniques: Coronography; Differential polarimetric imaging; high-resolution mm maps (Grady 2001 / 2003)

30 inner ~12 AU Influence on the Net - SED Inner Disk Wolf & D Angelo (2005)

31 inner ~12 AU Influence on the Net - SED Planet Wolf & D Angelo (2005)

32 inner ~12 AU Influence on the Net - SED Planetary Environment Wolf & D Angelo (2005)

33 inner ~12 AU Influence on the Net - SED Inner Disk + Planet + Planetary Environment Wolf & D Angelo (2005) No significant effect on the Net SED

34 Influence on the Net - SED Planetary Contribution (direct or scattered radiation, dust reemission) Disk reemission (inner 12 AU) < 0.4% (depending on the particular model) Planetary radiation significantly affects the dust reemission SED only in the near to mid-infrared wavelength range. This spectral region is influenced also by the warm upper layers of the disk and the inner disk structure, the planetary contribution. => The presence of a planet + the temperature / luminosity of the planet cannot be derived from the SED alone. In the case of a more massive planet / star the influence of the planet is even less pronounced in the mid-infrared wavelength range (lower luminosity ratio L P / L * ). see also Varniere et al. (2006)

35 High-Spatial Resolution Spectroscopy Spectroscopic verification of gaps through their dynamics R ~ 10 5, λ ~ 5-30μm GSMT Science Case Study [ ]

36 MHD simulations: Internal Stress arises self-consistently from turbulence generated by magnetorotational instability ( MHD turbulence ) >>> gaps are shallower and asymmetrically wider >>> rate of gap formation is slowed Gaps in young disks - MHD simulations (Winters et al. 2003; see also Nelson & Papaloizou 2003)

37 Sources of Astrometric Wobble 1. Planet s Gravitational Pull 2. Disk s Gravitational Pull 3. Disk s Photospheric Signal (center-of-light wobble) (G. Bryden, priv. comm.)

38 Center-of-Light-Wobble (G. Bryden, priv. comm.)

39 Protoplanetary Disks evolve Near-infrared photometric studies: sensitive to the inner ~ 0.1 AU around solar-type stars: Excess rate decreases from ~80% at an age of ~1 Myr to about 50% by an age of ~3 Myr (Haisch et al.~2001) By ages of ~10-15 Myr, the inner disk has diminished to nearly zero (Mamajek et al.2002). Far-infrared / millimeter continuum observations probe the colder dust and thus the global dust content in disks: Beckwith et al. (1990): no evidence of temporal evolution in the mass of cold, small (<1mm) dust particles between ages of 0.1 and 10Myr By an age of 300 Myr the dust masses were found to by decreased by at least 2 orders of magnitude (Zuckerman & Becklin 1993). Based on studies with the Infrared Space Observatory (ISO), the disk fraction amounts to much less than 10% for stars with ages > 1 Gyr (e.g., Spangler et al. 2001; Habing et al. 2001; Greaves et al. 2004; Dominik & Decin 2003).

40 but still the disk may outshine the planet. The exozodiacal dust disk around a target star, even at solar level, will likely be the dominant signal originating from the extrasolar system: Solar system twin: overall flux over the first 5 AU is about 400 times larger than the emission of the Earth at 10μm Zodiacal light of our own solar system: potential serious impact on the ability of space-born observations (e.g. DARWIN) attributed to the scattering of sunlight in the UV to near-ir, and the thermal dust reemission in the mid to far-ir > 1micron: signal from the zodiacal light is a major contributor to the diffuse sky brightness and dominates the mid-ir sky in nearly all directions, except for very low galactic latitudes (Gurfil et al. 2002).

41 IRAS Young disks / Debris disks Planet Disk interaction betapic AUMic Young circumstellar disks around T Tauri / HAe/Be stars Debris disks optically thick optically thin HK Tau Density structure dominated by Gravitation + BD Gas dynamics Radiation Pressure Poynting-Robertson effect Scattered light images (optical)

42 Characteristic Debris Disk Density Patterns A planet, via resonances and gravitational scattering produces [1] An asymmetric resonant dust belt with one or more clumps, intermittent with one or a few offcenter cavities, and Simulated surface density of circumstellar dust captured into particular mean motion resonances (Ozernoy et al. 2000) [2] A central cavity void of dust.

43 Resonant structures can serve as indicators of a planet in a circumstellar disk [1] Location [2] Major orbital parameters [3] Mass of the planet (static) equilibrium density distribution Scattered Light Image 10 4 particles dynamical simulation ~ 10 4 massless particles gravitational intercation with planet + star Poynting-Robertson effect + Radiation Pressure 10 7 particles [ Rodmann, Wolf, ] Spurzem, Henning, in prep.

44 Resonant structures can serve as indicators of a planet in a circumstellar disk [1] Location [2] Major orbital parameters [3] Mass of the planet (static) equilibrium density distribution Scattered Light Image 10 4 particles 10 7 particles Relative brightness distribution of individual clumps in optical to near-infrared scattered light images may sensitively depend on the disk inclination.

45 Debris disk around Vega Debris disk around Vega Dust reemission (Wilner et al. 2002) SOFIA, JWST (Holland et al. 1998, Wilner et al. 2002)

46 Su et al. (2005): No clumpy structure Inner disk radius: 11 +/-2 Extrapolated 850μm flux << than observed Explanation: Dust (Holland grains et al. of 1998, different Wilner et al. 2002) sizes are traced by Spitzer/SCUBA Spitzer 24μm 70μm Debris disk around Vega

47 Giant Planets in Debris Disks Characteristic Asymmetric Density Patterns Rodmann & Wolf (2006) Decreased Mid-Infrared Spectral Energy Distribution (but dust grain evolution makes detailed SED analysis difficult) Wolf & Hillenbrand (2003, 2005) [ aida28.mpia.de/~swolf/dds ]

48 Giant Planets in Debris Disks Characteristic Asymmetric Density Patterns Rodmann & Wolf (2006) Decreased Mid-Infrared Spectral Energy Distribution (but dust grain evolution makes detailed SED analysis difficult) Wolf & Hillenbrand (2003, 2005) [ aida28.mpia.de/~swolf/dds ]

49 Giant Planets in Debris Disks Characteristic Asymmetric Density Patterns Rodmann & Wolf (2006) Decreased Mid-Infrared Spectral Energy Distribution (but dust grain evolution makes detailed SED analysis difficult) Wolf & Hillenbrand (2003, 2005) [ aida28.mpia.de/~swolf/dds ]

50 Wolf & Hillenbrand (2003) Inner cavity in an optically thin disk surrounding a solar-type star Fe content Gaps SED Inner disk radius Grain size T Tauri Disks GM Aurigae, TW Hya [Koerner et al. 1993, Rice et al 2003, Calvet et al. 2002] Debris Disks β Pic (20AU), HR 4796A (30-50AU), ε Eri (50AU), Vega (80AU), Fomalhaut (125AU) + new Spitzer Debris Disks [Dent et al. 2000, Greaves et al. 2000, Wilner et al. 2002, Holland et al. 2003]

51 The Young Solar 50pc M dust = M sun with planets without planets Moro-Martin, Wolf, & Malhotra (2004)

52 Some problems with SEDs... Kim et al. 2005

53 Some problems with SEDs... Many of the debris disks observed with the Spitzer ST, show no or only very weak emission at wavelengths < micron (e.g. Kim et al. 2005) => No / weak constraints on the chemical composition of the dust Debris disks: Optically thin - azimuthal and vertical disk structure can not be traced via SED observations / modelling; - only constraints on radial structure can be derived: SED = f ( T(R) ) but even here ambiguities are difficult to resolve

54 Imaging required Moro-Martin, Wolf, & Malhotra (2005)

55 β Pictoris dust disk: Orientation : nearly edge-on Total mass : few tens... few lunar masses Maximum of the dust surface density distribution located between 80AU and 100AU (Schultz, Heap, NASA 1998) Warp in the β Pictoris Disk Model includes a Disk of Planetesimals Extending out to AU, perturbed gravitationally by a giant planet on an inclined orbit Source of a distribution of grains produced through collisional evolution (Zuckerman & Becklin 1993, Holland et al. 1998, Dent et al. 2000, Pantin et al. 1997) (Augereau et al. 2001, see also Mouillet et al. 1997)

56 Concluding Remarks 1. SED: (sub)mm slope 2. Shape of 10μm silicate feature 3. Scattered light polarization 4. Multi-wavelength imaging 5. Vertical Disk Structure

57 Concluding Remarks Vortices => Local Density Enhancements => enhanced grain growth (e.g., Wolf & Klahr 2003, Klahr & Bodenheimer 2006)

58 Concluding Remarks 1. Gaps 2. Global Spiral Structures 3. Planetary Accretion Region 4. Center-of-light-wobble 5. Inner holes SIM

59 Concluding Remarks 1. Characteristic Asymmetric Patterns 2. Shape of the mid-infrared Spectral Energy Distribution 3. Warps (β Pic)

60 Concluding Remarks Theoretical investigations show that the planet-disk interaction causes structures in circumstellar disks, which are usually much larger in size than the planet itself and thus more easily detectable. The specific result of the planet-disk interaction depends on the evolutionary stage of the disk. Numerical simulations convincingly demonstrate that high-resolution imaging performed with observational facilities which are already available or will become available in the near future will allow to trace these signatures of planets. These observations will provide a deep insight into specific phases of the formation and early evolution of planets in circumstellar disks.