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1. Ground-Based
Observations of Mars
and Venus
Jeremy Bailey, Sarah Chamberlain, Andrew Simpson
(Australian Centre for Astrobiology, Macquarie University, Sydney)
David Crisp, Vikki Meadows
(Jet Propulsion Laboratory/Caltech)
2. Polarimetric Detection and
Characterization of Extrasolar
Planets
Jeremy Bailey (ACA)
Jim Hough, Phil Lucas
(University of Hertfordshire)
Spectroscopic
Imaging data.
Narrow-band filter
images.
UKIRT –
•Excellent image quality.
•IR spectrograph with R up to 4000
and long slit.
•Ability to scan across Mars while
guiding (correcting automatically
for the motion of Mars).
UKIRT Mars Images (2003)
Long exposure image
(Mauna Kea natural
seeing)
Selected best short
exposure image
Further image processing
(unsharp masking and
smoothing)
UKIRT/UIST 0.06 arc sec pixels. 1.64mm 1Kx1K
InSb detector windowed to 512x512, 90ms exposure.
HST / GroundBased Comparison
UKIRT Sep 4
2003, 1.64mm
HST Aug 24
2003, ACS
Mars 2.12 mm Imaging
Spectral Cubes
250
0.12 arcsec
pixels
114 0.25 arcsec pixels
Spectra
Aug 17
Sep 4
2.25mm
Atmospheric
CO2 absorption
2.00mm
CO2 ice
absorption
2.29mm
Water ice
absorption
2.10mm
Aug 17 2003
Sep 4th 2003
UKIRT 2.2mm albedo
UKIRT CO2 band depth
MGS MOLA topography
UKIRT
MOLA
CO2 band pressure measurement
• Complications
– Dust.
– CO2 in Earth
atmosphere.
– Topography
removal.
• Sensitivity
– 4-5 Pa (in total
pressure of ~700
Pa).
Mars
Earth
Light passes twice through
Mars atmosphere and once
through Earth’s atmosphere
CO2 bands have unresolved
structure
White - Earth
Red - Earth+Mars
Green - Earth
White - Mars
Model Building Approach
Solar spectrum
Mars atmosphere
radiative transfer
model
High resolution
Surface reflectance
Correct for Mars
atmosphere
spectrum
Earth atmosphere
transmission model
Bin to observed
resolution
Correct for
Earth atmosphere
Compare
Observed spectrum
Observed spectrum
Venus night side
spectra in the near-IR
Spectra with SPEX on the
3m IRTF (R ~ 2000) Feb 19th 2001
H2SO4 clouds (2.3mm)
(40-70km altitudes)
Spectra: IRTF
SPEX, Feb 19th 2001
Images: AAT 3.9m
IRIS2, Jul 9th
2004
Venus O2 airglow at 1.27mm
(>100km altitudes)
Spectrum: IRTF
SPEX, Feb 19th 2001
Image: ANU 2.3m
CASPIR, Sep 26th
2002
1.27mm Airglow Variability
Images: ANU 2.3m CASPIR, Sep 20-26th 2002
Our Future Plans
• Instrument Development
– Demonstrate HST resolution or better from ground-based
telescopes.
– IR Spectroscopy R ~ 2000 and R > 100,000.
• Continued observing program of Mars and Venus.
– Long sequences of CO2 observations of Mars to look for
weather systems.
– High spectral resolution observations to measure winds and
trace gases.
• Development of modeling and analysis software
– Techniques for Earth Atmosphere correction.
– Retrieval algorithms for pressure, temperature, dust etc.
Polarimetric Detection of Hot Jupiters
• Light from planet is polarized and polarization
varies around orbit as scattering angle changes.
Star - unpolarized
Combined
light polarized
at <10–5
Planet polarized at 510%, <10–4 of star
Seager, Whitney and Sasselov,
2000, Ap. J. 540, 504.
“…. Polarization signatures …
are well under the current
limits of detectability which is
a few x 10–4 in fractional
polarization” (Seager et al.
2000).
Photoelastic Modulators (PEMs)
Calibration Slide
PEM
Aperture Wheel
Wollaston Prism
(3 wedge cemented)
Two Filter Wheels
Fabry Lenses
Avalanche Photodiode
Modules
Sky Channel
Star Channel
Each channel (blue section)
rotates about its axis
Entire instrument rotates
about star channel axis
Phil Lucas
Edwin Hirst
Jeremy
Bailey
PLANETPOL
Jim Hough
David Harrison
Residual instrument polarization effects
are removed by a “second-stage
chopping” achieved by rotating the
polarimeter channels (wollaston +
detectors) relative to the PEM from +45
to –45 degrees.
Telescope polarization is
measured by tracking stars over a
range of hour angle. With an
altazimuth mounted telescope the
telescope tube rotates relative to
the sky.
“Unpolarized” Stars
(10–6)
U/I
(10–6)
Star
Q/I
HR 5854
0.44 ± 0.53
2.56 ± 1.76
–1.50 ± 1.11
1.60 ± 0.93
1.26 ± 0.94
3.19 ± 1.93
4.5 ± 3.0
–0.1 ± 2.3
45.4 ± 1.3
–5.7 ± 2.3
(a Ser, K2IIIb, V=2.6, 22pc)
HR 5793
(a CrB, A0V, V = 2.2, 22pc)
HD 102870
(b Vir, F8V, V = 3.6, 11pc)
Procyon
(a CMi, F5IV-V, V = 0.4, 3.5pc)
HR 6075
(e2 Oph, G9.5IIIb, V = 3.2, 33pc)
Polarized Stars
(10–6)
U/I
(10–6)
Star
Q/I
HD 76621
28.7 ± 3.0
–710 ± 2.7
u Her
102.4 ± 6.8
–169.0 ± 7.3
–1362 ± 10
1274 ± 10
3074 ± 4
–12734 ± 20
4819 ± 25
20132 ± 164
(Eclipsing binary)
U Sge
(Eclipsing binary)
HD 187929
(Standard P = 1.8%)
HD 198478
(Standard P = 2.8%)
Tau Boo Data
Fig 7(a) Q residuals and (b) U residuals (the brown points are the
averages of each block of data)
What the Polarization Can Tell Us
• Position angle variation through orbit gives us
the inclination.
– and hence the mass of the planet removing the sin I
uncertainty.
• The presence or absence of Rayleigh scattering
polarization provides information on the pressure
at the cloud tops.
• The orbital variation of polarization tells us about
particle size and composition.
• We will have some idea of the albedo and this will
assist other direct detection techniques (e.g.
photometry and spectrscopy).
Summary of Results
• PLANETPOL works and delivers repeatable polarization
measurements at the 10–6 level.
• The telescope polarization of the WHT is low and seems
stable (over a few days at least).
– Good news for us — It could be much more difficult to get reliable
results in the presence of a telescope polarization at the 10–3 to 10–4
level.
• Normal nearby stars have very low polarization (~3 x 10–6 or
less).
– Also good for us — We shouldn’t have too many problems from star
polarization in interpreting the data from our extrasolar planet
systems.
• We are measuring t Boo to an accuracy of about 2-3 x 10–6
for a 24 minute integration.
– More extended observations should be sufficient for a detection or a
significant upper limit.
– We have a 13 night run on the WHT in April/May 2005.
Imaging Polarimetry
• Similar polarization techniques using an imaging
system can be used for detection and
characterization of resolved planetary images.
– e.g. From Adaptive Optics systems on large ground-based
telescopes.
– Space instruments such as TPF-C.
• Polarimetry can be used as a differential
technique to pick the planet out of the speckle
noise halo around the star.
• Polarimetry can be used to help characterize any
detected planet.