chasing shadows with TAOS: TAIWANESE AMERICAN OCCULTATION SURVEY

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chasing shadows with TAOSTAIWANESE AMERICAN
OCCULTATION SURVEY

• federica bianco, SAO - UPenn

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the TAOS collaboration
M. Lehner (CfA, UPenn) H. Liang (NCU) J.
Lissauer (NASA Ames) S.L. Marshall (SLAC) T.
Nihei (UPenn, CfA) I. de Pater (UC Berkeley) R.
Porrata (UC Berkeley) P. Protopapas (CfA) J. Rice
(UC Berkeley) M. Schwamb (UPenn) A. Wang
(ASIAA) S.-Y. Wang (ASIAA) C.-Y. Wen
(ASIAA) Z.-W. Zhang (NCU)
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an outer solar system blind occultation survey
TAOS aims to constrain the statistical
characteristics of the low size end of the Kuiper
belt
the only method to probe beyond direct
observational limits is occultations
(current observational limit R28.8 -gt d10km
with a0.04)
Bernstein et al. 2004
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chasing shadows an occultation survey
observing the flux variation of a background star
due to the transit of a KBO along the line of
sight the transit generates a diffraction pattern
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project descriptionstatusfuture
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project descriptionstatusfuture
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? fast zippermode photometry
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zippermode readout
rowblock
2048 x 2052 ccd cameras operating _at_ 5Hz with
zippermode readout
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zippermode readout

• it does get crowded!
• sky is added at every
• exposure
• (x27 for 76 row rbs)

2048 x 2052 ccd cameras operating _at_ 5Hz with
zippermode readout
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? fast zippermode photometry
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TAOS telescopes

• 4 telescopes
• 50cm aperture
• f/1.9
• 3 deg2 field

Lulin Observatory 2862m (9890 feet) Lulin
mountain Yu-Shan National Park, Taiwan
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current status of the TAOS system

• 3 operating telescopes, the 4th to come at the
  end of the summer
• automated operation mode completed
• a posteriori aperture photometry

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1 year data with 2-3 operating telescopes
we are analyzing the data collected between
02/07/05 and 02/15/06

• duty cycle 5 (13 of dark time)
• 99 TAOS fields observed
• 415 runs
• 348.9124 collection hours
• 5,315,232 rowblocks
• 6.6 Tb raw image data
• 105,000 star hours

No occultations yet, which is consistent with
most theoretical models
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observed occultation by asteroid Iclea

• Iclea
• diameter 97 km
• a 0.057
• pm 10.77/day
• D 2.34AU
• Mv 14mag
• Star
• Mv 11.83

02 february 2006
animation prepared by Andrew Wang
Zhi-Wei Zhang
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real time analysis

• real time PSF fitting photometry
• better S/N (we can follow more stars)
• allows follow up of occultations
• real time efficiency
• provides immediate completeness result

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frame transfer camerason their way
sky x27 sample _at_5Hz 50 duty cycle streaks
sky x4 sample _at_8Hz 100 duty cycle no
streaks
2k
2k
2k
1k
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frame transfer camerason their way
sky x27 sample _at_5Hz 50 duty cycle streaks
sky x4 sample _at_8Hz 100 duty cycle no
streaks
2k
2k
2k
1k
¼ reduction of the area overall improvement by a
factor 5-6 in S/N allows us to choose more
crowded fields
number of stars x3
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move to new site

• looking for a drier site

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move to new site

• looking for a drier site

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event rate
the formation process is reflected in the size
distribution most models are similar at dgt10km
but differ substantially at dlt10km where direct
observations are currently unfeasible
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projected event rate
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• thank you!

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event rate what should TAOS expect to see?
the formation process is reflected in the size
distribution
number and size distribution of KBOs is predicted
from theory (and confirmed by observations) Ngtdd-
q, q 3.5 -gt dgt100km
Qb
bb
power has to break at dgt1km (Olbers paradox,
Kenyon and Windhorst, 2000)
evidence for deviation from power q 3.5 at
dgt30km (Bernstain et al. 2004)
bg
Qg
Kenyon Bromley 2004
the shape of the theoretical distribution depends
upon disruptive energy, neptune stirring and
binding energy (tensile - Qbrbb erg g-1 and
gravitational Qgrbg erg g-1 )
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efficiency simulator
a 42AU
a0v 12 mag star
3.0km KBO
b 0.0km
finite exposure
point source
finite sampling
finite source
no simulated sky background noise needs to be
added
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efficiency simulator
a 42AU
b 0.0
3.0km KBO
varying magnitude
varying magnitude
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efficiency simulator
b 0.0
a0v 12 mag star
3.0km KBO
varying a
varying a
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efficiency simulator
b 0.0
a0v 12 mag star
10.0km KBO
varying a
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efficiency simulator
a 42AU
b 0.0
a0v 12 mag star
varying d
varying d
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efficiency simulator
a 42AU
3.0km KBO
a0v 12 mag star
varying b
varying b
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efficiency simulator
a 42AU
a0v 12 mag star
3.0km KBO
varying offset
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KBO space distribution