2005
Postdoctoral Fellows
Ruslan Belikov - Princeton University
The Terrestrial Planet Finder-Coronagraph (TPF-C) project requires a
high contrast
imaging system capable of attaining a contrast ratio of 10-10.
Many coronagraph designs have been proposed as a solution to this
formidable task. One of the designs currently being developed at
Princeton University is 2-mirror pupil mapping, whose significant
advantage is that it does not lose any light. This is an extremely
attractive feature, because the light from extrasolar planets is very
faint. However, some concerns were recently raised as to how well
conventional wavefront sensing and correction methods will work with
2-mirror pupil mapping. If these concerns can be resolved, and a
successful 2-mirror pupil mapping coronagraph demonstrated, there will
be a significant improvement in data collection times for the TPF
coronagraph mission, leading to both scientific and economic benefits.
The proposed work consists of a theoretical and experimental study of
2-mirror pupil mapping coronagraphs, focusing on wavefront correction.
The goal of the work is to demonstrate a prototype satisfying TPF
contrast requirements at the end of the 2-year funding period.
Michael Ireland
- California Institute of Technology
Optical Interferometric Polarimetry (OIP) offers a new and unique way
to explore the environments in which exoplanets form. I will undertake
a research program that will develop experimental OIP methods capable
of characterizing scattered light from disks around young stars. The
‘seeing’ that affects interferometric observations on earth affects all
polarization states of light equally. This means that as a differential
technique, OIP can be independent of atmospheric effects. I will
develop these techniques both at the Palomar Testbed Interferometer
(PTI) and at an aperture-masking system behind the PALAO adaptive
optics system at the Hale 200 inch telescope. Using this aperture
masking system I will also continue development of another high
contrast method: closure-phase based techniques for detecting faint
companions and asymmetric structure. Together, these techniques will
enable unique characterization of dust around Young Stellar Objects
(YSOs) such as Herbig Ae/Be stars, characterization of dust around
Vega-like stars and a survey for close brown dwarf companions around
young stars. OIP will open-up a new observable parameter space, and
represents one of the last remaining frontiers of ground-based optical
interferometry.
Amaya Moro-Martin
- Princeton University
In a planetary system with a belt of planetesimals and interior giant
planets, the trapping of dust in mean motion resonances with the
planet, and the ejection of particles due to gravitational scattering,
create structure in the dust disk. Because debris disk structure is
sensitive to long period planets, complementing a parameter space not
covered by other methods, we can learn about the diversity of planetary
systems by studying these "dusty fingerprints". Dr. Moro-Martin
proposes to use a self consistent combination of 3-D numerical tools
for the simulation of debris disk structure, and a 3-D radiative
transfer code for the calculation of their emergent SED and brightness
density distribution at different wavelengths. These models will be
useful for the interpretation of spatially resolved images e.g. by
ALMA, and spatially unresolved spectrophotometry observations by
Spitzer, in terms of planetary architectures. Physically realistic
initial conditions will be determined by a planetesimal formation code
that calculates the location of the dust-producing planetesimals and
the perturbing planets. Additionally, she proposes to explore the
effects of stochastic dust production, gas drag and mutual grain
collisions on the shaping of the disk's structure. 2004
Postdoctoral Fellows
Jennifer Patience -- California
Institute of Technology
The
Keck interferometer is the most powerful instrument currently available
in the Navigator Program and is an important precursor to both SIM and
TPF. With the unprecedented angular resolution and faint source
sensitivity provided by the Keck interferometer, it is possible to
study the circumstellar environments of young stars at spatial scales
as small as 0.1-0.4 AU and to begin to address a key scientific goal of
the Navigator Program: understanding the formation and evolution of
planetary systems. For a project working with researchers at Caltech
and the Michelson Science Center, I propose to observe a sample of
young stars at a variety of stages including FUor-type objects with
more active disks and weak-lined T Tauri stars and older stars with
weaker disks. With the proposed interferomeric data, I will
characterize the presence and distribution of circumstellar material in
the inner disk as a function of age and will compare these direct
measurements of the inner disks with theoretical models of disks and
with the properties inferred from previous unresolved photometric
observations.
Sean Brittain -- National Optical Astronomical Observatories
Understanding the formation of planetary systems remains one of
astronomy's most rewarding challenges. It represents a significant
component of the search for our own cosmic origins, as well as the
possibility of life on other worlds. Consequently, it figures
prominently in the recommendations of the most recent NRC Decadal
Survey for astronomy and astrophysics. Planet formation is tied to the
evolution of gas and dust in disks around young stars. Thus, a
comprehensive understanding of the physics and chemistry of young
circumstellar disks is essential to a complete picture of star and
planet formation, yet basic questions about this process remain
unanswered. The proposed research program combines many of the
advancements and accomplishments of the last few years and will build
on previous work (see publication list) using high-resolution near
infrared spectroscopy to peer into the inner 50 AU of disks around
young stars. This program will address fundamental questions regarding
circumstellar disk evolution and its potential for planet formation
including: 1. Does the evolution of gas in the inner disk follow the
evolution of dust? 2. Is there any evidence of gas/dust
stratification in the disk? 3. What is the CO/H2, ratio in the
inner disk around young stars? 4. What is the atmospheric
composition and lifetime of known exoplanets?
Christopher Tycner -- United States
Naval Observatory
With
the recent successful demonstration of the 6-way beam combination, and
the soon to be implemented long delay-line extension, the Navy
Prototype Optical
Interferometer (NPOI) is opening a window of opportunity to study
early-type
main-sequence stars in ways not possible before. This is because the
typically
large distances to stars hotter than the Sun require interferometric
observations
with baselines longer than previously available to resolve their small
apparent
diameters. I propose to use the NPOI's reconfigurable array, with
baselines of
up to 437 m, to investigate the circumstellar disks of Be stars and
measure the
angular diameters of hot main-sequence stars. These observations, which
will
achieve angular resolution at the sub-milli-arcsecond level, will also
be capable of
detecting deviations from circular symmetry in rapidly rotating stars.
The results
of this observational study will have direct influence on the current
state-of-the-
art models of stellar photospheres and interiors, as well as on our
understanding
of the formation and variability mechanisms in the circumstellar
environments of
Be stars.
2003
Postdoctoral Fellows
Jason
Aufdenberg -- National Optical Astronomical Observatories
Recently
commissioned interferometers on the earth (e.g. CHARA, VLTI,
NPOI, Keck) and those planned for space (SIM, TPF) will be key tools
for astrophysicists through the next decade and beyond. Recent
technological developments make possible now, for the first time in 30
years, the direct measurement of stellar diameters and limb-intensity
profiles of stars hotter than the sun. Using the Center for High
Resolution Astronomy (CHARA) interferometric array, such measurements
will be made and, by combining both experimental and theoretical
expertise, the uncertainties in the direct effective temperatures of
33 stars will be significantly reduced. These data are crucial for
testing state-of-the-art models of both stellar atmospheres and
stellar interiors, and thereby our understanding of stellar and
galactic evolution. The first limb-intensity profile measurements of
8 early-type giants and supergiants will double the number of stars
for which limb-darkening has been directly measured and provide rare
direct tests of model stellar atmosphere intensity predictions.
Furthermore, independent mass-loss rates for B and A-type supergiants,
critical for the calibration of these stars as independent distance
indicators, will be determined via interferometry for the first time
by comparing measurements with the predictions of expanding model
atmospheres.
Pascal
Borde -- Harvard-Smithsonian Center for Astrophysics
In
the context of NASA's Terrestrial Planet Finder, the
Harvard-Smithsonian Center for Astrophysics, Princeton University, and
Ball Aerospace have undertaken a program to demonstrate high-precision
coronagraphs. I propose to join their efforts for a combined
theoretical and experimental work to deepen our understanding and
ability to design powerful planet-finding coronagraphs. On the
theoretical side, I will optimize the shape and graded function of
Lyot stops in image-plane masks, model the electromagnetic interaction
between the light and the material constitutive of notch filter masks,
and explore the possibility of combining shaped pupil with image-plane
masks to further increase the instrumental dynamic range. On the
experimental side, I will compare the performance of different
coronagraphic designs, and work on the detection and correction of
amplitude and phase errors using a deformable mirror. In addition, I
will develop simple color and low-resolution diagnostics for the
characterization of planets detected by visible-light coronagraphs.
Andrew
Digby -- American Museum of Natural History
With
the existence of "exoplanets" only indirectly established, little
is known about their formation, evolution, and physical
characteristics. Knowledge of related circumstellars debris disks is
similarly uncertain. Direct imaging of exoplanets is given the
highest priority in the TPF Architecture Review. The work outlined in
this proposal represents some of the initial steps required before
TPF's goal of imaging Earth analogs is reached. In particular,
the coronagraph being constructed at AMNH for the US Air Force's
Advanced Electro-Optical System, a 941-actuator adaptive optics
instrument on a 3.6-m telescope, will achieve unprecedented levels of
contrast, enabling the first direct probe of companions and disks on
solar-system scales and in the sub-brown dwarf mass range. I will
make major contributions to the instrument testing, integration,
observations and science of the AEOS Coronagraph ("The Lyot Project"),
yielding significant advances in exoplanet, brown dwarf, and disk
research, and in technologies such as coronagraphic occulting mask
design, dual-stage adaptive optics and active alignment systems that
are crucial to future planet-finding missions. The results of this
work will be incorporated into museum exhibits and space shows seen by
over 3 million visitors each year. Ettore
Pedretti -- University of Michigan
The
Center for High Angular Resolution Astronomy (CHARA)
interferometric array is a state-of-the-art optical/infrared
interferometer comprising of six one-meter telescopes, with baselines
spanning hundreds of meters on a Y-shaped array. In collaboration
with Georgia State University, the University of Michigan is
developing an infrared imaging beam combiner capable of exploiting the
full potential of the multiple baselines of the CHARA array. I
propose to build a very-low noise infrared camera for this new
combiner, using the experience I have gained at the Infrared Optical
Telescope Array (IOTA), currently the lowest-noise infrared camera at
an interferometric facility. This camera will use the Rockwell PICNIC
detector and fast, very-low noise readout electronics based on Complex
Programmable Logic Devices (CPLDs). It will be used in connection
with a new fiber-fed image-plane beam combiner and a low-resolution
spectrograph in development at the University of Michigan. The camera
will deliver science data as dispersed fringes, which will be useful
the keep the array in coherence. I will work with the IOTA and CHARA
groups to obtain the first high-resolution images of a Young Stellar
Object (YSO) which are beyond the angular resolution of the current
ten-meter-class telescopes. This advance in instrumentation will be
immediately transferable to new-generation interferometers, and will
greatly enhance the understanding of the star and planet formation
process. Remi
Soummer -- Space Telescope Science Institute
I
will focus on a theoretical, experimental, and observational study
of high-contrast coronagraphic techniques aimed at the direct
detection and characterization of exoplanets and the study of faint
structure around nearby stars. I
will implement a test-bed version of the apodized-pupil Lyot
coronagraph, for which I have already developed a complete theory
demonstrating that its rejection is dramatically improved by a factor
of up to 10^5, for an extended search space. I
will help commission the AEOS near-IR coronagraph being fabricated
at AMNH. This instrument will deliver H-band on-sky Strehl ratios of
about 90%, and is available as an in-lab optical bandpass testbed. I
will use it to verify my simulations, as a step toward understanding
space coronagraphy. I
will extend my theoretical investigations of coronagraphy to explore
my apodized Lyot coronagraphic design, and also continue addressing
the chromatic problems, both in image scale as well as phase control,
of phase-mask coronagraphs (I have already shown that a 20% bandwidth
Roddier-style phase mask is possible without compromising dynamic
range). I
will participate in the NSF Center for Adaptive Optics Extreme AO
coronagraphic effort aimed at an existing 8--10m telescopes,
addressing the problem of atmospheric speckle noise.
2002
Postdoctoral Fellows
Brian
Kern -- California Institute of Technology
I have
designed and begun to test a novel technique
for rotation-shearing interferometry on single filled apertures
(Palomar 5-m and Keck 10-m telescopes), incorporating a 180-degree
rotation shear, simultaneous quadrature-phase measurement, and a
high-speed, low-noise CCD array. This technique promises to overcome
the limitations that have plagued previous rotation-shearing
interferometers. I have begun testing this design in the
laboratory. In addition to the scientific capabilities of this
technique, it is appealing because it is very low-cost and requires
relatively little investment of human capital and time to implement.
I
propose to continue this investigation, proving the quadrature-phase
measurements on astronomical data, and expanding the capabilities of
the interferometer to allow differential interferometric observations
of
the broad emission line regions of active galactic nuclei (AGNs). The
differential measurement converts a phase difference between the red
and blue wings of the broad H-alpha emission line into an angular
displacement. This would be the first direct measurement of the size
of broad-line emission regions in AGNs, and one of the first
interferometric measurements on any extragalactic object. The
quadrature-phase interferometer is uniquely suited to the differential
measurement, which could provide positive results on as small an
aperture as the Palomar 5-m telescope.
Jajadev
Ragagopal -- University of Maryland
My
current research has been in the area of modeling
synthesis imaging with optical interferometers, studying effects of
limited baseline coverage, confusion and noise issues. The other major
area of interest has been gas and dust in the Galaxy and beyond. I
believe that the Michelson fellowship would be a unique opportunity to
work and expand on all these themes of research. After having worked
on a variety of theoretical and modeling issues concerned with
IR/optical/UV interferometry, my plans for the next stage of my career
involve observing with and working on practical aspects of existing
interferometers. A considerable part of my graduate school training
was spent on implementing and observing with a ground-based single
aperture optical interferometer. I believe that ground-based
interferometry is currently poised to provide breakthroughs on a
number of issues that have been beyond its reach till now. Star
formation, structure and evolution of circumstellar disks and
planetary systems are all areas with considerable overlap with my
research interest in the ISM of our Galaxy and neighboring
galaxies. Large apertures, and multiple baselines along with adaptive
optics techniques in upcoming instruments like the Keck Interferometer,
LBT and VLTI open up imaging and study of extended, moderate surface
brightness sources.
Primarily
motivated by these considerations, I am applying to take up
the fellowship to work with Dr. William Danchi and his collaborators
at NASA-GSFC. I describe next how the projects there fit in with my
research interest and experience and what I envisage my contributions
to be.
There
are several exciting ongoing projects being pursued by
Dr. Danchi and his collaborators. Of these, I wish to focus on two
areas: 1) Multi- wavelength visibility observations of circumstellar
material with the Keck interferometer and 2) Design and modeling of a
mid-infrared imaging space- based interferometer.
Neda
Safizadeh -- California Institute of Technology
Currently,
I am building a single-telescope Fourier
Transform Spectrometer (FTS) to operate in the near
infrared. Initially the FTS will have the capability of obtaining
spectra with a resolution of 80. Later a resolution of ~50,000 will be
used to observe Mira variables, Be stars and late-type supergiants.
I
propose an extension to my current project that will involve
building and utilizing a spatio-spectral FTS, first operating in the
near IR with the goal of later pushing into the optical region. By
obtaining double Fourier spectra with long baseline interferometry,
the wavelength dependence of limb darkening and stellar diameters can
be measured. Spectral features of stellar objects can be resolved and
the atmospheric scale height inferred. Surface features associated
with distinct spectral structure can be separately resolved and
studied, e.g. convection plumes, magnetic fields in spots, and
circumstellar material. These measurements are useful for studying the
extended atmospheres and surface features of stars and for developing
more accurate stellar atmospheric models.
2001
Postdoctoral Fellows
Philip
Hinz -- Steward Observatory, University of Arizona
I
propose to undertake a comprehensive program at the
University of Arizona to advance the search for extrasolar planetary
systems through nulling interferometry, including a survey of nearby
main-sequence stars with nulling at the 6.5 m Multiple Mirror
Telescope (MMT), and developing a uniquely sensitive interferometric
beam combiner for the Large Binocular Telescope (LBT). The MMT survey
will be capable of detecting extrasolar dust down to 10-20 times the
solar level, a factor of 100 times fainter than with current
methods. The nulling instrument for the LBT will be designed to be
capable of detecting extrasolar zodiacal dust down to near solar
level. This work will be important in setting the stage, both
scientifically and technically, for the Terrestrial Planet Finder
(TPF) mission as currently envisioned by NASA.
Sam
Ragland -- Harvard-Smithsonian Center for Astrophysics
I
propose to investigate about three dozen Mira stars
with the state-of-art IOTA interferometer in order to (a) identify
mode of pulsation in Mira stars, (b) detect and characterize
photospheric asymmetries and stellar surface features. A byproduct
programmatic benefit is that we expect to produce a significant
contribution to astrophysics, and thereby improve the general
acceptance of infrared interferometry by our astrophysical colleagues
in the community.
2000
Postdoctoral Fellows
Jean-Philippe
Berger -- Harvard-Smithsonian Center for Astrophysics
The aim
of my research work is to study star
formation mechanisms with long baseline interferometers. Current
interferometers have provided us with the first high angular
observations of T Tauri and Herbig AeBe stars. The next step is to
obtain real images of young stars and their circumstellar
environment. My research work as a Michelson fellow will thus have
both instrumental and science components.
I
propose to promote a new generation of imaging instruments that
should considerably simplify long baseline interferometer
operations. It will open the way for real imaging capability with an
array of optical and infrared telescopes. This instrumental part of my
work is based upon the use of integrated optics technologies that
allow us to integrate optical waveguides on a small chip similar to
microelectronics.
From
a practical point of view a close collaboration with the CfA IOTA
team (in particular with R. Millan-Gabet, W. Traub and I. Porro) will
allow me to carry on first "on sky" tests of an integrated optics
2-way and 3-way beam combiner and to learn more about the practice of
integrated optics and its interfacing with classical bulk optics.
Following
this exploration a second collaboration with the CHARA team
(in collaboration with Theo ten Brummelaar, Steve Ridgway and Hall
McAlister) will explore instrumental solutions for beam combination of
a
6 telescope array which is a real technical challenge. This instrument
require to develop dedicated integrated optics 6-way beam combiners
and its associated instrumentation. With its six telescopes, CHARA,
which is operated by the Georgia State University, will be one of the
very first real imaging interferometers with enough sensitivity to
study star formation.
If
successful, these new instruments should allow to observe young
stellar objects observations with much higher precision (or dynamic
range). We expect that these new observations will allow tougher
constraints on the environmental models, in particular on the physical
mechanisms operating at the heart of the so-called accretion disks
which are still poorly understood (accretion
physics,accretion-ejection processes, planetary formation etc...)
Marc
Kuchner -- Harvard-Smithsonian Center for Astrophysics
I
want to directly detect light from extrasolar
planetary systems. The best way to do this without being overwhelmed
by starlight appears to be nulling interferometry. During my tenure as
Michelson fellow, I'll be continuing my work with Wes Traub at CfA and
Eugene Serabyn at JPL on strategies for using the Keck Interferometer
to study nearby stars in nulling mode to search for faint
circumstellar emission from evolved planetary systems.
I'm
also interested in applying interferometric techniques to study
the likely sites of planet formation, disks around young stars. I'm
hoping to work on high-resolution interferometric observations of
disks around young stars with IOTA and the MMT, and to learn from Phil
Hinz and Rafael Millan-Gabet. In particular, I want to use nulling to
study the temperature structure of Herbig AeBe disks, and to use IOTA
in
concert with submillimeter interferometry to search for gaps in Herbig
AeBe disks that might be related to the planet formation process.
I
have some relevant theoretical interests. In general, the most
visible component of planetary systems is not likely to be the planets
themselves, but dust produced by collisions and outgassing of
asteroids or comets. I am working on understanding the dynamics of
belts of small bodies and the interaction between dust clouds and
planets. I hope to continue this work with Scott Kenyon and Matthew
Holman at CfA. The results of our simulations should help explain
high-resolution observations of planetary systems.
Maciej
Konacki -- California Institute of Technology
High
precision astrometry requires not only advanced
technology but also elaborated methods of data analysis. The goal of
my research is to develop techniques of planet detection for
astrometric measurements obtained with the Space Interferometry
Mission. It can be accomplished by solving several different
problems. One of the most important is the derivation of orbital
parameters. Such task is especially challenging for multiplanetary
systems. Another one concerns the design of observing scenarios
optimal from the planet detection point of view. These issues can be
analyzed before the launch of SIM by means of numerical simulations
that among others include a realistic SIM model. The end product of my
research will be a number of theoretical and numerical tools that will
help to prepare and conduct with SIM an efficient and productive
planet search campaign.
1999
Postdoctoral Fellows
Rafael
Millan-Gabet -- Harvard-Smithsonian Center for Astrophysics
I will
conduct my research in interferometry at the IOTA
(Infrared Optical Telescope Array), both using the interferometer for
astronomical observations of young and evolved stars and contributing
to its instrumentation development.
On
the scientific side, I study the circumstellar environment of young
stars of intermediate mass, the Herbig AeBe stars, as well as (at the
opposite evolutionary end) the pulsation properties of Mira
variables. In the past year, I have also been involved in a program
(with J. D. Monnier and collaborators) to combine IOTA/FLUOR and Keck
aperture masking observations in order to better constrain models of
dust enshrouded young and old stars. We also hope to make use of the
Keck adaptive optics system to expand on the observations of the
Herbig AeBe systems. Instrumental upgrades currently underway
(described below) will also allow us to extend our investigations of
young stars to the T Tauri class, as well as to other very embedded
sources.
On
the instrumental side, my principal responsibility concerns the
development of our near-infrared detectors, based on NICMOS3 and
PICNIC arrays. I am working on adapting our previous NICMOS3 design to
PICNIC-based star tracker and upgrade science cameras. I also
collaborate with M. Shure in his adaptation of our camera design for
the CHARA array. At the IOTA, the new science camera will be used, in
addition of our current mode of operation with two telescopes, for
fringe detection from three simultaneous baselines, as work on our
third telescope nears completion. Part of this work will done with
J.P. Berger, who will bring the very interesting technology of
integrated optics to the IOTA. Finally, I will be involved in an
effort, led by J. D. Monnier, to build a prototype single mode fiber
system for visible wavelengths, in order to be able to directly
measure the sizes of Cepheid stars as they pulsate.
