Transcript Nulling Interferometer

31 Jan. 2000
PMH-1
Nulling Interferometry for Studying Other
Planetary Systems: Techniques and
Observations
Phil Hinz
PhD Thesis Defense
Wednesday Jan. 31, 2000
31 Jan. 2000
PMH-2
Challenges of Finding
Planets
Mass of Jupiter is 10-3 Msun
Giant Planet Brightness is:
Dust Disk is 10-4 Lsun in IR
10-9 Lsun in visible
10-6 Lsun in IR
Direct Detection Requirements:
large aperture telescopes
wavefront correction
suppression of starlight
Need instrumental development to make scientific progess.
31 Jan. 2000
PMH-3
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.
31 Jan. 2000
PMH-4
Bracewell Interferometry
ΔΦ
Stellar wavefront
Semi-transparent mirror
Collector 1
31 Jan. 2000
left output
right output
Collector 2
PMH-5
Fizeau Interferometry
Collector 1
31 Jan. 2000
Collector 2
PMH-6
Resolving Faint Companions
Fizeau interferometry is well –suited for
high spatial resulotion studies
Pupil-plane interferometry is well-suited for
suppression of starlight.
Star
Star+Companion
Companion
(1% of star brightness)
31 Jan. 2000
PMH-7
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
dust
Orientation 1
trdust
Orientation 22
trdust2
PSF of single element
31 Jan. 2000
PMH-8
Subtlety 1: Chromaticity of Null
Fraction of light remaining in nulled out put is given by
where
N ( ) 
1  cos(  ( ))
2
 ( ) 
0 1

4 4
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)
31 Jan. 2000
PMH-9
Subtlety 2: True Image Formation
In Bracewell’s 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.
31 Jan. 2000
PMH-10
First Telescope Demonstration
of Nulling
Nulling at the MMT
Nature 1998; 395, 251.
Ambient Temperature
Optics
31 Jan. 2000
PMH-11
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
λ0 /4 air gap
31 Jan. 2000
PMH-12
Phase Compensation of Null
Phase (waves)
0.54
0.52
0.5
0.48
0.46
9
9.5
10
Intensity
31 Jan. 2000
3
1  10
4
1  10
5
1  10
6
11
11.5
12
12.5
13
11.5
12
12.5
13
Wavelength (μm)
0.01
1  10
10.5
9
9.5
10
10.5
11
PMH-13
Reflection Intensity
Beam-splitter Performance
1
0.5
Phase difference (waves)
0
1
4
2
4
6
8
Wavelength (μm)
10
12
Nulling
passband
0.5
0
31 Jan. 2000
2
phase sensing
passband
6
8
10
12
PMH-14
The Bracewell Infrared Nulling
Cryostat
31 Jan. 2000
PMH-15
Mechanical Design
telescope beam
10 micron detector
2 μm detector
imaging “channel”
nulling “channel”
reimaging ellipsoid
31 Jan. 2000
beam-splitter
PMH-16
BLINC’s First Year
31 Jan. 2000
PMH-17
Laboratory Setup
Infrared Camera
Fold mirror Ball mirror
“Telescope” mirror
CO2
laser
Interferometer
31 Jan. 2000
HeNe laser
Dichroic
PMH-18
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.
31 Jan. 2000
PMH-19
Laboratory Results II
1
50% bandwidth causes
adjacent nulls to be
significantly > 0.
Intensity
0.75
Relative depth of the
adjacent nulls determines
achromaticity of central
null.
0.5
0.25
0
20
15
10
5
0
5
10
15
20
path-length (microns)
31 Jan. 2000
PMH-20
Laboratory Null
Constructive image
2% of peak
Scanning pathlength
White=5% of peak
0.5% of peak
31 Jan. 2000
PMH-21
Telescope Nulling
31 Jan. 2000
PMH-22
Observing at the MMT
•Commissioning run of MIRACBLINC, 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.
31 Jan. 2000
PMH-23
Pupil Alignment of BLINC
Right beam
outer edge
of primary
Left beam
outer edge
of primary
31 Jan. 2000
Left beam
secondary
obscuration
Pupil stop size
for nulling
observations
Right beam
secondary
obscuration
PMH-24
Dust outflow around Antares
constructive
α Boo
α Sco
31 Jan. 2000
destructive
Best nulls of α Boo
have a peak ratio of
3%. The integrated
light is 6% of the
constructive image.
The nulled images of
α Sco are 25% of the
constructive images.
Suppression of the
starlight allows us to
form direct images of the
dust outflow around the
star
PMH-25
Antares
5 arcsec
baseline horizontal
31 Jan. 2000
baseline vertical
PMH-26
IRC+10216
Constructive
--
Destructive
=
Point Source
Point source in IRC+10216 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 IRC+10216
31 Jan. 2000
PMH-27
IRC+10216
11.7 μm
1 arcsec
8.8 μm
nulled image
31 Jan. 2000
constructive - null
PMH-28
Herbig Ae/Be stars
τ=α
α
R*
τ=1
r
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 < 40\%.
31 Jan. 2000
PMH-29
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%
0±5%
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.
31 Jan. 2000
PMH-30
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.
31 Jan. 2000
PMH-31
Nulling Sensitivity
31 Jan. 2000
PMH-32
Depth of Null:Star Diameter
1
transmission
0.8
0.6
0.4
0.2
0
0.4
0.3
0.2
0.1
0
0.1
0.2
0.3
0.4
arcseconds
star diameter
31 Jan. 2000
PMH-33
MMT Nulling Error Budget
Error
Source
Star diameter
at 10 pc
Star leak
At 11 μm
Chromatic phase
errors
Beam-splitter
Chrom. and Pol. Amp.
Errors
Beam-splitter
Adaptive Optics
Spatial Error
Temporal Error
Atmosphere
Fitting error
Time lag of system
G2V star
1.6x10-6
4.0x10-6
3.8x10-5
Total flux:
31 Jan. 2000
Level
2.0x10-4
1.2x10-4
(1.6x10-5)
(1.70x10-5)
3.6x10-4
(7.7x10-5)
PMH-34
Expected Sensitivity
1  10
10
photons/s/m 2/μm/arcsec 2
1  10
N
9
M
1  10
8
1  10
7
1  10
6
1  10
MMT
Jy hour

L'
LBT
Jy hour

10-12.2 μm 660
45
M band
190
21
L‘ band
18
2.1

5
4
6
8
10
12
14
Wavelength (μm)
31 Jan. 2000
PMH-35
Flux in nulled output of MMT (μJy)
MMT Dust Limits for stars at 10 pc
1  10
4
1  10
3
MMT detection limit
100
10
1
10
100
1  10
3
Cloud density (zodis)
31 Jan. 2000
PMH-36
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.
31 Jan. 2000
Star
Spec. Type Distance
(pc)
Dust Limit Star Leak
(vs. solar)
Sirius
ε Eri
61 Cyg A
61 Cyg B
α Cmi
τ Ceti
Gl380
ω 2 Eri
70 Oph
Altair
A1V
K2V
K5Ve
K7Ve
F5IV-V
G8Vp
K2Ve
K1Ve
K0Ve
A7IV-V
0.1
10
29
50
0.9
7
34
29
23
0.6
2.64
3.22
3.48
3.50
3.50
3.65
4.87
5.04
5.09
5.14
9.4×10-5
1.0×10-5
7.0×10-6
6.0×10-6
2.3×10-5
9.5×10-6
4.4×10-6
4.3×10-6
4.6×10-6
1.6×10-5
PMH-37
LBT dust limits for stars at 10 pc

4

3
Flux in nulled output of LBT (μJy)
1 10
1 10
100
LBT detection limit
10
1
10
100
1  10
3
Cloud density (zodis)
31 Jan. 2000
PMH-38
Planet Limits
Flux of 5 MJ planet (μJy)
1  10
3
MMT 11 μm limit
MMT M band limit
100
MMT L' band limit
10
0.1
31 Jan. 2000
0.2
0.3
0.4
0.5
age (Gyr)
0.6
0.7
0.8
0.9
PMH-39
Planet Limits
L' band flux (μJy)
100
MMT limit
10
LBT limit
1
31 Jan. 2000
2
4
6
8
10
mass (MJ )
12
14
16
18
20
PMH-40
Phase space of Direct Detection
Mass (Jupiter masses)
100
10
LBT limit
1
0.1
0.1
31 Jan. 2000
MMT limit
1
Separation (AU)
10
100
PMH-41