Science with the SIM Lite Astrometric Observatory

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Science with the SIM Lite Astrometric Observatory
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Outline

• Introduce SIM Lite and the current program of SIM
  science
• Summarize the plan for future opportunities to
  propose for SIM Lite Astrometric Observatory
  observations
• Describe how SIM Lite works

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1. What is SIM Lite?

• SIM Lite is short for SIM Lite Astrometric
  Observatory, a fully capable but less expensive
  derivatove of the Space Interferometry Mission,
  SIM, and SIM PlanetQuest.
• One of key missions in NASAs Exoplanet
  Exploration Program.

• Precision astrometry on stars to V20.
• Optical interferometer on a 6 m structure.
• One science interferometer.
• One guide interferometer and one precision guide
  telescope to stabilize the fringes.
• Launch date in the coming decade
• Astrometry requires patience !
• Global astrometric accuracy 4 microarcseconds
  (µas).
• At end of 5 year mission lifetime.
• Narrow-field astrometric accuracy 1 µas, in a
  single measurement.
• Current state of the art is HST/FGS at 500 µas.
• Ground-based differential astrometry will reach
  20 µas.
• Typical observations take about 1 minute 5
  million observations in 5 years.

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SIM Lite Configuration
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SIM Science Objectives

• Broad program
• Searches for low-mass planets
• Study of planetary systems
• Stellar astrophysics
• Galactic structure
• Dynamics of the Galaxy and stellar systems
• Ages of stars and the Galaxy
• Structure and dynamics of Active Galactic Nuclei
• More information on SIM is at http//sim.jpl.nasa.
  gov and
• "Taking the Measure of the Universe Precision
  Astrometry with SIM,"
• SIM Science Team, 2008, PASP, 1203888,
  available at http//planetquest.jpl.nasa.gov/SIM/
  SIM-PASP2.pdf
• SIM Lite Astrometric Observatory, a soft-cover
  book released in January 2009, http//planetquest.
  jpl.nasa.gov/SIM/news/index.cfm?FuseActionShowNew
  sNewsID27
• See "Science with the Space Interferometry
  Mission" at http//planetquest.jpl.nasa.gov/Navig
  ator/library/SIM_Final_2.pdf
• Contains excellent 2-3 page summaries of each Key
  Project

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SIM Science Team Key Science Projects Dr.
Geoffrey Marcy U. California,
Berkeley Planetary Systems Dr. Michael Shao
NASA/JPL Extrasolar Planets Dr. Charles
Beichman MSC/Caltech Young Planetary Systems
and Stars Dr. Andrew Gould Ohio State
University Astrometric Micro-Lensing Dr. Edward
Shaya Univ. of Maryland Dynamic Observations
of Galaxies Dr. Kenneth Johnston U.S. Naval
Observatory Reference Frame-Tie Objects Dr. Brian
Chaboyer Dartmouth College Population II
Distances Globular Clusters Ages Dr. Todd
Henry Georgia State University Stellar
Mass-Luminosity Relation Dr. Steven Majewski
University of Virginia Measuring the Milky
Way Dr. Ann Wehrle Space Science
Institute Active Galactic Nuclei Mission
Scientists Dr. Guy Worthey Washington State
University Education Public Outreach
Scientist Dr. Andreas Quirrenbach University of
Heidelberg Data Scientist Dr. Stuart Shaklan
NASA/JPL Instrument Scientist Dr. Shrinivas
Kulkarni Caltech Interdisciplinary
Scientist Dr. Ronald Allen Space Telescope
Science Inst. Synthesis Imaging Scientist
Only Principal Investigators listed. Including
co-investigators the SIM Science Team has 86
members.
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Planet Detection with SIM

• Deep search for terrestrial planets
• Broad survey of planetary system architectures
• Planetary systems Around young stars

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Knowledge and Ignorance of Extrasolar Planets

• What we do know
• Giant planet occurrence is high 7
• Mass distribution extends to super-Earth masses
• Eccentric orbits are common scattering?
• Many multiple systems of giant planets are known
• What we dont know
• Existence of terrestrial planets
• Are there low-mass planets in habitable zone ?
• Planetary system architecture
• Coplanarity of orbits
• Mass distribution of planets is incomplete and
  has strong selection effects
• What about spectral type?
• Stellar age?
• Evolutionary state?

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Accurate masses are important

• Mass is a fundamental astrophysical quantity
• along with radius, density, temperature, chemical
  composition
• Accurate masses are notoriously difficult to
  measure
• Spiral galaxy mass from luminous matter vs.
  rotation curves ?
• dynamical masses preferred
• ? radial velocities and astrometry
• SIM will measure the mass of every planet it
  detects
• Accuracy depends only on the performance of the
  instrument
• not on models or assumptions
• Accurate masses are complementary
• Combine with transit data or direct detection to
  measure density of the planet

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Towards a Planetary Census

• Radial velocity studies have identified gas
  giants around 710 of nearby stars on orbits
  within 1-3 AU
• Transits will determine incidence of Earths in
  habitable zone around hundreds of stars Kepler.
  
• Next decade will yield a census of planets down
  to a few Mearth
• Astrometric interferometry will detect and
  characterize gas giants around 2,000 stars and
  rocky planets around 100 stars
• ? Target list for Terrestrial Planet Finder (TPF)

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Deep Search for Terrestrial Planets

• Are there Earth-like (rocky) planets orbiting the
  nearest stars?
• Sample of 100 of the nearest stars
• Focus on F, G, K stars within 10 pc
• Concentrate on the habitable zone
• Sensitivity limit is 0.7 ME in a 1 AU orbit, at
  10 pc (5.8 ? detection)
• Requires 1 µas single-measurement accuracy
• 25 measurements in each axis

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Deep Search for Terrestrial Planets
Masses of 104 known planets
E
J
S
U
N
V

• Ground-based radial velocity technique detects
  planets above several Earth masses.
• SIM will detect and measure planets down to 1
  Earth mass.

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Astrometry at 1 mas precision
Performance worth waiting for dynamical masses
of terrestrial planets
Error bars are 1 µas
Simulation of detection of terrestrial planets
around stars at 5 pc Data are positions of
solar-mass parent stars photocenter during 5
year mission.
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Broad Survey of Planetary Systems

• Out of all planetary systems discovered to-date,
  only one resembles our solar system
• We ask
• Is our solar system normal or unusual? E.g. gas
  giants
• Are planets more common around sun-like stars?
  Contrast with A, B type stars
• What are the architectures of other planetary
  systems? E.g., coplanar?

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Investigate Coplanarity of Doppler Detected
Multiple Systems
Weve assumed they are coplanar. We have
theoretical and simulation results supporting
this assumption. But are they really coplanar?
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Planets around Young Stars

• Questions
• 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?
• Search for Jupiter-mass planets around young
  stars to understand formation and evolution of
  planetary systems.
• Study 150 stars with ages from 1- 70 Myr
  Distances from 50 to 150 pc V 11-12
• A Jupiter at 1 AU around 0.8 Mo star produces 8
  µas signal at 140 pc.
• Determine physical properties of young stars
  through precise measurements of distances and
  orbits of young stars in multiple systems
• Masses, ages, evolutionary tracks of stars lt 1 M?
  are poorly known.

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Beyond Planet Detection SIM Covers the Entire
Galaxy

• Global astrometric precision to 4 µas
  (microarcseconds)
• and
• Faint targets down to 20th mag
• The combination of these two capabilities is not
  matched by any other instrument or mission

Hipparcos 100 pc
What is a parsec ? Parallax of one arcsecond At
1 pc Earth-Sun subtends 1 arcsec 1 parsec 3.26
light-years distance to closest stars
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Stellar Evolution and the Distance Scale

• Distances in the Universe are uncertain because
  we dont know the distances to standard candle
  stars
• SIM will measure accurate distances
• Masses of most stars are very poorly known
• SIM will measure accurate masses (to 1 ) by
  using binary orbits
• Stellar evolution models cant be further tested
  without accurate masses for exotic objects
• SIM will measure the masses of OB (massive)
  stars, supergiants, brown dwarfs

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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
• How?
• By observing samples of stars throughput the
  Galaxy
• By sampling different star populations

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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
• SIM provides
• Astrometric motions of stars out to 20 kpc
• Why SIM?
• Need astrometric accuracy
• and sensitivity

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Dynamics of Galaxy Groups within 5 Mpc

• Simulation
• Simulated 3-D motions projected onto a plane
• Smeared tracks show the simulated motions of
  galaxies
• Circles show current positions

• SIM will test this model
• SIM will measure current 2-D velocities across
  the sky

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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

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3. How SIM Works

• SIM sees 15 degrees in its field of regard, of
  which any 2 arcseconds can be observed with the
  science interferometer (one baseline
  orientation).
• Interferometer observes objects sequentially
  within a 15 degree tile, including reference
  grid stars (K giants) and science targets. Bright
  stars take about 60 seconds of observing time,
  including siderostat movement. A tile takes about
  an hour.
• Spacecraft then slews to the next tile and
  observes some of the same grid stars and new
  science targets. Continue around celestial
  sphere.
• Spacecraft baseline slowly rotates, eventually
  capturing perpendicular baseline orientation.
• SIM will execute about 5 million observations in
  5 years, which is a non-trivial scheduling
  challenge.

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Planet Search Observing Scenario
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Sky Coverage of Astrometric Grid Stars

• 1300 stars
• Magnitude 12
• Stable to 1 µas

• Monitoring
• Program
• Phase 1 complete candidate star identification
• Phase 2 ongoing precision radial-velocity
  monitoring

----- Celestial equator -----
Galactic plane
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Summary

• SIMs currently selected science program includes
  planetary searches, main-sequence and exotic
  star astronomy, Galactic dynamics, Local Group
  motions, and AGN astrophysics
• Astronomers will propose for additional science
  programs, including Science Team Key projects and
  General Observer projects.

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Backup
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Parameter space for planetary companions