J/AJ/151/164 Properties of asteroids in Karin cluster (Carruba+, 2016)
Detection of the YORP effect for small asteroids in the Karin cluster.
Carruba V., Nesvorny D., Vokrouhlicky D.
<Astron. J., 151, 164-164 (2016)>
=2016AJ....151..164C 2016AJ....151..164C (SIMBAD/NED BibCode)
ADC_Keywords: Minor planets
Keywords: celestial mechanics - minor planets, asteroids: general -
minor planets, asteroids: individual: Karin
Abstract:
The Karin cluster is a young asteroid family thought to have formed
only ∼5.75Myr ago. The young age can be demonstrated by numerically
integrating the orbits of Karin cluster members backward in time and
showing the convergence of the perihelion and nodal longitudes (as
well as other orbital elements). Previous work has pointed out that
the convergence is not ideal if the backward integration only accounts
for the gravitational perturbations from the solar system planets. It
improves when the thermal radiation force known as the Yarkovsky
effect is accounted for. This argument can be used to estimate the
spin obliquities of the Karin cluster members. Here we take advantage
of the fast growing membership of the Karin cluster and show that the
obliquity distribution of diameter D∼1-2km Karin asteroids is bimodal,
as expected if the YORP effect acted to move obliquities toward
extreme values (0° or 180°). The measured magnitude of the
effect is consistent with the standard YORP model. The surface thermal
conductivity is inferred to be 0.07-0.2W/m/K (thermal inertia
∼300--500J/m2/K/s1/2). We find that the strength of the YORP
effect is roughly ∼0.7 of the nominal strength obtained for a
collection of random Gaussian spheroids. These results are consistent
with a surface composed of rough, rocky regolith. The obliquity values
predicted here for 480 members of the Karin cluster can be validated
by the light-curve inversion method.
Description:
Many new asteroids have been discovered since the last dynamical
analysis of the Karin cluster. Here we repeat the analysis of Nesvorny
& Bottke (2004Icar..170..324N 2004Icar..170..324N) with an orbital catalog that contains
nearly seven times more asteroids than there were available back in
2004. We revise the Karin family membership by applying the usual
clustering method on the new orbital catalog. The taxonomical and
albedo interlopers are eliminated. We then apply a more stringent
criterion of the Karin family membership by requiring that orbits
converged with each other ∼5.75Myr ago. In Table1, we report the list
of 480 identified Karin cluster members.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table1.dat 67 480 Karin cluster members: absolute magnitudes,
proper elements and frequencies, Lyapunov
exponents, and estimated mean obliquities and
Yarkovsky drift speed
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See also:
B/astorb : Orbits of Minor Planets (Bowell+ 2014)
J/MNRAS/433/2075 : Asteroid families identification (Carruba+, 2013)
Byte-by-byte Description of file: table1.dat
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Bytes Format Units Label Explanations
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1- 6 I6 --- Number [832/389186] Karin cluster number
8- 12 F5.2 mag H [11.18/17.42] Asteroid absolute H magnitude
14- 20 F7.5 AU a [2.8/2.9] Asteroid proper semi-major axis
(ap)
22- 28 F7.5 --- e [0.041/0.049] Asteroid proper eccentricity
(ep)
30- 36 F7.5 --- sin(i) [0.035/0.039] Sine of asteroid proper
inclination (sin ip)
38- 43 F6.3 arcsec/yr g [70.1/71.5] Asteroid proper frequency of
precession of the pericenter (gp)
45- 51 F7.3 arcsec/yr s [-66/-64.7] Asteroid proper frequency of
precession of the node (sp)
53- 56 F4.2 10-6/yr Ly [0/7.72] Asteroid Lyapunov exponent (LCE) (1)
58- 60 I3 deg eps [0/180]? Estimated mean obliquity ε (2)
62- 67 F6.2 10-5AU/Myr Drift [-14.7/13.2]? Estimated mean Yarkovsky drift
speed
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Note (1): Lyapunov exponents with values near to 1.5*10-6/yr correspond to
objects for which the integration time was not long enough to obtain a
convergence.
Note (2): The obliquity values listed in this table are historical mean
obliquities and may not exactly coincide with the current values. Figure13
in text shows the correspondence between the historical obliquity values
given in Table1 and our estimate of the present obliquities.
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History:
From electronic version of the journal
(End) Prepared by [AAS]; Sylvain Guehenneux [CDS] 19-Jul-2016