Distant EKOs, Issue #74  (April 2011)


News & Announcements
Abstracts of 7 Accepted Papers
Titles of 2 Other Papers of Interest
Newsletter Information


There were 12 new TNO discoveries announced since the previous issue of Distant EKOs:

2004 HA79, 2004 HB79, 2004 HX78, 2004 HY78, 2004 HZ78, 2004 KB19, 2004 KC19, 2004 MS8, 2004 VX130, 2004 VY130, 2004 VZ130, 2005 CD81

and 1 new Centaur/SDO discovery:

2011 FY9

Reclassified objects:

2009 MF10 (TNO $\rightarrow$ SDO)

Objects recently assigned names:

2004 SB60 = Salacia

Current number of TNOs: 1175 (including Pluto)
Current number of Centaurs/SDOs: 293
Current number of Neptune Trojans: 7

Out of a total of 1475 objects:
   623 have measurements from only one opposition
     577 of those have had no measurements for more than a year
       322 of those have arcs shorter than 10 days
(for more details, see: http://www.boulder.swri.edu/ekonews/objects/recov_stats.jpg)


Optical and Infrared Colors of Transneptunian Objects with HST
S.D. Benecchi1,2, K.S. Noll3, D.C. Stephens4, W.M. Grundy5, and J. Rawlins4

1 Planetary Science Institute, 1700 East Fort Lowell, Suite 106, Tucson, AZ 85719, USA
2 Carnegie Institution of Washington, Department of Terrestrial Magnetism, 5241 Broad Branch Road, NW, Washington, DC 20015, USA
3 Space Telescope Science Institute, 3700 San Martin Dr., Baltimore, MD 21218, USA
4 Brigham Young University, Dept. of Physics & Astronomy, N145 ESC, Provo, UT 84602, USA
5 Lowell Observatory, 1400 W. Mars Hill Rd., Flagstaff, AZ 86001, USA

We present optical colors of 72 transneptunian objects (TNOs), and infrared colors of 80 TNOs obtained with the WFPC2 and NICMOS instruments, respectively, on the Hubble Space Telescope (HST). Both optical and infrared colors are available for 32 objects that overlap between the datasets. This dataset adds an especially uniform, consistent and large contribution to the overall sample of colors, particularly in the infrared. The range of our measured colors is consistent with other colors reported in the literature at both optical and infrared wavelengths. We find generally good agreement for objects measured by both us and others; 88.1% have better than 2-sigma agreement. The median HV magnitude of our optical sample is 7.2, modestly smaller ($\sim$0.5 mag) than for previous samples. The median absolute magnitude, HV, in our infrared sample is 6.7. We find no new correlations between color and dynamical properties (semi-major axis, eccentricity, inclination and perihelion). We do find that colors of Classical objects with $i<6\,^{\circ}$ come from a different distribution than either the Resonant or excited populations in the visible at the >99.99% level with a K-S test. The same conclusion is found in the infrared at a slightly lower significance level, 99.72%. Two Haumea collision fragments with strong near infrared ice bands are easily identified with broad HST infrared filters and point to an efficient search strategy for identifying more such objects. We find evidence for variability in (19255) 1999 VK8, 1999 OE4, 2000 CE105, 1998 KG62 and 1998 WX31.

To appear in: Icarus

For preprints, contact susank@psi.edu or sbenecchi@dtm.ciw.edu
or on the web at http://arxiv.org/abs/1103.2175

Physical Studies of Centaurs and Trans-Neptunian Objects with the Atacama Large Millimeter Array
A. Moullet1, E. Lellouch2, R. Moreno2, and M. Gurwell1

1 Harvard-Smithsonian Center for Astrophysics, Cambridge, MA 02138, USA
2 LESIA, Observatoire de Paris, Meudon, France

Once completed, the Atacama Large Millimeter Array (ALMA) will be the most powerful (sub)millimeter interferometer in terms of sensitivity, spatial resolution and imaging. This paper presents the capabilities of ALMA applied to the observation of Centaurs and Trans-Neptunian Objects, and their possible output in terms of physical properties. Realistic simulations were performed to explore the performances of the different frequency bands and array configurations, and several projects are detailed along with their feasibility, their limitations and their possible targets. Determination of diameters and albedos via the radiometric method appears to be possible on $\sim$500 objects, while sampling of the thermal lightcurve to derive the bodies' ellipticity could be performed at least 30 bodies that display a significant optical lightcurve. On a limited number of objects, the spatial resolution allows for direct measurement of the size or even surface mapping with a resolution down to 13 milliarcsec. Finally, ALMA could separate members of multiple systems with a separation power comparable to that of the HST. The overall performance of ALMA will make it an invaluable instrument to explore the outer Solar System, complementary to space-based telescopes and spacecrafts.

To appear in: Icarus

Preprints available on the web at http://arxiv.org/abs/1102.3872

First Results from the MIT Optical Rapid Imaging System (MORIS): A Stellar Occultation by Pluto and a Transit by Exoplanet XO-2b
A.A.S. Gulbis1,2, S.J. Bus3, J.L. Elliot2,4,5, J.T. Rayner3, W.E. Stahlberger3, F.E. Rojas6, E.R. Adams2, M.J. Person2, R. Chung3, A.T. Tokunaga3, and C.A. Zuluaga2

1 Southern African Large Telescope and South African Astronomical Observatory, P.O. Box 9, 7935 Cape Town, South Africa
2 Department of Earth, Atmospheric, and Planetary Sciences, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, MA 02139, USA
3 Institute for Astronomy, University of Hawaii, 640 North A'ohoku Place, 3 Room 209, Hilo, HI 96720, USA
4 Department of Physics, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, MA 02139, USA
5 Lowell Observatory, 1400 West Mars Hill Road, Flagstaff, AZ 86001, USA
6 Department of Mechanical Engineering, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, MA 02139, USA

We present a high-speed, visible-wavelength imaging instrument: MORIS (the MIT Optical Rapid Imaging System). MORIS is mounted on the 3 m Infrared Telescope Facility (IRTF) on Mauna Kea, Hawaii. Its primary component is an Andor iXon camera, a nearly 60'' square field of view with high quantum efficiency, low read noise, low dark current, and full-frame readout rates ranging from as slow as desired to a maximum of between 3.5 Hz and 35 Hz (depending on the mode; read noise of 6 e-/pixel and 49 e-/pixel with electron-multiplying gain = 1, respectively). User-selectable binning and subframing can increase the cadence to a few hundred hertz. An electron-multiplying mode can be employed for photon counting, effectively reducing the read noise to subelectron levels at the expense of dynamic range. Data cubes, or individual frames, can be triggered to several-nanosecond accuracy using the Global Positioning System. MORIS is mounted on the side-facing exit window of SpeX, allowing simultaneous near-infrared and visible observations. Here, we describe the components, setup, and measured characteristics of MORIS. We also report results from the first science observations: the 2008 June 24 stellar occultation by Pluto and an extrasolar planetary transit by XO-2b. The Pluto occultation of a 15.8 R magnitude star has a signal-to-noise ratio of 35 per atmospheric scale height and a midtime error of 0.32 s. The XO-2b transit reaches photometric precision of 0.5 mmag in 2 minutes and has a midtime timing precision of 23 s.

Published in: Publications of the Astronomical Society of the Pacific (2011 April)

For preprints, contact amanda@saao.ac.za
or on the web at http://arxiv.org/abs/1102.5248

Five New and Three Improved Mutual Orbits of Transneptunian Binaries
W.M. Grundy1, K.S. Noll2, F. Nimmo3, H.G. Roe1, M.W. Buie4, S.B. Porter1, S.D. Benecchi5,6, D.C. Stephens7, H.F. Levison4, and J.A. Stansberry8

1 Lowell Observatory, 1400 W. Mars Hill Rd., Flagstaff AZ 86001, USA
2 Space Telescope Science Institute, 3700 San Martin Dr., Baltimore MD 21218, USA
3 Department of Earth and Planetary Sciences, University of California, Santa Cruz CA 95064, USA
4 Southwest Research Institute, 1050 Walnut St. #300, Boulder CO 80302, USA
5 Planetary Science Institute, 1700 E. Fort Lowell, Suite 106, Tucson AZ 85719, USA
6 Carnegie Institution of Washington, Department of Terrestrial Magnetism, 5241 Broad Branch Rd. NW, Washington DC 20015, USA
7 Dept. of Physics and Astronomy, Brigham Young University, N283 ESC Provo UT 84602, USA
8 Steward Observatory, University of Arizona, 933 N. Cherry Ave., Tucson AZ 85721, USA

We present three improved and five new mutual orbits of transneptunian binary systems (58534) Logos-Zoe, (66652) Borasisi-Pabu, (88611) Teharonhiawako-Sawiskera, (123509) 2000 WK183, (149780) Altjira, 2001 QY297, 2003 QW111, and 2003 QY90 based on Hubble Space Telescope and Keck II laser guide star adaptive optics observations. Combining the five new orbit solutions with 17 previously known orbits yields a sample of 22 mutual orbits for which the period P, semimajor axis a, and eccentricity e have been determined. These orbits have mutual periods ranging from 5 to over 800 days, semimajor axes ranging from 1,600 to 37,000 km, eccentricities ranging from 0 to 0.8, and system masses ranging from 2 x 1017 to 2 x 1022 kg. Based on the relative brightnesses of primaries and secondaries, most of these systems consist of near equal-sized pairs, although a few of the most massive systems are more lopsided. The observed distribution of orbital properties suggests that the most loosely-bound transneptunian binary systems are only found on dynamically cold heliocentric orbits. Of the 22 known binary mutual orbits, orientation ambiguities are now resolved for 9, of which 7 are prograde and 2 are retrograde, consistent with a random distribution of orbital orientations, but not with models predicting a strong preference for retrograde orbits. To the extent that other perturbations are not dominant, the binary systems undergo Kozai oscillations of their eccentricities and inclinations with periods of the order of tens of thousands to millions of years, some with strikingly high amplitudes.

To appear in: Icarus

Preprints available at: http://www.lowell.edu/~grundy/abstracts/2011.5+3-orbits.html

High-contrast Observations of (136108) Haumea.
A Crystalline Water-ice Multiple System.
C. Dumas1, B. Carry2, D. Hestroffer3, and F. Merlin4

1 European Southern Observatory. Alonso de Córdova 3107, Vitacura, Casilla 19001, Santiago de Chile, Chile
2 European Space Astronomy Centre, ESA, PO Box 78, 28691 Villanueva de la Cañada, Madrid, Spain
3 IMCCE, Observatoire de Paris, CNRS. 77, Av. Denfert-Rochereau, 75014 Paris, France
4 Université Paris 7 Denis Diderot. 4 rue Elsa Morante, 75013 Paris, France

The trans-neptunian region of the Solar System is populated by a large variety of icy bodies showing great diversity in orbital behavior, size, surface color and composition. One can also note the presence of dynamical families and binary systems. One surprising feature detected in the spectra of some of the largest Trans-Neptunians is the presence of crystalline water-ice. This is the case for the large TNO (136108) Haumea (2003EL61).

We seek to constrain the state of the water ice of Haumea and its satellites, and investigate possible energy sources to maintain the water ice in its crystalline form.

Spectro-imaging observations in the near infrared have been performed with the integral field spectrograph SINFONI mounted on UT4 at the ESO Very Large Telescope. The spectra of both Haumea and its larger satellite Hi'iaka are analyzed. Relative astrometry of the components is also performed, providing a check of the orbital solutions and equinox seasons.

We describe the physical characteristics of the crystalline water-ice present on the surface of Haumea and its largest satellite Hi'iaka and analyze possible sources of heating to maintain water in crystalline state: tidal dissipation in the system components vs. radiogenic source. The surface of Hi'iaka appears to be covered by large grains of water ice, almost entirely in its crystalline form. Under some restricted conditions, both radiogenic heating and tidal forces between Haumea and Hi'iaka could provide the energy sufficient to maintain the ice in its crystalline state.

Published in: Astronomy & Astrophysics, 528, 105 (2011 April)

For preprints, contact cdumas@eso.org or online at http://arxiv.org/abs/1101.2102

Observed Binary Fraction Sets Limits on the Extent of Collisional Grinding in the Kuiper Belt
David Nesvorný1, David Vokrouhlický1,2, William F. Bottke1, Keith Noll3, and Harold F. Levison1

1 Department of Space Studies, Southwest Research Institute, 1050 Walnut St., Suite 300, Boulder, CO 80302, USA
2 Institute of Astronomy, Charles University, V Holešovickách 2, CZ-18000, Prague 8, Czech Republic
3 Space Telescope Science Institute, 3700 San Martin Dr., Baltimore, MD 21218, USA

The size distribution in the cold classical Kuiper belt can be approximated by two idealized power laws: one with steep slope for radii R>R* and one with shallow slope for R<R*, where $R^*\sim$25-50 km. Previous works suggested that the SFD roll-over at R* can be the result of extensive collisional grinding in the Kuiper belt that led to the catastrophic disruption of most bodies with R<R*. Here we use a new code to test the effect of collisions in the Kuiper belt. We find that the observed roll-over could indeed be explained by collisional grinding provided that the initial mass in large bodies was much larger than the one in the present Kuiper belt, and was dynamically depleted. In addition to the size distribution changes, our code also tracks the effects of collisions on binary systems. We find that it is generally easier to dissolve wide binary systems, such as the ones existing in the cold Kuiper belt today, than to catastrophically disrupt objects with $R\sim R^*$. Thus, the binary survival sets important limits on the extent of collisional grinding in the Kuiper belt. We find that the extensive collisional grinding required to produce the SFD roll-over at R* would imply a strong gradient of the binary fraction with R and separation, because it is generally easier to dissolve binaries with small components and/or those with wide orbits. The expected binary fraction for $R \leq R^*$ is $\leq $0.1. The present observational data do not show such a gradient. Instead, they suggest a large binary fraction of $\sim$0.4 for R=30-40 km. This may indicate that the roll-over was not produced by disruptive collisions, but is instead a fossil remnant of the KBO formation process.

Published in: The Astronomical Journal, 141, 159 (2011 May)

Preprints available on the web at http://arxiv.org/abs/1102.5706

Discovery of Carbon Monoxide in the Upper Atmosphere of Pluto
J.S. Greaves1, Ch. Helling1, and P. Friberg2

1 SUPA, Physics & Astronomy, University of St Andrews, Scotland, UK
2 Joint Astronomy Centre, Hawaii, USA

Pluto's icy surface has changed colour and its atmosphere has swelled since its last closest approach to the Sun in 1989. The thin atmosphere is produced by evaporating ices, and so can also change rapidly, and in particular carbon monoxide should be present as an active thermostat. Here we report the discovery of gaseous CO via the 1.3mm wavelength J=2-1 rotational transition, and find that the line-centre signal is more than twice as bright as a tentative result obtained by Bocké-Morvan et al. in 2000. Greater surface-ice evaporation over the last decade could explain this, or increased pressure could have caused the atmosphere to expand. The gas must be cold, with a narrow line-width consistent with temperatures around 50 K, as predicted for the very high atmosphere, and the line brightness implies that CO molecules extend up to $\approx$ 3 Pluto radii above the surface. The upper atmosphere must have changed markedly over only a decade since the prior search, and more alterations could occur by the arrival of the New Horizons mission in 2015.

To appear in: MNRAS

Preprints available on the web at http://arxiv.org/abs/1104.3014


Binary Planetesimals and Their Role in Planet Formation
Hagai B. Perets1

1 Harvard-Smithsonian Center for Astrophysics, 60 Garden St., Cambridge, MA 02138, USA

One of the main evolutionary stages of planet formation is the dynamical evolution of planetesimal disks. These disks are thought to evolve through gravitational encounters and physical collisions between single planetesimals. In recent years, many binary planetesimals (BPs) have been observed in the solar system, indicating that the binarity of planetesimals is high. However, current studies of planetesimal disk formation and evolution do not account for the role of binaries. Here, we point out that gravitational encounters of BPs can have an important role in the evolution of planetesimal disks. BPs catalyze close encounters between planetesimals and can strongly enhance their collision rate. Binaries may also serve as an additional heating source of the planetesimal disk, through the exchange of the binaries gravitational potential energy into the kinetic energy of planetesimals in the disk.

Published in: The Astrophysical Journal, 727, L3 (2011 January 20)

Preprints available at http://arxiv.org/abs/1012.0567

The Orbits of Neptune's Outer Satellites
M. Brozovic1, R.A. Jacobson1, and S.S. Sheppard2

1 Jet Propulsion Laboratory, California Institute of Technology, 4800 Oak Grove Drive, Pasadena, CA 91109-8099, USA
2 Carnegie Institution of Washington, Department of Terrestrial Magnetism, 5241 Broad Branch Road NW, Washington, DC 20015, USA

In 2009 we used the Subaru telescope to observe all the faint irregular satellites of Neptune for the first time since 2004. These observations extend the data arcs for Halimede, Psamathe, Sao, Laomedeia and Neso from a few years to nearly a decade. We also report on a search for unknown Neptune satellites in a half square degree of sky and a limiting magnitude of 26.2 in the R-band. No new satellites of Neptune were found.

We numerically integrated the orbits for the five irregulars and we summarize the results of the orbital fits in terms of the state vectors, post-fit residuals, and mean orbital elements. Sao and Neso are confirmed to be Kozai librators, while Psamathe is a "reverse circulator". Halimede and Laomedeia do not seem to experience any strong resonant effects.

Published in: The Astronomical Journal, 141, 135 (2011 April)

For preprints, contact marina.brozovic@jpl.nasa.gov
or on the web at http://iopscience.iop.org/1538-3881/141/4/135

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.

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Joel Parker 2011-04-20