Space Interferometry Mission: Planets & More

S. R. KulkarniCalifornia Insitute of Technology

Key Goals

• Inventory of Extra-solar planets• Search for terrestrial mass planets• Accurate Cosmic Distance Scale• Measure the Age of the Universe• Determine Mass & Matter Makeup of

Galaxy• Fundamental Stellar Astronomy• Define Fundamental Astrometric Frame

SIM: Modes

• Wide Angle Astrometry: Distance & Dynamics

position (ra, dec) & proper motion: 4 microarcsec

• Narrow Angle Astrometry: Planets angular difference: 1 microarcsecond

(These are the precision to be achieved by end of mission)

The Distance & Age Scale

• Cepheid distance to 1%• RR Lyrae stars in globular clusters Turnoff stars & estimate cluster age

• Rotational parallaxes to nearby galaxes

Dynamics of GalaxiesDark Matter and Merger History

• Gravitational potential of Milky Way - 3-d velocities of targets (to 100 kpc) tidal streams• Dynamics of Local group and nearby

galaxies - proper motion of V=16-20 mag stars

SIM: A Michelson Interferometer

Three Colinear Fixed Baseline Interferometers

Baseline: 10 mWavelength: 0.4-1 micron (CCD)Aperture: 0.3 mField of View: 0.3 arcsecondResolution: 10 milliarcsecond

Orbit: Earth Trailing (SIRTF)Launch: 2009 Lifetime: 5 yr (10 yr?)

How does SIM work?

Basic Interferometry Equation: Delay = B . s + C B = baseline s = source direction C = instrumental constant

Stabilize with 2 grid stars observed with “guide” interferometers

Measure B from observations of grid starsMeasure Delay with “science” interferometers

http://planetquest.jpl.nasa.gov/simcraft/sim_frames.html

SIM & Son of SIM

•15 external metrology beams (simpler because they’re not deployed)•No deployed boom •4 siderostats (8 telescopes)

•10m baseline only, for science•No Beam switchyard•No nulling beam combiner

http://planetquest.jpl.nasa.gov/simcraft/sim_frames.html

•36 external metrology beams•9m deployed boom (for external metrology)•7 siderostats/telescopes 1m to 10m baseline•Beam switchyard to combine any 2 telescopes•4 astrometric beam combiners, 1 nulling combiner

Rescoped Capabilities• Requirement: 30 microarcsecond Goal: 4 microarcsecond• Narrow Angle Astrometry Requirement: 3 microarcsecond Goal: 1 microarcsecond• Wide Angle Astrometry

LOST Capabilities

Imaging (no variable baselines) Nulling

Reference Frame: Critical

SIM Frame: 3,000 metal poor K giants

Tile: 15 degree diameter “Field of Regard” (FOR) or TileOverlap: 12 stars in any FORGrid Campaigns: 25% of mission lifetime

The 15-degree SIM Field of Regard is large enough to include most of Orion. A set of measurements within the same field of regard, about an hour long, forms a “tile.”

The bright star on the upper left is the red giant Betelgeuse. Red giants will form the grid of 1302 stars whose positions will be used to assess the attitude and length of the science baseline during each “tile”.

Wide Angle: Comparison

Narrow Angle Astrometry

Measure REFERENCE-TARGET angle

Ideally, REFERENCE star will be: - Bright (10 mag) - Close on sky (avoid field errors) - must lack planets

Planet Detection: Comparison

Detection LimitsSIM: 1 as over 5 years (mission lifetime)Keck Interferometer: 20 as over 10 years

1A.U. ~ 150,000,000 km

~80 A.U.

Orbital Parameter Planetary Property

Mass atmosphere?Semimajor axis temperatureEccentricity variation of tempOrbit Inclination Period (coplanarity)

Astrometry Yields All Orbital Parameters

Reference Stars: Requirements

Reference stars should not have planets!

Moderate distance K giants (mini-grid)

or Eccentric Binaries

Reference Star: K giants

Considerable Preparatory Work: Identification & Stability

Reference Stars: Eccentric G star binaries

Eccentric binaries do not possess planets over a range of orbital separation.

Risk: Uneasy Feeling

Accuracy & Precision

• 1 as ( 5 picoradian) is 50 picometers. - No mechanical structure is this accurate or even

this stable. - No optical surface is this accurate.

• SIM achieves the required precision:– Metrology (measures changes in the optical bench)– Calibration (to remove biases due to imperfect

optics)- Rapid Chopping (30 to 60 sec) to overcome thermal instability

100 mas 10 mas 1 mas 100 µas 10 µas 1 µas

Photo CCDFAME GAIA SIM

PTI KI

Planet Detection: Comparison

• SIM has highest sensitivity (fainter targets)

• SIM is a pointed spacecraft - optimize for planet detection/orbit

determination

• GAIA (FAME) are scanner• End of Mission precision for SIM is 20 times

better than GAIA

Single measurement accuracy

Hip.

SIM Science Team

Name Institution Key Project

Dr, Geoffrey Marcy University of California, Berkeley Planetary Systems

Dr. Michael Shao NASA/JP (science team chair) Extrasolar Planets (EPIcS)

Dr. Charles Beichman NASA/JPL Young Planetary Systems and Stars

Dr. Todd Henry Georgia State University Stellar Mass-Luminosity Relation

Dr. Steven Majewski University of Virginia Measuring the Milky Way

Dr. Brian Chaboyer Dartmouth College Pop II & Globular Clusters (Age)

Dr. Andrew Gould Ohio State University Astrometric Micro-Lensing

Dr. Edward Shaya Raytheon ITSS Corporation Dynamic Observations of Galaxies

Dr. Kenneth Johnston U.S. Naval Observatory Reference Frame-Tie Objects

Dr. Ann Wehrle NASA/JPL Active Galactic Nuclei

Mission Scientists

Dr. Guy Worthey Washington State Education & Public Outreach ScientistDr. Andreas Quirrenbach University of California, San Diego Data ScientistDr. Stuart Shaklan JPL Instrument ScientistDr. Shrinivas Kulkarni California Institute of Technology Interdisciplinary ScientistDr. Ronald Allen Space Telescope Science Institute Imaging and Nulling Scientist

Knowledge and Ignorance of Extrasolar Planets

What we know: Eccentric orbits are common:

scattering?– Several multiple systems of giant planets

are known– Mass distribution extends below Saturn

mass– Giant-Planet occurrence is high: ~7%

Knowledge and Ignorance of Extrasolar Planets

•What we don’t know– Existence of terrestrial planets– Planetary system architecture– Mass distribution

• Coplanarity of orbits, eccentricities• Only astrometry measures the mass of a planet

unambiguously

– Low-mass planets (rocky) in ‘habitable zone’ ?

EPIcs: A two-pronged search

Known extra-solar system planets (7%) are different (orbital period and eccentricity distribution)

Two possibilities:• Solar System is unique.• Planetary Systems are ubiquitous BUT diverse

Tier 1-Tier Program

100 nearby stars at 1.5 microarcsec 1000 nearby stars at 4 microarcsec

Extra-solar Planet Interferometric Survey(EPIcS)

M. Shao & S. R. Kulkarni (Co-PI)

S. Baliunas C. BeichmanA. Boden D. Kirkpatrick D. Lin D. StevensonT. Loredo S. UnwinD. Queloz S. Shaklan C. Gelino just joined S. TremaineA. Wolszczan

http://www.astro.caltech.edu/~srk

Tier-1: Search for Terrestrial Planets

~ 100 of the nearest stars (FGK)

• Habitable zone• Sensitivity: ~3

Me

Tier-2 Sample

1000 stars in approx. 30-pc radius

• Span the spectral range• Span range of ages• Span range of metallicty• Span range of debris disks (SIRTF)• Binary Stars

Tier-2 Addresses Broad Issues

• What is the mass function of planets?• How is composition related to mass? [sub-Jupiters, superGanymede]• How common are terrestrial planets?• How does the presence of planet affect

others?• How do properties of planetary systems

depend on the nature of their host stars?

SIM’s anticipated Contribution

• First terrestrial planets (within 10 pc)• Comprehensive view of planetary architecture• Unambiguous masses of known planets

• Planetary Demographics

• Reconnaissance for TPF– Specific targets for TPF around nearby stars– Target masses known (needed to calculate planet

density)

Interdisciplinary Program

S. R. Kulkarni (PI), B. Hansen, E. S. Phinney, M. H. van Kerkwijk, G. Vasisht

Goals:• Planets around white dwarfs• Masses of neutron stars and black holes• Distances (hence radii) of neutron stars (e.g. Cen

X-4)• Origin of high latitude OB stars & velocity kicks• Frame tie between SIM and ecliptic coordinate

system

Now!

• Palomar Testbed Interferometer Development of Phase referencing (B. Lane PhD) M-dwarf diameters Cepheid Pulsations

• Keck Interferometer Fundamental Stellar Astronomy (Comm. Team)

• Binaries: Very Narrow Angle Interferometry Adaptive Optics Precision Radial Velocity

Astrometry: Regimes

Very Narrow Angle Astrometry

Shao & Colavita

The Gl 569 System

• Apparent binary star system located at a distance of 9.8 pc

• Primary is a M0V • Companion located

~5 arcsec away. Appears to be late-M type.

The Orbit of Gl 569 B

P = 892 ± 25 d a = 0.90 ± 0.02 AU e = 0.32 ± 0.02 i = 34 ± 3 deg

Residuals ~ 2 mas

The Total Mass of the System

• From the period and semi-major axis we can determine the total mass of the Ba-Bb pair to high precision

• 3 upper mass limit for the pair is 0.148 Solar masses

Palomar Testbed Interferometer

• 100-m baseline, 40-cm siderostats• H, K bands • Highlights: M dwarf diameter

determination Pulsations of Cepheid

variable Herbig Ae/Be star

Distance to Pleiades via Atlas

X-P Pan, M. Shao & S. Kulkarni(Nature, negotiating with Editor)

• Pleiades is a gold standard for intermediate mass stars, brown dwarfs and Cepheid distance scale

• Hipparcos team published distance to Pleiades

D = 118 +/- 4 pc• Traditional distance (color-mag diagram) D = 131 +/- 3 pc

Hipparcos result generated “lively” controversy.

Orbit of Atlas (Mark III & PTI)

P(orbit)= 291day

a = 13 mase = 0.245 Inclination=10

8d

Distance via Kepler’s 3rd lawA3 = d3 a3= (m1+m2)P2

Search for Planets in Speckle Binaries

• Lane and Mutterspaugh have demonstrated very narrow angle astrometry with PTI (fringe scanning)

• We are starting a 3-yr survey to search astrometrically for planets

-> achieved 20 microarcsec• Konacki has successfully achieved 10

m/s RV for binary stars with HIRES

IR Spectroscopy

Resulting spectral types: M8.5 and M9