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Benson, J. A.

Overview
Works: 27 works in 30 publications in 1 language and 55 library holdings
Classifications: SD397.B53, 634.97527
Publication Timeline
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Publications about J. A Benson
Publications by J. A Benson
Most widely held works by J. A Benson
Black spruce in Saskatchewan by J. A Benson( Book )
2 editions published in 1973 in English and held by 12 libraries worldwide
Observations of a Geosynchronous Satellite with Optical Interferometry ( file )
2 editions published between 2008 and 2009 in English and held by 3 libraries worldwide
We report a tentative interferometric detection of an earth-orbiting artificial satellite using optical interferometry. We targeted four geosynchronous communications satellites with the Navy Prototype Optical Interferometer (NPOI) near Flagstaff, AZ, and obtained interferometric fringes on one of them, DIRECTV-9S. We used an east-west 15.9-meter baseline of the NPOI and took data in 16 spectral channels covering the 500-850 nm wavelength range. Observations took place during the "glint season" of 28 February to 3 March 2008, when the geometry of the solar panel arrays and the Sun's position creates glints as bright as 2nd magnitude of a few minutes' duration each night. We detected fringes on the satellite at approximately the 2 sigma level on 1 March at magnitude 4.5. Subsequent analysis shows that the fringe amplitudes are consistent with a size scale of 2 meters (50 nanoradians at GEO) in an east-west direction. This detection shows that interferometric detection of satellites at visual wavelengths is possible, and suggests that a multi-baseline interferometer array tailored to the angular size and brightness of geosynchronous satellites could lead to images of these satellites
From Fringes to the USNO Navy Prototype Optical Interferometer Astrometric Catalog ( Book )
1 edition published in 2010 in English and held by 2 libraries worldwide
We report progress on the United States Naval Observatory, Navy Prototype Optical Interferometer, Astrometric Catalog (UNAC). This catalog uses observations from eight astrometric observation runs (Jan. 2005 - Nov. 2009) at the Navy Prototype Optical Interferometer (NPOI). The goal of the first release of the UNAC is to provide an astrometric catalog of at least 100 bright (V < 6) stars with precise positions accurate to < 16 milliarcseconds. In this paper we report on some of the data processing methods used to obtain absolute astrometric positions from optical interferometer data. We also discuss plans for assessing the accuracy of our interferometrically derived absolute astrometric positions
NPOI: Recent Technology and Science ( file )
1 edition published in 2004 in English and held by 2 libraries worldwide
We describe recent science projects that the Navy Prototype Optical Interferometer (NPOI) scientific staff and collaborators are pursuing. Recent results from the wide angle astrometric program and imaging programs (rapid rotators, binaries and Be stars) will be summarized. We discuss some of the technology that enables the NPOI to operate routinely as an observatory astronomical instrument
The Circumstellar Envelope of Zeta Tauri through Optical Interferometry ( file )
1 edition published in 2004 in English and held by 2 libraries worldwide
We present optical interferometric observations of the Be star Zeta Tauri obtained using the Navy Prototype Optical Interferometer (NPOI). The multichannel capability of the NPOI allows a high-quality internal calibration of the squared visibilities corresponding to the H(alpha) emission from the circumstellar environment. The observations suggest a strong departure from circular symmetry and thus are described by an elliptical Gaussian model. We use a nonlinear least-squares fit to the data to obtain the likeliest parameters and the corresponding uncertainties are determined using a Monte Carlo simulation. We obtain 3.14 +/- 0.21 mas for the angular size of the major axis -62.3 deg +/- 4.4 deg for the position angle and 0.310 +/- 0.072 for the axial ratio. By comparing our results with those already in the literature we conclude that the model parameters describing the general characteristics of the circumstellar envelope of Zeta Tau appear to be stable on timescales of years. We also compare our results with the known parameters describing the binary nature of Zeta Tau and we conclude that the envelope surrounds only the primary component and is well within its Roche lobe
Constraining Disk Parameters of Be Stars Using Narrowband Halpha Interferometry With the Navy Prototype Optical Interferometer ( file )
1 edition published in 2006 in English and held by 2 libraries worldwide
Interferometric observations of two well-known Be stars, gamma Cas and phi Per, were collected and analyzed to determine the spatial characteristics of their circumstellar regions. The observations were obtained using the Navy Prototype Optical Interferometer equipped with custom-made narrowband filters. The filters isolate the H(alpha) emission line from the nearby continuum radiation, which results in an increased contrast between the interferometric signature due to the H(alpha)-emitting circumstellar region and the central star. Because the narrowband filters do not significantly attenuate the continuum radiation at wavelengths 50 nm or more away from the line, the interferometric signal in the H(alpha) channel is calibrated with respect to the continuum channels. The observations used in this study represent the highest spatial resolution measurements of the H -emitting regions of Be stars obtained to date. These observations allow us to demonstrate for the first time that the intensity distribution in the circumstellar region of a Be star cannot be represented by uniform disk or ringlike structures, whereas a Gaussian intensity distribution appears to be fully consistent with our observations
Resolving the Effects of Rotation in Altair with Long-Baseline Interferometry ( file )
1 edition published in 2006 in English and held by 2 libraries worldwide
We report the successful fitting of a Roche model, with a surface temperature gradient following the von Zeipel gravity darkening law, to observations of Altair made with the Navy Prototype Optical Interferometer. We confirm the claim by Ohishi et al. that Altair displays an asymmetric intensity distribution due to rotation, the first such detection in an isolated star. Instrumental effects due to the high visible flux of this first magnitude star appear to be the limiting factor in the accuracy of this fit, which nevertheless indicates that Altair is rotating at 0:90 +or- 0:02 of its breakup (angular) velocity. Our results are consistent with the apparent oblateness found by van Belle et al. and show that the true oblateness is significantly larger owing to an inclination of the rotational axis of ~64 degrees to the line of sight. Of particular interest, we conclude that instead of being substantially evolved as indicated by its classification, A7 IV V, Altair is only barely off the zero-age main sequence and represents a good example of the difficulties rotation can introduce in the interpretation of this part of the HR diagram
The Spatially Resolved H(alpha)-Emitting Wind Structure of P Cygni ( file )
1 edition published in 2010 in English and held by 2 libraries worldwide
High spatial resolution observations of the H(alpha)-emitting wind structure associated with the luminous blue variable star P Cygni were obtained with the Navy Prototype Optical Interferometer. These observations represent the most comprehensive interferometric data set on P Cyg to date. We demonstrate how the apparent size of the H(alpha)-emitting region of the wind structure of P Cyg compares between the 2005, 2007, and 2008 observing seasons and how this relates to the H(alpha) line spectroscopy. Using the data sets from 2005, 2007, and 2008 observing seasons, we fit a circularly symmetric Gaussian model to the interferometric signature from the H(alpha)-emitting wind structure of P Cyg. Based on our results, we conclude that the radial extent of the H(alpha)-emitting wind structure around P Cyg is stable at the 10% level. We also show how the radial distribution of the H(alpha) flux from the wind structure deviates from a Gaussian shape, whereas a two-component Gaussian model is sufficient to fully describe the H(alpha)-emitting region around P Cyg
First Observations with a Co-Phased Six-Station Optical Long-Baseline Array: Application to the Triple Star eta Virginis ( file )
1 edition published in 2003 in English and held by 2 libraries worldwide
We report on the first successful simultaneous combination of six independent optical telescopes in an interferometric array. This is double the number of independent telescopes and 5 times the number of independent baselines heretofore combined simultaneously. This was accomplished with the Navy Prototype Optical Interferometer at Lowell Observatory near Flagstaff Arizona. We describe the main technologies demonstrated including hybrid six-way beam combination nonredundant multiple optical path modulation for fringe separation and the fringe detection electronics. To test the arrays suitability for high- resolution stellar imaging we observed the hierarchical triple star eta Virginis and we present the first images resolving all three components. The orbital motions of these stars were followed during winter and spring of 2002. Preliminary astrometrically determined orbits of the two components in the close pair by reference to the tertiary were derived. This enabled the estimation of the mass ratio (1.27) of the components in the close pair. We also determined the relative orbital inclination to be 31 deg. Future work needed to improve the calibration of the data is discussed
The Navy Prototype Optical Interferometer: Recent Developments Since 2004 ( file )
1 edition published in 2006 in English and held by 2 libraries worldwide
The technical status of the Navy Prototype Optical Interferometer (NPOI) since the last SPIE meeting is summarized along with the current science programs. The instrument is operated in an automatic observational mode, obtaining over 10,000 stellar observations in the period, June 2004 through March 2006. The scientific program has been directed at astrometry, TPF candidate stars, binary stars and other interesting targets such as Be stars. A significant database of NPOI observations obtained in 1997-2004 is being analyzed for binaries and single stars such as rapid rotating stars: Altair and Vega
A Parameter Study of Classical Be Star Disk Models Constrained by Optical Interferometry ( file )
1 edition published in 2008 in English and held by 2 libraries worldwide
We have computed theoretical models of circumstellar disks for the classical Be stars kappa Dra, Beta Psc, and upsilon Cyg. Models were constructed using a non-LTE radiative transfer code developed by Sigut and Jones (2007), which incorporates a number of improvements over previous treatments of the disk thermal structure, including a realistic chemical composition. Our models are constrained by direct comparison with long-baseline optical interferometric observations of the H(alpha)-emitting regions and by contemporaneous H(alpha) line profiles. Detailed comparisons of our predictions with H(alpha) interferometry and spectroscopy place very tight constraints on the density distributions for these circumstellar disks
Disks Surrounding Massive Stars: When Computational Models are Confronted by Observations ( file )
1 edition published in 2010 in English and held by 2 libraries worldwide
Many massive stars are embedded within gaseous circumstellar matter; sometimes dust and molecules are also present. Though the disks are sometimes too small to be detected directly, this material can be detected in the spectrum of radiation we observe from the star. Often, the circumstellar material has a disk-like distribution, but the physical processes that form and maintain these disks are not well understood. Be stars are an example of rapidly rotating, hot stars, whose spectra at optical wavelengths show both hydrogen emission lines and, frequently, emission lines from singly ionized metals due to the presence of a disk. We have computed theoretical models of circumstellar disks for Be stars, using a non-LTE radiative transfer code which incorporates a number of improvements over previous treatments of the disk thermal structure, including a realistic chemical composition. These models can predict spectral line profiles and equivalent widths, spectral energy distributions, and continuum polarization. Models with accurate thermal structures and radiation fields are essential to interpreting observations correctly. These models can also predict images on the plane of the sky in important wavelengths and are therefore ideally suited for comparison with interferometric observations. I will demonstrate that our models can be constrained by direct comparison with optical interferometric observations for the H emitting region and by contemporaneous H line profiles. Detailed comparisons of our predictions with H interferometry and spectroscopy place very tight constraints on the model free parameters for these star-disks systems
Vega is a Rapidly Rotating Star ( file )
1 edition published in 2006 in English and held by 2 libraries worldwide
Vega, the second brightest star in the northern hemisphere, serves as a primary spectral type standard. Although its spectrum is dominated by broad hydrogen lines, the narrower lines of the heavy elements suggested slow to moderate rotation, giving confidence that the ground-based calibration of its visible spectrum could be safely extrapolated into the ultraviolet near-infrared (through atmosphere models), where it also serves as the primary photometric calibrator. But there have been problems: the star is too bright compared to its peers and it has unusually shaped absorption line profiles, leading some to suggest that it is a distorted, rapidly rotating star seen pole-on. Here we report optical interferometric observations that show that Vega has the asymmetric brightness distribution of the bright, slightly offset polar axis of a star rotating at 93 per cent of its breakup speed. In addition to explaining the unusual brightness and line shape peculiarities, this result leads to the prediction of an excess of near-infrared emission compared to the visible, in agreement with observations. The large temperature differences predicted across its surface call into question composition determinations, adding uncertainty to Vega's age and opening the possibility that its debris disk could be substantially older than previously thought
Oat Varieties For Idaho by Idaho Agricultural Experiment Station( Book )
2 editions published between 1974 and 1977 in English and held by 2 libraries worldwide
Navy Prototype Optical Interferometer Imaging of Line Emission Regions of Beta Lyrae Using Differential Phase Referencing ( Book )
1 edition published in 2009 in English and held by 2 libraries worldwide
We present the results of an experiment to image the interacting binary star Beta Lyrae with data from the Navy Prototype Optical Interferometer using a differential phase technique to correct for the effects of the instrument and atmosphere on the interferometer phases. We take advantage of the fact that the visual primary of Beta Lyrae and the visibility calibrator we used are both nearly unresolved and nearly centrally symmetric, and consequently have interferometric phases near zero. We used this property to correct for the effects of the instrument and atmosphere on the phases of Beta Lyrae and to obtain differential phases in the channel containing the H alpha emission line. Combining the H alpha-channel phases with information about the line strength, we recovered complex visibilities and imaged the H alpha emission using standard radio interferometry methods. Our images show the position of the H alpha-emitting regions relative to the continuum photocenter as a function of orbital phase, indicating a major axis line of nodes along Omega = 249 degrees +/- 4 degrees. The orbit is smaller than previously predicted, a discrepancy that can be alleviated if we assume that the system is at a larger distance, or if the stellar continuum contribution to the H alpha channel was underestimated. We do not detect a jet in the H alpha images, which may be due to the limited resolution of the observations along the direction perpendicular to the orbital plane. We find that the differential phase results are consistent with those obtained from a more standard analysis using squared visibilities (V(exp 2)s) and closure phases, which also indicate an H alpha disk radius of 0.6 +/- 0.1 mas, and V = 1.30 +/- 0.1 and R = 1.20 +/- 0.1 mag for the magnitude difference between the stars
Strawberry production in the Idaho Panhandle by James A Benson( Book )
1 edition published in 1975 in English and held by 1 library worldwide
A servo controller for pneumatic cylinders by J. A Marchant( Book )
1 edition published in 1988 in English and held by 1 library worldwide
A Study of the Angular Diameters of Dust Shells Around Red Giants ( Book )
1 edition published in 1991 in English and held by 1 library worldwide
A summary of observations of the angular diameters of the shells around evolved red giants is reported. Many of these sources are partially resolved with a ground-based 2.4-m telescope. We have concentrated our efforts in the 8 - 13 micron spectral range because this corresponds to the emission excesses observed in the spectra of oxygen-rich stars. These excesses are commonly thought to arise from small 'silicate' mineral grains in the circumstellar shells. The shell structure has been fully resolved for the bright supergiant alpha Orionis. A study of the results shows that the opacity of the silicate mineral grains around that star is similar to that inferred for other evolved stars and for the Trapezium
Safflower - a Potential Crop For Northern Idaho by Idaho Agricultural Experiment Station( Book )
1 edition published in 1978 in English and held by 1 library worldwide
 
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