There were 2 new TNO discoveries announced since the previous issue of Distant EKOs:
2007 PS45, 2008 CS190
and 4 new Centaur/SDO discoveries:
2008 FC76, 2004 VP112, 2005 UN524, 2008 CT190
Objects recently assigned numbers:
1993 FW = (181708)
1998 WT31 = (181855)
1999 CG119 = (181868)
1999 CO153 = (181871)
1999 CV118 = (181867)
1999 HW11 = (181874)
1999 RD215 = (181902)
2000 YC2 = (182223)
2000 YU1 = (182222)
2001 KU76 = (182294)
2001 QW297 = (182397)
2002 FU6 = (182926)
2002 GJ32 = (182934)
2002 GZ31 = (182933)
2003 TG58 = (183595)
2004 DJ64 = (183963)
2004 DJ71 = (183964)
2004 PB112 = (184212)
2005 EO302 = (184314)
Current number of TNOs: 1076 (including Pluto)
Current number of Centaurs/SDOs: 227
Current number of Neptune Trojans: 6
Out of a total of 1309 objects:
557 have measurements from only one opposition
536 of those have had no measurements for more than a year
281 of those have arcs shorter than 10 days
(for more details, see:
http://www.boulder.swri.edu/ekonews/objects/recov_stats.gif)
Eris is the largest dwarf planet currently known in the solar
system. Knowledge about its physical parameters is necessary to
interpret the characteristics of these kinds of bodies. The goal
of this work is to study Eris' short-term and long-term
variability in order to determine the amplitude of the lightcurve,
which can be linked to the degree of elongation of the body or to
the degree of albedo heterogeneity on the surface of the dwarf
planet. In addition, the rotation period can be determined. CCD
photometric observations of the trans Neptunian object Eris in R
band on 16 nights spanning two years were carried out using the
1.5m telescope at Sierra Nevada Observatory (OSN), the 2.5m Isaac
Newton Telescope (INT) telescope at the Roque de los Muchachos
Observatory, and the 2.2m Telescope at Calar Alto Observatory. The
time-series analysis leads to indications of a short-term
variability whose nature is not clear. It could be real or a
result of data-reduction artifacts, such as contamination by
close, faint-background stars. The most significant periodicities
are 14 h or its double, but other possibilities cannot be ruled
out, like a 32 h weaker peak in the periodogram. As for the
amplitude of the lightcurve, we get a peak-to-peak variability of
0.01
0.01 mag. The study of the long-term variability
indicates that a long rotation period cannot be rejected, but the
amplitude would be smaller than 0.06 mag. These results are
compatible with a nearly spherical body that has a homogeneous
surface.
Published in: Astronomy & Astrophysics, 479, 877, (2008 March)
For preprints, contact duffard@iaa.es
The Pluto-Charon system has complex photometric variations on all
time scales; due to rotational modulations of dark markings across
the surface, the changing orientation of the system as viewed from
Earth, occultations and eclipses between Pluto and Charon, as well
as the sublimation and condensation of frosts on the surface. The
earliest useable light curve for Pluto is from 1953-1955 when Pluto
was 35 AU from the Sun. Earlier data on Pluto has the potential
to reveal properties of the surface at a greater heliocentric
distance with nearly identical illumination and viewing geometry.
We are reporting on a new accurate photographic light curve of Pluto
for 1933-1934 when the heliocentric distance was 40 AU. We used 43
B-band and V-band images of Pluto on 32 plates taken on 15 nights
from 19 March 1933 to 10 March 1934. Most of these plates were
taken with the Mount Wilson 60-inch and 100-inch telescopes, but 7 of the
plates (now at the Harvard College Observatory) were taken with the
12-inch and 16-inch Metcalf doublets at Oak Ridge. The plates were measured
with an iris diaphragm photometer, which has an average one-sigma
photometric error on these plates of 0.08 mag as measured by the
repeatability of constant comparison stars. The modern B and V
magnitudes for the comparison stars were measured with the Lowell
Observatory Hall 1.1-m telescope. The magnitudes in the plate's
photographic system were converted to the Johnson B- and V-system
after correction with color terms, even though they are small in
size. We find that the average B-band mean opposition magnitude
of Pluto in 1933-1934 was 15.730.01, and we see a roughly
sinusoidal modulation on the rotational period (6.38 days) with a
peak-to-peak amplitude of 0.110.03 mag. With this, we show
that Pluto darkened by 5% from 1933-1934 to 1953-1955. This
darkening from 1933-1934 to 1953-1955 cannot be due to changing
viewing geometry (as both epochs had identical sub-Earth latitudes),
so our observations must record a real albedo change over the
southern hemisphere. The later darkening trend from 1954 to the
1980s has been explained by changing viewing geometry (as more of
the darker northern hemisphere comes into view). Thus, we now have
strong evidence for albedo changes on the surface of Pluto, and
these are most easily explained by the systematic sublimation of
frosts from the sunward pole that led to a drop in the mean surface
albedo.
To appear in: Icarus
For preprints, contact schaefer@lsu.edu
or on the web at
http://arxiv.org/abs/0805.2097
Nereid is a small irregular moon of Neptune that displays large-,
moderate-, and small-amplitude photometric variations on both fast
and slow time scales. The central mystery of Nereid is now to
explain the physical mechanism of these unique brightness changes
and why they change with time. To characterize Nereid's variability,
we have been using the SMARTS telescopes on Cerro Tololo for synoptic
monitoring from 1999 to 2006. We present a well-sampled photometric
time series of 493 magnitudes on 246 nights mostly in the V-band.
In combination with our earlier data (for 774 magnitudes over 362
nights), our 20-year data set is the most comprehensive for any
small icy body in our Solar System. Our yearly light curves show
that Nereid displays various types of behaviors: large amplitude
brightenings and fadings (1987 to 1990); moderate-amplitude variation
about the average phase curve (1993-1997, 2003, 2005), moderate-amplitude
variation and systematically brighter by roughly one-quarter magnitude
throughout the entire season (2004); and nearly constant light
curves superimposed on a surprisingly large-amplitude opposition
surge (1998, 1999, 2000, 2006). Other than in 2004, Nereid's
variations were closely centered around a constant phase curve that
is well fit with a Hapke model for the coherent backscattering
opposition surge mechanism with angular scale of 0.70.1
degrees. In our entire data set from 1987-2006, we find no significant
periodicity. We propose that the year-to-year changes in the
variability of Nereid are caused by forced precession (caused by
tidal forces from Neptune) on the spin axis of a nonspherical Nereid,
such that cross-sectional areas and average albedos change as viewed
from Earth.
To appear in: Icarus
For preprints, contact schaefer@lsu.edu
or on the web at
http://arxiv.org/abs/0804.2835
Chang and coworkers reported millisecond duration dips in the X-ray intensity of Sco X-1 and attributed them to occultations of the source by small trans-Neptunian objects (TNOs). We have found multiple lines of evidence that these dips are not astronomical in origin, but rather the result of high-energy charged particle events in the RXTE PCA detectors. Our analysis of the RXTE data indicates that at most 10% of the observed dips in Sco X-1 could be due to occultations by TNOs, and, furthermore, we find no positive or supporting evidence for any of them being due to TNOs. We therefore believe that it is a mistake to conclude that any TNOs have been detected via occultation of Sco X-1.
Published in: The Astrophysical Journal, 677, 1241 (2008 April)
Preprint available on the web at
http://arxiv.org/abs/0710.0837
Millisecond dips in the RXTE/PCA archival data of Sco X-1 taken from 1996 to 2002 were reported recently. Those dips were found to be most likely caused by instrumental dead time but may also contain some true astronomical events, which were interpreted as the occultation of X-rays from Sco X-1 by Trans-Neptunian Objects (TNO) of 100-m size. Here we report the results of search for millisecond dip events with the new RXTE/PCA data of Sco X-1 taken in year 2007. Adopting the same selection criteria as that in the previous study, we found only 3 dip events in 72-ks data, much fewer than the 107 events found in the 560-ks data taken from 1996 to 2002 reported earlier. The new data provides more detailed information of individual `very large events' (VLEs), which is not available in the old archival data. Although the number of VLEs does not obviously increase during the occurrence of dip events, all the 3 dip events are coincident in time with VLEs that have no flags set for any of the propane or the 6 main xenon anodes. It is a strong indication of instrumental effects. No significant dips which might be real occultation by 60-100 m TNOs were observed. With only 72-ks data, however, the previously proposed possibility that about 10% of the dip events might not be instrumental still cannot be strictly excluded. Using the absence of those anomalous VLEs as the criterion for identifying non-instrumental dip events, we found, at a lower confidence level, 4 dip events of duration 8-10 ms in the 72-ks data. Upper limits to the size distribution of TNOs at the small size end are suggested.
To appear in: Monthly Notices of the Royal Astronomical Society
For preprints, contact hkchang@phys.nthu.edu.tw
We describe a strategy for scheduling astrometric observations to
minimize the number required to determine the mutual orbits of
binary transneptunian systems. The method is illustrated by
application to Hubble Space Telescope observations of
(42355) Typhon-Echidna, revealing that Typhon and Echidna orbit one
another with a period of 18.971 0.006 days and a semimajor
axis of 1628 29 km, implying a system mass of (9.49 0.52)
x 1017 kg. The eccentricity of the orbit is
0.526 0.015. Combined with a radiometric size determined
from Spitzer Space Telescope data and the assumption that Typhon
and Echidna both have the same albedo, we estimate that their radii
are 76+14-16 and 42+8-9 km, respectively. These
numbers give an average bulk density of only 0.44
+0.440.17
g cm-3, consistent with very low bulk densities recently
reported for two other small transneptunian binaries.
To appear in: Icarus
Preprints available at
http://arxiv.org/abs/0804.2495
A substantial fraction of the Edgeworth-Kuiper belt objects are presently known to move in resonance with Neptune (the principal commensurabilities are 1/2, 3/5, 2/3, and 3/4). We have found that many of the distant (with orbital semimajor axes a > 50 AU) trans-Neptunian objects (TNOs) also execute resonant motions. Our investigation is based on symplectic integrations of the equations of motion for all multiple-opposition TNOs with a > 50 AU with allowance made for the uncertainties in their initial orbits. Librations near such commensurabilities with Neptune as 4/9, 3/7, 5/12, 2/5, 3/8, 4/27, and others have been found. The largest number of distant TNOs move near the 2/5 resonance with Neptune: 12 objects librate with a probability higher than 0.75. The multiplicity of objects moving in 2/5 resonance and the longterm stability of their librations suggest that this group of resonant objects was formed at early formation stages of the Solar system. For most of the other resonant objects, the librations are temporary. We also show the importance of asymmetric resonances in the large changes in TNO perihelion distances.
Published in: Astronomy Letters, 34, 271 (2008 April)
For preprints, contact kleo@susu.ac.ru
By numerically integrating the orbits of the giant planets and of
test particles for four billion years, we follow the evolution of
the location of the midplane of the Kuiper belt. The Classical
Kuiper belt conforms to a warped sheet that precesses with a 1.9 Myr
period. The present-day location of the Kuiper belt plane can be
computed using linear secular perturbation theory: the local normal
to the plane is given by the theory's forced inclination vector,
which is specific to every semi-major axis. The Kuiper belt plane
does not coincide with the invariable plane, but deviates from it
by up to a few degrees in stable zones. A Kuiper belt object keeps
its free inclination relative to the Kuiper belt plane nearly
constant, even while the plane departs from the trajectory predicted
by linear theory. The constancy of free inclination simply reflects
the undamped amplitude of free oscillation. Current observations
of Classical Kuiper belt objects are consistent with the plane being
warped by the giant planets alone, but the sample size will need
to increase by a few times before confirmation exceeds 3
in confidence. In principle, differences between the theoretically
expected plane and the observed plane could be used to infer as yet
unseen masses orbiting the Sun, but carrying out such a program
would be challenging.
To appear in: The Astronomical Journal
For preprints, contact echiang@astro.berkeley.edu
or on the web at http://arxiv.org/abs/0804.4687
Context: Small body (12929) 1999 TZ1 is listed by the Minor
Planet Center (MPC) as a Centaur. However, its location close to
the Lagrangian point L5 of Jupiter is typical of a Trojan object
with large inclination.
Aims: The aim of this work is to provide a global physical and dynamical characterization of this object and to reassess its classification.
Methods: We obtained multi-wavelength observations with IRTF (Hawaii), OSN and IRAM-30 m (Spain), and performed a dynamical simulation of the evolution of its orbital parameters.
Results: Visible photometry monitoring shows a rotation curve
with a period (if considered double-peaked) of 
h and
an absolute R magnitude
. Near-IR spectroscopy
indicates a featureless reflectance spectra, with a low spectral
slope of 
%/100 nm. Thermal observations at 250 GHz
provide a 4.5 detection with a flux of 
mJy.
The combination of the visible and millimeter datasets, assuming a
standard thermal model, leads to a geometric albedo
pv =
0.053+0.015-0.010 and a mean diameter of 51.55 km.
Conclusions: The low albedo and spectral slope measured are typical of Jupiter's Trojans, but cannot exclude a Centaur nature. However, the dynamical lifetime of the object was estimated to be longer than 1 Gy, which is unlikely for a Centaur and suggests that (12929) 1999 TZ1 is a Trojan asteroid.
Published in: Astronomy & Astrophysics, 483, 17 (2008 May)
For information, contact arielle.moullet@obspm.fr
We present the results of a survey for trans-neptunian objects
(TNOs) based on Subaru archival images, originally collected by
Sheppard et al. (2005) as part of a search for irregular satellites
of Uranus. The survey region covers 2.8 deg2, centered on
Uranus and observed near opposition on two adjacent nights. Our
survey reaches half its maximum detection efficiency at R=
.
The objects detected correspond to 82 TNOs, five Centaurs, and
five irregular satellites. We model the cumulative number of TNOs
brighter than a given apparent magnitude with both a single and
double power law. The best fit single power law, with one object
per square degree at magnitude R0=
22.6-0.4+0.3 and a
slope of 
=
0.51-0.6+0.5, is inconsistent with the
results of similar searches with shallower limiting magnitudes. The
best fit double power law, with a bright-end slope
=
0.7-0.1+0.2, a faint-end slope 
=
0.3-0.2+0.2, a differential number density at R=23
=
2.0-0.5+0.5 and a magnitude break in the slope
at Req=
24.3-0.1+0.8, is more likely than the single
power law by a Bayes factor of 
26. This is the first survey
with sufficient depth and areal coverage to identify the magnitude
at which the break occurs without relying on the results of other
surveys.
We estimate barycentric distances for the 73 objects that have 24 hr
arcs; only two have heliocentric distances as large as 50 AU.
We combine the distribution of observed distances with the size
distribution that corresponds to a double power law luminosity
function to set a tight constraint on the existence of a distant
TNO population. We can exclude such a population at 60 AU, with
95% confidence, assuming it has the same size distribution and
albedo as the observed TNOs, if it exceeds 8% of mass of the
observed TNOs.
To appear in: The Astronomical Journal
For preprints, contact cfuentes@cfa.harvard.edu
or on the web at http://arxiv.org/abs/0804.3392
Ejecta Exchange, Color Evolution in the Pluto System,
and Implications for KBOs and Asteroids with Satellites
S. Alan Stern1
1 Visiting Scientist, Lunar and Planetary Laboratory, Houston, TX
Submitted to: Icarus
For preprints, contact alan@boulder.swri.edu
The Youthful Appearance of the 2003 EL61 Collisional Family
David L. Rabinowitz1, Bradley E. Schaefer2, Martha W. Schaefer3,
and
Suzanne W. Tourtellotte4
1 Center for Astronomy and Astrophysics, Yale University,
P.O. Box 208121, New Haven CT 06520-8121, USA
2 Department of Physics & Astronomy, Louisiana State University,
243 Nicholson, Baton Rouge LA 70803-0001, USA
3 Department of Geology & Geophysics, Louisiana State
University, 341 Howe-Russell, Baton Rouge LA 70803, USA
4 Astronomy Department, Yale University, P. O. Box 208121,
New Haven CT 06520-8121, USA
Submitted to: The Astronomical Journal
For preprints, contact david.rabinowitz@yale.edu
or on the web at
http://arxiv.org/abs/0804.2864
Scientists and educators will convene in Maryland this summer to explore a basic, but controversial, question: What is a planet?
The Great Planet Debate (GPD) conference includes two days (August 14-15) of scientific sessions to discuss and debate the processes leading to planet formation and the characteristics and criteria used to define and categorize planets. An open-to-the-public debate between Dr. Mark Sykes of the Planetary Science Institute and Dr. Neil deGrasse Tyson of the American Museum of Natural History is scheduled on the afternoon of August 14th.
During the first two days of the conference, speakers will present what we have learned about planetary bodies over more than 40 years of robotic exploration of the Solar System and what we are learning about planets around other stars. The IAU's dynamical definition of a planet will be presented, as well as an alternative geophysical definition. The utility of each will be debated, along with other potential planet definitions.
The invited speakers are leading researchers in the field of planetary
system formation and evolution. The schedule of talks can be found
at: http://gpd.jhuapl.edu/schedule/
The third day of the meeting will be an Educator Workshop to discuss how the question of "The Great Planet Debate" should be treated in schools and how that can be used as a springboard to discuss science as a process, as well as other topics in planetary science.
Deadline for Abstracts and Early Registration: June 27, 2008
To register go to: http://gpd.jhuapl.edu/
Meeting Organizers: Mark Sykes, Hal Weaver, and Keith Noll
We accept submissions for the following sections:
Distant EKOs is not a refereed publication, but is a tool for furthering communication among people interested in Kuiper belt research. Publication or listing of an article in the Newsletter or the web page does not constitute an endorsement of the article's results or imply validity of its contents. When referencing an article, please reference the original source; Distant EKOs is not a substitute for peer-reviewed journals.
