2,434 research outputs found

    Water/Icy Super-Earths: Giant Impacts and Maximum Water Content

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    Water-rich super-Earth exoplanets are expected to be common. We explore the effect of late giant impacts on the final bulk abundance of water in such planets. We present the results from smoothed particle hydrodynamics simulations of impacts between differentiated water(ice)-rock planets with masses between 0.5 and 5 M_Earth and projectile to target mass ratios from 1:1 to 1:4. We find that giant impacts between bodies of similar composition never decrease the bulk density of the target planet. If the commonly assumed maximum water fraction of 75wt% for bodies forming beyond the snow line is correct, giant impacts between similar composition bodies cannot serve as a mechanism for increasing the water fraction. Target planets either accrete materials in the same proportion, leaving the water fraction unchanged, or lose material from the water mantle, decreasing the water fraction. The criteria for catastrophic disruption of water-rock planets are similar to those found in previous work on super-Earths of terrestrial composition. Changes in bulk composition for giant impacts onto differentiated bodies of any composition (water-rock or rock-iron) are described by the same equations. These general laws can be incorporated into future N-body calculations of planet formation to track changes in composition from giant impacts.Comment: 9 pages, 4 figures, Accepted for publication in ApJ Letter

    Method of identifying clusters representing statistical dependencies in multivariate data

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    Approach is first to cluster and then to compute spatial boundaries for resulting clusters. Next step is to compute, from set of Monte Carlo samples obtained from scrambled data, estimates of probabilities of obtaining at least as many points within boundaries as were actually observed in original data

    Detection of Other Planetary Systems Using Photometry

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    Detection of extrasolar short-period planets, particularly if they are in the liquid-water zone, would be one of the most exciting discoveries of our lifetime. A well-planned space mission has the capability of making this discovery using the photometric method. An Earth-sized planet transiting a Sun-like star will cause a decrease in the apparent luminosity of the star by one part in 10,000 with a duration of about 12 hours and a period of about one year. Given a random orientation of orbital plane alignments with the line-of-sight to a star, and assuming our solar system to be typical, one would expect 1 percent of the stars monitored to exhibit planetary transits. A null result would also be significant and indicate that Earth-sized planets are rare. For the mission to be successful one needs a sensor system that can simultaneously monitor many thousands of stars with a photometric precision of one part in 30,000 per hour of integration. Confirmation of a detection will involve detection of a second transit that will yield a period and predict the time for a third and subsequent transits. The technology issues that need to be addressed are twofold: one is for an appropriate optical design; the other is for a detector system with the necessary photometric precision. Two candidates for the detector system are silicon diodes and CCD's

    A rigorous comparison of different planet detection algorithms

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    The idea of finding extrasolar planets (ESPs) through observations of drops in stellar brightness due to transiting objects has been around for decades. It has only been in the last ten years, however, that any serious attempts to find ESPs became practical. The discovery of a transiting planet around the star HD 209458 (Charbonneau et al. 2000) has led to a veritable explosion of research, because the photometric method is the only way to search a large number of stars for ESPs simultaneously with current technology. To this point, however, there has been limited research into the various techniques used to extract the subtle transit signals from noise, mainly brief summaries in various papers focused on publishing transit-like signatures in observations. The scheduled launches over the next few years of satellites whose primary or secondary science missions will be ESP discovery motivates a review and a comparative study of the various algorithms used to perform the transit identification, to determine rigorously and fairly which one is the most sensitive under which circumstances, to maximize the results of past, current, and future observational campaigns.Comment: Accepted for publications by Astronomy and Astrophysic

    Comparison of the Nimbus-4 BUV ozone data with the Ames two-dimensional model

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    A comparison is made of the first two years of Nimbus 4 backscattered ultraviolet (BUV) ozone measurements with the predictions of the Ames two dimensional model. The ozone observations used consist of the mixing ratio on the 1, 2, 5, and 10 mb pressure surfaces. The data are zone and time averaged to obtain seasonal means for 1970 and 1971 and are found to show strong and repeatable meridional and seasonal dependencies. The model used for comparison with the observations extends from 80 N to 80 S latitude and from altitudes of 0 to 60 km with 5 deg horizontal grid spacing and 2.5 km vertical grid spacing. Chemical reaction and photolysis rates are diurnally averaged and the photodissociation rates are corrected for the effects of scattering. The large altitude, latitude, and seasonal changes in the ozone data agree with the model predictions. Model predictions of the sensitivity of the comparisons to changes in the assumed mixing ratios of water vapor, odd nitrogen, and odd chlorine, as well as to changes in the ambient temperature and transport parameters are also shown

    Eastern Equine Encephalitis Virus

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    The phenomenon of the Dunajec River Gorge formation in the Pieniny Mts. in the narrative folklore, literature and the 19th century scientific views

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    The Dunajec River Gorge in the Pieniny Mts. is a landscape phenomenon on a European scale. For ages it has aroused people's curiosity and imagination. Highlanders have created a lot of legends and stories around it, especially about the miracles wrought by Saint Kinga (Cunegunda) of Poland. In the 19th century it became a place of artistic inspirations. The mystery of its origin intrigued scientists and researchers who created various theories on this topic. The Polish poet and geographer Wincenty Pol formulated a theory about the runoff of lacustrine water from the Orava-Podhale Depression and the formation of gorges draining its rivers. The most popular was a literary motif of the Polish king BolesŇāaw Chrobry, who cut the sword out of rock in the Pieniny Mts. and lowered the water of legendary lake around the Tatra Mts. The researchers suggest similar motifs in the legends of chivalry of the West, especially associated with the most famous French chivalric epic: The Song of Roland. The convergences between the archetypes identified in the mythologies of Indo-European peoples: ancient Greece, Kashmir and Nepal, and also ancient Chinese and American Indians (in Colombia in South America) are particularly interesting. This article is a synthesis and comparative analysis of the contents in narrative folklore, literary motifs and the 19th century scientific views. It is based on relevant literature, archival materials and makes a critical review of them

    Slave Law and the Politics of Resistance in the Early Atlantic World

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    Edward B. Rugemer substantially repositions the significance of the actions of the enslaved, by examining how slave rebellions (and more broadly, the behavior of enslaved people) shaped certain contours of slave law in Barbados, Jamaica, and South Carolina. He surveys how the political significance of slave resistance was reflected into the deliberation and writing of slave laws in the British Atlantic

    Planetary Transits Toward the Galactic Bulge

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    The primary difficulty with using transits to discover extrasolar planets is the low probability a planet has of transiting its parent star. One way of overcoming this difficulty is to search for transits in dense stellar fields, such as the Galactic bulge. Here I estimate the number of planets that might be detected from a monitoring campaign toward the bulge. A campaign lasting 10 nights on a 10 meter telescope (assuming 8 hours of observations per night and a 5'x5' field of view) would detect about 100 planets with radius \rp=1.5 \rjup, or about 30 planets with \rp=1.0 \rjup, if the frequency and distribution of planets in the bulge is similar to that in the solar neighborhood. Most of these planets will be discovered around stars just below the turn-off, i.e. slightly evolved G-dwarfs. Campaigns involving 1- or 4-m class telescopes are unlikely to discover any planets, unless there exists a substantial population of companions with \rp > 1.5 \rjup.Comment: 4 pages, 4 figures. Submitted to ApJ Letter
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