Beyond TAOS: Future Blind Field Surveys

Beyond TAOS: Future Blind Field Surveys

Charles AlcockUniversity of PennsylvaniaWith major contributions from

The TAOS Science Team &

Ball Aerospace

Charles AlcockUniversity of PennsylvaniaWith major contributions from

The TAOS Science Team &

Ball Aerospace

Plan of the talk:

• The scientific need for an occultation survey that is more capable than TAOS

• Description of occultations by TNO’s– What TAOS will do– What TAOS will not be able to do

• Beyond TAOS: – An expanded ground-based array– A space-based survey

The Scientific Needs (beyond TAOS):

• Census of TNO’s with size < 1 km to study the collisionally eroded regime

• Better estimates of sizes• Shape determination• Distance estimates are critical!• Ultimate goal should be to survey the entire

Solar System – out to the Oort Cloud!

R = 5 km

= 845 nm

r = 50 AU

The basics of TNO occultations (again!):

The basics of TNO occultations

r

2R

λ

A “representative”sequence of occultations by “spherical TNO’s” (1 FSU = (r/2)1/2)

Next Generation TAOS: an expanded ground-based array

• Larger telescopes for more stars at greater S/N (1 meter class with field of view > 1.5o)

• More telescopes (~10) spread out over several kilometers to sample the diffraction patterns– Distance estimates become possible– Sample smaller objects

Multiple telescopes are useful

• Help to control false positives (critical in TAOS)• A spatially expanded array can sample the

shadow pattern (shape & distance information)– Spacing ~1 km North-South– Spacing >10 km East-West (may need to move

telescopes seasonally)– Real estate problem (Atacama plateau?)!

Site selection not straightforward:

• Dark sky, good seeing for photometric precision

• Accommodate array kilometers across• Possible need to move telescopes seasonally

– Western US– Northern Chile

Need to operate faster than 5 Hz:

• Use “frame-buffer” CCDs– Increase sampling rate (~10 Hz)– Eliminate streaking characteristic of zipper

mode– Scalable to large focal planes

• May upgrade TAOS using this architecture (TAOS II)

Beyond TAOS: a space-based system similar to Kepler

• S/N > 10 on ~150,000 stars at 30 Hz

• Potential to survey down to ~100 meters

• Reliable statistical estimates of distances

• Crude shape estimates• Thousands of events• Oort Cloud …?

“Straw man” design based upon Kepler

• Kepler will follow 160,000 stars in one field to search for planetary transits

• Aperture 95 cm

• Schmidt design gives wide field of view (8o)

• Photometric samples taken every 2.5 seconds– Co-added into 15 minute bins to give very high

precision photometry

“Straw man” design based upon Kepler

• Occultation mission similar, but:– Add small angle prism to corrector lens to give

modest spectral dispersion– Sample frequently (nominally 30 Hz)– Lower S/N ~ 10 is acceptable– Extremely high data rate – Multiple pointings along and near the invariable

plane

10:23:38

KEPLER Telescope Scale: 0.06Positions: 1-5

06-Aug-03

403.23 MM

Add small angle prism to corrector lens to give modest spectral dispersion

The focal plane and data path are very challenging:

• 50-100 million imaging pixels

• Each star spectrally dispersed over 5-10 pixels

• Sample at ~30 Hz

• Need substantial pre-processing on board

Need substantial pre-processing on board

Summary:

• Substantial growth potential beyond TAOS for ground-based occultation work

• Space-based occultation survey needed to address all the key questions:– Size spectrum in collision-eroded regime– Nature and distribution of objects beyond

the Kuiper Belt