Distant EKOs, Issue #67  (December 2009)


News & Announcements
Abstracts of 9 Accepted Papers
Titles of 2 Submitted Papers
Titles of 1 Other Paper of Interest
Titles of 2 Conference Contribution
Newsletter Information


IAUC 9050 announced that the IAU Committee on Small Bodies Nomenclature has approved the name for Quaoar's satellite: ``Weywot''. The name was chosen by the Native American Tongva tribe. The name Quaoar is the Tongva god of creation, and as mentioned in MPC 67220, ``Weywot is the god of the sky in Tongva Mythology. Weywot was created by Quaoar when he sang the song of creation.''

There were 3 new TNO discoveries announced since the previous issue of Distant EKOs:

2008 AP129, 2008 QB43, 2009 YE7

and 5 new Centaur/SDO discoveries:

2005 VD, 2009 HW77, 2008 ST291, 2009 YF7, 2009 YD7

Objects recently assigned numbers:

2007 OR10 = (225088)

Current number of TNOs: 1100 (including Pluto)
Current number of Centaurs/SDOs: 253
Current number of Neptune Trojans: 6

Out of a total of 1359 objects:
   551 have measurements from only one opposition
     539 of those have had no measurements for more than a year
       290 of those have arcs shorter than 10 days
(for more details, see: http://www.boulder.swri.edu/ekonews/objects/recov_stats.jpg)


A Single Sub-kilometre Kuiper Belt Object from a Stellar Occultation in Archival Data
H.E. Schlichting1,2, E.O. Ofek2, M. Wenz3, R. Sari1,4, A. Gal-Yam5, M. Livio6, E. Nelan6, and S. Zucker7

1 California Institute of Technology
2 CITA, University of Toronto
3 Goddard Space Flight Center
4 Hebrew University
5 Weizmann Institute of Science
6 Space Telescope Science Institute
7 Tel Aviv University

The Kuiper belt is a remnant of the primordial Solar System. Measurements of its size distribution constrain its accretion and collisional history, and the importance of material strength of Kuiper belt objects (KBOs). Small, sub-km sized, KBOs elude direct detection, but the signature of their occultations of background stars should be detectable. Observations at both optical and X-ray wavelengths claim to have detected such occultations, but their implied KBO abundances are inconsistent with each other and far exceed theoretical expectations. Here, we report an analysis of archival data that reveals an occultation by a body with a 500 m radius at a distance of 45 AU. The probability of this event to occur due to random statistical fluctuations within our data set is about 2%. Our survey yields a surface density of KBOs with radii larger than 250 m of 2.1+4.8-1.7 x 107 deg-2, ruling out inferred surface densities from previous claimed detections by more than 5 sigma. The fact that we detected only one event, firmly shows a deficit of sub-km sized KBOs compared to a population extrapolated from objects with r>50 km. This implies that sub-km sized KBOs are undergoing collisional erosion, just like debris disks observed around other stars.

Published in: Nature, 462, 895 (2009 December 17)

For preprints, contact hilke.schlichting@gmail.com
or on the web at http://arxiv.org/abs/0912.2996
and http://www.nature.com/nature/journal/v462/n7275/full/nature08608.html

Diffractive Microlensing - I. Flickering Planetesimals at the Edge of the Solar System
Jeremy Heyl1

1 Department of Physics and Astronomy, University of British Columbia, Vancouver, British Columbia V6T 1Z1, Canada

Microlensing and occultation are generally studied in the geometric optics limit. However, diffraction may be important when recently discovered Kuiper Belt objects (KBOs) occult distant stars. In particular, the effects of diffraction become more important as the wavelength of the observation and the distance to the KBO increase. For sufficiently distant and massive KBOs or Oort cloud objects not only is diffraction important but so is gravitational lensing. For an object similar to Eris but located in the Oort cloud, the signature of gravitational lensing would be detected easily during an occultation and would give constraints on the mass and radius of the object.

To appear in: Monthly Notices of the Royal Astronomical Society

For preprints, contact heyl@phas.ubc.ca
or on the web at http://arxiv.org/abs/0910.3922

Upper Limits on the Number of Small Bodies in Sedna-Like Orbits by the TAOS Project
J.H. Wang1,2, M.J. Lehner1,3,4, Z.W. Zhang2, F.B. Bianco3,4, C. Alcock4, W.P. Chen2, T. Axelrod5, Y.I. Byun6, N.K. Coehlo7, K.H. Cook8, R. Dave4, I. de Pater9, R. Porrata9, D.W. Kim6, S.K. King1, T.Lee1, H.C. Lin2, J.J. Lissauer10, S.L. Marshall8,11, P. Protopapas4, J.A. Rice7, M.E. Schwamb12, S.Y. Wang1, and C.Y. Wen1

1 Institute of Astronomy and Astrophysics, Academia Sinica. P.O. Box 23-141, Taipei 106, Taiwan
2 Institute of Astronomy, National Central University, No. 300, Jhongda Rd, Jhongli City, Taoyuan County 320, Taiwan
3 Department of Physics and Astronomy, University of Pennsylvania, 209 South 33rd Street, Philadelphia, PA 19104, USA
4 Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138, USA
5 Steward Observatory, 933 North Cherry Avenue, Room N204, Tucson AZ 85721, USA
6 Department of Astronomy, Yonsei University, 134 Shinchon, Seoul 120-749, Korea
7 Department of Statistics, University of California Berkeley, 367 Evans Hall, Berkeley, CA 94720, USA
8 Institute for Geophysics and Planetary Physics, Lawrence Livermore National Laboratory, Livermore, CA 94550, USA
9 Department of Astronomy, University of California Berkeley, 601 Campbell Hall, Berkeley CA 94720, USA
10 Space Science and Astrobiology Division 245-3, NASA Ames Research Center, Moffett Field, CA, 94035, USA
11 Kavli Institute for Particle Astrophysics and Cosmology, 2575 Sand Hill Road, MS 29, Menlo Park, CA 94025, USA
12 Division of Geological and Planetary Sciences, California Institute of Technology, 1201 E. California Blvd., Pasadena, CA 91125, USA

We present the results of a search for occultation events by objects at distances between 100 and 1000 AU in lightcurves from the Taiwanese-American Occultation Survey (TAOS). We searched for consecutive, shallow flux reductions in the stellar lightcurves obtained by our survey between 7 February 2005 and 31 December 2006 with a total of $\sim4.5\times10^{9}$ three-telescope simultaneous photometric measurements. No events were detected, allowing us to set upper limits on the number density as a function of size and distance of objects in Sedna-like orbits, using simple models.

Published in: Astronomical Journal, 138, 1893 (2009 December)

Preprint available on the web at http://arxiv.org/abs/0910.5282

Rotations and Densities of Trans-Neptunian Objects
D. Perna1,2,3, E. Dotto3, M.A. Barucci1, A. Rossi4, S. Fornasier1,5, and C. de Bergh1

1 LESIA, Observatoire de Paris, 5 Place Jules Janssen, 92195 Meudon Principal Cedex, France
2 Università di Roma Tor Vergata, Dipartimento di Fisica, Via della Ricerca Scientifica 1, 00133 Roma, Italy
3 INAF-Osservatorio Astronomico di Roma, Via di Frascati 33, 00040 Monte Porzio Catone, Italy
4 ISTI-CNR, Via G. Moruzzi 1, 56124 Pisa, Italy
5 Université Paris Diderot - Paris 7, France

Context. Trans-Neptunian objects (TNOs) represent a new frontier in the study of our Solar System. In particular, the investigation of their rotational properties can provide important hints about their internal structure and collisional evolution.

Aims. We expand the limited sample of TNOs with known rotation rates, and improve the knowledge of the physical nature of these bodies.

Methods. We carried out photometric observations of 5 TNOs -- (144897) 2004 UX10, (145451) 2005 RM43, (145453) 2005 RR43, 2003 UZ117, and 2003 UZ413 -- using the New Technology Telescope of the European Southern Observatory.

Results. We determined the spin rates of four targets, while only an estimation of the period was possible for 2003 UZ117.

Conclusions. From the computed rotational periods and the obtained light curve amplitudes of four TNOs, we derived the lower limit to their axis ratio a/b, and hence estimated their density. Combining our new results with literature data, we investigated the density statistics of the small bodies of the outer Solar System.

Published in: Astronomy and Astrophysics, 508, 451 (2009 December)

(47171) 1999 TC36, A Transneptunian Triple
S.D. Benecchi1, K.S. Noll1, W.M. Grundy2, and H.F. Levison3

1 Space Telescope Science Institute, 3700 San Martin Dr., Baltimore, MD 21218, USA
2 Lowell Observatory, 1400 W. Mars Hill Rd., Flagstaff, AZ 86001, USA
3 Dept. of Space Studies, Southwest Research Institute, 1050 Walnut St. #400, Boulder, CO 80302, USA

We present new analysis of HST images of (47171) 1999 TC36 that confirm it as a triple system. Fits to the point-spread function consistently show that the apparent primary is itself composed of two similar-sized components. The two central components, A1 and A2, can be consistently identified in each of nine epochs spread over seven years of time. In each instance the component separation, ranging from $0.023\pm0.002$ to $0.031\pm0.003$ arcsec, is roughly one half of the Hubble Space Telescope’s diffraction limit at 606 nm. The orbit of the central pair has a semi-major axis of $a\sim867$ km with a period of $P\sim1.9$ days. These orbital parameters yield a system mass that is consistent with $M_{sys} = 12.75\pm0.06$ 1018 kg derived from the orbit of the more distant secondary, component B. The diameters of the three components are dA1= 286+45-38 km, dA2= 265+41-35 km and dB= 139+22-18 km. The relative sizes of these components are more similar than in any other known multiple in the solar system. Taken together, the diameters and system mass yield a bulk density of $\rho= 542^{+317}_{-211} $ kg m-3. HST Photometry shows that component B is variable with an amplitude of $\ge0.17\pm0.05$ magnitudes. Components A1 and A2 do not show variability larger than $0.08\pm0.03$ magnitudes approximately consistent with the orientation of the mutual orbit plane and tidally-distorted equilibrium shapes. The system has high specific angular momentum of $J/J^{\prime}=0.93$, comparable to most of the known Transneptunian binaries.

To appear in: Icarus

Preprints available on the web at http://arxiv.org/abs/0912.2074

The Trans-Neptunian Object (42355) Typhon:
Composition and Dynamical Evolution
A. Alvarez-Candal1,2, M.A Barucci1, F. Merlin3, C. de Bergh1, S. Fornasier1, A. Guilbert1, and S. Protopapa4

1 LESIA/Observatoire de Paris, 5, Place Jules Janssen, 92195, Meudon Cedex, France
2 European Southern Observatory, Alonso de Córdova 3107, Vitacura Casilla 19001, Santiago 19, Chile
3 Department of Astronomy, University of Maryland, College Park, MD 20742, USA
4 Max-Planck Institute for Solar System Research, Max-Planck-Str. 2, 37191 Katlenburg-Lindau, Germany

Context. The scattered disk object (42355) Typhon showed interesting features in visible and near-infrared spectra. In particular, the visible spectra shows evidence for aqueously altered materials.

Aims. This article presents a possible origin for absorption features on the surface of (42355) Typhon due to an episode of aqueous alteration, and seeks to understand this event in the context of its dynamical evolution.

Methods. We observed (42355) Typhon at the ESO / Very Large Telescope using FORS2 and ISAAC on telescope unit 1, and SINFONI on telescope unit 4. We compare these data with those previously published, in order to confirm features found in the visible and near infrared spectra, and to study possible surface heterogeneities. We interpret the surface composition using the Hapke radiative transfer model on the whole available spectral range $\sim 0.5-2.4~\mu$m.

To complete the portrait of (42355) Typhon, we followed its dynamical evolution using the code EVORB v.13 for 20 Myr.

Results. We confirm the detection of a subtle absorption feature in the visible at $\sim 0.6$ $\mu$m, which we interpret as due to water-altered silicates. In the near infrared we confirm the presence of water ice, by the 2.0 $\mu$m absorption feature. The best fit models to our data point the presence of water ice.

Conclusions. (42355) Typhon is too small to have suffered water alteration, but this event could happen in a larger parent body from which (42355) Typhon is a remnant after a catastrophic disruption.

To appear in: Astronomy & Astrophysics

For preprints, contact aalvarez@eso.org

Neptune Trojans and Plutinos:
Colors, Sizes, Dynamics, and their Possible Collisions
A.J.C. Almeida1,2, N. Peixinho3,4, and A.C.M. Correia1,5

1 Departamento de Física, Universidade de Aveiro, Campus de Santiago, 3810-193 Aveiro, Portugal
2 Instituto de Telecomunicações, IT - Aveiro, Campus de Santiago, 3810-193 Aveiro, Portugal
3 Center for Computational Physics, University of Coimbra, Portugal
4 Astronomical Observatory of the University of Coimbra, Portugal
5 Astronomie et Systèmes Dynamiques, IMCCE-CNRS UMR8028, 77 Av. Denfert-Rochereau, 75014 Paris, France

Neptune Trojans and Plutinos are two sub-populations of Trans-Neptunian Objects located in the 1:1 and the 3:2 mean motion resonances with Neptune, respectively, and therefore protected from close encounters with the planet. However, the orbits of these two kinds of objects may cross very often, allowing a higher collisional rate between them than with other kinds of Trans-Neptunian Objects and a consequent and size distribution alteration of the two sub-populations.

Observational colors and absolute magnitudes of Neptune Trojans and Plutinos show that: i) there are no intrinsically bright (large) Plutinos at small inclinations; ii) there is an apparent excess of blue and intrinsically faint (small) Plutinos; and iii) Neptune Trojans possess the same blue colors as Plutinos within the same (estimated) size range do.

For the present sub-populations we analyze the most favorable conditions for close encounters / collisions to occur and address if there could be a link between those encounters and the sizes and/or colors of Plutinos and Neptune Trojans. We also perform a simultaneous numerical simulation of the outer Solar System over 1 Gyr for all these bodies in order to estimate their collisional rate.

We conclude that orbital overlap between Neptune Trojans and Plutinos is favored for Plutinos with high libration amplitudes, high eccentricities and low inclinations. Additionally, with the assumption that the collisions can be disruptive creating smaller objects not necessarily with similar colors, the present high concentration of small Plutinos at low inclinations can thus be a consequence of a collisional interaction with Neptune Trojans and such hypothesis should be further analyzed.

To appear in: Astronomy & Astrophysics

For preprints, contact correia@ua.pt
or on the web at http://arxiv.org/abs/0910.0865

Phase Curves of Nine Trojan Asteroids over a Wide Range of Phase Angles
M.W. Schaefer1, B.E. Schaefer2, D.L. Rabinowitz3, and S.W. Tourtellotte4

1 Geology and Geophysics and Physics and Astronomy, Louisiana State University, Baton Rouge, LA, USA
2 Physics and Astronomy, Louisiana State University, Baton Rouge, LA, USA
3 Center for Astronomy and Astrophysics, Yale University, New Haven, CT, USA
4 Department of Astronomy, Yale University, New Haven, CT, USA

We have observed well-sampled phase curves for nine Trojan asteroids in B-, V-, and I-bands. These were constructed from 778 magnitudes taken with the 1.3-m telescope on Cerro Tololo as operated by a service observer for the SMARTS consortium. Over our typical phase range of 0.2-10$^{\circ}$, we find our phase curves to be adequately described by a linear model, for slopes of 0.04-0.09 mag/$^{\circ}$ with average uncertainty less than 0.02 mag/$^{\circ}$. (The one exception, 51378 (2001 AT33), has a formally negative slope of -0.02$\pm$0.01 mag/$^{\circ}$.) These slopes are too steep for the opposition surge mechanism to be shadow hiding (SH), so we conclude that the dominant surge mechanism must be coherent backscattering (CB). In a detailed comparison of surface properties (including surge slope, B-R color, and albedo), we find that the Trojans have surface properties similar to the P and C class asteroids prominent in the outer main belt, yet they have significantly different surge properties (at a confidence level of 99.90%). This provides an imperfect argument against the traditional idea that the Trojans were formed around Jupiter’s orbit. We also find no overlap in Trojan properties with either the main belt asteroids or with the small icy bodies in the outer Solar System. Importantly, we find that the Trojans are indistinguishable from other small bodies in the outer Solar System that have lost their surface ices (such as the gray Centaurs, gray Scattered Disk Objects, and dead comets). Thus, we find strong support for the idea that the Trojans originally formed as icy bodies in the outer Solar System, were captured into their current orbits during the migration of the gas giant planets, and subsequently lost all their surface ices.

To appear in: Icarus

For preprints, contact mws@lsu.edu

Colors and Taxonomy of Centaurs and Trans-Neptunian Objects
D. Perna1,2,3, M.A. Barucci1, S. Fornasier1,4, F.E. DeMeo1, A. Alvarez-Candal1,5, F. Merlin1,6, E. Dotto3, A. Doressoundiram1, and C. de Bergh1

1 LESIA, Observatoire de Paris, 5 Place Jules Janssen, 92195 Meudon Principal Cedex, France
2 Università di Roma Tor Vergata, Dipartimento di Fisica, Via della Ricerca Scientifica 1, 00133 Roma, Italy
3 INAF-Osservatorio Astronomico di Roma, Via di Frascati 33, 00040 Monte Porzio Catone, Italy
4 Université Paris Diderot - Paris 7, France
5 European Southern Observatory, Avenida Alonso de Cordova 3107, Vitacura, Santiago, Chile
6 Department of Astronomy, University of Maryland, College Park, MD 20742-2421, USA

Context. The study of the surface properties of Centaurs and Trans-Neptunian Objects (TNOs) provides essential information about the early conditions and evolution of the outer Solar System. Due to the faintness of most of these distant and icy bodies, photometry currently constitutes the best technique to survey a statistically significant number of them.

Aims. Our aim is to investigate color properties of a large sample of minor bodies of the outer Solar System, and set their taxonomic classification.

Methods. We carried out visible and near-infrared photometry of Centaurs and TNOs, making use, respectively, of the FORS2 and ISAAC instruments at the Very Large Telescope (European Southern Observatory). Using G-mode analysis, we derived taxonomic classifications according to the Barucci et al. (2005a) system.

Results. We report photometric observations of 31 objects, 10 of them have their colors reported for the first time ever. 28 Centaurs and TNOs have been assigned to a taxon.

Conclusions. We combined the entire sample of 38 objects taxonomically classified in the framework of our programme (28 objects from this work; 10 objects from DeMeo et al. 2009a) with previously classified TNOs and Centaurs, looking for correlations between taxonomy and dynamics. We compared our photometric results to literature data, finding hints of heterogeneity for the surfaces of 4 objects.

To appear in: Astronomy and Astrophysics

Preprints available on the web at http://arxiv.org/abs/0912.2621


Searching for Sub-kilometer TNOs using Pan-STARRS Video Mode
Lightcurves: Preliminary Study and Evaluation using Engineering Data

J.-H. Wang1,2, P. Protopapas3,4, W.-P. Chen2, C. R. Alcock3, W. S. Burgett5, T. Dombeck6, T. Grav7, J. S. Morgan5, P. A. Price5, and J. L. Tonry5

1 Institute of Astronomy and Astrophysics, Academia Sinica. P.O. Box 23-141, Taipei 106, Taiwan
2 Institute of Astronomy, National Central University, No. 300, Jhongda Rd, Jhongli City, Taoyuan County 320, Taiwan
3 Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138, USA
4 Initiative in Innovative Computing, School of Engineering and Applied Sciences, 29 Oxford Street, Cambridge, MA 02138, USA
5 Physics Department, University of Hawaii, 2680 Woodlawn Drive, Honolulu, HI, 96822, USA
6 Institute for Astronomy, University of Hawaii, 2680 Woodlawn Drive, Honolulu, HI, 96822, USA
7 Department of Physics and Astronomy, John Hopkins University, 366 Bloomberg Center, 3400 N. Charles Street, Baltimore, MD 21218, USA

Submitted to: The Astronomical Journal

Preprints available on the web at http://arxiv.org/abs/0910.5598

The Size, Density, and Formation of the Orcus-Vanth System in the Kuiper Belt

M.E. Brown1, D. Ragozzine1,2, J. Stansberry3, and W.C. Fraser1

1 Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, CA 91125, USA
2 now at Harvard-Smithsonian Center for Astrophysics, Cambridge, MA 02138, USA
3 Steward Observatory, University of Arizona, Tucson, AZ 08544, USA

Submitted to: The Astronomical Journal

For preprints, contact mbrown@caltech.edu
or on the web at http://arxiv.org/abs/0910.4784


Will the Large Synoptic Survey Telescope Detect Extra-solar Planetesimals Entering the Solar System?

A. Moro-Martín1,2, Edwin L. Turner3,4 and Abraham Loeb5

1 Centro de Astrobiología (CSIC-INTA), 28850 Torrejón de Ardoz, Madrid, Spain
2 Department of Astrophysical Sciences, Princeton University, Princeton, NJ 08544, USA
3 Princeton University Observatory, Princeton, NJ 08544, USA
4 Institute for the Physics and Mathematics of the Universe, University of Tokyo, Kashiwa, Chiba 277-8568, Japan
5 Harvard University, Center for Astrophysics, MS 51, 60 Garden Street, Cambridge MA 02138, USA

The Astrophysical Journal, 704, 733 (2009 October 10)

For preprints, contact amaya@astro.princeton.edu
or on the web at http://arXiv.org/abs/0908.3948
and http://www.astro.princeton.edu/~amaya/publications/publications.html


The Sizes of Kuiper Belt Objects

Pedro Lacerda1

1 Queen’s University, Belfast BT7 1NN, United Kingdom

To appear in: proceedings of ``The Space Infrared Telescope for Cosmology & Astrophysics: Revealing the Origins of Planets and Galaxies''

Preprints available on the web at http://arxiv.org/abs/0911.0004

The Dark Red Spot on KBO Haumea

Pedro Lacerda1

1 Newton Fellow, Queen’s University, Belfast BT7 1NN, United Kingdom

To appear in: proceedings of IAU 2009 Symposium S263 ``Icy Bodies of the Solar System''

Preprints available on the web at http://arxiv.org/abs/0911.0009

Newsletter Information

The Distant EKOs Newsletter is dedicated to provide researchers with easy and rapid access to current work regarding the Kuiper belt (observational and theoretical studies), directly related objects (e.g., Pluto, Centaurs), and other areas of study when explicitly applied to the Kuiper belt.

We accept submissions for the following sections:

A LaTeX template for submissions is appended to each issue of the newsletter, and is sent out regularly to the e-mail distribution list. Please use that template, and send your submission to:
The Distant EKOs Newsletter is available on the World Wide Web at:
Recent and back issues of the Newsletter are archived there in various formats. The web pages also contain other related information and links.

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.

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If you move or your e-mail address changes, please send the editor your new address. If the Newsletter bounces back from an address for three consecutive issues, the address will be deleted from the mailing list. All address changes, submissions, and other correspondence should be sent to:

Joel Parker 2009-12-29