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Post Info TOPIC: Survey of the Trans-Neptunian Region


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Posts: 131433
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Survey of the Trans-Neptunian Region
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Title: TNOs are Cool: A survey of the trans-Neptunian region V. Physical characterisation of 18 Plutinos using Herschel PACS observations
Authors: Michael Mommert, A. W. Harris, C. Kiss, A. Pal, P. Santos-Sanz, J. Stansberry, A. Delsanti, E. Vilenius, T. G. Mueller, N. Peixinho, E. Lellouch, N. Szalai, F. Henry, R. Duffard, S. Fornasier, P. Hartogh, M. Mueller, J. L. Ortiz, S. Protopapa, M. Rengel, A. Thirouin

We present Herschel PACS photometry of 18 Plutinos and determine sizes and albedos for these objects using thermal modelling. We analyse our results for correlations, draw conclusions on the Plutino size distribution, and compare to earlier results. Flux densities are derived from PACS mini scan-maps using specialised data reduction and photometry methods. In order to improve the quality of our results, we combine our PACS data with existing Spitzer MIPS data where possible, and refine existing absolute magnitudes for the targets. The physical characterisation of our sample is done using a thermal model. Uncertainties of the physical parameters are derived using customised Monte Carlo methods. The correlation analysis is performed using a bootstrap Spearman rank analysis. We find the sizes of our Plutinos to range from 150 to 730 km and geometric albedos to vary between 0.04 and 0.28. The average albedo of the sample is 0.08 0.03, which is comparable to the mean albedo of Centaurs, Jupiter Family comets and other Trans-Neptunian Objects. We were able to calibrate the Plutino size scale for the first time and find the cumulative Plutino size distribution to be best fit using a cumulative power law with q = 2 at sizes ranging from 120-400 km and q = 3 at larger sizes. We revise the bulk density of 1999 TC36 and find a density of 0.64 (+0.15/-0.11) g cm-3. On the basis of a modified Spearman rank analysis technique our Plutino sample appears to be biased with respect to object size but unbiased with respect to albedo. Furthermore, we find biases based on geometrical aspects and color in our sample. There is qualitative evidence that icy Plutinos have higher albedos than the average of the sample.

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Sub-kilometre TNOs
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Title: Searching for sub-kilometre TNOs using Pan-STARRS video mode lightcurves: Preliminary study and evaluation using engineering data
Authors: J.-H. Wang, P. Protopapas, W.-P. Chen, C. R. Al****, T. Dombeck, J. S. Morgan, P. A. Price, J. L. Tonry

We present a pre-survey study of using Pan-STARRS high cadence video mode guide star images to search for TNOs. With suitable selection of the guide stars within the Pan-STARRS 7 deg^{2} field of view, the lightcurves of these guide stars can also be used to search for occultations by TNOs. The best target stars for this purpose are stars with high signal-to-noise ratio (SNR) and small angular size. In order to do this, we compiled a catalogue using the SNR calculated from stars with m_V <13 mag in the Tycho2 catalogue then cross matched these stars with the 2MASS catalogue and estimated their angular sizes from (V-K) colour. We also outlined a new detection method based on matched filter that is optimised to search for diffraction patterns in the lightcurves due to occultation by sub-kilometre TNOs. A detection threshold is set to compromise between real detections and false positives. Depending on the theoretical size distribution model used, we expect to find up to a hundred events during the three-year life time of the Pan-STARRS-1 project. We have tested the detection algorithm and the pipeline on a set of engineering data (taken at 10Hz in stead of 30Hz). No events were found within the engineering data, which is consistent with the small size of the data set and the theoretical models. Meanwhile, with a total of ~ 22 star-hours video mode data (|\beta| < 10), we are able to set an upper limit of N(>0.5 km) ~ 2.47x10^10 deg^-2 at 95% confidence limit.

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Posts: 131433
Date:
Survey of the Trans-Neptunian Region
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In the framework of the key program "TNOs Are Cool: A Survey of the Trans-Neptunian Region," Herschel will reveal the physical properties of the poorly known objects orbiting beyond Neptune.
The Herschel Space Observatory, one of the cornerstone missions of the European Space Agency with participation from NASA, was launched successfully in May this year. Herschel is the only space facility ever developed to cover the far-infrared to submillimetre parts of the electromagnetic spectrum to capture the thermal radiation of celestial objects.
Herschel is set up to start this month the phase of science demonstration, and afterwards the phase of routine observations. Scientists are looking forward to these scientifically exciting data in the years to come, including observations of trans-Neptunian objects (TNOs).
The project "TNOs Are Cool: A Survey of the Trans-Neptunian Region," described at the 41st Annual Meeting of the American Astronomical Society's Division for Planetary Sciences in Fajardo, Puerto Rico, has been given one of the largest amounts of observing time (400 hours) in the worldwide call for open-time projects on the Herschel Space Observatory.

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