"Imaging Extrasolar Planets with MEMS Deformable Mirrors"
Exciting developments in the fields of adaptive optics, coronagraphy, interferometry, and image processing will furnish direct images of extrasolar planets within the next decade. This feat requires high-order wavefront correction systems with low residual error, whether on Earth or in space. To this end, the deformable mirror (DM) must exhibit exemplary performance, with thousands of well-controlled actuators. Micro-electrical mechanical systems (MEMS) technology offers reliable, compact, high-actuator-count DMs at an accessible cost. At the UCSC Laboratory for Adaptive Optics, MEMS have been shown to operate in closed-loop with sub-nanometer flattening, stability, and repeatability. I propose to further these experiments to address: 1. operational performance limitations; 2. modeling and control algorithms; and 3. on-sky testing. First, through complete understanding of MEMS performance under typical aberrations, requirements can be specified to compensate for stroke limitations. Second, improved MEMS modeling and control will reduce residual wavefront errors and will enable open-loop MEMS control for advanced wavefront-correction architectures. Finally, operating MEMS on-sky will prove the technology in the observing environment. These studies will not only inform the design of the Gemini Planet Imager, but will also benefit space missions like TPF-C that require high-order DMs for wavefront control.
"Using Near-Infrared CO Emission to Identify the Presence of Planets in Transitional Disks"
Recent observations of spectral energy distributions of young stars have revealed exciting detail in transitional disks, which are the birthplace of planets. Data from Spitzer have allowed detailed modeling of the dust distribution in the inner disk, which show AU-sized gaps that may be caused by a massive planet. However there are other scenarios, where a planet does not exist, that produce identical spectral energy distributions (SEDs). Therefore, it is crucial to probe the gas in the inner disk to determine if there truly is a planet in the transitional disk. A good tracer of gas in the inner disk is CO, with ro-vibrational lines in atmospheric windows in the near-infrared. This research will look at ro-vibrational CO emission in transitional disks in order to determine if a planet truly exists.
"Direct Detection and Characterization of Hot Jupiters Using Closure Phase"
We propose to use the closure phase and differential phase measurements obtained with the MIRC combiner at the CHARA array to directly detect and characterize nearby “hot Jupiters”. CHARA-MIRC is currently a unique ground-based facility that combines the highest (milli-arcsecond) angular resolution with high contrast imaging. We demonstrate that, under precise calibration schemes combined with high enough sensitivity, CHARA-MIRC will be able to detect emission from hot Jupiters. This project will consists of three parts: 1. Develop calibration and data reduction tools for MIRC; 2. Test these tools and schemes on scientific objects with CHARA-MIRC observations; 3. On sky test of detecting nearby hot Jupiters and characterizing succeeded dectections with available planetary atmospheric models. This work will be a substantial part of my Ph.D thesis and will be conducted under Prof. Monnier’s instruction at the University of Michigan.
With high-resolution mid-IR instrumentation, we will image a large sample of planetary debris disks with a wide range of infrared excess levels in order to make inferences about their evolutionary processes. These disks will provide insight into the later stages of planet formation and are therefore highly relevant to interpreting the observations of exoplanet research supported by the Michelson Science Center. There have been many observations where asymmetric features in debris disks may indicate the presence of planets, either with dust-clearing rings, resonant clumping of dust, flaring due to planetesimal breakup, or other processes, but a coherent model of debris disk evolution has yet to be constructed. Without this model based on high spatial resolution images of debris disks over a broad range of stellar ages, companion candidates near a star may be misinterpreted; thus this study of physical events in these disks and their resultant observational appearance is crucial to understanding planetary formation.
Despite the vast strides made by radial velocity planet searches in the last decade in detecting and characterizing extrasolar planets, direct imaging surveys have been relatively quiet in increasing knowledge about planetary systems. Simultaneous Differential Imaging (SDI) provides the highest contrast images currently achievable (from the ground or space), and with two instruments fully commissioned and taking data on two large, AO-equipped telescopes our project will shortly complete a survey of young, nearby stars to begin to constrain planet populations at larger separations than can be reached with the radial velocity method. In particular, Mr. Nielsen's role will be to continue to maintain the target list, reflecting the latest measurements of age indicators in nearby stars, while ensuring that by the end of the survey, the team has investigated an unbiased sample of stars. This will allow him to use the results of the SDI survey to make meaningful conclusions about planet populations, even in the case of no planet detections. In addition, Mr. Nielsen will use my experience reducing spectra of AB Dor C, an M8 0.16 arcseconds from a K1 primary which is 80 times brighter (Close et. al 2004, submitted to Nature) to characterize any companions that are discovered during the SDI survey.
Ms. Putnam proposes to lead the optical development of a prototype focal plane coronagraphic interferometer to test methods to improve the potential for detection of extrasolar planets with space and ground based telescopes. The purpose is to correct mid-frequency aberrations in a telescope to allow a coronagraph to reach its full potential. The instrument will measure the phase of speckles formed in an image of the halo around a star using starlight from the core as a phase reference. The wavefront correction to remove the halo can then be derived directly by Fourier transform and applied by means of an Adaptive Optics (AO) deformable mirror. The development of this prototype extends the contrast possible with coronagraphy by removing all non-common path errors and aliasing effects. In a space-based search for Earth-like planets this method will be invaluable to reach the required contrast of 1010 at 0.1Ó, the goal for Terrestrial Planet Finder. On a ground-based telescope, the star background could be suppressed enough to achieve contrasts as high as 107 from 0.1-1.5Ó allowing the detection of Jupiter-like planets. From this prototype, we will gain insight into the practical strengths and difficulties of this approach.
Deborah Howell proposes, as her doctoral research work, to develop a metric to quantify the level of fidelity in any simulation or hardware model of a complex opto-mechanical system. She further proposes to optimize the scheduling of both the simulation and hardware models efforts in order to get the required information from these models, using the fidelity metric as a guide.
We are developing a new type of instrument known as a dispersed fixed-delay interferometer for performing multi-object Doppler radial velocity measurements for extra-solar planet detection. It has the potential for rapid large-scale radial velocity surveys, observing thousands of stars per night, and could dramatically impact the search for extra-solar planets.
We present a new method for searching for planets around white dwarf stars, with a different sensitivity to other methods, using the pulsations of white dwarf stars as stable clocks. A subset of pulsating white dwarf stars have pulsation stability that exceeds most pulsars and rivals that of atomic clocks. When a planet is in orbit around a star the reflect orbital motion of the star will produce a detectable change in arrival time of the pulses which is linearly dependent on both the mass and orbital separation of the planet. Most stars eventually become white dwarfs stars so we are able to sample a wide range of stellar ages and types.
A novel device is being designed at Princeton University for imaging extra solar planets. The challenge for optical detection of terrestrial planets is to overcome the 10 orders of magnitude contrast between the planet and its host star, coupled with their small angular separation. The approach used at Princeton University is an optimized shaped-pupil coronagraph that results in a point spread function with the needed contrast supression as close as 4 lambda/D to the center of the star in the image plane. The brightness contrast requirement along with the angular separation needed for detection of extra solar planets poses an immense technical challenge on the active correction of wavefront errors. These wavefront errors are caused by spacecraft vibration and miniscule (order of 0.1 nm) imperfections in the surfaces of the optical system used for observation and measurements.
The proposed work involves designing and implementing an active correction system that will estimate the wavefront errors and correct them to acheive the needed contrast supression goals.
In this proposal I present an outline to carry out the first survey of nearby, early-type main sequence stars using nulling interferometry and adaptive optics. The main goal of this survey is the detection of zodical dust emission surrounding other stars, which is indicative of the presence of planetesimals and/or giant planets. From this survey, we will gain insight into the frequency of planetary systems around stars of different spectral type and age. This survey will be possible using the Bracewell Infrared Nulling Cryostat (BLINC), a nulling interferometer constructed for the MMT, used in conjunction with the MMT's adaptive secondary, currently in the final stages of development. The ability to detect zodical dust is currently unique to this instrument and facility. This project is also a key part in the continued development of nulling interferometry as a viable technique for the Large Binocular Telescope (LBT) and the Terrestrial Planet Finder (TPF).
Diffraction-limited coranagraphy offers exciting possibilities for the direct detection of planets around other stars. Combined with an adaptive optics system, a coronagraph enables high-contrast imaging by supressing diffracted starlight, potentially allowing imaging of planetary companions. My proposal focuses on the design and development of two coronagraphs in pursuit of this goal, in collaboration with researchers at UC Berkeley and elsewhere: 1) the AEOS Coronagraph will take advantage of the high-precision wavefront correction of the Air Force AEOS telescope to provide an unparalleled on-the-sky testbed for innovative coronagraphic techniques. This instrument will valudate theoretical models and allow quantitative performance estimates of alternative coronagraph architectures in a high-Strehl regime. 2) The results of these investigations will provide critical input into the development of XAOPI, a proposed extreme adaptive optics system and coronagraphic imager currently under design study by the Center for Adaptive Optics. As part of the XAOPI team, I will conduct coronagraphic trade studies and evaluate alternativeobserving techniques including integral-field spectroscopy and AO speckle methods. XAOPI offers the near-future possibility of detecting young Jovian planets using existing 10m telescopes. This will serve as a proving ground for precision wavefront control and coronagraphic techniques applicable to future space missions.
Abstract not available.
A new instrument is being designed at Penn State for precise measurement of stellar radial velocities. The novel instrument design combines a Michelson interferometer with a standard dispersive element. The main thrust of this instrument will be to provide accurate stellar radial velocities with significantly higher throughput than conventional methods. My research will focus on increasing the throughput and accuracy of the instrument and building a new instrument will be used for regular observations at the Hobby-Eberly telescope. The higher throughput will allow a fast and accurate survey of the Space Interferometry Mission (SIM) reference grid. The stability of the reference grid is essential to the success of SIM and this new method will allow a much faster survey without compromising on the accuracy. A prototype instrument called The Exoplanet Tracker (ET) has already been built and is achieving radial velocity precision in the 10-50 m/s range.
A limited amount of information about low-luminosity stellar companions is available because direct observations of them have been difficult due to the brightness contrast in such systems. I propose to use several techniques of near-infrared interferometry study such objects, with the majority of the research being done using dual star modules for narrow angle astrometry. It is anticipated that this work will develop observational techniques useful in future extrasolar planets studies.
The Large Binocular Telescope (LBT) will have a coherent (Fizeau) focus that combines adaptively corrected images from two mirrors on the same alt-az mount, covering high angular resolution with wide field imaging capability. I propose to design a 1 to 5 micron camera for this focus. The camera will maximize use of the 40" by 40" field of view delivered by the beam combiner, and incorporate anamorphic magnification with 3:1 aspect ratio. Some key science goals are wide field surveys of high-z galaxies; the study of black holes and active nuclei in nearby galaxies, and star/planet formation regions. High precision astrometry will be needed to obtain stellar masses in stellar nurseries, low mass binaries, or brown dwarf candidates. Thus, a second component of this study will be to determine how adaptive optics (AO) corrections can improve astrometric accuracy, by way of computer simulations of the system performance, including AO with Kolmogorov atmosphere. This will lead to a study of how the camera should interface with the AO system to best maintain a coherent phase combination from the two beams. I will do this work at Steward Observatory, under the guidance of R. Angel.
Julie Wertz proposes to conduct research on reliability and productivity optimization in an effort to answer systems questions facing any separated spacecraft interferometer project. All work will be conducted at the Massachusetts Institute of Technology (MIT) Space Systems Laboratory (SSL) under the supervision of Associate Professor David Miller. The MIT SSL has a wide range of both current and previous projects involving distributed satellite and interferometer systems. In addition, the MIT SSL is one of the few research laboratories in the country to conduct research in spacecraft systems engineering. The proposed work will lead to quantitative methods of answering several important questions such as how many spacecraft are needed in a system and how to distribute money to create the highest reliability system possible. This could be a great benefit to individual programs such as Terrestrial Planet Finder (TPF) and StarLight, as well as distributed satellite systems and interferometers in general.
Rebecca Masterson proposes to develop key strategies for design optimization of space-based interferometers. The work described in this proposal will be supported by the Massachusetts Institute of Technology (MIT) Space Systems Laboratory (SSL) under the supervision of Dr. David Miller, Director of the MIT SSL. The proposed work will build directly upon Ms. Masterson's past experience in modelling and dynamic analysis of spaceborne interferometers obtained through her work as a Master's student in the MIT SSL and as a structural dynamicist at TRW Space & Electronics Group. The research is closely linked to interferometry research currently underway in the MIT SSL and promises to provide new tools for the design and dynamic analysis of these next generation space telescopes. Methods will be developed to incorporate dynamic analyses into high-level configuration and architecture trades in order to flow down optical performance requirements to hardware jitter and control requirements and to improve significantly the design optimization process.
For my PhD reserach I will be working on the fringe tracking system for the CHARA array. In this proposal I give a brief review of fringe tracking methods, with emphasis on group delay tracking. The CHARA array will track group delay using a Fast Fourrier Transform algorithm to determine the frequency of channel fringes. Particular attention will go towrds possible ways of improving upon the existing method.
My research project is to design a Longitudinal Dispersion Correction (LDC) system for the CHARA Array. This involves modeling the refractive index of air inside the Optical Path Length Equalization (OPLE) building, selecting a glass with the same dispersive properties, and then implementing LDCs which will vary the thickness of the glass according to the air path length. One of the goals of this project is to increase bandwidth without significant reduction of fringe visibility. Another is to take simultaneous observations in the visible and IR which could then be used to do wavelength bootstrapping where one can fringe track in one bandpass while taking measurements in the other.
My research will focus on the development of new tools for imaging optical interferometers that will provide feedback on system performance and the image reconstruction process. The development of such tools will be based on information theory. Central to information theory is the concept of statistical information. Shannon defined statistical information as the information gained about a quantity upon learning its value from an ensemble of possible values. In communication theory, this ensemble of possible values represents a statistical model of a source message for a communication channel. By analyzing how a noisy communication channel transmits the statistical model, one can quantify the amount of information successfully transmitted by the channel.
If one models an interferometric imaging system as a communication channel, one can apply the concepts of statistical information. In our model, noise in the communication channel is caused by atmospheric turbulence and detector noise. Statistical models of certain classes of astronomical objects such as binary stars, AGN's and stellar surface features can then be processed by the interferometer, or communication channel. Emphasis will be placed on an analysis of how phase recovery and image reconstruction algorithms, such as CLEAN and MEM, alter the information content of the statistical model. Of particular importance will be the convergence of these algorithms for certain classes of astronomical objects.
The goal of the research is to develop enabling technologies for drift-through interferometric observation using hybrid control and estimation strategies. This research aims to develop multi-staged control and estimation techniques to address spacecraft and optical instrument couplings for separated spacecraft interferometers. If interferometric observation could be maintained while spacecraft move relative to each other or during thruster firings, the number of science targets observed would be greatly increased, and the propellant used for nulling spacecraft movements could be reduced, extending the spacecraft mission life.
It is important to note that spacecraft control is only one stage in the control of optical interferometers. Phasing and pointing control using delay lines, fast steering mirrors, and fringe tracking provide over six orders of magnitude stabilization of the optical path in order to achieve the requisite nanometer performance. Similarly, spacecraft sensors provide only coarse levels of measurements, at best in the centimeter and arcsecond range. However, space interferometry missions will require sub-centimeter, possibly down to picometer, levels of accuracy. Thus, an optical communication system using laser metrology is required to refine these measurements. If the spacecraft and optical control layers are developed separately, such systems will be hard pressed to achieve these unprecedented levels of dynamic range. Therefore, it is necessary to develop hybrid spacecraft and instrument control and estimation algorithms which address couplings between these stages.
The defining problem for the Space Interferometry Mission is to select a group of grid stars based on which all other astrometric observations are performed. To ensure the stability of the grid, a significant effort will be mounted to identify multiple systems among the grid candidates. SIM holds the promise of improving on the current state of the art in astrometric accuracy by more than two orders of magnitude. It seems only justified if SIM itself can be used as a filter of last resort in the effort to detect unsuspected companions. We are investigating such a possibility.
To this end, we developed a method trying to detect wavelength dependent change in the position of the light centroid, induced by companions with significantly different colors from the primaries, as proposed by Wielen (1996). The simulations based on SIM specs showed remarkable sensitivity. Moreover, if the separation of the system is larger than a fringe width, the centroid shift occurs in both directions, and exhibits a periodic behavior as a function of wavelength, while becoming less color dependent. The subsequent Periodogram analysis has similar sensitivity, and in addition, can provide parameters of the system.
The techniques we developed could in principle, be applied on any broad band Michelson type interferometer. We are attempting to implement them on the ground based Navy Prototype Optical Interferometer (NPOI). First, this effort serves as a testbed for SIM developments. Secondly, if the sensitivity of the NPOI observations is close to our simulations, we can make major contributions to the binary studies, as optical interferometers cover different parameter spaces of binaries from traditional methods such as Radial Velocity studies and K-band Imaging.
I am developing a nulling interferometer capable of use on the 6.5m MMT telescope. The instrument (called BLINC for Bracewell Infrared Nulling Cryostat) has recently been completed and seen "first null" on the MMT in June 2000. Some of the features of the instrument are cryogenically cooled optics, an active phase feedback loop which keeps the star nulled, and the ability to align and phase the interferometer while cooled. BLINC will be used to explore faint circumstellar structure around various types of stars such as AGB stars with dust outflows and Herbig Ae/Be stars with circumstellar disks. Coupled with the deformable secondary of the MMT BLINC will be able to take advantage of the corrected wavefront to achieve very precise cancellation of the star to begin looking for even fainter structure around main-sequence stars such as zodiacal emission or massive substellar companions. The work will also advance our understanding of the technology required to make the Terrestrial Planet Finder a reality.
During the past two years I have been involved with ongoing science and technical development at the Palomar Testbed Interferometer (PTI). Specifically I have been working implement phase-referenced narrow-angle astrometry. This technique promises sub-100 micro-arcsecond precision astrometry between close pairs of stars, and is of particular interest since it is expected to make possible the detection and mass determination of extra-solar planets. During the 1999 observing season the PTI collaboration (of which I am a member) demonstrated a single night measurement precision of approximantely 80 micro-arcseconds, and a night-to-night repeatability of 97 microarcseconds. During that same season we demonstrated for the first time phase-referenced observations, a technique that improves the limiting sensitivity of an interferometer.
I have also been working on a variety of stellar astrophysics projects, including measuring the component masses of spectroscopic binary stars, and measuring the diameters of low-mass stars. Finally I have been working to measure the distances to nearby Cepheid variable stars by directly resolving the radial pulsations of this class of star.
The number of known extra-solar planets is increasing. These planets have been detected by indirect means ? the effect they have on the orbit of their suns, for example. Eventually, NASA hopes to image extra-solar planets directly. To do this, the collecting area of space telescopes needs to be made much larger for greater sensitivity and higher resolution. At the same time, the current rocket shrouds available limit the weight and size of systems that can be sent into space. Therefore, planet imagers will have to be interferometers. The smaller segments of an interferometer will fit into current rocket shrouds and can be assembled into a final instrument in space.
Current earth-based interferometers change their baselines in order to adjust their resolution. To do this, these systems must choose a field of view of virtually zero. For an interferometer to image planets, we must choose a wide field of view and a fixed baseline, instead. We refer to these systems as imaging interferometers.
New materials will be needed for the optics of these systems, since they will need large collecting areas but must have low weights. To meet this challenge, our group is developing gossamer mirrors. These are reflective, flat mirrors made by stretching membranes inside a frame. Flat membranes are the most stable, but weak curvatures can also be added electrostatically. The membranes can be assembled in groups to create imaging interferometers of any size.
I am working on the design of hundred-meter baseline inteferometers with wide fields of view using flat membrane mirrors. As well as specific designs, I am working to clearly state and explain the conditions that must be satisfied for wide-field imaging in any multiple aperture system. Current lens design theory and programs are equipped to model rotationally symmetric systems. The gossamer systems, however, are highly asymmetric, and their design requires an aberration theory that includes all systems with only a single plane of symmetry. My dissertation covers the aberration theory of multiple aperture systems and demonstrates using the theory to design gossamer interferometers for planet imaging.