* Astronomy

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RE: Trans-Neptunian objects

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Title: Polarimetry of transneptunian objects (136472) Makemake and (90482) Orcus
Authors: I. N. Belskaya, S. Bagnulo, A. Stinson, G. P. Tozzi, K. Muinonen, Yu. G. Shkuratov, M. A. Barucci, S. Fornasier

Context. We study the surface properties of transneptunian populations of Solar-system bodies.
Aims. We investigate the surface characteristics of the dwarf planet (136472) Makemake and the resonant object (90482) Orcus.
Methods. Using the FORS2 instrument of the ESO-VLT we have carried out linear polarisation measurements of Makemake and Orcus.
Results. Polarisation of Orcus is similar to that of smaller size objects. The polarimetric properties of Makemake are very close to those of Eris and Pluto. We have not found any significant differences in the polarisation properties of objects from different dynamical classes. However, there are significant differences in polarisation of large and smaller size objects, and between large TNOs with water-ice and methane-ice dominated surfaces.
Conclusions. We confirm the different types of polarisation phase behaviour for the largest and smaller size TNOs. To explain subtle surface polarisation of Pluto, Makemake and Eris we assume that their surfaces are covered by a thin layer of hoarfrost masking the surface structure.

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Title: Short-term variability of 10 trans-Neptunian objects
Authors: A. Thirouin, J. L. Ortiz, A. Campo Bagatin, P. Pravec, N. Morales, O. Hainaut, R. Duffard

We present our latest results about the short-term variability of trans-Neptunian objects (TNOs). We performed broad-band CCD photometric observations using several telescopes in Spain and Chile. We present results based on three years of observations and report the short-term variability of 10 TNOs. Our sample of studied targets contains classical objects: (275809) 2001 QY297, (307251) 2002 KW14, (55636) 2002 TX300, 2004 NT33, (230965) 2004 XA192, and (202421) 2005 UQ513, a resonant body: (84522) 2002 TC302, a scattered target: (44594) 1999 OX3, and two detached objects: (145480) 2005 TB190, and (40314) 1999 KR16. For each target, light curves as well as possible rotation periods and photometric amplitudes are reported. The majority of the observed objects present a low peak-to-peak amplitude, <0.15mag. Only two objects exhibit light curve amplitudes higher than 0.15mag: (275809) 2001 QY297, and (307251) 2002 KW14. We remark two biases in the literature, previously studied in Thirouin et al. (2010) and confirmed by this new study: a bias towards objects with a small amplitude light curve and a second one against objects with a long rotational period in the data base of published rotational periods. We derived constraints on physical properties of some targets. We also report the solar phase curves of (40314) 1999 KR16, and (44594) 1999 OX3 for solar phase angles from 0 degree to around 2 degrees. Part of our discussion is focused on the study of (275809) 2001 QY297 which turned out to be an asynchronous binary system.

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Title: The Resonant Transneptunian Populations
Authors: B. Gladman, S. M. Lawler, J-M. Petit, J. Kavelaars, R. L. Jones, J. Wm. Parker, C. Van Laerhoven, P. Nicholson, P. Rousselot, A. Bieryla, M. L. N. Ashby

The transneptunian objects (TNOs) trapped in mean-motion resonances with Neptune were likely emplaced there during planet migration late in the giant-planet formation process. We perform detailed modelling of the resonant objects detected in the Canada-France Ecliptic Plane Survey (CFEPS) in order to provide population estimates and, for some resonances, constrain the complex internal orbital element distribution. Detection biases play a critical role because phase relationships with Neptune make object discovery more likely at certain longitudes. This paper discusses the 3:2, 5:2, 2:1, 3:1, 5:1, 4:3, 5:3, 7:3, 5:4, and 7:4 mean-motion resonances, all of which had CFEPS detections, along with our upper limit on 1:1 Neptune Trojans (which is consistent with their small population estimated elsewhere). For the plutinos (TNOs in the 3:2 resonance) we refine the orbital element distribution given in Kavelaars et al. (2009) and show that steep H-magnitude distributions (N(H) proportional to 10aH, with a=0.8-0.9) are favoured in the range Hg=8-9, and confirm that this resonance does not share the inclination distribution of the classical Kuiper Belt. We give the first population estimate for the 5:2 resonance and find that, to within the uncertainties, the population is equal to that of the 3:2 (13,000 TNOs with Hg < 9.16), whereas the 2:1 population is smaller by a factor of 3-4 compared to the other two resonances. We also measure significant populations inhabiting the 4:3, 5:3, 7:3, 5:4, 7:4, 3:1, and 5:1 resonances, with Hg < 9.16 (D >100 km) populations in the thousands. We compare our intrinsic population and orbital-element distributions with several published models of resonant-TNO production; the most striking discrepancy is that resonances beyond the 2:1 are in reality more heavily populated than in published models.

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Title: "TNOs are Cool": A survey of the trans-Neptunian region -- VII. Size and surface characteristics of (90377) Sedna and 2010 EK139
Authors: András Pál (1,2), Csaba Kiss (1), Thomas G. Müller (3), Pablo Santos-Sanz (4), Esa Vilenius (3), Nikolett Szalai (1), Michael Mommert (5), Emmanuel Lellouch (4), Miriam Rengel (6), Paul Hartogh (6), Silvia Protopapa (7,6), John Stansberry (8), Jose-Luis Ortiz (9), René Duffard (9), Audrey Thirouin (9), Florence Henry (4), Audrey Delsanti (4,10) ((1) Konkoly Observatory, MTA Research Centre for Astronomy and Earth Sciences, (2) Department of Astronomy, Loránd Eötvös University, (3) Max-Planck-Institut für extraterrestrische Physik, (4) LESIA-Observatoire de Paris, CNRS, (5) Deutsches Zentrum für Luft- und Raumfahrt, Institut für Planetenforschung, (6) Max-Planck-Institut für Sonnensystemforschung, (7) Department of Astronomy, University of Maryland, (8) Steward Observatory, University of Arizona, (9) Instituto de Astrofísica de Andalucía, (10) Laboratoire d'Astrophysique de Marseille, CNRS and Université de Provence)

We present estimates of the basic physical properties (size and albedo) of (90377) Sedna, a prominent member of the detached trans-Neptunian object population and the recently discovered scattered disk object 2010 EK139, based on the recent observations acquired with the Herschel Space Observatory, within the "TNOs are Cool!" key programme. Our modelling of the thermal measurements shows that both objects have larger albedos and smaller sizes than the previous expectations, thus their surfaces might be covered by ices in a significantly larger fraction. The derived diameter of Sedna and 2010 EK139 are 995 ±80 km and 470 +35/-10 km, while the respective geometric albedos are pV 0.32 ±0.06 and 0.25 +0.02/-0.05. These estimates are based on thermophysical model techniques.

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Title: "TNOs are Cool": A survey of the trans-Neptunian region VI. Herschel/PACS observations and thermal modelling of 19 classical Kuiper belt objects
Authors: E. Vilenius, C. Kiss, M. Mommert, T. Müller, P. Santos-Sanz, A. Pal, J. Stansberry, M. Mueller, N. Peixinho, S. Fornasier, E. Lellouch, A. Delsanti, A. Thirouin, J. L. Ortiz, R. Duffard, D. Perna, N. Szalai, S. Protopapa, F. Henry, D. Hestroffer, M. Rengel, E. Dotto, P. Hartogh

Trans-Neptunian objects (TNO) represent the leftovers of the formation of the Solar System. Their physical properties provide constraints to the models of formation and evolution of the various dynamical classes of objects in the outer Solar System. Based on a sample of 19 classical TNOs we determine radiometric sizes, geometric albedos and beaming parameters. Our sample is composed of both dynamically hot and cold classicals. We study the correlations of diameter and albedo of these two subsamples with each other and with orbital parameters, spectral slopes and colours. We have done three-band photometric observations with Herschel/PACS and we use a consistent method for data reduction and aperture photometry of this sample to obtain monochromatic flux densities at 70.0, 100.0 and 160.0 µ m. Additionally, we use Spitzer/MIPS flux densities at 23.68 and 71.42 µ m when available, and we present new Spitzer flux densities of eight targets. We derive diameters and albedos with the near-Earth asteroid thermal model (NEATM). As auxiliary data we use reexamined absolute visual magnitudes from the literature and data bases, part of which have been obtained by ground based programs in support of our Herschel key program. We have determined for the first time radiometric sizes and albedos of eight classical TNOs, and refined previous size and albedo estimates or limits of 11 other classicals. The new size estimates of 2002 MS4 and 120347 Salacia indicate that they are among the 10 largest TNOs known. Our new results confirm the recent findings that there are very diverse albedos among the classical TNOs and that cold classicals possess a high average albedo (0.17 ±0.04). Diameters of classical TNOs strongly correlate with orbital inclination in our sample. We also determine the bulk densities of six binary TNOs.

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Title: "TNOs are Cool": A Survey of the Transneptunian Region IV. Size/albedo characterisation of 15 scattered disk and detached objects observed with Herschel Space Observatory-PACS
Authors: P. Santos-Sanz, E. Lellouch, S. Fornasier, C. Kiss, A. Pal, T.G. Müller, E. Vilenius, J. Stansberry, M. Mommert, A. Delsanti, M. Mueller, N. Peixinho, F. Henry, J.L. Ortiz, A. Thirouin, S. Protopapa, R. Duffard, N. Szalai, T. Lim, C. Ejeta, P. Hartogh, A.W. Harris, M. Rengel

Physical characterisation of Trans-Neptunian objects, a primitive population of the outer solar system, may provide constraints on their formation and evolution. The goal of this work is to characterise a set of 15 scattered disk (SDOs) and detached objects, in terms of their size, albedo, and thermal properties. Thermal flux measurements obtained with the Herschel-PACS instrument at 70, 100 and 160 \mu m, and whenever applicable, with Spitzer-MIPS at 24 and 70 \mu m, are modelled with radiometric techniques, in order to derive the objects' individual size, albedo and when possible beaming factor. Error bars are obtained from a Monte-Carlo approach. We look for correlations between these and other physical and orbital parameters. Diameters obtained for our sample range from 100 to 2400 km, and the geometric albedos (in V band) vary from 3.8 % to 84.5 %. The unweighted mean V geometric albedo for the whole sample is 11.2 % (excluding Eris); 6.9 % for the SDOs, and 17.0 % for the detached objects (excluding Eris). We obtain new bulk densities for three binary systems: Ceto/Phorcys, Typhon/Echidna and Eris/Dysnomia. Apart from correlations clearly due to observational bias, we find significant correlations between albedo and diameter (more reflective objects being bigger), and between albedo, diameter and perihelion distance (brighter and bigger objects having larger perihelia). We discuss possible explanations for these correlations.

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36 New TNOS

MPEC 2011 - H58

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Title: Optical and Infrared Colours of Transneptunian Objects Observed with HST
Authors: S. D. Benecchi, K. S. Noll, D. C. Stephens, W. M. Grundy, J. Rawlins

We present optical colours of 72 transneptunian objects (TNOs), and infrared colours of 80 TNOs obtained with the WFPC2 and NICMOS instruments, respectively, on the Hubble Space Telescope (HST). Both optical and infrared colours 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 colours, particularly in the infrared. The range of our measured colours is consistent with other colours 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 (~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 colour and dynamical properties (semi-major axis, eccentricity, inclination and perihelion). We do find that colours of Classical objects with i<6{\deg} 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.

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Title: Trans-Neptunian Objects with Hubble Space Telescope ACS/WFC
Authors: Cesar I. Fuentes, Matthew J. Holman, David E. Trilling, Pavlos Protopapas

We introduce a novel search technique that can identify trans-neptunian objects in three to five exposures of a pointing within a single Hubble Space Telescope orbit. The process is fast enough to allow the discovery of candidates soon after the data are available. This allows sufficient time to schedule follow up observations with HST within a month. We report the discovery of 14 slow-moving objects found within 5° of the ecliptic in archival data taken with the Wide Field Channel of the Advanced Camera for Surveys. The luminosity function of these objects is consistent with previous ground-based and space-based results. We show evidence that the size distribution of both high and low inclination populations is similar for objects smaller than 100 km, as expected from collisional evolution models, while their size distribution differ for brighter objects. We suggest the two populations formed in different parts of the protoplanetary disk and after being dynamically mixed have collisionally evolved together. Among the objects discovered there is an equal mass binary with an angular separation ~ 0."53.

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