# Presentation: 366553

## The Fourier-Kelvin Stellar Interferometer:

- A Concept for an Interferometric Mission for Discovering and Investigating Extrasolar Giant Planets and a Progress Report
- R.K. Barry (1), W.C. Danchi (1), J. Rajagopal (6), V. J. Chambers (1), L.J. Richardson (7), A.J. Martino (1),
- R.J. Allen (2), D. Deming(1), M. Kuchner(1),  D.T. Leisawitz(1),  R. Linfield(4),  J.D. Monnier(5),  L.G. Mundy(7),
- C. Noecker(4), S. Seager(7), W. Traub (3)
- ____________________________
- (1) NASA Goddard Space Flight Center, (2) Space Telescope Science Institute, (3) Harvard-Smithsonian Center for Astrophysics, (4) Ball Aerospace, (5) University of Michigan, (6) University of Maryland, (7) Carnegie Institution of Washington

- The Fourier-Kelvin Stellar Interferometer (FKSI) is a mission concept for a nulling interferometer for the near-to-mid-infrared spectral region (3-8 microns). FKSI is conceived as a scientific and technological precursor to TPF.  The scientific emphasis of the mission is on the evolution of protostellar systems, from just after the collapse of the precursor molecular cloud core, through the formation of the disk surrounding the protostar, the formation of planets in the disk, and eventual dispersal of the disk material.

- FKSI will answer key questions about extrasolar planets:
- • What are the characteristics of the  known extrasolar giant planets?
- • What are the characteristics of the extrasolar zodiacal clouds around nearby stars?
- • Are there giant planets around classes of stars other than those already studied?

- We present preliminary results of a detailed design study of the FKSI.  Using a nulling interferometer configuration, the optical system consists of two 0.5m telescopes on a 12.5m boom feeding a Mach-Zehnder beam combiner with a fiber wavefront error reducer to produce a 0.01% null of the central starlight. With this system, planets around nearby stars can be detected and characterized using a combination of spectral and spatial resolution.

- The Role of FKSI
- •	Is a practical interferometric system for discovering/investigating 		extrasolar giant planets
- •	Represents a significant near term step in planet finding & 			characterization
- •	Supports NASA Strategic Plan objectives
- •	Serves as a pathfinder for TPF/Darwin missions
- To answer key questions about extrasolar giant planets, FKSI will:
- •	Detect >25 EGPs
- •	Characterize their atmospheres with R=20 spectroscopy
- •	Observe secular changes in spectrum
- •	Observe orbit of the planet
- •	Estimate density of planet; determine if rocky or gaseous
- •	Determine main constituents of atmospheres
- •	Search for exoplanets around nearby stars not planned for 		observations with TPF
- •	Survey nearby M dwarfs (>30 such stars) at distances within 10 pc
- •	Survey nearby F,G,K giants and subgiants, luminosity classes III 	and IV (>50 stars) within 30 pc
- •	Study circumstellar material
- •	Exozodiacal  measurements of nearby stars
- •	Search for companions
- •	Debris disks, looking for dust wakes due to planets
- •	See star formation at high angular resolution
- •	Evolution of circumstellar disks
- •	Characterize morphology, gaps, rings, etc.

- FKSI Mission Concept
- FKSI is a two-element nulling interferometer.  The two telescopes, separated by 12.5m, are precisely targeted (by small steering mirrors) on the target star.  The two path lengths are accurately controlled to be precisely the same.  A phase shifter / beam combiner (via Mach-Zender interferometer) produces an output beam consisting of the nulled sum of the planet’s light and the star’s light.  When properly oriented, the starlight is nulled by a factor of 10-4, and the planet light is undimmed.  Accurate stellar spectroscopy is used to subtract this residual starlight, permitting the detection of planets much fainter than the host star, and at distances less than the ~0.005” required for a similar imaging interferometer.

- Engineering Realization of FKSI

- Finding Planets with FKSI
- FKSI’s sensitivity is sufficient to detect and characterize extrasolar giant planets within ~30pc.  FKSI is comparable to other missions in the ~5μm range (SIRTF, JWST), and superior to ground-based facilities.  This is illustrated in the figure below (Seager, 2004 unpublished).

- .05 AU
- .10 AU
- .50 AU

- Below is given the predicted flux density of a giant planet as a function of distance from the star, in the near-infrared, at a distance of 20pc.  FKSI can detect at least 25 planets.

- Operational Fourier-Kelvin Stellar Interferometer testbed.

- _Simulated FKSI planet detection_
- Below are simulations of FKSI response as it rotates about its axis. At a single wavelength, the intensity varies as a function of this rotation angle.  Ratios of various wavelengths produce the spectrum of the star, unmodulated, and the planet, modulated.

- Simulated image at 5 microns but with the ring and wake enhanced by 100.  The main features are recovered in spite of significant foreground local-zodi emission.

- Simulated image at 10 microns.  The reconstruction includes thermal noise from mirrors at 40 K and emission from the local zodi.

- _Simulated FKSI planet detection_
- Below are images of a model zodiacal wake about Epsilon Eridani with source brightness distribution generated using Zodipic.pro (Kuchner, M. J., & Serabyn, E. 2001) and instrument response simulated using software developed by Jay Rajagopal.