1. Ron Allen - 1 18 May 2004 Science with the Space Interferometry Mission Ron Allen, STScI With thanks to: Ann E. Wehrle Michelson Science Center, Caltech …and others on the SIM Science Team

2. Ron Allen - 2 18 May 2004 1. What is SIM ? SIM is the Space Interferometry Mission –One of key missions in NASA’s Origins Program Precision astrometry on stars to V=20 Optical interferometer on a 10-m structure –One science interferometer –Two guide interferometers to stabilize the fringes Launch date: February 2010 –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 ~1 minute; ~ 5 million observations in 5 years

3. Ron Allen - 3 18 May 2004 10 meter science baselines 8.9 meter guide baselines Bay 2 Bay 1 Astrometric Beam Combiners Optical Delay Lines Guide FOV Science FOV External Metrology “Truss” SIM Configuration

4. Ron Allen - 4 18 May 2004 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 at: sim.jpl.nasa.gov See “Science with SIM” on our website –Contains excellent 2-3 page summaries of each Key Project

5. Ron Allen - 5 18 May 2004 Science Requirements on the Instrument Instrument Sensitivity –Less than 1.5 µas photon contribution for a V=10 star observed for 60 seconds –Magnitude limit V=18 Photon noise dominates CCD read noise/dark current –Practical magnitude limit is V=20 SIM can observe the brightest individual stars in nearby galaxies Instrument Calibration –Visibility accuracy of < 1% –Relative photometric accuracy of < 1% Imaging Demo –Ability to reconstruct an image of a few point sources –< 18 (u,v) points –Use radio astronomy “synthesis imaging” (like the VLA)

6. Ron Allen - 6 18 May 2004 Parallax is a small effect: James Bradley searched for it in 1725 - but discovered Stellar Aberration instead (± 20 arcsec) Nearest star (Proxima Cen)0.77 arcsec Sirius0.38 arcsec Galactic Center (8.5 kpc)0.00012 arcsec = 118  as Far edge of Galactic disk (~20 kpc) 50  as Nearest spiral galaxy (Andromeda Nebula) 1.3  as Measuring distances using parallax

7. Ron Allen - 7 18 May 2004 Hipparcos Positional Error Circle (0.64 mas) How Precise is SIM? HST Positional Error Circle (~1.5 mas) Microarcsecond precision opens a new window to a multitude of phenomena observable with SIM. Reflex Motion of Sun from 100pc (axes 100 µas) Parallactic Displacement of Galactic Center Apparent Gravitational Displacement of a Distant Star due to Jupiter 1 degree away SIM Positional Error Circle (4µas).

8. Ron Allen - 8 18 May 2004 SIM Science Team Key Science Projects Dr. Geoffrey Marcy U. California, BerkeleyPlanetary Systems Dr. Michael Shao NASA/JPLExtrasolar Planets Dr. Charles Beichman MSC/CaltechYoung Planetary Systems and Stars Dr. Andrew Gould Ohio State UniversityAstrometric Micro-Lensing Dr. Edward Shaya Univ. of MarylandDynamic Observations of Galaxies Dr. Kenneth Johnston U.S. Naval ObservatoryReference Frame-Tie Objects Dr. Brian Chaboyer Dartmouth CollegePopulation II Distances & Globular Clusters Ages Dr. Todd Henry Georgia State UniversityStellar Mass-Luminosity Relation Dr. Steven Majewski University of VirginiaMeasuring the Milky Way Dr. Ann Wehrle MSC/CaltechActive Galactic Nuclei Mission Scientists Dr. Guy Worthey Washington State UniversityEducation & Public Outreach Scientist Dr. Andreas Quirrenbach Leiden University Data Scientist Dr. Stuart Shaklan NASA/JPLInstrument Scientist Dr. Shrinivas Kulkarni MSC/CaltechInterdisciplinary 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.

9. Ron Allen - 9 18 May 2004 Planet Detection with SIM Deep search for terrestrial planets Broad survey of planetary system architectures Planetary systems Around young stars

10. Ron Allen - 10 18 May 2004 Masses and Orbits of Planets SIM Can Detect Planetary systems inducing low radial velocities (<10m/s) in their central star can be detected through the astrometric displacement of the parent star. Systems accessible only with SIM. SIM will be able to detect planets of a few Earth masses around nearby stars. Ground based astrometric techniques.

11. Ron Allen - 11 18 May 2004 Knowledge and Ignorance of Extrasolar Planets What we do know –Giant planet occurrence is high: ~7% –Mass distribution extends below Saturn mass –Eccentric orbits are common: scattering? –Many multiple systems of giant planets are known What we don’t 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?

12. Ron Allen - 12 18 May 2004 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

13. Ron Allen - 13 18 May 2004 Towards a Planetary Census Radial velocity studies have identified gas giants around 7~10 % of nearby stars on orbits within ~1-3 AU Transits will determine incidence of Earths in habitable zone around hundreds of stars Next decade will yield a census of planets down to a few M earth Astrometric interferometry will detect and characterize gas giants around 2,000 stars and rocky planets around 200 stars:  Target list for Terrestrial Planet Finder (TPF)

14. Ron Allen - 14 18 May 2004 Deep Search for Terrestrial Planets Are there Earth-like (rocky) planets orbiting the nearest stars? Sample of ~250 of the nearest stars –Focus on F, G, K stars within 10 pc –Concentrate on the habitable zone Sensitivity limit is ~3 M E in a 1 AU orbit, at 10 pc (~5  detection) –Requires 1 µas single-measurement accuracy –25 measurements in each axis

15. Ron Allen - 15 18 May 2004 EJS Masses of 104 known planets UNV Deep Search for Terrestrial Planets Ground-based radial velocity technique detects planets above a Saturn mass SIM will detect planets down to a few Earth masses and measure their masses

16. Ron Allen - 16 18 May 2004 ± 3 µas ± 5 µas ± 7 µas Error bars are 1 µas Astrometry at 1  as precision Simulation of detection of terrestrial planets around stars at 5 pc: Data are positions of solar-mass parent star’s photocenter during 5-year mission Performance worth waiting for: dynamical masses of terrestrial planets

17. Ron Allen - 17 18 May 2004 Broad Survey of Planetary Systems Out of 100 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?

18. Ron Allen - 18 18 May 2004 Investigate Coplanarity of Doppler Detected Multiple Systems We’ve assumed they are coplanar. We have theoretical and simulation results supporting this assumption. But are they really coplanar?

19. Ron Allen - 19 18 May 2004 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 M o 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 < 1 M o are poorly known

20. Ron Allen - 20 18 May 2004 Beyond Planet Detection: SIM Covers the Entire Galaxy Hipparcos 100 pc SIM 25 kpc (10 %) SIM 2.5 kpc (1 %) You are here 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 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

21. Ron Allen - 21 18 May 2004 Stellar Evolution and the Distance Scale Distances in the Universe are uncertain because we don’t 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 can’t be further tested without accurate masses for ‘exotic objects’ –SIM will measure the masses of OB (massive) stars, supergiants, brown dwarfs

22. Ron Allen - 22 18 May 2004 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) and a variety of metallicities SIM will use astrometry and photometry of micro-lensing events to determine physical properties of lensing stars

23. Ron Allen - 23 18 May 2004 SIM measures distances to “standard candles” Period proportional to luminosity, but also metallicity Distances to galactic Cepheids to a Kpc and RR Lyraes in globular clusters can be measured to <1% accuracy, a key element in the cosmic distance scale

24. Ron Allen - 24 18 May 2004 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 Cover page from S. Majewski Key Project proposal

25. Ron Allen - 25 18 May 2004 Dynamics of Galaxies SIM will investigate the dynamics of our Milky Way –Determine 3-D gravitational potential of Milky Way via precise distances to stars, globular clusters and satellite galaxies to ~100 kpc –Determine precise coordinates of the Sun relative to the Milky Way SIM will investigate galaxy dynamics based on true orbit determinations –SIM will measure proper motions of 30 Local Group and other nearby galaxies (50  as/yr) from observations of individual V=16 ~ 20 mag stars – Results will include dark matter distribution, merger history, mutual influence of groups

26. Ron Allen - 26 18 May 2004 Simulated ‘time-lapse’ photo of 30 galaxies closest to our Milky Way (1-billion year exposure) 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 You are here Dynamics of Galaxy Groups within 5 Mpc

27. Ron Allen - 27 18 May 2004 Three AGN questions which SIM will address: 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. Does the separation of the radio core and optical photocenter of the quasars used for the reference frame tie change on the timescales of their photometric variability, or is the separation stable ?

28. Ron Allen - 28 18 May 2004 Probably a poor choice for reference frame tie object ! Reference Frame Tie - two requirements (1) SIM needs a non-rotating frame (for Galactic structure studies) –We don’t have to select radio- loud quasars –Maybe radio-quiet quasars are more suitable? (2) Need to reference to the ICRF –internationally recognized –Need radio and optically loud quasars to tie SIM to the ICRF Could pick two different quasar samples: radio-loud radio-quiet –not yet a solved problem

29. Ron Allen - 29 18 May 2004 3. Future Opportunities for Proposing to Use SIM Science Team: –15 member Team already in place –New members to be selected through AO-2 in ~2006 –Review and selection by NASA HQ Guest Observers –To be selected via Guest Observer (GO) call for proposals in ~2008 Reviewed and administered at Caltech/MSC –Second GO call after launch Community Science Program –Parallaxes and proper motions to intermediate accuracy –Large number of targets, observed and reduced in a standard mode –Proposal call (part of AO-2?) in ~2006 Support a large user community; funded to analysis and publish results Reviewed and administered at Caltech/MSC Archival Research Program –To be selected post-launch –Reviewed and administered at Caltech/MSC

30. Ron Allen - 30 18 May 2004 Summary SIM’s currently selected science program includes planetary searches, main-sequence and “exotic star” astronomy, Galactic dynamics, Local Group motions, and AGN astrophysics. The SIM project is on track for completion on schedule and within budget. SIM is viewed as a well-managed project and enjoys strong support at NASA-HQ. SIM launch is presently planned for February 2010. –launch date maintained at December 2009 for 3 years! –slipped 2 months very recently to accommodate a budget reduction by NASA-HQ. An opportunity to propose for new SIM science will soon be announced.

31. Ron Allen - 31 18 May 2004 Space Interferometry Mission Beginning the search for other earths…

32. Ron Allen - 32 18 May 2004 4. 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 rotates 90 degrees to get the other baseline orientation. SIM will execute about 5 million observations in 5 years which is a non-trivial scheduling challenge.

33. Ron Allen - 33 18 May 2004 10 meter science baselines 8.9 meter guide baselines Bay 2 Bay 1 Astrometric Beam Combiners Optical Delay Lines Guide FOV Science FOV External Metrology “Truss” SIM Configuration

34. Ron Allen - 34 18 May 2004 Science target Planet Search Observing Scenario ~1º field Reference star 15º Field of Regard Grid star

35. Ron Allen - 35 18 May 2004 15deg field Spacecraft slew direction Science stars Global Astrometry Observing Scenario Grid stars ~3.5 - 5deg

36. Ron Allen - 36 18 May 2004 Sky Coverage of Astrometric Grid Stars ----- Celestial equator ----- Monitoring Program Phase 1 complete: candidate star identification Phase 2 starting: precision radial-velocity monitoring Galactic plane ~1300 stars Magnitude ~12 Stable to ~1 µas