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

Ron Allen - 118 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


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


10 meter science baselines8.9 meter guide baselines

Bay 2

Bay 1

AstrometricBeam Combiners

OpticalDelay Lines

Gui

de F

OV

Scie

nce

FOV

External Metrology “Truss”

SIM Configuration


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


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)


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• Sirius 0.38 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) 1.3as

Measuring distances using parallax

1234131 AUSunEarthParallaxangle π

( )arcseconds

Distant starsπDDistance D= 1 / π ( )parsecs= 3.26 / π (lt )years

Star


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)

.


SIM Science TeamKey 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 MSC/Caltech Active Galactic Nuclei

Mission ScientistsDr. Guy Worthey Washington State University Education & Public Outreach Scientist

Dr. Andreas Quirrenbach Leiden University Data Scientist

Dr. Stuart Shaklan NASA/JPL Instrument Scientist

Dr. Shrinivas Kulkarni MSC/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.


Planet Detection with SIM

• Deep search for terrestrial planets

• Broad survey of planetary system architectures

• Planetary systems Around young stars


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.


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?


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


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 Mearth

• 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)


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 ME in a 1 AU orbit, at 10 pc (~5 detection)

– Requires 1 µas single-measurement accuracy

– 25 measurements in each axis


1

10

100

0.1 0.3 1.0 3.2 10.0 31.6100.0316.21,000.03,162.210,000.031,622.0

Planetary Mass (Earths) .

Number of Detected Planets

E JS

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


± 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


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?


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?


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 < 1 Mo are poorly known


Beyond Planet Detection: SIM Covers the Entire Galaxy

Hipparcos100 pc

SIM 25 kpc(10 %)

SIM2.5 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 arcsec1 parsec = 3.26 light-years~ distance to closest stars


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


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


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


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


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


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


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 ?


• 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


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


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.


Space Interferometry Mission

Beginning the search for other earths…


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.


10 meter science baselines8.9 meter guide baselines

Bay 2

Bay 1

AstrometricBeam Combiners

OpticalDelay Lines

Gui

de F

OV

Scie

nce

FOV

External Metrology “Truss”

SIM Configuration


Science target

Planet Search Observing Scenario

~1º field

Reference star

15º Fieldof

Regard

Grid star


15deg field

Spacecraft slew directionScience stars

Global Astrometry Observing Scenario

Grid stars

~3.5 - 5deg


Sky Coverage of Astrometric Grid Stars

----- Celestial equator -----

Monitoring

Program

• Phase 1 complete: candidate star identification

• Phase 2 starting: precision radial-velocity monitoring

Galacticplane

• ~1300 stars• Magnitude ~12• Stable to ~1 µas

Documents

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