Transcript Borucki2001b-27.ppt

CCD OVERVIEW
Kepler will have 42 CCDs
2,200 column x 1,024 row full frame CCDs
Field of View (FOV) > 100 square degrees (113 w/ vignetting)
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DATA: SOLAR SYSTEM
A great deal of information, But…
• Single example.
• Biased example – We are here!
Comets
Giant
Planets
Moons
Meteorites
Terrestrial Planets
Asteroids
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KEPLER and The Planet Finder (TPF)
Excerpts from the
National Research Council (NRC)
report with regard to TPF:
“…. TPF will revolutionize major areas
of planetary and non-planetary science…
…...it is important to determine prior to
the start of the mission that it is likely
that there will be an adequate number of
Earth-sized planets for TPF to study." (p.
112)
National Research Council
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MORE PLANETARY SCIENCE
• Terrestrial planet multiplicity.
• Terrestrial planet coplanarity (~ 12% chance of
seeing both Venus & Earth if either is seen).
• Single transits of ~30 cold Jupiters (SNR =
400).
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TRANSIT
Transit observation by HST of a jovian-size planet
orbiting hd209458
Ten-minute to ten-minute binned data from several orbits
have a precision of 60 ppm (Brown et al. 2001).
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BINARY SEPARATION
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MAIN SEQUENCE STARS
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PLANETS PER DURATION
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KEPLER SPACECRAFT
Sunshade
Photometer
Radiator
Solar
Array
Spacecraft
High gain
Antenna
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DETECTION CAPABILITIES
PLANET DETECTION CAPABILITES FOR SOLAR- LIKE STARS
0.001
Brown Dwarf
min. mass
Orbital Period (yr)
0.01
0.1
1
10
100
1000
1000
• Solar-system planets
•
Astrometry gnd based
² > 1 marcsec, 10 pc
J
•
10
Roche Limit
S
Stellar Interior
Planetary Mass
Mp /M
100
Radial velocity gnd based
²v sin i * > 3 m/s
•U •N
Astrometry spacebased
² > 2 arcsec, 10 pc
1
••
VE
0.1
•
M
0.001
0.01
Photometry spacebased
²L/L > 0.002%
•
M
0.1
1
Semi-Major Axis (AU)
10
100
10/99
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TRANSIT PROPERTIES
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EXPECTED TRANSITS
EXPECTED NUMBER OF GRAZING TRANSITS BY TARGET STARS
50% of target stars are binaries => 50,000 targets are binaries
20% have orbital periods of order days to weeks
10,000 stars with transit probabilities near 10%
1000 stars will show stellar transits
Of these 1,000 stars,
~ 6.5% (i.e., 65) stars will show 1% deep transits
~ 1.4% (i.e., 14) stars will show 0.1% deep transits
~ 0.3% (i.e., 3) stars will show 0.01% deep transits
20% have orbital periods between a few months and a few years
10,000 stars with transit probabilities near 1%
100 stars will show stellar transits
Of these 100 stars;
~ 6.5% (i.e., 6 ) stars will show 1% deep transits
~ 1.4% (i.e., 1.4 ) stars will show 0.1% deep transits
~ 0.3% (i.e., 0.3 ) stars will show 0.01% deep transits
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REQUIRED SENSITIVITY
• ∆L/L = area Earth/area Sun = 1/12,000 = 8x10-5
• Require total noise to be <2x10-5 for 4-sigma detection in 5 hours
• Three sources of noise and their contributions:
- Stellar variability:<1x10-5, typically for the Sun on timescale of ~1/2 day
- Shot noise:1.4x10-5, in 5 hr for mv=12 solar-like star and 1-meter aperture
- Instrument noise: <1x10-5, including detector dark current, electronics
read noise, thermal effects, spacecraft pointing jitter, and shutterless
operation.
• Detector of choice: array of 42–2kx1k CCDs with 27µm pixels and dual
readout
- Both SITe and EEV are thinned, back-illuminated, delta-doped, AR
coated
• Limiting bright magnitude of mv=9 and full-well depth of 825 e-/µm2
requires:
- Defocus image to 5 pixel diameter and readout every 3 seconds.
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MEASUREMENT TECHNIQUE
• Use differential photometry (common mode rejection):
- Brightness of each star is re-normalized to the ensemble of thousands of
stars in each quadrant of each CCD, readout with a single amplifier;
• Transits only last several hours:
- Long term photometric stability not necessary;
• Defocus the star image to five pixel diameter:
- Mitigates saturation (109 e-/hr) and sensitivity to motion;
• Control pointing to 28 millipixels (0.1 arc sec);
- Star images remain on the same group of pixels, eliminates effects of interpixel variations in sensitivity;
• Operate CCDs near full-well capacity:
- Dark current and read-noise effects become negligible;
• Place the photometer in a heliocentric orbit (SIRTF-like):
- Provides for a very stable thermal and stray light environment.
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ORGANIZATION
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SINGLE TRANSIT SNR’S
Approximate Single Transit SNR's for a 12th mag Star
Conditions
Nominal*
Solar Variability X 1
Instrument Noise X 1.4
Solar Variability X 2
Instrument Noise X 1.4
Solar Variability X 1.4
Instrument Noise X 1
Solar Variability X 1
Instrument Noise X 2
Solar Variability X 1
Instrument Noise X 3
Solar Variability X 1
Instrument noise X 1
Double Stellar Rotation Rate
5-Hour Transit
4.3
13-Hour Transit
5.1
3.7
4.8
3.2
3.5
3.7
4.3
3.5
4.7
3.3
4.3
3.1
4.0
*Shot Noise for a 12th mag star (1.4 x 10 -5 at 5 hours), Instrument Noise of 0.7 x 10 -5 at 5 hours
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DETECTABLE SIZE
Detectable planet size vs. Orbital semi-major axis and star mass
Each plot is for
a given stellar
brightness.
Planets of a
given size are
detectable to
the left of each
contour.
Detection are
based on a
total SNR> 8 s
and > 3
transits in 4
years.
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DETECTABLE STARS
Number of stars that can be detected vs planet size as a function of stellar type
105
Earth
Size
Large
Terra
Giant
Cores
Gas
Giants
Total
F
A
104
B
G
K
M
Approx. magnitude
12-12.5
13-13.5
103
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1
2
3
4
Planetary Radius (Re)
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The solid lines show the number of dwarf stars of each spectral type for which a planet of
a given radius can be detected at 8. These numbers are based on 4 near-grazing transits
with a 1-yr period and stars with mv < 14. The dashed lines show a significant increase in
the number of stars when assuming 4 near-central transits .
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SNR
SNR as a Function of Transit Duration and Stellar Variability
The three curves give the SNR for 4 combined transits about an mv=12 solar-like
star at times of low, medium, and high stellar variability.
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DETECTABLE RADIUS
Effect of Stellar Variability on Detectable Planetary Radius
1.1
Min Rp, Earth=1
1
0.9
0.8
mv=12, 4 Transits
mv=12, 6 Transits
0.7
mv=9, 4 Transits
mv=9, 6 Transits
0.6
0.5
0
5
10
Stellar Variability, ppm
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20
Earth-sized transits are readily detectable for stars with
variability comparable to that of the Sun.
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Test bed: BRIGHT STAR EFFECT
Test 125 with optimal pixel weighting
1.0
0.875
Measured noise
0.75
Shot noise
Max. allowed noise
0.625
0.5
0.375
0.25
0.125
0.0
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8
9
10
11
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Magnitude
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Within the planned
Kepler Mission field-ofview there are several
stars as bright as mv=4.
To simulate the impact of
a bright star in the field,
fiber optics were used to
generate mv=4 stars at
various distances from
stars in the field. The
effect of a bright star
does not raise the general
system noise above the
red line noise limit. Only
the nearest star within a
few CCD columns of the
mv=4 star was
15 significantly affected.
Both its noise and
apparent brightness
increase.
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Test bed: S/C MOTION EFFECT
In this 46 hour test the
camera was moved at various
amplitudes and rates
characteristic of the
spacecraft guidance system
performance. The jitter
model used predicted a 1
standard deviation in
pointing of 0.01 arcsec in
each axis, corresponding to
2.8 millipixels on the CCD.
Deviations were typically
less than 4 during the test,
i.e., 11 millipixels.
The test results show that the
system noise is still below
the maximum allowable
noise except for a small
number of deviant stars.
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SUMMARY
• The Kepler Mission is designed to detect hundreds of Earth-size planets by
looking for transits. To demonstrate the technology to be utilized, a Testbed
Facility has been built and operated with a flight type CCD. The facility
simulates all of the features of the sky and the spacecraft/instrument that are
important for the success of the mission.
• Optimum operating conditions for defocus, photometric aperture size vs
stellar brightness and maximum operating temperature have been measured.
• The required photometric precision has been demonstrated while operating
without a shutter during readout, having some saturated pixels in the brightest
stars, working in a crowded field with a star density the same as planned for
the mission, inclusion of spacecraft jitter, and over a dynamic range of five
stellar magnitudes.
• Tests of comic-ray hits and field rotation (which occurs every three months
during the mission) also do not appear to have detrimental affects.
• Transits have been injected and detected at the required statistical significance
under all operating conditions during all tests.
• The Kepler Mission is ready for flight status.
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SPECTRAL TYPE
SPECTRAL TYPE AND LUMINOSITY CLASSIFICATION
1.5
1.4
Spectral Type
K0
G0
Sr II / Fe I
1.3
1.2
1.1
1.0
Dwarfs (V)
0.9
Sub-Giants (III-IV)
0.8
Giants (I-II)
0.7
0.4
0.6
0.8
1.0
H/ Fe I
1.2
1.4
1.6
(Based on method of Rose, 1984)
5/96
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TRANSITS OBSERVED BY VULCAN
HD 209458
Cygnus #937
Cygnus #3047
Perseus #0831
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Cygnus #3047
Cygnus #1433
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DETECTION RATE
Expected detection rate for hot Jupiters
Probability that:
• the target star is dwarf:
0.5
• the star is single or a widely space binary:
0.5 to 0.8
• the star has a hot Jupiter:
0.01 to 0.02
• the orbital plane is correctly aligned:
0.1
• six weeks of data show at least three transits: 0.6
• Product of the probabilities: 1.5 to 4.8 x10-4
• Yield = Product of probabilities times number of stars
monitored = 1.5x10-4 x 104 stars = 1.5 to 5 planets
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VULCAN
Vulcan transit search of 6,000 stars for extrasolar planets
• OBJECTIVES:
• Monitor 6000 stars
“continuously” for periods
of at least 6 weeks
• Detect jovian-size planets
in short period orbits
• Use Doppler-velocity
measurements to determine
mass and density
• TELESCOPE:
• Aperture: 10 cm
• Focal length: 30 cm
• Field of View: 7x 7 degrees
• Detector: 4096x4096 CCD
with 9 m pixels
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