5,558 research outputs found
Direct Imaging of Multiple Planets Orbiting the Star HR 8799
Direct imaging of exoplanetary systems is a powerful technique that can
reveal Jupiter-like planets in wide orbits, can enable detailed
characterization of planetary atmospheres, and is a key step towards imaging
Earth-like planets. Imaging detections are challenging due to the combined
effect of small angular separation and large luminosity contrast between a
planet and its host star. High-contrast observations with the Keck and Gemini
telescopes have revealed three planets orbiting the star HR 8799, with
projected separations of 24, 38, and 68 astronomical units. Multi-epoch data
show counter-clockwise orbital motion for all three imaged planets. The low
luminosity of the companions and the estimated age of the system imply
planetary masses between 5 and 13 times that of Jupiter. This system resembles
a scaled-up version of the outer portion of our Solar System.Comment: 30 pages, 5 figures, Research Article published online in Science
Express Nov 13th, 200
Cross-language Wikipedia Editing of Okinawa, Japan
This article analyzes users who edit Wikipedia articles about Okinawa, Japan,
in English and Japanese. It finds these users are among the most active and
dedicated users in their primary languages, where they make many large,
high-quality edits. However, when these users edit in their non-primary
languages, they tend to make edits of a different type that are overall smaller
in size and more often restricted to the narrow set of articles that exist in
both languages. Design changes to motivate wider contributions from users in
their non-primary languages and to encourage multilingual users to transfer
more information across language divides are presented.Comment: In Proceedings of the SIGCHI Conference on Human Factors in Computing
Systems, CHI 2015. AC
Decay rate and other properties of the positronium negative ion
A new method for detecting the positronium minus ion is described, and the possibility of a long positronium mean free path in a solid is discussed
Two Extrasolar Asteroids with Low Volatile-Element Mass Fractions
Using ultraviolet spectra obtained with the Cosmic Origins Spectrograph on
the Hubble Space Telescope, we extend our previous ground-based optical
determinations of the composition of the extrasolar asteroids accreted onto two
white dwarfs, GD 40 and G241-6. Combining optical and ultraviolet spectra of
these stars with He-dominated atmospheres, 13 and 12 polluting elements are
confidently detected in GD 40 and G241-6, respectively. For the material
accreted onto GD 40, the volatile elements C and S are deficient by more than a
factor of 10 and N by at least a factor of 5 compared to their mass fractions
in primitive CI chondrites and approach what is inferred for bulk Earth. A
similar pattern is found for G241-6 except that S is undepleted. We have also
newly detected or placed meaningful upper limits for the amount of Cl, Al, P,
Ni and Cu in the accreted matter. Extending results from optical studies, the
mass fractions of refractory elements in the accreted parent bodies are similar
to what is measured for bulk Earth and chondrites. Thermal processing, perhaps
interior to a snow line, appears to be of central importance in determining the
elemental compositions of these particular extrasolar asteroids.Comment: 37 pages, 13 figures, 5 tables, ApJ, accepte
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