Balloon-based Balloon-based observations of stellar observations of stellar

occultationsoccultations

Cathy OlkinCathy Olkin

Southwest Research InstituteSouthwest Research Institute

April 27, 2007April 27, 2007

What is a stellar occultation?What is a stellar occultation?A stellar occultation is a planet passing in front of a star.A stellar occultation is a planet passing in front of a star.

This star light probes the planet’s atmosphere or ring system This star light probes the planet’s atmosphere or ring system at a higher spatial resolution than available any other ways at a higher spatial resolution than available any other ways near Earth observations.near Earth observations.

What science can be derived What science can be derived from this technique?from this technique?

-Sizes of asteroids or other -Sizes of asteroids or other airless bodies. KBOs in the airless bodies. KBOs in the future.future.

-Discovery and kinematic -Discovery and kinematic models of ring systemsmodels of ring systems

- Discovery of the rings Discovery of the rings around Uranus around Uranus

- Improved kinematic Improved kinematic models of ring systemsmodels of ring systems

HST FOC stellar occultation light curveof Saturn’s rings(Bosh, Olkin, French, Nicholson 2003)

What science can be derived What science can be derived from this technique?from this technique?

-Sizes of asteroids or other -Sizes of asteroids or other airless bodiesairless bodies

- Discovery and kinematic - Discovery and kinematic understanding of ring understanding of ring systemssystems

- Discovery and - Discovery and characterization of planetary characterization of planetary atmospheresatmospheres

R (km) v. T (K) R (km) v. dT/dr(K/km)

dry adiabat

An example of howAn example of howwe do this nowwe do this now

We choose events We choose events with shadow paths with shadow paths goes over arid goes over arid locations - severely locations - severely limits possible limits possible eventsevents

Accurate, timely Accurate, timely prediction critical for prediction critical for for successfor success

Pluto June 12, 2006

An example of howAn example of howwe do this now, cont.we do this now, cont.

Expensive to Expensive to cover all these cover all these sites and ship sites and ship portable portable telescopes. telescopes.

Pluto June 12, 2006

Predicted occultations Predicted occultations

• • More than half the More than half the events happen events happen during daylightduring daylight

• • More than half the More than half the events happen events happen over the ocean or over the ocean or otherwise not otherwise not amenable amenable locationslocations

Other ways to make this Other ways to make this measurementmeasurement

• • AdvantagesAdvantages-mobile-mobile-above most weather-above most weather

• • DisadvantagesDisadvantages-KAO de-commissioned-KAO de-commissioned-awaiting SOFIA-awaiting SOFIA-SOFIA will be a heavily -SOFIA will be a heavily desired resourcedesired resource

- does not give multiple - does not give multiple chordschords

Our idea Our idea Deploy balloons out of an airplane traveling Deploy balloons out of an airplane traveling

perpendicular across the shadow pathperpendicular across the shadow path

AdvantagesAdvantages

Nearly global accessNearly global access Day and night events possibleDay and night events possible

Depends on background levelDepends on background level Multiple chordsMultiple chords Above cloudsAbove clouds Good seeingGood seeing

Questions?Questions? What is the background level at wavelengths of 8000 What is the background level at wavelengths of 8000

Angstroms at both day and night at ballooning Angstroms at both day and night at ballooning altitudealtitude Impacts telescope aperture; payload weight; expenseImpacts telescope aperture; payload weight; expense

Stability and telescope pointingStability and telescope pointing Feasibility of deploying from airplanesFeasibility of deploying from airplanes Communications/Operations of multiple balloonsCommunications/Operations of multiple balloons Cost per unitCost per unit

BalloonBalloon Instrumentation/TelescopeInstrumentation/Telescope Campaign costsCampaign costs