1. The Census of Binary TNOs
Keith Noll
Catania
4 July 2006

2. 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

3. nB ≥ 34

4. Inventory

5. Binary Search Programs
Program n* nB instrument limits
DES Various / ?
S+B Palomar ~1 / ?
NICMOS 0.08†/ 22(H)
STIS ~0.10¡ /
WPFC /
STIS ~0.10¡ /
NICMOS 0.08†/ 23.5(H)
HRC / 27.5(v)
HRC /
? HRC /
HRC / ‡
~50 TBD HRC / 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

6. Currently known TNO and Centaur multiples
TOTAL systems 34
Groundbased 8
HST 26

11. Lies, Damn Lies, and …

12. …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

13. Relative sizes of known secondaries
Bias or reality?
number
Delta magnitude

14. Magnitude difference of binaries found in ACS survey of 61 TNOs and Centaurs (Vmed = 22.7)

15. Binary Size Ratio
Surveys are magnitude limited (approximately)
ACS/HRC images in 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

16. 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)

17. Are these the right classes?
Caveats
Are these the right classes?
Are objects correctly assigned to classes?
Are there missing/as yet unrecognized classes?

18. 10514 (HRC)
Class n nB % C
R <10 S X ¢ H

19. 10514 (HRC) /7858 (NICMOS)
Class n nB % C
R < 6 S X ¢ H

20. 10514 (HRC) /7858 (NICMOS)
Class n nB % C
R < 6
SX¢ H

21. 10514 (HRC) /7858 (NICMOS)
Class n nB % C
SX¢ RH

22. 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.

23. Binaries as a function of HV (ACS+NICMOS)
number
< > 8
HV (mag)

24. Binaries as a function of HV (scattered)
number
≤ > 4
< > 8
HV (mag)

25. Magnitude difference vs. absolute mag for all. known TNO binaries (
Magnitude difference vs. absolute mag for all* known TNO binaries (*with published mags).

26. 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

27. 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

28. Special Cases

29. 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.

30. A Binary Centaur
Objects on giant-planet-crossing orbits have chaotic orbits.

31. Objects on CR46 like orbits have a good chance of surviving close encounters with giant planets.

32. Is 2003 QR91 really Hot??? HV = 6.2 a = 46.3 AU e = 0.18 i = 3.5°
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

33. Names Too many! QT297, QY297, CS29, CQ29, QC298,
CQ114, CM114, CM105, CF105
RZ253, RZ143…

34. Names for (58534) 1997 CQ29
Logos
Zoe

35. Synthesis

36. 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

37. 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.