1. Ground-Based 1. Ground-Based Observations of Mars Observations of Mars

and Venusand Venus

Jeremy Bailey, Sarah Chamberlain, Andrew SimpsonJeremy Bailey, Sarah Chamberlain, Andrew Simpson(Australian Centre for Astrobiology, Macquarie University, Sydney)(Australian Centre for Astrobiology, Macquarie University, Sydney)

David Crisp, Vikki MeadowsDavid Crisp, Vikki Meadows(Jet Propulsion Laboratory/Caltech)(Jet Propulsion Laboratory/Caltech)

2. Polarimetric Detection and 2. Polarimetric Detection and Characterization of Extrasolar Characterization of Extrasolar

PlanetsPlanets

Jeremy Bailey Jeremy Bailey (ACA)(ACA)

Jim Hough, Phil LucasJim Hough, Phil Lucas(University of Hertfordshire)(University of Hertfordshire)

UKIRT – UKIRT – •Excellent image quality.Excellent image quality.•IR spectrograph with R up to 4000 IR spectrograph with R up to 4000 and long slit.and long slit.•Ability to scan across Mars while Ability to scan across Mars while guiding (correcting automatically guiding (correcting automatically for the motion of Mars).for the motion of Mars).

Spectroscopic Spectroscopic Imaging data.Imaging data.

Narrow-band filter Narrow-band filter images.images.

UKIRT Mars Images (2003)

Long exposure image(Mauna Kea naturalseeing)

Selected best shortexposure image

Further image processing(unsharp masking and smoothing)

UKIRT/UIST 0.06 arc sec pixels. 1.64UKIRT/UIST 0.06 arc sec pixels. 1.64m 1Kx1K m 1Kx1K InSb detector windowed to 512x512, 90ms exposure. InSb detector windowed to 512x512, 90ms exposure.

HST / Ground-Based Comparison

HST Aug 24HST Aug 242003, ACS2003, ACS

UKIRT Sep 4 UKIRT Sep 4 2003, 1.642003, 1.64mm

Mars 2.12 Mars 2.12 m Imagingm Imaging

Spectral Cubes

2500.12 arcsecpixels

114 0.25 arcsec pixels

1024 spect

ral pixels

Spectra

Aug 17

Sep 4

2.25m AtmosphericCO2 absorption2.00m

CO2 iceabsorption2.29m

Water iceabsorption2.10m

UKIRT 2.2UKIRT 2.2m albedo UKIRT COm albedo UKIRT CO22 band depth MGS MOLA topography band depth MGS MOLA topography

Aug 17 2003Aug 17 2003

Sep 4th 2003Sep 4th 2003

UKIRTUKIRT MOLAMOLA

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

White - EarthWhite - EarthRed - Earth+MarsRed - Earth+Mars

Green - EarthGreen - EarthWhite - MarsWhite - Mars

COCO22 bands have unresolved bands have unresolved

structurestructure

Model Building Approach Solar spectrumSolar spectrum

Mars atmosphereMars atmosphereradiative transferradiative transfer

modelmodel

Earth atmosphereEarth atmospheretransmission modeltransmission model

High resolutionHigh resolution spectrumspectrum

Observed spectrumObserved spectrum

CompareCompare

Bin to observed Bin to observed resolutionresolution

Correct for MarsCorrect for Marsatmosphereatmosphere

Correct for Correct for Earth atmosphereEarth atmosphere

Observed spectrumObserved spectrum

Surface reflectanceSurface reflectance

Venus night side spectra in the near-IR

Spectra with SPEX on the3m IRTF (R ~ 2000) - Feb 19th 2001

H2SO4 clouds (2.3m)

(40-70km altitudes)

Images: AAT 3.9mIRIS2, Jul 9th2004

Spectra: IRTFSPEX, Feb 19th 2001

Venus O2 airglow at 1.27m

Image: ANU 2.3mCASPIR, Sep 26th2002

Spectrum: IRTFSPEX, Feb 19th 2001

(>100km altitudes)

1.27m 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.

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).

Star - unpolarizedStar - unpolarized

Planet polarized at 5-Planet polarized at 5-10%, <1010%, <10–4–4 of star of star

Combined Combined light polarized light polarized at <10at <10–5–5

Photoelastic Modulators (PEMs)

PEMPEM

Aperture WheelAperture Wheel

Wollaston PrismWollaston Prism(3 wedge cemented)(3 wedge cemented)

Two Filter WheelsTwo Filter Wheels

Fabry LensesFabry Lenses

Avalanche PhotodiodeAvalanche PhotodiodeModulesModules

Star ChannelStar ChannelSky ChannelSky Channel

Calibration SlideCalibration Slide

Each channel (blue section) Each channel (blue section) rotates about its axisrotates about its axis

Entire instrument rotatesEntire instrument rotatesabout star channel axisabout star channel axis

Edwin HirstEdwin Hirst

Phil LucasPhil Lucas

Jim HoughJim Hough David HarrisonDavid Harrison

JeremyJeremyBaileyBailey

PLANETPOLPLANETPOL

Telescope polarization is Telescope polarization is measured by tracking stars over a measured by tracking stars over a range of hour angle. With an range of hour angle. With an altazimuth mounted telescope the altazimuth mounted telescope the telescope tube rotates relative to telescope tube rotates relative to the sky.the sky.

Residual instrument polarization effects Residual instrument polarization effects are removed by a “second-stage are removed by a “second-stage chopping” achieved by rotating the chopping” achieved by rotating the polarimeter channels (wollaston + polarimeter channels (wollaston + detectors) relative to the PEM from +45 detectors) relative to the PEM from +45 to –45 degrees.to –45 degrees.

“Unpolarized” StarsStar Q/I (10–6) U/I (10–6)

HR 5854( Ser, K2IIIb, V=2.6, 22pc)

0.44 ±0.53 2.56 ± 1.76

HR 5793( CrB, A0V, V = 2.2, 22pc)

–1.50 ± 1.11 1.60 ± 0.93

HD 102870( Vir, F8V, V = 3.6, 11pc)

1.26 ± 0.94 3.19 ± 1.93

Procyon( CMi, F5IV-V, V = 0.4, 3.5pc)

4.5 ± 3.0 –0.1 ± 2.3

HR 6075(2 Oph, G9.5IIIb, V = 3.2, 33pc)

45.4 ± 1.3 –5.7 ± 2.3

Polarized StarsStar Q/I (10–6) U/I (10–6)

HD 76621 28.7 ± 3.0 –710 ± 2.7

u Her(Eclipsing binary)

102.4 ± 6.8 –169.0 ± 7.3

U Sge(Eclipsing binary)

–1362 ± 10 1274 ± 10

HD 187929(Standard P = 1.8%)

3074 ± 4 –12734 ± 20

HD 198478(Standard P = 2.8%)

4819 ± 25 20132 ± 164

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 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.