2,443 research outputs found

    International perspectives on validity in action research: introduction to the special issue

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    This special issue has its roots in a series of meetings at the annual EGOS conferences held between 2001 and 2007. The Action Research sub-theme at these annual meetings has attracted almost 200 papers from authors on every continent. A particular focus of the group has been the socio-economic approach to action research developed by Henri Savall and the ISEOR team which discusses what Savall describes as "Generic Contingencies” and a “qualimetrics research methodology” (2003). The meetings have drawn together a truly international grouping of researchers who share a common interest in working closely with the world of practice to “make a difference.

    Alien Registration- Dechene, Irene M. (Ashland, Aroostook County)

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    https://digitalmaine.com/alien_docs/27392/thumbnail.jp

    High-contrast imaging in the Hyades with snapshot LOCI

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    To image faint substellar companions obscured by the stellar halo and speckles, scattered light from the bright primary star must be removed in hardware or software. We apply the "locally-optimized combination of images" (LOCI) algorithm to 1-minute Keck Observatory snapshots of GKM dwarfs in the Hyades using source diversity to determine the most likely PSF. We obtain a mean contrast of 10^{-2} at 0.01", 10^{-4} at <1", and 10^{-5} at 5". New brown dwarf and low-mass stellar companions to Hyades primaries are found in a third of the 84 targeted systems. This campaign shows the efficacy of LOCI on snapshot imaging as well as on bright wide binaries with off-axis LOCI, reaching contrasts sufficient for imaging 625-Myr late-L/early-T dwarfs purely in post-processing.Comment: 12 pages, 12 figures, to appear in SPIE Astronomy 2012, paper 8447-16

    Astrometric Monitoring of the HR 8799 Planets: Orbit Constraints from Self-Consistent Measurements

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    We present new astrometric measurements from our ongoing monitoring campaign of the HR 8799 directly imaged planetary system. These new data points were obtained with NIRC2 on the W.M. Keck II 10 meter telescope between 2009 and 2014. In addition, we present updated astrometry from previously published observations in 2007 and 2008. All data were reduced using the SOSIE algorithm, which accounts for systematic biases present in previously published observations. This allows us to construct a self-consistent data set derived entirely from NIRC2 data alone. From this dataset, we detect acceleration for two of the planets (HR 8799b and e) at >>3σ\sigma. We also assess possible orbital parameters for each of the four planets independently. We find no statistically significant difference in the allowed inclinations of the planets. Fitting the astrometry while forcing coplanarity also returns χ2\chi^2 consistent to within 1σ\sigma of the best fit values, suggesting that if inclination offsets of \lesssim20o^{o} are present, they are not detectable with current data. Our orbital fits also favor low eccentricities, consistent with predictions from dynamical modeling. We also find period distributions consistent to within 1σ\sigma with a 1:2:4:8 resonance between all planets. This analysis demonstrates the importance of minimizing astrometric systematics when fitting for solutions to highly undersampled orbits.Comment: 18 pages, 11 figures. Accepted for publication in A

    Discovery of a 66 mas Ultracool Binary with Laser Guide Star Adaptive Optics

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    We present the discovery of 2MASS J21321145+1341584AB as a closely separated (0.066") very low-mass field dwarf binary resolved in the near-infrared by the Keck II Telescope using laser guide star adaptive optics. Physical association is deduced from the angular proximity of the components and constraints on their common proper motion. We have obtained a near-infrared spectrum of the binary and find that it is best described by an L5+/-0.5 primary and an L7.5+/-0.5 secondary. Model-dependent masses predict that the two components straddle the hydrogen burning limit threshold with the primary likely stellar and the secondary likely substellar. The properties of this sytem - close projected separation (1.8+/-0.3 AU) and near unity mass ratio - are consistent with previous results for very low-mass field binaries. The relatively short estimated orbital period of this system (~7-12 yr) makes it a good target for dynamical mass measurements. Interestingly, the system's angular separation is the tightest yet for any very low-mass binary published from a ground-based telescope and is the tightest binary discovered with laser guide star adaptive optics to date.Comment: 10 pages, 3 figures; accepted for publication to A
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