Курс Лекций: «Современные Проблемы Астрономии» для студентов Государственного Астрономического Института им. П.К. Штернберга 7 февраля 23мая 2011

Transcription

1 Lecture 3.2: Space Interferometry Mission: SIM PlanetQuest, it s Design, Technology & Science В. Г. Турышев Jet Propulsion Laboratory, California Institute of Technology 4800 Oak Grove Drive, Pasadena, CA USA Государственный Астрономический Институт им. П.К. Штернберга Университетский проспект, дом 13, Москва, Россия Курс Лекций: «Современные Проблемы Астрономии» для студентов Государственного Астрономического Института им. П.К. Штернберга 7 февраля 23мая 2011

2 Overview What is SIM PlanetQuest? Overview of the current design Observing mode What does SIM measure? How does SIM work? Science with SIM: Earth-like planet-hunting Measuring distances with SIM Taking the measure of the Universe

3 Scales for Comparison Hydrogen atom radius ~ 26 pm Helium atom radius ~ 31 pm Salt crystal cell width ~ 560 nm Sucrose (table sugar) cell width ~ 1 nm stellar wobble due to planet motion Delay change for 1 as angle ~ 44 pm 9 m 44 pm 1 as Science Baseline

4 1 μas = thickness of a nickel on the Moon, as seen from Earth Hydrogen atom radius ~ 26 pm Delay change for 1 as angle ~ 44 pm

5 Scale: Units and Objects Objects: Full Moon: ½ degree = 1800 arcsec Jupiter s disk (apparent equatorial diameter): arcsec Parallax of: Nearest star (Proxima Centauri, ~1.3 pc): 0.77 arcsec Sirius (brightest star in the night sky, 2.7 pc = 8.6 light years): 0.38 arcsec Galactic Center (8.5 kpc distant, Sagittarius): arcsec =118 µas Far edge of Galactic disk (~20 kpc; look above Taurus in winter): 50 µas Nearest spiral galaxy (Andromeda Galaxy, ~0.7 Mpc; see it in autumn with binoculars or unaided eye): 1.3 µas ******************************************************************************************* Hair diameter 100 µm = 100,000 nm Light waves nm Atoms 0.1 nm = 100 pm

6 Space Interferometry Mission

7 The size of SIM ~12 m

8 SIM Configuration Science Interferometer Field of Regard Guide Interferometer Fields of View External Metrology Beams Guide Corner Cube Guide Compressor Optical Delay Lines (ODLs) Astrometric Beam Combiners (ABCs) External MET Beam Launchers Science Compressor

9 SIM PlanetQuest Design and Performance Science Interferometer Baseline Guide Interferometer Baselines Wavelength range Telescope Aperture Astrometric Fieldof Regard Narrow Angle Field of Regard Detector Orbit Science Mission Duration 9 m 7.2 m m 0.30 m diameter 15degrees 1 degree Si CCD Earth trailing solar orbit 5 years Global l Astrometric Gid& Grid Wide Angle Astrometry 4 µas mission i accuracy Narrow Angle & Planet finding Astrometry (1 ) Limiting Magnitude 1 µas single measurement accuracy 20 mag More information on SIM is available at:

10 What s An Orange Peel? Orange peel coverage means that the celestial sphere iscovered ina spiral pattern that moves from one side of the sphere to the opposite side. Escher

11 Observing scenario containing objects of interest

12 SIM Astrometric Measurements Astrometric Tiles B d s B c Grid of stars is measured over entire sky Grid is referenced to extra galactic objects Position, parallax, proper motion are measured for all grid stars Science targets are measured wrt grid Grid is subdivided into 15 degree tiles 6-8 grid stars per tile Up to 50 additional science targets Tiles centered on grid stars Tiles overlap SIM measures angle between stars in a grid. S/C attitude is held fixed Instrument scans over 15 degree tile

13 Astrometric Field of Regard G G W G G R Guide N R R W W R R G G W G The Field Of Regard covers Orion red giants form the grid of reference stars.

14 All objects are moving, twisting and turning, so what is fixed? QSO We are here

15 How Precise is SIM? Microarcsecond precision opens a new window to a multitude of phenomena observable with SIM. Jupiter SIM Positional Error Circle (4 µas) Diameter arcsec Moons ~1-2 arcsec. Reflex Motion of Sun from 100 pc (axes 100 µas) Parallactic Displacement of Galactic Center Hipparcos Positional Error Circle (0.64 mas) Apparent Gravitational Displacement of a Distant Star due to Jupiter 1 HST Positional Error Circle degree away (~1.5 mas)

16 Astrometry with an Interferometer External path delay x = B sin( ) i( ) detected intensity Siderostat 1 Baseline Vector external internal dl delay 0 Siderostat 2 detector Beam Combiner Internal path delay Delay Line Astrometric quantity is the change in delay-line position between targets

17 Astrometry with an Interferometer External path delay x = B sin( ) i( ) detected intensity Siderostat 1 Baseline Vector external internal dl delay 0 Siderostat 2 detector Beam Combiner Internal path delay Delay Line Astrometric quantity is the change in delay-line position between targets

18 SIM PlanetQuest Flight System Architecture Science and Guide Collector Bay #1 Optical Delay Lines (8) Astrometric Beam Combiners (4) Star Trackers Science and Guide Collector Bay #2 Sun Shades(4) Spacecraft Precision Structure Subsystem (MLI removed) Instrument Backpack High Gain Antenna Solar Array

19 Global Astrometry Observing Scenario 15deg field ~3.5-5deg Science stars Grid stars Spacecraft slew direction

20 Planet Search Observing Scenario ~1 o field 15 o Field of Regard Science target Grid star Science target Reference star

21 Ready to build! External Metrology Launcher Metrology Source Instrument Double Corner Cube Nanometer Control & Picometer Knowledge: Flight Ready Hardware (TRL6 since 2005) Spacecraft& Instrument Electronics Internal Metrology Launcher

22 SIM Covers the Galaxy The history of astronomy is entwined with the determination of reliable distances Size of the Galaxy Size of the Local Group Size of the Universe Origin of Gamma ray bursts SIM is a distance measuring machine Hipparcos (10%, 11 mag max) SIM (10%, 20 mag max) Gaia (10%, 15 mag max) Accuracy 1% 10% (20 th mag and brighter) SIM 2.5 kpc 25 kpc GAIA 0.4 kpc 4 kpc Hipparcos kpc 0.1 kpc

23 Principle of Astrometric Planet Detection How Much Wobble? Orbit parameter Mass Semi major axis Eccentricity Orbit Inclination Period Planet Property Atmosphere? Temperature Variation of temp Coplanar planets? The wobble effect : our Solar System as seen at 10 pc 1 tick mark = 200 µas SIM accuracy = 1 µas (single meas.) Sun-Jupiter wobble = 500 µas Sun-Earth wobble = 0.3 µas

24 SIM Earth Analog Discovery Space? After Ida & Lin (2004, ApJ, 604, 388) Current harvest of 264 planets by Radial Velocity (RV): Adds empirical constraints to planetary system formation. Jupiter & Neptune appear to be the tip of the planetary iceberg Radialvelocity (RV) will press on icy planets and close in planets Transit & Microlensing will provide statistical census of rocky planets eg. Kepler, 1 kpc eg. Microlensing, 5 kpc SIM: uniquely probes 1~10 M Earth (0.4~6.0AU) for nearby stars Orbital parameters and mass for RV planets

25 SIM Planet Finding Capabilities Potentially Habitable Planets defined as: Terrestrial planets in the habitable zone, where HZ = (0.7 to 1.5)(L star /L sun ) 0.5 AU Mass: 0.33 M to 10 M Radius: 0.5 R to22r 2.2 Orbit: e 0.35 Deep search of 120 nearby stars within 30 parsecs Based on a 5 year science mission with 1 µas single measurement accuracy with a 1.4 μas differential measurement in ~ 20 minutes, and An allocation of 17% of SIM mission An allocation of 17% of SIM mission observing time

26 How Do Stars Evolve? SIM will permit 1% mass measurements over the whole range of stellar types, including Black holes, OB stars to brown dwarfs, and white dwarfs. SIM can obtain precision masses for stars in clusters covering a range of ages (1 Myr -- 5 Gyr) y) and a variety of metallicities SIM will use astrometry and photometry of micro-lensing events to determine physical properties of lensing stars

27 Calibrating the Cosmic Distance Scale Current parallax measurements reach only to ~100 pc. SIM can improve the value of the Hubble Constant, H 0, to between 1-2%. Rotational Parallaxes Cepheids RR Lyrae Stars

28 Gravitational Lensing to Probe Dark Matter Background star (dark) lens SIM Image Events are detected by Brightness enhancement (~days) ground based Astrometric perturbation (~weeks to months) SIM, ~100 µas Symmetry of track broken by Earth orbit motion due to lens parallax Hence: distance to lens Determine themassspectrum Derive: mass, distance, and velocity of the Milky Way of the lensing object

29 Taking Measure of the Milky Way SIM will probe the structure of our Galaxy: Fundamental measurements of: Total mass of the Galaxy Distribution of mass in the Galaxy Rotation of the Galactic disk Bar and spiral structure Mixing in the Milky Way s halo How? By observing samples of stars throughout the Galaxy By sampling different star populations Cover page from S. Majewski Key Project proposal

30 Extrasolar planetary systems: a growing and diverse field Discovery of first extrasolar planets around normal stars in 1995 started a renaissance of interest in the field Many instruments t and missions i bring key pieces to the overall picture: Ground-based radial velocities (RV) Ground-based transit and microlensing searches KI and LBTI - debris disks in the habitable zone HST - transits, and images of debris disks around planet-forming stars Spitzer - profiles of dust disks through h spectroscopy (and transits!) JWST - direct imaging and spectroscopy of warm Jupiters Kepler - statistics of terrestrial planet frequency Terrestrial planets around nearby stars: SIM PlanetQuest TPF-C TPF-I

31 Searching for Terrestrial Planets with SIM What We Don t Know Are planetary systems like our own common? What is the distribution of planetary masses? - Only astrometry measures planet masses unambiguously Are there low mass planets in habitable zone? A Broad Survey for Planets Is our solar system unusual? What is the range of planetary system architectures? Sample 2,000 stars within ~25 pc with sensitivity <<Jupiter mass A Deep Search for Earths Are there Earth like (rocky) planets orbiting the nearest stars? Focus on ~250 stars like the Sun (F, G, K) within 10 pc Detection limit of ~3 M e at 10 pc Sensitivity limit of ~1 M e at 3 pc Evolution of Planets How do systems evolve? Is the evolution conducive to the formation of Earth like planets in stable orbits? Do multiple Jupiters form and only a few (or none) survive?

32 Broad Survey of Planetary Systems Sample ~2000 stars within ~25 pc with sensitivity << Jupiter mass Questions: Is our solar system typical or unusual? Are planets more common around sun- like stars? What are the architectures of other planetary systems 55 Cancri: a planetary system like our own?

33 Planets around Young Stars What fraction of young stars have gas giant planets? Only SIM astrometry can find planets around young stars since active stellar atmospheres and rapid rotation preclude radial velocity or transit searches Do gas giant planets form at the water condensation line? SIM will survey ~200 stars to a level adequate to find Jovian or smaller planets on orbits <1 AU to >5 AU around stars from pc Does the incidence, distribution, and orbital parameters of planets change with age and protostellar disk mass? Study of clusters with ages spanning Myr to test orbital migration theories Correlate with Spitzer results on disks (at 4 24 m) Where, when, and how do terrestrial planets form? Understand the formation and orbital migration mechanisms of the giant planets No other technique before and possibly including TPF (RV, AO imaging, IR interferometry) can credibly claim to find planets down to Saturn Jupiter mass within 1 10 AU of parent stars at pc

34 What Will We Learn About Other Earths? Orbital Parameters (SIM) Stable orbit in habitable zone Characteristics for habitability Mass (SIM) Temperature (TPF) Temperature Variability (SIM) Radius (TPF) Albedo (TPF) Surface gravity (SIM+TPF) Composition (TPF) Atmospheric conditions (TPF) Indicators of Life (TPF) Presence of water (TPF) Multiple spectral lines in different Temporal variability (TPF) wavebands confirm initial detections and extend physical interpretation Solar System Characteristics For planets with atmospheres (and modest Influence of other planets (SIM) cloud cover), IR characterizes atmosphere Presence of comets or asteroids (TPF) while visible sees planetary surface

35 SIM Astrophysics Targets

36 SIM and GAIA: Different Science Virtually all SIM Science Team targets are beyond the reach of GAIA s capability

37 SIM: Searching for Other Earths......Studying the Foundations and Frontiers of Astrophysics SIM PlanetQuest sim.jpl.nasa.gov

38 Back-Up

39 Matter Distribution: Galaxy & Local Group SIM s precision is needed to understand the dynamics & mass/energy distribution in our Galaxy and in the Local Group. This will enable accurate time reversal simulations to understand how halo objects & our Local Group evolved with time. SIM s microlensing measurements will yield the true mass spectrum of the Galaxy. SIM will also obtain accurate masses for black holes and neutron stars, which are laboratories for strong ggravity, y,j jet formation, and dense matter. Tidal disruption of a Milky Way companion. Simulated 1 Gyr trajectories of our neighbors.

40 SIM Science (and fraction accomplished by GAIA) Key SIM Science Project Objectives GAIA % Find candidate habitable planets 0% Reconnaissance of young planetary systems ~0% Exo Planetary system contents census >Jupiter Unbiased galactic mass function (from micro lensing) 0% Local Galaxy group mass distribution (from motions) 8% Age of galaxy (from globular clusters and stellar models) 20% Star masses to 1% (SIM program emphasizes difficult types) ~0% Structure of Galaxy (size, spiral arms, tidal dlstreams, bulge, halo) hl) ~50% Motion in/of QSO s, AGN s 0% Coordinate frame tie to cosmological standard of rest (QSO s) ~90%

41 Cosmic scales Our whole Solar System Our Milky Way Galaxy And the neighborhood h would be this big would be the size of the United States. where we ve found new planets would only be the size of Manhattan.

42 Peer Reviewed Technology Gates Managing Technology Development Accomplishment of Technology Gates Against Original Due Dates Stated in May 2001 Letter Technology Gate 1 Description Next generation metrology beam launcher performance at 100pm uncompensated cyclic error, 20pm/mK thermal sensitivity Due Date 8/01 Complete Date 8/01 Performance Exceeded objective 2 Achieve 50dB fringe motion attenuation on STB-3 testbed (demonstrates science star tracking) 12/01 11/01 Exceeded objective 3 Demonstrate MAM Testbed performance of 150pm over its narrow angle field of regard 7/02 9/02 Exceeded objective 4 Demonstrate Kite Testbed performance at 50pm narrow angle, 300pm wide angle 7/02 10/02 Exceeded objectives 5 Demonstrate MAM Testbed performance at 4000pm wide angle 2/03 3/03 Exceeded objective 6 Benchmark MAM Testbed performance against narrow angle goal of 24pm 8/03 9/03 Exceeded objective 7 Benchmark MAM Testbed performance against wide angle goal of 280pm 2/04, 5/04* 6/04 Met objective 8 Demonstrate SIM instrument performance via testbed anchored predicts against science requirements 4/05 7/05 Met objective Legend pm = picometer mk = millikelvin db = decibel (50dB = factor of 300) *HQ directed a scope increase (by adding a numerical goal to what had been a benchmark Gate) and provided a three month extension when performance fell short.

43 SIM Technology Nearly Complete NASA HQ and SIM project laid out 8 Technology Milestones in Milestones prior to Phase B start 4 more Milestones prior to Phase C/D start Technology is on schedule! One Milestone remains Component Subsystem/System y Modeling/Testbed Technology Testbeds 5-7 Integration Complete! Complete! June 2005 Goal level performance has already been demonstrated in the SIM Testbeds! Technology Milestone 8 MAM KITE STB-3 TOM-3 Subsystem level Testbeds System level Testbed Modeling/Testbed Integration

44 Deep Search for Terrestrial Planets SIM will search for terrestrial ( Earth mass) planets, with a survey of ~250 nearby stars Direct mass measurement for each detection Detection limit is ~ 1-2 Earth mass at 3 pc First detections of terrestrial planets could occur within the first 1-2 years of observation

45 Earth Analog Survey TPF-C (8 m) Red curves: best, median, worst of 69 Earth Analog Survey targets, labeled by HIPPARCOS catalog number.

46 SIM: Unique Astrophysics Masses of stars Accurate dynamical masses for neutron stars and black holes - no more rough estimates The Galaxy and star clusters Ages of globular clusters; ages and evolution of open clusters Mass distribution of dark matter through microlensing and tidal tails Nearby galaxies Mass distribution, including dark matter, of the Local Group - directly measure galaxy motions Cosmology Unambiguous geometric distances to nearby galaxies; calibrate standard candles Ho to 2% - strongly constrain the equation of state of dark energy

47 Dynamics of Galaxy Groups within 5 Mpc Simulation from dynamical model Can t verify model because only 1-D velocity info is available (RV) SIM will provide critical data for improving the models SIM will measure current 2-D velocities across the sky Models will then sample the full 6-D phase space Simulated time lapse photo of 30 galaxies closest to our Milky Way (1 billion year exposure)

48 Dark Halo of our Galaxy Dwarf spheroidal galaxy orbits the Milky Way Gravitational forces pull out tidal tails of stars The orbits of these tails trace the past history of the dwarf They also trace the mass distribution of the Milky Way They are dynamically cold SIM provides: Astrometric motions of stars out to > 20 kpc Why SIM? Need astrometric accuracy Simulation by Kth Kathryn Johnston and sensitivity (Wesleyan University)

49 SIM and GAIA - Missions and Performance Narrow Angle single visit accuracy goal Wide angle end of mission absolute accuracy goal Operation mode Other functionality SIM GAIA 1 arcsec ~70 arcsec 4 arcsec arcsec Pointed observations of science targets plus reference grid Interferometric imaging (selected sources) GO program Yes No Limiting magnitude V ~ 20 V ~ 20 Phase/Launch B/2015 B/2011 All sky scanning survey Concurrent photometry, radial velocity

50 SIM and GAIA: Different Science Both SIM and GAIA use astrometry to address a wide range of astrophysical questions: GAIA observes a large number of stars at low accuracy Science relies entirely on averaging data from many stars SIM selects samples of targets tailored to science questions Observes each star at very high accuracy Most are too faint to observe with GAIA SIM s ability to detect planets is 70 times better than GAIA Virtually all SIM Science Team targets are beyond the reach of Virtually all SIM Science Team targets are beyond the reach of GAIA s capability

51 Quasar Astrophysics Using Astrometry Quasars are the most powerful objects in the universe Many quasars emit twin jets of relativistic plasma Optical observations average the entire region Accretion disk, hot corona, jets Jets have been studied by VLBI (radio) at ~100 µas scales SIM will measure: position shifts due to variability color-dependent relative positions of the emission These measurements will open up a research area only studied with VLBI SIM can determine if the visible light from quasars originates in hot gas around an accretion disk or from a relativistic plasma jet SIM can detect the orbital motions of two merging black holes in the centers of massive galaxies

52 Observing Mode: Astrometry for the masses You don t need to be a black-belt astrometrist to use this mode Mode will deliver the 5 standard astrometric parameters : Position (RA, dec), parallax, proper motion (RA, dec) Accuracy ~10-50 µas, and magnitude range V ~ minutes per target, spread over 2 years; 5 visits x 2 coordinates Large number of targets (total ~20,000) Magnitude

53 Laboratory Demonstration R 2 R 3 T R 1 MicroArcsecond Metrology Testbed Narrow angle chopping sequence. SIM science interferometer T R 1 T R 2 T R 3 T R 4 Pseudo star + metrology connecting Repeated twice pseudostar to interferometer R 4

54 Demonstration of SIM Performance

55 Planet detection with SIM - minimum masses For each candidate star in turn, evaluate the mimimum detectable mass within the habitable zone Rank-order the stars, then plot as a cumulative distribution

56 SIM and GAIA Wide Angle Astrometry SIM Science Targets Accura acy arcs sec Wide Angle, end of mission limit performance Radio Ref Frame Nearby Galaxies Active Galactic Nuclei Precision masses Globular clusters SIM Magnitude

57 SIM & GAIA - Exo-Planet Detection Capability 100 GAIA Accu uracy a arcsec 10 1 Jupiters 1 5 AU Jupiters >5 AU SIM Earth like Planets End of mission effective Magnitude

58 NRC endorses SIM PlanetQuest Decadal (Bahcall) Review endorses AIM [now SIM PlanetQuest] (1991) would permit definitive searches for planets around nearby stars trigonometric distances throughout the galaxy would demonstrate the technology required for future missions Decadal (McKee & Taylor) Review (2001) reaffirms the 1991 NRC Committee by endorsing the completion of AIM enable the discovery of planets much more similar to Earth in mass and orbit than those detectable now survey the Milky Way 1000 times more accurately than is possible now CAA reaffirms scientific importance of SIM (2002) The CAA reaffirms the scientific excitement of the 2001 AASC for the important new planet-finding narrow-angle science capability of SIM NRC Decadal Review

59 Finding Planets & feeding candidates to TPF Finding a M E planet requires a high degree of confidence (~0.5 % false alarm probability) Enriching the sample for TPF-C can tolerate a much higher false alarm probability, up to ~10% Hypothetical SIM search program Survey best 35 stars 150 (2-D) visits Survey another 165 stars, 50 visits Total SIM time ~20% of 5 yr mission If terrestrial planets are common, should concentrate on a few stars with low mass planets If uncommon, search a larger sample at lower sensitivity Cumulative distribution function for terrestrial planet detection averaged over best 35 stars in TPF target list

60 SIM enrichment of the TPF candidate list Enrichment factor is ~3 Insensitive to and insensitive to false alarm rate Single visit precision: 1 µas 114 x 2 measurements on the best 35 stars 57 x 2 measurements on the next 183

61 SIM and TPF work well together Definite it targets: t stars with terrestrial-mass planets in Habitable Zone (HZ) Potential targets: stars with low SNR sign of a planet in HZ Low priority targets: stars with no hint of terrestrial-mass planets Avoid targets: stars with a giant planet in HZ Schedule TPF observations using SIM orbital information TPF much more efficient Joint solutions of TPF and SIM data allow better use of (low SNR) SIM detections Masses and orbits TPF inner working Angle

62 SIM s Reach Extends Across our Entire Galaxy to What makes SIM unique: Extreme astrometric precision 4 µas (microarcsec) positions 4 µas/yr proper motions 1 µas differential positions Ability to observe faint targets V <~ 20 Flexible scheduling optimize for specific science objectives Hipparcos 100 pc (distances to 10 %) You are here SIM 25k 2.5 kpc (distances to 1 %) SIM 25 kpc (distances to 10 %)

63 Dynamics of Galaxy Groups within 5 Mpc Simulation from dynamical model Fidelity is limited because only 1-D velocity info is available (RV) SIM will provide critical data for improving the models SIM will measure current 2- D velocities across the sky Models will then sample the full 6-D phase space Simulated time lapse photo of 30 galaxies closest to our Milky Way (1 billion year exposure)

64 Galactic Tidal Tails Much new info on Sgr Dwarf system Initial 2MASS work reveals >360deg arms Radial-velocity constraints With only 4-D constraints, t problems/contradictions remain: Modeling of Sgr and Galactic halo Leading Arm RVs wrong ; Prolate vs. Oblate ambiguity

65 Probing Active Galactic Nuclei w Astrometry 1. Does the most compact non thermal optical emission from an AGN come from an accretion disk or from a relativistic jet? 2. Do the cores of galaxies harbor binary supermassive black holes remaining from galaxy mergers? 3. Is the separation of the radio core and optical photocenter of the quasars used for the reference frame tie stable? Or does it change on the timescales of their photometric variability? SIM measurements: Relative astrometry between QSO and reference stars (or other QSOs) Global astrometry: motion of QSOs relative to global reference frame Departures from Hubble flow: z = 0.1, v = 10,000 km/s 6 µas / yr Astrometric shifts as a function of wavelength

66 Sample tile for relative astrometry SIM instrument field ( tile ) is 15 diameter Select tile centers for objects of interest Virgo tile contains: M87 3C 273 Two ICRF quasars ~6 halo K-giants

67 Astrometric signatures of AGN Expect no color shift, (or small shift ~1 5 µas) with no preferred axis; no preferred variability direction Up to ~100 µas? Expected variability direction: along jet Radio quiet AGN Radio loud AGN (Jet is weak, poorly collimated, or absent) Nonthermal central ionizing i i source (corona or wind) Optical jet (non thermal) Big blue bump (center of thermal accretion disk

68 Estimating the emission region size Accretion disks are small ~ 160 µas at 15 Mpc (M87) ~ 2 µas at z = 0.6 (3C 345) Hot corona region is also small ~ 70 R s corresponds to ~ 1 µas at z = 0.6 Konigl-type relativistic jet [e.g., Hutter and Mufson 1986] Power-law variation of particle density and magnetic field with radius Spectrum is superposition of emission from all radii Optical-depth variations results in shifts of position with frequency Large size: 100s x size of accretion disk Predicted large shift between radio and optical (>~ 100 µas) Example: 3C 345 (z = 0.6) Offset from BH expected to be ~ 80 µas Photocenter shift from red to blue ~ µas - in direction of jet Radio peak (22-GHz) offset ~ µas from BH

69 Astrometric Signature of a Black Hole Binary Binary black holes can be detected by astrometric reflex motion of their photocenter, just like we detect planets around stars Example: OJ 287 (z = 0.306) from Lehto & Valtonen (1996) P = 12 years; assumed mass ratio ~ 170 Semi-major axis ~ 0.06 pc = 22 µas (for H 0 = 100) Expected motion in 5 years ~ 18 µas and systematic, if emission comes from secondary ~ 0 (or random) if emission comes from primary Another example: 3C390.3 (z = 0.057) from Gaskell (1996) suggests a ~200yr period, and signal of ~ 10 µas

70 Nominal Allocation of Observing Time (5yr mission) OBSERVING CATEGORY % alloc Science observing time: Science Team (AO 1) (already awarded in 2000)* 36 % Science Team AO 2 (more terrestrial planet searches) (proposal call in 2006) 10 % (other key science) 10 % General Observer (GO 1) program (proposal call in 2007) 10 % General Observer (GO) 2 program (proposal p call in ~2011) (10 %) Director s Discretionary Time 3 % Astrometric grid observation (excluding slews) 9 % Spacecraft slews (~1 turn per hour) 12 % Engineering time (including reserve) 10 % Total 100 % *Searches for terrestrial planets: 10.3%; other Key Projects 22.9%; Mission Scientists 2.9%

71 Principle of Astrometric Planet Detection How Much Wobble? Orbit parameter Mass Semi major axis Eccentricity Orbit Inclination Period Planet Property Atmosphere? Temperature Variation of temp Coplanar planets? The wobble effect : our Solar System as seen at 10 pc 1 tick mark = 200 µas SIM accuracy = 1 µas (single meas.) Sun-Jupiter wobble = 500 µas Sun-Earth wobble = 0.3 µas

72 Keys to Understanding the Universe To understand the universe, we must first learn about objects distances and motions. To determine these parameters for an object, we measure, as precisely as possible: Position, the science of astrometry ( star-measure ). Position measurements, in turn, permit the determination of Parallax Distance Proper Motion Radial Velocity Unit of Distance: Space Velocity Parsec [pc] parallax second. A measure of distance based on a measurement of 1 arcsec of parallax. It corresponds to a distance of 3.26 light years. Objects: Full Moon (apparent diameter) 1800 arcsec Parallax of: Nearest star (Proxima Centauri, ~1.3 pc): 0.77 arcsec Nearest spiral galaxy (Andromeda Galaxy, ~0.7 Mpc): 1.3 µas

73 Units: SPACE INTERFEROMETRY MISSION Scale: Units and Objects - 1 arcsec second of arc. There are 360 degrees in a circle, 60 minutes of arc in a degree, and 60 seconds of arc in a minute. µas micro arc second (really, microsecond of arc). One millionth (10-6 ) of a second of arc. parsec parallax second. A measure of distance based on a measurement of 1 arcsec of parallax. It corresponds to a distance of 3.26 light years. Kpc kiloparsec: One thousand parsecs. Mpc megaparsec: One million parsecs. *************************************************************************** nm nanometer : 10-9 meter pm picometer: meter

74 Scale: Units and Objects - 2 Objects: Full Moon: ½ degree = 1800 arcsec Jupiter s disk (apparent equatorial diameter): arcsec Parallax of: Nearest star (Proxima Centauri, ~1.3 pc): 0.77 arcsec Sirius (brightest star in the night sky, 2.7 pc = 8.6 light years): 0.38 arcsec Galactic Center (8.5 kpc distant, Sagittarius): arcsec =118 µas Far edge of Galactic disk (~20 kpc; look above Taurus in winter): 50 µas Nearest spiral galaxy (Andromeda Galaxy, ~0.7 Mpc; see it in autumn with binoculars or unaided eye): 1.3 µas ******************************************************************************************* Hair diameter 100 µm = 100,000 nm Light waves nm Atoms 0.1 nm = 100 pm