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Space Interferometry Mission:
Planets & More
S. R. Kulkarni
California Insitute of Technology
Key Goals
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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 Galaxies
Dark 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:
Wavelength:
Aperture:
Field of View:
Resolution:
10 m
0.4-1 micron (CCD)
0.3 m
0.3 arcsecond
10 milliarcsecond
Orbit:
Launch:
Lifetime:
Earth Trailing (SIRTF)
2009
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 stars
Measure Delay with “science” interferometers
http://planetquest.jpl.nasa.gov/simcraft/sim_frames.html
SIM & Son of SIM
•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
•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/simcra
ft/sim_frames.html
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 Tile
Overlap:
12 stars in any FOR
Grid 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 Limits
SIM: 1 as over 5 years (mission lifetime)
Keck Interferometer: 20 as over 10 years
Astrometry Yields All Orbital Parameters
1A.U. ~ 150,000,000 km
~80 A.U.
Orbital Parameter
Planetary Property
Mass
Semimajor axis
Eccentricity
Orbit Inclination
Period
(coplanarity)
atmosphere?
temperature
variation of temp
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
Planet Detection: Comparison
100 mas
Photo
Hip.
CCD
10 mas
1 mas
PTI
FAME
KI
GAIA
100 µas
10 µas
SIM
Single
measurement
accuracy
1 µas
• 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
SIM Science Team
Name
Dr, Geoffrey Marcy
Dr. Michael Shao
Dr. Charles Beichman
Dr. Todd Henry
Dr. Steven Majewski
Dr. Brian Chaboyer
Dr. Andrew Gould
Dr. Edward Shaya
Dr. Kenneth Johnston
Dr. Ann Wehrle
Institution
University of California, Berkeley
NASA/JP (science team chair)
NASA/JPL
Georgia State University
University of Virginia
Dartmouth College
Ohio State University
Raytheon ITSS Corporation
U.S. Naval Observatory
NASA/JPL
Key Project
Planetary Systems
Extrasolar Planets (EPIcS)
Young Planetary Systems and Stars
Stellar Mass-Luminosity Relation
Measuring the Milky Way
Pop II & Globular Clusters (Age)
Astrometric Micro-Lensing
Dynamic Observations of Galaxies
Reference Frame-Tie Objects
Active Galactic Nuclei
Mission Scientists
Dr. Guy Worthey
Dr. Andreas Quirrenbach
Dr. Stuart Shaklan
Dr. Shrinivas Kulkarni
Dr. Ronald Allen
Washington State
University of California, San Diego
JPL
California Institute of Technology
Space Telescope Science Institute
Education & Public Outreach Scientist
Data Scientist
Instrument Scientist
Interdisciplinary Scientist
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
A. Boden
D. Lin
T. Loredo
D. Queloz
S. Shaklan
S. Tremaine
A. Wolszczan
C. Beichman
D. Kirkpatrick
D. Stevenson
S. Unwin
C. Gelino  just joined
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
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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 BaBb 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 mas
e = 0.245
Inclination=108d
Distance via Kepler’s 3rd law
A3 = 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