Jian-Yang Li, University of Maryland Marc Kuchner, NASA Goddard Space Flight Center Ron Allen, Space Telescope Science Institute Scott Sheppard, Carnegie Institution of Washington, DTM 7/24/2009Li et al., BDEP, Shanghai, China 1

Precision astrometry on stars to V=20. Optical interferometer on a 6 m structure. –One science interferometer. –One guide interferometer (4.2 m baseline) and one precision guide telescope to stabilize the fringes. Global astrometric accuracy: 4 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.

RV will press on icy planets and close-in planets. Transit & microlensing will provide statistical census of rocky planets (e.g., 1 kpc, and 5 kpc. Together with some other instruments, SIM probes 1-10 M Earth  ( AU for nearby stars). It provides orbital parameters and masses for RV planets.

7/24/2009Li et al., BDEP, Shanghai, China4 The outer solar system objects (KBOs and Centaurs) will help us understand the characteristics and formation of big planets far away from the star

7/24/2009Li et al., BDEP, Shanghai, China5

7/24/20096Li et al., BDEP, Shanghai, China

D=34.3 mas D=40.4 mas 7/24/20097Li et al., BDEP, Shanghai, China

Brown et al Shape+ Period  Density T Radius Size  Escape Velocity 7/24/20098Li et al., BDEP, Shanghai, China Density+shape => internal structure Iapetus: Brightness variations

7/24/2009Li et al., BDEP, Shanghai, China9 109 KBOs + 26 Centaurs in total: 20 KBOs and 18 Centaurs are identified to be observable for SIM SIM can measure the: Size Shape Rotational status

7/24/2009Li et al., BDEP, Shanghai, China10 2 Jinc(2πR) Three visibilities, solve for two axes and one angle  B1B1 B3B3 B2B2  B1B1 B2B2 B3B3 Inverse jinc function to get the size of a circular disk with uniform brightness distribution

 Rotation period 3.92 hr (Rabinowitz et al., 2006)  Jacobi ellipsoid  Axial ratio b/a=0.86, c/a=0.54 (Lacerda and Jewitt, 2007)  Density 2551 (+115, -10) km m-3 (Lacerda and Jewitt, 2007)  Mass from two satellites  Size km (Rabinowitz et al., 2006)  Albedo ~0.6  Dark red spots from photometric lightcurves (Lacerda et al., 2008)  Almost pure water ice on the surface (Trujillo et al., 2007)  Strong limb-darkening, k=0.85 7/24/2009Li et al., BDEP, Shanghai, China11

7/24/2009Li et al., BDEP, Shanghai, China12 1% uncertainty of visibility from SIM Size can be determined to better than 5% uncertainty

7/24/2009Li et al., BDEP, Shanghai, China13 SIM can achieve ~10 µas in visibility phase SIM tracks the photocenter of the object precisely. Rotational period Pole orientation Sense of rotation

7/24/2009Li et al., BDEP, Shanghai, China14 Complicated pattern for a surface with albedo features: Not a problem for period determination Should not be a problem for pole orientation determination May be used to track surface features

k=0.4 k=0.5 k=0.8 Low albedo objects SSA < 0.2, Moon Minnaert limb-darkening model: I/F = A cos k (i) cos (k-1) (e) High albedo, high roughness objects SSA = 0.99, Θ=50 deg, g=0 High albedo, low roughness objects Triton: SSA=0.99, Θ=14 deg, g= /24/2009Li et al., BDEP, Shanghai, China15

7/24/2009Li et al., BDEP, Shanghai, China16 Stellar limb-darkening from simultaneously visibility measurement at multiple λ/B (e.g. Quirrenbach et al., 1996) Limb-darkening from k=0.5 (uniform disk) to k=1 (strongest limb-darkening) Visibility uncertainty 1% Simultaneously measurement of visibility at multiple wavelengths from µm Guide interferometer can be used to extend the λ/B range

 Outer solar system object help us understand planetary system formation at large distances from the star.  Fundamental properties of KBOs and Centarus, such as their sizes, shapes, and rotations, can only be measured to be good at 20% level from radiometry.  SIM can observe about 40 KBOs and Centaurs  Better than a few percent in size  Determine 3-D shape  Constrain rotational status, including pole orientation and sense of rotation  Limb-darkening can be measured by SIM through simultaneously visibility measurements at multiple λ/B. 7/24/2009Li et al., BDEP, Shanghai, China17