National Science Foundation

About: National Science Foundation is a government organization based out in Alexandria, Virginia, United States. It is known for research contribution in the topics: Galaxy & Population. The organization has 4729 authors who have published 6040 publications receiving 298150 citations. The organization is also known as: NSF & N.S.F..

Discovery of the First Retrograde Transneptunian Object

Abstract: We report the discovery of the first transneptunian object known to be on a retrograde orbit. The discovery was made during an outer solar system survey using the Canada–France–Hawaii Telescope (CFHT). After recovery observations on the MMT, CTIO-Blanco, Gemini-South, and CFHT telescopes, we can state with certainty that the object is both transneptunian and orbits the Sun in a retrograde sense, with an orbital inclination i = 104 deg. The object has IAU Minor Planet Center provisional designation 2008 KV42 and temporary nickname “Drac.” Numerical integration of a set of initial states consistent with the astrometry shows that the semimajor axis is a � 42 AU, the perihelion distance is q ∼21 AU, and that the object’s orbit evolves on ∼30 million year timescales via gravitational encounters with Uranus and Neptune. The object is unlikely to be primordial and thus needs a supply mechanism from a long-lived source. We outline several scenarios which could have emplaced the object on its current orbit, including a currently unobserved reservoir of large-inclination orbits beyond Neptune which may also supply the Halley-type comets.

Spectroscopy of Giants in LMC Clusters. III. Velocities and Abundances for NGC 1841 and Reticulum and the Properties of the Metal-Poor Clusters

Abstract: Velocities and metallicities for giant star members of the distant globular clusters Reticulum (C0435 -590) and NGC 1841 (C0444-840) based on spectroscopy with the CTIO Argus multi-fiber system show that these two clusters are likely members of the Large Magellanic Cloud (LMC). The velocity, [Fe/H] metallicity, and absolute visual magnitude for Reticulum are 241.5±1.5 km s −1 , −1.71, and −6.0±0,2, and for NGC 1841, 212.5±1.8 km s −1 , −2.11, and −7.9±0.2

Hubble Space Telescope Detection of Optical Companions of WR 86, WR 146, and WR 147: Wind Collision Model Confirmed

Abstract: Hubble Space Telescope (HST) Wide Field Planetary Camera 2 images of the rado-binary Wolf-Rayet stars WR 146 and WR 147, as well as the 02 visual binary WR 86, resolve each of them into two very close optical components. The colors of these optical pairs are similar, indicating that they are likely to be physically bound WR + OB systems at the same distance. Comparison of the locations of the optical components of WR 146 and WR 147 with high-resolution radio maps strikingly demonstrates that the nonthermal radio components arise between the optical binary components, closer to the OB component than the WR. This is as expected if the nonthermal radio emission results from the collision of the stellar winds of the binary components seen in the HST images. The similar magnitudes and colors determined for the components of WR 86 from our HST images, combined with an analysis of the unresolved, combined WC7 + OB optical spectrum, indicates an absolute magnitude for the WC7 component of about MV ~ -5.

Sampling With Synthesis: A New Approach for Releasing Public Use Census Microdata

Abstract: Many statistical agencies disseminate samples of census microdata, that is, data on individual records, to the public. Before releasing the microdata, agencies typically alter identifying or sensitive values to protect data subjects’ confidentiality, for example by coarsening, perturbing, or swapping data. These standard disclosure limitation techniques distort relationships and distributional features in the original data, especially when applied with high intensity. Furthermore, it can be difficult for analysts of the masked public use data to adjust inferences for the effects of the disclosure limitation. Motivated by these shortcomings, we propose an approach to census microdata dissemination called sampling with synthesis. The basic idea is to replace the identifying or sensitive values in the census with multiple imputations, and release samples from these multiply-imputed populations. We demonstrate that sampling with synthesis can improve the quality of public use data relative to sampling followe...