Observatory Systems Engineering

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Nulling Interferometry for Studying Other
Planetary Systems Techniques and Observations
Phil Hinz PhD Thesis Defense Wednesday Jan. 31,
2000
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Challenges of Finding Planets
Mass of Jupiter is 10-3 Msun Giant Planet
Brightness is 10-9 Lsun in visible 10-6
Lsun in IR Dust Disk is 10-4 Lsun in IR Direct
Detection Requirements large aperture
telescopes wavefront correction suppress
ion of starlight Need instrumental development
to make scientific progess.
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Advantages of Direct Detection

• We want to see planets not just infer their
  existence.
• Direct emission from planets can tell us about
  their chemical make-up, temperature, etc. . . We
  can learn more about it.
• Wide orbit planets such as Jupiter or Saturn
  require prohibitive time baselines for Doppler
  velocity detection.

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Bracewell Interferometry
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Fizeau Interferometry
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Resolving Faint Companions
Fizeau interferometry is well suited for high
spatial resulotion studies
Pupil-plane interferometry is well-suited
for suppression of starlight.
Star
StarCompanion
Companion (1 of star brightness)
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Nulling Measurements
Nulling interferometry measures the total flux
transmitted by the interference pattern of the
two elements, convolved with the PSF of a single
element.
Source Orientation 1
Orientation 22
PSF of single element
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Subtlety 1 Chromaticity of Null
Fraction of light remaining in nulled out put is
given by where Level of suppression is
good over only a narrow bandwidth. Three fixes
Rotate one beam 180 degrees (Shao and
Colavita) Send one beam through focus (Gay and
Rabbia) Balance dispersion in air by dispersion
in glass (Angel, Burge and Woolf) Dispersion
Compensation allows out-of band light to be used
to sense phase (Angel and Woolf 1997)
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Subtlety 2 True Image Formation
In Bracewells concept the beams form images
which are mirror versions of one
another. Rotation nulls create images which are
rotated versions of one another. It is only
possible to create a true image of the field
using dispersion compensation for the suppression
and an interferometer which has an equal number
of reflections in each beam.
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First Telescope Demonstration of Nulling
Nulling at the MMT Nature 1998 395, 251.
Ambient Temperature Optics
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Beam-splitter design
Requirements Equal reflection and transmission
at nulling wavelength Equal reflection and
transmission at phasing wavelength Symmetric
design (to avoid chromatic phase
shifts) Substrate suitable for dispersion
compensation. Design
difference in substrate thickness of 39 µm
ZnSe substrate
?0 /4 air gap
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Phase Compensation of Null
Phase (waves)
Wavelength (µm)
Intensity
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Beam-splitter Performance
Reflection Intensity
phase sensing passband
Nulling passband
Wavelength (µm)
Phase difference (waves)
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The Bracewell Infrared Nulling Cryostat
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Mechanical Design
telescope beam
10 micron detector
2 µm detector
imaging channel nulling channel
reimaging ellipsoid
beam-splitter
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BLINCs First Year
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Laboratory Setup
Ball mirror
Telescope mirror
Fold mirror
Infrared Camera
CO2 laser
HeNe laser
Interferometer
Dichroic
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Laboratory Results
0.5 s exposure images at 10.6 µm
CO2 laser source yielded a null with an
integrated flux of 3x10-4 Entire Airy
pattern along with the scattered light
disappears in nulled image.
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Laboratory Results II
50 bandwidth causes adjacent nulls to be
significantly gt 0. Relative depth of
the adjacent nulls determines achromaticity of
central null.
Intensity
path-length (microns)
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Laboratory Null
Constructive image Scanning pathlength
White5 of peak
2 of peak
0.5 of peak
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Telescope Nulling
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Observing at the MMT

• Commissioning run of MIRAC-BLINC, June 10-17,
  2000.
• Aligned and phased the interferometer during the
  first night of observing
• Observed AGB stars, several Herbig Ae stars, and
  several main-sequence stars.
• Observed again in October, but weather was poor.

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Pupil Alignment of BLINC
Left beam secondary obscuration
Right beam outer edge of primary
Pupil stop size for nulling observations
Left beam outer edge of primary
Right beam secondary obscuration
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Dust outflow around Antares
constructive destructive
Best nulls of a Boo have a peak ratio of 3. The
integrated light is 6 of the constructive
image. The nulled images of a Sco are 25 of
the constructive images. Suppression of the
starlight allows us to form direct images of
the dust outflow around the star
a Boo
a Sco
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Antares
5 arcsec
baseline vertical
baseline horizontal
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IRC10216
Constructive -- Destructive
Point Source
Point source in IRC10216 is faint compared to
its extended dust nebula. By modulating the
point source we can determine its contribution as
well as its registration to the nebula. This has
been a source of confusion for IRC10216
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IRC10216
11.7 µm
N
E
1 arcsec
8.8 µm
nulled image
constructive - null
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Herbig Ae/Be stars
Chiang and Goldreich (1997) have created models
to explain the spectral energy distribution of T
Tauri stars and Herbig Ae/Be stars. Disk would
be only 0.2 across, so too small for direct
imaging detection, but would not have a null of lt
40\.
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Herbig Ae/Be stars
Three nearby Herbig Ae stars observed with BLINC,
June 2000.
star d (pc) Expected Residual Flux Measured Residual Flux Position Angle
HD150193 150 41 05 97 º
HD163296 122 49 -1 7 3 3 94 º 10 º
HD179218 240 41 3 3 1 3 162 º 87 º
Indicates region of emission is smaller than
predicted by model.
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Main Sequence Stars
Two nearby main sequence stars observed with
BLINC, June 2000 Vega and Altair.
Star Null Residual Flux Wavelength Position Angle
Vega 14 3 1 4 11.7 µm 133 º
Vega 13 3 0 4 10.3 µm 135 º
Altair 8 4 -5 5 10.3 µm 97º
Using the DIRBE model for our solar zodiacal
cloud (Kelsall et al. 1998), a limit of
approximately 3700 times solar level for Vega
and 2500 times solar level for Altair. IRAS
photometric limits at 12 µm are approximately
1800 times solar level for both stars.
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Nulling Sensitivity
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Depth of NullStar Diameter
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MMT Nulling Error Budget
Error Source Level
Star diameter at 10 pc Star leak At 11 µm G2V star 1.6x10-6
Chromatic phase errors Beam-splitter 4.0x10-6
Chrom. and Pol. Amp. Errors Beam-splitter 3.8x10-5
Adaptive Optics Spatial Error Temporal Error Atmosphere Fitting error Time lag of system 2.0x10-4 (1.6x10-5) 1.2x10-4 (1.70x10-5)
Total flux 3.6x10-4 (7.7x10-5)
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Expected Sensitivity
MMT LBT
10-12.2 µm 660 45
M band 190 21
L band 18 2.1
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MMT Dust Limits for stars at 10 pc
F0 star
dust around an A0 star
G0 star
K0 star
MMT detection limit
Flux in nulled output of MMT (µJy)
M0 star
Cloud density (zodis)
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MMT zodiacal dust detection
The short baseline of the MMT gives it 13 times
better suppression of a star than LBT and 450
times better than Keck.
Star Spec. Type Distance (pc) Dust Limit (vs. solar) Star Leak
Sirius e Eri 61 Cyg A 61 Cyg B a Cmi t Ceti Gl380 ? 2 Eri 70 Oph Altair A1V K2V K5Ve K7Ve F5IV-V G8Vp K2Ve K1Ve K0Ve A7IV-V 2.64 3.22 3.48 3.50 3.50 3.65 4.87 5.04 5.09 5.14 0.1 10 29 50 0.9 7 34 29 23 0.6 9.410-5 1.010-5 7.010-6 6.010-6 2.310-5 9.510-6 4.410-6 4.310-6 4.610-6 1.610-5
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LBT dust limits for stars at 10 pc
dust around an A0 star
F0 star
G0 star
K0 star
Flux in nulled output of LBT (µJy)
M0 star
LBT detection limit
Cloud density (zodis)
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Planet Limits
MMT 11 µm limit
M band flux of 5 MJ planet
MMT M band limit
N band flux
Flux of 5 MJ planet (µJy)
L' band flux
MMT L' band limit
age (Gyr)
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Planet Limits
1 Gyr
flux of 0.5 Gyr old planet
MMT limit
5 Gyr
L' band flux (µJy)
LBT limit
mass (MJ )
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Phase space of Direct Detection
MMT limit
Mass (Jupiter masses)
LBT limit
Radial velocity limit
Separation (AU)