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تسجيل مستخدم جديدPhotometric observations of nine Transneptunian objects and Centaurs
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We present the results of photometric observations of six Transneptunian objects and three Centaurs, estimations of their rotational periods and corresponding amplitudes. For six of them we present also lower limits of density values. All observations were made using 3.6-m TNG telescope (La Palma, Spain). For four objects -- (148975) 2001 XA255, (281371) 2008 FC76, (315898) 2008 QD4, and 2008 CT190 -- the estimation of short-term variability was made for the first time. We confirm rotation period values for two objects: (55636) 2002 TX300 and (202421) 2005 UQ513, and improve the precision of previously reported rotational period values for other three -- (120178) 2003 OP32, (145452) 2005 RN43, (444030) 2004 NT33 -- by using both our and literature data. We also discuss here that small distant bodies, similarly to asteroids in the Main belt, tend to have double-peaked rotational periods caused by the elongated shape rather than surface albedo variations.
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We analyze albedo data obtained using the Herschel Space Observatory that reveal the existence of two distinct types of surface among midsized transneptunian objects. A color-albedo diagram shows two large clusters of objects, one redder and higher a
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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 inst
rument 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 behavior 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.
In terms of scientific output, the best way to study solar system bodies is sending spacecraft to make in-situ measurements or to observe at close distance. Probably, the second best means to learn about important physical properties of solar system
objects is through stellar occultations. By combining occultation observations from several sites, size and shape can be derived with kilometric accuracy. Also, atmospheric properties can be derived if the body has an atmosphere. Furthermore, the technique can detect rings and even satellites (although rarely) around the main body. Except for the very special cases of Pluto and Charon, stellar occultations by Transneptunian Objects (TNOs) had never been observed until October 2009. This was because the ephemeris of the TNOs have much larger uncertainties than their angular diameters (typically of the order of ~10 milliarcsecond) and also because stellar catalogs were not accurate to the milliarcsecond level. Despite the difficulties, at the time of this writing, 43 occultations by 22 different Trans-Neptunian Objects, and 17 occultations by 5 Centaurs have been detected thanks to the efforts of several teams. Due to the complications of accurately predicting and observing these events, most of the successes have been achieved through wide international collaboration, which is a key issue to succeed in observing stellar occultations by TNOs. Multichord occultations are typically detected at a rate of ~3 per year on average, whereas the majority of the observed occultations are single-chord detections, which means that only one site detects the occultation. In these cases, no tight constraints on size and shape can be derived from those observations alone. Here we review most of the aspects involved in the complex process to successfully observe occultations, and present some of the lessons learned.
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