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The Census of Binary TNOs. Keith Noll Catania 4 July 2006. The Census of Binary TNOs. Will Grundy, Hal Levison, Denise Stephens, Marc Buie, Jim Elliot, Ian Griffin, Susan Kern, David Osip, Scott Sheppard, John Spencer, John Stansberry. Illustration credit: G. Bacon, STScI. n B ≥ 34.

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the census of binary tnos

The Census of Binary TNOs

Keith Noll

Catania

4 July 2006

the census of binary tnos1

The Census of Binary TNOs

Will Grundy, Hal Levison, Denise Stephens,

Marc Buie, Jim Elliot, Ian Griffin, Susan Kern, David Osip, Scott Sheppard, John Spencer, John Stansberry

Illustration credit: G. Bacon, STScI

slide5

Binary Search Programs

Program n* nB instrument limits

DES 485 2 Various .3-2 / ?

S+B 150 0 Palomar ~1 / ?

7858 4 0 NICMOS 0.08†/ 22(H)

8258 2 0 STIS ~0.10¡ /

9060 78 3 WPFC2 0.2 /

9110 25 2 STIS ~0.10¡ /

9386 77 9 NICMOS 0.08†/ 23.5(H)

10514 61 10 HRC 0.05 / 27.5(v)

10545 19 2 HRC 0.05 /

10555 4 ? HRC 0.05 /

10781 1 0 HRC 0.05 / ‡

10800 ~50 TBD HRC 0.05 / 27.5(v)

* Number of previously unknown binaries observed

† Detection limit with PSF fitting

¡ Perpendicular to direction of target drift only

‡ Images not dithered, hot pixels not removeable

slide6

Currently known TNO and Centaur multiples

TOTAL systems 34

Groundbased 8

HST 26

slide12

…Statistics!

Intrinsic:

Binary fraction as function of dynamical class

Binary fraction as function of primary diameter, rp

Diameter ratio of binaries, rs/rp

Binary fraction as function of a/rp

Observational:

Binary fraction as function of resolution

slide13

Relative sizes of known secondaries

Bias or reality?

number

0 - 1 1 - 2 2 -3 3 - 4 4 - 5 5 - 6 6 - 7 7 - 8 8 - 9

Delta magnitude

slide15

Binary Size Ratio

  • Surveys are magnitude limited (approximately)
  • ACS/HRC images in 10514 probe to 27.5 mag
  • For most objects Dmag ≥ 4 mag
  • Underabundance of asymmetric binaries appears to be real
  • Consistent with Astakhov et al. (2005) formation model
  • Shallower surveys (e.g. NICMOS) will miss only a few asymmetric systems
slide16

DES dynamical classification+

R = Resonant: order ≤ 4; 6:5 (34AU) to 5:1 (88AU)

Non Resonant:

C = Cold Classical T>3, e<0.2, i<5°

H = Hot Classical T>3, e<0.2, i ≥ 5°

S = Scattered Near T<3

X = Scattered Extended T>3, e>0.2

¢ = Centaur q<aN

D = Detached ?

________

Note: T = aN/a + 2cos iKN √a/aN (1-e2)

slide17

Caveats

  • Are these the right classes?
  • Are objects correctly assigned to classes?
  • Are there missing/as yet unrecognized classes?
slide18

10514 (HRC)

Class n nB %

C 15 5 33 +14-10

R 16 0 <10

S 2 1 50 +25-25

X 5 1 20 +25-8

¢ 12 2 17 +15-6

H 11 1 9 +16-3

slide19

10514 (HRC) + 9386/7858 (NICMOS)

Class n nB %

C 43 11 26 +7-6

R 33 0 < 6

S 23 2 9 +9-4

X 10 3 30 +17-11

¢ 13 2 15 +15-5

H 20 1 5 +10-2

slide20

10514 (HRC) + 9386/7858 (NICMOS)

Class n nB %

C 43 11 26 +7-6

R 33 0 < 6

SX¢ 46 7 15 +7-4

H 20 1 5 +10-2

slide21

10514 (HRC) + 9386/7858 (NICMOS)

Class n nB %

C 43 11 26 +7-6

SX¢ 46 7 15 +7-4

RH 53 1 2 +4-1

slide22

Binaries as a function of class

Despite new data sets, quantity of data falls short of what is needed to obtain robust statistics for all dynamical classes

Cold classicals remain the most abundant, well constrained population with ~25% binaries at 0.08 arcsec

Resonant and Hot populations have very low fraction of binaries, significantly different than the cold classical population

Scattered (near and extended) and Centaurs appear to be intermediate, but data are lacking.

slide23

Binaries as a function of HV (ACS+NICMOS)

number

< 4 4.1 -- 6 6.1 -- 7 7.1 -- 8 > 8

HV (mag)

slide24

Binaries as a function of HV (scattered)

number

≤ 4 > 4

< 3 3.1 -- 4 4.1 -- 5 5.1 -- 6 6.1 -- 7 7.1 -- 8 > 8

HV (mag)

slide26

Binaries as a function of size

  • More binaries around large objects?
    • difficult to prove with statistics because:
      • different underlying rates of binarity in dynamical classes
      • poor statistics
  • Few binaries around small objects?
    • same problems as above
  • Possibly stronger case when coupled with relative size to primary --> supports collision hypothesis
slide27

Completeness correction

Requires knowledge of distribution of orbital parameters (a, e) as a function of dynamical class, HV, etc.

Can be estimated by number of repeat observation discoveries: 0 of 3 classicals observed in 9110 were found to be binary with STIS; 2 were later identified as binaries with NICMOS.

--> Significant incompleteness is likely even at 0.05 arcsec

slide29

A Binary Centaur:

Survival

42355 (2002 CR46) is the first binary Centaur to be detected. It is on an unstable giant-planet-crossing orbit with a mean lifetime of 107 years.

slide30

A Binary Centaur

Objects on giant-planet-crossing orbits have chaotic orbits.

slide32

Is 2003 QR91 really Hot???

HV = 6.2

a = 46.3 AU

e = 0.18

i = 3.5°

<i> = 5.01° $@^&%^*#!

C = Cold Classical T>3, e<0.2, i<5°

H = Hot Classical T>3, e<0.2, i ≥ 5°

S = Scattered Near T<3

X = Scattered Extended T>3, e>0.2

slide33

Names

Too many!

QT297, QY297,

CS29, CQ29, QC298,

CQ114, CM114, CM105, CF105

RZ253, RZ143…

slide36

Binaries: An Historical Fiction

  • Accretion in protoplanetary disk
    • Very high fraction of binaries and multiples formed through capture and collisions; fraction may vary in disk with radius
    • Low collision speeds in dynamically cold disk
  • Giant planet embryos form
    • Accretion of small bodies stops, collisions become erosive
    • Dynamical stirring of disk increases mean encounter speeds
    • Binaries destroyed through collision and disruptive close approaches
    • Scattered disk forms from cold classical belt, some binaries disrupted
  • Giant planet migration
    • Loss of 99% remaining disk mass
    • Rearrangement of populations results in capture of Resonant and Hot populations
  • Last 4 Gyr
    • No additional dynamical captures, possible formation of binaries through collision
    • Continual evolution of Centaur population
    • Tidal/collisional disruption of weakly bound binaries
slide37

Conclusions

Asymmetric binaries are rare.

2. a. Cold classicals have high fraction of binaries.

b. Resonant and Hot populations have very low fraction of binaries.

c. Scattered and Centaurs are intermediate, but too few to distinguish between subgroups.

3. No correlation with HV when sorted by dynamical class because of poor statistics. Better case when coupled with primary-secondary size difference.