Title: HST Astrometry of Transneptunian Objects Authors: Susan D. Benecchi, Keith S. Noll

We present 1428 individual astrometric measurements of 256 Transneptunian objects made with HST. The observations were collected over three years with two instruments, the Wide Field Planetary Camera 2 and the Advanced Camera for Surveys High Resolution Camera, as part of four HST programs. We briefly describe the data and our analysis procedures. The submission of these measurements to the Minor Planet Centre increased the individual arc length of objects by 1.83 days to 8.11 years. Of the 256 total objects, 62 (24.2%) had arc length increases \ge 3 years. The arc length for 60 objects (23.4%) was increased by a factor of two or greater.

Title: Short-term variability of a sample of 29 trans-Neptunian objects and Centaurs Authors: A. Thirouin, J.L. Ortiz, R. Duffard, P. Santos-Sanz, F.J. Aceituno, N. Morales

We present results of 6 years of observations, reduced and analysed with the same tools in a systematic way. We report completely new data for 15 objects, for 5 objects we present a new analysis of previously published results plus additional data and for 9 objects we present a new analysis of data already published. Lightcurves, possible rotation periods and photometric amplitudes are reported for all of them. The photometric variability is smaller than previously thought: the mean amplitude of our sample is 0.1mag and only around 15% of our sample has a larger variability than 0.15mag. The smaller variability than previously thought seems to be a bias of previous observations. We find a very weak trend of faster spinning objects towards smaller sizes, which appears to be consistent with the fact that the smaller objects are more collisionally evolved, but could also be a specific feature of the Centaurs, the smallest objects in our sample. We also find that the smaller the objects, the larger their amplitude, which is also consistent with the idea that small objects are more collisionally evolved and thus more deformed. Average rotation rates from our work are 7.5h for the whole sample, 7.6h for the TNOs alone and 7.3h for the Centaurs. All of them appear to be somewhat faster than what one can derive from a compilation of the scientific literature and our own results. Maxwellian fits to the rotation rate distribution give mean values of 7.5h (for the whole sample) and 7.3h (for the TNOs only). Assuming hydrostatic equilibrium we can determine densities from our sample under the additional assumption that the lightcurves are dominated by shape effects, which is likely not realistic. The resulting average density is 0.92g/cm³ which is not far from the density constraint that one can derive from the apparent spin barrier that we observe.

Title: TNOs and Centaurs from light curves Authors: R. Duffard, J.L. Ortiz, A. Thirouin, P. Santos-Sanz, N. Morales

We analyse a vast light curve database by obtaining mean rotational properties of the entire sample, determining the spin frequency distribution and comparing those data with a simple model based on hydrostatic equilibrium. For the rotation periods, the mean value obtained is 6.95 h for the whole sample, 6.88 h for the Trans-neptunian objects (TNOs) alone and 6.75 h for the Centaurs. From Maxwellian fits to the rotational frequencies distribution the mean rotation rates are 7.35 h for the entire sample, 7.71 h for the TNOs alone and 8.95 h for the Centaurs. These results are obtained by taking into account the criteria of considering a single-peak light curve for objects with amplitudes lower than 0.15 mag and a double-peak light curve for objects with variability >0.15mag. The best Maxwellian fits were obtained with the threshold between 0.10 and 0.15mag. The mean light-curve amplitude for the entire sample is 0.26 mag, 0.25mag for TNOs only, and 0.26mag for the Centaurs. The amplitude versus Hv correlation clearly indicates that the smaller (and collisionally evolved) objects are more elongated than the bigger ones. From the model results, it appears that hydrostatic equilibrium can explain the statistical results of almost the entire sample, which means hydrostatic equilibrium is probably reached by almost all TNOs in the H range [-1,7]. This implies that for plausible albedos of 0.04 to 0.20, objects with diameters from 300km to even 100km would likely be in equilibrium. Thus, the great majority of objects would qualify as being dwarf planets because they would meet the hydrostatic equilibrium condition. The best model density corresponds to 1100 kg/m³.

Title: A Search for Distant Solar System Bodies in the Region of Sedna Authors: Megan E. Schwamb, Michael E. Brown, David L. Rabinowitz

We present the results of a wide-field survey for distant Sedna-like bodies in the outer solar system using the 1.2-m Samuel Oschin Telescope at Palomar Observatory. We searched ~12,000 square degrees down to a mean limiting magnitude of 21.3 in R. A total number of 53 Kuiper belt objects and Centaurs have been detected; 25 of which were discovered in this survey. No additional Sedna-like bodies with perihelia beyond 70 AU were found despite a sensitivity to motions out to ~1000 AU. We place constraints on the size and distribution of objects on Sedna orbits.

Title: Mutual Orbits and Masses of Six Transneptunian Binaries Authors: W.M. Grundy, K.S. Noll, M.W. Buie, S.D. Benecchi, D.C. Stephens, H.F. Levison (Version v2)

We present Hubble Space Telescope observations of six binary transneptunian systems: 2000 QL251, 2003 TJ58, 2001 XR254, 1999 OJ4, (134860) 2000 OJ67, and 2004 PB108. The mutual orbits of these systems are found to have periods ranging from 22 to 137 days, semimajor axes ranging from 2360 to 10500 km, and eccentricities ranging from 0.09 to 0.55. These orbital parameters enable estimation of system masses ranging from 0.2 to 9.7 x 10+18 kg. For reasonable assumptions of bulk density (0.5 to 2.0 g cm-3), the masses can be combined with visible photometry to constrain sizes and albedos. The resulting albedos are consistent with an emerging picture of the dynamically "Cold" Classical subpopulation having relatively high albedos, compared with comparably sized objects on more dynamically excited orbits.

Title: Mutual Orbits and Masses of Six Transneptunian Binaries Authors: W.M. Grundy, K.S. Noll, M.W. Buie, S.D. Benecchi, D.C. Stephens, H.F. Levison

We present Hubble Space Telescope observations of six binary transneptunian systems: 2000 QL251, 2003 TJ58, 2001 XR254, 1999 OJ4, (134860) 2000 OJ67, and 2004 PB108. The mutual orbits of these systems are found to have periods ranging from 22 to 137 days, semimajor axes ranging from 2360 to 10500 km, and eccentricities ranging from 0.09 to 0.55. These orbital parameters enable estimation of system masses ranging from 0.2 to 9.7 x 10+18 kg. For reasonable assumptions of bulk density (0.5 to 2.0 g cm-3), the masses can be combined with visible photometry to constrain sizes and albedos. The resulting albedos are consistent with an emerging picture of the dynamically "Cold" Classical subpopulation having relatively high albedos, compared with comparably sized objects on more dynamically excited orbits.

With the recent discoveries of near-planet-sized objects out beyond Neptune, it makes you wonder just how much junk is floating around out there. Usually, when you see some big stuff, it means theres probably lots of little stuff. For example, asteroids collide and shatter. You get a few big pieces, but lots and lots of little shrapnel. Also, little guys can stick together to make bigger guys, and it takes a lot of little ones to make a big one. So if we see a handful of big objects, we kind of expect to see lots of smaller ones.

Title: A Subaru Pencil-beam Search for m_R~27 Trans-neptunian bodies Authors: Cesar I.Fuentes, Matthew R. George, Matthew J. Holman

We present the results of an archival search for Trans-neptunian objects (TNOs) in an ecliptic field observed with Subaru in 2002. The depth of the search allowed us to find 20 new TNOs with magnitudes between R=24 and 27. We fit a double power law model to the data; the most likely values for the parameters are: alpha_1=0.73_{-0.09}^{+0.08}, alpha_2=0.20_{-0.14}^{+0.12}, sigma_{23}=1.46_{-0.12}^{+0.14} and R_{eq}=25.0_{-0.6}^{+0.8}. This is the most precise measurement of the break in the TNO luminosity function to date. The break in the size distribution corresponds to a diameter of D = 90±30 km assuming a 4% albedo.

Title: First Results From The Taiwanese-American Occultation Survey (TAOS) Authors: Z.-W. Zhang, F. B. Bianco, M. J. Lehner, N. K. Coehlo, J.-H. Wang, S. Mondal, C. Al****, T. Axelrod, Y.-I. Byun, W.-P. Chen, K. H. Cook, R. Dave, I. de Pater, R. Porrata, D.-W. Kim, S.-K. King, T. Lee, H.-C. Lin, J. J. Lissauer, S. L. Marshall, P. Protopapas, J. A. Rice, M. E. Schwamb, S.-Y. Wang, C.-Y. Wen

Results from the first two years of data from the Taiwanese-American Occultation Survey (TAOS) are presented. Stars have been monitored photometrically at 4 Hz or 5 Hz to search for occultations by small (~3 km) Kuiper Belt Objects (KBOs). No statistically significant events were found, allowing us to present an upper bound to the size distribution of KBOs with diameters 0.5 km < D < 28 km.