Correlated and Zonal Errors of Global Astrometric Missions: A Spherical Harmonic Solution

NASA Astrophysics Data System (ADS)

Makarov, V. V.; Dorland, B. N.; Gaume, R. A.; Hennessy, G. S.; Berghea, C. T.; Dudik, R. P.; Schmitt, H. R.

2012-07-01

We propose a computer-efficient and accurate method of estimating spatially correlated errors in astrometric positions, parallaxes, and proper motions obtained by space- and ground-based astrometry missions. In our method, the simulated observational equations are set up and solved for the coefficients of scalar and vector spherical harmonics representing the output errors rather than for individual objects in the output catalog. Both accidental and systematic correlated errors of astrometric parameters can be accurately estimated. The method is demonstrated on the example of the JMAPS mission, but can be used for other projects in space astrometry, such as SIM or JASMINE.

Implementing the Gaia Astrometric Global Iterative Solution (AGIS) in Java

NASA Astrophysics Data System (ADS)

O'Mullane, William; Lammers, Uwe; Lindegren, Lennart; Hernandez, Jose; Hobbs, David

2011-10-01

This paper provides a description of the Java software framework which has been constructed to run the Astrometric Global Iterative Solution for the Gaia mission. This is the mathematical framework to provide the rigid reference frame for Gaia observations from the Gaia data itself. This process makes Gaia a self calibrated, and input catalogue independent, mission. The framework is highly distributed typically running on a cluster of machines with a database back end. All code is written in the Java language. We describe the overall architecture and some of the details of the implementation.

LSST Astrometric Science

NASA Astrophysics Data System (ADS)

Saha, A.; Monet, D.

2005-12-01

Continued acquisition and analysis for short-exposure observations support the preliminary conclusion presented by Monet et al. (BAAS v36, p1531, 2004) that a 10-second exposure in 1.0-arcsecond seeing can provide a differential astrometric accuracy of about 10 milliarcseconds. A single solution for mapping coefficients appears to be valid over spatial scales of up to 10 arcminutes, and this suggests that numerical processing can proceed on a per-sensor basis without the need to further divide the individual fields of view into several astrometric patches. Data from the Subaru public archive as well as from the LSST Cerro Pachon 2005 observing campaign and various CTIO and NOAO 4-meter engineering runs have been considered. Should these results be confirmed, the expected astrometric accuracy after 10 years of LSST observations should be around 1.0 milliarcseconds for parallax and 0.2 milliarcseconds/year for proper motions.

CCD Astrometry of the Four Components of STF 1088

NASA Astrophysics Data System (ADS)

Martin, Stuart; Daclison, Linsey; Ramos, Cathrina; Castaneda, Diana; Genet, Russell; Mohanan, Kakkala; Carro, Joseph M.

2016-01-01

Fifty CCD astrometric measurements were made of the separations and position angles of the AB, AC, AD, and AE components of STF 1088. Longer integration times provided more stars in the astrometric solution which may have significantly improved the precision of the measurements. The precision of the measurements did not appear to be a function of component separation, although the smallest separation (that of STF 1088 AB) was only 11".

New Geometric-distortion Solution for STIS FUV-MAMA

NASA Astrophysics Data System (ADS)

Sohn, S. Tony

2018-04-01

We derived a new geometric distortion solution for the STIS FUV-MAMA detector. To do this, positions of stars in 89 FUV-MAMA observations of NGC 6681 were compared to an astrometric standard catalog created using WFC3/UVIS imaging data to derive a fourth-order polynomial solution that transforms raw (x, y) positions to geometrically- corrected (x, y) positions. When compared to astrometric catalog positions, the FUV- MAMA position measurements based on the IDCTAB showed residuals with an RMS of ∼ 30 mas in each coordinate. Using the new IDCTAB, the RMS is reduced to ∼ 4 mas, or 0.16 FUV-MAMA pixels, in each coordinate. The updated IDCTAB is now being used in the HST STIS pipeline to process all STIS FUV-MAMA images.

Combining and Comparing Astrometric Data from Different Epochs: A Case Study with Hipparcos and Nano-JASMINE

NASA Astrophysics Data System (ADS)

Michalik, D.; Lindegren, L.; Hobbs, D.; Lammers, U.; Yamada, Y.

2012-09-01

The Hipparcos mission (1989-1993) resulted in the first space-based stellar catalogue including measurements of positions, parallaxes and annual proper motions accurate to about one milli-arcsecond. More space astrometry missions will follow in the near future. The ultra-small Japanese mission Nano-JASMINE (launch in late 2013) will determine positions and annual proper motions with some milli-arcsecond accuracy. In mid 2013 the next-generation ESA mission Gaia will deliver some tens of micro-arcsecond accurate astrometric parameters. Until the final Gaia catalogue is published in early 2020 the best way of improving proper motion values is the combination of positions from different missions separated by long time intervals. Rather than comparing positions from separately reduced catalogues, we propose an optimal method to combine the information from the different data sets by making a joint astrometric solution. This allows to obtain good results even when each data set alone is insufficient for an accurate reduction. We demonstrate our method by combining Hipparcos and simulated Nano-JASMINE data in a joint solution. We show a significant improvement over the conventional catalogue combination.

The Future of Astrometric Education

NASA Astrophysics Data System (ADS)

van Altena, W.; Stavinschi, M.

2005-10-01

Astrometry is poised to enter an era of unparalleled growth and relevance due to the wealth of highly accurate data expected from the SIM and GAIA space missions. Innovative ground-based telescopes, such as the LSST, are planned which will provide less precise data, but for many more stars. The potential for studies of the structure, kinematics and dynamics of our Galaxy as well as for the physical nature of stars and the cosmological distance scale is without equal in the history of astronomy. It is therefore ironic that in two years not one course in astrometry will be taught in the US, leaving all astrometric education to Europe, China and Latin America. Who will ensure the astrometric quality control for the JWT, SIM, GAIA, LSST, to say nothing about the current large ground-based facilities, such as the VLT, Gemini, Keck, NOAO, Magellan, LBT, etc.? Hipparcos and the HST were astrometric successes due only to the dedicated work of specialists in astrometry who fought to maintain the astrometric characteristics of those satellites and their data pipelines. We propose a renewal of astrometric education in the universities to prepare qualified scientists so that the scientific returns from the investment of billions of dollars in these unique facilities will be maximized. The funding agencies are providing outstanding facilities. The universities, national and international observatories and agencies should acknowledge their responsibility to hire qualified full-time astrometric scientists to teach students, and to supervise existing and planned astronomical facilities so that quality data will be obtained and analyzed. A temporary solution to this problem is proposed in the form of a series of international summer schools in Astrometry. The Michelson Science Center of the SIM project has offered to hold an astrometry summer school in 2005 to begin this process. A one-semester syllabus is suggested as a means of meeting the needs of Astronomy by educating students in astrometric techniques that might be most valuable for careers associated with modern astrophysics.

Potential Refinement of the ICRF

NASA Technical Reports Server (NTRS)

Ma, Chopo

2003-01-01

The analysis and data used for the ICRF represented the state of the art in global, extragalactic, X/S band microwave astrometry in 1995. The same general analysis method was used to extend the ICRF with subsequent VLBI data in a manner consistent with the original catalog. Since 1995 there have been considerable advances in the geodetic/astrometric VLBI data set and in the analysis that would significantly improve the systematic errors, stability, and density of the next realization of the ICRS when the decision is made to take this step. In particular, data acquired since 1990, including extensive use of the VLBA, are of higher quality and astrometric utility because of changes in instrumentation, schedule design, and networks as well as specifically astrometric intent. The IVS (International VLBI Service for Geodesy and Astrometry) continues to devote a portion of its observing capability to systematic extension of the astrometric data set. Sufficient data distribution exists to select a better set of defining sources. Improvements in troposphere modeling will minimize known systematic astrometric errors while accurate modeling and estimation of station effects from loading and nonlinear motions will permit the reintegration of the celestial reference frame, terrestrial reference frame and Earth orientation parameters though a single VLBI solution. The differences between the current ICRF and the potential next realization will be described.

Little Stars Don't Like Big Planets: An Astrometric Search for Super-Jupiters Around Red Dwarfs

NASA Astrophysics Data System (ADS)

Lurie, John C.; Henry, T. J.; Jao, W.; Koerner, D. W.; Riedel, A. R.; Subasavage, J.; RECONS

2013-01-01

The astrometric detection and characterization of extrasolar planets presents considerable technical challenges, but also promises to greatly enhance our understanding of these systems. Nearly all currently confirmed exoplanets have been discovered using transit or radial velocity techniques. The former is geometrically biased towards planets with small orbits, while the latter is biased towards massive planets with short periods that exert large gravitational accelerations on their host stars. Astrometric techniques are limited by the minimum detectable perturbation of a star's position due to a planet, but allow for the determination of orbit inclination and an accurate planetary mass. Here we present astrometric solutions for five nearby stars with known planets: four M dwarfs (GJ 317, GJ 581, GJ 849, and GJ 1214) and one K dwarf (BD -10 3166). Observations have baselines of three to thirteen years, and were made using the 0.9 m telescope at CTIO as part of the RECONS long-term astrometry program. We provide improved parallaxes for the stars and find that there are no planets of several Jupiter masses or brown dwarfs orbiting these stars with periods up to twice the length of the astrometric coverage. In the broader context, these results are consistent with the paucity of super-Jupiter and brown dwarf companions we find among the roughly 200 red dwarfs searched in our astrometric program. This effort has been supported by the National Science Foundation via grant AST 09-08402 and the long-term cooperative efforts of the National Optical Astronomy Observatories and the members of the SMARTS Consortium.

The M 4 Core Project with HST - V. Characterizing the PSFs of WFC3/UVIS by focus★

NASA Astrophysics Data System (ADS)

Anderson, J.; Bedin, L. R.

2017-09-01

As part of the astrometric Hubble Space Telescope (HST) large program GO-12911, we conduct an in-depth study to characterize the point spread function (PSF) of the Uv-VISual channel of the Wide Field Camera 3 (WFC3), as a necessary step to achieve the astrometric goals of the program. We extracted a PSF from each of the 589 deep exposures taken through the F467M filter over the course of a year and find that the vast majority of the PSFs lie along a 1-D locus that stretches continuously from one side of focus, through optimal focus, to the other side of focus. We constructed a focus-diverse set of PSFs and find that with only five medium-bright stars in an exposure it is possible to pin down the focus level of that exposure. We show that the focus-optimized PSF does a considerably better job fitting stars than the average 'library' PSF, especially when the PSF is out of focus. The fluxes and positions are significantly improved over the 'library' PSF treatment. These results are beneficial for a much broader range of scientific applications than simply the program at hand, but the immediate use of these PSFs will enable us to search for astrometric wobble in the bright stars in the core of the globular cluster M 4, which would indicate a dark, high-mass companion, such as a white dwarf, neutron star or black hole.

Fizeau interferometry from space: a challenging frontier in global astrometry

NASA Astrophysics Data System (ADS)

Loreggia, Davide; Gardiol, Daniele; Gai, Mario; Lattanzi, Mario G.; Busonero, Deborah

2004-10-01

The design and performance of a Fizeau interferometer with long focal length and large field of view are discussed. The optical scheme presented is well suited for very accurate astrometric measurements from space, being optimised, in terms of geometry and aberrations, to observe astronomical targets down to the visual magnitude mV=20, with a measurement accuracy of 10 microarcseconds at mV=15. This study is in the context of the next generation astrometric space missions, in particular for a mission profile similar to that of the Gaia mission of the European Space Agency. Beyond the accuracy goal, the great effort in optical aberrations reduction, particularly distortion, aims at the optimal exploitation of data acquisition done with CCD arrays working in Time Delay Integration mode. The design solution we present reaches the astrometric goals with a field of view of 0.5 square degrees.

Preliminary Astrometric Results from the PS1 Demo Month and Routine Survey Operations

DTIC Science & Technology

2010-09-01

with the  2MASS  catalog 3 to  produce preliminary astrometric solutions.  Using these  coordinates, the NOFS astrometric pipeline correlates PS1...objects with other catalogs (USNO‐B1.0, SDSS, Tycho‐2,  2MASS , etc.) so that unique star identification numbers can  be assigned across all catalogs. This...correlated  pair, and the standard deviation for these pairings is about  0.3 arcsec.  Whereas the  2MASS  catalog error for a brighter  star is believed to be

A predicted astrometric microlensing event by a nearby white dwarf

NASA Astrophysics Data System (ADS)

McGill, Peter; Smith, Leigh C.; Evans, N. Wyn; Belokurov, Vasily; Smart, R. L.

2018-07-01

We used the Tycho-Gaia Astrometric Solution catalogue, part of Gaia Data Release 1, to search for candidate astrometric microlensing events expected to occur within the remaining lifetime of the Gaia satellite. Our search yielded one promising candidate. We predict that the nearby DQ type white dwarf LAWD 37 (WD 1142-645) will lens a background star and will reach closest approach on 2019 November 11 (±4 d) with impact parameter 380 ± 10 mas. This will produce an apparent maximum deviation of the source position of 2.8 ± 0.1 mas. In the most propitious circumstance, Gaia will be able to determine the mass of LAWD 37 to {˜ }3 per cent. This mass determination will provide an independent check on atmospheric models of white dwarfs with helium rich atmospheres, as well as tests of white dwarf mass radius relationships and evolutionary theory.

A Predicted Astrometric Microlensing Event by a Nearby White Dwarf

NASA Astrophysics Data System (ADS)

McGill, Peter; Smith, Leigh C.; Wyn Evans, N.; Belokurov, Vasily; Smart, R. L.

2018-04-01

We used the Tycho-Gaia Astrometric Solution catalogue, part of Gaia Data Release 1, to search for candidate astrometric microlensing events expected to occur within the remaining lifetime of the Gaia satellite. Our search yielded one promising candidate. We predict that the nearby DQ type white dwarf LAWD 37 (WD 1142-645) will lens a background star and will reach closest approach on November 11th 2019 (± 4 days) with impact parameter 380 ± 10 mas. This will produce an apparent maximum deviation of the source position of 2.8 ± 0.1 mas. In the most propitious circumstance, Gaia will be able to determine the mass of LAWD 37 to ˜3%. This mass determination will provide an independent check on atmospheric models of white dwarfs with helium rich atmospheres, as well as tests of white dwarf mass radius relationships and evolutionary theory.

A SEARCH FOR STELLAR-MASS BLACK HOLES VIA ASTROMETRIC MICROLENSING

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lu, J. R.; Sinukoff, E.; Ofek, E. O.

While dozens of stellar-mass black holes (BHs) have been discovered in binary systems, isolated BHs have eluded detection. Their presence can be inferred when they lens light from a background star. We attempt to detect the astrometric lensing signatures of three photometrically identified microlensing events, OGLE-2011-BLG-0022, OGLE-2011-BLG-0125, and OGLE-2012-BLG-0169 (OB110022, OB110125, and OB120169), located toward the Galactic Bulge. These events were selected because of their long durations, which statistically favors more massive lenses. Astrometric measurements were made over one to two years using laser-guided adaptive optics observations from the W. M. Keck Observatory. Lens model parameters were first constrained bymore » the photometric light curves. The OB120169 light curve is well fit by a single-lens model, while both OB110022 and OB110125 light curves favor binary lens models. Using the photometric fits as prior information, no significant astrometric lensing signal was detected and all targets were consistent with linear motion. The significant lack of astrometric signal constrains the lens mass of OB110022 to 0.05–1.79 M {sub ⊙} in a 99.7% confidence interval, which disfavors a BH lens. Fits to OB110125 yielded a reduced Einstein crossing time and insufficient observations during the peak, so no mass limits were obtained. Two degenerate solutions exist for OB120169, which have a lens mass between 0.2–38.8 M {sub ⊙} and 0.4–39.8 M {sub ⊙} for a 99.7% confidence interval. Follow-up observations of OB120169 will further constrain the lens mass. Based on our experience, we use simulations to design optimal astrometric observing strategies and show that with more typical observing conditions the detection of BHs is feasible.« less

Reduction of astrometric plates

NASA Technical Reports Server (NTRS)

Stock, J.

1984-01-01

A rapid and accurate method for the reduction of comet or asteroid plates is described. Projection equations, scale length correction, rotation of coordinates, linearization, the search for additional reference stars, and the final solution are examined.

Toward the ICRF3: Astrometric Comparison of the USNO 2016A VLBI Solution with ICRF2 and Gaia DR1

NASA Astrophysics Data System (ADS)

Frouard, Julien; Johnson, Megan C.; Fey, Alan; Makarov, Valeri V.; Dorland, Bryan N.

2018-06-01

The VLBI USNO 2016A (U16A) solution is part of a work-in-progress effort by USNO toward the preparation of the ICRF3. Most of the astrometric improvement with respect to the ICRF2 is due to the re-observation of the VCS sources. Our objective in this paper is to assess U16A’s astrometry. A comparison with ICRF2 shows statistically significant offsets of size 0.1 mas between the two solutions. While Gaia DR1 positions are not precise enough to resolve these offsets, they are found to be significantly closer to U16A than ICRF2. In particular, the trend for typically larger errors for southern sources in VLBI solutions is decreased in U16A. Overall, the VLBI-Gaia offsets are reduced by 21%. The U16A list includes 718 sources not previously included in ICRF2. Twenty of those new sources have statistically significant radio-optical offsets. In two-thirds of the cases, these offsets can be explained from PanSTARRS images.

Tycho- Gaia Astrometric Solution Parallaxes and Proper Motions for Five Galactic Globular Clusters

DOE Office of Scientific and Technical Information (OSTI.GOV)

Watkins, Laura L.; Van der Marel, Roeland P., E-mail: lwatkins@stsci.edu

2017-04-20

We present a pilot study of Galactic globular cluster (GC) proper motion (PM) determinations using Gaia data. We search for GC stars in the Tycho- Gaia Astrometric Solution (TGAS) catalog from Gaia Data Release 1 (DR1), and identify five members of NGC 104 (47 Tucanae), one member of NGC 5272 (M3), five members of NGC 6121 (M4), seven members of NGC 6397, and two members of NGC 6656 (M22). By taking a weighted average of member stars, fully accounting for the correlations between parameters, we estimate the parallax (and, hence, distance) and PM of the GCs. This provides a homogeneousmore » PM study of multiple GCs based on an astrometric catalog with small and well-controlled systematic errors and yields random PM errors similar to existing measurements. Detailed comparison to the available Hubble Space Telescope ( HST ) measurements generally shows excellent agreement, validating the astrometric quality of both TGAS and HST . By contrast, comparison to ground-based measurements shows that some of those must have systematic errors exceeding the random errors. Our parallax estimates have uncertainties an order of magnitude larger than previous studies, but nevertheless imply distances consistent with previous estimates. By combining our PM measurements with literature positions, distances, and radial velocities, we measure Galactocentric space motions for the clusters and find that these also agree well with previous analyses. Our analysis provides a framework for determining more accurate distances and PMs of Galactic GCs using future Gaia data releases. This will provide crucial constraints on the near end of the cosmic distance ladder and provide accurate GC orbital histories.« less

Astrometric and Photometric Analysis of the September 2008 ATV-1 Re-Entry Event

NASA Technical Reports Server (NTRS)

Mulrooney, Mark K.; Barker, Edwin S.; Maley, Paul D.; Beaulieu, Kevin R.; Stokely, Christopher L.

2008-01-01

NASA utilized Image Intensified Video Cameras for ATV data acquisition from a jet flying at 12.8 km. Afterwards the video was digitized and then analyzed with a modified commercial software package, Image Systems Trackeye. Astrometric results were limited by saturation, plate scale, and imposed linear plate solution based on field reference stars. Time-dependent fragment angular trajectories, velocities, accelerations, and luminosities were derived in each video segment. It was evident that individual fragments behave differently. Photometric accuracy was insufficient to confidently assess correlations between luminosity and fragment spatial behavior (velocity, deceleration). Use of high resolution digital video cameras in future should remedy this shortcoming.

The overture to a new era in Galactic science: Gaia's first data release

NASA Astrophysics Data System (ADS)

Altmann, M.; Bouquillon, S.

2018-01-01

Less than 3 years after ESA's ambitious astrometric space mission, Gaia, had been launched, the first data release (Gaia DR1) appeared in September 2016. The largest part of the Gaia DR1 is a catalogue of positions and broad band photometry for 1143 million stars - of greater scientific relevance will however be the Tycho Gaia Astrometric Solution (TGAS), which includes significantly improved full 5-parameter astrometry for the 2 million Hipparcos and Tycho2 stars. I will report on this release demonstrating its scientific potential with examples, as well as giving an outlook on the upcoming release, which will then include all 5 parameters for all Gaia stars.

Astrometric detectability of systems with unseen companions: effects of the Earth orbital motion

NASA Astrophysics Data System (ADS)

Butkevich, Alexey G.

2018-06-01

The astrometric detection of an unseen companion is based on an analysis of the apparent motion of its host star around the system's barycentre. Systems with an orbital period close to 1 yr may escape detection if the orbital motion of their host stars is observationally indistinguishable from the effects of parallax. Additionally, an astrometric solution may produce a biased parallax estimation for such systems. We examine the effects of the orbital motion of the Earth on astrometric detectability in terms of a correlation between the Earth's orbital position and the position of the star relative to its system barycentre. The χ2 statistic for parallax estimation is calculated analytically, leading to expressions that relate the decrease in detectability and accompanying parallax bias to the position correlation function. The impact of the Earth's motion critically depends on the exoplanet's orbital period, diminishing rapidly as the period deviates from 1 yr. Selection effects against 1-yr-period systems is, therefore, expected. Statistical estimation shows that the corresponding loss of sensitivity results in a typical 10 per cent increase in the detection threshold. Consideration of eccentric orbits shows that the Earth's motion has no effect on detectability for e≳ 0.5. The dependence of the detectability on other parameters, such as orbital phases and inclination of the orbital plane to the ecliptic, are smooth and monotonic because they are described by simple trigonometric functions.

The research of the accuracy of asteroid orbit fitting using both radar and astrometric observations. (Russian Title: Исследование точности решения задачи улучшения орбит астероидов по данным их радарных и угловых наблюдений)

NASA Astrophysics Data System (ADS)

Baturin, A. P.; Kinzersky, V. V.

2014-12-01

The least-square orbit fitting problem for asteroids using their radar and astrometric observations has been considered. The both types of radar observations have been taken into account: the time delay observations and the Doppler observations. The research of accuracy increase due to the using of radar observations in addition to astrometric ones has been carried out. This research has been done by means of several orbit fittings using different samples of observations of some asteroids. The samples contain all radar observations and different numbers of astrometric ones. The orbit arc of radar observations of chosen asteroids is very short (several days) while the arcs of astrometric observations for all used samples are much longer. It has been demonstrated that the using of radar observations in the orbit fitting may increase the accuracy of obtained solution by 1-3 orders even in the cases of very long astromeric arcs (several years). During the research the convenient windows-interface for the calculating program has been developed. The functions of the program also have been expanded. Particularly, the ability of perturbations calculation from different planet ephemerides and of calculations with different machine precision have been added to the program.

Astrometric Calibration and Performance of the Dark Energy Camera

DOE PAGES

Bernstein, G. M.; Armstrong, R.; Plazas, A. A.; ...

2017-05-30

We characterize the ability of the Dark Energy Camera (DECam) to perform relative astrometry across its 500 Mpix, 3more » $deg^2$ science field of view, and across 4 years of operation. This is done using internal comparisons of $~ 4 x 10^7$ measurements of high-S/N stellar images obtained in repeat visits to fields of moderate stellar density, with the telescope dithered to move the sources around the array. An empirical astrometric model includes terms for: optical distortions; stray electric fields in the CCD detectors; chromatic terms in the instrumental and atmospheric optics; shifts in CCD relative positions of up to $$\\approx 10 \\mu m$$ when the DECam temperature cycles; and low-order distortions to each exposure from changes in atmospheric refraction and telescope alignment. Errors in this astrometric model are dominated by stochastic variations with typical amplitudes of 10-30 mas (in a 30 s exposure) and $$5^{\\prime}-10^{\\prime}$$ arcmin coherence length, plausibly attributed to Kolmogorov-spectrum atmospheric turbulence. The size of these atmospheric distortions is not closely related to the seeing. Given an astrometric reference catalog at density $$\\approx 0.7$$ $$arcmin^{-2}$$, e.g. from Gaia, the typical atmospheric distortions can be interpolated to $$\\approx$$ 7 mas RMS accuracy (for 30 s exposures) with $$1^{\\prime}$$ arcmin coherence length for residual errors. Remaining detectable error contributors are 2-4 mas RMS from unmodelled stray electric fields in the devices, and another 2-4 mas RMS from focal plane shifts between camera thermal cycles. Thus the astrometric solution for a single DECam exposure is accurate to 3-6 mas ( $$\\approx$$ 0.02 pixels, or $$\\approx$$ 300 nm) on the focal plane, plus the stochastic atmospheric distortion.« less

ROTATING STARS FROM KEPLER OBSERVED WITH GAIA DR1

DOE Office of Scientific and Technical Information (OSTI.GOV)

Davenport, James R. A.

2017-01-20

Astrometric data from the recent Gaia Data Release 1 have been matched against the sample of stars from Kepler with known rotation periods. A total of 1299 bright rotating stars were recovered from the subset of Gaia sources with good astrometric solutions, most with temperatures above 5000 K. From these sources, 894 were selected as lying near the main sequence using their absolute G -band magnitudes. These main-sequence stars show a bimodality in their rotation period distribution, centered roughly around a 600 Myr rotation isochrone. This feature matches the bimodal period distribution found in cooler stars with Kepler , butmore » was previously undetected for solar-type stars due to sample contamination by subgiants. A tenuous connection between the rotation period and total proper motion is found, suggesting that the period bimodality is due to the age distribution of stars within ∼300 pc of the Sun, rather than a phase of rapid angular momentum loss. This work emphasizes the unique power for understanding stellar populations that is created by combining temporal monitoring from Kepler with astrometric data from Gaia .« less

Astrometric and Photometric Follow-Up of Faint Near Earth Objects

NASA Technical Reports Server (NTRS)

Spahr, Timothy

2004-01-01

During the last year, the Near-Earth Object (NEO) follow-up program at Mt. Hopkins funded by the Near-Earth Object Observations (NEOO) program continued to improve. The Principal Investigator was again granted all the requested observing time. In addition to the requested time on the 4 8 in. telescope, 2 nights were also granted on the MMT for observations of extremely faint main-belt asteroids and NEOs. It is expected that the MMT can easily reach V = 25 over a 24 X 24 arcminute field of view. Improvements in the last year included more tweaks to the automatic astrometric routine for higher-quality astrometric fits. Use of the new USNO-B1.0 reference catalog has allowed the PI to push the average RMS of reference star solutions below 0.2 in.. Shift-and- stack techniques are used to improve the signal-to-noise ratio of the target objects. The 48 in. telescope at Mt. Hopkins is completely automated, and can be run remotely from either the Principal Investigator's office at SAO, or even his study at home. Most observing runs are now done remotely.

Improving distance estimates to nearby bright stars: Combining astrometric data from Hipparcos, Nano-JASMINE and Gaia

NASA Astrophysics Data System (ADS)

Michalik, Daniel; Lindegren, Lennart; Hobbs, David; Lammers, Uwe; Yamada, Yoshiyuki

2013-02-01

Starting in 2013, Gaia will deliver highly accurate astrometric data, which eventually will supersede most other stellar catalogues in accuracy and completeness. It is, however, limited to observations from magnitude 6 to 20 and will therefore not include the brightest stars. Nano-JASMINE, an ultrasmall Japanese astrometry satellite, will observe these bright stars, but with much lower accuracy. Hence, the Hipparcos catalogue from 1997 will likely remain the main source of accurate distances to bright nearby stars. We are investigating how this might be improved by optimally combining data from all three missions through a joint astrometric solution. This would take advantage of the unique features of each mission: the historic bright-star measurements of Hipparcos, the updated bright-star observations of Nano-JASMINE, and the very accurate reference frame of Gaia. The long temporal baseline between the missions provides additional benefits for the determination of proper motions and binary detection, which indirectly improve the parallax determination further. We present a quantitative analysis of the expected gains based on simulated data for all three missions.

Application of time transfer functions to Gaia's global astrometry. Validation on DPAC simulated Gaia-like observations

NASA Astrophysics Data System (ADS)

Bertone, Stefano; Vecchiato, Alberto; Bucciarelli, Beatrice; Crosta, Mariateresa; Lattanzi, Mario G.; Bianchi, Luca; Angonin, Marie-Christine; Le Poncin-Lafitte, Christophe

2017-12-01

Context. A key objective of the ESA Gaia satellite is the realization of a quasi-inertial reference frame at visual wavelengths by means of global astrometric techniques. This requires accurate mathematical and numerical modeling of relativistic light propagation, as well as double-blind-like procedures for the internal validation of the results, before they are released to the scientific community at large. Aims: We aim to specialize the time transfer functions (TTF) formalism to the case of the Gaia observer and prove its applicability to the task of global sphere reconstruction (GSR), in anticipation of its inclusion in the GSR system, already featuring the Relativistic Astrometric MODel (RAMOD) suite, as an additional semi-external validation of the forthcoming Gaia baseline astrometric solutions. Methods: We extended the current GSR framework and software infrastructure (GSR2) to include TTF relativistic observation equations compatible with Gaia's operations. We used simulated data generated by the Gaia Data Processing and Analysis Consortium (DPAC) to obtain different least-squares estimations of the full (five-parameter) stellar spheres and gauge results. These were compared to analogous solutions obtained with the current RAMOD model in GSR2 (RAMOD@GSR2) and to the catalog generated with the Gaia RElativistic Model (GREM), the model baselined for Gaia and used to generate the DPAC synthetic data. Results: Linearized least-squares TTF solutions are based on spheres of about 132 000 primary stars uniformly distributed on the sky and simulated observations spanning the entire 5 yr range of Gaia's nominal operational lifetime. The statistical properties of the results compare well with those of GREM. Finally, comparisons to RAMOD@GSR2 solutions confirmed the known lower accuracy of that model and allowed us to establish firm limits on the quality of the linearization point outside of which an iteration for non-linearity is required for its proper convergence. This has proved invaluable as RAMOD@GSR2 is prepared to go into operations on real satellite data.

VizieR Online Data Catalog: Wide binaries in Tycho-Gaia: search method (Andrews+, 2017)

NASA Astrophysics Data System (ADS)

Andrews, J. J.; Chaname, J.; Agueros, M. A.

2017-11-01

Our catalogue of wide binaries identified in the Tycho-Gaia Astrometric Solution catalogue. The Gaia source IDs, Tycho IDs, astrometry, posterior probabilities for both the log-flat prior and power-law prior models, and angular separation are presented. (1 data file).

Observational Model for Precision Astrometry with the Space Interferometry Mission

NASA Technical Reports Server (NTRS)

Turyshev, Slava G.; Milman, Mark H.

2000-01-01

The Space Interferometry Mission (SIM) is a space-based 10-m baseline Michelson optical interferometer operating in the visible waveband that is designed to achieve astrometric accuracy in the single digits of the microarcsecond domain. Over a narrow field of view SIM is expected to achieve a mission accuracy of 1 microarcsecond. In this mode SIM will search for planetary companions to nearby stars by detecting the astrometric "wobble" relative to a nearby reference star. In its wide-angle mode, SIM will provide 4 microarcsecond precision absolute position measurements of stars, with parallaxes to comparable accuracy, at the end of its 5-year mission. The expected proper motion accuracy is around 3 microarcsecond/year, corresponding to a transverse velocity of 10 m/ s at a distance of 1 kpc. The basic astrometric observable of the SIM instrument is the pathlength delay. This measurement is made by a combination of internal metrology measurements that determine the distance the starlight travels through the two arms of the interferometer, and a measurement of the white light stellar fringe to find the point of equal pathlength. Because this operation requires a non-negligible integration time, the interferometer baseline vector is not stationary over this time period, as its absolute length and orientation are time varying. This paper addresses how the time varying baseline can be "regularized" so that it may act as a single baseline vector for multiple stars, as required for the solution of the astrometric equations.

Application of Gaia Analysis Software AGIS to Nano-JASMINE

NASA Astrophysics Data System (ADS)

Yamada, Y.; Lammers, U.; Gouda, N.

2011-07-01

The core data reduction for the Nano-JASMINE mission is planned to be done with Gaia's Astrometric Global Iterative Solution (AGIS). Nano-JASMINE is an ultra small (35 kg) satellite for astrometry observations in Japan and Gaia is ESA's large (over 1000 kg) next-generation astrometry mission. The accuracy of Nano-JASMINE is about 3 mas, comparable to the Hipparcos mission, Gaia's predecessor some 20 years ago. It is challenging that such a small satellite can perform real scientific observations. The collaboration for sharing software started in 2007. In addition to similar design and operating principles of the two missions, this is possible thanks to the encapsulation of all Gaia-specific aspects of AGIS in a Parameter Database. Nano-JASMINE will be the test bench for the Gaia AGIS software. We present this idea in detail and the necessary practical steps to make AGIS work with Nano-JASMINE data. We also show the key mission parameters, goals, and status of the data reduction for the Nano-JASMINE.

The Solar Neighborhood. XXXIX. Parallax Results from the CTIOPI and NOFS Programs: 50 New Members of the 25 parsec White Dwarf Sample

NASA Astrophysics Data System (ADS)

Subasavage, John P.; Jao, Wei-Chun; Henry, Todd J.; Harris, Hugh C.; Dahn, Conard C.; Bergeron, P.; Dufour, P.; Dunlap, Bart H.; Barlow, Brad N.; Ianna, Philip A.; Lépine, Sébastien; Margheim, Steven J.

2017-07-01

We present 114 trigonometric parallaxes for 107 nearby white dwarf (WD) systems from both the Cerro Tololo Inter-American Observatory Parallax Investigation (CTIOPI) and the U. S. Naval Observatory Flagstaff Station (NOFS) parallax programs. Of these, 76 parallaxes for 69 systems were measured by the CTIOPI program and 38 parallaxes for as many systems were measured by the NOFS program. A total of 50 systems are confirmed to be within the 25-pc horizon of interest. Coupled with a spectroscopic confirmation of a common proper-motion companion to a Hipparcos star within 25 pc as well as confirmation parallax determinations for two WD systems included in the recently released Tycho Gaia Astrometric Solution catalog, we add 53 new systems to the 25-pc WD sample—a 42% increase. Our sample presented here includes four strong candidate halo systems, a new metal-rich DAZ WD, a confirmation of a recently discovered nearby short-period (P = 2.85 hr) double degenerate, a WD with a new astrometric perturbation (long period, unconstrained with our data), and a new triple system where the WD companion main-sequence star has an astrometric perturbation (P ˜ 1.6 year).

Gaia: focus, straylight and basic angle

NASA Astrophysics Data System (ADS)

Mora, A.; Biermann, M.; Bombrun, A.; Boyadjian, J.; Chassat, F.; Corberand, P.; Davidson, M.; Doyle, D.; Escolar, D.; Gielesen, W. L. M.; Guilpain, T.; Hernandez, J.; Kirschner, V.; Klioner, S. A.; Koeck, C.; Laine, B.; Lindegren, L.; Serpell, E.; Tatry, P.; Thoral, P.

2016-07-01

The Gaia all-sky astrometric survey is challenged by several issues affecting the spacecraft stability. Amongst them, we find the focus evolution, straylight and basic angle variations Contrary to pre-launch expectations, the image quality is continuously evolving, during commissioning and the nominal mission. Payload decontaminations and wavefront sensor assisted refocuses have been carried out to recover optimum performance. An ESA-Airbus DS working group analysed the straylight and basic angle issues and worked on a detailed root cause analysis. In parallel, the Gaia scientists have also analysed the data, most notably comparing the BAM signal to global astrometric solutions, with remarkable agreement. In this contribution, a status review of these issues will be provided, with emphasis on the mitigation schemes and the lessons learned for future space missions where extreme stability is a key requirement.

Gaia Data Release 1. Summary of the astrometric, photometric, and survey properties

NASA Astrophysics Data System (ADS)

Gaia Collaboration; Brown, A. G. A.; Vallenari, A.; Prusti, T.; de Bruijne, J. H. J.; Mignard, F.; Drimmel, R.; Babusiaux, C.; Bailer-Jones, C. A. L.; Bastian, U.; Biermann, M.; Evans, D. W.; Eyer, L.; Jansen, F.; Jordi, C.; Katz, D.; Klioner, S. A.; Lammers, U.; Lindegren, L.; Luri, X.; O'Mullane, W.; Panem, C.; Pourbaix, D.; Randich, S.; Sartoretti, P.; Siddiqui, H. I.; Soubiran, C.; Valette, V.; van Leeuwen, F.; Walton, N. A.; Aerts, C.; Arenou, F.; Cropper, M.; Høg, E.; Lattanzi, M. G.; Grebel, E. K.; Holland, A. D.; Huc, C.; Passot, X.; Perryman, M.; Bramante, L.; Cacciari, C.; Castañeda, J.; Chaoul, L.; Cheek, N.; De Angeli, F.; Fabricius, C.; Guerra, R.; Hernández, J.; Jean-Antoine-Piccolo, A.; Masana, E.; Messineo, R.; Mowlavi, N.; Nienartowicz, K.; Ordóñez-Blanco, D.; Panuzzo, P.; Portell, J.; Richards, P. J.; Riello, M.; Seabroke, G. M.; Tanga, P.; Thévenin, F.; Torra, J.; Els, S. G.; Gracia-Abril, G.; Comoretto, G.; Garcia-Reinaldos, M.; Lock, T.; Mercier, E.; Altmann, M.; Andrae, R.; Astraatmadja, T. L.; Bellas-Velidis, I.; Benson, K.; Berthier, J.; Blomme, R.; Busso, G.; Carry, B.; Cellino, A.; Clementini, G.; Cowell, S.; Creevey, O.; Cuypers, J.; Davidson, M.; De Ridder, J.; de Torres, A.; Delchambre, L.; Dell'Oro, A.; Ducourant, C.; Frémat, Y.; García-Torres, M.; Gosset, E.; Halbwachs, J.-L.; Hambly, N. C.; Harrison, D. L.; Hauser, M.; Hestroffer, D.; Hodgkin, S. T.; Huckle, H. E.; Hutton, A.; Jasniewicz, G.; Jordan, S.; Kontizas, M.; Korn, A. J.; Lanzafame, A. C.; Manteiga, M.; Moitinho, A.; Muinonen, K.; Osinde, J.; Pancino, E.; Pauwels, T.; Petit, J.-M.; Recio-Blanco, A.; Robin, A. C.; Sarro, L. M.; Siopis, C.; Smith, M.; Smith, K. W.; Sozzetti, A.; Thuillot, W.; van Reeven, W.; Viala, Y.; Abbas, U.; Abreu Aramburu, A.; Accart, S.; Aguado, J. J.; Allan, P. M.; Allasia, W.; Altavilla, G.; Álvarez, M. A.; Alves, J.; Anderson, R. I.; Andrei, A. H.; Anglada Varela, E.; Antiche, E.; Antoja, T.; Antón, S.; Arcay, B.; Bach, N.; Baker, S. G.; Balaguer-Núñez, L.; Barache, C.; Barata, C.; Barbier, A.; Barblan, F.; Barrado y Navascués, D.; Barros, M.; Barstow, M. A.; Becciani, U.; Bellazzini, M.; Bello García, A.; Belokurov, V.; Bendjoya, P.; Berihuete, A.; Bianchi, L.; Bienaymé, O.; Billebaud, F.; Blagorodnova, N.; Blanco-Cuaresma, S.; Boch, T.; Bombrun, A.; Borrachero, R.; Bouquillon, S.; Bourda, G.; Bouy, H.; Bragaglia, A.; Breddels, M. A.; Brouillet, N.; Brüsemeister, T.; Bucciarelli, B.; Burgess, P.; Burgon, R.; Burlacu, A.; Busonero, D.; Buzzi, R.; Caffau, E.; Cambras, J.; Campbell, H.; Cancelliere, R.; Cantat-Gaudin, T.; Carlucci, T.; Carrasco, J. M.; Castellani, M.; Charlot, P.; Charnas, J.; Chiavassa, A.; Clotet, M.; Cocozza, G.; Collins, R. S.; Costigan, G.; Crifo, F.; Cross, N. J. G.; Crosta, M.; Crowley, C.; Dafonte, C.; Damerdji, Y.; Dapergolas, A.; David, P.; David, M.; De Cat, P.; de Felice, F.; de Laverny, P.; De Luise, F.; De March, R.; de Martino, D.; de Souza, R.; Debosscher, J.; del Pozo, E.; Delbo, M.; Delgado, A.; Delgado, H. E.; Di Matteo, P.; Diakite, S.; Distefano, E.; Dolding, C.; Dos Anjos, S.; Drazinos, P.; Duran, J.; Dzigan, Y.; Edvardsson, B.; Enke, H.; Evans, N. W.; Eynard Bontemps, G.; Fabre, C.; Fabrizio, M.; Faigler, S.; Falcão, A. J.; Farràs Casas, M.; Federici, L.; Fedorets, G.; Fernández-Hernández, J.; Fernique, P.; Fienga, A.; Figueras, F.; Filippi, F.; Findeisen, K.; Fonti, A.; Fouesneau, M.; Fraile, E.; Fraser, M.; Fuchs, J.; Gai, M.; Galleti, S.; Galluccio, L.; Garabato, D.; García-Sedano, F.; Garofalo, A.; Garralda, N.; Gavras, P.; Gerssen, J.; Geyer, R.; Gilmore, G.; Girona, S.; Giuffrida, G.; Gomes, M.; González-Marcos, A.; González-Núñez, J.; González-Vidal, J. J.; Granvik, M.; Guerrier, A.; Guillout, P.; Guiraud, J.; Gúrpide, A.; Gutiérrez-Sánchez, R.; Guy, L. P.; Haigron, R.; Hatzidimitriou, D.; Haywood, M.; Heiter, U.; Helmi, A.; Hobbs, D.; Hofmann, W.; Holl, B.; Holland, G.; Hunt, J. A. S.; Hypki, A.; Icardi, V.; Irwin, M.; Jevardat de Fombelle, G.; Jofré, P.; Jonker, P. G.; Jorissen, A.; Julbe, F.; Karampelas, A.; Kochoska, A.; Kohley, R.; Kolenberg, K.; Kontizas, E.; Koposov, S. E.; Kordopatis, G.; Koubsky, P.; Krone-Martins, A.; Kudryashova, M.; Kull, I.; Bachchan, R. K.; Lacoste-Seris, F.; Lanza, A. F.; Lavigne, J.-B.; Le Poncin-Lafitte, C.; Lebreton, Y.; Lebzelter, T.; Leccia, S.; Leclerc, N.; Lecoeur-Taibi, I.; Lemaitre, V.; Lenhardt, H.; Leroux, F.; Liao, S.; Licata, E.; Lindstrøm, H. E. P.; Lister, T. A.; Livanou, E.; Lobel, A.; Löffler, W.; López, M.; Lorenz, D.; MacDonald, I.; Magalhães Fernandes, T.; Managau, S.; Mann, R. G.; Mantelet, G.; Marchal, O.; Marchant, J. M.; Marconi, M.; Marinoni, S.; Marrese, P. M.; Marschalkó, G.; Marshall, D. J.; Martín-Fleitas, J. M.; Martino, M.; Mary, N.; Matijevič, G.; Mazeh, T.; McMillan, P. J.; Messina, S.; Michalik, D.; Millar, N. R.; Miranda, B. M. H.; Molina, D.; Molinaro, R.; Molinaro, M.; Molnár, L.; Moniez, M.; Montegriffo, P.; Mor, R.; Mora, A.; Morbidelli, R.; Morel, T.; Morgenthaler, S.; Morris, D.; Mulone, A. F.; Muraveva, T.; Musella, I.; Narbonne, J.; Nelemans, G.; Nicastro, L.; Noval, L.; Ordénovic, C.; Ordieres-Meré, J.; Osborne, P.; Pagani, C.; Pagano, I.; Pailler, F.; Palacin, H.; Palaversa, L.; Parsons, P.; Pecoraro, M.; Pedrosa, R.; Pentikäinen, H.; Pichon, B.; Piersimoni, A. M.; Pineau, F.-X.; Plachy, E.; Plum, G.; Poujoulet, E.; Prša, A.; Pulone, L.; Ragaini, S.; Rago, S.; Rambaux, N.; Ramos-Lerate, M.; Ranalli, P.; Rauw, G.; Read, A.; Regibo, S.; Reylé, C.; Ribeiro, R. A.; Rimoldini, L.; Ripepi, V.; Riva, A.; Rixon, G.; Roelens, M.; Romero-Gómez, M.; Rowell, N.; Royer, F.; Ruiz-Dern, L.; Sadowski, G.; Sagristà Sellés, T.; Sahlmann, J.; Salgado, J.; Salguero, E.; Sarasso, M.; Savietto, H.; Schultheis, M.; Sciacca, E.; Segol, M.; Segovia, J. C.; Segransan, D.; Shih, I.-C.; Smareglia, R.; Smart, R. L.; Solano, E.; Solitro, F.; Sordo, R.; Soria Nieto, S.; Souchay, J.; Spagna, A.; Spoto, F.; Stampa, U.; Steele, I. A.; Steidelmüller, H.; Stephenson, C. A.; Stoev, H.; Suess, F. F.; Süveges, M.; Surdej, J.; Szabados, L.; Szegedi-Elek, E.; Tapiador, D.; Taris, F.; Tauran, G.; Taylor, M. B.; Teixeira, R.; Terrett, D.; Tingley, B.; Trager, S. C.; Turon, C.; Ulla, A.; Utrilla, E.; Valentini, G.; van Elteren, A.; Van Hemelryck, E.; van Leeuwen, M.; Varadi, M.; Vecchiato, A.; Veljanoski, J.; Via, T.; Vicente, D.; Vogt, S.; Voss, H.; Votruba, V.; Voutsinas, S.; Walmsley, G.; Weiler, M.; Weingrill, K.; Wevers, T.; Wyrzykowski, Ł.; Yoldas, A.; Žerjal, M.; Zucker, S.; Zurbach, C.; Zwitter, T.; Alecu, A.; Allen, M.; Allende Prieto, C.; Amorim, A.; Anglada-Escudé, G.; Arsenijevic, V.; Azaz, S.; Balm, P.; Beck, M.; Bernstein, H.-H.; Bigot, L.; Bijaoui, A.; Blasco, C.; Bonfigli, M.; Bono, G.; Boudreault, S.; Bressan, A.; Brown, S.; Brunet, P.-M.; Bunclark, P.; Buonanno, R.; Butkevich, A. G.; Carret, C.; Carrion, C.; Chemin, L.; Chéreau, F.; Corcione, L.; Darmigny, E.; de Boer, K. S.; de Teodoro, P.; de Zeeuw, P. T.; Delle Luche, C.; Domingues, C. D.; Dubath, P.; Fodor, F.; Frézouls, B.; Fries, A.; Fustes, D.; Fyfe, D.; Gallardo, E.; Gallegos, J.; Gardiol, D.; Gebran, M.; Gomboc, A.; Gómez, A.; Grux, E.; Gueguen, A.; Heyrovsky, A.; Hoar, J.; Iannicola, G.; Isasi Parache, Y.; Janotto, A.-M.; Joliet, E.; Jonckheere, A.; Keil, R.; Kim, D.-W.; Klagyivik, P.; Klar, J.; Knude, J.; Kochukhov, O.; Kolka, I.; Kos, J.; Kutka, A.; Lainey, V.; LeBouquin, D.; Liu, C.; Loreggia, D.; Makarov, V. V.; Marseille, M. G.; Martayan, C.; Martinez-Rubi, O.; Massart, B.; Meynadier, F.; Mignot, S.; Munari, U.; Nguyen, A.-T.; Nordlander, T.; Ocvirk, P.; O'Flaherty, K. S.; Olias Sanz, A.; Ortiz, P.; Osorio, J.; Oszkiewicz, D.; Ouzounis, A.; Palmer, M.; Park, P.; Pasquato, E.; Peltzer, C.; Peralta, J.; Péturaud, F.; Pieniluoma, T.; Pigozzi, E.; Poels, J.; Prat, G.; Prod'homme, T.; Raison, F.; Rebordao, J. M.; Risquez, D.; Rocca-Volmerange, B.; Rosen, S.; Ruiz-Fuertes, M. I.; Russo, F.; Sembay, S.; Serraller Vizcaino, I.; Short, A.; Siebert, A.; Silva, H.; Sinachopoulos, D.; Slezak, E.; Soffel, M.; Sosnowska, D.; Straižys, V.; ter Linden, M.; Terrell, D.; Theil, S.; Tiede, C.; Troisi, L.; Tsalmantza, P.; Tur, D.; Vaccari, M.; Vachier, F.; Valles, P.; Van Hamme, W.; Veltz, L.; Virtanen, J.; Wallut, J.-M.; Wichmann, R.; Wilkinson, M. I.; Ziaeepour, H.; Zschocke, S.

2016-11-01

Context. At about 1000 days after the launch of Gaia we present the first Gaia data release, Gaia DR1, consisting of astrometry and photometry for over 1 billion sources brighter than magnitude 20.7. Aims: A summary of Gaia DR1 is presented along with illustrations of the scientific quality of the data, followed by a discussion of the limitations due to the preliminary nature of this release. Methods: The raw data collected by Gaia during the first 14 months of the mission have been processed by the Gaia Data Processing and Analysis Consortium (DPAC) and turned into an astrometric and photometric catalogue. Results: Gaia DR1 consists of three components: a primary astrometric data set which contains the positions, parallaxes, and mean proper motions for about 2 million of the brightest stars in common with the Hipparcos and Tycho-2 catalogues - a realisation of the Tycho-Gaia Astrometric Solution (TGAS) - and a secondary astrometric data set containing the positions for an additional 1.1 billion sources. The second component is the photometric data set, consisting of mean G-band magnitudes for all sources. The G-band light curves and the characteristics of 3000 Cepheid and RR Lyrae stars, observed at high cadence around the south ecliptic pole, form the third component. For the primary astrometric data set the typical uncertainty is about 0.3 mas for the positions and parallaxes, and about 1 mas yr-1 for the proper motions. A systematic component of 0.3 mas should be added to the parallax uncertainties. For the subset of 94 000 Hipparcos stars in the primary data set, the proper motions are much more precise at about 0.06 mas yr-1. For the secondary astrometric data set, the typical uncertainty of the positions is 10 mas. The median uncertainties on the mean G-band magnitudes range from the mmag level to 0.03 mag over the magnitude range 5 to 20.7. Conclusions: Gaia DR1 is an important milestone ahead of the next Gaia data release, which will feature five-parameter astrometry for all sources. Extensive validation shows that Gaia DR1 represents a major advance in the mapping of the heavens and the availability of basic stellar data that underpin observational astrophysics. Nevertheless, the very preliminary nature of this first Gaia data release does lead to a number of important limitations to the data quality which should be carefully considered before drawing conclusions from the data.

VizieR Online Data Catalog: Comoving stars in Gaia DR1 (Oh+, 2017)

NASA Astrophysics Data System (ADS)

Oh, S.; Price-Whelan, A. M.; Hogg, D. W.; Morton, T. D.; Spergel, D. N.

2017-08-01

The primary data set used in this article is the Tycho-Gaia Astrometric Solution (TGAS), released as a part of Data Release 1 (DR1) of the Gaia mission (Gaia Collaboration et al. 2016, Cat. I/337; Lindegren et al. 2016A&A...595A...4L). (3 data files).

Impact of basic angle variations on the parallax zero point for a scanning astrometric satellite

NASA Astrophysics Data System (ADS)

Butkevich, Alexey G.; Klioner, Sergei A.; Lindegren, Lennart; Hobbs, David; van Leeuwen, Floor

2017-07-01

Context. Determination of absolute parallaxes by means of a scanning astrometric satellite such as Hipparcos or Gaia relies on the short-term stability of the so-called basic angle between the two viewing directions. Uncalibrated variations of the basic angle may produce systematic errors in the computed parallaxes. Aims: We examine the coupling between a global parallax shift and specific variations of the basic angle, namely those related to the satellite attitude with respect to the Sun. Methods: The changes in observables produced by small perturbations of the basic angle, attitude, and parallaxes were calculated analytically. We then looked for a combination of perturbations that had no net effect on the observables. Results: In the approximation of infinitely small fields of view, it is shown that certain perturbations of the basic angle are observationally indistinguishable from a global shift of the parallaxes. If these kinds of perturbations exist, they cannot be calibrated from the astrometric observations but will produce a global parallax bias. Numerical simulations of the astrometric solution, using both direct and iterative methods, confirm this theoretical result. For a given amplitude of the basic angle perturbation, the parallax bias is smaller for a larger basic angle and a larger solar aspect angle. In both these respects Gaia has a more favourable geometry than Hipparcos. In the case of Gaia, internal metrology is used to monitor basic angle variations. Additionally, Gaia has the advantage of detecting numerous quasars, which can be used to verify the parallax zero point.

VLT/SPHERE robust astrometry of the HR8799 planets at milliarcsecond-level accuracy. Orbital architecture analysis with PyAstrOFit

NASA Astrophysics Data System (ADS)

Wertz, O.; Absil, O.; Gómez González, C. A.; Milli, J.; Girard, J. H.; Mawet, D.; Pueyo, L.

2017-02-01

Context. HR8799 is orbited by at least four giant planets, making it a prime target for the recently commissioned Spectro-Polarimetric High-contrast Exoplanet REsearch (VLT/SPHERE). As such, it was observed on five consecutive nights during the SPHERE science verification in December 2014. Aims: We aim to take full advantage of the SPHERE capabilities to derive accurate astrometric measurements based on H-band images acquired with the Infra-Red Dual-band Imaging and Spectroscopy (IRDIS) subsystem, and to explore the ultimate astrometric performance of SPHERE in this observing mode. We also aim to present a detailed analysis of the orbital parameters for the four planets. Methods: We performed thorough post-processing of the IRDIS images with the Vortex Imaging Processing (VIP) package to derive a robust astrometric measurement for the four planets. This includes the identification and careful evaluation of the different contributions to the error budget, including systematic errors. Combining our astrometric measurements with the ones previously published in the literature, we constrain the orbital parameters of the four planets using PyAstrOFit, our new open-source python package dedicated to orbital fitting using Bayesian inference with Monte-Carlo Markov Chain sampling. Results: We report the astrometric positions for epoch 2014.93 with an accuracy down to 2.0 mas, mainly limited by the astrometric calibration of IRDIS. For each planet, we derive the posterior probability density functions for the six Keplerian elements and identify sets of highly probable orbits. For planet d, there is clear evidence for nonzero eccentricity (e 0.35), without completely excluding solutions with smaller eccentricities. The three other planets are consistent with circular orbits, although their probability distributions spread beyond e = 0.2, and show a peak at e ≃ 0.1 for planet e. The four planets have consistent inclinations of approximately 30° with respect to the sky plane, but the confidence intervals for the longitude of the ascending node are disjointed for planets b and c, and we find tentative evidence for non-coplanarity between planets b and c at the 2σ level. Based on observations collected at the European Organisation for Astronomical Research in the Southern Hemisphere under ESO programme 60.A-9352.

Implementation and simulations of the sphere solution in FAST

NASA Astrophysics Data System (ADS)

Murgolo, F. P.; Schirone, M. G.; Lattanzi, M.; Bernacca, P. L.

1989-06-01

The details of the implementation of the sphere solution software in the Fundamental Astronomy by Space Techniques (FAST) consortium, are described. The simulation results for realistic data sets, both with and without grid-step errors are given. Expected errors on the astrometric parameters of the primary stars and the precision of the reference great circle zero points, are provided as a function of mission duration. The design matrix, the diagrams of the context processor and the processors experimental results are given.

Wide Binaries in TGAS: Search Method and First Results

NASA Astrophysics Data System (ADS)

Andrews, Jeff J.; Chanamé, Julio; Agüeros, Marcel A.

2018-04-01

Half of all stars reside in binary systems, many of which have orbital separations in excess of 1000 AU. Such binaries are typically identified in astrometric catalogs by matching the proper motions vectors of close stellar pairs. We present a fully Bayesian method that properly takes into account positions, proper motions, parallaxes, and their correlated uncertainties to identify widely separated stellar binaries. After applying our method to the >2 × 106 stars in the Tycho-Gaia astrometric solution from Gaia DR1, we identify over 6000 candidate wide binaries. For those pairs with separations less than 40,000 AU, we determine the contamination rate to be ~5%. This sample has an orbital separation (a) distribution that is roughly flat in log space for separations less than ~5000 AU and follows a power law of a -1.6 at larger separations.

Get Ready for Gaia: Cool White Dwarfs in Common Proper Motion with Tycho Stars

NASA Astrophysics Data System (ADS)

Hambly, N.; Rowell, N.; Lam, M.

2017-03-01

We discuss the Gaia Data Release 1 (September 2016) and preliminary work on maximising the benefit for cool white dwarf (WD) science in advance of the full parallax catalogue which will appear around one year later in DR2. The Tycho catalogue is used in conjunction with the all-sky ground based astrometric/ photometric SuperCOSMOS Sky Survey in order to identify candidate faint common proper motion objects to the Tycho stars. Gaia DR1 is supplemented by the Tycho-Gaia Astrometric Solution catalogue containing some 2 million parallaxes with Hipparcos-like precision for Tycho stars. While hotter, brighter WDs are present in Tycho, cooler examples are much rarer (if present at all) and CPM offers one method to infer precision distances for a statistically useful sample of these very faint WDs.

GSFC VLBI Analysis Center Annual Report

NASA Technical Reports Server (NTRS)

Gordon, David; Ma, Chopo; MacMillan, Dan

1999-01-01

The GSFC VLBI group, located at NASA's Goddard Space Flight Center in Greenbelt, MD, is a part of the NASA Space Geodesy Program. Since its inception in the mid 1970's, this group has been involved with and been a leader in most aspects of geodetic and astrometric VLBI. Current major activities include coordination of the international geodetic observing program; coordination and analysis of the CORE program; VLBI technique development; and all types of data processing, analysis, and research activities.

Astrometric light-travel time signature of sources in nonlinear motion. I. Derivation of the effect and radial motion

NASA Astrophysics Data System (ADS)

Anglada-Escudé, G.; Torra, J.

2006-04-01

Context: .Very precise planned space astrometric missions and recent improvements in imaging capabilities require a detailed review of the assumptions of classical astrometric modeling.Aims.We show that Light-Travel Time must be taken into account in modeling the kinematics of astronomical objects in nonlinear motion, even at stellar distances.Methods.A closed expression to include Light-Travel Time in the current astrometric models with nonlinear motion is provided. Using a perturbative approach the expression of the Light-Travel Time signature is derived. We propose a practical form of the astrometric modelling to be applied in astrometric data reduction of sources at stellar distances(d>1 pc).Results.We show that the Light-Travel Time signature is relevant at μ as accuracy (or even at mas) depending on the time span of the astrometric measurements. We explain how information on the radial motion of a source can be obtained. Some estimates are provided for known nearby binary systemsConclusions.Given the obtained results, it is clear that this effect must be taken into account in interpreting precise astrometric measurements. The effect is particularly relevant in measurements performed by the planned astrometric space missions (GAIA, SIM, JASMINE, TPF/DARWIN). An objective criterion is provided to quickly evaluate whether the Light-Travel Time modeling is required for a given source or system.

Global astrometry with the space interferometry mission

NASA Technical Reports Server (NTRS)

Boden, A.; Unwin, S.; Shao, M.

1997-01-01

The prospects for global astrometric measurements with the space interferometry mission (SIM) are discussed. The SIM mission will perform four microarcsec astrometric measurements on objects as faint as 20 mag using the optical interferometry technique with a 10 m baseline. The SIM satellite will perform narrow angle astrometry and global astrometry by means of an astrometric grid. The sensitivities of the SIM global astrometric performance and the grid accuracy versus instrumental parameters and sky coverage schemes are reported on. The problems in finding suitable astrometric grid objects to support microarcsec astrometry, and related ground-based observation programs are discussed.

VizieR Online Data Catalog: USNO Photographic Parallaxes. I. (Monet+, 1992)

NASA Astrophysics Data System (ADS)

Monet, D. G.; Dahn, C. C.; Vrba, F. J.; Harris, H. C.; Pier, J. R.; Luginbuhl, C. B.; Ables, H. D.

2000-11-01

The U.S. Naval Observatory CCD trigonometric parallax program is described in detail, including the instrumentation employed, observing procedures followed, and reduction procedures applied. Astrometric results are presented for 72 stars ranging in apparent brightness from V=15.16 to 19.58. Photometry (V and V-I on the Kron-Cousins system) is presented for the parallax stars and for all 426 individual reference stars employed in the astrometric solutions. Corrections for differential color refraction, calibrated to the observed V-I colors, have been applied to all astrometric measures. The mean errors in the relative parallaxes range from ±0.0005" to ±0.0027" with a median value of ±0.0010". Seventeen of the 23 stars with Vtan>200km/s form a well-delineated sequence of extreme subdwarfs covering 11.5

The Solar Neighborhood. XXXIX. Parallax Results from the CTIOPI and NOFS Programs: 50 New Members of the 25 parsec White Dwarf Sample

DOE Office of Scientific and Technical Information (OSTI.GOV)

Subasavage, John P.; Harris, Hugh C.; Dahn, Conard C.

We present 114 trigonometric parallaxes for 107 nearby white dwarf (WD) systems from both the Cerro Tololo Inter-American Observatory Parallax Investigation (CTIOPI) and the U. S. Naval Observatory Flagstaff Station (NOFS) parallax programs. Of these, 76 parallaxes for 69 systems were measured by the CTIOPI program and 38 parallaxes for as many systems were measured by the NOFS program. A total of 50 systems are confirmed to be within the 25-pc horizon of interest. Coupled with a spectroscopic confirmation of a common proper-motion companion to a Hipparcos star within 25 pc as well as confirmation parallax determinations for two WD systems included inmore » the recently released Tycho Gaia Astrometric Solution catalog, we add 53 new systems to the 25-pc WD sample—a 42% increase. Our sample presented here includes four strong candidate halo systems, a new metal-rich DAZ WD, a confirmation of a recently discovered nearby short-period ( P  = 2.85 hr) double degenerate, a WD with a new astrometric perturbation (long period, unconstrained with our data), and a new triple system where the WD companion main-sequence star has an astrometric perturbation ( P  ∼ 1.6 year).« less

Improving the astrometric performance of VLTI-PRIMA

NASA Astrophysics Data System (ADS)

Woillez, J.; Abuter, R.; Andolfato, L.; Berger, J.-P.; Bonnet, H.; Delplancke, F.; Derie, F.; Di Lieto, N.; Guniat, S.; Mérand, A.; Duc, T. Phan; Schmid, C.; Schuhler, N.; Henning, T.; Launhardt, R.; Pepe, F.; Queloz, D.; Quirrenbach, A.; Reffert, S.; Sahlmann, J.; Segransan, D.

2014-07-01

In the summer of 2011, the first on-sky astrometric commissioning of PRIMA-Astrometry delivered a performance of 3 m″ for a 10 ″ separation on bright objects, orders of magnitude away from its exoplanet requirement of 50 μ″ ~ 20 μ″ on objects as faint as 11 mag ~ 13 mag in K band. This contribution focuses on upgrades and characterizations carried out since then. The astrometric metrology was extended from the Coudé focus of the Auxillary Telescopes to their secondary mirror, in order to reduce the baseline instabilities and improve the astrometric performance. While carrying out this extension, it was realized that the polarization retardance of the star separator derotator had a major impact on both the astrometric metrology and the fringe sensors. A local compensation of this retardance and the operation on a symmetric baseline allowed a new astrometric commissioning. In October 2013, an improved astrometric performance of 160 μ″ was demonstrated, still short of the requirements. Instabilities in the astrometric baseline still appear to be the dominating factor. In preparation to a review held in January 2014, a plan was developed to further improve the astrometric and faint target performance of PRIMA Astrometry. On the astrometric aspect, it involved the extension of the internal longitudinal metrology to primary space, the design and implementation of an external baseline metrology, and the development of an astrometric internal fringes mode. On the faint target aspect, investigations of the performance of the fringe sensor units and the development of an AO system (NAOMI) were in the plan. Following this review, ESO decided to take a proposal to the April 2014 STC that PRIMA be cancelled, and that ESO resources be concentrated on ensuring that Gravity and Matisse are a success. This proposal was recommended by the STC in May 2014, and endorsed by ESO.

VizieR Online Data Catalog: Parameters and IR excesses of Gaia DR1 stars (McDonald+, 2017)

NASA Astrophysics Data System (ADS)

McDonald, I.; Zijlstra, A. A.; Watson, R. A.

2017-08-01

Spectral energy distribution fits are presented for stars from the Tycho-Gaia Astrometric Solution (TGAS) from Gaia Data Release 1. Hipparcos-Gaia stars are presented in a separate table. Effective temperatures, bolometric luminosities, and infrared excesses are presented (alongside other parameters pertinent to the model fits), plus the source photometry used. (3 data files).

How and Why to Do VLBI on GPS

NASA Technical Reports Server (NTRS)

Dickey, J. M.

2010-01-01

In order to establish the position of the center of mass of the Earth in the International Celestial Reference Frame, observations of the Global Positioning Satellite (GPS) constellation using the IVS network are important. With a good frame-tie between the coordinates of the IVS telescopes and nearby GPS receivers, plus a common local oscillator reference signal, it should be possible to observe and record simultaneously signals from the astrometric calibration sources and the GPS satellites. The standard IVS solution would give the atmospheric delay and clock offsets to use in analysis of the GPS data. Correlation of the GPS signals would then give accurate orbital parameters of the satellites in the ICRF reference frame, i.e., relative to the positions of the astrometric sources. This is particularly needed to determine motion of the center of mass of the earth along the rotation axis.

Quasar Astrophysics with the Space Interferometry Mission

NASA Technical Reports Server (NTRS)

Unwin, Stephen; Wehrle, Ann; Meier, David; Jones, Dayton; Piner, Glenn

2007-01-01

Optical astrometry of quasars and active galaxies can provide key information on the spatial distribution and variability of emission in compact nuclei. The Space Interferometry Mission (SIM PlanetQuest) will have the sensitivity to measure a significant number of quasar positions at the microarcsecond level. SIM will be very sensitive to astrometric shifts for objects as faint as V = 19. A variety of AGN phenomena are expected to be visible to SIM on these scales, including time and spectral dependence in position offsets between accretion disk and jet emission. These represent unique data on the spatial distribution and time dependence of quasar emission. It will also probe the use of quasar nuclei as fundamental astrometric references. Comparisons between the time-dependent optical photocenter position and VLBI radio images will provide further insight into the jet emission mechanism. Observations will be tailored to each specific target and science question. SIM will be able to distinguish spatially between jet and accretion disk emission; and it can observe the cores of galaxies potentially harboring binary supermassive black holes resulting from mergers.

Mid infrared observations of Van Maanen 2: no substellar companion.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Farihi, J; Becklin, E; Macintosh, B

2004-11-03

The results of a comprehensive infrared imaging search for the putative 0.06 M{sub {circle_dot}} astrometric companion to the 4.4 pc white dwarf van Mannen 2 are reported. Adaptive optics images acquired at 3.8 {micro}m reveal a diffraction limited core of 0.09 inch and no direct evidence of a secondary. Models predict that at 5 Gyr, a 50 M{sub J} brown dwarf would be only 1 magnitude fainter than van Maanen 2 at this wavelength and the astrometric analysis suggested a separation of 0.2 inch. In the case of a chance alignment along the line of sight, a 0.4 mag excessmore » should be measured. An independent photometric observation at the same wavelength reveals no excess. In addition, there exist published ISO observations of van Maanen 2 at 6.8 {micro}m and 15.0 {micro}m which are consistent with photospheric flux of a 6750 K white dwarf. If recent brown dwarf models are correct, there is no substellar companion with T{sub eff} {approx}> 500 K.« less

Verification of the astrometric performance of the Korean VLBI network, using comparative SFPR studies with the VLBA AT 14/7 mm

DOE Office of Scientific and Technical Information (OSTI.GOV)

Rioja, María J.; Dodson, Richard; Jung, TaeHyun

The Korean VLBI Network (KVN) is a new millimeter VLBI dedicated array with the capability to simultaneously observe at multiple frequencies, up to 129 GHz. The innovative multi-channel receivers present significant benefits for astrometric measurements in the frequency domain. The aim of this work is to verify the astrometric performance of the KVN using a comparative study with the VLBA, a well-established instrument. For that purpose, we carried out nearly contemporaneous observations with the KVN and the VLBA, at 14/7 mm, in 2013 April. The KVN observations consisted of simultaneous dual frequency observations, while the VLBA used fast frequency switchingmore » observations. We used the Source Frequency Phase Referencing technique for the observational and analysis strategy. We find that having simultaneous observations results in superior compensation for all atmospheric terms in the observables, in addition to offering other significant benefits for astrometric analysis. We have compared the KVN astrometry measurements to those from the VLBA. We find that the structure blending effects introduce dominant systematic astrometric shifts, and these need to be taken into account. We have tested multiple analytical routes to characterize the impact of the low-resolution effects for extended sources in the astrometric measurements. The results from the analysis of the KVN and full VLBA data sets agree within 2σ of the thermal error estimate. We interpret the discrepancy as arising from the different resolutions. We find that the KVN provides astrometric results with excellent agreement, within 1σ, when compared to a VLBA configuration that has a similar resolution. Therefore, this comparative study verifies the astrometric performance of the KVN using SFPR at 14/7 mm, and validates the KVN as an astrometric instrument.« less

On the uncertain nature of the core of α Cen A

NASA Astrophysics Data System (ADS)

Bazot, M.; Christensen-Dalsgaard, J.; Gizon, L.; Benomar, O.

2016-08-01

High-quality astrometric, spectroscopic, interferometric and, importantly, asteroseismic observations are available for α Cen A, which is the closest binary star system to earth. Taking all these constraints into account, we study the internal structure of the star by means of theoretical modelling. Using the Aarhus STellar Evolution Code (ASTEC) and the tools of Computational Bayesian Statistics, in particular a Markov chain Monte Carlo algorithm, we perform statistical inferences for the physical characteristics of the star. We find that α Cen A has a probability of approximately 40 per cent of having a convective core. This probability drops to few per cent if one considers reduced rates for the 14N(p,γ)15O reaction. These convective cores have fractional radii less than 8 per cent when overshoot is neglected. Including overshooting also leads to the possibility of a convective core mostly sustained by the ppII chain energy output. We finally show that roughly 30 per cent of the stellar models describing α Cen A are in the subgiant regime.

NGC 2548: clumpy spatial and kinematic structure in an intermediate-age Galactic cluster

NASA Astrophysics Data System (ADS)

Vicente, Belén; Sánchez, Néstor; Alfaro, Emilio J.

2016-09-01

NGC 2548 is a ˜400-500 Myr old open cluster with evidence of spatial substructures likely caused by its interaction with the Galactic disc. In this work we use precise astrometric data from the Carte du Ciel - San Fernando (CdC-SF) catalogue to study the clumpy structure in this cluster. We confirm the fragmented structure of NGC 2548 but, additionally, the relatively high precision of our kinematic data lead us to the first detection of substructures in the proper motion space of a stellar cluster. There are three spatially separated cores each of which has its own counterpart in the proper motion distribution. The two main cores lie nearly parallel to the Galactic plane whereas the third one is significantly fainter than the others and it moves towards the Galactic plane separating from the rest of the cluster. We derive core positions and proper motions, as well as the stars belonging to each core.

Astrometric Observation of MACHO Gravitational Microlensing

NASA Technical Reports Server (NTRS)

Boden, A. F.; Shao, M.; Van Buren, D.

1997-01-01

This paper discusses the prospects for astrometric observation of MACHO gravitational microlensing events. We derive the expected astrometric observables for a simple microlensing event assuming a dark MACHO, and demonstrate that accurate astrometry can determine the lens mass, distance, and proper motion in a very general fashion.

Comparison of photogrammetric and astrometric data reduction results for the wild BC-4 camera

NASA Technical Reports Server (NTRS)

Hornbarger, D. H.; Mueller, I., I.

1971-01-01

The results of astrometric and photogrammetric plate reduction techniques for a short focal length camera are compared. Several astrometric models are tested on entire and limited plate areas to analyze their ability to remove systematic errors from interpolated satellite directions using a rigorous photogrammetric reduction as a standard. Residual plots are employed to graphically illustrate the analysis. Conclusions are made as to what conditions will permit the astrometric reduction to achieve comparable accuracies to those of photogrammetric reduction when applied for short focal length ballistic cameras.

Astrometric Detection of Exo-Earths in the Presence of Stellar Noise

NASA Astrophysics Data System (ADS)

Catanzarite, Joseph; Law, N.; Shao, M.

2008-03-01

Astrometry from space is capable of making extremely precise measurements of the positions of stars, well below 1 uas (microarcsecond) at each visit. A hundred such visits over a period of several years could result in a relative astrometric precision for the mission of 0.1 uas, which is below the astrometric signature of 0.3 uas for a Sun-Earth system at a distance of 10 pc. Stellar photometric fluctuations on timescales of months to years introduce astrophysical noise in radial velocity and astrometric measurements of stars. These fluctuations are dominated by rotation and evolution of magnetic surface features (sunspots and faculae). We describe a dynamic model of starspot noise which is consistent with the power spectrum of the Sun and several other stars. We use the model to predict the noise in astrometric and RV observing campaigns for this small sample of stars. We also use empirical stellar activity models to estimate the astrometric and radial velocity jitter for a much larger sample of nearby solar-type stars. We find that for most of these stars, starspot noise does not significantly interfere with astrometric detection of habitable zone planets down to well below an Earth mass. This work was carried out at the Jet Propulsion Laboratory, California Institute of Technology, under contract with NASA.

Gaia DR1 documentation Chapter 7: Catalogue consolidation and validation

NASA Astrophysics Data System (ADS)

Arenou, F.; Babusiaux, C.; Blanco-Cuaresma, S.; Borrachero, R.; Cantat-Gaudin, T.; Fabricius, C.; Findeisen, K.; Helmi, A.; Hutton, A.; Luri, X.; Marrese, P.; Marinoni, S.; Marrese, P.; Robin, A.; Sordo, R.; Soria, S.; Turon, C.; Utrilla Molina, E.; Vallenari, A.

2017-12-01

The Gaia Catalogue does not only produce a wealth of data, it also represents a complex processing before a Catalogue can be issued. The main data processing is being handled by three DPAC Coordination Units, CU3 for the astrometric data, CU5 for the photometric data and CU6 for the spectroscopic data. Then three Coordination Units analyse the processed data, CU4 for optical or binary stars, solar system objects and extended objects, CU7 for variable stars, and CU8 for classification. Finally, CU9 takes care of the intermediate and final publication of the Gaia data. For Gaia DR1, the situation has been simplified in the sense that CU4, CU6 and CU8 did not contribute to the first Catalogue. At the last step, several data fields may have been computed by several Coordination Units (e.g., parallaxes computed by CU3, then again by CU4 with a fit of an astrometric + binary model if the star happens to have a significant binary motion; or a mean magnitude computed by CU5 may be superseded by another estimation from CU7 if the stars happens to be a periodic variable; etc.), in several Data Processing Centres, so an (a) homogeneous, (b) convenient, (c) consistent Catalogue has to be built. First, to a so-called CompleteSource is attached astrometric and photometric information, then possible variability information is integrated, producing an homogeneous Catalogue. Second, sources that do not meet some minimum astrometric or photometric quality are filtered out. The filters applied are described in Section 4 of Gaia Collaboration et al. (2016a). Third, while flat files are kept for further operations, the data is integrated inside the Gaia Archive Core System (GACS) database; crossmatch with external catalogues is also performed, providing the convenient access to the data. Fourth, the consistency of the Catalogue is obtained through a dedicated validation of its content. Sources that do not pass the validation criteria are then filtered out. This chapter describes these successive steps which are being followed for the consolidation of the Catalogue.

The search for other planetary systems - Progress to date and future prospects (The Rudolph Pesek Lecture)

NASA Technical Reports Server (NTRS)

Black, David C.

1991-01-01

The notion is addressed which links the formation of stars and the existence of planets, and the lack of supporting observational data is discussed in relation to a NASA astrometric project. The program cited is called Towards Other Planetary Systems (TOPS) and includes ground-based astrometric and radial-velocity studies for both direct and indirect scrutiny of unknown planets. The TOPS program also envisages space-based astrometric systems that can operate with an accuracy of not less than 10 microarcseconds, and the possibility is mentioned of a moon-based astrometric platform.

Gaia Data Release 1. Astrometry: one billion positions, two million proper motions and parallaxes

NASA Astrophysics Data System (ADS)

Lindegren, L.; Lammers, U.; Bastian, U.; Hernández, J.; Klioner, S.; Hobbs, D.; Bombrun, A.; Michalik, D.; Ramos-Lerate, M.; Butkevich, A.; Comoretto, G.; Joliet, E.; Holl, B.; Hutton, A.; Parsons, P.; Steidelmüller, H.; Abbas, U.; Altmann, M.; Andrei, A.; Anton, S.; Bach, N.; Barache, C.; Becciani, U.; Berthier, J.; Bianchi, L.; Biermann, M.; Bouquillon, S.; Bourda, G.; Brüsemeister, T.; Bucciarelli, B.; Busonero, D.; Carlucci, T.; Castañeda, J.; Charlot, P.; Clotet, M.; Crosta, M.; Davidson, M.; de Felice, F.; Drimmel, R.; Fabricius, C.; Fienga, A.; Figueras, F.; Fraile, E.; Gai, M.; Garralda, N.; Geyer, R.; González-Vidal, J. J.; Guerra, R.; Hambly, N. C.; Hauser, M.; Jordan, S.; Lattanzi, M. G.; Lenhardt, H.; Liao, S.; Löffler, W.; McMillan, P. J.; Mignard, F.; Mora, A.; Morbidelli, R.; Portell, J.; Riva, A.; Sarasso, M.; Serraller, I.; Siddiqui, H.; Smart, R.; Spagna, A.; Stampa, U.; Steele, I.; Taris, F.; Torra, J.; van Reeven, W.; Vecchiato, A.; Zschocke, S.; de Bruijne, J.; Gracia, G.; Raison, F.; Lister, T.; Marchant, J.; Messineo, R.; Soffel, M.; Osorio, J.; de Torres, A.; O'Mullane, W.

2016-11-01

Context. Gaia Data Release 1 (DR1) contains astrometric results for more than 1 billion stars brighter than magnitude 20.7 based on observations collected by the Gaia satellite during the first 14 months of its operational phase. Aims: We give a brief overview of the astrometric content of the data release and of the model assumptions, data processing, and validation of the results. Methods: For stars in common with the Hipparcos and Tycho-2 catalogues, complete astrometric single-star solutions are obtained by incorporating positional information from the earlier catalogues. For other stars only their positions are obtained, essentially by neglecting their proper motions and parallaxes. The results are validated by an analysis of the residuals, through special validation runs, and by comparison with external data. Results: For about two million of the brighter stars (down to magnitude 11.5) we obtain positions, parallaxes, and proper motions to Hipparcos-type precision or better. For these stars, systematic errors depending for example on position and colour are at a level of ± 0.3 milliarcsecond (mas). For the remaining stars we obtain positions at epoch J2015.0 accurate to 10 mas. Positions and proper motions are given in a reference frame that is aligned with the International Celestial Reference Frame (ICRF) to better than 0.1 mas at epoch J2015.0, and non-rotating with respect to ICRF to within 0.03 mas yr-1. The Hipparcos reference frame is found to rotate with respect to the Gaia DR1 frame at a rate of 0.24 mas yr-1. Conclusions: Based on less than a quarter of the nominal mission length and on very provisional and incomplete calibrations, the quality and completeness of the astrometric data in Gaia DR1 are far from what is expected for the final mission products. The present results nevertheless represent a huge improvement in the available fundamental stellar data and practical definition of the optical reference frame.

CCD Astrometric Measurements of WDS 04155+0611

NASA Astrophysics Data System (ADS)

Cao, Zhixin; Li, Junyao; Li, Jeff; Qu, Steve; Fene, Michael; Boyce, Grady; Boyce, Pat

2016-01-01

Twenty-two separations and position angle astrometric measurements were made of the multiple star system WDS 04155+0611. This system includes the pairs STTA 45 AB, H 6 98 AC, H 6 98 CD, and STU 18 CE. All measurements were compared with historical measurements from the Washington Double Star Catalog. Our astrometric results compare favorably with other recent observations.

A setup for Gaia-DR1: the star formation history of our thin disc environment

NASA Astrophysics Data System (ADS)

Miret-Roig, N.; Romero-Gómez, M.; Figueras, F.; Mor, R.

2017-03-01

The first Gaia Data Release (Gaia-DR1, 14 September 2016) primes the pump and paves the way for a new golden age of the galactic astronomy. Gaia-DR1 will provide new parallaxes and proper motions for about two million well-behaved Tycho-2 stars placed in the solar neighborhood. This TGAS (Tycho-Gaia Astrometric Solution) catalogue is being obtained through the combination of the Gaia observations with the positions of the stars obtained by Hipparcos (ESA 1997) when available, or Tycho-2. The aim of the work presented here has been to evaluate the capabilities of Gaia and future on-ground spectroscopic surveys to derive the dynamical age and place of birth of the Young Local Associations (YLAs). Test particle simulations in realistic galactic potentials and different scenarios for the accuracy on astrometric and spectroscopic data allow us to quantify our future capabilities to trace back in time the star formation history of our thin disc environment.

The effect of unresolved contaminant stars on the cross-matching of photometric catalogues

NASA Astrophysics Data System (ADS)

Wilson, Tom J.; Naylor, Tim

2017-07-01

A fundamental process in astrophysics is the matching of two photometric catalogues. It is crucial that the correct objects be paired, and that their photometry does not suffer from any spurious additional flux. We compare the positions of sources in Wide-field Infrared Survey Explorer (WISE), INT Photometric H α Survey, Two Micron All Sky Survey and AAVSO Photometric All Sky Survey with Gaia Data Release 1 astrometric positions. We find that the separations are described by a combination of a Gaussian distribution, wider than naively assumed based on their quoted uncertainties, and a large wing, which some authors ascribe to proper motions. We show that this is caused by flux contamination from blended stars not treated separately. We provide linear fits between the quoted Gaussian uncertainty and the core fit to the separation distributions. We show that at least one in three of the stars in the faint half of a given catalogue will suffer from flux contamination above the 1 per cent level when the density of catalogue objects per point spread function area is above approximately 0.005. This has important implications for the creation of composite catalogues. It is important for any closest neighbour matches as there will be a given fraction of matches that are flux contaminated, while some matches will be missed due to significant astrometric perturbation by faint contaminants. In the case of probability-based matching, this contamination affects the probability density function of matches as a function of distance. This effect results in up to 50 per cent fewer counterparts being returned as matches, assuming Gaussian astrometric uncertainties for WISE-Gaia matching in crowded Galactic plane regions, compared with a closest neighbour match.

Astrometry and Geostationary Satellites in Venezuela

NASA Astrophysics Data System (ADS)

Lacruz, E.; Abad, C.

2015-10-01

We present the current status and the first results of the astrometric project CIDA - ABAE for tracking geo-stationary satellites. This project aims to determine a preliminary orbit for the Venezuelan satellite VENESAT-1, using astrometric positions obtained from an optical telescope. The results presented here are based on observations from the Luepa space tracking ground station in Venezuela, which were processed using astrometric procedures.

Astrometric Detection of a Low Mass Companion Orbiting the Star AB Doradus

NASA Technical Reports Server (NTRS)

Soderhjelm, S.; Guirado, J. C.; Reynolds, J. E.; Lestrade, J. F.; Preston, R. A.; Jauncey, D. L.; Jones, D. L.; Tzioumis, A. K.; Ferris, R. H.; King, E. A.;

Breakthrough in orbit determination of a binary. - In expectation of astrometric observations with high precision such as VERA and JASMINE -

NASA Astrophysics Data System (ADS)

Asada, Hideki

2006-11-01

There exists a very classical inverse problem regarding orbit determination of a binary system: "when an orbital plane of two bodies is inclined with respect to the line of sight, observables are their positions projected onto a celestial sphere. How do we determine the orbital elements from observations?" A "complete exact solution" has been found. It is reviewed with some related topics.

CCD Astrometry with Robotic Telescopes

NASA Astrophysics Data System (ADS)

AlZaben, Faisal; Li, Dewei; Li, Yongyao; Dennis, Aren Fene, Michael; Boyce, Grady; Boyce, Pat

2016-01-01

CCD images were acquired of three binary star systems: WDS06145+1148, WDS06206+1803, and WDS06224+2640. The astrometric solution, position angle, and separation of each system were calculated with MaximDL v6 and Mira Pro x64 software suites. The results were consistent with historical measurements in the Washington Double Star Catalog. Our analysis found some differences in measurements between single-shot color CCD cameras and traditional monochrome CCDs using a filter wheel.

DISCOVERY OF A WANDERING RADIO JET BASE AFTER A LARGE X-RAY FLARE IN THE BLAZAR MARKARIAN 421

DOE Office of Scientific and Technical Information (OSTI.GOV)

Niinuma, K.; Kino, M.; Doi, A.

2015-07-01

We investigate the location of the radio jet bases (“radio cores”) of blazars in radio images and their stationarity by means of dense very long baseline interferometry (VLBI) observations. In order to measure the position of a radio core, we conducted a 12 epoch astrometric observation of the blazar Markarian 421 with the VLBI Exploration of Radio Astrometry at 22 GHz immediately after a large X-ray flare, which occurred in the middle of 2011 September. For the first time,we find that the radio core is not stationary but rather changes its location toward 0.5 mas downstream. This angular scale correspondsmore » to the de-projected length of a scale of 10{sup 5} Schwarzschild radii (R{sub s}) at the distance of Markarian 421. This radio-core wandering may be a new type of manifestation associated with the phenomena of large X-ray flares.« less

GaiaGrid : Its Implications and Implementation

NASA Astrophysics Data System (ADS)

Ansari, S. G.; Lammers, U.; Ter Linden, M.

2005-12-01

Gaia is an ESA space mission to determine positions of 1 billion objects in the Galaxy at micro-arcsecond precision. The data analysis and processing requirements of the mission involves about 20 institutes across Europe, each providing specific algorithms for specific tasks, which range from relativistic effects on positional determination, classification, astrometric binary star detection, photometric analysis, spectroscopic analysis etc. In an initial phase, a study has been ongoing over the past three years to determine the complexity of Gaia's data processing. Two processing categories have materialised: core and shell. While core deals with routine data processing, shell tasks are algorithms to carry out data analysis, which involves the Gaia Community at large. For this latter category, we are currently experimenting with use of Grid paradigms to allow access to the core data and to augment processing power to simulate and analyse the data in preparation for the actual mission. We present preliminary results and discuss the sociological impact of distributing the tasks amongst the community.

Core-shifts and proper-motion constraints in the S5 polar cap sample at the 15 and 43 GHz bands

NASA Astrophysics Data System (ADS)

Abellán, F. J.; Martí-Vidal, I.; Marcaide, J. M.; Guirado, J. C.

2018-06-01

We have studied a complete radio sample of active galactic nuclei with the very-long-baseline-interferometry (VLBI) technique and for the first time successfully obtained high-precision phase-delay astrometry at Q band (43 GHz) from observations acquired in 2010. We have compared our astrometric results with those obtained with the same technique at U band (15 GHz) from data collected in 2000. The differences in source separations among all the source pairs observed in common at the two epochs are compatible at the 1σ level between U and Q bands. With the benefit of quasi-simultaneous U and Q band observations in 2010, we have studied chromatic effects (core-shift) at the radio source cores with three different methods. The magnitudes of the core-shifts are of the same order (about 0.1 mas) for all methods. However, some discrepancies arise in the orientation of the core-shifts determined through the different methods. In some cases these discrepancies are due to insufficient signal for the method used. In others, the discrepancies reflect assumptions of the methods and could be explained by curvatures in the jets and departures from conical jets.

BD+43° 3654 - a blue straggler?

NASA Astrophysics Data System (ADS)

Gvaramadze, V. V.; Bomans, D. J.

2008-07-01

The astrometric data on the runaway star BD+43° 3654 are consistent with the origin of this O4If star in the center of the Cyg OB2 association, while BD+43° 3654 is younger than the association. To reconcile this discrepancy, we suggest that BD+43° 3654 is a blue straggler formed via a close encounter between two tight massive binaries in the core of Cyg OB2. A possible implication of this suggestion is that the very massive (and therefore apparently very young) stars in Cyg OB2 could be blue stragglers as well. We also suggest that the binary-binary encounter producing BD+43° 3654 might be responsible for ejection of two high-velocity stars (the stripped helium cores of massive stars) - the progenitors of the pulsars B2020+28 and B2021+51.

Gamma astrometric measurement experiment -science and implementation

NASA Astrophysics Data System (ADS)

Gai, Mario; Vecchiato, Alberto; Lattanzi, Mario G.; Ligori, Sebastiano; Loreggia, Davide; Fineschi, Silvano

GAME (Gamma Astrometric Measurement Experiment) is a mission concept taking advantage of astronomical techniques for high precision measurements of interest to Fundamental Physics, and in particular the γ parameter of the Parameterized Post-Newtonian formulation of gravi-tation theories modifying the General Relativity. A space based telescope, looking close to the Solar limb thanks to coronagraphic techniques, may implement astrometric measurements sim-ilar to those performed in the solar eclipse of 1919, when Dyson, Eddington and collaborators measured for the first time the gravitational bending of light. Simulations show that the final accuracy of GAME can reach the 10-7 level. GAME will be a decisive experiment for the understanding of gravity physics, cosmology and the Universe evolution. The observations leading to Dark Matter (e.g. galaxy rotation curves) and Dark Energy (accelerated expansion of the Universe) might be explained with a modified version of General Relativity, e.g. in which the curvature invariant R is no longer constant as in Einstein's equations, i.e. the f (R) gravity theories. A 10-7 level determination of γ will provide stringent constraints on acceptable theories. Also, high precision astrometry makes accessible other appealing measurements, e.g. the light deflection induced by the quadrupole moment of giant planets, like Jupiter or Saturn, and, by high precision determination of the orbits of Mercury and high elongation asteroids, the PPN parameter β. GAME may also carry out measurements on selected astrophysical targets, e.g. nearby, bright stars known to host companions with minimum masses in the planetary/brown dwarf regime, and orbital radii in the 3-7 AU range, which are observed by no other present or planned campaigns. GAME, also thanks to high-cadence, high-precision photometry on transit-ing exoplanet systems, will thus improve on our understanding of the actual mass distribution and multiplicity of sub-stellar companions. The GAME measurement principle is based on the differential astrometric signature on the stellar positions. Calibration is implemented by observation of stellar fields affected by neg-ligible deflection. The instrument concept is based on a dual field, multiple aperture Fizeau interferometer, observing simultaneously sky regions close to the Solar limb. Coronagraphic solutions are embedded in the astrometric telescope design, to achieve a rejection factor of the Sun disk and stray light of ˜ 10-9 . An array of apertures implemented by pupil masking on an underlying telescope with primary diameter below one meter, with long focal length, fulfills the mission specifications by providing individual photo-center precision better than 1 milli-arcsecond for source magnitude 15 or brighter.

Interstellar Medium, Young Stars, and Astrometric Binaries in Galactic Archaeology Spectroscopic Surveys

NASA Astrophysics Data System (ADS)

Zwitter, T.; Kos, J.; Žerjal, M.; Traven, G.

2016-10-01

Current ongoing stellar spectroscopic surveys (RAVE, GALAH, Gaia-ESO, LAMOST, APOGEE, Gaia) are mostly devoted to studying Galactic archaeology and the structure of the Galaxy. But they allow also for important auxiliary science: (i) the Galactic interstellar medium can be studied in four dimensions (position in space plus radial velocity) through weak but numerous diffuse interstellar bands and atomic absorptions seen in spectra of background stars, (ii) emission spectra which are quite frequent even in field stars can serve as a good indicator of their youth, pointing e.g. to stars recently ejected from young stellar environments, (iii) an astrometric solution of the photocenter of a binary to be obtained by Gaia can yield accurate masses when joined by spectroscopic information obtained serendipitously during a survey. These points are illustrated by first results from the first three surveys mentioned above. These hint at the near future: spectroscopic studies of the dynamics of the interstellar medium can identify and quantify Galactic fountains which may sustain star formation in the disk by entraining fresh gas from the halo; RAVE already provided a list of ˜ 14,000 field stars with chromospheric emission in Ca II lines, to be supplemented by many more observations by Gaia in the same band, and by GALAH and Gaia-ESO observations of Balmer lines; several millions of astrometric binaries with periods up to a few years which are being observed by Gaia can yield accurate masses when supplemented with measurements from only a few high-quality ground based spectra.

BINARY ASTROMETRIC MICROLENSING WITH GAIA

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sajadian, Sedighe, E-mail: sajadian@ipm.ir; Department of Physics, Sharif University of Technology, P.O. Box 11155-9161, Tehran

2015-04-15

We investigate whether or not Gaia can specify the binary fractions of massive stellar populations in the Galactic disk through astrometric microlensing. Furthermore, we study whether or not some information about their mass distributions can be inferred via this method. In this regard, we simulate the binary astrometric microlensing events due to massive stellar populations according to the Gaia observing strategy by considering (i) stellar-mass black holes, (ii) neutron stars, (iii) white dwarfs, and (iv) main-sequence stars as microlenses. The Gaia efficiency for detecting the binary signatures in binary astrometric microlensing events is ∼10%–20%. By calculating the optical depth duemore » to the mentioned stellar populations, the numbers of the binary astrometric microlensing events being observed with Gaia with detectable binary signatures, for the binary fraction of about 0.1, are estimated to be 6, 11, 77, and 1316, respectively. Consequently, Gaia can potentially specify the binary fractions of these massive stellar populations. However, the binary fraction of black holes measured with this method has a large uncertainty owing to a low number of the estimated events. Knowing the binary fractions in massive stellar populations helps with studying the gravitational waves. Moreover, we investigate the number of massive microlenses for which Gaia specifies masses through astrometric microlensing of single lenses toward the Galactic bulge. The resulting efficiencies of measuring the mass of mentioned populations are 9.8%, 2.9%, 1.2%, and 0.8%, respectively. The numbers of their astrometric microlensing events being observed in the Gaia era in which the lens mass can be inferred with the relative error less than 0.5 toward the Galactic bulge are estimated as 45, 34, 76, and 786, respectively. Hence, Gaia potentially gives us some information about the mass distribution of these massive stellar populations.« less

PARALLAX AND ORBITAL EFFECTS IN ASTROMETRIC MICROLENSING WITH BINARY SOURCES

DOE Office of Scientific and Technical Information (OSTI.GOV)

Nucita, A. A.; Paolis, F. De; Ingrosso, G.

2016-06-01

In gravitational microlensing, binary systems may act as lenses or sources. Identifying lens binarity is generally easy, in particular in events characterized by caustic crossing since the resulting light curve exhibits strong deviations from a smooth single-lensing light curve. In contrast, light curves with minor deviations from a Paczyński behavior do not allow one to identify the source binarity. A consequence of gravitational microlensing is the shift of the position of the multiple image centroid with respect to the source star location — the so-called astrometric microlensing signal. When the astrometric signal is considered, the presence of a binary sourcemore » manifests with a path that largely differs from that expected for single source events. Here, we investigate the astrometric signatures of binary sources taking into account their orbital motion and the parallax effect due to the Earth’s motion, which turn out not to be negligible in most cases. We also show that considering the above-mentioned effects is important in the analysis of astrometric data in order to correctly estimate the lens-event parameters.« less

CCD Parallaxes for 309 Late-type Dwarfs and Subdwarfs

NASA Astrophysics Data System (ADS)

Dahn, Conard C.; Harris, Hugh C.; Subasavage, John P.; Ables, Harold D.; Canzian, Blaise J.; Guetter, Harry H.; Harris, Fred H.; Henden, Arne H.; Leggett, S. K.; Levine, Stephen E.; Luginbuhl, Christian B.; Monet, Alice B.; Monet, David G.; Munn, Jeffrey A.; Pier, Jeffrey R.; Stone, Ronald C.; Vrba, Frederick J.; Walker, Richard L.; Tilleman, Trudy M.

2017-10-01

New, updated, and/or revised CCD parallaxes determined with the Strand Astrometric Reflector at the Naval Observatory Flagstaff Station are presented. Included are results for 309 late-type dwarf and subdwarf stars observed over the 30+ years that the program operated. For 124 of the stars, parallax determinations from other investigators have already appeared in the literature and we compare the different results. Also included here are new or updated VI photometry on the Johnson-Kron-Cousins system for all but a few of the faintest targets. Together with 2MASS JHK s near-infrared photometry, a sample of absolute magnitude versus color and color versus color diagrams are constructed. Because large proper motion was a prime criterion for targeting the stars, the majority turn out to be either M-type subdwarfs or late M-type dwarfs. The sample also includes 50 dwarf or subdwarf L-type stars, and four T dwarfs. Possible halo subdwarfs are identified in the sample based on tangential velocity, subluminosity, and spectral type. Residuals from the solutions for parallax and proper motion for several stars show evidence of astrometric perturbations.

THE APPLICATION OF MULTIVIEW METHODS FOR HIGH-PRECISION ASTROMETRIC SPACE VLBI AT LOW FREQUENCIES

DOE Office of Scientific and Technical Information (OSTI.GOV)

Dodson, R.; Rioja, M.; Imai, H.

2013-06-15

High-precision astrometric space very long baseline interferometry (S-VLBI) at the low end of the conventional frequency range, i.e., 20 cm, is a requirement for a number of high-priority science goals. These are headlined by obtaining trigonometric parallax distances to pulsars in pulsar-black hole pairs and OH masers anywhere in the Milky Way and the Magellanic Clouds. We propose a solution for the most difficult technical problems in S-VLBI by the MultiView approach where multiple sources, separated by several degrees on the sky, are observed simultaneously. We simulated a number of challenging S-VLBI configurations, with orbit errors up to 8 mmore » in size and with ionospheric atmospheres consistent with poor conditions. In these simulations we performed MultiView analysis to achieve the required science goals. This approach removes the need for beam switching requiring a Control Moment Gyro, and the space and ground infrastructure required for high-quality orbit reconstruction of a space-based radio telescope. This will dramatically reduce the complexity of S-VLBI missions which implement the phase-referencing technique.« less

A New Astrometric Reduction of Photographic Plates Using the DAMIAN Digitizer: Improving the Dynamics of the Jovian System

DTIC Science & Technology

2011-01-01

weighted least-squares solutions. In order to perform the instrumental calibration, we evaluated with Praesepe and Pleiades cluster images (50 reference...measurements and in order to use the trail- scale method, the scale factors were calculated with diaphragmed Praesepe and undiaphragmed Pleiades plates taken in...0.002 arcsec mm−1 should be used. In the case of the DAMIAN star link method, we determined the scale factors with the same Praesepe and Pleiades images

Kyiv UkrVO glass archives: new life

NASA Astrophysics Data System (ADS)

Pakuliak, L.; Golovnya, V.; Andruk, V.; Shatokhina, S.; Yizhakevych, O.; Kazantseva, L.; Lukianchuk, V.

In the framework of UkrVO national project the new methods of plate digital image processing are developed. The photographic material of the UkrVO Joint Digital Archive (JDA) is used for the solution of classic astrometric problem - positional and photometric determinations of objects registered on the plates. The results of tested methods show that the positional rms errors are better than ±150 mas for both coordinates and photometric ones are better than ±0.20m with the Tycho-2 catalogue as reference.

Improvements in Ross type astrometric objectives

NASA Technical Reports Server (NTRS)

Baker, J.

1971-01-01

It is shown that aspheric deformations of the first and fourth elements of the four element Ross objective can be introduced to permit one to obtain improved color corrections for astrometric purposes. The usual monochromatic aberrations are as well corrected as for the standard Ross lens. In addition, one can eliminate or reduce additional aberrations, such as secondary spectrum, chromatic spherical aberration, chromatic coma and chromatic distortion. The resulting objectives are suitable for use as intermediate and long focus astrometric objectives covering large angle fields.

On an Allan variance approach to classify VLBI radio-sources on the basis of their astrometric stability

NASA Astrophysics Data System (ADS)

Gattano, C.; Lambert, S.; Bizouard, C.

2017-12-01

In the context of selecting sources defining the celestial reference frame, we compute astrometric time series of all VLBI radio-sources from observations in the International VLBI Service database. The time series are then analyzed with Allan variance in order to estimate the astrometric stability. From results, we establish a new classification that takes into account the whole multi-time scales information. The algorithm is flexible on the definition of ``stable source" through an adjustable threshold.

Global astrometry with OSI

NASA Astrophysics Data System (ADS)

Loiseau, Sacha; Malbet, Fabien; Yu, Jeffrey W.

1995-06-01

We present a method for performing global astrometry with the proposed Orbiting Stellar Interferometer. Because it is dedicated to wide-angle astrometry, OSI has the intrinsic capabilities to achieve global astrometry, even though it doesn't measure directly relative angles between pairs of stars, such as HIPPARCOS. In this paper, a time-independent model is shown, leading to a coherent solution for the positions of reference stars on the whole sky. With an initial measurement accuracy of 10 micro-arcseconds, corresponding to an accuracy of 340 picometers in the knowledge of the delay-line position of the observing interferometer, the consistent least-squares solution gives an accuracy by which the astrometric parameters can be obtained around 2 - 3 micro-arcseconds.

The Großschwabhausen binary survey

NASA Astrophysics Data System (ADS)

Mugrauer, M.; Buder, S.; Reum, F.; Birth, A.

2017-01-01

Background: Since 2009, the Großschwabhausen binary survey is being carried out at the University Observatory Jena. This new imaging survey uses available time slots during photometric monitoring campaigns, caused by nonphotometric weather conditions, which often exhibit good atmospheric seeing. The goal of the project is to obtain current relative astrometric measurements of the binary systems that are listed in the Washington Visual Double Star Catalog. Materials and Methods: For the survey we use the Refraktor-Teleskop-Kamera at the University Observatory Jena to take imaging data of selected visual binary systems. Results: In this paper, we characterize the target sample of the survey, describe the imaging observations and the astrometric measurements including the astrometric calibration, and present the relative astrometric measures of 352 binaries that could be obtained during the course of the Großschwabhausen binary survey, so far.

Pluto-Charon: a test of the astrometric approach for finding asteroid satellites

NASA Astrophysics Data System (ADS)

Kikwaya, J.-B.; Thuillot, W.; Berthier, J.

2003-05-01

The astrometric method to find asteroid satellites is based on the search for the reflex effect on the primary object due to the orbital motion of a possible satellite (Monet & Monet 1998, Kikwaya et al. 2002). As reported by Kikwaya et al. (2003), the astrometric signature of a satellite of 146 Lucina may reach several mas. Spectral analysis might then detect the signal under good conditions of signal/noise ratio, with high quality astrometric measurements and large coverage by different sites of observation. However, the astrometric method cannot be applied to any binary system of asteroids. It depends strongly on the mass ratio of the two bodies and the distance between them (Kikwaya et al. 2002). Pluto-Charon provides a good test of this method. Previous works based on direct imaging of Charon show that its period is 6.357 days and the mass ratio is 0.122 (Wasserman et al. 2000), putting this system into the range that can be observed by our method. Using archived photographic observations (1914-1995) and CCD observations from US Naval Observatory, Flagstaff station (1995-1998), Bordeaux observatory (1996-1997) and Mc Donald Observatory (1997), we are analyzing the position of Pluto to see if its wobble effect due to Charon (amplitude around 95 mas) can be detected and if the orbital period of Charon can be recovered through a spectral analysis. If successful, this will reinforce the ability of our astrometric method to find asteroid satellites.

The Very Low Mass Component of the Gliese 105 System

NASA Astrophysics Data System (ADS)

Golimowski, David A.; Henry, Todd J.; Krist, John E.; Schroeder, Daniel J.; Marcy, Geoffrey W.; Fischer, Debra A.; Butler, R. Paul

2000-10-01

Multiple-epoch, multicolor images of the astrometric binary Gliese 105A and its very low mass companion Gliese 105C have been obtained using the Hubble Space Telescope's Wide Field Planetary Camera 2 (WFPC2) and near-infrared camera and multiobject spectrometer (NICMOS). The optical and near-infrared colors of Gl 105C strongly suggest a spectral type of M7 V for that star. Relative astrometric measurements spanning 3 yr reveal the first evidence of Gl 105C's orbital motion. Previous long-term astrometric studies at Sproul and McCormick Observatories have shown that the period of Gl 105A's perturbation is ~60 yr. To satisfy both the observed orbital motion and Gl 105A's astrometric period, Gl 105C's orbit must have an eccentricity of ~0.75 and a semimajor axis of ~15 AU. Measurements of Gl 105A's radial velocity over 12 yr show a linear trend with a slope of 11.3 m s-1 yr-1, which is consistent with these orbital constraints and a nearly face-on orbit. As no other faint companions to Gl 105A have been detected, we conclude that Gl 105C is probably the source of the 60 yr astrometric perturbation.

On the detection of other planetary systems by astrometric techniques

NASA Technical Reports Server (NTRS)

Black, D. C.; Scargle, J. D.

1982-01-01

A quantitative method for astrometrically detecting perturbations induced in a star's motion by the presence of a planetary object is described. A periodogram is defined, wherein signals observed from a star show exactly periodic variations, which can be extracted from observational data using purely statistical methods. A detection threshold is defined for the frequency of occurrence of some detectable signal, e.g., the Nyquist frequency. Possible effects of a stellar orbital eccentricity and multiple companions are discussed, noting that assumption of a circular orbit assures the spectral purity of the signal described. The periodogram technique was applied to 12 yr of astrometric data from the U.S. Naval Observatory for three stars with low mass stellar companions. Periodic perturbations were confirmed. A comparison of the accuracy of different astrometric systems shows that the detection accuracy of a system is determined by the measurement accuracy and the number of observations, although the detection efficiency can be maximized by minimizing the number of data points for the case when observational errors are proportional to the square root of the number of data points. It is suggested that a space-based astrometric telescope is best suited to take advantage of the method.

Accuracy of the HST Standard Astrometric Catalogs w.r.t. Gaia

NASA Astrophysics Data System (ADS)

Kozhurina-Platais, V.; Grogin, N.; Sabbi, E.

2018-02-01

The goal of astrometric calibration of the HST ACS/WFC and WFC3/UVIS imaging instruments is to provide a coordinate system free of distortion to the precision level of 0.1 pixel 4-5 mas or better. This astrometric calibration is based on two HST astrometric standard fields in the vicinity of the globular clusters, 47 Tuc and omega Cen, respectively. The derived calibration of the geometric distortion is assumed to be accurate down to 2-3 mas. Is this accuracy in agreement with the true value? Now, with the access to globally accurate positions from the first Gaia data release (DR1), we found that there are measurable offsets, rotation, scale and other deviations of distortion parameters in two HST standard astrometric catalogs. These deviations from the distortion-free and properly aligned coordinate system should be accounted and corrected for, so that the high precision HST positions are free of any systematic errors. We also found that the precision of the HST pixel coordinates is substantially better than the accuracy listed in the Gaia DR1. Therefore, in order to finalize the components of distortion in the HST standard catalogs, the next release of Gaia data is needed.

Deblending Microlensing Events Using Astrometric Shifts

NASA Astrophysics Data System (ADS)

Goldberg, D. M.; Wozniak, P.; Paczynski, B.

1997-12-01

In this poster, we present the prospect that astrometric shifts can be used to identify blended microlensing events in crowded fields. Moreover, by measuring an astrometric shift, one can determine the position of the true lensed star with respect to the local field with very high precision. We first perform several simulations of microlensing searches in crowded fields and find that if we assume a dark lens, and that the lensed star obeys a power law luminosity function, n(L)~ L(-beta ) , over half the simulated events show a measurable astrometric shift. For simulations of 20000 stars on a 256x 256 Nyquist sampled CCD frame, we found that with beta =2, 58% of the events were significantly blended (F_{*}/Ftot <= 0.9), and of those, 73% had a large astrometric shift (>= 0.5 pixels). For beta =3, we found that 85% were significantly blended, and that 85% of those had a significant shift. Since we expect most blended events to show a significant shift, we look in the OGLE I database (Wozniak & Szymanski 1997), and find measurable and systematic shifts in over half the candidate microlensing events, including OGLE # 5, which was considered to be blended from photometric data.

On the orbit calculation of visual binaries with a very short arc: application to the PMS binary system, FW Tau AB

NASA Astrophysics Data System (ADS)

Docobo, J. A.; Tamazian, V. S.; Campo, P. P.

2018-05-01

In the vast majority of cases when available astrometric measurements of a visual binary cover a very short orbital arc, it is practically impossible to calculate a good quality orbit. It is especially important for systems with pre-main-sequence components where standard mass-spectrum calibrations cannot be applied nor can a dynamical parallax be calculated. We have shown that the analytical method of Docobo allows us to put certain constraints on the most likely orbital solutions, using an available realistic estimate of the global mass of the system. As an example, we studied the interesting PMS binary, FW Tau AB, located in the Taurus-Auriga as well as investigated a range of its possible orbital solutions combined with an assumed distance between 120 and 160 pc. To maintain the total mass of FW Tau AB in a realistic range between 0.2 and 0.6M_{⊙}, minimal orbital periods should begin at 105, 150, 335, and 2300 yr for distances of 120, 130, 140, and 150 pc, respectively (no plausible orbits were found assuming a distance of 160 pc). An original criterion to establish the upper limit of the orbital period is applied. When the position angle in some astrometric measurements was flipped by 180°, orbits with periods close to 45 yr are also plausible. Three example orbits with periods of 44.6, 180, and 310 yr are presented.

Forthcoming Occultations of Astrometric Radio Sources by Planets

NASA Technical Reports Server (NTRS)

L'vov, Victor; Malkin, Zinovy; Tsekmeister, Svetlana

2010-01-01

Astrometric observations of radio source occultations by solar system bodies may be of large interest for testing gravity theories, dynamical astronomy, and planetary physics. In this paper, we present an updated list of the occultations of astrometric radio sources by planets expected in the coming years. Such events, like solar eclipses, generally speaking can only be observed in a limited region. A map of the shadow path is provided for the events that will occurr in regions with several VLBI stations and hence will be the most interesting for radio astronomy experiments.

The Full-sky Astrometric Mapping Explorer - Astrometry for the New Millennium

NASA Astrophysics Data System (ADS)

Horner, S. D.; Germain, M. E.; Greene, T. P.; Harris, F. H.; Johnson, M. S.; Johnson, K. J.; Monet, D. G.; Murison, M. A.; Phillips, J. D.; Reasenberg, R. D.; Seidelmann, P. K.; Urban, S. E.; Vassar, R. H.

FAME is designed to perform an all-sky, astrometric survey with unprecedented accuracy. It will create a rigid astrometric catalog of ~40,000,000 stars with visual band magnitudes 5 < V < 15. For bright stars, 5 < V < 9, FAME will determine positions and parallaxes accurate to < 50 microarcseconds, with proper motion errors < 50 microarcseconds/year. For fainter stars, 9 < V < 15, FAME will determine positions and parallaxes accurate to < 300 microarcseconds, with proper motion errors < 300 microarcseconds/year. It will also collect photometric data on these 40,000,000 stars in four Sloan DSS colors. The FAME data will provide a rigid, accurate, optical, astrometric grid. The proper motion data, combined with Hipparcos and other data should be ideal for use by the Space Interferometry Mission (SIM) to select its astrometric reference grid stars. FAME will also identify stars with nonlinear proper motions as candidates for further study by SIM, Terrestrial Planet Finder, and future ground based interferometers as possible planetary systems. The fundamental astrometric data provided at relatively low cost by FAME will help optimize the scientific return from these future projects. This is in addition to the considerable direct scientific return from FAME. It will redefine the extragalactic distance scale and provide a large, rich database of information on stellar properties that will enable numerous science investigations into stellar structure and evolution, the dynamics of the Milky Way, and stellar companions including brown dwarfs and giant planets. NASA has selected the Full-sky Astrometric Mapping Explorer (FAME) to be one of five MIDEX missions to be funded for a concept study. This concept study will be submitted to NASA on 18 June, with final selection, scheduled for September, of two of these missions for fli ght in 2003 or 2004. FAME is a joint development e ffort of the U.S. Naval Observatory, the Smithsonian Astrophysical Observatory, the Infrared Processing and Analysis Center, Lockheed Martin Missiles and Space, the Naval Research Laboratory, and Omitron Incorporated.

Inferring Binary and Trinary Stellar Populations in Photometric and Astrometric Surveys

NASA Astrophysics Data System (ADS)

Widmark, Axel; Leistedt, Boris; Hogg, David W.

2018-04-01

Multiple stellar systems are ubiquitous in the Milky Way but are often unresolved and seen as single objects in spectroscopic, photometric, and astrometric surveys. However, modeling them is essential for developing a full understanding of large surveys such as Gaia and connecting them to stellar and Galactic models. In this paper, we address this problem by jointly fitting the Gaia and Two Micron All Sky Survey photometric and astrometric data using a data-driven Bayesian hierarchical model that includes populations of binary and trinary systems. This allows us to classify observations into singles, binaries, and trinaries, in a robust and efficient manner, without resorting to external models. We are able to identify multiple systems and, in some cases, make strong predictions for the properties of their unresolved stars. We will be able to compare such predictions with Gaia Data Release 4, which will contain astrometric identification and analysis of binary systems.

Astrometric cosmology .

NASA Astrophysics Data System (ADS)

Lattanzi, M. G.

The accurate measurement of the motions of stars in our Galaxy can provide access to the cosmological signatures in the disk and halo, while astrometric experiments from within our Solar System can uniquely probe possible deviations from General Relativity. This article will introduce to the fact that astrometry has the potential, thanks also to impressive technological advancements, to become a key player in the field of local cosmology. For example, accurate absolute kinematics at the scale of the Milky Way can, for the first time in situ, account for the predictions made by the cold dark matter model for the Galactic halo, and eventually map out the distribution of dark matter, or other formation mechanisms, required to explain the signatures recently identified in the old component of the thick disk. Final notes dwell on to what extent Gaia can fulfill the expectations of astrometric cosmology and on what must instead be left to future, specifically designed, astrometric experiments.

Evidence for Unresolved Exoplanet-hosting Binaries in Gaia DR2

NASA Astrophysics Data System (ADS)

Evans, Daniel F.

2018-05-01

This note describes an effort to detect additional stellar sources in known transiting exoplanet (TEP) systems, which are unresolved or barely resolved in the Gaia Data Release 2 (DR2) catalogue. The presence of multiple unresolved stars in photometric and spectroscopic observations of a transiting planetary system biases measurements of the planet's radius, mass, and atmospheric conditions. In addition to the effect on individual planetary systems, the presence of unresolved stars across the sample of known exoplanets biases our overall understanding of planetary systems, due to the systematic underestimation of both masses and radii. This work uses the Astrometric Goodness of Fit in the Along-Scan direction (GOF_AL) and the Astrometric Excess Noise as indicators of poorly-resolved binaries. Many known close binaries in the exoplanet host star sample have highly significant GOF_AL and Astrometric Excess Noise values, such as WASP-20AB with Astrometric Excess Noise significant at $4720\\sigma$ and GOF_AL=124.

VizieR Online Data Catalog: 5 Galactic GC proper motions from Gaia DR1 (Watkins+, 2017)

NASA Astrophysics Data System (ADS)

Watkins, L. L.; van der Marel, R. P.

2017-11-01

We present a pilot study of Galactic globular cluster (GC) proper motion (PM) determinations using Gaia data. We search for GC stars in the Tycho-Gaia Astrometric Solution (TGAS) catalog from Gaia Data Release 1 (DR1), and identify five members of NGC 104 (47 Tucanae), one member of NGC 5272 (M3), five members of NGC 6121 (M4), seven members of NGC 6397, and two members of NGC 6656 (M22). By taking a weighted average of member stars, fully accounting for the correlations between parameters, we estimate the parallax (and, hence, distance) and PM of the GCs. This provides a homogeneous PM study of multiple GCs based on an astrometric catalog with small and well-controlled systematic errors and yields random PM errors similar to existing measurements. Detailed comparison to the available Hubble Space Telescope (HST) measurements generally shows excellent agreement, validating the astrometric quality of both TGAS and HST. By contrast, comparison to ground-based measurements shows that some of those must have systematic errors exceeding the random errors. Our parallax estimates have uncertainties an order of magnitude larger than previous studies, but nevertheless imply distances consistent with previous estimates. By combining our PM measurements with literature positions, distances, and radial velocities, we measure Galactocentric space motions for the clusters and find that these also agree well with previous analyses. Our analysis provides a framework for determining more accurate distances and PMs of Galactic GCs using future Gaia data releases. This will provide crucial constraints on the near end of the cosmic distance ladder and provide accurate GC orbital histories. (4 data files).

New high-precision orbital and physical parameters of the double-lined low-mass spectroscopic binary BY Draconis

NASA Astrophysics Data System (ADS)

Hełminiak, K. G.; Konacki, M.; Muterspaugh, M. W.; Browne, S. E.; Howard, A. W.; Kulkarni, S. R.

2012-01-01

We present the most precise to date orbital and physical parameters of the well-known short period (P= 5.975 d), eccentric (e= 0.3) double-lined spectroscopic binary BY Draconis (BY Dra), a prototype of a class of late-type, active, spotted flare stars. We calculate the full spectroscopic/astrometric orbital solution by combining our precise radial velocities (RVs) and the archival astrometric measurements from the Palomar Testbed Interferometer (PTI). The RVs were derived based on the high-resolution echelle spectra taken between 2004 and 2008 with the Keck I/high-resolution echelle spectrograph, Shane/CAT/HamSpec and TNG/SARG telescopes/spectrographs using our novel iodine-cell technique for double-lined binary stars. The RVs and available PTI astrometric data spanning over eight years allow us to reach 0.2-0.5 per cent level of precision in Msin 3i and the parallax but the geometry of the orbit (i≃ 154°) hampers the absolute mass precision to 3.3 per cent, which is still an order of magnitude better than for previous studies. We compare our results with a set of Yonsei-Yale theoretical stellar isochrones and conclude that BY Dra is probably a main-sequence system more metal rich than the Sun. Using the orbital inclination and the available rotational velocities of the components, we also conclude that the rotational axes of the components are likely misaligned with the orbital angular momentum. Given BY Dra's main-sequence status, late spectral type and the relatively short orbital period, its high orbital eccentricity and probable spin-orbit misalignment are not in agreement with the tidal theory. This disagreement may possibly be explained by smaller rotational velocities of the components and the presence of a substellar mass companion to BY Dra AB.

HIGH-PRECISION RADIO AND INFRARED ASTROMETRY OF LSPM J1314+1320AB. I. PARALLAX, PROPER MOTIONS, AND LIMITS ON PLANETS

DOE Office of Scientific and Technical Information (OSTI.GOV)

Forbrich, Jan; Dupuy, Trent J.; Rizzuto, Aaron

2016-08-10

We present multi-epoch astrometric radio observations with the Very Long Baseline Array (VLBA) of the young ultracool-dwarf binary LSPM J1314+1320AB. The radio emission comes from the secondary star. Combining the VLBA data with Keck near-infrared adaptive-optics observations of both components, a full astrometric fit of parallax (π {sub abs} = 57.975 ± 0.045 mas, corresponding to a distance of d = 17.249 ± 0.013 pc), proper motion (μ {sub α} {sub cos} {sub δ} = −247.99 ± 0.10 mas yr{sup −1}, μ {sub δ} = −183.58 ± 0.22 mas yr{sup −1}), and orbital motion is obtained. Despite the fact thatmore » the two components have nearly identical masses to within ±2%, the secondary’s radio emission exceeds that of the primary by a factor of ≳30, suggesting a difference in stellar rotation history, which could result in different magnetic field configurations. Alternatively, the emission could be anisotropic and beamed toward us for the secondary but not for the primary. Using only reflex motion, we exclude planets of mass 0.7–10 M {sub jup} with orbital periods of 600–10 days, respectively. Additionally, we use the full orbital solution of the binary to derive an upper limit for the semimajor axis of 0.23 au for stable planetary orbits within this system. These limits cover a parameter space that is inaccessible with, and complementary to, near-infrared radial velocity surveys of ultracool dwarfs. Our absolute astrometry will constitute an important test for the astrometric calibration of Gaia .« less

A Unified tool to estimate Distances, Ages, and Masses (UniDAM) from spectrophotometric data

NASA Astrophysics Data System (ADS)

Mints, Alexey; Hekker, Saskia

2017-08-01

Context. Galactic archaeology, the study of the formation and evolution of the Milky Way by reconstructing its past from its current constituents, requires precise and accurate knowledge of stellar parameters for as many stars as possible. To achieve this, a number of large spectroscopic surveys have been undertaken and are still ongoing. Aims: So far consortia carrying out the different spectroscopic surveys have used different tools to determine stellar parameters of stars from their derived effective temperatures (Teff), surface gravities (log g), and metallicities ([Fe/H]); the parameters can be combined with photometric, astrometric, interferometric, or asteroseismic information. Here we aim to homogenise the stellar characterisation by applying a unified tool to a large set of publicly available spectrophotometric data. Methods: We used spectroscopic data from a variety of large surveys combined with infrared photometry from 2MASS and AllWISE and compared these in a Bayesian manner with PARSEC isochrones to derive probability density functions (PDFs) for stellar masses, ages, and distances. We treated PDFs of pre-helium-core burning, helium-core burning, and post helium-core burning solutions as well as different peaks in multimodal PDFs (I.e. each unimodal sub-PDF) of the different evolutionary phases separately. Results: For over 2.5 million stars we report mass, age, and distance estimates for each evolutionary phase and unimodal sub-PDF. We report Gaussian, skewed, Gaussian, truncated Gaussian, modified truncated exponential distribution or truncated Student's t-distribution functions to represent each sub-PDF, allowing us to reconstruct detailed PDFs. Comparisons with stellar parameter estimates from the literature show good agreement within uncertainties. Conclusions: We present UniDAM, the unified tool applicable to spectrophotometric data of different surveys, to obtain a homogenised set of stellar parameters. The unified tool and the tables with results are available at the CDS via anonymous ftp to http://cdsarc.u-strasbg.fr (http://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/604/A108

Comparative feasibility study of two concepts for a space-based astrometric satellite

NASA Technical Reports Server (NTRS)

Bamdermann, L.; Bareket, N.; Metheny, W.

1982-01-01

A comparative feasibility study of two concepts for an astrometric satellite: a visual imaging telescope with a 16.5 meter focal length and a white light interferometer with a 15 meter baseline separation was conducted.

Project Orion: A Design Study of a System for Detecting Extrasolar Planets

NASA Technical Reports Server (NTRS)

Black, D. C. (Editor)

1980-01-01

A design concept for a ground based astrometric telescope that could significantly increase the potential accuracy of astrometric observations is considered. The state of current techniques and instrumentation is examined in the context of detecting extrasolar planets. Emphasis is placed on the direct detection of extrasolar planets at either visual or infrared wavelengths. The design concept of the imaging stellar interferometer (ISI), developed under Project Orion, is described. The Orion ISI employs the state-of-the-art technology and is theoretically capable of attaining 0.00010 arc sec/yr accuracy in relative astrometric observations.

Microlensing Constraints on the Mass of Single Stars from HST Astrometric Measurements

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kains, N.; Calamida, A.; Sahu, K. C.

Here, we report on the first results from a large-scale observing campaign aiming to use astrometric microlensing to detect and place limits on the mass of single objects, including stellar remnants. We used the Hubble Space Telescope to monitor stars near the Galactic Center for three years, and we measured the brightness and positions of ~2 million stars at each observing epoch. In addition to this, we monitored the same pointings using the VIMOS imager on the Very Large Telescope. The stars we monitored include several bright microlensing events observed from the ground by the OGLE collaboration. In this paper,more » we present the analysis of our photometric and astrometric measurements for six of these events, and derive mass constraints for the lens in each of them. Although these constraints are limited by the photometric precision of ground-based data, and our ability to determine the lens distance, we were able to constrain the size of the Einstein ring radius thanks to our precise astrometric measurements—the first routine measurements of this type from a large-scale observing program. In conclusion, this demonstrates the power of astrometric microlensing as a tool to constrain the masses of stars, stellar remnants, and, in the future, extrasolar planets, using precise ground- and space-based observations.« less

Microlensing Constraints on the Mass of Single Stars from HST Astrometric Measurements

DOE PAGES

Kains, N.; Calamida, A.; Sahu, K. C.; ...

2017-07-14

Here, we report on the first results from a large-scale observing campaign aiming to use astrometric microlensing to detect and place limits on the mass of single objects, including stellar remnants. We used the Hubble Space Telescope to monitor stars near the Galactic Center for three years, and we measured the brightness and positions of ~2 million stars at each observing epoch. In addition to this, we monitored the same pointings using the VIMOS imager on the Very Large Telescope. The stars we monitored include several bright microlensing events observed from the ground by the OGLE collaboration. In this paper,more » we present the analysis of our photometric and astrometric measurements for six of these events, and derive mass constraints for the lens in each of them. Although these constraints are limited by the photometric precision of ground-based data, and our ability to determine the lens distance, we were able to constrain the size of the Einstein ring radius thanks to our precise astrometric measurements—the first routine measurements of this type from a large-scale observing program. In conclusion, this demonstrates the power of astrometric microlensing as a tool to constrain the masses of stars, stellar remnants, and, in the future, extrasolar planets, using precise ground- and space-based observations.« less

DOE Office of Scientific and Technical Information (OSTI.GOV)

Casey, Andrew R.; Hawkins, Keith; Koposov, Sergey

The orbits, atmospheric parameters, chemical abundances, and ages of individual stars in the Milky Way provide the most comprehensive illustration of galaxy formation available. The Tycho- Gaia Astrometric Solution (TGAS) will deliver astrometric parameters for the largest ever sample of Milky Way stars, though its full potential cannot be realized without the addition of complementary spectroscopy. Among existing spectroscopic surveys, the RAdial Velocity Experiment (RAVE) has the largest overlap with TGAS (≳200,000 stars). We present a data-driven re-analysis of 520,781 RAVE spectra using The Cannon . For red giants, we build our model using high-fidelity APOGEE stellar parameters and abundancesmore » for stars that overlap with RAVE. For main sequence and sub-giant stars, our model uses stellar parameters from the K2/EPIC . We derive and validate effective temperature T {sub eff}, surface gravity log g , and chemical abundances of up to seven elements (O, Mg, Al, Si, Ca, Fe, and Ni). We report a total of 1,685,851 elemental abundances with a typical precision of 0.07 dex, a substantial improvement over previous RAVE data releases. The synthesis of RAVE-on and TGAS is the most powerful data set for chemo-dynamic analyses of the Milky Way ever produced.« less

CCD Parallaxes for 309 Late-type Dwarfs and Subdwarfs

DOE Office of Scientific and Technical Information (OSTI.GOV)

Dahn, Conard C.; Harris, Hugh C.; Subasavage, John P.

2017-10-01

New, updated, and/or revised CCD parallaxes determined with the Strand Astrometric Reflector at the Naval Observatory Flagstaff Station are presented. Included are results for 309 late-type dwarf and subdwarf stars observed over the 30+ years that the program operated. For 124 of the stars, parallax determinations from other investigators have already appeared in the literature and we compare the different results. Also included here are new or updated VI photometry on the Johnson–Kron-Cousins system for all but a few of the faintest targets. Together with 2MASS JHK{sub s} near-infrared photometry, a sample of absolute magnitude versus color and color versusmore » color diagrams are constructed. Because large proper motion was a prime criterion for targeting the stars, the majority turn out to be either M-type subdwarfs or late M-type dwarfs. The sample also includes 50 dwarf or subdwarf L-type stars, and four T dwarfs. Possible halo subdwarfs are identified in the sample based on tangential velocity, subluminosity, and spectral type. Residuals from the solutions for parallax and proper motion for several stars show evidence of astrometric perturbations.« less

Uncovering the identities of compact objects in high-mass X-ray binaries and gamma-ray binaries by astrometric measurements

NASA Astrophysics Data System (ADS)

Yamaguchi, M. S.; Yano, T.; Gouda, N.

2018-03-01

We develop a method for identifying a compact object in binary systems with astrometric measurements and apply it to some binaries. Compact objects in some high-mass X-ray binaries and gamma-ray binaries are unknown, which is responsible for the fact that emission mechanisms in such systems have not yet confirmed. The accurate estimate of the mass of the compact object allows us to identify the compact object in such systems. Astrometric measurements are expected to enable us to estimate the masses of the compact objects in the binary systems via a determination of a binary orbit. We aim to evaluate the possibility of the identification of the compact objects for some binary systems. We then calculate probabilities that the compact object is correctly identified with astrometric observation (= confidence level) by taking into account a dependence of the orbital shape on orbital parameters and distributions of masses of white dwarfs, neutron stars and black holes. We find that the astrometric measurements with the precision of 70 μas for γ Cas allow us to identify the compact object at 99 per cent confidence level if the compact object is a white dwarf with 0.6 M⊙. In addition, we can identify the compact object with the precision of 10 μas at 97 per cent or larger confidence level for LS I +61° 303 and 99 per cent or larger for HESS J0632+057. These results imply that the astrometric measurements with the 10 μas precision level can realize the identification of compact objects for γ Cas, LS I +61° 303, and HESS J0632+057.

CCD Astrometric Measurements of WDS 08167+4053 Using the iTelescope Network

NASA Astrophysics Data System (ADS)

Riley, Bill; Li, Dewei; Li, Junyao; Dennis, Aren; Boyce, Grady; Boyce, Pat

2016-10-01

Separations and position angle astrometric measurements were made of the multiple star system WDS 08167+4053 AB, AC, and BC components. Our measurements compared favorably with historical measurements from the United States Naval Observatory Washington Double Star Catalog, confirming the trend.

CCD Astrometric Measurements of WDS 05247+3723

NASA Astrophysics Data System (ADS)

Chasin, Mike; Adas, Matthew; Tanon, Naylynn; Boyce, Grady; Boyce, Pat

2017-07-01

Theta and rho astrometric measurements were made of the double star system WDS 05247+3723 pairs AB, AC, and CD. These measurements compared favorably with the historic data from the Washington Double Star Catalog (WDS). We also measured the AD, BC, & BD pair relative astrometry.

The science, technology and mission design for the Laser Astrometric test of relativity

NASA Technical Reports Server (NTRS)

Turyshev, Slava G.

2006-01-01

The Laser Astrometric Test of Relativity (LATOR) is a Michelson-Morley-type experiment designed to test the Einstein's general theory of relativity in the most intense gravitational environment available in the solar system - the close proximity to the Sun.

ON THE CONNECTION OF THE APPARENT PROPER MOTION AND THE VLBI STRUCTURE OF COMPACT RADIO SOURCES

DOE Office of Scientific and Technical Information (OSTI.GOV)

Moor, A.; Frey, S.; Lambert, S. B.

2011-06-15

Many of the compact extragalactic radio sources that are used as fiducial points to define the celestial reference frame are known to have proper motions detectable with long-term geodetic/astrometric very long baseline interferometry (VLBI) measurements. These changes can be as high as several hundred microarcseconds per year for certain objects. When imaged with VLBI at milliarcsecond (mas) angular resolution, these sources (radio-loud active galactic nuclei) typically show structures dominated by a compact, often unresolved 'core' and a one-sided 'jet'. The positional instability of compact radio sources is believed to be connected with changes in their brightness distribution structure. For themore » first time, we test this assumption in a statistical sense on a large sample rather than on only individual objects. We investigate a sample of 62 radio sources for which reliable long-term time series of astrometric positions as well as detailed 8 GHz VLBI brightness distribution models are available. We compare the characteristic direction of their extended jet structure and the direction of their apparent proper motion. We present our data and analysis method, and conclude that there is indeed a correlation between the two characteristic directions. However, there are cases where the {approx}1-10 mas scale VLBI jet directions are significantly misaligned with respect to the apparent proper motion direction.« less

High Astrometric Precision in the Calculation of the Coordinates of Orbiters in the GEO Ring

NASA Astrophysics Data System (ADS)

Lacruz, E.; Abad, C.; Downes, J. J.; Hernández-Pérez, F.; Casanova, D.; Tresaco, E.

2018-04-01

We present an astrometric method for the calculation of the positions of orbiters in the GEO ring with a high precision, through a rigorous astrometric treatment of observations with a 1-m class telescope, which are part of the CIDA survey of the GEO ring. We compute the distortion pattern to correct for the systematic errors introduced by the optics and electronics of the telescope, resulting in absolute mean errors of 0.16″ and 0.12″ in right ascension and declination, respectively. These correspond to ≍25 m at the mean distance of the GEO ring, and are thus good quality results.

Astrometric Calibrations of HST Images in the Era of Gaia.

NASA Astrophysics Data System (ADS)

Kozhurina-Platais, Vera; Grogin, Norman A.; Sabbi, Elena

2018-06-01

It is well-known that HST images, taken with ACS/WFC and WFC3/UVIS, have substantial geometric distortion. Over the years our knowledge about this distortion has been vastly improved. Nevertheless, in certain applications it may not be good enough. Preliminary results of comparison state-of-the-art HST astrometric standards and the Gaia DR1 indicate significant scale difference, global rotation, and edge effects in the HST data. However, in terms of positional precision the HST standards are not surpassed yet. The next release of Gaia data DR2 were used to finalize and improve the HST astrometric calibrations down to 0.5 mas or better.

The Gaia Catalogue Second Data Release and Its Implications to Optical Observations of Man-Made Earth Orbiting Objects

NASA Technical Reports Server (NTRS)

Frith, James M.; Buckalew, Brent A.; Cowardin, Heather M.; Lederer, Susan M.

2018-01-01

The Gaia catalogue second data release and its implications to optical observations of man-made Earth orbiting objects. Abstract and not the Final Paper is attached. The Gaia spacecraft was launched in December 2013 by the European Space Agency to produce a three-dimensional, dynamic map of objects within the Milky Way. Gaia's first year of data was released in September 2016. Common sources from the first data release have been combined with the Tycho-2 catalogue to provide a 5 parameter astrometric solution for approximately 2 million stars. The second Gaia data release is scheduled to come out in April 2018 and is expected to provide astrometry and photometry for more than 1 billion stars, a subset of which with a the full 6 parameter astrometric solution (adding radial velocity) and positional accuracy better than 0.002 arcsec (2 mas). In addition to precise astrometry, a unique opportunity exists with the Gaia catalogue in its production of accurate, broadband photometry using the Gaia G filter. In the past, clear filters have been used by various groups to maximize likelihood of detection of dim man-made objects but these data were very difficult to calibrate. With the second release of the Gaia catalogue, a ground based system utilizing the G band filter will have access to 1.5 billion all-sky calibration sources down to an accuracy of 0.02 magnitudes or better. In this talk, we will discuss the advantages and practicalities of implementing the Gaia filters and catalogue into data pipelines designed for optical observations of man-made objects.

VizieR Online Data Catalog: URAT Parallax Catalog (UPC) (Finch+, 2016)

NASA Astrophysics Data System (ADS)

Finch, C. T.; Zacharias, N.

2016-04-01

The URAT Parallax Catalog (UPC) consists of 112177 parallaxes. The catalog utilizes all Northern Hemisphere epoch data from the United States Naval Observatory (USNO) Robotic Astrometric Telescope (URAT). This data includes all individual exposures from April 2012 to June 2015 giving a larger epoch baseline for determining parallaxes over the 2-year span of the First USNO Robotic Astrometric Telescope Catalog (URAT1) (Zacharias et al., 2015, Cat. I/329) published data. The URAT parallax pipeline is custom code that utilizes routines from (Jao, C.-W., 2004, PhD thesis Georgia Stat), the JPL DE405 ephemeris and Green's parallax factor (Green, R.M., 1985, Spherical Astronomy) for determining parallaxes from a weighted least-squares reduction. The relative parallaxes have been corrected to absolute by using the distance color relation described in (Finch et. al, 2014, Cat. J/AJ/148/119) to determine a mean distance of all UCAC4 reference stars (R=8-16 mag) used in the astrometric reductions. Presented here are all significant parallaxes from the URAT Northern Hemisphere epoch data comprising of 2 groups: a) URAT parallax results for stars with prior published parallax, and b) first time trigonometric parallaxes as obtained from URAT data of stars without prior published parallax. Note, more stringent selection criteria have been applied to the second group than the first in order to keep the rate of false detections low. For specific information about the astrometric reductions please see 'The First U.S. Naval Observatory Robotic Astrometric Telescope Catalog' published paper (Zacharias et al., 2015AJ....150..101Z, Cat. I/329). For complete details regarding the parallax pipeline please see 'Parallax Results From URAT Epoch Data' (Finch and Zacharias, 2016, AJ, in press). This catalog gives all positions on the ICRS at Epoch J2014.0; it covers the magnitude range 6.56 to 16.93 in the URAT band-pass, with an average parallax precision of 4.3mas for stars having no known parallax and 10.8mas for stars matched to external parallax sources. This catalog covers the sky from about North of -12.75° declination. This catalog was matched with the Hipparcos catalog, Yale Parallax Catalog, (Finch & Zacharias, 2016, AJ, in press), MEarth (Dittmann et. al., 2014ApJ...784..156D) and the SIMBAD database to obtain known parallax and star names. For stars matched to SIMBAD using the automated search feature, only the parallaxes are given so no information on the parallax errors or source for the parallax are reported for those stars in this catalog. A flag is included to show which catalog or database the URAT parallax was matched with. Only the data from the first catalog that was matched is reported here according to the following priority list. This means for example, if a star was matched with Hipparcos, that information was used while possible other catalog data are not listed here. -------------------------------------------------------- # stars flg catalog -------------------------------------------------------- 53500 0 no catalog match 55549 1 Hipparcos 254 2 Yale Parallax Catalog 1041 3 Finch and Zacharias 2016 (UPM NNNN-NNNN) 1431 4 MEarth parallaxes 402 5 SIMBAD Database (w/parallax) -------------------------------------------------------- 112177 total number stars in catalog -------------------------------------------------------- Not all parallaxes from the URAT epoch data are included in this catalog. Only those data meeting the following criteria have been included. For the epoch data we only used data having a FWHM<=7.0pixel; amplitude between 500 and 30000ADU; sigma x,y <=90.0mas; number of observations >=20 and epoch span>=1.0 years. The limits imposed on individual image amplitude, image profile width (FWHM) and position fit errors (sigma) are set to not allow saturated stars, stars with too few photons or poorly determined positions to be used in the parallax solution. We present all URAT parallax solutions having a known parallax from an external data source regardless of the quality of the solution (srcflg=1-5). This was done for the user to better understand the limitations for determining parallaxes with the current URAT epoch data. For the remaining URAT parallaxes without a match to any published trigonometric parallax (srcflg=0) we only present a parallax solutions having: 1) a parallax error <=10mas 2) a parallax error <=1/4 the relative parallax 3) epoch span >=1.5 years 4) number of observations used >=30 5) fit sigma<=1.4 (unit weight) 6) average image elongation <1.1. All of these cuts have been implemented in an attempt to lower the number of possible erroneous parallax solutions entering our catalog. However, the URAT reduction process does not take provisions for close doubles (blended images) of arcsecond-level separations. Many of the parallaxes, particularly those with large mean elongation, large parallax error, large fit sigma and many rejected observations are possibly blended images leading to a higher chance of an erroneous parallax solutions. A visual inspection of all residual plots and real sky images would not be practical for the entire catalog. However, we have included information in the catalog to help the user to determine if a solution should be investigated further. (1 data file).

Unrecognized astrometric confusion in the Galactic Centre

NASA Astrophysics Data System (ADS)

Plewa, P. M.; Sari, R.

2018-06-01

The Galactic Centre is a crowded stellar field and frequent unrecognized events of source confusion, which involve undetected faint stars, are expected to introduce astrometric noise on a sub-mas level. This confusion noise is the main non-instrumental effect limiting the astrometric accuracy and precision of current near-infrared imaging observations and the long-term monitoring of individual stellar orbits in the vicinity of the central supermassive black hole. We self-consistently simulate the motions of the known and the yet unidentified stars to characterize this noise component and show that a likely consequence of source confusion is a bias in estimates of the stellar orbital elements, as well as the inferred mass and distance of the black hole, in particular if stars are being observed at small projected separations from it, such as the star S2 during pericentre passage. Furthermore, we investigate modelling the effect of source confusion as an additional noise component that is time-correlated, demonstrating a need for improved noise models to obtain trustworthy estimates of the parameters of interest (and their uncertainties) in future astrometric studies.

The RAVE-on Catalog of Stellar Atmospheric Parameters and Chemical Abundances for Chemo-dynamic Studies in the Gaia Era

NASA Astrophysics Data System (ADS)

Casey, Andrew R.; Hawkins, Keith; Hogg, David W.; Ness, Melissa; Rix, Hans-Walter; Kordopatis, Georges; Kunder, Andrea; Steinmetz, Matthias; Koposov, Sergey; Enke, Harry; Sanders, Jason; Gilmore, Gerry; Zwitter, Tomaž; Freeman, Kenneth C.; Casagrande, Luca; Matijevič, Gal; Seabroke, George; Bienaymé, Olivier; Bland-Hawthorn, Joss; Gibson, Brad K.; Grebel, Eva K.; Helmi, Amina; Munari, Ulisse; Navarro, Julio F.; Reid, Warren; Siebert, Arnaud; Wyse, Rosemary

2017-05-01

The orbits, atmospheric parameters, chemical abundances, and ages of individual stars in the Milky Way provide the most comprehensive illustration of galaxy formation available. The Tycho-Gaia Astrometric Solution (TGAS) will deliver astrometric parameters for the largest ever sample of Milky Way stars, though its full potential cannot be realized without the addition of complementary spectroscopy. Among existing spectroscopic surveys, the RAdial Velocity Experiment (RAVE) has the largest overlap with TGAS (≳200,000 stars). We present a data-driven re-analysis of 520,781 RAVE spectra using The Cannon. For red giants, we build our model using high-fidelity APOGEE stellar parameters and abundances for stars that overlap with RAVE. For main sequence and sub-giant stars, our model uses stellar parameters from the K2/EPIC. We derive and validate effective temperature T eff, surface gravity log g, and chemical abundances of up to seven elements (O, Mg, Al, Si, Ca, Fe, and Ni). We report a total of 1,685,851 elemental abundances with a typical precision of 0.07 dex, a substantial improvement over previous RAVE data releases. The synthesis of RAVE-on and TGAS is the most powerful data set for chemo-dynamic analyses of the Milky Way ever produced.

Optical design for the Laser Astrometric Test of Relativity

NASA Technical Reports Server (NTRS)

Turyshev, Slava G.; Shao, Michael; Nordtvedt, Kenneth L., Jr.

2004-01-01

This paper discusses the Laser Astrometric Test of Relativity (LATOR) mission. LATOR is a Michelson-Morley-type experiment designed to test the pure tensor metric nature of gravitation the fundamental postulate of Einstein's theory of general relativity. With its focus on gravity's action on light propagation it complements other tests which rely on the gravitational dynamics of bodies.

Astrometric Improvements for the USNO-A Catalog

NASA Astrophysics Data System (ADS)

Monet, D.

1997-12-01

The USNO-A1.0 catalog (Monet et al. 1996; 10 CD-ROMs; USNO) contains astrometric and photometric information for 488,006,860 objects. Since its compilation, many areas for improvement have been identified. This paper presents a progress report on the implementation of these improvements and discusses the schedule for the compilation of USNO-A2.0. The most significant improvement will be the incorporation of the International Celestial Reference Frame through the adoption of the ACT Catalog (Urban et al. in preparation; CD-ROM; USNO). (The ACT uses data from the Astrographic Catalog to compute proper motions for stars found in the Hipparcos and Tycho catalogs.) In addition to providing the realization of the astrometric reference frame, the ACT catalog contains a high enough source density to allow for a GSC-free derivation of the systematic components of the astrometric distortions found in the Schmidt telescopes that took the survey plates, and for a determination of the magnitude terms for the Palomar Schmidt using the data from the scans of the UJ plates. Other topics include the development of a numerical refocusing technique to improve the quality of existing scans, and the lessons being learned from the scanning of the Lick Northern Proper Motion survey plates.

Automated Astrometric Analysis of Satellite Observations using Wide-field Imaging

NASA Astrophysics Data System (ADS)

Skuljan, J.; Kay, J.

2016-09-01

An observational trial was conducted in the South Island of New Zealand from 24 to 28 February 2015, as a collaborative effort between the United Kingdom and New Zealand in the area of space situational awareness. The aim of the trial was to observe a number of satellites in low Earth orbit using wide-field imaging from two separate locations, in order to determine the space trajectory and compare the measurements with the predictions based on the standard two-line elements. This activity was an initial step in building a space situational awareness capability at the Defence Technology Agency of the New Zealand Defence Force. New Zealand has an important strategic position as the last land mass that many satellites selected for deorbiting pass before entering the Earth's atmosphere over the dedicated disposal area in the South Pacific. A preliminary analysis of the trial data has demonstrated that relatively inexpensive equipment can be used to successfully detect satellites at moderate altitudes. A total of 60 satellite passes were observed over the five nights of observation and about 2600 images were collected. A combination of cooled CCD and standard DSLR cameras were used, with a selection of lenses between 17 mm and 50 mm in focal length, covering a relatively wide field of view of 25 to 60 degrees. The CCD cameras were equipped with custom-made GPS modules to record the time of exposure with a high accuracy of one millisecond, or better. Specialised software has been developed for automated astrometric analysis of the trial data. The astrometric solution is obtained as a two-dimensional least-squares polynomial fit to the measured pixel positions of a large number of stars (typically 1000) detected across the image. The star identification is fully automated and works well for all camera-lens combinations used in the trial. A moderate polynomial degree of 3 to 5 is selected to take into account any image distortions introduced by the lens. A typical RMS error of the least-squares fit is about 0.1 pixels, which corresponds to about 4 to 10 seconds of arc in the sky, depending on the pixel scale (field of view). This gives a typical uncertainty between 10 and 25 metres in measuring the position of a satellite at a characteristic range of 500 kilometres. The results of this trial have confirmed that wide-field measurements based on standard photographic equipment and using automated astrometric analysis techniques can be used to improve the current orbital models of satellites in low Earth orbit.

Integrating Analysis Goals for EOP, CRF and TRF

NASA Technical Reports Server (NTRS)

Ma, Chopo; MacMillan, D.; Petrov, L.; Smith, David E. (Technical Monitor)

2001-01-01

In a simplified, idealized way the TRF can be considered a set of positions at epoch and corresponding linear rates of change while the CRF is a set of fixed directions in space. VLBI analysis can be optimized for CRF and TRF separately while handling some of the complexity of geodetic and astrometric reality. For EOP time series both CRF and TRF should be accurate at the epoch of interest and well defined over time. The optimal integral EOP, TRF and CRF in a single VLBI solution configuration requires a detailed consideration of the data set and the possibly conflicting nature of reference frames.

IVS Organization

NASA Technical Reports Server (NTRS)

2004-01-01

International VLBI Service (IVS) is an international collaboration of organizations which operate or support Very Long Baseline Interferometry (VLBI) components. The goals are: To provide a service to support geodetic, geophysical and astrometric research and operational activities. To promote research and development activities in all aspects of the geodetic and astrometric VLBI technique. To interact with the community of users of VLBI products and to integrate VLBI into a global Earth observing system.

What stellar orbit is needed to measure the spin of the Galactic centre black hole from astrometric data?

NASA Astrophysics Data System (ADS)

Waisberg, Idel; Dexter, Jason; Gillessen, Stefan; Pfuhl, Oliver; Eisenhauer, Frank; Plewa, Phillip M.; Bauböck, Michi; Jimenez-Rosales, Alejandra; Habibi, Maryam; Ott, Thomas; von Fellenberg, Sebastiano; Gao, Feng; Widmann, Felix; Genzel, Reinhard

2018-05-01

Astrometric and spectroscopic monitoring of individual stars orbiting the supermassive black hole in the Galactic Center offer a promising way to detect general relativistic effects. While low-order effects are expected to be detected following the periastron passage of S2 in Spring 2018, detecting higher order effects due to black hole spin will require the discovery of closer stars. In this paper, we set out to determine the requirements such a star would have to satisfy to allow the detection of black hole spin. We focus on the instrument GRAVITY, which saw first light in 2016 and which is expected to achieve astrometric accuracies 10-100 μas. For an observing campaign with duration T years, total observations Nobs, astrometric precision σx, and normalized black hole spin χ, we find that a_orb(1-e^2)^{3/4} ≲ 300 R_S √{T/4 {yr}} (N_obs/120)^{0.25} √{10 μ as/σ _x} √{χ /0.9} is needed. For χ = 0.9 and a potential observing campaign with σ _x = 10 μas, 30 observations yr-1 and duration 4-10 yr, we expect ˜0.1 star with K < 19 satisfying this constraint based on the current knowledge about the stellar population in the central 1 arcsec. We also propose a method through which GRAVITY could potentially measure radial velocities with precision ˜50 km s-1. If the astrometric precision can be maintained, adding radial velocity information increases the expected number of stars by roughly a factor of 2. While we focus on GRAVITY, the results can also be scaled to parameters relevant for future extremely large telescopes.

An Astrometric Analysis of eta Carinae’s Eruptive History Using HST WF/PC2 and ACS Observations

DTIC Science & Technology

2007-07-11

Std Z39-18 to address the question of binarity. Based on an astrometric analysis of the data, binary reflex motion is detected in the primary and, by...Measurement Results 96 5.1 Primary Luminosity and Mass . . . . . . . . . . . . . . . . . . . . . . 96 5.2 Secondary Mass and Luminosity...Binary Models . . . . . . . . . . . 100 5.5 Primary –Secondary Distance . . . . . . . . . . . . . . . . . . . . . . . 102 5.6 Periastron passage

Optical truss and retroreflector modeling for picometer laser metrology

NASA Astrophysics Data System (ADS)

Hines, Braden E.

1993-09-01

Space-based astrometric interferometer concepts typically have a requirement for the measurement of the internal dimensions of the instrument to accuracies in the picometer range. While this level of resolution has already been achieved for certain special types of laser gauges, techniques for picometer-level accuracy need to be developed to enable all the various kinds of laser gauges needed for space-based interferometers. Systematic errors due to retroreflector imperfections become important as soon as the retroreflector is allowed to either translate in position or articulate in angle away from its nominal zero-point. Also, when combining several laser interferometers to form a three-dimensional laser gauge (a laser optical truss), systematic errors due to imperfect knowledge of the truss geometry are important as the retroreflector translates away from its nominal zero-point. In order to assess the astrometric performance of a proposed instrument, it is necessary to determine how the effects of an imperfect laser metrology system impact the astrometric accuracy. This paper show the development of an error propagation model from errors in the 1-D metrology measurements through the impact on the overall astrometric accuracy for OSI. Simulations are then presented based on this development which were used to define a multiplier which determines the 1-D metrology accuracy required to produce a given amount of fringe position error.

Klenot Project - Near Earth Objects Follow-Up Program

NASA Astrophysics Data System (ADS)

Tichý, Miloš; Tichá, Jana; Kočer, Michal

2016-01-01

NEO research is a great challenge just now - for science, for exploration and for planetary defence. Therefore NEO discoveries, astrometric follow-up, orbit computations as well as physical studies are of high interest both to science community and humankind. The KLENOT Project of the Klet Observatory, South Bohemia, Czech Republic pursued the confirmation, early follow-up, long-arc follow-up and recovery of Near Earth Objects since 2002. Tens of thousands astrometric measurements helped to make inventory of NEOs as well as to understand the NEO population. It ranked among the world most prolific professional NEO follow-up programmes during its first phase from 2002 to 2008. The fundamental improvement of the 1.06-m KLENOT Telescope was started in autumn 2008. The new computer controlled paralactic mount was built to substantially increase telescope-time efficiency, the number of observations, their accuracy and limiting magnitude. The testing observations of the KLENOT Telescope Next Generation (NG) were started in October 2011. The new more efficient CCD camera FLI ProLine 230 was installed in summer 2013. The original Klet Software Package has been continually upgraded over the past two decades of operation. Along with huge hardware changes we have decided for essential changes in software and the whole KLENOT work-flow. Using the current higher computing power available, enhancing and updating our databases and astrometry program, the core of our software package, will prove highly beneficial. Moreover, the UCAC4 as the more precise astrometric star catalog was implemented. The modernized KLENOT System was put into full operation in September 2013. This step opens new possibilities for the KLENOT Project, the long-term European Contribution to Monitoring and Cataloging Near Earth Objects. KLENOT Project Goals are confirmatory observations of newly discovered fainter NEO candidates, early follow-up of newly discovered NEOs, long-arc follow-up astrometry of NEOs in need of further data. The higher priority is given to Potentially Hazardous Asteroids (PHAs) and Virtual Impactors (VIs), recoveries of NEOs in the second opposition and also follow-up astrometry of radar or mission targets, special follow-up requests and follow-up astrometry of other unusual objects (comets, bright TNOs) including analysis of cometary features of suspected bodies, and also search for new asteroids, especially NEOs as well as other objects showing unusual motion. The KLENOT Telescope is located at the Klet Observatory, South Bohemia, Czech Republic (Central Europe), at geographical position: latitude 14° 17' 17'' E, longitude 48° 51' 48''N, elevation 1068 meters above sea level, in a rather dark site in the middle of the Protected Landscape Area Blanský les. Average number of clear nights per year about 120. Our IAU/MPC code is 246 KLENOT Project Advantages: • full observing time is dedicated to the KLENOT team • quick changes in an observing plan possible, even during an observing night • long-term NEO activities at Klet (since 1992) • experienced observers/measurers visually validate each moving object candidate • real-time processing of targeted objects KLENOT Next Generation Telescope technical data (since 2013): • new computer controlled paralactic mount • 1.06-m f/3 main mirror (Zeiss) • four lenses primary focus corrector • 1.06-m f/2.7 optical system • CCD camera FLI ProLine PL230 • chip e2v 2048 × 2048 pixels, pixel size 15 microns, Peltier cooling • FOV 37 × 37 arcminutes, image scale 1.1 arcseconds per pixel • limiting magnitude m V=21.5 mag. for 120-sec exposure time KLENOT Project First Phase Results(2002-2008) total of 52,658 astrometric measurements of 5,867 bodies, it contains: • 13,342 astrometric measurements of 1,369 NEAs (MPC,NEODys) • confirmation and astrometry of 623 NEAs from NEOCP (MPECs) • recoveries of 4 comets and 16 NEAs (including 196P/Tichý) • astrometry of 157 Virtual Impactors (CLOMON, SENTRY) • detection of cometary features of 34 bodies (IAUCs) • discovery of splitting of comet C/2004 S1 (Van Ness) • independent discovery of 4 fragments of comet 73P/S-W 3 • asteroid discoveries - 750 bodies • 3 NEOs - Apollo 2002 LK, Aten 2003 UT55, Apollo 2006 XR4, 1 JFA 2004 RT109 The first KLENOT Project Next Generation Results (since 2011) total of 10,054 astrometric measurements of 1,298 bodies, it contains: • 2,211 astrometric measurements of 263 NEAs(MPC,NEODys) • confirmation and astrometry of 143 NEAs from NEOCP (MPECs) • astrometry of 18 Virtual Impactors (CLOMON, SENTRY) • detection of cometary features of 5 bodies (IAUCs)

Astrometric Jitter of the Sun as a Star

DTIC Science & Technology

2010-05-01

active, fast-rotating stars. The research described in this paper was carried out at the Jet Propulsion Laboratory, California Institute of Technology...as the Sun is not affected by star spot noise, but the prospects for more active stars may be limited to giant planets. Subject headings: open clusters ...nearby dwarfs should be as amenable to exoplanet detection as the Sun. The aim of this paper is to determine the solar astrometric jitter directly

International VLBI Service for Geodesy and Astrometry 2014 Annual Report

NASA Technical Reports Server (NTRS)

Baver, Karen D. (Editor); Behrend, Dirk (Editor); Armstrong, Kyla L. (Editor)

2015-01-01

IVS is an international collaboration of organizations which operate or support Very Long Baseline Interferometry (VLBI) components. The goals are: 1. To provide a service to support geodetic, geophysical and astrometric research and operational activities. 2. To promote research and development activities in all aspects of the geodetic and astrometric VLBI technique. 3. To interact with the community of users of VLBI products and to integrate VLBI into a global Earth observing system.

A 3D Search for Companions to 12 Nearby M Dwarfs

DTIC Science & Technology

2015-02-19

infrared radial velocities (RVs) and optical astrometric measurements in an effort to search for Jupiter -mass, brown dwarf, and stellar-mass companions. Our...around mid to late M dwarfs are still incomplete. Preliminary surveys show that Jupiter -mass companions are rare around M dwarfs. Using RV measurements...precise infrared radial velocities (RVs) and optical astrometric measurements in an effort to search for Jupiter -mass, brown dwarf, and stellar-mass

An Overview of Geodetic and Astrometric VLBI at the Hartebeesthoek Radio Astronomy Observatory

NASA Astrophysics Data System (ADS)

de Witt, A.; Gaylard, M.; Quick, J.; Combrinck, L.

2013-08-01

For astronomical Very Long Baseline Interferometry (VLBI), the Hartebeesthoek Radio Astronomy Observatory (HartRAO), in South Africa operates as part of a number of networks including the European and Australian VLBI networks, global arrays and also space VLBI. HartRAO is the only African representative in the international geodetic VLBI network and participates in regular astrometric and geodetic VLBI programmes. HartRAO will play a major role in the realization of the next generation full-sky celestial reference frame, especially the improvement of the celestial reference frame in the South. The observatory also provides a base for developing the African VLBI Network (AVN), a project to convert redundant satellite Earth-station antennas across Africa to use for radio astronomy. The AVN would greatly facilitate VLBI observations of southern objects. We present an overview of the current capabilities as well as future opportunities for astrometric and geodetic VLBI at HartRAO.

Optical monitoring of QSO in the framework of the Gaia space mission

NASA Astrophysics Data System (ADS)

Taris, F.; Damljanovic, G.; Andrei, A.; Klotz, A.; Vachier, F.

2015-08-01

The Gaia astrometric mission of the European Space Agency has been launched the 19th December 2013. It will provide an astrometric catalogue of 500 000 extragalactic sources that could be the basis of a new optical reference frame. On the other hand, the current International Celestial Reference Frame (ICRF) is based on the observations of extragalactic sources at radio wavelength. The astrometric coordinates of sources in these two reference systems will have roughly the same uncertainty. It is then mandatory to observe a set of common targets at both optical and radio wavelength to link the ICRF with what could be called the GCRF (Gaia Celestial Reference Frame). We will show in this paper some results obtained with the TJO, Telescopi Juan Oro, from Observatori Astronomic del Montsec in Spain. It also presents some results obtained with the Lomb-Scargle and CLEAN algorithm methods applied to optical magnitude obtained with the TAROT telescopes.

Absolute Astrometry in the next 50 Years - II

NASA Astrophysics Data System (ADS)

Høg, E.

2018-01-01

With the Gaia astrometric satellite in orbit since December 2013 it is time to look at the future of fundamental astrometry and a time frame of 50 years is needed in this matter. A space mission with Gaia-like astrometric performance is required, but not necessarily a Gaia-like satellite. A dozen science issues for a Gaia successor mission in twenty years, with launch about 2035, are presented and in this context also other possibilities for absolute astrometry with milliarcsecond (mas) or sub-mas accuracies are discussed in my report at http://arxiv.org/abs/1408.2190. In brief, the two missions (2013 and 2035) would provide an astrometric foundation for all branches of astronomy from the solar system and stellar systems, including exo-planet systems with long periods, to compact galaxies, quasars and Dark Matter substructures by data which cannot be surpassed in the next 50 years.

Overall properties of the Gaia DR1 reference frame

NASA Astrophysics Data System (ADS)

Liu, N.; Zhu, Z.; Liu, J.-C.; Ding, C.-Y.

2017-03-01

Aims: The first Gaia data release (Gaia DR1) provides 2191 ICRF2 sources with their positions in the auxiliary quasar solution and five astrometric parameters - positions, parallaxes, and proper motions - for stars in common between the Tycho-2 catalogue and Gaia in the joint Tycho-Gaia astrometric solution (TGAS). We aim to analyze the overall properties of Gaia DR1 reference frame. Methods: We compare quasar positions of the auxiliary quasar solution with ICRF2 sources using different samples and evaluate the influence on the Gaia DR1 reference frame owing to the Galactic aberration effect over the J2000.0-J2015.0 period. Then we estimate the global rotation between TGAS with Tycho-2 proper motion systems to investigate the property of the Gaia DR1 reference frame. Finally, the Galactic kinematics analysis using the K-M giant proper motions is performed to understand the property of Gaia DR1 reference frame. Results: The positional comparison between the auxiliary quasar solution and ICRF2 shows negligible orientation and validates the declination bias of -0.1mas in Gaia quasar positions with respect to ICRF2. Galactic aberration effect is thought to cause an offset 0.01mas of the Z axis direction of Gaia DR1 reference frame. The global rotation between TGAS and Tycho-2 proper motion systems, obtained by different samples, shows a much smaller value than the claimed value 0.24mas yr-1. For the Galactic kinematics analysis of the TGAS K-M giants, we find possible non-zero Galactic rotation components beyond the classical Oort constants: the rigid part ωYG = -0.38±0.15mas yr-1 and the differential part ω^primeYG = -0.29±0.19mas yr-1 around the YG axis of Galactic coordinates, which indicates possible residual rotation in Gaia DR1 reference frame or problems in the current Galactic kinematical model. Conclusions: The Gaia DR1 reference frame is well aligned to ICRF2, and the possible influence of the Galactic aberration effect should be taken into consideration for the future Gaia-ICRF link. The cause of the rather small global rotation between TGAS and Tycho-2 proper motion systems is unclear and needs further investigation. The possible residual rotation in Gaia DR1 reference frame inferred from the Galactic kinematic analysis should be noted and examined in future data release.

Astrometric Detection of Extrasolar Planets: Results of a Feasibility Study with the Palomar 5 Meter Telescope

NASA Technical Reports Server (NTRS)

Pravdo, Steven H.; Shaklan, Stuart B.

1996-01-01

The detection of extrasolar planets around stars like the Sun remains an important goal of astronomy. We present results from Palomar 5 m observations of the open cluster NGC 2420 in which we measure some of the sources of noise that will be present in an astrometric search for extrasolar planets. This is the first time that such a large aperture has been used for high-precision astrometry. We find that the atmospheric noise is 150 micro-arcsec hr(exp 1/2) across a 90 sec field of view and that differential chromatic refraction (DCR) can be calibrated to 128 micro-arcsec for observations within 1 hr of the meridian and 45 deg of zenith. These results confirm that a model for astrometric measurements can be extrapolated to large apertures. We demonstrate, based upon these results, that a large telescope achieves the sensitivity required to perform a statistically significant search for extra solar planets. We describe an astrometric technique to detect planets, the astrometric signals expected, the role of reference stars, and the sources of measurement noise: photometric noise, atmospheric motion between stars, sky background, instrumental noise, and DCR. For the latter, we discuss a method to reduce the noise further to 66 micro-arcsecond for observations within 1 hr of the meridian and 45 deg of zenith. We discuss optimal lists of target stars taken from the latest Gliese & Jahreiss catalog of nearby stars with the largest potential astrometric signals, declination limits for both telescope accessibility and reduced DCR, and galactic latitude limits for a sufficiant number of reference stars. Two samples are described from which one can perform statistically significant searches for gas giant planets around nearby stars. One sample contains 100 "solar class" stars with an average stellar mass of 0.82 solar mass; the other maximizes the number of stars, 574, by searching mainly low-mass M stars. We perform Monte Carlo simulations of the statistical significance of the expected results by using measured and estimated noise quantities. We show the semimajor axis parameter spaces that are searched for each star and how an increase in the length of the observing program expands these spaces. The search over semimajor axis parameter space relates to the theory of gas giant planet formation.

Astrometric Results of NEOs from the Characterization and Astrometric Follow-up Program at Adler Planetarium

NASA Astrophysics Data System (ADS)

Nault, Kristie A.; Brucker, Melissa J.; Hammergren, Mark; Gyuk, Geza; Solontoi, Mike R.

2015-11-01

We present astrometric results of near-Earth objects (NEOs) targeted in fourth quarter 2014 and in 2015. This is part of Adler Planetarium’s NEO characterization and astrometric follow-up program, which uses the Astrophysical Research Consortium (ARC) 3.5-m telescope at Apache Point Observatory (APO). The program utilizes a 17% share of telescope time, amounting to a total of 500 hours per year. This time is divided up into two hour observing runs approximately every other night for astrometry and frequent half-night runs approximately several times a month for spectroscopy (see poster by M. Hammergren et. al.) and light curve studies (see poster by M. J. Brucker et. al.).Observations were made using Seaver Prototype Imaging Camera (SPIcam), a visible-wavelength, direct imaging CCD camera with 2048 x 2048 pixels and a field of view of 4.78’ x 4.78’. Observations were made using 2 x 2 binning.Special emphasis has been made to focus on the smallest NEOs, particularly around 140m in diameter. Targets were selected based on absolute magnitude (prioritizing for those with H > 25 mag to select small objects) and a 3σ uncertainty less than 400” to ensure that the target is in the FOV. Targets were drawn from the Minor Planet Center (MPC) NEA Observing Planning Aid, the JPL What’s Observable tool, and the Spaceguard priority list and faint NEO list.As of August 2015, we have detected 670 NEOs for astrometric follow-up, on point with our goal of providing astrometry on a thousand NEOs per year. Astrometric calculations were done using the interactive software tool Astrometrica, which is used for data reduction focusing on the minor bodies of the solar system. The program includes automatic reference star identification from new-generation star catalogs, access to the complete MPC database of orbital elements, and automatic moving object detection and identification.This work is based on observations done using the 3.5-m telescope at Apache Point Observatory, owned and operated by the Astrophysical Research Consortium. We acknowledge the support from the NASA NEOO award NNX14AL17G and thank the University of Chicago Astronomy and Astrophysics Department for observing time in 2014.

Separated before birth: pulsars B2020+28 and B2021+51 as the remnants of runaway stars

NASA Astrophysics Data System (ADS)

Gvaramadze, V. V.

2007-08-01

Astrometric data on the pulsars B2020+28 and B2021+51 suggest that they originated within several parsecs of each other in the direction of the Cyg OB2 association. It was proposed that the pulsars share their origin in a common massive binary and were separated at the birth of the second pulsar following the asymmetric supernova explosion. We consider a different scenario for the origin of the pulsar pair based on a possibility that the pulsars were separated before their birth and that they are the remnants of runaway stars ejected (with velocities similar to those of the pulsars) from the core of Cyg OB2 due to strong three- or four-body dynamical encounters. Our scenario does not require any asymmetry in supernova explosions.

Elucidation of kinematical and dynamical structure of the Galactic bulge

NASA Astrophysics Data System (ADS)

Yano, T.; Gouda, N.; Ueda, H.; Koyama, H.; Kan-ya, Y.; Taruya, A.

2008-07-01

Future space mission of astrometric satellite, GAIA and JASMINE (Japan Astrometry Satellite Mission for Infrared Exploration), will produce astrometric parameter, such as positions, parallaxes, and proper motions of stars in the Galactic bulge. Then kinematical information will be obtained in the future. Accordingly it is expected that our understanding of the dynamical structure will be greatly improved. Therefore it is important to make a method to construct a kinematical and dynamical structure of the Galactic bulge immediately.

Astrometric Research of Asteroidal Satellites

NASA Astrophysics Data System (ADS)

Kikwaya, J.-B.; Thuillot, W.; Rocher, P.; Vieira Martins, R.; Arlot, J.-E.; Angeli, Cl.

2002-09-01

Several observational methods have been applied in order to detect asteroidal satellites. Some of them were rather successful, such as the stellar occultations and mutual eclipse methods. Recently other techniques such as the space imaging, the adaptive optics and the radar imaging inferred a great improvement in the search for these objects. However several limitations appear in the type of data that each of them allow us to access. We propose to apply an astrometric method in order as well to detect new asteroidal satellites as to get complementary data of some already detected objects (mainly their orbital period). This method is founded on the search of the reflex effect of the primary object due to the orbital motion of a possible satellite. Such an astrometric signature, already searched by Monet & Monet (1998), may reach several tens of MAS. Only a spectral analysis could then detect this signal under good conditions of signal/noise ratio and thanks to high quality astrometric measurements and coverage by different sites of observation. We have applied such a method for several asteroids. A preliminary result is obtained thanks to 377 CCD observations of 146 Lucina made at the Haute-Provence Observatory in South of France. A periodical signal appears in this analysis, leading to data compatible with a first detection of a probable satellite made previously (Arlot et al. 1985) by the occultation method.

VizieR Online Data Catalog: 1995 Saturnian satellite observations (Vienne+, 2001)

NASA Astrophysics Data System (ADS)

Vienne, A.; Thuillot, W.; Veiga, C. H.; Arlot, J.-E.; Vieira Martins, R.

2001-11-01

6006 differential positions of the main Saturnian satellites issued from astrometric measurements of CCD observations performed in 1995 at the Laboratorio Nacional de Astrofisica at Itajuba in Brazil. Most of these frames have no reference stars, then we applied an inter-satellites reduction. We have used the positions of Tethys, Dione, Rhea and Titan given by TASS1.7 to determine the scale factor and the orientation of the receptor (1995A&A...297..588V, 1997 Cat. ). The comparison of the observed positions and the computed positions shows that the dispersion of the observations is 0.07". Furthermore, the quality and the number of the positions of the satellites not used in the calibration is good: 0.08" for the 216 positions of Mimas, 0.14" for Hyperion (324), 0.11" for Iapetus (524). The format and the conventions of the present catalog are very near to the one of Strugnell & Taylor (1990A&AS...83..289S). The coordinates are given apart from a scale factor and from a rotation, but all astrometric corrections are done. So, these positions are really astrometric ones in that meaning that, no astrometric consideration is necessary to use them, even if one wants to touch up the calibration. Nevertheless, the raw pixels are also given in order to allow anyone to reduce again the frames. (1 data file).

An Astrometric Study of the Low-Mass Binary Star Ross 614

NASA Astrophysics Data System (ADS)

Gatewood, George; Coban, Louis; Han, Inwoo

2003-03-01

Long accepted as the quintessential low-mass star, the secondary of the nearby diminutive astrometric binary Ross 614 has attracted considerable astrophysical interest. Unfortunately, the orbital period of 16.6 yr exceeds the duration of the mission-limited studies of most space-borne or instrumental-proving observational programs. As with most such binaries, the only full-orbit studies are based on photographic materials. The last extended study of this system was based upon the plate collections of the McCormick and Sproul Observatories. The work reported here combines data from the Multichannel Astrometric Photometer, the Hipparcos Intermediate Astrometric Data, the previously unmeasured photographic plates of the Allegheny Observatory, published observations of the visual binary, and recently published radial velocities of the system. Together, these data span more than three orbits of the low-mass binary system. Limiting our analysis to the most recent observations of the binary, and five older observations that are in fair agreement with them, we find masses of 0.2228+/-0.0055 and 0.1107+/-0.0028 Msolar for the primary and secondary, respectively, with the largest source of error being the visual separations of the system. We find a parallax of 244.07+/-0.73 mas, a period of 16.595+/-0.0077 yr, and an increased estimate of the semimajor axis of 1101.2+/-8.2 mas. The latter led to a significant increase in the computed masses. All other aspects of the orbital elements and astrometry are in excellent agreement with those found in the independent study of the McCormick and Sproul plates. The importance of long-term astrometric coverage is pointed out by the fact that the orbital motion of the system only resulted in an acceleration during the compilation of the Hipparcos Catalogue. No orbital parameters or mass estimates can be discerned from these high-precision but short-term data.

SIM PlanetQuest: Science with the Space Interferometry Mission

NASA Technical Reports Server (NTRS)

Unwin, Stephen (Editor); Turyshev, Slava (Editor)

2004-01-01

SIM - the Space Interferometry Mission - will perform precision optical astrometry on objects as faint as R magnitude 20. It will be the first space-based astrometric interferometer, operating in the optical band with a 10-m baseline. The Project is managed by the Jet Propulsion Laboratory, California Institute of Technology, in close collaboration with two industry partners, Lockheed Martin Missiles and Space, and TRW Inc., Space and Electronics Group. Launch of SIM is currently planned for 2009. In its wide-angle astrometric mode, SIM will yield 4 microarcsecond absolute position and parallax measurements. Astrometric planet searches will be done in a narrow-angle mode, with an accuracy of 4 microarcseconds or better in a single measurement. As a pointed rather than a survey instrument, SIM will maintain.its astrometric accuracy down to the faintest, magnitudes, opening up the opportunity for astrometry of active galactic nuclei to better than 10 pas. SIM will define a new astrometric reference frame, using a grid of approximately 1500 stars with positions accurate to 4 microarcseconds. The SIM Science Team comprises the Principal Investigators of ten Key Projects, and five Mission Scientists contributing their expertise to specific areas of the mission. Their science programs cover a wide range of topics in Galactic and extragalactic astronomy. They include: searches for low-mass planets - including analogs to our own solar system - tlie formation and dynamics of our Galaxy, calibration of the cosmic distance scale, and fundamental stellar astrophysics. All of the science observing on SIM is competitively awarded; the Science Team programs total about 40% of the total available, and the remainder will be assigned via future NASA competitions. This report is a compilation of science summaries by members of the Science Team, and it illustrates the wealth of scientific problems that microarcsecond-precision astrometry can contribute to. More information on SIM, including copies of this report, may be obtained from the project web site, at http://sim. jpl.nasa.gov.

Establishing Alpha Oph as a Prototype Rotator: Improved Astrometric Orbit

DTIC Science & Technology

2011-01-10

astrometric characterization of the companion orbit. We also use photometry from these observations to derive a model-based estimate of the companion mass. A...uncertainties. In addition to the dynamically derived masses, we use IJHK photometry to derive a model-based mass for α Oph B, of 0.77 ± 0.05 M...man 1966; Gatewood 2005) with a 8.62 yr period, well estab- lished over several decades of monitoring and first resolved by McCarthy (1983). But a

VizieR Online Data Catalog: Gaia DR1 (Gaia Collaboration, 2016)

NASA Astrophysics Data System (ADS)

Gaia Collaboration

2016-06-01

Gaia DR1 is based on observations collected between 25 July 2014 and 16 September 2015. Gaia DR1 contains positions (RA,DE) and G magnitudes for all sources with acceptable formal standard errors on positions. Positions and individual uncertainties are computed using a generic prior and Bayes' rule (detailed description in "Gaia astrometry for stars with too few observations. A Bayesian approach", Michalik et al., 2015A&A...583A..68M). The five-parameter astrometric solution - positions, parallaxes, and proper motions - for stars in common between the Tycho-2 Catalogue and Gaia is contained in Gaia DR1. This part of Gaia DR1 is based on the Tycho-Gaia Astrometric Solution (paper with detailed description (Michalik et al., 2015A&A...574A.115M); paper describing theory and background (Michalik et al., 2014A&A...571A..85M); paper describing quasar extension (Michalik & Lindegren, 2016A&A...586A..26M)). At the beginning of the routine phase, for a period of 4 weeks, a special scanning mode repeatedly covering the ecliptic poles on every spin was executed for calibration purposes. Photometric data of selected RR Lyrae and Cepheid variable stars based on these high-cadence measurements are contained in Gaia DR1. Positions (RA,DE) and G magnitudes for 2152 ICRF quasars (F. Mignard et al., 2016, A&A, in press.). The Gaia Archive DR1 data is available at archives.esac.esa.int/gaia. Tgas and Gaia Sources can be downloaded as VOTables, FITS or CSV at http://cdn.gea.esac.esa.int/Gaia/ If you use public Gaia DR1 data in your paper, please take note of our guide on how to acknowledge and cite Gaia DR1: http://gaia.esac.esa.int/documentation/GDR1/Miscellaneous/\\ seccreditandcitationinstructions.html (9 data files).

Asteroid masses with Gaia from ground and space-based observations

NASA Astrophysics Data System (ADS)

Ivantsov, Anatoliy; Hestroffer, Daniel; Thuillot, William; Bancelin, David

2013-04-01

Determination of masses of large asteroids is one of the expected scientific outputs from the future Gaia astrometric space mission. With the exception of binary asteroids or fly-by with a space probe, the error in mass determination depends on the size of perturbation effect produced on the motion of small asteroids. Considering the 5 years nominal duration of the Gaia mission, there will be mutual close encounters between asteroids occurring either close to the beginning or to the end of the mission. So that the maximum of deflection angle pertained to the perturbation maxima will not be observed directly by Gaia. Since astrometric data of the perturbed body before and after the encounter are mandatory to derive a perturber mass, the precision of mass determinations based solely on the Gaia observations will deteriorate in such cases. The possible way out consists in acquiring ground-based observations of high astrometric precision in time either before or after the Gaia operations, as it was suggested in [1]. By adding such data, it is expected to increase the number of derived asteroids masses [2]. This paper updates earlier predictions of encounters of large asteroids with smaller ones, e.g. [3], in terms of newly discovered asteroids and available ground-based observations. The method used consists in the computation of the offsets in right ascension and declination between the unperturbed and perturbed solutions fitted to the available observations for each small (perturbed) asteroid. For the purpose of decreasing CPU time, a special filter was applied based on the solution of the two-body problem and systematical search for close encounters, e.g. less than 0.1 A.U., of all known asteroids with the large (perturber) ones. The obtained list of asteroids-candidates was used as the input file for the mentioned above accurate calculations. Such a procedure was used for a few asteroids in [2]. The maximum visible offset corresponds to the dates when the complementary ground-based observations will be useful. [1] Hestroffer, D., Thuillot, W., Mouret, S., Colas, F., Tanga, P., Mignard, F., Delbo, M., Carry, B.: Ground-based observations of solar system bodies in complement to Gaia, SF2A-2008: Proceedings of the Annual meeting of the French Society of Astronomy and Astrophysics, 30 June - 4 July 2008, Paris, France, 2008. [2] Mouret, S., Hestroffer, D., and Mignard, F.: Asteroid masses and Gaia, Astronomy and Astrophysics, Vol. 472, pp. 1017-1027, 2007. [3] Mouret, S.: Investigations on the dynamics of minor planets with GAIA: orbits, masses and fundamental physics, PhD thesis, Paris Observatory, 2007. [4] Hilton, J.L., Seidelmann, P.K., and Middour, J.: Prospects for determining asteroid masses, Astronomical Journal, Vol. 112, pp. 2319-2329, 1996.

A Gaia study of the Hyades open cluster

NASA Astrophysics Data System (ADS)

Reino, Stella; de Bruijne, Jos; Zari, Eleonora; d'Antona, Francesca; Ventura, Paolo

2018-03-01

We present a study of the membership of the Hyades open cluster, derive kinematically-modelled parallaxes of its members, and study the colour-absolute magnitude diagram of the cluster. We use Gaia DR1 Tycho-Gaia Astrometric Solution (TGAS) data complemented by Hipparcos-2 data for bright stars not contained in TGAS. We supplement the astrometric data with radial velocities collected from a dozen literature sources. By assuming that all cluster members move with the mean cluster velocity to within the velocity dispersion, we use the observed and the expected motions of the stars to determine individual cluster membership probabilities. We subsequently derive improved parallaxes through maximum-likelihood kinematic modelling of the cluster. This method has an iterative component to deal with 'outliers', caused for instance by double stars or escaping members. Our method extends an existing method and supports the mixed presence of stars with and without radial velocities. We find 251 candidate members, 200 of which have a literature radial velocity, and 70 of which are new candidate members with TGAS astrometry. The cluster is roughly spherical in its centre but significantly flattened at larger radii. The observed colour-absolute magnitude diagram shows a clear binary sequence. The kinematically-modelled parallaxes that we derive are a factor ˜1.7 / 2.9 more precise than the TGAS / Hipparcos-2 values and allow to derive an extremely sharp main sequence. This sequence shows evidence for fine-detailed structure which is elegantly explained by the full spectrum turbulence model of convection.

VIRAC: the VVV Infrared Astrometric Catalogue

NASA Astrophysics Data System (ADS)

Smith, L. C.; Lucas, P. W.; Kurtev, R.; Smart, R.; Minniti, D.; Borissova, J.; Jones, H. R. A.; Zhang, Z. H.; Marocco, F.; Contreras Peña, C.; Gromadzki, M.; Kuhn, M. A.; Drew, J. E.; Pinfield, D. J.; Bedin, L. R.

2018-02-01

We present VIRAC version 1, a near-infrared proper motion and parallax catalogue of the VISTA Variables in the Via Lactea (VVV) survey for 312 587 642 unique sources averaged across all overlapping pawprint and tile images covering 560 deg2 of the bulge of the Milky Way and southern disc. The catalogue includes 119 million high-quality proper motion measurements, of which 47 million have statistical uncertainties below 1 mas yr-1. In the 11 < Ks < 14 magnitude range, the high-quality motions have a median uncertainty of 0.67 mas yr-1. The catalogue also includes 6935 sources with quality-controlled 5σ parallaxes with a median uncertainty of 1.1 mas. The parallaxes show reasonable agreement with the Tycho-Gaia Astrometric Solution, though caution is advised for data with modest significance. The SQL data base housing the data is made available via the web. We give example applications for studies of Galactic structure, nearby objects (low-mass stars and brown dwarfs, subdwarfs, white dwarfs) and kinematic distance measurements of young stellar objects. Nearby objects discovered include LTT 7251 B, an L7 benchmark companion to a G dwarf with over 20 published elemental abundances, a bright L subdwarf, VVV 1256-6202, with extremely blue colours and nine new members of the 25 pc sample. We also demonstrate why this catalogue remains useful in the era of Gaia. Future versions will be based on profile fitting photometry, use the Gaia absolute reference frame and incorporate the longer time baseline of the VVV extended survey.

Design of Astrometric Mission (JASMINE) by Applying Model Driven System Engineering

NASA Astrophysics Data System (ADS)

Yamada, Y.; Miyashita, H.; Nakamura, H.; Suenaga, K.; Kamiyoshi, S.; Tsuiki, A.

2010-12-01

We are planning space astrometric satellite mission named JASMINE. The target accuracy of parallaxes in JASMINE observation is 10 micro arc second, which corresponds to 1 nm scale on the focal plane. It is very hard to measure the 1 nm scale deformation of focal plane. Eventually, we need to add the deformation to the observation equations when estimating stellar astrometric parameters, which requires considering many factors such as instrument models and observation data analysis. In this situation, because the observation equations become more complex, we may reduce the stability of the hardware, nevertheless, we require more samplings due to the lack of rigidity of each estimation. This mission imposes a number of trades-offs in the engineering choices and then decide the optimal design from a number of candidates. In order to efficiently support such decisions, we apply Model Driven Systems Engineering (MDSE), which improves the efficiency of the engineering by revealing and formalizing requirements, specifications, and designs to find a good balance among various trade-offs.

Space geodesy vs. classical astrometry: a high complementarity

NASA Astrophysics Data System (ADS)

Lainey, V.

2017-12-01

Astrometry is the discipline that aims to provide positions of celestial objects in space with the highest accuracy. While natural satellites have been observed with telescopes since the XVIIth century, accurate astrometric observations (few hundred milli-arcsec, or mas) which are still useful today, have only been available since the end of the XIXth century thanks to the use of photographic plates. Modern observations now benefit from CCD/CMOS devices and accurate star catalogues which permit accuracy typically up to 20-30 mas. In that context, the use of astrometry for planetology may not seem obvious. In particular, spacecraft radio data have long since superseded astrometric data in the determination of gravity fields of planetary systems. While the former are much more precise and numerous, astrometric data have a unique advantage in covering a much-extended time span. We will review the pros and cons of each method, with emphasize on recent results showing how these two disciplines complements perfectly each other.

Improvements in Space Surveillance Processing for Wide Field of View Optical Sensors

NASA Astrophysics Data System (ADS)

Sydney, P.; Wetterer, C.

2014-09-01

For more than a decade, an autonomous satellite tracking system at the Air Force Maui Optical and Supercomputing (AMOS) observatory has been generating routine astrometric measurements of Earth-orbiting Resident Space Objects (RSOs) using small commercial telescopes and sensors. Recent work has focused on developing an improved processing system, enhancing measurement performance and response while supporting other sensor systems and missions. This paper will outline improved techniques in scheduling, detection, astrometric and photometric measurements, and catalog maintenance. The processing system now integrates with Special Perturbation (SP) based astrodynamics algorithms, allowing covariance-based scheduling and more precise orbital estimates and object identification. A merit-based scheduling algorithm provides a global optimization framework to support diverse collection tasks and missions. The detection algorithms support a range of target tracking and camera acquisition rates. New comprehensive star catalogs allow for more precise astrometric and photometric calibrations including differential photometry for monitoring environmental changes. This paper will also examine measurement performance with varying tracking rates and acquisition parameters.

A study of astrometric distortions due to “tree rings” in CCD sensors using LSST Photon Simulator

DOE PAGES

Beamer, Benjamin; Nomerotski, Andrei; Tsybychev, Dmitri

2015-05-22

Imperfections in the production process of thick CCDs lead to circularly symmetric dopant concentration variations, which in turn produce electric fields transverse to the surface of the fully depleted CCD that displace the photogenerated charges. We use PhoSim, a Monte Carlo photon simulator, to explore and examine the likely impacts these dopant concentration variations will have on astrometric measurements in LSST. The scale and behavior of both the astrometric shifts imparted to point sources and the intensity variations in flat field images that result from these doping imperfections are similar to those previously observed in Dark Energy Camera CCDs, givingmore » initial confirmation of PhoSim's model for these effects. In addition, the organized shape distortions were observed as a result of the symmetric nature of these dopant variations, causing nominally round sources to be imparted with a measurable ellipticity either aligned with or transverse to the radial direction of this dopant variation pattern.« less

A Weekend Workshop on Double Stars for Students

NASA Astrophysics Data System (ADS)

Brewer, Mark; Estrada, Chris; Estrada, Reed; Gillette, Sean

2016-01-01

A weekend double star workshop was held by Vanguard Preparatory for selected eighth grade students with the purpose of introducing them to astrometric observational science. The students were selected based on an essay provided by their language arts class. Collaboration with local visiting astronomers was established to provide telescopes equipped with an astrometric eyepiece, observational supervision, and expertise. During the workshop students learned how to determine the scale constant of an astrometric eyepiece, and the procedure for measuring separations and position angles of double stars. The students compared their data to past measurements reported in the Washington Double Star Catalog. Three goals were set for the student's outcome: 1) observe, record, and report observations of double stars, 2) write a scientific paper for publication in the Journal of Double Star Observations, and 3) present a PowerPoint presentation to their peers. This paper chronicles the planning, preparation, funding, and execution required to complete a double star workshop at a public middle school.

VizieR Online Data Catalog: HD 128311 radial velocity and astrometric data (McArthur+, 2014)

NASA Astrophysics Data System (ADS)

McArthur, B. E.; Benedict, G. F.; Henry, G. W.; Hatzes, A.; Cochran, W. D.; Harrison, T. E.; Johns-Krull, C.; Nelan, E.

2017-05-01

The High Resolution Spectrograph (HRS; Tull, 1998SPIE.3355..387T) at the HET at McDonald Observatory was used to make the spectroscopic observations using the iodine absorption cell method (Butler et al. 1996PASP..108..500B). Our reduction of HET HRS data is given in Bean et al. (2007AJ....134..749B), which uses the REDUCE package (Piskunov & Valenti, 2002A&A...385.1095P). Our observations include a total of 355 high-resolution spectra which were obtained between 2005 April and 2011 January. Because typically two or more observations were made in less than 1 hr per night, we observed at 161 epochs with the HET HRS. The astrometric observations were made with the Hubble Space Telescope (HST) Fine Guidance Sensor (FGS) 1r, a two-axis interferometer, in position (POS) "fringe-tracking" mode. Twenty-nine orbits of HST astrometric observations were made between 2007 December and 2009 August. (2 data files).

THE CELESTIAL REFERENCE FRAME AT 24 AND 43 GHz. II. IMAGING

DOE Office of Scientific and Technical Information (OSTI.GOV)

Charlot, P.; Boboltz, D. A.; Fey, A. L.

2010-05-15

We have measured the submilliarcsecond structure of 274 extragalactic sources at 24 and 43 GHz in order to assess their astrometric suitability for use in a high-frequency celestial reference frame (CRF). Ten sessions of observations with the Very Long Baseline Array have been conducted over the course of {approx}5 years, with a total of 1339 images produced for the 274 sources. There are several quantities that can be used to characterize the impact of intrinsic source structure on astrometric observations including the source flux density, the flux density variability, the source structure index, the source compactness, and the compactness variability.more » A detailed analysis of these imaging quantities shows that (1) our selection of compact sources from 8.4 GHz catalogs yielded sources with flux densities, averaged over the sessions in which each source was observed, of about 1 Jy at both 24 and 43 GHz, (2) on average the source flux densities at 24 GHz varied by 20%-25% relative to their mean values, with variations in the session-to-session flux density scale being less than 10%, (3) sources were found to be more compact with less intrinsic structure at higher frequencies, and (4) variations of the core radio emission relative to the total flux density of the source are less than 8% on average at 24 GHz. We conclude that the reduction in the effects due to source structure gained by observing at higher frequencies will result in an improved CRF and a pool of high-quality fiducial reference points for use in spacecraft navigation over the next decade.« less

Optical Characteristics of Astrometric Radio Sources OCARS

NASA Astrophysics Data System (ADS)

Malkin, Z.

2013-04-01

In this paper, the current status of the catalog of Optical Characteristics of Astrometric Radio Sources OCARS is presented. The catalog includes radio sources observed in various astrometric and geodetic VLBI programs in 1979-2012. For these sources the physical object type, redshift and visual or infrared magnitude is given when available. Detailed comments are provided when some problems with published data were encountered. Since the first version created in December 2007, the catalog is continuously developed and expanded in respect to inclusion of new radio sources and addition of new or correction of old astrophysical data. Several sources of information are used for OCARS. The main of them are the NASA/IPAC Extragalactic Database (NED) and SIMBAD astronomical databases. Besides several astronomical journals and arXiv depository are regularly monitored, so that new data is included in OCARS just after publication. The redshift for about 150 sources have been determined from dedicated optical spectroscopic observations. As of October 2012, OCARS catalog includes 7173 radio sources. 3898 sources have known redshift, and 4860 sources have known magnitude. In 2009, it was used as a supplement material to the ICRF2. The list of radio sources with a good observational history but lacking astrophysical information is provide for planning of optical observations of the most important astrometric sources. The OCARS catalog is updated, in average every several weeks and is available at http://www.gao.spb.ru/english/as/ac_vlbi/ocars.txt.

MODELING MULTI-WAVELENGTH STELLAR ASTROMETRY. I. SIM LITE OBSERVATIONS OF INTERACTING BINARIES

DOE Office of Scientific and Technical Information (OSTI.GOV)

Coughlin, Jeffrey L.; Harrison, Thomas E.; Gelino, Dawn M.

Interacting binaries (IBs) consist of a secondary star that fills or is very close to filling its Roche lobe, resulting in accretion onto the primary star, which is often, but not always, a compact object. In many cases, the primary star, secondary star, and the accretion disk can all be significant sources of luminosity. SIM Lite will only measure the photocenter of an astrometric target, and thus determining the true astrometric orbits of such systems will be difficult. We have modified the Eclipsing Light Curve code to allow us to model the flux-weighted reflex motions of IBs, in a codemore » we call REFLUX. This code gives us sufficient flexibility to investigate nearly every configuration of IB. We find that SIM Lite will be able to determine astrometric orbits for all sufficiently bright IBs where the primary or secondary star dominates the luminosity. For systems where there are multiple components that comprise the spectrum in the optical bandpass accessible to SIM Lite, we find it is possible to obtain absolute masses for both components, although multi-wavelength photometry will be required to disentangle the multiple components. In all cases, SIM Lite will at least yield accurate inclinations and provide valuable information that will allow us to begin to understand the complex evolution of mass-transferring binaries. It is critical that SIM Lite maintains a multi-wavelength capability to allow for the proper deconvolution of the astrometric orbits in multi-component systems.« less

A comparative study on liquid core formulation on the diameter on the alginate capsules

NASA Astrophysics Data System (ADS)

Ong, Hui-Yen; Lee, Boon-Beng; Radzi, AkmalHadi Ma'; Zakaria, Zarina; Chan, Eng-Seng

2015-08-01

Liquid core capsule has vast application in biotechnology related industries such as pharmaceutical, medical, agriculture and food. Formulation of different types of capsule was important to determine the performance of the capsule. Generally, the liquid core capsule with different formulations generated different size of capsule.Therefore, the aim of this project is to investigate the effect of different liquid core solution formulations on the diameter of capsule. The capsule produced by extruding liquid core solutions into sodium alginate solution. Three types of liquid core solutions (chitosan, xanthan gum, polyethylene glycol (PEG)) were investigated. The results showed that there is significant change in capsule diameter despite in different types of liquid core solution were used and a series of capsule range in diameter of 3.1 mm to 4.5 mm were produced. Alginate capsule with chitosan formulation appeared to be the largest capsule among all.

Evolution and seismology of Procyon

NASA Technical Reports Server (NTRS)

Guenther, D. B.; Demarque, P.

1993-01-01

We have calculated an array of stellar models for Procyon A that are based on the best physics available to us, including the latest opacities and nuclear cross sections. The array of models spans the error space centered on Procyon's mass, chemical composition, effective temperature, and luminosity. We find that with OPAL opacities no convective overshoot is needed at the edge of the convective core to match Procyon's position in the H-R diagram. We discuss the discrepancy between the astrophysical mass and the astrometric mass, which is reduced by the more up-to-date physics in the models, and describe how oscillation data can be used to distinguish among the possible models and help resolve the discrepancy. We have calculated oscillation frequencies for the l = 0, 1, 2, and 3 p-modes and oscillation periods for the l = 1, 2, and 3 g-modes for several of these models.

Integrating Analysis Goals for EOP, CRF and TRF

NASA Technical Reports Server (NTRS)

Ma, Chopo; MacMillan, Daniel; Petrov, Leonid

2002-01-01

In a simplified, idealized way the TRF (Terrestrial Reference Frame) can be considered a set of positions at epoch and corresponding linear rates of change while the CRF (Celestial Reference Frame) is a set of fixed directions in space. VLBI analysis can be optimized for CRF and TRF separately while handling some of the complexity of geodetic and astrometric reality. For EOP (Earth Orientation Parameter) time series both CRF and TRF should be accurate at the epoch of interest and well defined over time. The optimal integration of EOP, TRF and CRF in a single VLBI solution configuration requires a detailed consideration of the data set and the possibly conflicting nature of the reference frames. A possible approach for an integrated analysis is described.

Pulsating star research and the Gaia revolution

NASA Astrophysics Data System (ADS)

Eyer, Laurent; Clementini, Gisella; Guy, Leanne P.; Rimoldini, Lorenzo; Glass, Florian; Audard, Marc; Holl, Berry; Charnas, Jonathan; Cuypers, Jan; Ridder, Joris De; Evans, Dafydd W.; de Fombelle, Gregory Jevardat; Lanzafame, Alessandro; Lecoeur-Taibi, Isabelle; Mowlavi, Nami; Nienartowicz, Krzysztof; Riello, Marco; Ripepi, Vincenzo; Sarro, Luis; Süveges, Maria

2017-09-01

In this article we present an overview of the ESA Gaia mission and of the unprecedented impact that Gaia will have on the field of variable star research. We summarise the contents and impact of the first Gaia data release on the description of variability phenomena, with particular emphasis on pulsating star research. The Tycho-Gaia astrometric solution, although limited to 2.1 million stars, has been used in many studies related to pulsating stars. Furthermore a set of 3,194 Cepheids and RR Lyrae stars with their times series have been released. Finally we present the plans for the ongoing study of variable phenomena with Gaia and highlight some of the possible impacts of the second data release on variable, and specifically, pulsating stars.

The TGAS HR diagram of S-type stars

NASA Astrophysics Data System (ADS)

Shetye, Shreeya; van Eck, Sophie; Jorissen, Alain; van Winckel, Hans; Siess, Lionel

2018-04-01

S-type stars are late-type giants enhanced with s-process elements originating either from nucleosynthesis during the Asymptotic Giant Branch (AGB) or from a pollution by a binary companion. The former are called intrinsic S stars, and the latter extrinsic S stars. The atmospheric parameters of S stars are more numerous than those of M-type giants (C/O ratio and s-process abundances affect the thermal structure and spectral synthesis), and hence they are more difficult to derive. Nevertheless, high-resolution spectroscopic data of S stars combined with the TGAS (Tycho-Gaia Astrometric solution) parallaxes were used to derive effective temperatures, surface gravities, and luminosities. These parameters allow to locate the intrinsic and extrinsic S stars in the Hertzsprung-Russell diagram.

Nonlinear core deflection in injection molding

NASA Astrophysics Data System (ADS)

Poungthong, P.; Giacomin, A. J.; Saengow, C.; Kolitawong, C.; Liao, H.-C.; Tseng, S.-C.

2018-05-01

Injection molding of thin slender parts is often complicated by core deflection. This deflection is caused by molten plastics race tracking through the slit between the core and the rigid cavity wall. The pressure of this liquid exerts a lateral force of the slender core causing the core to bend, and this bending is governed by a nonlinear fifth order ordinary differential equation for the deflection that is not directly in the position along the core. Here we subject this differential equation to 6 sets of boundary conditions, corresponding to 6 commercial core constraints. For each such set of boundary conditions, we develop an explicit approximate analytical solution, including both a linear term and a nonlinear term. By comparison with finite difference solutions, we find our new analytical solutions to be accurate. We then use these solutions to derive explicit analytical approximations for maximum deflections and for the core position of these maximum deflections. Our experiments on the base-gated free-tip boundary condition agree closely with our new explicit approximate analytical solution.

Astrometry with A-Track Using Gaia DR1 Catalogue

NASA Astrophysics Data System (ADS)

Kılıç, Yücel; Erece, Orhan; Kaplan, Murat

2018-04-01

In this work, we built all sky index files from Gaia DR1 catalogue for the high-precision astrometric field solution and the precise WCS coordinates of the moving objects. For this, we used build-astrometry-index program as a part of astrometry.net code suit. Additionally, we added astrometry.net's WCS solution tool to our previously developed software which is a fast and robust pipeline for detecting moving objects such as asteroids and comets in sequential FITS images, called A-Track. Moreover, MPC module was added to A-Track. This module is linked to an asteroid database to name the found objects and prepare the MPC file to report the results. After these innovations, we tested a new version of the A-Track code on photometrical data taken by the SI-1100 CCD with 1-meter telescope at TÜBİTAK National Observatory, Antalya. The pipeline can be used to analyse large data archives or daily sequential data. The code is hosted on GitHub under the GNU GPL v3 license.

Emergency deployable core catcher

DOE Office of Scientific and Technical Information (OSTI.GOV)

Rosewell, M.P.

An emergency melt down core catcher apparatus for a nuclear reactor having a retrofitable eutectic solute holding vessel connected to a core containment vessel with particle transferring fluid and particles or granules of solid eutectic solute materials contained therein and transferable by automatically operated valve means to transport and position the solid eutectic solute material in a position below the core to catch and react with any partial or complete melt down of the fuel core.

Study of the true performance limits of the Astrometric Multiplexing Area Scanner (AMAS)

NASA Technical Reports Server (NTRS)

Frederick, L. W.; Mcalister, H. A.

1975-01-01

The Astrometric Multiplexing Area Scanner (AMAS) is an instrument designed to perform photoelectric long focus astrometry of small fields. Modulation of a telescope focal plane with a rotating Ronchi ruling produces a frequency modulated signal from which relative positions and magnitudes can be extracted. Evaluation instrumental precision, accuracy and resolution characteristics with respect to a variety of instrumental and cosmical parameters indicates 1.5 micron precision and accuracy for single stars under specific conditions. This value decreases for increased number of field stars, particularly for fainter stars.

Microarcsecond Astrometry As A Probe Of Circumstellar Structure

NASA Astrophysics Data System (ADS)

Velusamy, T.; Turyshev, S. G.

1999-12-01

The Space Interferometry Mission (SIM) is a space-based long-baseline optical interferometer for precision astrometry. This mission will open up many areas of astrophysics, via astrometry with unprecedented accuracy. Wide-angle measurements, which include annual parallax, will reach a design accuracy of 4 μ as. Over a narrow field of view the relative accuracy is better, and SIM is expected to achieve an accuracy of 1 μ as. In this mode, SIM will search for planetary companions to nearby stars, by detecting the astrometric `wobble' relative to a nearby (<= 1o) reference star. The expected proper motion accuracy is 2 μ as yr-1, corresponding to a transverse velocity of 10 m s-1 at a distance of 1 kpc. Such an accuracy of the future SIM instrument provides a very useful astrometric tool for probing the circumstellar structure. The motion of the photo center as detected by SIM is not necessarily that of the center of mass. It is expected that unmodelled dynamics of the stellar systems may be a potential source for systematic astrometric errors. In this paper we discuss the possibility of using SIM's precision astrometry not only to detect Keplerian signatures due to the planetary motion around nearby stars, but also to characterize the structure of the planetary and proto-planetary orbits, accretions disks, debris disks, circumstellar material, jets and other types of the mass transfer mechanisms. We evaluate possible astrometric signatures due to different types of dynamical processes (both gravitational, non-gravitational) and characterize the magnitude of the corresponding astrometric signal. We attempt to address the most natural scenario of non-Keplerian motion, caused by an extended structure and complex dynamics of the stellar systems that may produce a detectable wobble in the motion of the optical center of a target star. We examine the use of μ as astrometry, as complementary to high resolution imaging, to detect some of the structures present around stars. This work was performed by the Jet Propulsion Laboratory, California Institute of Technology, under contract with the National Aeronautics and Space Administration.

Catalog based two-color, relative photometry of NEOs at McDonald Observatory

NASA Astrophysics Data System (ADS)

Barker, E. S.; Györgyey Ries, J.; Shelus, P. J.; Ricklefs, R. L.

2001-11-01

The McDonald Observatory astrometry group has been involved in Solar System positional observations since the early 1970's. Since 1995, it has evolved to a CCD-based, almost totally automated, astrometry package. We are focusing our observational program on Near Earth Objects (NEOs) as part of NASA's mission to discover and catalogue 90 percent of NEOs with diameters larger than 1 km by 2008. We carry out confirmation observations of newly discovered objects and contribute to orbit improvements of under-observed objects. Understanding the overall hazard that these objects pose to Earth requires their dynamical and physical characterization. We recently adopted the USNO-A2.0 catalogue to improve our astrometric results. The catalog, however, also provides stellar magnitudes in the standard Johnson R and B photometric bands. After completing the night’s observing program, we now regularly provide the IAU with R magnitudes in addition to astrometric positions. Our limiting magnitude in R is near 22 in a 15 minute exposure over a 46 arcmin field on the 0.8m prime focus camera. Typically, we are scheduled for 4 nights each lunation, but our semi-automated, IRAF/ICE based program can be used by other 0.8m users. We are testing procedures that will include B and V exposures as part of our standard confirmation triplet. We have confirmed that switching filters between exposures on standard fields does not compromise the astrometric accurary. Thus, we should be able to provide two color, sequential, relative photometry of any newly discovered asteroid, as part of the confirmation process. The time interval between exposures is less than 20 minutes, short compared to most asteroid rotation times. Consequently, a meaningful color index can be obtained in parallel with the astrometric positions. Although B-R is not the usual color index used in asteroid classification studies, we are testing whether we can use it as a quick diagnostic tool to roughly classify newly discovered NEOs as by product of our astrometric observing sequence. Preliminary results will be presented at the meeting. This research is funded by NASA's NEO Observation Program grants NAG5-6863 and NAG5-10183.

Methods for multiple-telescope beam imaging and guiding in the near-infrared

NASA Astrophysics Data System (ADS)

Anugu, N.; Amorim, A.; Gordo, P.; Eisenhauer, F.; Pfuhl, O.; Haug, M.; Wieprecht, E.; Wiezorrek, E.; Lima, J.; Perrin, G.; Brandner, W.; Straubmeier, C.; Le Bouquin, J.-B.; Garcia, P. J. V.

2018-05-01

Atmospheric turbulence and precise measurement of the astrometric baseline vector between any two telescopes are two major challenges in implementing phase-referenced interferometric astrometry and imaging. They limit the performance of a fibre-fed interferometer by degrading the instrument sensitivity and the precision of astrometric measurements and by introducing image reconstruction errors due to inaccurate phases. A multiple-beam acquisition and guiding camera was built to meet these challenges for a recently commissioned four-beam combiner instrument, GRAVITY, at the European Southern Observatory Very Large Telescope Interferometer. For each telescope beam, it measures (a) field tip-tilts by imaging stars in the sky, (b) telescope pupil shifts by imaging pupil reference laser beacons installed on each telescope using a 2 × 2 lenslet and (c) higher-order aberrations using a 9 × 9 Shack-Hartmann. The telescope pupils are imaged to provide visual monitoring while observing. These measurements enable active field and pupil guiding by actuating a train of tip-tilt mirrors placed in the pupil and field planes, respectively. The Shack-Hartmann measured quasi-static aberrations are used to focus the auxiliary telescopes and allow the possibility of correcting the non-common path errors between the adaptive optics systems of the unit telescopes and GRAVITY. The guiding stabilizes the light injection into single-mode fibres, increasing sensitivity and reducing the astrometric and image reconstruction errors. The beam guiding enables us to achieve an astrometric error of less than 50 μas. Here, we report on the data reduction methods and laboratory tests of the multiple-beam acquisition and guiding camera and its performance on-sky.

Modeling Multi-wavelength Stellar Astrometry. III. Determination of the Absolute Masses of Exoplanets and Their Host Stars

NASA Astrophysics Data System (ADS)

Coughlin, J. L.; López-Morales, Mercedes

2012-05-01

Astrometric measurements of stellar systems are becoming significantly more precise and common, with many ground- and space-based instruments and missions approaching 1 μas precision. We examine the multi-wavelength astrometric orbits of exoplanetary systems via both analytical formulae and numerical modeling. Exoplanets have a combination of reflected and thermally emitted light that causes the photocenter of the system to shift increasingly farther away from the host star with increasing wavelength. We find that, if observed at long enough wavelengths, the planet can dominate the astrometric motion of the system, and thus it is possible to directly measure the orbits of both the planet and star, and thus directly determine the physical masses of the star and planet, using multi-wavelength astrometry. In general, this technique works best for, though is certainly not limited to, systems that have large, high-mass stars and large, low-mass planets, which is a unique parameter space not covered by other exoplanet characterization techniques. Exoplanets that happen to transit their host star present unique cases where the physical radii of the planet and star can be directly determined via astrometry alone. Planetary albedos and day-night contrast ratios may also be probed via this technique due to the unique signature they impart on the observed astrometric orbits. We develop a tool to examine the prospects for near-term detection of this effect, and give examples of some exoplanets that appear to be good targets for detection in the K to N infrared observing bands, if the required precision can be achieved.

Combinations of Earth Orientation Measurements: SPACE94, COMB94, and POLE94

NASA Technical Reports Server (NTRS)

Gross, Richard S.

1996-01-01

A Kalman filter has been used to combine independent measurements of the Earth's orientation taken by the space-geodetic observing techniques of lunar laser ranging, satellite laser ranging, very long baseline interferometry, and the Global Positioning System. Prior to their combination, the data series were adjusted to have the same bias and rate, the stated uncertainties of the measurements were adjusted, and data points considered to be outliers were deleted. The resulting combination, SPACE94, consists of smoothed, interpolated polar motion and UT1-UTC values spanning October 6, 1976, to January 27, 1995, at 1-day intervals. The Kalman filter was then used to combine the space-geodetic series comprising SPACE94 with two different, independent series of Earth orientation measurements taken by the technique of optical astrometry. Prior to their combination with SPACE94, the bias, rate and annual term of the optical astrometric series were corrected, the stated uncertainties of the measurements were adjusted, and data points considered to be outliers were deleted. The adjusted optical astrometric series were then combined with SPACE94 in two steps: (1) the Bureau International de l'Heure (BIH) optical astrometric series was combined with SPACE94 to form COMB94, a combined series of smoothed, interpolated polar motion and UT1-UTC values spanning January 20, 1962, to January 27, 1995, at 5-day intervals, and (2) the International Latitude Service (ILS) optical astrometric series was combined with COMB94 to form POLE94, a combined series of smoothed, interpolated polar motion values spanning January 20, 1900, to January 21, 1995, at 30.4375-day intervals.

On-sky verification of the 6-h periodic basic angle variations of the Gaia satellite

NASA Astrophysics Data System (ADS)

Liao, Shilong; Lattanzi, Mario G.; Vecchiato, Alberto; Qi, Zhaoxiang; Crosta, Mariateresa; Tang, Zhenghong

2018-04-01

A Basic Angle (BA) of 106.5° separates the view directions of Gaia's two fields of view (FoV). A precise determination of the BA variations (BAV) is essential to guarantee a correct reconstruction of the global astrometric sphere, as residual systematic errors would result in, e.g., a bias in the parallaxes of the final Gaia catalog. The Basic Angle Monitoring (BAM) device, which provides a reliable and accurate estimation of BAV, shows that there exists a ~1 mas amplitude, 6-h period BA oscillation. It's essential to verify to what extent this signal is caused by real BAV, or is at least in part an effect of the BAM device itself. Here, we propose an astrometric on-sky approach to re-determine the 6-h periodic BAV. The results of this experiment, which treated a full day (17 Oct 2016) of Gaia astrometric data, recover a value for the 6-h oscillation of 1.856+/-0.857 mas. This is consistent, within the errors, with the BAM finding for that day.

The Actual Mass of the Object Orbiting Epsilon Eridani

NASA Astrophysics Data System (ADS)

Gatewood, G.

2000-10-01

We have tested our 112 Multichannel Astrometric Photometer (MAP) (Gatewood 1987, AJ 94, 213) observations (beginning in 1988) of Epsilon Eridani against the orbital elements provided to us by W. Cochran (private communication). The reduction algorithm is detailed most recently by Gatewood, Han, and Black (2000 ApJ Letters, in press). The seven year period is clearly shown in a variance vs trial periods plot. Although it is near the limit of the current instrument, the astrometric orbital motion is apparent in the residuals to a standard derivation of the star's proper motion and parallax. The astrometric orbital parameters derived by forcing the spectroscopic elements are: semimajor axis = 1.51 +/- 0.44 mas, node of the orbit on the sky = 120 +/- 28 deg, inclination out of the plane of the sky = 46 +/- 17 deg, actual mass = 1.2 +/- 0.33 times that of Jupiter. Our study confirms this object (this is not a minimum mass) as the nearest extrasolar Jupiter mass companion to our solar system. In view of its large orbital eccentricity, however, its exact nature remains unclear.

Analyzing the Proper Motion of Two Double Star Systems from Astrometric Measurements

NASA Astrophysics Data System (ADS)

Falatoun, Alex; Barrera, Janet; de Neef, Anna; Gonzalez, Aura; Calanog, Jae; Boyce, Pat; Boyce, Grady

2018-04-01

The iTelescope network was used to obtain astrometric measurements of double star systems WDS 12202-1408 (STF 1631) and WDS 12339+5522 (STI 2286). Through astrometric measurement softwares SAOImage DS9 and Mira Pro x64, a mean position angle for STF 1631 of 304.8° ± 0.9° and a mean separation 14.7" ± 0.2" was measured. For STI 2286, a newly measured mean position angle of 85.9° ± 0.9° and mean separation 11.5" ± 0.3" were obtained. The relative proper motion of 1631 shows that the system could be demonstrating a linear path or an approximately circular orbit with a period of 1400 years. Parallax measurements of the secondary star will aid in classifying if this system is a physical or a visual pair. The proper motion of STI 2286 indicates that it could be a physical pair, featuring an orbit nearing a turning point. Follow-up observations in three to four year intervals will further validate or refute this claim and constrain the shape of a possible orbit.

Astrometric and photometric measurements of binary stars with adaptive optics: observations from 2001 to 2006

NASA Astrophysics Data System (ADS)

Roberts, Lewis C.; Mason, Brian D.

2018-02-01

The adaptive optics system at the 3.6 m Advanced Electro-Optical System telescope was used to measure the astrometry and differential magnitude in I band of binary star systems between 2002 and 2006. We report 413 astrometric and photometric measurements of 373 stellar pairs. The astrometric measurements will be of use for future orbital determination, and the photometric measurements will be of use in estimating the spectral types of the component stars. For 21 binaries that had not been observed in decades, we are able to confirm that the systems share common proper motion. Candidate new companions were detected in 24 systems; for these we show the discovery images. Follow-up observations should be able to determine if these systems share common proper motion and are gravitationally bound objects. We computed orbits for nine binaries. Of these, the orbits of five systems are improved compared to prior orbits and four systems have their orbits computed for the first time. In addition, 315 stars were unresolved and the full-width half maxima of the images are presented.

HIGH-PRECISION ASTROMETRIC MILLIMETER VERY LONG BASELINE INTERFEROMETRY USING A NEW METHOD FOR ATMOSPHERIC CALIBRATION

DOE Office of Scientific and Technical Information (OSTI.GOV)

Rioja, M.; Dodson, R., E-mail: maria.rioja@icrar.org

2011-04-15

We describe a new method which achieves high-precision very long baseline interferometry (VLBI) astrometry in observations at millimeter (mm) wavelengths. It combines fast frequency-switching observations, to correct for the dominant non-dispersive tropospheric fluctuations, with slow source-switching observations, for the remaining ionospheric dispersive terms. We call this method source-frequency phase referencing. Provided that the switching cycles match the properties of the propagation media, one can recover the source astrometry. We present an analytic description of the two-step calibration strategy, along with an error analysis to characterize its performance. Also, we provide observational demonstrations of a successful application with observations using themore » Very Long Baseline Array at 86 GHz of the pairs of sources 3C274 and 3C273 and 1308+326 and 1308+328 under various conditions. We conclude that this method is widely applicable to mm-VLBI observations of many target sources, and unique in providing bona fide astrometrically registered images and high-precision relative astrometric measurements in mm-VLBI using existing and newly built instruments, including space VLBI.« less

Saturnian satellite observations made in Brazil during the 1995 opposition with an astrometric analysis

NASA Astrophysics Data System (ADS)

Vienne, A.; Thuillot, W.; Veiga, C. H.; Arlot, J.-E.; Vieira Martins, R.

2001-12-01

This paper provides an analysis of astrometric measurements of the main Saturnian satellites made thanks to CCD observations performed in 1995 at the Laboratório Nacional de Astrofísica at Itajubá in Brazil. The astrometric reduction is discussed especially the small corrections done here, but most of time neglected elsewhere. A catalog of 6006 differential positions has been obtained. They have been compared to different ephemerides, the Vienne & Duriez ephemerides (TASS 1.7), the Harper & Taylor ephemerides and the Dourneau ephemerides. These observations provide a large set of modern observations, and appear to be of good precision. This accuracy is needed for future use of these data to improve the dynamical models. These positions are included in the data base NSDC dedicated to the natural satellites (ftp://ftp.bdl.fr/pub/NSDC/saturn/raw_data/position/). They are also available at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/380/727

Predictions of stellar occultations by TNOs/Centaurs using Gaia

NASA Astrophysics Data System (ADS)

Desmars, Josselin; Camargo, Julio; Berard, Diane; Sicardy, Bruno; Leiva, Rodrigo; Vieira-Martins, Roberto; Braga-Ribas, Felipe; Assafin, Marcelo; Rossi, Gustavo; Chariklo occultations Team, Rio Group, Lucky Star Occultation Team, Granada Occultation Team

2017-10-01

Stellar occultations are the unique technique from the ground to access physical parameters of the distant solar system objects, such as the measure of the size and the shape at kilometric level, the detection of tenuous atmospheres (few nanobars), and the investigation of close vicinity (satellites, rings, jets).Predictions of stellar occultations require accurate positions of the star and the object.The Gaia DR1 catalog now allows to get stellar position to the milliarcsecond (mas) level. The main uncertainty in the prediction remains in the position of the object (tens to hundreds of mas).Now, we take advantage of the NIMA method for the orbit determination that uses the most recent observations reduced by the Gaia DR1 catalog and the astrometric positions derived from previous positive occultations.Up to now, we have detected nearly 50 positive occultations for about 20 objects that provide astrometric positions of the object at the time of the occultation. The uncertainty of these positions only depends on the uncertainty on the position of the occulted stars, which is a few mas with the Gaia DR1 catalog. The main limitation is now on the proper motion of the star which is only given for bright stars in the Tycho-Gaia Astrometric Solution. This limitation will be solved with the publicationof the Gaia DR2 expected on April 2018 giving proper motions and parallaxes for the Gaia stars. Until this date, we use hybrid stellar catalogs (UCAC5, HSOY) that provide proper motions derived from Gaia DR1 and another stellar catalog.Recently, the Gaia team presented a release of three preliminary Gaia DR2 stellar positions involved in the occultations by Chariklo (22 June and 23 July 2017) and by Triton (5 October 2017).Taking the case of Chariklo as an illustration, we will present a comparison between the proper motions of DR2 and the other catalogs and we will show how the Gaia DR2 will lead to a mas level precision in the orbit and in the prediction of stellar occultations.**Part of the research leading to these results has received funding from the European Research Council under theEuropean Community’s H2020 (2014-2020/ ERC Grant Agreement n 669416 ”LUCKY STAR”).

Gaia: Mapping the Milky Way: The Scientific Promise of Gaia DR2

NASA Astrophysics Data System (ADS)

Walton, Nicholas; ESA Gaia, Data Processing and Analysis Consortium (DPAC)

2018-06-01

The ESA Gaia mission will release its first major all sky astrometric catalogue (Gaia DR2), of more than 1.3 billion stars in our Galaxy, on 25 April 2018.This presentation will provide an overview of the Gaia mission, focussing on the significant scientific potential of the Gaia DR2 release. This is based on 22 months of input data and allows for a full Gaia stand alone astrometric solution, including parallaxes and proper motions, of over 1.3 billion sources. The astrometric uncertainties in Gaia DR2 will be at the level of tens of micro-arcsec for sources G<15.The Gaia DR2 release provides not only high precision full five parameter astrometry, but also a complete photometric catalogue of the sources on an all sky homogeneous photometric system in the Gaia G band and broad bands G_BP and G_RP. The release will include median radial velocities for more than six million stars (brighter that G_RVS = 12) together with a set of astrophysical parameters (including stellar temperatures) for some 150 million stars. Finally the Gaia DR2 release will include a set of additional data products including the light curves of more than half a million variable stars, and the positions of more than thirteen thousand objects in our Solar System.Together with the Gaia DR2 data products and associated release documentation, a small number of performance verification papers, using Gaia DR2 data only to provide new insights into a number of key areas of Gaia science, will be published in a special edition of A&A. These will provide demonstrations of the scientific potential of the Gaia DR2 catalogue, and also highlight some of the issues and limitations involved in the use of the Gaia DR2 data.The Gaia mission and Gaia Data Releases are made possible through the dedication and expertise of the community scientists and engineers involved in the design, construction, and operation of Gaia (led by ESA) and the collaboration of some 450 scientists and software engineers responsible for the complex task of analysing the processed data (the DPAC). The role of both will be covered in the presentation.The presentation will conclude with a brief look ahead to the longer term Gaia data release schedule.

Astrometric Measurements of Triple Star System 15379+3006 STF 1963AB, STF 1963AC

NASA Astrophysics Data System (ADS)

Russell, Harker; Miller, Lindsey; Beltzer-Sweeney, Alexander; Shilts, Trey; Stojimirovic, Irena

2018-04-01

Research team PRSM reports astrometric measurements of the double star system WDS 15379+3006 (STF 1963AB, STF 1963AC) obtained using the iTelescope Network. By performing CCD astrometry, the team determined a position angle of 298.4° ± 0.1° with an angular separation of 05. 28" ± 0.1" for STF 1963AB, and a position angle of 116.1° ± 0.1° with an angular separation of 32.35" ± 0.1" for STF 1963AC. The angular separation and position angle have changed from previous measurements.

Does Pluto Have a Haze Layer?

NASA Technical Reports Server (NTRS)

Elliot, James L.

1997-01-01

The goal of this research was to determine whether Pluto has a haze layer through observations (with the Kuiper Airborne Observatory) of a stellar occultation by Pluto that was originally predicted to occur on 1993 October 3. As described in the attached material, our extensive astrometric measurements determined that this occultation would not be visible from Earth, and we canceled plans to observe it with the KAO. Efforts were then directed toward improving our astrometric techniques so that we could find future occultations with which we could satisfy the original goals of the research proposed for this grant.

Data Mining for Double Stars in Astrometric Catalogs

NASA Astrophysics Data System (ADS)

Wycoff, Gary L.; Mason, Brian D.; Urban, Sean E.

2006-07-01

The US Naval Observatory has mined over 140 astrometric catalogs, including the Astrographic Catalogue and the Two Micron All Sky Survey, for measures of double stars. This resulted in 114,218 new measures of 47,007 different systems spanning 110 years; these are now included in the Washington Double Star catalog (WDS). This is the single largest data set ever added to the WDS. The measures are typically of wider pairs, most between 4" and 30" thus, their value in aiding orbit determination is limited. However, they have proven invaluable in the verification of systems and the determination of rectilinear motions of systems.

SCDU (Spectral Calibration Development Unit) Testbed Narrow Angle Astrometric Performance

NASA Technical Reports Server (NTRS)

Wang, Xu; Goullioud, Renaud; Nemati, Bijan; Shao, Michael; Wehmeier, Udo J.; Weilert, Mark A.; Werne, Thomas A.; Wu, Janet P.; Zhai, Chengxing

2010-01-01

The most stringent astrometric performance requirements on NASA's SIM(Space Interferometer Mission)-Lite mission will come from the so-called Narrow-Angle (NA) observing scenario, aimed at finding Earth-like exoplanets, where the interferometer chops between the target star and several nearby reference stars multiple times over the course of a single visit. Previously, about 20 pm NA error with various shifts was reported. Since then, investigation has been under way to understand the mechanisms that give rise to these shifts. In this paper we report our findings, the adopted mitigation strategies, and the resulting testbed performance.

Comoving Stars in Gaia DR1: An Abundance of Very Wide Separation Comoving Pairs

NASA Astrophysics Data System (ADS)

Oh, Semyeong; Price-Whelan, Adrian M.; Hogg, David W.; Morton, Timothy D.; Spergel, David N.

2017-06-01

The primary sample of the Gaia Data Release 1 is the Tycho-Gaia Astrometric Solution (TGAS): ≈2 million Tycho-2 sources with improved parallaxes and proper motions relative to the initial catalog. This increased astrometric precision presents an opportunity to find new binary stars and moving groups. We search for high-confidence comoving pairs of stars in TGAS by identifying pairs of stars consistent with having the same 3D velocity using a marginalized likelihood ratio test to discriminate candidate comoving pairs from the field population. Although we perform some visualizations using (bias-corrected) inverse parallax as a point estimate of distance, the likelihood ratio is computed with a probabilistic model that includes the covariances of parallax and proper motions and marginalizes the (unknown) true distances and 3D velocities of the stars. We find 13,085 comoving star pairs among 10,606 unique stars with separations as large as 10 pc (our search limit). Some of these pairs form larger groups through mutual comoving neighbors: many of these pair networks correspond to known open clusters and OB associations, but we also report the discovery of several new comoving groups. Most surprisingly, we find a large number of very wide (> 1 pc) separation comoving star pairs, the number of which increases with increasing separation and cannot be explained purely by false-positive contamination. Our key result is a catalog of high-confidence comoving pairs of stars in TGAS. We discuss the utility of this catalog for making dynamical inferences about the Galaxy, testing stellar atmosphere models, and validating chemical abundance measurements.

The Candidate Progenitor of the Type IIn SN 2010jl Is Not an Optically Luminous Star

NASA Technical Reports Server (NTRS)

Fox, Ori D.; Van Dyk, Schuyler D.; Dwek, Eli; Smith, Nathan; Filippenko, Alexei V.; Andrews, Jennifer; Arendt, Richard G.; Foley, Ryan J.; Kelly, Patrick L.; Miller, Adam;

Astrometric observations of visual binaries using 26-inch refractor during 2007-2014 at Pulkovo

NASA Astrophysics Data System (ADS)

Izmailov, I. S.; Roshchina, E. A.

2016-04-01

We present the results of 15184 astrometric observations of 322 visual binaries carried out in 2007-2014 at Pulkovo observatory. In 2007, the 26-inch refractor ( F = 10413 mm, D = 65 cm) was equipped with the CCD camera FLI ProLine 09000 (FOV 12' × 12', 3056 × 3056 pixels, 0.238 arcsec pixel-1). Telescope automation and weather monitoring system installation allowed us to increase the number of observations significantly. Visual binary and multiple systems with an angular distance in the interval 1."1-78."6 with 7."3 on average were included in the observing program. The results were studied in detail for systematic errors using calibration star pairs. There was no detected dependence of errors on temperature, pressure, and hour angle. The dependence of the 26-inch refractor's scale on temperature was taken into account in calculations. The accuracy of measurement of a single CCD image is in the range of 0."0005 to 0."289, 0."021 on average along both coordinates. Mean errors in annual average values of angular distance and position angle are equal to 0."005 and 0.°04 respectively. The results are available here http://izmccd.puldb.ru/vds.htmand in the Strasbourg Astronomical Data Center (CDS). In the catalog, the separations and position angles per night of observation and annual average as well as errors for all the values and standard deviations of a single observation are presented. We present the results of comparison of 50 pairs of stars with known orbital solutions with ephemerides.

Precise predictions of stellar occultations by Pluto, Charon, Nix, and Hydra for 2008-2015

NASA Astrophysics Data System (ADS)

Assafin, M.; Camargo, J. I. B.; Vieira Martins, R.; Andrei, A. H.; Sicardy, B.; Young, L.; da Silva Neto, D. N.; Braga-Ribas, F.

2010-06-01

Context. We investigate transneptunian objects, including Pluto and its satellites, by stellar occultations. Aims: Our aim is to derive precise, astrometric predictions for stellar occultations by Pluto and its satellites Charon, Hydra and Nix for 2008-2015. We construct an astrometric star catalog in the UCAC2 system covering Plutoarcmins sky path. Methods: We carried out in 2007 an observational program at the ESO2p2/WFI instrument covering the sky path of Pluto from 2008 to 2015. We made the astrometry of 110 GB of images with the Platform for Reduction of Astronomical Images Automatically (PRAIA). By relatively simple astrometric techniques, we treated the overlapping observations and derived a field distortion pattern for the WFI mosaic of CCDs to within 50 mas precision. Results: Positions were obtained in the UCAC2 frame with errors of 50 mas for stars up to magnitude R = 19, and 25 mas up to R = 17. New stellar proper motions were also determined with 2MASS and the USNO B1.0 catalog positions as first epoch. We generated 2252 predictions of stellar occultations by Pluto, Charon, Hydra and Nix for 2008-2015. An astrometric catalog with proper motions was produced, containing 2.24 million stars covering Plutoarcmins sky path with 30arcmin width. Its magnitude completeness is about R = 18-19 with a limit about R = 21. Based on the past 2005-2008 occultations successfully predicted, recorded and fitted, a linear drift with time in declination with regard to DE418/plu017 ephemerides was determined for Pluto and used in the current predictions. For offset (mas) = A * (t (yr) - 2005.0) + B, we find A = +30.5 ± 4.3 mas yr-1 and B = -31.5 ± 11.3 mas, with standard deviation of 14.4 mas for the offsets. For these past occultations, predictions and follow-up observations were made with the 0.6 m and 1.6 m telescopes at the Laboratório Nacional de Astrofísica/Brazil. Conclusions: Recurrent issues in stellar occultation predictions were addressed and properly overcome: body ephemeris offsets, catalog zero-point position errors and field-of-view size, long-term predictions and stellar proper motions, faint-visual versus bright-infrared stars and star/body astrometric follow-up. In particular, we highlight the usefulness of the obtained astrometric catalog as a reference frame for star/body astrometric follow-up before and after future events involving the Pluto system. Besides, it also furnishes useful photometric information for field stars in the flux calibration of observed light curves. Updates on the ephemeris offsets and candidate star positions (geometric conditions of predictions and finding charts) are made available by the group at http://www.lesia.obspm.fr/perso/bruno-sicardy Tables of predictions for stellar occultations by Pluto, Charon, Nix and Hydra for 2008-2015 and Catalog of star positions for 2008-2015 sky path of Pluto are only available in electronic form at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/515/A32Observations made through the ESO run 079.A-9202(A), 075.C-0154, 077.C-0283 and 079.C-0345.Also based on observations made at the Laboratório Nacional de Astrofísica (LNA), Itajubá-MG, Brazil.

More flexibility in representing geometric distortion in astronomical images

NASA Astrophysics Data System (ADS)

Shupe, David L.; Laher, Russ R.; Storrie-Lombardi, Lisa; Surace, Jason; Grillmair, Carl; Levitan, David; Sesar, Branimir

2012-09-01

A number of popular software tools in the public domain are used by astronomers, professional and amateur alike, but some of the tools that have similar purposes cannot be easily interchanged, owing to the lack of a common standard. For the case of image distortion, SCAMP and SExtractor, available from Astromatic.net, perform astrometric calibration and source-object extraction on image data, and image-data geometric distortion is computed in celestial coordinates with polynomial coefficients stored in the FITS header with the PV i_j keywords. Another widely-used astrometric-calibration service, Astrometry.net, solves for distortion in pixel coordinates using the SIP convention that was introduced by the Spitzer Science Center. Up until now, due to the complexity of these distortion representations, it was very difficult to use the output of one of these packages as input to the other. New Python software, along with faster-computing C-language translations, have been developed at the Infrared Processing and Analysis Center (IPAC) to convert FITS-image headers from PV to SIP and vice versa. It is now possible to straightforwardly use Astrometry.net for astrometric calibration and then SExtractor for source-object extraction. The new software also enables astrometric calibration by SCAMP followed by image visualization with tools that support SIP distortion, but not PV . The software has been incorporated into the image-processing pipelines of the Palomar Transient Factory (PTF), which generate FITS images with headers containing both distortion representations. The software permits the conversion of archived images, such as from the Spitzer Heritage Archive and NASA/IPAC Infrared Science Archive, from SIP to PV or vice versa. This new capability renders unnecessary any new representation, such as the proposed TPV distortion convention.

Orbital Monitoring of the AstraLux Large M-dwarf Multiplicity Sample

NASA Astrophysics Data System (ADS)

Janson, Markus; Bergfors, Carolina; Brandner, Wolfgang; Bonnefoy, Mickaël; Schlieder, Joshua; Köhler, Rainer; Hormuth, Felix; Henning, Thomas; Hippler, Stefan

2014-10-01

Orbital monitoring of M-type binaries is essential for constraining their fundamental properties. This is particularly useful in young systems, where the extended pre-main-sequence evolution can allow for precise isochronal dating. Here, we present the continued astrometric monitoring of the more than 200 binaries of the AstraLux Large Multiplicity Survey, building both on our previous work, archival data, and new astrometric data spanning the range of 2010-2012. The sample is very young overall—all included stars have known X-ray emission, and a significant fraction (18%) of them have recently also been identified as members of young moving groups in the solar neighborhood. We identify ~30 targets that both have indications of being young and for which an orbit either has been closed or appears possible to close in a reasonable time frame (a few years to a few decades). One of these cases, GJ 4326, is, however, identified as probably being substantially older than has been implied from its apparent moving group membership, based on astrometric and isochronal arguments. With further astrometric monitoring, these targets will provide a set of empirical isochrones, against which theoretical isochrones can be calibrated, and which can be used to evaluate the precise ages of nearby young moving groups. Based on observations collected at the European Southern Observatory, Chile, under observing programs 081.C-0314(A), 082.C-0053(A), and 084.C-0812(A), and on observations collected at the Centro Astronómico Hispano Alemán (CAHA) at Calar Alto, operated jointly by the Max-Planck Institute for Astronomy and the Instituto de Astrofísica de Andalucía (CSIC).

Reconnaissance of the HR 8799 Exosolar System. II. Astrometry and Orbital Motion

NASA Astrophysics Data System (ADS)

Pueyo, L.; Soummer, R.; Hoffmann, J.; Oppenheimer, R.; Graham, J. R.; Zimmerman, N.; Zhai, C.; Wallace, J. K.; Vescelus, F.; Veicht, A.; Vasisht, G.; Truong, T.; Sivaramakrishnan, A.; Shao, M.; Roberts, L. C., Jr.; Roberts, J. E.; Rice, E.; Parry, I. R.; Nilsson, R.; Lockhart, T.; Ligon, E. R.; King, D.; Hinkley, S.; Hillenbrand, L.; Hale, D.; Dekany, R.; Crepp, J. R.; Cady, E.; Burruss, R.; Brenner, D.; Beichman, C.; Baranec, C.

2015-04-01

We present an analysis of the orbital motion of the four substellar objects orbiting HR 8799. Our study relies on the published astrometric history of this system augmented with an epoch obtained with the Project 1640 coronagraph with an integral field spectrograph (IFS) installed at the Palomar Hale telescope. We first focus on the intricacies associated with astrometric estimation using the combination of an extreme adaptive optics system (PALM-3000), a coronagraph, and an IFS. We introduce two new algorithms. The first one retrieves the stellar focal plane position when the star is occulted by a coronagraphic stop. The second one yields precise astrometric and spectrophotometric estimates of faint point sources even when they are initially buried in the speckle noise. The second part of our paper is devoted to studying orbital motion in this system. In order to complement the orbital architectures discussed in the literature, we determine an ensemble of likely Keplerian orbits for HR 8799bcde, using a Bayesian analysis with maximally vague priors regarding the overall configuration of the system. Although the astrometric history is currently too scarce to formally rule out coplanarity, HR 8799d appears to be misaligned with respect to the most likely planes of HR 8799bce orbits. This misalignment is sufficient to question the strictly coplanar assumption made by various authors when identifying a Laplace resonance as a potential architecture. Finally, we establish a high likelihood that HR 8799de have dynamical masses below 13 MJup, using a loose dynamical survival argument based on geometric close encounters. We illustrate how future dynamical analyses will further constrain dynamical masses in the entire system.

Eclipses of the inner satellites of Jupiter observed in 2015

NASA Astrophysics Data System (ADS)

Saquet, E.; Emelyanov, N.; Colas, F.; Arlot, J.-E.; Robert, V.; Christophe, B.; Dechambre, O.

2016-06-01

Aims: During the 2014-2015 campaign of mutual events, we recorded ground-based photometric observations of eclipses of Amalthea (JV) and, for the first time, Thebe (JXIV) by the Galilean moons. We focused on estimating whether the positioning accuracy of the inner satellites determined with photometry is sufficient for dynamical studies. Methods: We observed two eclipses of Amalthea and one of Thebe with the 1 m telescope at Pic du Midi Observatory using an IR filter and a mask placed over the planetary image to avoid blooming features. A third observation of Amalthea was taken at Saint-Sulpice Observatory with a 60 cm telescope using a methane filter (890 nm) and a deep absorption band to decrease the contrast between the planet and the satellites. After background removal, we computed a differential aperture photometry to obtain the light flux, and followed with an astrometric reduction. Results: We provide astrometric results with an external precision of 53 mas for the eclipse of Thebe, and 20 mas for that of Amalthea. These observation accuracies largely override standard astrometric measurements. The (O - C)s for the eclipse of Thebe are 75 mas on the X-axis and 120 mas on the Y-axis. The (O - C)s for the total eclipses of Amalthea are 95 mas and 22 mas, along the orbit, for two of the three events. Taking into account the ratio of (O - C) to precision of the astrometric results, we show a significant discrepancy with the theory established by Avdyushev and Ban'shikova in 2008, and the JPL JUP 310 ephemeris. Three of the four eclipse observations where recorded at the 1 m telescope of Pic du Midi Observatory (S2P), the other at Saint-Sulpice Observatory.

Liquid-core photonic crystal fiber platform for raman scattering measurements of microliter analyte solutions

NASA Astrophysics Data System (ADS)

Han, Yun; Oo, Maung Khaing; Zhu, Yinian; Sukhishvili, Svetlana; Xiao, Limin; Demokan, M. Süleyman; Jin, Wei; Du, Henry

2007-09-01

We have explored the use of index-guiding liquid-core photonic crystal fiber (LC-PCF) as a platform for sensing and measurements of analyte solutions of minute volume by normal and surface-enhanced Raman scattering (SERS). The index-guiding LC-PCF was fabricated by selectively sealing via fusion splicing the cladding air channels of a hollow-core PCF (HC-PCF) while leaving the center core open at both ends of the fiber. The center core of the resultant fiber was subsequently filled with water-ethanol solution mixtures at various ethanol concentrations for normal Raman scattering measurements and with water-thiocynate solutions containing Ag nanoparticle aggregates for SERS detection of thiocynate at trace concentrations. The light-guiding nature in the solution phase inside the LC-PCF allows direct and strong light-field overlap with the solution phase over the entire length of the PCF (~30 cm). This detection scheme also dramatically reduces the contribution of silica to Raman spectral background, compared with the solid-core counterpart, thus its potential interference in spectral analysis. These features attribute to ready normal Raman measurements of water, ethanol, and water (99 vol.%)-ethanol (1 vol.%) solutions as well as sensitive and reproducible SERS detection of ~10 ppb thiocynate in water, all at a volume of ~0.1 μL.

Barnard’s Star: Planets or Pretense

NASA Astrophysics Data System (ADS)

Bartlett, Jennifer L.; Ianna, P. A.

2014-01-01

Barnard’s Star remains popular with planet hunters because it is not only an extremely near, high proper motion star, but also the object of early planet-detection claims. In 1963, van de Kamp explained perturbations in its proper motion by the presence of a planet. In 1969, he produced another single-planet solution and a two-planet solution to the astrometric wobbles detected. At least 19 studies have failed to confirm his results using a range of techniques, including radial velocity, direct imaging, and speckle interferometry. However, most of them lacked the sensitivity to detect the planets he described, including astrometric studies at the McCormick and Naval Observatories. However, radial-velocity monitoring of Barnard’s Star at Lick and Keck Observatories from 1987 through 2012 appears to have ruled out such planets. Based upon observations made at the Sproul Observatory between 1916 and 1962, van de Kamp claimed that Barnard’s Star had a planet with about 1.6 times the mass of Jupiter and an orbital period of 24 years. After accounting for instrumentation effects that might have been partially responsible for his initial results, he continued to assert that this red dwarf had two planets. In his 1982 analysis of ~20,000 exposures collected between 1938 and 1981, he calculated that two planets with 0.7- and 0.5-Jupiter masses in 12- and 20-year orbits, respectively, orbited the second-closest stellar system to our own. Starting in 1995, the dramatic successes of radial velocity searches for extrasolar planets drove van de Kamp’s unsubstantiated claims from popular consciousness. Although many low-mass stellar companions were discovered through astrometry, the technique has been less successful for planets: “The Extrasolar Planets Encyclopaedia” identifies one such discovery out of the 997 planets listed on 2013 September 23. Although Barnard’s Star has lost its pretensions to hosting the first extrasolar planets known, its intrinsic properties will keep it under observation. NSF grant AST 98-20711, Litton Marine Systems, Levinson Fund, University of Virginia, Hampden-Sydney College, and US Naval Observatory supported this research.

Astrometric Quality of the USNO CCD Astrograph (UCA)

NASA Astrophysics Data System (ADS)

Zacharias, N.

1997-05-01

The USNO 8-inch astrograph has been equipped with a Kodak 1536x1024 pixel CCD since June 1995, operating in a 570-650 nm bandpass. With 3-minute exposures well exposed images are obtained in the magnitude range R ~ 8.5 - 13.5(m) . An astrometric precision of 10 to 15 mas for those stars is estimated from frame-to-frame comparisons. External comparisons reveal an accuracy of about 15 mas for those stars in a 20' field of view. For fainter stars, the error budget is dominated by the S/N ratio, reaching ~ 100 mas at R=16(m) under good observing conditions.

Automatic measurement of images on astrometric plates

NASA Astrophysics Data System (ADS)

Ortiz Gil, A.; Lopez Garcia, A.; Martinez Gonzalez, J. M.; Yershov, V.

1994-04-01

We present some results on the process of automatic detection and measurement of objects in overlapped fields of astrometric plates. The main steps of our algorithm are the following: determination of the Scale and Tilt between charge coupled devices (CCD) and microscope coordinate systems and estimation of signal-to-noise ratio in each field;--image identification and improvement of its position and size;--image final centering;--image selection and storage. Several parameters allow the use of variable criteria for image identification, characterization and selection. Problems related with faint images and crowded fields will be approached by special techniques (morphological filters, histogram properties and fitting models).

Albireo: 260 Years of Astrometric Observations

NASA Astrophysics Data System (ADS)

Hass, Jacob; Phung, Kevin; Carro, Joseph; Hock, Emily; Loveland, Donald; Nibbe, Tristan; Sharp, Zoe; Smit, Jenny; Genet, Russell

2016-03-01

The historical record of Albireo's observations reflects the progress of double star research. Some 294 astrometric observations have been published starting with Bradley's 1755 observation and ending with our 2015 observation. Several observation techniques were used over this 260 year span. Noteworthy are the historic contributions of astronomers such as James Bradley, Christian Mayer, William Herschel, Giuseppe Piazzi, Friedrich Georg Wilhelm von Struve, Sir John Herschel, Sir James South, Edward Skinner King, and Andrei Tokovinin. Overall trend lines of the past observations of Albireo are compared to our current observation, and are generally concurrent. Dividing Albireo's past observations of separation into time segments shows evidence of a known third star in Albireo's system.

Systems Engineering and Application of System Performance Modeling in SIM Lite Mission

NASA Technical Reports Server (NTRS)

Moshir, Mehrdad; Murphy, David W.; Milman, Mark H.; Meier, David L.

2010-01-01

The SIM Lite Astrometric Observatory will be the first space-based Michelson interferometer operating in the visible wavelength, with the ability to perform ultra-high precision astrometric measurements on distant celestial objects. SIM Lite data will address in a fundamental way questions such as characterization of Earth-mass planets around nearby stars. To accomplish these goals it is necessary to rely on a model-based systems engineering approach - much more so than most other space missions. This paper will describe in further detail the components of this end-to-end performance model, called "SIM-sim", and show how it has helped the systems engineering process.

Astrometric photographic observations of Helene

NASA Astrophysics Data System (ADS)

Veiga, C. H.; Vieira Martins, R.

2000-05-01

Astrometric photographic positions of the Saturnian satellite Helene obtained from 22 plates taken in 6 nights are presented. The observations are distributed between 5 missions in 1985 and 1987. All positions are compared with those calculated by \\cite[Jacobson (1999).]{J99} The residuals have mean and standard deviation smaller than 0farcs25 and 0farcs30 respectively. Based on observations made at Laboratório Nacional de Astrofísica/CNPq/MCT-Itajubá-Brazil. Table 1 is also available in electronic form at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsweb.u-strabg.fr/Abstract.html

THE POSITION/STRUCTURE STABILITY OF FOUR ICRF2 SOURCES

DOE Office of Scientific and Technical Information (OSTI.GOV)

Fomalont, Ed; Johnston, Kenneth; Fey, Alan

2011-03-15

Four close radio sources in the International Celestial Reference Frame (ICRF) catalog were observed using phase referencing with the VLBA at 43, 23, and 8.6 GHz, and with VERA at 23 GHz over a one-year period. The goal was to determine the stability of the radio cores and to assess structure effects associated with positions in the ICRF. Although the four sources were compact at 8.6 GHz, the VLBA images at 43 GHz with 0.3 mas resolution showed that all were composed of several components. A component in each source was identified as the radio core using some or allmore » of the following emission properties: compactness, spectral index, location at the end of the extended emission region, and stationary in the sky. Over the observing period, the relative positions between the four radio cores were constant to 0.02 mas, the phase-referencing positional accuracy obtained at 23 and 43 GHz among the sources, suggesting that once a radio core is identified, it remains stationary in the sky to this accuracy. Other radio components in two of the four sources had detectable motion in the radio jet direction. Comparison of the 23 and 43 GHz VLBA images with the VLBA 8.6 GHz images and the ICRF positions suggests that some ICRF positions are dominated by a moving jet component; hence, they can be displaced up to 0.5 mas from the radio core and may also reflect the motion of the jet component. Future astrometric efforts to determine a more accurate quasar reference frame at 23 and 43 GHz and from the VLBI2010 project are discussed, and supporting VLBA or European VLBI Network observations of ICRF sources at 43 GHz are recommended in order to determine the internal structure of the sources. A future collaboration between the radio (ICRF) and the optical frame of GAIA is discussed.« less

Micro-Arcsec mission: implications of the monitoring, diagnostic and calibration of the instrument response in the data reduction chain. .

NASA Astrophysics Data System (ADS)

Busonero, D.; Gai, M.

The goals of 21st century high angular precision experiments rely on the limiting performance associated to the selected instrumental configuration and observational strategy. Both global and narrow angle micro-arcsec space astrometry require that the instrument contributions to the overall error budget has to be less than the desired micro-arcsec level precision. Appropriate modelling of the astrometric response is required for optimal definition of the data reduction and calibration algorithms, in order to ensure high sensitivity to the astrophysical source parameters and in general high accuracy. We will refer to the framework of the SIM-Lite and the Gaia mission, the most challenging space missions of the next decade in the narrow angle and global astrometry field, respectively. We will focus our dissertation on the Gaia data reduction issues and instrument calibration implications. We describe selected topics in the framework of the Astrometric Instrument Modelling for the Gaia mission, evidencing their role in the data reduction chain and we give a brief overview of the Astrometric Instrument Model Data Analysis Software System, a Java-based pipeline under development by our team.

An astrometric facility for planetary detection on the space station

NASA Technical Reports Server (NTRS)

Nishioka, Kenji; Scargle, Jeffrey D.; Givens, John J.

1987-01-01

An Astrometric Telescope Facility (ATF) for planetary detection is being studied as a potential space station initial operating capability payload. The primary science objective of this mission is the detection and study of planetary systems around other stars. In addition, the facility will be capable of other astrometric measurements such as stellar motions of other galaxies and highly precise direct measurement of stellar distance within the Milky Way Galaxy. The results of a recently completed ATF preliminary systems definition study are summarized. Results of this study indicate that the preliminary concept for the facility is fully capable of meeting the science objective without the development of any new technologies. A simple straightforward operations approach was developed for the ATF. A real-time facility control is not normally required, but does maintain a near real-time ground monitoring capability for the facility and science data stream on a full-time basis. Facility observational sequences are normally loaded once a week. In addition, the preliminary system is designed to be fail-safe and single-fault tolerant. Routine interactions by the space station crew with the ATF will not be necessary, but onboard controls are provided for crew override as required for emergencies and maintenance.

The First Data from Gaia

NASA Astrophysics Data System (ADS)

Fabricius, C.; Torra, J.

2018-01-01

The Gaia astrometric satellite is in its science operational phase since July 2014. At an average rate of 50 million observations per day, Gaia scans the full sky once every six months. The first data release (Gaia DR1), issued in September 2016, contains astrometric and photometric results for more than 1 billion stars brighter than magnitude 21 based on observations acquired during the first 14 months of operations. For more than two million stars brighter than 11.5 mag, positions, parallaxes, and proper motions have been obtained to HIPPARCOS-type precision through a combination with the earlier HIPPARCOS and Tycho-2 positions. For the remaining stars, positions at epoch J2015.0 have been obtained by essentially neglecting their proper motions and parallaxes. Positions and proper motions are in the ICRF radio/ VLBI frame. We give an overview of the current status of the mission, the astrometric challenges, the Data Processing and Analysis Consortium operations, the validation processes, the contents of Gaia DR1, and the prospects for the coming releases. We emphasise that although Gaia DR1 data are based on provisional and incomplete calibrations of the instrument, the results represent a huge improvement in the available fundamental stellar data, and discuss some of the first results.

The PHEMU15 catalogue and astrometric results of the Jupiter's Galilean satellite mutual occultation and eclipse observations made in 2014-2015

NASA Astrophysics Data System (ADS)

Saquet, E.; Emelyanov, N.; Robert, V.; Arlot, J.-E.; Anbazhagan, P.; Baillié, K.; Bardecker, J.; Berezhnoy, A. A.; Bretton, M.; Campos, F.; Capannoli, L.; Carry, B.; Castet, M.; Charbonnier, Y.; Chernikov, M. M.; Christou, A.; Colas, F.; Coliac, J.-F.; Dangl, G.; Dechambre, O.; Delcroix, M.; Dias-Oliveira, A.; Drillaud, C.; Duchemin, Y.; Dunford, R.; Dupouy, P.; Ellington, C.; Fabre, P.; Filippov, V. A.; Finnegan, J.; Foglia, S.; Font, D.; Gaillard, B.; Galli, G.; Garlitz, J.; Gasmi, A.; Gaspar, H. S.; Gault, D.; Gazeas, K.; George, T.; Gorda, S. Y.; Gorshanov, D. L.; Gualdoni, C.; Guhl, K.; Halir, K.; Hanna, W.; Henry, X.; Herald, D.; Houdin, G.; Ito, Y.; Izmailov, I. S.; Jacobsen, J.; Jones, A.; Kamoun, S.; Kardasis, E.; Karimov, A. M.; Khovritchev, M. Y.; Kulikova, A. M.; Laborde, J.; Lainey, V.; Lavayssiere, M.; Le Guen, P.; Leroy, A.; Loader, B.; Lopez, O. C.; Lyashenko, A. Y.; Lyssenko, P. G.; Machado, D. I.; Maigurova, N.; Manek, J.; Marchini, A.; Midavaine, T.; Montier, J.; Morgado, B. E.; Naumov, K. N.; Nedelcu, A.; Newman, J.; Ohlert, J. M.; Oksanen, A.; Pavlov, H.; Petrescu, E.; Pomazan, A.; Popescu, M.; Pratt, A.; Raskhozhev, V. N.; Resch, J.-M.; Robilliard, D.; Roschina, E.; Rothenberg, E.; Rottenborn, M.; Rusov, S. A.; Saby, F.; Saya, L. F.; Selvakumar, G.; Signoret, F.; Slesarenko, V. Y.; Sokov, E. N.; Soldateschi, J.; Sonka, A.; Soulie, G.; Talbot, J.; Tejfel, V. G.; Thuillot, W.; Timerson, B.; Toma, R.; Torsellini, S.; Trabuco, L. L.; Traverse, P.; Tsamis, V.; Unwin, M.; Abbeel, F. Van Den; Vandenbruaene, H.; Vasundhara, R.; Velikodsky, Y. I.; Vienne, A.; Vilar, J.; Vugnon, J.-M.; Wuensche, N.; Zeleny, P.

2018-03-01

During the 2014-2015 mutual events season, the Institut de Mécanique Céleste et de Calcul des Éphémérides (IMCCE), Paris, France, and the Sternberg Astronomical Institute (SAI), Moscow, Russia, led an international observation campaign to record ground-based photometric observations of Galilean moon mutual occultations and eclipses. We focused on processing the complete photometric observations data base to compute new accurate astrometric positions. We used our method to derive astrometric positions from the light curves of the events. We developed an accurate photometric model of mutual occultations and eclipses, while correcting for the satellite albedos, Hapke's light scattering law, the phase effect, and the limb darkening. We processed 609 light curves, and we compared the observed positions of the satellites with the theoretical positions from IMCCE NOE-5-2010-GAL satellite ephemerides and INPOP13c planetary ephemeris. The standard deviation after fitting the light curve in equatorial positions is ±24 mas, or 75 km at Jupiter. The rms (O-C) in equatorial positions is ±50 mas, or 150 km at Jupiter.

Photometry and Astrometry of the Jovian satellites Amalthea and Thebe

NASA Astrophysics Data System (ADS)

Saquet, Eléonore; Emelyanov, Nicolai; Colas, François; Robert, Vincent; Arlot, Jean-Eudes

2016-10-01

During the 2014-2015 campaign of mutual events, we realized ground-based observations of Amalthea (JV) and Thebe (JXIV). We recorded two eclipses of Amalthea and, for the first time, one of Thebe by the Galilean moons. We used the 1-m telescope at Pic du Midi Observatory with an IR filter and a mask placed over the planetary image to reduce the light intensity of Jupiter. A third observation of Amalthea was taken at Saint-Sulpice Observatory with a 60-cm telescope using a methane filter (890 nm) and a deep absorption band to decrease the contrast between the planet and the satellites. We provide astrometric results derived from the photometry with an overall accuracy of 34 mas, or 100 km at Jupiter.In the same time, we realized 45 astrometric observations of Amalthea and 41 of Thebe to compare the photometric technique with direct astrometry, using the UCAC4 reference star catalog. We provide astrometric results with an overall accuracy of 100 mas for Amalthea, or 300 km at Jupiter, and 90 mas for Thebe, or 270 km at Jupiter. These results are better than those from previous ground-based and old reduced space measurements.

Calculating Proper Motions in the WFCAM Science Archive for the UKIRT Infrared Deep Sky Surveys

NASA Astrophysics Data System (ADS)

Collins, R.; Hambly, N.

2012-09-01

The ninth data release from the UKIRT Infrared Deep Sky Surveys (hereafter UKIDSS DR9), represents five years worth of observations by its wide-field camera (WFCAM) and will be the first to include proper motion values in its source catalogues for the shallow, wide-area surveys; the Large Area Survey (LAS), Galactic Clusters Survey (GCS) and (ultimately) Galactic Plane Survey (GPS). We, the Wide Field Astronomy Unit (WFAU) at the University of Edinburgh who prepare these regular data releases in the WFCAM Science Archive (WSA), describe in this paper how we make optimal use of the individual detection catalogues from each observation to derive high-quality astrometric fits for the positions of each detection enabling us to calculate a proper motion solution across multiple epochs and passbands when constructing a merged source catalogue. We also describe how the proper motion solutions affect the calculation of the various attributes provided in the database source catalogue tables, what measures of data quality we provide and a demonstration of the results for observations of the Pleiades cluster.

A Multiple-star Combined Solution Program - Application to the Population II Binary μ Cas

NASA Astrophysics Data System (ADS)

Gudehus, D. H.

2001-05-01

A multiple-star combined-solution computer program which can simultaneously fit astrometric, speckle, and spectroscopic data, and solve for the orbital parameters, parallax, proper motion, and masses has been written and is now publicly available. Some features of the program are the ability to scale the weights at run time, hold selected parameters constant, handle up to five spectroscopic subcomponents for the primary and the secondary each, account for the light travel time across the system, account for apsidal motion, plot the results, and write the residuals in position to a standard file for further analysis. The spectroscopic subcomponent data can be represented by reflex velocities and/or by independent measurements. A companion editing program which can manage the data files is included in the package. The program has been applied to the Population II binary μ Cas to derive improved masses and an estimate of the primordial helium abundance. The source code, executables, sample data files, and documentation for OpenVMS and Unix, including Linux, are available at http://www.chara.gsu.edu/\\rlap\\ \\ gudehus/binary.html.

A Combined Length-of-Day Series Spanning 1832-1997

NASA Technical Reports Server (NTRS)

Gross, Richard S.

1999-01-01

The Earth's rotation is not constant but exhibits minute changes on all observable time scales ranging from subdaily to secular. This rich spectrum of observed Earth rotation changes reflects the rich variety of astronomical and geophysical phenomena that are causing the Earth's rotation to change, including, but not limited to, ocean and solid body tides, atmospheric wind and pressure changes, oceanic current and sea level height changes, post-glacial rebound, and torques acting at the core-mantle boundary. In particular, the decadal-scale variations of the Earth's rotation are thought to be largely caused by interactions between the Earth's outer core and mantle. Comparing the inferred Earth rotation variations caused by the various core-mantle interactions to observed variations requires Earth rotation observations spanning decades, if not centuries. During the past century many different techniques have been used to observe the Earth's rotation. By combining the individual Earth rotation series determined by each of these techniques, a series of the Earth's rotation can be obtained that is based upon independent measurements spanning the greatest possible time interval. In this study, independent observations of the Earth's rotation are combined to generate a length-of-day series spanning 1832-1997. The observations combined include lunar occultation measurements spanning 1832-1955, optical astrometric measurements spanning 1956-1982, lunar laser ranging measurements spanning 1970-1997, and very long baseline interferometric measurements spanning 1978-1998. These series are combined using a Kalman filter developed at JPL for just this purpose. The resulting combined length-of-day series will be presented and compared with other available length-of-day series of similar duration.

Reconciling Optical and Radio Observations of the Binary Millisecond Pulsar PSR J1640+2224

NASA Astrophysics Data System (ADS)

Vigeland, Sarah J.; Deller, Adam T.; Kaplan, David L.; Istrate, Alina G.; Stappers, Benjamin W.; Tauris, Thomas M.

2018-03-01

Previous optical and radio observations of the binary millisecond pulsar PSR J1640+2224 have come to inconsistent conclusions about the identity of its companion, with some observations suggesting that the companion is a low-mass helium-core (He-core) white dwarf (WD), while others indicate that it is most likely a high-mass carbon–oxygen (CO) WD. Binary evolution models predict PSR J1640+2224 most likely formed in a low-mass X-ray binary based on the pulsar’s short spin period and long-period, low-eccentricity orbit, in which case its companion should be a He-core WD with mass about 0.35–0.39 M ⊙, depending on metallicity. If instead it is a CO WD, it would suggest that the system has an unusual formation history. In this paper we present the first astrometric parallax measurement for this system from observations made with the Very Long Baseline Array (VLBA), from which we determine the distance to be {1520}-150+170 {pc}. We use this distance and a reanalysis of archival optical observations originally taken in 1995 with the Wide Field Planetary Camera 2 on the Hubble Space Telescope (HST) to measure the WD’s mass. We also incorporate improvements in calibration, extinction model, and WD cooling models. We find that the existing observations are not sufficient to tightly constrain the companion mass, but we conclude the WD mass is >0.4 M ⊙ with >90% confidence. The limiting factor in our analysis is the low signal-to-noise ratio of the original HST observations.

Fluorescent solute-partitioning characterization of layered soft contact lenses.

PubMed

Dursch, T J; Liu, D E; Oh, Y; Radke, C J

2015-03-01

Partitioning of aqueous packaging, wetting, and care-solution agents into and out of soft contact lenses (SCLs) is important for improving wear comfort and also for characterizing lens physico-chemical properties. We illustrate both features of partitioning by application of fluorescent-solute partitioning into DAILIES TOTAL1® (delefilcon A) water-gradient SCLs, which exhibit a layered structure of a silicone-hydrogel (SiHy) core sandwiched between thin surface-gel layers. Two-photon fluorescence confocal laser-scanning microscopy and attenuated total-reflectance Fourier-transform infrared spectroscopy (ATR-FTIR) characterize the lens and assess uptake profiles of six prototypical fluorescent solutes. Comparison of solute uptake in a SiHy-core prototype lens (i.e., O2OPTIX(TM)) validates the core SiHy structure of DAILIESTOTAL1®. To establish surface-layer charge, partition coefficients and water contents are obtained for aqueous pH values of 4 and 7.4. Solute fluorescence-intensity profiles clearly confirm a layered structure for the DAILIES TOTAL1® lenses. In all cases, aqueous solute partition coefficients are greater in the surface layers than in the SiHy core, signifying higher water in the surface gels. ATR-FTIR confirms surface-layer mass water contents of 82±3%. Water uptake and hydrophilic-solute uptake at pH 4 compared with that at pH 7.4 reveal that the surface-gel layers are anionic at physiologic pH 7.4, whereas both the SiHy core and O2OPTIX™ (lotrafilcon B) are nonionic. We successfully confirm the layered structure of DAILIES TOTAL1®, consisting of an 80-μm-thick SiHy core surrounded by 10-μm-thick polyelectrolyte surface-gel layers of significantly greater water content and aqueous solute uptake compared with the core. Accordingly, fluorescent-solute partitioning in SCLs provides information on gel structure and composition, in addition to quantifying uptake and release amounts and rates. Copyright © 2014 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Spotting stellar activity cycles in Gaia astrometry

NASA Astrophysics Data System (ADS)

Morris, Brett M.; Agol, Eric; Davenport, James R. A.; Hawley, Suzanne L.

2018-06-01

Astrometry from Gaia will measure the positions of stellar photometric centroids to unprecedented precision. We show that the precision of Gaia astrometry is sufficient to detect starspot-induced centroid jitter for nearby stars in the Tycho-Gaia Astrometric Solution (TGAS) sample with magnetic activity similar to the young G-star KIC 7174505 or the active M4 dwarf GJ 1243, but is insufficient to measure centroid jitter for stars with Sun-like spot distributions. We simulate Gaia observations of stars with 10 year activity cycles to search for evidence of activity cycles, and find that Gaia astrometry alone likely cannot detect activity cycles for stars in the TGAS sample, even if they have spot distributions like KIC 7174505. We review the activity of the nearby low-mass stars in the TGAS sample for which we anticipate significant detections of spot-induced jitter.

New orbit recalculations of comet C/1890 F1 Brooks and its dynamical evolution

NASA Astrophysics Data System (ADS)

Królikowska, Małgorzata; Dybczyński, Piotr A.

2016-08-01

C/1890 F1 Brooks belongs to a group of 19 comets used by Jan Oort to support his famous hypothesis on the existence of a spherical cloud containing hundreds of billions of comets with orbits of semi-major axes between 50 000 and 150 000 au. Comet Brooks stands out from this group because of a long series of astrometric observations as well as a nearly 2-yr-long observational arc. Rich observational material makes this comet an ideal target for testing the rationality of an effort to recalculate astrometric positions on the basis of original (comet-star) measurements using modern star catalogues. This paper presents the results of such a new analysis based on two different methods: (I) automatic re-reduction based on cometary positions and the (comet-star) measurements and (II) partially automatic re-reduction based on the contemporary data for the reference stars originally used. We show that both methods offer a significant reduction in the uncertainty of orbital elements. Based on the most preferred orbital solution, the dynamical evolution of comet Brooks during three consecutive perihelion passages is discussed. We conclude that C/1890 F1 is a dynamically old comet that passed the Sun at a distance below 5 au during its previous perihelion passage. Furthermore, its next perihelion passage will be a little closer than during the 1890-1892 apparition. C/1890 F1 is interesting also because it suffered extremely small planetary perturbations when it travelled through the planetary zone. Therefore, in the next passage through perihelion, it will once again be a comet from the Oort spike.

The Candidate Progenitor of the Type IIn SN 2010jl Is Not an Optically Luminous Star

DOE Office of Scientific and Technical Information (OSTI.GOV)

Fox, Ori D.; Dyk, Schuyler D. Van; Dwek, Eli

A blue source in pre-explosion Hubble Space Telescope ( HST )/Wide-Field Planetary Camera 2 (WFPC2) images falls within the 5 σ astrometric error circle (∼0.″24) derived from post-explosion ground-based imaging of SN 2010jl. At the time the ground-based astrometry was published, however, the SN had not faded sufficiently for post-explosion HST follow-up observations to determine a more precise astrometric solution and/or confirm if the pre-explosion source had disappeared, both of which are necessary to ultimately disentangle the possible progenitor scenarios. Here we present HST /WFC3 imaging of the SN 2010jl field obtained in 2014, 2015, and 2016 when the SNmore » had faded sufficiently to allow for new constraints on the progenitor. The SN, which is still detected in the new images, is offset by 0.″061 ± 0.″008 (15 ± 2 pc) from the underlying and extended source of emission that contributes at least partially, if not entirely, to the blue source previously suggested as the candidate progenitor in the WFPC2 data. This point alone rules out the possibility that the blue source in the pre-explosion images is the exploding star, but may instead suggest an association with a young (<5–6 Myr) cluster and still argues for a massive (>30 M {sub ⊙}) progenitor. We obtain new upper limits on the flux from a single star at the SN position in the pre-explosion WFPC2 and Spitzer /IRAC images that may ultimately be used to constrain the progenitor properties.« less

VizieR Online Data Catalog: Astrometric observations of Phobos (Pasewaldt+, 2015)

NASA Astrophysics Data System (ADS)

Pasewaldt, A.; Oberst, J.; Willner, K.; Beisembin, B.; Hoffmann, H.; Matz, K. D.; Roatsch, T.; Michael, G.; Cardesin-Moinelo, A.; Zubarev, A. E.

2015-04-01

The data is given in the form of two tables. Each table contains the same set of observations: Data in tablea1.dat has been reduced using MEX navigation orbits and predicted attitude by the European Space Operations Centre (ESOC). tablea2.dat data has been derived using MEX accurate orbits by the Royal Observatory of Belgium (ROB) and measured attitude by the European Space Astronomy Centre (ESAC). >From 158 astrometric observations 103 were determined by means of both methods, 27 using only control point measurements, and 28 performing only limb fit observations. Hence, each data table contains 261 entries, namely 130 control point measurements and 131 limb fit observations. (2 data files).

Northern Hemisphere observations of ICRF sources on the USNO stellar catalogue frame

NASA Astrophysics Data System (ADS)

Fienga, A.; Andrei, A. H.

2004-06-01

The most recent USNO stellar catalogue, the USNO B1.0 (Monet et al. \\cite{Monet03}), provides positions for 1 042 618 261 objects, with a published astrometric accuracy of 200 mas and five-band magnitudes with a 0.3 mag accuracy. Its completeness is believed to be up to magnitude 21th in V-band. Such a catalogue would be a very good tool for astrometric reduction. This work investigates the accuracy of the USNO B1.0 link to ICRF and give an estimation of its internal and external accuracies by comparison with different catalogues, and by computation of ICRF sources using USNO B1.0 star positions.

New Astronomical Reduction of Old Observations (the NAROO project)

NASA Astrophysics Data System (ADS)

Arlot, Jean-Eudes; Robert, Vincent; Lainey, Valery; Neiner, Coralie; Thouvenin, Nicolas

2018-04-01

The Gaia astrometric reference catalogue will provide star proper motions with an accuracy of one mas one century ago for stars of magnitude 14 or brighter. Our project is to re-reduced the old observations with the new catalogue allowing to have an astrometric accuracy only limited by the observational biases and not by reference stars. Then, we plan to get an accuracy of 50 mas where the old reductions were not better than 500 mas! For our purpose, we will digitize old photographic plates with a sub-micrometric scanner. Tests were made using the UCAC catalogue showing that old photographic plates have an intrinsect accuracy of 30 to 60 mas.

A study of the asteroid (367943) Duende at Pulkovo Observatory

NASA Astrophysics Data System (ADS)

Devyatkin, A. V.; Gorshanov, D. L.; Yershov, V. N.; Melnikov, A. V.; Martyusheva, A. A.; Petrova, S. N.; L'vov, V. N.; Tsekmeister, S. D.; Naumov, K. N.

2016-07-01

Using the telescopes ZA-320 M and MTM-500 M of Pulkovo Observatory (Russia), we have carried out astrometric and photometric observations of the asteroid (367943) Duende (2012 DA14) immediately after its close approach to the Earth occurred on 2013 February 15. We have obtained a series of its astrometric positions, colour indices and two fragments of its light curve. By numerically integrating, we have studied the evolution of the asteroid's orbit. Also, the influence of solar radiation pressure and Yarkovsky effect on the asteroid was estimated. The fitting of the asteroid rotation model to the observed light curve indicates that during its closest approach to the Earth, it had tumbling rotation regime.

Systems analysis for ground-based optical navigation

NASA Technical Reports Server (NTRS)

Null, G. W.; Owen, W. M., Jr.; Synnott, S. P.

1992-01-01

Deep-space telecommunications systems will eventually operate at visible or near-infrared regions to provide increased information return from interplanetary spacecraft. This would require an onboard laser transponder in place of (or in addition to) the usual microwave transponder, as well as a network of ground-based and/or space-based optical observing stations. This article examines the expected navigation systems to meet these requirements. Special emphasis is given to optical astrometric (angular) measurements of stars, solar system target bodies, and (when available) laser-bearing spacecraft, since these observations can potentially provide the locations of both spacecraft and target bodies. The role of astrometry in the navigation system and the development options for astrometric observing systems are also discussed.

LBT observations of the HR8799 planetary system

NASA Astrophysics Data System (ADS)

Mesa, D.; Arcidiacono, C.; Claudi, R. U.; Desidera, S.; Esposito, S.; Gratton, R.; Masciadri, E.

2013-09-01

We present here observations of the HR8799 planetary system performed in H and Ks band exploiting the AO system at the Large Binocular Telescope and the PISCES camera. Thanks to the excellent performence of the instrument we were able to detect for the first time the inner known planet of the system (HR8799) in the H band. Precise photometric and astrometric measures have been taken for all the four planets. Further, exploiting ours and previous astrometric results, we were able to put some limits on the planetary orbits of the four planets. The analysis of the dinamical stability of the system seems to show lower planetary masses than the ones adopted until now.

Using Gaia as an Astrometric Tool for Deep Ground-based Surveys

NASA Astrophysics Data System (ADS)

Casetti-Dinescu, Dana I.; Girard, Terrence M.; Schriefer, Michael

2018-04-01

Gaia DR1 positions are used to astrometrically calibrate three epochs' worth of Subaru SuprimeCam images in the fields of globular cluster NGC 2419 and the Sextans dwarf spheroidal galaxy. Distortion-correction ``maps'' are constructed from a combination of offset dithers and reference to Gaia DR1. These are used to derive absolute proper motions in the field of NGC 2419. Notably, we identify the photometrically-detected Monoceros structure in the foreground of NGC 2419 as a kinematically-cold population of stars, distinct from Galactic-field stars. This project demonstrates the feasibility of combining Gaia with deep, ground-based surveys, thus extending high-quality astrometry to magnitudes beyond the limits of Gaia.

Shaped nanocrystal particles and methods for making the same

DOEpatents

Alivisatos, A Paul [Oakland, CA; Scher, Erik C [Menlo Park, CA; Manna, Liberato [Berkeley, CA

2011-11-22

Shaped nanocrystal particles and methods for making shaped nanocrystal particles are disclosed. One embodiment includes a method for forming a branched, nanocrystal particle. It includes (a) forming a core having a first crystal structure in a solution, (b) forming a first arm extending from the core having a second crystal structure in the solution, and (c) forming a second arm extending from the core having the second crystal structure in the solution.

Shaped nanocrystal particles and methods for making the same

DOEpatents

Alivisatos, A. Paul; Scher, Erik C; Manna, Liberato

2013-12-17

Shaped nanocrystal particles and methods for making shaped nanocrystal particles are disclosed. One embodiment includes a method for forming a branched, nanocrystal particle. It includes (a) forming a core having a first crystal structure in a solution, (b) forming a first arm extending from the core having a second crystal structure in the solution, and (c) forming a second arm extending from the core having the second crystal structure in the solution.

Shaped nanocrystal particles and methods for working the same

DOEpatents

Alivisatos, A. Paul; Sher, Eric C.; Manna, Liberato

2007-12-25

Shaped nanocrystal particles and methods for making shaped nanocrystal particles are disclosed. One embodiment includes a method for forming a branched, nanocrystal particle. It includes (a) forming a core having a first crystal structure in a solution, (b) forming a first arm extending from the core having a second crystal structure in the solution, and (c) forming a second arm extending from the core having the second crystal structure in the solution.

Shaped Nonocrystal Particles And Methods For Making The Same

DOEpatents

Alivisatos, A. Paul; Scher, Erik C.; Manna, Liberato

2005-02-15

Shaped nanocrystal particles and methods for making shaped nanocrystal particles are disclosed. One embodiment includes a method for forming a branched, nanocrystal particle. It includes (a) forming a core having a first crystal structure in a solution, (b) forming a first arm extending from the core having a second crystal structure in the solution, and (c) forming a second arm extending from the core having the second crystal structure in the solution.

Recent Status of SIM Lite Astrometric Observatory Mission: Flight Engineering Risk Reduction Activities

NASA Technical Reports Server (NTRS)

Goullioud, Renaud; Dekens, Frank; Nemati, Bijan; An, Xin; Carson, Johnathan

2010-01-01

The SIM Lite Astrometric Observatory is a mission concept for a space-borne instrument to perform micro-arc-second narrow-angle astrometry to search 60 to 100 nearby stars for Earth-like planets, and to perform global astrometry for a broad astrophysics program. The instrument consists of two Michelson stellar interferometers and a telescope. The first interferometer chops between the target star and a set of reference stars. The second interferometer monitors the attitude of the instrument in the direction of the target star. The telescope monitors the attitude of the instrument in the other two directions. The main enabling technology development for the mission was completed during phases A & B. The project is currently implementing the developed technology onto flight-ready engineering models. These key engineering tasks will significantly reduce the implementation risks during the flight phases C & D of the mission. The main optical interferometer components, including the astrometric beam combiner, the fine steering optical mechanism, the path-length-control and modulation optical mechanisms, focal-plane camera electronics and cooling heat pipe, are currently under development. Main assemblies are built to meet flight requirements and will be subjected to flight qualification level environmental testing (random vibration and thermal cycling) and performance testing. This paper summarizes recent progress in engineering risk reduction activities.

Astrometry of Single-Chord Occultations: Application to the 1993 Triton Event

NASA Technical Reports Server (NTRS)

Olkin, Catherine B.; Elliot, J. L.; Bus, Schelte J.; McDonald, Stephen W.; Dahn, Conrad C.

1996-01-01

This paper outlines a method for reducing astrometric data to derive the closest approach time and distance to the center of an occultation shadow for a single observer. The method applies to CCD frames, strip scans or photographic plates and uses a set of field stars of unknown positions to define a common coordinate system for all frames. The motion of the occulting body is used to establish the transformation between this common coordinate system and the celestial coordinate system of the body's ephemeris. This method is demonstrated by application to the Tr6O occultation by Triton on 1993 July 10 UT. Over an interval of four nights that included the occultation time, 80 frames of Triton and Tr6O were taken near the meridian with the U.S. Naval Observatory (USNO) 61-inch astrometric reflector. Application of the method presented here to these data yields a closest approach distance of 359 +/- 133 km (corresponding to 0.017 +/- 0.006 arcsec) for the occultation chord obtained with the Kuiper Airborne Observatory (KAO). Comparison of the astrometric closest approach time with the KAO light-curve midtime shows a difference of 2.2 +/- 4.1 s. Relative photometry of Triton and Tr6O, needed for photometric calibration of the occultation light curve, is also presented.

Determining dynamical parameters of the Milky Way Galaxy based on high-accuracy radio astrometry

NASA Astrophysics Data System (ADS)

Honma, Mareki; Nagayama, Takumi; Sakai, Nobuyuki

2015-08-01

In this paper we evaluate how the dynamical structure of the Galaxy can be constrained by high-accuracy VLBI (Very Long Baseline Interferometry) astrometry such as VERA (VLBI Exploration of Radio Astrometry). We generate simulated samples of maser sources which follow the gas motion caused by a spiral or bar potential, with their distribution similar to those currently observed with VERA and VLBA (Very Long Baseline Array). We apply the Markov chain Monte Carlo analyses to the simulated sample sources to determine the dynamical parameter of the models. We show that one can successfully determine the initial model parameters if astrometric results are obtained for a few hundred sources with currently achieved astrometric accuracy. If astrometric data are available from 500 sources, the expected accuracy of R0 and Θ0 is ˜ 1% or higher, and parameters related to the spiral structure can be constrained by an error of 10% or with higher accuracy. We also show that the parameter determination accuracy is basically independent of the locations of resonances such as corotation and/or inner/outer Lindblad resonances. We also discuss the possibility of model selection based on the Bayesian information criterion (BIC), and demonstrate that BIC can be used to discriminate different dynamical models of the Galaxy.

Linking Deep Astrometric Standards to the ICRF

NASA Astrophysics Data System (ADS)

Frey, S.; Platais, I.; Fey, A. L.

2007-07-01

The next-generation large aperature and large field-of-view telescopes will address fundamantal questions of astrophysica and cosmology such as the nature of dark matter and dark energy. For a variety of applications, the CCD mosaic detectors in the focal plane arrays require astronomic calibrationat the milli-arcsecond (mas) level. The existing optical reference frames are insufficient to support such calibrations. To address this problem, deep optical astronomic fields are being established near the Galactic plane. In order to achiev a 5-10-mas or better positional accuracyfor the Deepp Astrometric Standards (DAS), and to obtain bsolute stellar proper motions for the study of Galactic structure, it is crucial to link these fields to the International Celestial Reference Frame (ICRF). To this end, we selected 15 candidate compact extragalactic radio sources in the Gemini-Orion-Taurus (GOT) field. These sources were observed with the European VLBI Network (EVN) at 5 GHz in phase-reference mode. The bright compact calibrator source J0603+2159 and seven other sources were detected and imaged at the angular resolution of -1.5-8 mas. Relative astrometric positions were derived for these sources at a milli-arcsecond accuracy level. The detection of the optical counterparts of these extragalactic radio sources will allow us to establish a direct link to the ICRF locally in the GOT field.

StreakDet data processing and analysis pipeline for space debris optical observations

NASA Astrophysics Data System (ADS)

Virtanen, Jenni; Flohrer, Tim; Muinonen, Karri; Granvik, Mikael; Torppa, Johanna; Poikonen, Jonne; Lehti, Jussi; Santti, Tero; Komulainen, Tuomo; Naranen, Jyri

We describe a novel data processing and analysis pipeline for optical observations of space debris. The monitoring of space object populations requires reliable acquisition of observational data, to support the development and validation of space debris environment models, the build-up and maintenance of a catalogue of orbital elements. In addition, data is needed for the assessment of conjunction events and for the support of contingency situations or launches. The currently available, mature image processing algorithms for detection and astrometric reduction of optical data cover objects that cross the sensor field-of-view comparably slowly, and within a rather narrow, predefined range of angular velocities. By applying specific tracking techniques, the objects appear point-like or as short trails in the exposures. However, the general survey scenario is always a “track before detect” problem, resulting in streaks, i.e., object trails of arbitrary lengths, in the images. The scope of the ESA-funded StreakDet (Streak detection and astrometric reduction) project is to investigate solutions for detecting and reducing streaks from optical images, particularly in the low signal-to-noise ratio (SNR) domain, where algorithms are not readily available yet. For long streaks, the challenge is to extract precise position information and related registered epochs with sufficient precision. Although some considerations for low-SNR processing of streak-like features are available in the current image processing and computer vision literature, there is a need to discuss and compare these approaches for space debris analysis, in order to develop and evaluate prototype implementations. In the StreakDet project, we develop algorithms applicable to single images (as compared to consecutive frames of the same field) obtained with any observing scenario, including space-based surveys and both low- and high-altitude populations. The proposed processing pipeline starts from the segmentation of the acquired image (i.e., the extraction of all sources), followed by the astrometric and photometric characterization of the candidate streaks, and ends with orbital validation of the detected streaks. A central concept of the pipeline is streak classification which guides the actual characterization process by aiming to identify the interesting sources and to filter out the uninteresting ones, as well as by allowing the tailoring of algorithms for specific streak classes (e.g. point-like vs. long, disintegrated streaks). To validate the single-image detections, the processing is finalized by orbital analysis, resulting in preliminary orbital classification (Earth-bound vs. non-Earth-bound orbit) for the detected streaks.

VizieR Online Data Catalog: Hubble Source Catalog (V1 and V2) (Whitmore+, 2016)

NASA Astrophysics Data System (ADS)

Whitmore, B. C.; Allam, S. S.; Budavari, T.; Casertano, S.; Downes, R. A.; Donaldson, T.; Fall, S. M.; Lubow, S. H.; Quick, L.; Strolger, L.-G.; Wallace, G.; White, R. L.

2016-10-01

The HSC v1 contains members of the WFPC2, ACS/WFC, WFC3/UVIS and WFC3/IR Source Extractor source lists from HLA version DR8 (data release 8). The crossmatching process involves adjusting the relative astrometry of overlapping images so as to minimize positional offsets between closely aligned sources in different images. After correction, the astrometric residuals of crossmatched sources are significantly reduced, to typically less than 10mas. The relative astrometry is supported by using Pan-STARRS, SDSS, and 2MASS as the astrometric backbone for initial corrections. In addition, the catalog includes source nondetections. The crossmatching algorithms and the properties of the initial (Beta 0.1) catalog are described in Budavari & Lubow (2012ApJ...761..188B). The HSC v2 contains members of the WFPC2, ACS/WFC, WFC3/UVIS and WFC3/IR Source Extractor source lists from HLA version DR9.1 (data release 9.1). The crossmatching process involves adjusting the relative astrometry of overlapping images so as to minimize positional offsets between closely aligned sources in different images. After correction, the astrometric residuals of crossmatched sources are significantly reduced, to typically less than 10mas. The relative astrometry is supported by using Pan-STARRS, SDSS, and 2MASS as the astrometric backbone for initial corrections. In addition, the catalog includes source nondetections. The crossmatching algorithms and the properties of the initial (Beta 0.1) catalog are described in Budavari & Lubow (2012ApJ...761..188B). Hubble Source Catalog Acknowledgement: Based on observations made with the NASA/ESA Hubble Space Telescope, and obtained from the Hubble Legacy Archive, which is a collaboration between the Space Telescope Science Institute (STScI/NASA), the Space Telescope European Coordinating Facility (ST-ECF/ESAC/ESA) and the Canadian Astronomy Data Centre (CADC/NRC/CSA). (2 data files).

NEAT: an astrometric space telescope to search for habitable exoplanets in the solar neighborhood

NASA Astrophysics Data System (ADS)

Crouzier, A.; Malbet, F.; Kern, P.; Feautrier, P.; Preiss, O.; Martin, G.; Henault, F.; Stadler, E.; Lafrasse, S.; Behar, E.; Saintpe, M.; Dupont, J.; Potin, S.; Lagage, P.-O.; Cara, C.; Leger, A.; Leduigou, J.-M.; Shao, M.; Goullioud, R.

2014-03-01

The last decade has witnessed a spectacular development of exoplanet detection techniques, which led to an exponential number of discoveries and a great diversity of known exoplanets. However, it must be noted that the quest for the holy grail of astrobiology, i.e. a nearby terrestrial exoplanet in habitable zone around a solar type star, is still ongoing and proves to be very hard. Radial velocities will have to overcome stellar noise if there are to discover habitable planets around stars more massive than M ones. For very close systems, transits are impeded by their low geometrical probability. Here we present an alternative concept: space astrometry. NEAT (Nearby Earth Astrometric Telescope) is a concept of astrometric mission proposed to ESA which goal is to make a whole sky survey of close (less then 20 pc) planetary systems. The detection limit required for the instrument is the astrometric signal of an Earth analog (at 10 pc). Differential astrometry is a very interesting tool to detect nearby habitable exoplanets. Indeed, for F, G and K main sequence stars, the astrophysical noise is smaller than the astrometric signal, contrary to the case for radial velocities. The difficulty lies in the fact that the signal of an exo-Earth around a G type star at 10 pc is a tiny 0.3 micro arc sec, which is equivalent to a coin on the moon, seen from the Earth: the main challenge is related to instrumentation. In order to reach this specification, NEAT consists of two formation flying spacecraft at a 40m distance, one carries the mirror and the other one the focal plane. Thus NEAT has a configuration with only one optical surface: an off-axis parabola. Consequently, beamwalk errors are common to the whole field of view and have a small effect on differential astrometry. Moreover a metrology system projects young fringes on the focal plane, which can characterize the pixels whenever necessary during the mission. NEAT has two main scientific objectives: combined with radial velocities and direct imaging, it will explore in a quasi systematic way the nearby planetary systems. The resulting catalog of planetary systems will be very useful to constrain planetary formation models. The second objective is to find very close Earth analogs. These will be top priority targets for a spectroscopic mission aimed at detecting biomarquers. The current activities related to NEAT revolve around 3 themes: i) a lab demonstration: an optical bench replicates the NEAT optical configuration and metrology system in order to demonstrate the feasibility of measuring centroids with a differential accuracy of 5 µpixels (corresponding to 0.3 micro arc sec on sky) ii) a definition phase study of the NEAT mission done by CNES (the "French Space Agency") iii) an end to end simulation of the NEAT data reduction pipeline: from astrometric and RVs measurements to planets All of these activities are focused on the need to answer the next ESA call for M class missions in 2014 with an improved NEAT concept.

Characterizing Mobile/Less-Mobile Porosity and Solute Exchange in Dual-Domain Media Using Tracer Experiments and Electrical Measurements in a Hassler-Type Core Holder

NASA Astrophysics Data System (ADS)

Falzone, S.; Slater, L. D.; Day-Lewis, F. D.; Parker, B. L.; Keating, K.; Robinson, J.

2017-12-01

Mass transfer is the process by which solute is retained in less-mobile porosity domains, and later released into the mobile porosity domain. This process is often responsible for the slow arrival and gradual release of contaminants and solute tracers. Recent studies have outlined methods using dual-domain mass transfer (DDMT) models for characterizing this phenomenon. These models use the non-linear relationship of bulk (σb) and fluid (σf) conductivity, collected from electrical methods during tracer experiments, to characterize the less-mobile/mobile porosity ratio (β) and the mass-transfer rate coefficient (α). DDMT models use the hysteretic σb-σf relationship observed while solute tracers are injected and then flushed from a sample media. Due to limitations in observing the hysteretic σb-σf relationship, this method has not been used to characterize low permeability samples. We have developed an experimental method for testing porous rock cores that allows us to develop a fundamental understanding of contaminant storage and release in consolidated rock. We test the approach on cores from sedimentary rock sites where mass transfer is expected to occur between hydraulically connected fractures and the adjacent low permeability rock matrix. Our method uses a Hassler-type core holder, designed to apply confining pressure around the outside of a sample core, which hydraulically isolates the sample core, allowing water to be injected into it at increased pressures. The experimental apparatus was also designed to measure σb with spectral induced polarization (SIP) measurements, and σf from a sampling port located at the center of the core. Cores were initially saturated with a solution with high electrical conductivity ( 80000 μS/cm). DI water was then injected into the cores at elevated pressures (>60 psi) and the saturating solution was flushed from the cores, in order to generate flow rates fast enough to capture the non-linear σb-σf relationship expected when DDMT occurs. Our initial results demonstrate the existence of a non-linear σb-σf relationship indicative of DDMT for a tight sandstone core from a contaminated fractured rock site. Integrating the electrical results with known physical characteristics of the cores, we are able to quantify the mass transfer characteristics of the cores.

Nearby Exo-Earth Astrometric Telescope (NEAT)

NASA Technical Reports Server (NTRS)

Shao, M.; Nemati, B.; Zhai, C.; Goullioud, R.

2011-01-01

NEAT (Nearby Exo ]Earths Astrometric Telescope) is a modest sized (1m diameter telescope) It will be capable of searching approx 100 nearby stars down to 1 Mearth planets in the habitable zone, and 200 @ 5 Mearth, 1AU. The concept addresses the major issues for ultra -precise astrometry: (1) Photon noise (0.5 deg dia field of view) (2) Optical errors (beam walk) with long focal length telescope (3) Focal plane errors , with laser metrology of the focal plane (4) PSF centroiding errors with measurement of the "True" PSF instead of using a "guess " of the true PSF, and correction for intra pixel QE non-uniformities. Technology "close" to complete. Focal plane geometry to 2e-5 pixels and centroiding to approx 4e -5 pixels.

Puesta en marcha de un microdensitómetro automático basado en CCD

NASA Astrophysics Data System (ADS)

Calderón, J. H.; Bustos Fierro, I. H.

We present the commisioning of a CCD-based microdensitometer intended to perform astrometric measurements of photographic plates. The work done consisted in the installation of a CCD camera, the modification of the motion system, the construction of a new illumination device, the adaptation of the electronics, and the development of software. The instrument is intended to be used for the astrometric measurement mainly of plates of the Astrographic Catalog and Carte du Ciel collections from Córdoba Observatory. In this phase of the project we counted with the collaboration of the Instituto Provincial de Enseñanza Media No 59, 25 de Mayo, Cruz Alta (Province of Córdoba). The origin and importance of such collaboration is commented.

First Light for USNO 1.3-meter Telescope

NASA Astrophysics Data System (ADS)

Monet, A. K. B.; Harris, F. H.; Harris, H. C.; Monet, D. G.; Stone, R. C.

2001-11-01

The US Naval Observatory Flagstaff Station has recently achieved first light with its newest telescope -- a 1.3--meter, f/4 modified Ritchey-Chretien,located on the grounds of the station. The instrument was designed to produce a well-corrected field 1.7--degrees in diameter, and is expected to provide wide-field imaging with excellent astrometric properties. A number of test images have been obtained, using a temporary CCD camera in both drift and stare mode, and the results have been quite encouraging. Several astrometric projects are planned for this instrument, which will be operated in fully automated fashion. This paper will describe the telescope and its planned large-format mosaic CCD camera, and will preview some of the research for which it will be employed.

Astrometrica: Astrometric data reduction of CCD images

NASA Astrophysics Data System (ADS)

Raab, Herbert

2012-03-01

Astrometrica is an interactive software tool for scientific grade astrometric data reduction of CCD images. The current version of the software is for the Windows 32bit operating system family. Astrometrica reads FITS (8, 16 and 32 bit integer files) and SBIG image files. The size of the images is limited only by available memory. It also offers automatic image calibration (Dark Frame and Flat Field correction), automatic reference star identification, automatic moving object detection and identification, and access to new-generation star catalogs (PPMXL, UCAC 3 and CMC-14), in addition to online help and other features. Astrometrica is shareware, available for use for a limited period of time (100 days) for free; special arrangements can be made for educational projects.

Software for Photometric and Astrometric Reduction of Video Meteors

NASA Astrophysics Data System (ADS)

Atreya, Prakash; Christou, Apostolos

2007-12-01

SPARVM is a Software for Photometric and Astrometric Reduction of Video Meteors being developed at Armagh Observatory. It is written in Interactive Data Language (IDL) and is designed to run primarily under Linux platform. The basic features of the software will be derivation of light curves, estimation of angular velocity and radiant position for single station data. For double station data, calculation of 3D coordinates of meteors, velocity, brightness, and estimation of meteoroid's orbit including uncertainties. Currently, the software supports extraction of time and date from video frames, estimation of position of cameras (Azimuth, Altitude), finding stellar sources in video frames and transformation of coordinates from video, frames to Horizontal coordinate system (Azimuth, Altitude), and Equatorial coordinate system (RA, Dec).

Precision Photometry and Astrometry from Pan-STARRS

NASA Astrophysics Data System (ADS)

Magnier, Eugene A.; Pan-STARRS Team

2018-01-01

The Pan-STARRS 3pi Survey has been calibrated with excellent precision for both astrometry and photometry. The Pan-STARRS Data Release 1, opened to the public on 2016 Dec 16, provides photometry in 5 well-calibrated, well-defined bandpasses (grizy) astrometrically registered to the Gaia frame. Comparisons with other surveys illustrate the high quality of the calibration and provide tests of remaining systematic errors in both Pan-STARRS and those external surveys. With photometry and astrometry of roughly 3 billion astronomical objects, the Pan-STARRS DR1 has substantial overlap with Gaia, SDSS, 2MASS and other surveys. I will discuss the astrometric tie between Pan-STARRS DR1 and Gaia and show comparisons between Pan-STARRS and other large-scale surveys.

Candidate Nearby, Young Stars in Gaia's First Data Release

NASA Astrophysics Data System (ADS)

Chalifour, Matthieu; Kastner, Joel H.; Binks, Alex; Rodriguez, David; Punzi, Kristina; Zuckerman, Ben; Sacco, Germano

2018-01-01

The nearest examples of young stars are essential subjects for the study of planet and star formation. The recent data release from Gaia, which contains accurate parallax distances for ~2.5 million stars, allows age determinations via isochronal analysis for thousands of stars within ~100 pc. We have selected nearly 400 candidates nearby, young, late-type stars in the approximate mass range 0.5-1.0 Msun from the Tycho Gaia Astrometric Solution catalog on the basis of (a) D < 100 pc, (b) Galex UV detection, and (c) isochronal age <~ 80 Myr. Approximately 10% of these candidates lie within 50 pc of Earth and, hence, may represent excellent targets for direct-imaging searches for young, self-luminous planets. We discuss our ongoing efforts to assess the accuracy of these stars' isochronal ages via various diagnostic tools, including galactic kinematics, UV excess, relative X-ray luminosity, andoptical spectroscopic indicators of youth.

Youpi: YOUr processing PIpeline

NASA Astrophysics Data System (ADS)

Monnerville, Mathias; Sémah, Gregory

2012-03-01

Youpi is a portable, easy to use web application providing high level functionalities to perform data reduction on scientific FITS images. Built on top of various open source reduction tools released to the community by TERAPIX (http://terapix.iap.fr), Youpi can help organize data, manage processing jobs on a computer cluster in real time (using Condor) and facilitate teamwork by allowing fine-grain sharing of results and data. Youpi is modular and comes with plugins which perform, from within a browser, various processing tasks such as evaluating the quality of incoming images (using the QualityFITS software package), computing astrometric and photometric solutions (using SCAMP), resampling and co-adding FITS images (using SWarp) and extracting sources and building source catalogues from astronomical images (using SExtractor). Youpi is useful for small to medium-sized data reduction projects; it is free and is published under the GNU General Public License.

CosmoQuest Transient Tracker: Opensource Photometry & Astrometry software

NASA Astrophysics Data System (ADS)

Myers, Joseph L.; Lehan, Cory; Gay, Pamela; Richardson, Matthew; CosmoQuest Team

2018-01-01

CosmoQuest is moving from online citizen science, to observational astronomy with the creation of Transient Trackers. This open source software is designed to identify asteroids and other transient/variable objects in image sets. Transient Tracker’s features in final form will include: astrometric and photometric solutions, identification of moving/transient objects, identification of variable objects, and lightcurve analysis. In this poster we present our initial, v0.1 release and seek community input.This software builds on the existing NIH funded ImageJ libraries. Creation of this suite of opensource image manipulation routines is lead by Wayne Rasband and is released primarily under the MIT license. In this release, we are building on these libraries to add source identification for point / point-like sources, and to do astrometry. Our materials released under the Apache 2.0 license on github (http://github.com/CosmoQuestTeam) and documentation can be found at http://cosmoquest.org/TransientTracker.

SPECKLE INTERFEROMETRY AT SOAR IN 2014

DOE Office of Scientific and Technical Information (OSTI.GOV)

Tokovinin, Andrei; Mason, Brian D.; Hartkopf, William I.

2015-08-15

The results of speckle interferometric observations at the Southern Astrophysical Research Telescope (SOAR) telescope in 2014 are given. A total of 1641 observations were taken, yielding 1636 measurements of 1218 resolved binary and multiple stars and 577 non-resolutions of 441 targets. We resolved for the first time 56 pairs, including some nearby astrometric or spectroscopic binaries and ten new subsystems in previously known visual binaries. The calibration of the data is checked by linear fits to the positions of 41 wide binaries observed at SOAR over several seasons. The typical calibration accuracy is 0.°1 in angle and 0.3% in pixelmore » scale, while the measurement errors are on the order of 3 mas. The new data are used here to compute 194 binary star orbits, 148 of which are improvements on previous orbital solutions and 46 are first-time orbits.« less

Photometer Performance Assessment in TESS SPOC Pipeline

NASA Astrophysics Data System (ADS)

Li, Jie; Caldwell, Douglas A.; Jenkins, Jon Michael; Twicken, Joseph D.; Wohler, Bill; Chen, Xiaolan; Rose, Mark; TESS Science Processing Operations Center

2018-06-01

This poster describes the Photometer Performance Assessment (PPA) software component in the Transiting Exoplanet Survey Satellite (TESS) Science Processing Operations Center (SPOC) pipeline, which is developed based on the Kepler science pipeline. The PPA component performs two tasks: the first task is to assess the health and performance of the instrument based on the science data sets collected during each observation sector, identifying out of bounds conditions and generating alerts. The second is to combine the astrometric data collected for each CCD readout channel to construct a high fidelity record of the pointing history for each of the 4 cameras and an attitude solution for the TESS spacecraft for each 2-min data collection interval. PPA is implemented with multiple pipeline modules: PPA Metrics Determination (PMD), PMD Aggregator (PAG), and PPA Attitude Determination (PAD). The TESS Mission is funded by NASA's Science Mission Directorate. The SPOC is managed and operated by NASA Ames Research Center.

The vertical metallicity gradients of mono-age stellar populations in the Milky Way with the RAVE and Gaia data

NASA Astrophysics Data System (ADS)

Ciucǎ, Ioana; Kawata, Daisuke; Lin, Jane; Casagrande, Luca; Seabroke, George; Cropper, Mark

2018-03-01

We investigate the vertical metallicity gradients of five mono-age stellar populations between 0 and 11 Gyr for a sample of 18 435 dwarf stars selected from the cross-matched Tycho-Gaia Astrometric Solution and Radial Velocity Experiment (RAVE) Data Release 5. We find a correlation between the vertical metallicity gradients and age, with no vertical metallicity gradient in the youngest population and an increasingly steeper negative vertical metallicity gradient for the older stellar populations. The metallicity at disc plane remains almost constant between 2 and 8 Gyr, and it becomes significantly lower for the 8 < τ ≤ 11 Gyr population. The current analysis also reveals that the intrinsic dispersion in metallicity increases steadily with age. We discuss that our results are consistent with a scenario that (thin) disc stars formed from a flaring (thin) star-forming disc.

Simulating the minimum core for hydrophobic collapse in globular proteins.

PubMed Central

Tsai, J.; Gerstein, M.; Levitt, M.

1997-01-01

To investigate the nature of hydrophobic collapse considered to be the driving force in protein folding, we have simulated aqueous solutions of two model hydrophobic solutes, methane and isobutylene. Using a novel methodology for determining contacts, we can precisely follow hydrophobic aggregation as it proceeds through three stages: dispersed, transition, and collapsed. Theoretical modeling of the cluster formation observed by simulation indicates that this aggregation is cooperative and that the simulations favor the formation of a single cluster midway through the transition stage. This defines a minimum solute hydrophobic core volume. We compare this with protein hydrophobic core volumes determined from solved crystal structures. Our analysis shows that the solute core volume roughly estimates the minimum core size required for independent hydrophobic stabilization of a protein and defines a limiting concentration of nonpolar residues that can cause hydrophobic collapse. These results suggest that the physical forces driving aggregation of hydrophobic molecules in water is indeed responsible for protein folding. PMID:9416609

THE TIMING OF NINE GLOBULAR CLUSTER PULSARS

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lynch, Ryan S.; Freire, Paulo C. C.; Ransom, Scott M.

2012-02-01

We have used the Robert C. Byrd Green Bank Telescope to time nine previously known pulsars without published timing solutions in the globular clusters (GCs) M62, NGC 6544, and NGC 6624. We have full timing solutions that measure the spin, astrometric, and (where applicable) binary parameters for six of these pulsars. The remaining three pulsars (reported here for the first time) were not detected enough to establish solutions. We also report our timing solutions for five pulsars with previously published solutions, and find good agreement with other authors, except for PSR J1701-3006B in M62. Gas in this system is probablymore » responsible for the discrepancy in orbital parameters, and we have been able to measure a change in the orbital period over the course of our observations. Among the pulsars with new solutions we find several binary pulsars with very low mass companions (members of the so-called 'black widow' class) and we are able to place constraints on the mass-to-light ratio in two clusters. We confirm that one of the pulsars in NGC 6624 is indeed a member of the rare class of non-recycled pulsars found in GCs. We have also measured the orbital precession and Shapiro delay for a relativistic binary in NGC 6544. If we assume that the orbital precession can be described entirely by general relativity, which is likely, we are able to measure the total system mass (2.57190(73) M{sub Sun }) and companion mass (1.2064(20) M{sub Sun }), from which we derive the orbital inclination (sin i = 0.9956(14)) and the pulsar mass (1.3655(21) M{sub Sun }), the most precise such measurement ever obtained for a millisecond pulsar. The companion is the most massive known around a fully recycled pulsar.« less

NEUTRONIC REACTOR OPERATIONAL METHOD AND CORE SYSTEM

DOEpatents

Winters, C.E.; Graham, C.B.; Culver, J.S.; Wilson, R.H.

1960-07-19

Homogeneous neutronic reactor systems are described wherein an aqueous fuel solution is continuously circulated through a spherical core tank. The pumped fuel solution-is injected tangentially into the hollow spherical interior, thereby maintaining vigorous rotation of the solution within the tank in the form of a vortex; gaseous radiolytic decomposition products concentrate within the axial vortex cavity. The evolved gas is continuously discharged through a gas- outlet port registering with an extremity of the vortex cavity. and the solution stream is discharged through an annular liquid outlet port concentrically encircling the gas outlet by virtue of which the vortex and its cavity are maintained precisely axially aligned with the gas outlet. A primary heat exchanger extracts useful heat from the hot effluent fuel solution before its recirculation into the core tank. Hollow cylinders and other alternative core- tank configurations defining geometric volumes of revolution about a principal axis are also covered. AEC's Homogeneous Reactor Experiment No. 1 is a preferred embodiment.

Analysis of the multiple system with chemically peculiar component φ Draconis

NASA Astrophysics Data System (ADS)

Liška, J.

2016-09-01

The star ϕ Dra comprises a spectroscopic binary and a third star that together form a visual triple system. It is one of the brightest chemically peculiar stars of the upper main sequence. Despite these facts, no comprehensive study of its multiplicity has been performed yet. In this work, we present a detailed analysis of the triple system based on available measurements. We use radial velocities taken from four sources in the literature in a re-analysis of the inner spectroscopic binary (Aab). An incorrect value of the orbital period of the inner system Aab about 27 d was accepted in literature more than 40 yr. A new solution of orbit with the 128-d period was determined. Relative position measurements of the outer visual binary system (AB) from Washington Double Star Catalog were compared with known orbital models. Furthermore, it was shown that astrometric motion in system AB is well described by the model of Andrade with a 308-yr orbital period. Parameters of A and B components were utilized to estimate individual brightness for all components and their masses from evolutionary tracks. Although we found several facts which support the gravitational bond between them, unbound solution cannot be fully excluded yet.

A near-Infrared SETI Experiment: Alignment and Astrometric precision

NASA Astrophysics Data System (ADS)

Duenas, Andres; Maire, Jerome; Wright, Shelley; Drake, Frank D.; Marcy, Geoffrey W.; Siemion, Andrew; Stone, Remington P. S.; Tallis, Melisa; Treffers, Richard R.; Werthimer, Dan

2016-06-01

Beginning in March 2015, a Near-InfraRed Optical SETI (NIROSETI) instrument aiming to search for fast nanosecond laser pulses, has been commissioned on the Nickel 1m-telescope at Lick Observatory. The NIROSETI instrument makes use of an optical guide camera, SONY ICX694 CCD from PointGrey, to align our selected sources into two 200µm near-infrared Avalanche Photo Diodes (APD) with a field-of-view of 2.5"x2.5" each. These APD detectors operate at very fast bandwidths and are able to detect pulse widths extending down into the nanosecond range. Aligning sources onto these relatively small detectors requires characterizing the guide camera plate scale, static optical distortion solution, and relative orientation with respect to the APD detectors. We determined the guide camera plate scale as 55.9+- 2.7 milli-arcseconds/pixel and magnitude limit of 18.15mag (+1.07/-0.58) in V-band. We will present the full distortion solution of the guide camera, orientation, and our alignment method between the camera and the two APDs, and will discuss target selection within the NIROSETI observational campaign, including coordination with Breakthrough Listen.

Lunar Rotation and the Lunar Interior

NASA Technical Reports Server (NTRS)

Williams, J. G.; Boggs, D. H.; Ratcliff, J. T.; Dickey, J. O.

2003-01-01

Variations in rotation and orientation of the Moon are sensitive to solid-body tidal dissipation, dissipation due to relative motion at the fluid-core/ solid-mantle boundary, and tidal Love number k2. There is weaker sensitivity to flattening of the core-mantle boundary (CMB) and fluid core moment of inertia. Accurate Lunar Laser Ranging (LLR) measurements of the distance from observatories on the Earth to four retroreflector arrays on the Moon are sensitive to lunar rotation and orientation variations and tidal displacements. Past solutions using the LLR data have given results for dissipation due to solid-body tides and fluid core plus Love number. Past detection of CMB flattening has been marginal but is improving, while direct detection of the core moment has not yet been achieved. Three decades of Lunar Laser Ranging (LLR) data are analyzed using a weighted least-squares approach. The lunar solution parameters include dissipation at the fluid-core/solid-mantle boundary, tidal dissipation, dissipation-related coefficients for rotation and orientation terms, potential Love number k2, a correction to the constant term in the tilt of the equator to the ecliptic which is meant to approximate the influence of core-mantle boundary flattening, and displacement Love numbers h2 and l2. Several solutions, with different combinations of solution parameters and constraints, are considered.

Hollow Polycaprolactone Microspheres with/without a Single Surface Hole by Co-Electrospraying

PubMed Central

2017-01-01

We describe the co-electrospraying of hollow microspheres from a polycaprolactone (PCL) shell solution and various core solutions including water, cyclohexane, poly(ethylene oxide) (PEO), and polyethylene glycol (PEG), using different collectors. The morphologies of the resultant microspheres were characterized by scanning electron microscopy (SEM), confocal microscopy, and nano-X-ray computed tomography (nano-XCT). The core/shell solution miscibility played an important role in the co-electrospraying process and the formation of microsphere structures. Spherical particles were more likely to be produced from miscible combinations of core/shell solutions than from immiscible ones. Hollow PCL microspheres with a single hole in their surfaces were produced when an ethanol bath was used as the collector. The mechanism by which the core/shell structure is transformed into single-hole hollow microspheres is proposed to be primarily based on the evaporation through the shell and extraction by ethanol of the core solution and is described in detail. Additionally, we present a 3D macroscopic tubular structure composed of hollow PCL microspheres, directly assembled on a copper wire collector during co-electrospraying. SEM and nano-XCT confirm that microspheres in the 3D bulk structure remain hollow. PMID:28901145

ON THE SOURCE OF ASTROMETRIC ANOMALOUS REFRACTION

DOE Office of Scientific and Technical Information (OSTI.GOV)

Taylor, M. Suzanne; McGraw, John T.; Zimmer, Peter C.

2013-03-15

More than a century ago, astronomers using transit telescopes to determine precise stellar positions were hampered by an unexplained periodic shifting of the stars they were observing. With the advent of CCD transit telescopes in the past three decades, this unexplained motion, termed 'anomalous refraction' by these early astronomers, is again being observed. Anomalous refraction is described as a low-frequency, large angular scale ({approx}2 Degree-Sign ) motion of the entire image plane with respect to the celestial coordinate system as observed and defined by astrometric catalogs. These motions, of typically several tenths of an arcsecond amplitude with timescales on themore » order of 10 minutes, are ubiquitous to ground-based drift-scan astrometric measurements regardless of location or telescopes used and have been attributed to the effect of tilting of equal-density layers of the atmosphere. The cause of this tilting has often been attributed to atmospheric gravity waves, but this cause has never been confirmed. Although theoretical models of atmospheric refraction show that atmospheric gravity waves are a plausible cause of anomalous refraction, an observational campaign specifically directed at defining this relationship provides clear evidence that anomalous refraction is not consistent with the passage of atmospheric gravity waves. The source of anomalous refraction is found to be meter-scale, slowly evolving quasi-coherent dynamical structures in the boundary layer below 60 m above ground level.« less

On the role of differenced phase-delays in high-precision wide-field multi-source astrometry

NASA Astrophysics Data System (ADS)

Martí-Vidal, I.; Marcaide, J. M.; Guirado, J. C.

2007-07-01

Phase-delay is, by far, the most precise observable used in interferometry. In typical very-long-baseline-interferometry (VLBI) observations, the uncertainties of the phase-delays can be about 100 times smaller than those of the group delays. However, the phase-delays have an important handicap: they are ambiguous, since they are computed from the relative phases of the signals of the different antennas, and an indeterminate number of complete 2¶- cycles can be added to those phases leaving them unchanged. There are different approaches to solve the ambiguity problem of the phase delays (Shapiro et al., 1979; Beasley & Conway, 1995), but none of them has been ever used in observations involving more than 2.3 sources. In this contribution, we will report for the first-time wide-field multi-source astrometric analysis that has been performed on a complete set of radio sources using the phase-delay observable. The target of our analysis is the S5 polar cap sample, consisting on 13 bright ICRF sources near the North Celestial Pole. We have developed new algorithms and updated existing software to correct, in an automatic way, the ambiguities of the phase-delay and, therefore, perform a phasedelay astrometric analysis of all the sources in the sample. We will also discuss on the impact of the use of phase-delays in the astrometric precision.

Astrometric confirmation and preliminary orbital parameters of the young exoplanet 51 Eridani b with the Gemini Planet Imager

DOE Office of Scientific and Technical Information (OSTI.GOV)

De Rosa, Robert J.; Nielsen, Eric L.; Blunt, Sarah C.

We present new Gemini Planet Imager observations of the young exoplanet 51 Eridani b that provide further evidence that the companion is physically associated with 51 Eridani. Combining this new astrometric measurement with those reported in the literature, we significantly reduce the posterior probability that 51 Eridani b is an unbound foreground or background T-dwarf in a chance alignment with 51 Eridani to 2 × 10 –7, an order of magnitude lower than previously reported. If 51 Eridani b is indeed a bound object, then we have detected orbital motion of the planet between the discovery epoch and the latest epoch. By implementing a computationally efficient Monte Carlo technique, preliminary constraints are placed on the orbital parameters of the system. The current set of astrometric measurements suggest an orbital semimajor axis ofmore » $${14}_{-3}^{+7}$$ AU, corresponding to a period of $${41}_{-12}^{+35}$$ years (assuming a mass of 1.75 M⊙ for the central star), and an inclination of $${138}_{-13}^{+15}$$ deg. The remaining orbital elements are only marginally constrained by the current measurements. As a result, these preliminary values suggest an orbit that does not share the same inclination as the orbit of the distant M-dwarf binary, GJ 3305, which is a wide physically bound companion to 51 Eridani.« less

Astrometric confirmation and preliminary orbital parameters of the young exoplanet 51 Eridani b with the Gemini Planet Imager

DOE PAGES

De Rosa, Robert J.; Nielsen, Eric L.; Blunt, Sarah C.; ...

2015-11-13

We present new Gemini Planet Imager observations of the young exoplanet 51 Eridani b that provide further evidence that the companion is physically associated with 51 Eridani. Combining this new astrometric measurement with those reported in the literature, we significantly reduce the posterior probability that 51 Eridani b is an unbound foreground or background T-dwarf in a chance alignment with 51 Eridani to 2 × 10 –7, an order of magnitude lower than previously reported. If 51 Eridani b is indeed a bound object, then we have detected orbital motion of the planet between the discovery epoch and the latest epoch. By implementing a computationally efficient Monte Carlo technique, preliminary constraints are placed on the orbital parameters of the system. The current set of astrometric measurements suggest an orbital semimajor axis ofmore » $${14}_{-3}^{+7}$$ AU, corresponding to a period of $${41}_{-12}^{+35}$$ years (assuming a mass of 1.75 M⊙ for the central star), and an inclination of $${138}_{-13}^{+15}$$ deg. The remaining orbital elements are only marginally constrained by the current measurements. As a result, these preliminary values suggest an orbit that does not share the same inclination as the orbit of the distant M-dwarf binary, GJ 3305, which is a wide physically bound companion to 51 Eridani.« less

SIM Lite Astrometric Observatory progress report

NASA Astrophysics Data System (ADS)

Marr, James C., IV; Shao, Michael; Goullioud, Renaud

2010-07-01

The SIM Lite Astrometric Observatory (aka SIM Lite), a micro-arcsecond astrometry space mission, has been developed in response to NASA's indefinite deferral of the SIM PlanetQuest mission. The SIM Lite mission, while significantly more affordable than the SIM PlanetQuest mission concept, still addresses the full breadth of SIM science envisioned by two previous National Research Council (NRC) Astrophysics Decadal Surveys at the most stringent "Goal" level of astrometric measurement performance envisioned in those surveys. Over the past two years, the project has completed the conceptual design of the SIM Lite mission using only the completed SIM technology; published a 250 page book describing the science and mission design (available at the SIM website: http://sim.jpl.nasa.gov); been subject to an independent cost and technical readiness assessment by the Aerospace Corporation; and submitted a number of information responses to the NRC Astro2010 Decadal Survey. The project also conducted an exoplanet-finding capability double blind study that clearly demonstrated the ability of the mission to survey 60 to 100 nearby sun-like dwarf stars for terrestrial, habitable zone planets in complex planetary systems. Additionally, the project has continued Engineering Risk Reduction activities by building brassboard (form, fit & function to flight) version of key instrument elements and subjecting them to flight qualification environmental and performance testing. This paper summarizes the progress over the last two years and the current state of the SIM Lite project.

Asymptotic solutions for the case of nearly symmetric gravitational lens systems

NASA Astrophysics Data System (ADS)

Wertz, O.; Pelgrims, V.; Surdej, J.

2012-08-01

Gravitational lensing provides a powerful tool to determine the Hubble parameter H0 from the measurement of the time delay Δt between two lensed images of a background variable source. Nevertheless, knowledge of the deflector mass distribution constitutes a hurdle. We propose in the present work interesting solutions for the case of nearly symmetric gravitational lens systems. For the case of a small misalignment between the source, the deflector and the observer, we first consider power-law (ɛ) axially symmetric models for which we derive an analytical relation between the amplification ratio and source position which is independent of the power-law slope ɛ. According to this relation, we deduce an expression for H0 also irrespective of the value ɛ. Secondly, we consider the power-law axially symmetric lens models with an external large-scale gravitational field, the shear γ, resulting in the so-called ɛ-γ models, for which we deduce simple first-order equations linking the model parameters and the lensed image positions, the latter being observable quantities. We also deduce simple relations between H0 and observables quantities only. From these equations, we may estimate the value of the Hubble parameter in a robust way. Nevertheless, comparison between the ɛ-γ and singular isothermal ellipsoid (SIE) models leads to the conclusion that these models remain most often distinct. Therefore, even for the case of a small misalignment, use of the first-order equations and precise astrometric measurements of the positions of the lensed images with respect to the centre of the deflector enables one to discriminate between these two families of models. Finally, we confront the models with numerical simulations to evaluate the intrinsic error of the first-order expressions used when deriving the model parameters under the assumption of a quasi-alignment between the source, the deflector and the observer. From these same simulations, we estimate for the case of the ɛ-γ family of models that the standard deviation affecting H0 is ? which merely reflects the adopted astrometric uncertainties on the relative image positions, typically ? arcsec. In conclusions, we stress the importance of getting very accurate measurements of the relative positions of the multiple lensed images and of the time delays for the case of nearly symmetric gravitational lens systems, in order to derive robust and precise values of the Hubble parameter.

Stability of core-shell nanowires in selected model solutions

NASA Astrophysics Data System (ADS)

Kalska-Szostko, B.; Wykowska, U.; Basa, A.; Zambrzycka, E.

2015-03-01

This paper presents the studies of stability of magnetic core-shell nanowires prepared by electrochemical deposition from an acidic solution containing iron in the core and modified surface layer. The obtained nanowires were tested according to their durability in distilled water, 0.01 M citric acid, 0.9% NaCl, and commercial white wine (12% alcohol). The proposed solutions were chosen in such a way as to mimic food related environment due to a possible application of nanowires as additives to, for example, packages. After 1, 2 and 3 weeks wetting in the solutions, nanoparticles were tested by Infrared Spectroscopy, Atomic Absorption Spectroscopy, Transmission Electron Microscopy and X-ray diffraction methods.

Cometary Astrometry

NASA Technical Reports Server (NTRS)

Yeomans, D. K. (Editor); West, R. M. (Editor); Harrington, R. S. (Editor); Marsden, B. G. (Editor)

1984-01-01

Modern techniques for making cometary astrometric observations, reducing these observations, using accurate reference star catalogs, and computing precise orbits and ephemerides are discussed in detail and recommendations and suggestions are given in each area.

Carte du Ciel, San Fernando zone

NASA Astrophysics Data System (ADS)

Abad, C.

2014-06-01

An updated summary of a future large astrometric catalogue is presented, based on the two most important astrometric projects carried out by the Real Instituto y Observatorio de la Armada de San Fernando (ROA). The goal is to make a catalogue of positions and proper motions based on ROA's Cart du Ciel (CdC) and the Astrographic Catalogue (AC) San Fernando zone plates, and the HAMC2 meridian circle catalogue. The CdC and AC plates are being reduced together to provide first-epoch positions while HAMC2 will provide second-epoch ones. New techniques have been applied, that range from using a commercial flatbed scanner to the proper reduction schemes to avoid systematics from it. Only thirty plates (out of 540) remain to be processed, due to scanning problems that are being solved.

An Assessment of Ground-Based Techniques for Detecting Other Planetary Systems. Volume 2: Position papers

NASA Technical Reports Server (NTRS)

Black, D. C.; Brunk, W. E.

1980-01-01

The capabilities of several astronomical interferomenter system concepts are assessed and the effects of the Earth's atmosphere on astrometric precision are examined in detail. Included is an examination of the use of small aperture interferometry to detect planets in binary star systems. It is estimated that, for differential astrometric observation, an amplitude interferometer having two separate telescopes should permit observations of stars as faint as 14th magnitude and a positional accuracy of 0.00005 arc-sec. Instrumental, atmospheric, and photon noise errors that apply to interferometric observation are examined. It is suggested that the effects of atmospheric turbulence may be eliminated with the use of two color refractometer systems. Several sites for future telescopes dedicated to the search for planetary systems are identified.

Numerically Integrated Orbits of the Major Saturnian Satellites fit to Earthbased Observations

NASA Technical Reports Server (NTRS)

Jacobson, R. A.; Vaughan, R. M.

1993-01-01

We have fit numerically integrated orbits of the eight major satellites of Saturn to all available astrometric and meridian circle observations for the period of 1971 to 1992. The integration was carried out in cartesian coordinates in the J2000 system. The force model included the gravitational effects of the oblate primary, the mutual perturbations of the satellites, and perturbations due to Jupiter and the Sun. Values of the gravitational parameters of the Saturnian system, e.g. planet and satellite masses, were taken from Campbell, et. al., 1989, only the epoch state vectors of the satellites were adjusted to obtain orbits which fit the observations. All astrometric data was processed in the form of satellite relative positions which were weighted according to observer and opposition to reflect the varying data quality...

Astrometry for New Reductions: The ANR method

NASA Astrophysics Data System (ADS)

Robert, Vincent; Le Poncin-Lafitte, Christophe

2018-04-01

Accurate positional measurements of planets and satellites are used to improve our knowledge of their orbits and dynamics, and to infer the accuracy of the planet and satellite ephemerides. With the arrival of the Gaia-DR1 reference star catalog and its complete release afterward, the methods for ground-based astrometry become outdated in terms of their formal accuracy compared to the catalog's which is used. Systematic and zonal errors of the reference stars are eliminated, and the astrometric process now dominates in the error budget. We present a set of algorithms for computing the apparent directions of planets, satellites and stars on any date to micro-arcsecond precision. The expressions are consistent with the ICRS reference system, and define the transformation between theoretical reference data, and ground-based astrometric observables.

Scientific data processing for Hipparcos

NASA Astrophysics Data System (ADS)

van der Marel, H.

1988-04-01

The scientific aims of the ESA Hipparcos astrometric satellite are reviewed, and the fundamental principles and practical implementation of the data-analysis and data-reduction procedures are discussed in detail. Hipparcos is to determine the positions and proper motions of a catalog of 110,000 stars to a limit of 12 mag with accuracy a few marcsec and obtain photometric observations of 400,000 stars (the Tycho mission). Consideration is given to the organization of the data-processing consortia FAST, NDAC, and TDAC; the basic problems of astrometry; the measurement principle; the large amounts of data to be generated during the 2.5-year mission; and the three-step iterative method to be applied (positional reconstruction and reduction to a reference great circle, spherical reconstruction, and extraction of the astrometric parameters). Diagrams and a flow chart are provided.

The chemical composition of the cores of the terrestrial planets and the moon

NASA Technical Reports Server (NTRS)

Kuskov, O. L.; Khitarov, N. I.

1977-01-01

Using models of the quasi-chemical theory of solutions, the activity coefficients of silicon are calculated in the melts Fe-Si, Ni-Si, and Fe-Ni-Si. The calculated free energies of solution of liquid nickel and silicon in liquid iron in the interval 0 to 1400 kbar and 1500 to 4000 K, shows that Fe-Ni-Si alloy is stable under the conditions of the outer core of the earth and the cores of the terrestrial planets. The oxidation-reduction conditions are studied, and the fugacity of oxygen in the mantles of the planets and at the core-mantle boundary are calculated. The mechanism of reduction of silicon is analyzed over a broad interval of p and T. The interaction between the matter of the core and mantle is studied, resulting in the extraction of silicon from the mantle and its solution in the material of the core. It is concluded that silicon can enter into the composition of the outer core of the earth and Venus, but probably does not enter into the composition of the cores of Mercury, Mars, and the moon, if in fact the latter possesses one.

Numerical studies of the margin of vortices with decaying cores

NASA Technical Reports Server (NTRS)

Liu, G. C.; Ting, L.

1986-01-01

The merging of vortices to a single one is a canonical incompressible viscous flow problem. The merging process begins when the core sizes or the vortices are comparable to their distances and ends when the contour lines of constant vorticity lines are circularized around one center. Approximate solutions to this problem are constructed by adapting the asymptotic solutions for distinct vortices. For the early stage of merging, the next-order terms in the asymptotic solutions are added to the leading term. For the later stage of merging, the vorticity distribution is reinitialized by vortices with overlapping core structures guided by the 'rule of merging' and the velocity of the 'vortex centers' are then defined by a minimum principle. To show the accuracy of the approximate solution, it is compared with the finite-difference solution.

Controlled core removal from a D-shaped optical fiber.

PubMed

Markos, Douglas J; Ipson, Benjamin L; Smith, Kevin H; Schultz, Stephen M; Selfridge, Richard H; Monte, Thomas D; Dyott, Richard B; Miller, Gregory

2003-12-20

The partial removal of a section of the core from a continuous D-shaped optical fiber is presented. In the core removal process, selective chemical etching is used with hydrofluoric (HF) acid. A 25% HF acid solution removes the cladding material above the core, and a 5% HF acid solution removes the core. A red laser with a wavelength of 670 nm is transmitted through the optical fiber during the etching. The power transmitted through the optical fiber is correlated to the etch depth by scanning electron microscope imaging. The developed process provides a repeatable method to produce an optical fiber with a specific etch depth.

Application of Direct Current Atmospheric Pressure Glow Microdischarge Generated in Contact with a Flowing Liquid Solution for Synthesis of Au-Ag Core-Shell Nanoparticles.

PubMed

Dzimitrowicz, Anna; Jamroz, Piotr; Nyk, Marcin; Pohl, Pawel

2016-04-06

A direct current atmospheric pressure glow microdischarge (dc-μAPGD) generated between an Ar nozzle microjet and a flowing liquid was applied to produce Au-Ag core-shell nanoparticles (Au@AgCSNPs) in a continuous flow system. Firstly, operating dc-μAPGD with the flowing solution of the Au(III) ions as the cathode, the Au nanoparticles (AuNPs) core was produced. Next, to produce the core-shell nanostructures, the collected AuNPs solution was immediately mixed with an AgNO₃ solution and passed through the system with the reversed polarity to fabricate the Ag nanoshell on the AuNPs core. The formation of Au@AgCSNPs was confirmed using ultraviolet-visible (UV-Vis) absorbance spectrophotometry, transmission electron microscopy (TEM), and energy-dispersive X-ray spectroscopy (EDS). Three localized surface plasmon resonance absorption bands with wavelengths centered at 372, 546, and 675 nm were observed in the UV-Vis spectrum of Au@AgCSNPs, confirming the reduction of both the Au(III) and Ag(I) ions. The right configuration of metals in Au@AgCSNPs was evidenced by TEM. The Au core diameter was 10.2 ± 2.0 nm, while the thickness of the Ag nanoshell was 5.8 ± 1.8 nm. The elemental composition of the bimetallic nanoparticles was also confirmed by EDS. It is possible to obtain 90 mL of a solution containing Au@AgCSNPs per hour using the applied microdischarge system.

Orbit of the young very low-mass spectroscopic binary CHXR 74

NASA Astrophysics Data System (ADS)

Joergens, V.; Janson, M.; Müller, A.

2012-01-01

The pre-main sequence star CHXR 74 (M4.25) in Chamaeleon I was found a few years ago to be a very low-mass spectroscopic binary. A determination of its mass would provide a valuable dynamical mass measurement at young ages in the poorly constrained mass regime of <0.3 M⊙. We carried out follow-up radial velocity monitoring with UVES/VLT between 2008 and 2011 and high-resolution adaptive-optic-assisted imaging with NACO/VLT in 2008 with the aim of constraining the binary orbit. We present an orbital solution of the system based on the combined radial velocity data set, which spans more than eleven years of UVES monitoring for CHXR 74. The best-fit Kepler model has an orbital period of 13.1 years, zero eccentricity, and a radial velocity semi-amplitude of 2.2 km s-1. A companion mass M2sini (which is a lower limit due to the unknown orbital inclination i) of 0.08 M⊙ is derived by using a model-dependent mass estimate for the primary of 0.24 M⊙. The binary separation (a1sini + a2) for an inclination of 90° is 3.8 AU, which corresponds to 23 mas. Complementary NACO/VLT images of CHXR 74 were taken with the aim to directly resolve the binary. While there are marginal signs of an extended point spread function (PSF), we have detected no convincing companion to CHXR 74 in the NACO images. From the non-detection of the companion together with a prediction of the binary separation at the time of the NACO observations, we derive an upper limit for the K-band brightness ratio of the two binary components of 0.5. This allows us to estimate an upper limit of the companion mass of 0.14 M⊙ by applying evolutionary models. Thus, we confirm that CHXR 74 is a very low-mass spectroscopic binary and constrain the secondary mass to lie within the range of about 0.08 and 0.14 M⊙. We predict an astrometric signal of the primary between 0.2 and 0.4 mas when taking into account the luminosity of the companion. The Gaia astrometric mission might well be able to solve the astrometric orbit of the primary and in combination with the presented radial velocity data determine an absolute companion mass. Based on observations obtained at the Very Large Telescope of the European Southern Observatory at Paranal, Chile with UVES in program 65.I-0011(A), 72.C-0653(A), 75.C-0851(C), 77.C-0831(A+D), 380.C-0596(A), 082.C-0023(A), 087.C-0962(B), and with NACO in program 380.C-0596(B).

Passively mode-locked fiber laser based on a hollow-core photonic crystal fiber filled with few-layered graphene oxide solution.

PubMed

Liu, Zhi-Bo; He, Xiaoying; Wang, D N

2011-08-15

We demonstrate a nanosecond-pulse erbium-doped fiber laser that is passively mode locked by a hollow-core photonic crystal fiber filled with few-layered graphene oxide solution. Owing to the good solution processing capability of few-layered graphene oxide, which can be filled into the core of a hollow-core photonic crystal fiber through a selective hole filling process, a graphene saturable absorber can be successfully fabricated. The output pulses obtained have a center wavelength, pulse width, and repetition rate of 1561.2 nm, 4.85 ns, and 7.68 MHz, respectively. This method provides a simple and efficient approach to integrate the graphene into the optical fiber system. © 2011 Optical Society of America

Precise Absolute Astrometry from the VLBA Imaging and Polarimetry Survey at 5 GHz

NASA Technical Reports Server (NTRS)

Petrov, L.; Taylor, G. B.

2011-01-01

We present accurate positions for 857 sources derived from the astrometric analysis of 16 eleven-hour experiments from the Very Long Baseline Array imaging and polarimetry survey at 5 GHz (VIPS). Among the observed sources, positions of 430 objects were not previously determined at milliarcsecond-level accuracy. For 95% of the sources the uncertainty of their positions ranges from 0.3 to 0.9 mas, with a median value of 0.5 mas. This estimate of accuracy is substantiated by the comparison of positions of 386 sources that were previously observed in astrometric programs simultaneously at 2.3/8.6 GHz. Surprisingly, the ionosphere contribution to group delay was adequately modeled with the use of the total electron content maps derived from GPS observations and only marginally affected estimates of source coordinates.

A catalogue of ground-based astrometric observations of the Martian satellites, 1877-1982

NASA Astrophysics Data System (ADS)

Morley, T. A.

1989-02-01

A catalog of 5767 ground-based astrometric observations of the Martian satellites, Phobos and Deimos, has been compiled. The position measurements comprise: 2497 of Phobos relative to Mars 3116 of Deimos relative to Mars and 154 of Deimos relative to Phobos. The data have been extracted from both published and unpublished sources and have been tabulated in a consistent format. All the observation times have been converted to the same time system, UTC. The catalog contains accuracy figures which can be used to differentially weigh the data when they are used for orbit determination purposes. Bad quality measurements have been identified and some obvious blunders have been corrected. The catalog is the official source of ground-based observations to be used for improving the satellite ephemerides in support of the Soviet Phobos mission.

Search for Terrestrial Planets with SIM Planet Quest

NASA Technical Reports Server (NTRS)

Shao, Michael; Tanner, Angelle M.; Catanzarite, Joseph H.

2006-01-01

SIM is an astrometric mission that will be capable of 1 microarcsec relative astrometric accuracy in a single measurement of approx.1000 sec. The search for terrestrial planets in the habitable zone around nearby stars is one of the main science goals of the project. In 2001, NASA through the peer review process selected 10 key projects, two of which had as its goal, the search for terrestrial planets around nearby stars. The two teams, one led by G. Marcy (UC Berkeley) and one lead by M. Shao (JPL), have an extensive preparatory science program underway. This paper describes the status of this activity as well as the technology status of SIM's narrow angle astrometry capability, to reach 1 uas in a single epoch measure and its ability to average multiple epoch measurements to well below 1 uas.

Brassboard Astrometric Beam Combiner (ABC) Development for the Space Interferometry Mission (SIM)

NASA Technical Reports Server (NTRS)

Jeganathan, Muthu; Kuan, Gary; Rud, Mike; Lin, Sean; Sutherland, Kristen; Moore, James; An, Xin

2008-01-01

The Astrometric Beam Combiner (ABC) is a critical element of the Space Interferometry Mission (SIM) that performs three key functions: coherently combine starlight from two siderostats; individually detect starlight for angle tracking; and disperse and detect the interferometric fringes. In addition, the ABC contains: a stimulus, cornercubes and shutters for in-orbit calibration; several tip/tilt mirror mechanisms for in-orbit alignment; and internal metrology beam launcher for pathlength monitoring. The detailed design of the brassboard ABC (which has the form, fit and function of the flight unit) is complete, procurement of long-lead items is underway, and assembly and testing is expected to be completed in Spring 2009. In this paper, we present the key requirements for the ABC, details of the completed optical and mechanical design as well as plans for assembly and alignment.

Spitzer Parallax Observations of Long Duration Gaia Microlensing Events

NASA Astrophysics Data System (ADS)

Carey, Sean; Calchi-Novati, Sebastiano; Wyrzykowski, Lukasz; Kruszynska, Katarzyna; Gromadzki, Mariusz; Rybicki, Krzysztof

2018-05-01

We proposed to observe of order ten long duration (>100 day) microlensing events identified in Gaia survey data with the Spitzer Space Telescope. The long duration events are likely due to massive lenses, hence they could be isolated black holes. These observations could make defintive mass measurements for the first time of isolated stellar remanant black holes in our Galaxy. The Spitzer data provide a key component to making an umabiguous mass measurement by providing the microlensing parallax (as has been done for >500 event by Spitzer so far). The Gaia data is used for the detection of the events and measurement of the astrometric motion caused by the microlensing event. From the astrometric microlensing signature, the Einstein radius of the lens can be measured and combined with the microlensing parallax yields the lens mass and distance.

Astrometry with LSST: Objectives and Challenges

NASA Astrophysics Data System (ADS)

Casetti-Dinescu, D. I.; Girard, T. M.; Méndez, R. A.; Petronchak, R. M.

2018-01-01

The forthcoming Large Synoptic Survey Telescope (LSST) is an optical telescope with an effective aperture of 6.4 m, and a field of view of 9.6 square degrees. Thus, LSST will have an étendue larger than any other optical telescope, performing wide-field, deep imaging of the sky. There are four broad categories of science objectives: 1) dark-energy and dark matter, 2) transients, 3) the Milky Way and its neighbours and, 4) the Solar System. In particular, for the Milky-Way science case, astrometry will make a critical contribution; therefore, special attention must be devoted to extract the maximum amount of astrometric information from the LSST data. Here, we outline the astrometric challenges posed by such a massive survey. We also present some current examples of ground-based, wide-field, deep imagers used for astrometry, as precursors of the LSST.

Update of membership and mean proper motion of open clusters from UCAC5 catalog

NASA Astrophysics Data System (ADS)

Dias, W. S.; Monteiro, H.; Assafin, M.

2018-06-01

We present mean proper motions and membership probabilities of individual stars for optically visible open clusters, which have been determined using data from the UCAC5 catalog. This follows our previous studies with the UCAC2 and UCAC4 catalogs, but now using improved proper motions in the GAIA reference frame. In the present study results were obtained for a sample of 1108 open clusters. For five clusters, this is the first determination of mean proper motion, and for the whole sample, we present results with a much larger number of identified astrometric member stars than on previous studies. It is the last update of our Open cluster Catalog based on proper motion data only. Future updates will count on astrometric, photometric and spectroscopic GAIA data as input for analyses.

Astrometric Discovery of GJ 164B

NASA Technical Reports Server (NTRS)

Pravdo, Steven H.; Shaklan, Stuart B.; Henry, Todd; Benedict, G. Fritz

2004-01-01

We discovered a low-mass companion to the M dwarf GJ 164 with the CCD-based imaging system of the Stellar Planet Survey astrometric program. The existence of GJ 164B was confirmed with Hubble Space Telescope NICMOS imaging observations. A high-dispersion spectral observation in V sets a lower limit of Deltam > 2.2 mag between the two components of the system. Based on our parallax value of 82 +/- 8 mas, we derive the following orbital parameters: P = 2.04 +/- 0.03 yr, a = 103 +/- 0.03, and M-total 0.265 +/- 0.020 M-circle dot. The component masses are M-A = 0.170 +/- 0.015 M-circle dot and M-B = 0.095 +/- 0/015 M-circle dot. Based on its mass, colors, and spectral properties, GJ 164B has spectral type M6-M8 V.

Interior properties of the inner Saturnian moons from space astrometry data

NASA Astrophysics Data System (ADS)

Lainey, Valery; Noyelles, Benoît; Cooper, Nick; Murray, Carl; Park, Ryan; Rambaux, Nicolas

2018-04-01

During thirteen years in orbit around Saturn before its final plunge, the Cassini spacecraft provided more than ten thousand astrometric measurements. Such large amounts of accurate data enable the search for extremely faint signals in the orbital motion of the moons. Among those, the detection of the dynamical feedback of the rotation of the inner moons of Saturn on their respective orbits becomes possible. Using all the currently available astrometric data associated with Atlas, Prometheus, Pandora, Janus and Epimetheus, we provide a detailed analysis of the ISS data, with special emphasis on their statistical behavior and source of biases. Then, we try quantifying the physical librations of Prometheus, Pandora, Epimetheus and Janus from the monitoring of their orbits. Last, we show how introducing measurements directly derived from imaging can provide tighter constraints on these quantities.

The astrometric lessons of Gaia-GBOT experiment

NASA Astrophysics Data System (ADS)

Bouquillon, S.; Mendez, R. A.; Altmann, M.

2017-07-01

To ensure the full capabilities of the Gaia's measurements, a programme of daily observations with Earth-based telescopes of the satellite itself - called Ground Based Optical Tracking (GBOT) - was implemented since the beginning of the Gaia mission (for more details concerning GBOT operating see Altmann et al. 2014 and concerning GBOT software facilities see Bouquillon et al. 2014). These observations are carried out mainly with two facilities: the 2.6m VLT Survey Telescope (ESO's VST) at the Cerro Paranal in Chile and the 2.0m Liverpool Telescope (LT) on the Canary Island of La Palma. The constraint of 20 mas on the tracking astrometric quality and the fact that Gaia is a faint and relatively fast moving target (its magnitude in a red passband is around 21 and its apparent speed around 0.04"/s), lead us to rigorously analyse the reachable astrometric precision for CCD observations of this kind of celestial objects. During LARIM 2016, we presented the main results of this study which uses the Cramér-Rao lower bound to characterize the precision limit for the PSF center when drifting in the CCD-frame. This work extends earlier studies dealing with one-dimensional detectors and stationary sources (Mendez et al. 2013 & 2014) firstly to the case of standard two-dimensional CCD sensors, and then, to moving sources. These new results have been submitted for a publication in A&A journal this year (Bouquillon et al. 2017).

Estimation of position and velocity for a low dynamic vehicle in near space using nonresolved photometric and astrometric data.

PubMed

Jing, Nan; Li, Chuang; Chong, Yaqin

2017-01-20

An estimation method for indirectly observable parameters for a typical low dynamic vehicle (LDV) is presented. The estimation method utilizes apparent magnitude, azimuth angle, and elevation angle to estimate the position and velocity of a typical LDV, such as a high altitude balloon (HAB). In order to validate the accuracy of the estimated parameters gained from an unscented Kalman filter, two sets of experiments are carried out to obtain the nonresolved photometric and astrometric data. In the experiments, a HAB launch is planned; models of the HAB dynamics and kinematics and observation models are built to use as time update and measurement update functions, respectively. When the HAB is launched, a ground-based optoelectronic detector is used to capture the object images, which are processed using aperture photometry technology to obtain the time-varying apparent magnitude of the HAB. Two sets of actual and estimated parameters are given to clearly indicate the parameter differences. Two sets of errors between the actual and estimated parameters are also given to show how the estimated position and velocity differ with respect to the observation time. The similar distribution curve results from the two scenarios, which agree within 3σ, verify that nonresolved photometric and astrometric data can be used to estimate the indirectly observable state parameters (position and velocity) for a typical LDV. This technique can be applied to small and dim space objects in the future.

Atmospheric Dispersion Effects in Weak Lensing Measurements

DOE PAGES

Plazas, Andrés Alejandro; Bernstein, Gary

2012-10-01

The wavelength dependence of atmospheric refraction causes elongation of finite-bandwidth images along the elevation vector, which produces spurious signals in weak gravitational lensing shear measurements unless this atmospheric dispersion is calibrated and removed to high precision. Because astrometric solutions and PSF characteristics are typically calibrated from stellar images, differences between the reference stars' spectra and the galaxies' spectra will leave residual errors in both the astrometric positions (dr) and in the second moment (width) of the wavelength-averaged PSF (dv) for galaxies.We estimate the level of dv that will induce spurious weak lensing signals in PSF-corrected galaxy shapes that exceed themore » statistical errors of the DES and the LSST cosmic-shear experiments. We also estimate the dr signals that will produce unacceptable spurious distortions after stacking of exposures taken at different airmasses and hour angles. We also calculate the errors in the griz bands, and find that dispersion systematics, uncorrected, are up to 6 and 2 times larger in g and r bands,respectively, than the requirements for the DES error budget, but can be safely ignored in i and z bands. For the LSST requirements, the factors are about 30, 10, and 3 in g, r, and i bands,respectively. We find that a simple correction linear in galaxy color is accurate enough to reduce dispersion shear systematics to insignificant levels in the r band for DES and i band for LSST,but still as much as 5 times than the requirements for LSST r-band observations. More complex corrections will likely be able to reduce the systematic cosmic-shear errors below statistical errors for LSST r band. But g-band effects remain large enough that it seems likely that induced systematics will dominate the statistical errors of both surveys, and cosmic-shear measurements should rely on the redder bands.« less

Role Of Impurities On Deformation Of HCP Crystal: A Multi-Scale Approach

NASA Astrophysics Data System (ADS)

Bhatia, Mehul Anoopkumar

Commercially pure (CP) and extra low interstitial (ELI) grade Ti-alloys present excellent corrosion resistance, lightweight, and formability making them attractive materials for expanded use in transportation and medical applications. However, the strength and toughness of CP titanium are affected by relatively small variations in their impurity/solute content (IC), e.g., O, Al, and V. This increase in strength is due to the fact that the solute either increases the critical stress required for the prismatic slip systems ({10- 10}) or activates another slip system ((0001), {10-11}). In particular, solute additions such as O can effectively strengthen the alloy but with an attendant loss in ductility by changing the behavior from wavy (cross slip) to planar nature. In order to understand the underlying behavior of strengthening by solutes, it is important to understand the atomic scale mechanism. This dissertation aims to address this knowledge gap through a synergistic combination of density functional theory (DFT) and molecular dynamics. Further, due to the long-range strain fields of the dislocations and the periodicity of the DFT simulation cells, it is difficult to apply ab initio simulations to study the dislocation core structure. To alleviate this issue we developed a multiscale quantum mechanics/molecular mechanics approach (QM/MM) to study the dislocation core. We use the developed QM/MM method to study the pipe diffusion along a prismatic edge dislocation core. Complementary to the atomistic simulations, the Semi-discrete Variational Peierls-Nabarro model (SVPN) was also used to analyze the dislocation core structure and mobility. The chemical interaction between the solute/impurity and the dislocation core is captured by the so-called generalized stacking fault energy (GSFE) surface which was determined from DFT-VASP calculations. By taking the chemical interaction into consideration the SVPN model can predict the dislocation core structure and mobility in the presence and absence of the solute/impurity and thus reveal the effect of impurity/solute on the softening/hardening behavior in alpha-Ti. Finally, to study the interaction of the dislocation core with other planar defects such as grain boundaries (GB), we develop an automated method to theoretically generate GBs in HCP type materials.

Effect of alloying on screw dislocation structure in Mo: atomistic modelling approach with ab-initio parametrization

NASA Astrophysics Data System (ADS)

Gornostyrev, Yu. N.

2005-03-01

The plastic deformation in bcc metals is realized by the motion of screw dislocations with a complex star-like non-planar core. In this case, the direct investigation of the solute effect by first principles electronic structure calculations is a challenging problem for which we follow a combined approach that includes atomistic dislocation modelling with ab-initio parametrization of interatomic interactions. The screw dislocation core structure in Mo alloys is described within the model of atomic row displacements along a dislocation line with the interatomic row potential estimated from total energy full-potential linear muffin-tin orbital (FLMTO) calculations with the generalized gradient approximation (GGA) for the exchange-correlation potential. We demonstrate (1) that the solute effect on the dislocation structure is different for ``hard'' and ``easy'' cores and (2) that the softener addition in a ``hard'' core gives rise to a structural transformation into a configuration with a lower energy through an intermediate state. The softener solute is shown to disturb locally the three-fold symmetry of the dislocation core and the dislocation structure tends to the split planar core.

ETD QA CORE TEAM: AN ELOQUENT SOLUTION TO A COMPLEX PROBLEM

EPA Science Inventory

ETD QA CORE TEAM: AN ELOQUENT SOLUTION TO A COMPLEX PROBLEMThomas J. Hughes, QA and Records Manager, Experimental Toxicology Division (ETD), National Health and Environmental Effects Research Laboratory (NHEERL), ORD, U.S. EPA, RTP, NC 27709

ETD is the largest health divis...

DDC Systems for Searching for Near-Earth Asteroids

NASA Technical Reports Server (NTRS)

Harris, A.

1994-01-01

Large format CCD systems are superior to photographic systems in terms of quantum efficiency and that they yield digital output directly, which can be computer analyzed to detect moving objects and to obtain astrometric measurements.

Stellar, remnant, planetary, and dark-object masses from astrometric microlensing

NASA Technical Reports Server (NTRS)

Boden, A.; Gould, A. P.; Bennett, D. P.; Depoy, D. L.; Gaudi, S. B.; Griest, K.; Han, C.; Paczynski, B.; Reid, I. N.

2002-01-01

With SIM, we will break the microlensing degeneracy, and allow detailed interpretation of individual microlensing events. We will thus develop a detailed census of the dark and luminous stellar population of the Galaxy.

Application of Direct Current Atmospheric Pressure Glow Microdischarge Generated in Contact with a Flowing Liquid Solution for Synthesis of Au-Ag Core-Shell Nanoparticles

PubMed Central

Dzimitrowicz, Anna; Jamroz, Piotr; Nyk, Marcin; Pohl, Pawel

2016-01-01

A direct current atmospheric pressure glow microdischarge (dc-μAPGD) generated between an Ar nozzle microjet and a flowing liquid was applied to produce Au-Ag core-shell nanoparticles (Au@AgCSNPs) in a continuous flow system. Firstly, operating dc-μAPGD with the flowing solution of the Au(III) ions as the cathode, the Au nanoparticles (AuNPs) core was produced. Next, to produce the core-shell nanostructures, the collected AuNPs solution was immediately mixed with an AgNO3 solution and passed through the system with the reversed polarity to fabricate the Ag nanoshell on the AuNPs core. The formation of Au@AgCSNPs was confirmed using ultraviolet-visible (UV-Vis) absorbance spectrophotometry, transmission electron microscopy (TEM), and energy-dispersive X-ray spectroscopy (EDS). Three localized surface plasmon resonance absorption bands with wavelengths centered at 372, 546, and 675 nm were observed in the UV-Vis spectrum of Au@AgCSNPs, confirming the reduction of both the Au(III) and Ag(I) ions. The right configuration of metals in Au@AgCSNPs was evidenced by TEM. The Au core diameter was 10.2 ± 2.0 nm, while the thickness of the Ag nanoshell was 5.8 ± 1.8 nm. The elemental composition of the bimetallic nanoparticles was also confirmed by EDS. It is possible to obtain 90 mL of a solution containing Au@AgCSNPs per hour using the applied microdischarge system. PMID:28773393

A strong radio brightening at the jet base of M 87 during the elevated very high energy gamma-ray state in 2012

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hada, K.; Giroletti, M.; Giovannini, G.

2014-06-20

We report our intensive, high angular resolution radio monitoring observations of the jet in M 87 with the VLBI Exploration of Radio Astrometry (VERA) and the European VLBI Network (EVN) from 2011 February to 2012 October, together with contemporaneous high-energy (100 MeV 100 GeV) γ rays by VERITAS. We detected a remarkable (up to ∼70%) increase of the radio flux density from the unresolved jet base (radio core) with VERA at 22 and 43 GHz coincident with the VHE activity. Meanwhile, we confirmed with EVN at 5 GHz that the peculiar knot, HST-1, which is an alternative favored γ-ray productionmore » site located at ≳120 pc from the nucleus, remained quiescent in terms of its flux density and structure. These results in the radio bands strongly suggest that the VHE γ-ray activity in 2012 originates in the jet base within 0.03 pc or 56 Schwarzschild radii (the VERA spatial resolution of 0.4 mas at 43 GHz) from the central supermassive black hole. We further conducted VERA astrometry for the M 87 core at six epochs during the flaring period, and detected core shifts between 22 and 43 GHz, a mean value of which is similar to that measured in the previous astrometric measurements. We also discovered a clear frequency-dependent evolution of the radio core flare at 43, 22, and 5 GHz; the radio flux density increased more rapidly at higher frequencies with a larger amplitude, and the light curves clearly showed a time-lag between the peaks at 22 and 43 GHz, the value of which is constrained to be within ∼35-124 days. This indicates that a new radio-emitting component was created near the black hole in the period of the VHE event, and then propagated outward with progressively decreasing synchrotron opacity. By combining the obtained core shift and time-lag, we estimated an apparent speed of the newborn component propagating through the opaque region between the cores at 22 and 43 GHz. We derived a sub-luminal speed (less than ∼0.2c) for this component. This value is significantly slower than the super-luminal (∼1.1c) features that appeared from the core during the prominent VHE flaring event in 2008, suggesting that stronger VHE activity can be associated with the production of a higher Lorentz factor jet in M 87.« less

Astrometric properties of the Tautenburg Plate Scanner

NASA Astrophysics Data System (ADS)

Brunzendorf, Jens; Meusinger, Helmut

The Tautenburg Plate Scanner (TPS) is an advanced plate-measuring machine run by the Thüringer Landessternwarte Tautenburg (Karl Schwarzschild Observatory), where the machine is housed. It is capable of digitising photographic plates up to 30 cm × 30 cm in size. In our poster, we reported on tests and preliminary results of its astrometric properties. The essential components of the TPS consist of an x-y table movable between an illumination system and a direct imaging system. A telecentric lens images the light transmitted through the photographic emulsion onto a CCD line of 6000 pixels of 10 µm square size each. All components are mounted on a massive air-bearing table. Scanning is performed in lanes of up to 55 mm width by moving the x-y table in a continuous drift-scan mode perpendicular to the CCD line. The analogue output from the CCD is digitised to 12 bit with a total signal/noise ratio of 1000 : 1, corresponding to a photographic density range of three. The pixel map is produced as a series of optionally overlapping lane scans. The pixel data are stored onto CD-ROM or DAT. A Tautenburg Schmidt plate 24 cm × 24 cm in size is digitised within 2.5 hours resulting in 1.3 GB of data. Subsequent high-level data processing is performed off-line on other computers. During the scanning process, the geometry of the optical components is kept fixed. The optimal focussing of the optics is performed prior to the scan. Due to the telecentric lens refocussing is not required. Therefore, the main source of astrometric errors (beside the emulsion itself) are mechanical imperfections in the drive system, which have to be divided into random and systematic ones. The r.m.s. repeatability over the whole plate as measured by repeated scans of the same plate is about 0.5 µm for each axis. The mean plate-to-plate accuracy of the object positions on two plates with the same epoch and the same plate centre has been determined to be about 1 µm. This accuracy is comparable to results obtained with established measuring machines used for astrometric purposes and is mainly limited by the emulsion itself. The mechanical design of the x-y table introduces low-frequency systematic errors of up to 5 µm on both axes. Because of the high stability of the machine it is expected that these deviations from a perfectly uniform coordinate system will remain systematic on a long timescale. Such systematic errors can be corrected either directly once they have been determined or in the course of the general astrometric reduction process. The TPS is well suited for accurate relative measurements like proper motions on plates with the same scale and plate centre. The systematic errors of the x-y table can be determined by interferometric means, and there are plans for this in the next future.

Combinatorial optimization games

DOE Office of Scientific and Technical Information (OSTI.GOV)

Deng, X.; Ibaraki, Toshihide; Nagamochi, Hiroshi

1997-06-01

We introduce a general integer programming formulation for a class of combinatorial optimization games, which immediately allows us to improve the algorithmic result for finding amputations in the core (an important solution concept in cooperative game theory) of the network flow game on simple networks by Kalai and Zemel. An interesting result is a general theorem that the core for this class of games is nonempty if and only if a related linear program has an integer optimal solution. We study the properties for this mathematical condition to hold for several interesting problems, and apply them to resolve algorithmic andmore » complexity issues for their cores along the line as put forward in: decide whether the core is empty; if the core is empty, find an imputation in the core; given an imputation x, test whether x is in the core. We also explore the properties of totally balanced games in this succinct formulation of cooperative games.« less

Parsec's astrometry direct approaches .

NASA Astrophysics Data System (ADS)

Andrei, A. H.

Parallaxes - and hence the fundamental establishment of stellar distances - rank among the oldest, keyest, and hardest of astronomical determinations. Arguably amongst the most essential too. The direct approach to obtain trigonometric parallaxes, using a constrained set of equations to derive positions, proper motions, and parallaxes, has been labeled as risky. Properly so, because the axis of the parallactic apparent ellipse is smaller than one arcsec even for the nearest stars, and just a fraction of its perimeter can be followed. Thus the classical approach is of linearizing the description by locking the solution to a set of precise positions of the Earth at the instants of observation, rather than to the dynamics of its orbit, and of adopting a close examination of the never many points available. In the PARSEC program the parallaxes of 143 brown dwarfs were aimed at. Five years of observation of the fields were taken with the WIFI camera at the ESO 2.2m telescope, in Chile. The goal is to provide a statistically significant number of trigonometric parallaxes to BD sub-classes from L0 to T7. Taking advantage of the large, regularly spaced, quantity of observations, here we take the risky approach to fit an ellipse in ecliptical observed coordinates and derive the parallaxes. We also combine the solutions from different centroiding methods, widely proven in prior astrometric investigations. As each of those methods assess diverse properties of the PSFs, they are taken as independent measurements, and combined into a weighted least-square general solution.

Protostellar Collapse with a Shock

NASA Technical Reports Server (NTRS)

Tsai, John C.; Hsu, Juliana J.

1995-01-01

We reexamine both numerically and analytically the collapse of the singular isothermal sphere in the context of low-mass star formation. We consider the case where the onset of collapse is initiated by some arbitrary process which is accompanied by a central output of either heat or kinetic energy. We find two classes of numerical solutions describing this manner of collapse. The first approaches in time the expansion wave solution of Shu, while the second class is characterized by an ever-decreasing central accretion rate and the presence of an outwardly propagating weak shock. The collapse solution which represents the dividing case between these two classes is determined analytically by a similarity analysis. This solution shares with the expansion wave solution the properties that the gas remains stationary with an r(exp -2) density profile at large radius and that, at small radius, the gas free-falls onto a nascent core at a constant rate which depends only on the isothermal sound speed. This accretion rate is a factor of approx. 0.1 that predicted by the expansion wave solution. This reduction is due in part to the presence of a weak shock which propagates outward at 1.26 times the sound speed. Gas in the postshock region first moves out subsonically but is then decelerated and begins to collapse. The existence of two classes of numerical collapse solutions is explained in terms of the instability to radial perturbations of the analytic solution. Collapse occurring in the manner described by some of our solutions would eventually unbind a finite-sized core. However, this does not constitute a violation of the instability properties of the singular isothermal sphere which is unstable both to collapse and to expansion. To emphasize this, we consider a purely expanding solution for isothermal spheres. This solution is found to be self-similar and results in a uniform density core in the central regions of the gas. Our solutions may be relevant to the 'luminosity' problem of protostellar cores since the predicted central accretion rates are significantly reduced relative to that of the expansion wave solution. Furthermore, our calculations indicate that star-forming cloud cores are not very tightly bound and that modest disturbances can easily result in both termination of infall and dispersal of unaccreted material.

Protostellar Collapse with a Shock

NASA Technical Reports Server (NTRS)

Tsai, John C.; Hsu, Juliana J. L.

1995-01-01

We reexamine both numerically and analytically the collapse of the singular isothermal sphere in the context of low-mass star formation. We consider the case where the onset of collapse is initiated by some arbitrary process which is accompanied by a central output of either heat or kinetic energy. We find two classes of numerical solutions describing this manner of collapse. The first approaches in time the expansion wave solution of Shu, while the second class is characterized by an ever-decreasing central accretion rate and the presence of an outwardly propagating weak shock. The collapse solution which represents the dividing case between these two classes is determined analytically by a similarity analysis. This solution shares with the expansion wave solution the properties that the gas remains stationary with an r(sup -2) density profile at large radius and that, at small radius, the gas free-falls onto a nascent core at a constant rate which depends only on the isothermal sound speed. This accretion rate is a factor of approx. 0.1 that predicted by the expansion wave solution. This reduction is due in part to the presence of a weak shock which propagates outward at 1.26 times the sound speed. Gas in the postshock region first moves out subsonically but is then decelerated and begins to collapse. The existence of two classes of numerical collapse solutions is explained in terms of the instability to radial perturbations of the analytic solution. Collapse occurring in the manner described by some of our solutions would eventually unbind a finite-sized core. However, this does not constitute a violation of the instability properties of the singular isothermal sphere which is unstable both to collapse and to expansion. To emphasize this, we consider a purely expanding solution for isothermal spheres. This solution is found to be self-similar and results in a uniform density core in the central regions of the gas. Our solutions may be relevant to the 'luminosity' problem of protostellar cores since the predicted central accretion rates are significantly reduced relative to that of the expansion wave solution. Furthermore, our calculations indicate that star-forming cloud cores are not very tightly bound and that modest disturbances can easily result in both termination of infall and dispersal of unaccreted material.

Near-Earth Object Astrometric Interferometry

NASA Technical Reports Server (NTRS)

Werner, Martin R.

2005-01-01

Using astrometric interferometry on near-Earth objects (NEOs) poses many interesting and difficult challenges. Poor reflectance properties and potentially no significant active emissions lead to NEOs having intrinsically low visual magnitudes. Using worst case estimates for signal reflection properties leads to NEOs having visual magnitudes of 27 and higher. Today the most sensitive interferometers in operation have limiting magnitudes of 20 or less. The main reason for this limit is due to the atmosphere, where turbulence affects the light coming from the target, limiting the sensitivity of the interferometer. In this analysis, the interferometer designs assume no atmosphere, meaning they would be placed at a location somewhere in space. Interferometer configurations and operational uncertainties are looked at in order to parameterize the requirements necessary to achieve measurements of low visual magnitude NEOs. This analysis provides a preliminary estimate of what will be required in order to take high resolution measurements of these objects using interferometry techniques.

Commission 8: Astrometry

NASA Astrophysics Data System (ADS)

Evans, Dafydd Wyn; Zacharias, Norbert; Kumkova, Irina; Andrei, Alexandre; Brown, Anthony; Gouda, Naoteru; Popescu, Petre; Souchay, Jean; Unwin, Stephen; Zhu, Zi

2012-04-01

Gaia is continuing well with its development and construction and is expected to achieve parallax accuracies of about 10 to 300 μas for 6 to 20 mag. It is scheduled to launch in 2013. The ICRF2 was adopted by the IAU in 2009 as the new fundamental celestial reference frame. The UCAC project concluded with the publication of its 4th data release (all-sky, over 100 million stars). The JASMINE project will launch the Nano-JASMINE satellite in 2012 and continues with the development of its other satellites which will complement the Gaia project. The PPMXL (Heidelberg) and XPM (Ukraine) catalogues provide improved astrometric accuracies from new reductions of USNO-B (USNO-A) and 2MASS data. It is disappointing that the SIM project was cancelled during this triennium. It would have further complemented the above two satellite projects and would have gone even beyond Gaia in astrometric accuracy.

The Hubble Space Telescope UV Legacy Survey of Galactic globular clusters - XIII. ACS/WFC parallel-field catalogues

NASA Astrophysics Data System (ADS)

Simioni, M.; Bedin, L. R.; Aparicio, A.; Piotto, G.; Milone, A. P.; Nardiello, D.; Anderson, J.; Bellini, A.; Brown, T. M.; Cassisi, S.; Cunial, A.; Granata, V.; Ortolani, S.; van der Marel, R. P.; Vesperini, E.

2018-05-01

As part of the Hubble Space Telescope UV Legacy Survey of Galactic globular clusters, 110 parallel fields were observed with the Wide Field Channel of the Advanced Camera for Surveys, in the outskirts of 48 globular clusters, plus the open cluster NGC 6791. Totalling about 0.3 deg2 of observed sky, this is the largest homogeneous Hubble Space Telescope photometric survey of Galalctic globular clusters outskirts to date. In particular, two distinct pointings have been obtained for each target on average, all centred at about 6.5 arcmin from the cluster centre, thus covering a mean area of about 23 arcmin2 for each globular cluster. For each field, at least one exposure in both F475W and F814W filters was collected. In this work, we publicly release the astrometric and photometric catalogues and the astrometrized atlases for each of these fields.

New astrometric observations of Triton in 2007-2009

NASA Astrophysics Data System (ADS)

Qiao, R. C.; Zhang, H. Y.; Dourneau, G.; Yu, Y.; Yan, D.; Shen, K. X.; Cheng, X.; Xi, X. J.; Hu, X. Y.; Wang, S. H.

2014-06-01

Astrometric positions of the Neptunian satellite Triton with a visual magnitude of 13.5 were obtained during three successive oppositions in 2007, 2008 and 2009. A total of 1095 new observed positions of Triton were collected during 46 nights of observations, involving eight missions and three telescopes. We compared our observations to the best ephemerides of Triton available now. This comparison has shown that our observations present a high level of accuracy as they provide standard deviations of residuals hardly higher than 50 mas and mean residuals lower than 30 mas, corresponding to about only 500 km in the position of the very distant satellite Triton. Moreover, we have compared most of the different planetary ephemerides of Neptune available now as well as two recent orbit models of Triton. These new comparisons have clearly shown the differences between all of these ephemerides which can be significant and that are presented in this work.

Determining open cluster membership. A Bayesian framework for quantitative member classification

NASA Astrophysics Data System (ADS)

Stott, Jonathan J.

2018-01-01

Aims: My goal is to develop a quantitative algorithm for assessing open cluster membership probabilities. The algorithm is designed to work with single-epoch observations. In its simplest form, only one set of program images and one set of reference images are required. Methods: The algorithm is based on a two-stage joint astrometric and photometric assessment of cluster membership probabilities. The probabilities were computed within a Bayesian framework using any available prior information. Where possible, the algorithm emphasizes simplicity over mathematical sophistication. Results: The algorithm was implemented and tested against three observational fields using published survey data. M 67 and NGC 654 were selected as cluster examples while a third, cluster-free, field was used for the final test data set. The algorithm shows good quantitative agreement with the existing surveys and has a false-positive rate significantly lower than the astrometric or photometric methods used individually.

Geodetic and Astrometric Measurements with Very-Long-Baseline Interferometry. Ph.D. Thesis - MIT

NASA Technical Reports Server (NTRS)

Robertson, D. S.

1975-01-01

The use of very-long-baseline interferometry (VLBI) observations for the estimation of geodetic and astrometric parameters is discussed. Analytic models for the dependence of delay and delay rate on these parameters are developed and used for parameter estimation by the method of weighted least squares. Results are presented from approximately 15,000 delay and delay-rate observations, obtained in a series of nineteen VLBI experiments involving a total of five stations on two continents. The closure of baseline triangles is investigated and found to be consistent with the scatter of the various baseline-component results. Estimates are made of the wobble of the earth's pole and of the irregularities in the earth's rotation rate. Estimates are also made of the precession constant and of the vertical Love number, for which a value of 0.55 + or - 0.05 was obtained.

Astrometric Search Method for Individually Resolvable Gravitational Wave Sources with Gaia

NASA Astrophysics Data System (ADS)

Moore, Christopher J.; Mihaylov, Deyan P.; Lasenby, Anthony; Gilmore, Gerard

2017-12-01

Gravitational waves (GWs) cause the apparent position of distant stars to oscillate with a characteristic pattern on the sky. Astrometric measurements (e.g., those made by Gaia) provide a new way to search for GWs. The main difficulty facing such a search is the large size of the data set; Gaia observes more than one billion stars. In this Letter the problem of searching for GWs from individually resolvable supermassive black hole binaries using astrometry is addressed for the first time; it is demonstrated how the data set can be compressed by a factor of more than 1 06, with a loss of sensitivity of less than 1%. This technique was successfully used to recover artificially injected GW signals from mock Gaia data and to assess the GW sensitivity of Gaia. Throughout the Letter the complementarity of Gaia and pulsar timing searches for GWs is highlighted.

Triton stellar occultation candidates - 1992-1994

NASA Technical Reports Server (NTRS)

Mcdonald, S. W.; Elliot, J. T.

1992-01-01

A search for Triton stellar occultation candidates for the period 1992-1994 has been completed with CCD strip-scanning observations. The search reached an R magnitude of about 17.4 and found 129 candidates within 1.5 arcsec of Triton's ephemeris during this period. Of these events, around 30 occultations are expected to be visible from the earth, indicating that a number of Triton occultation events should be visible from major observatories. Even the faintest of the present candidate events could produce useful occultation data if observed with a large enough telescope. The present astrometric accuracy is inadequate to identify which of these appulse events will produce occultations on the earth; further astrometry is needed to refine the predictions for positive occultation identification. To aid in selecting candidates for additional astrometric and photometric studies, finder charts and earth-based visibility charts for each event are included.

Characterization of the Mysteriously Cool Brown Dwarf HD 4113

NASA Astrophysics Data System (ADS)

Ednie, Michaela; Follette, Katherine; Ward-Duong, Kimberly

2018-01-01

Characterizing the physical properties of brown dwarfs is necessary to expand and improve our understanding of low mass companions, including exoplanets. Systems with both close radial velocity companions and distant directly imaged companions are particularly powerful in understanding planet formation mechanisms. Early in 2017, members of the SPHERE team discovered a companion brown dwarf in the HD 4113 system, which also contains a known RV planet. Atmospheric model fits to the Y and J-band spectra and H2/H3 photometry of the brown dwarf suggested it is unusually cool. We obtained new Magellan data in the Z and K’ bands in mid-2017. This data will help us to complete a more detailed atmospheric and astrometric characterization of this unusually cool companion. Broader wavelength coverage will help in accurate spectral typing and estimations of luminosity, temperature, surface gravity, radius, and composition. Additionally, a second astrometric epoch will help constrain the architecture of the system.

Observations of Anomalous Refraction with Co-housed Telescopes

NASA Astrophysics Data System (ADS)

Taylor, Malinda S.; McGraw, J. T.; Zimmer, P. C.

2013-01-01

Anomalous refraction is described as a low frequency, large angular scale motion of the entire image plane with respect to the celestial coordinate system as observed and defined by previous astrometric catalogs. These motions of typically several tenths of an arcsecond with timescales on the order of ten minutes are ubiquitous to drift-scan ground-based astrometric measurements regardless of location or telescopes used and have been attributed to meter scale slowly evolving coherent dynamical structures in the boundary-layer below 60 meters. The localized nature of the effect and general inconsistency of the motions seen by even closely spaced telescopes in individual domes has led to the hypothesis that the dome or other type of telescope housing may be responsible. This hypothesis is tested by observing anomalous refraction using two telescopes housed in a single roll-off roof observatory building with the expected outcome that the two telescopes will see correlated anomalous refraction induced motions.

Astrometric masses of 21 asteroids, and an integrated asteroid ephemeris

NASA Astrophysics Data System (ADS)

Baer, James; Chesley, Steven R.

2008-01-01

We apply the technique of astrometric mass determination to measure the masses of 21 main-belt asteroids; the masses of 9 Metis (1.03 ± 0.24 × 10-11 M⊙), 17 Thetis (6.17 ± 0.64 × 10-13 M⊙), 19 Fortuna (5.41 ± 0.76 × 10-12 M⊙), and 189 Phthia (1.87 ± 0.64 × 10-14 M⊙) appear to be new. The resulting bulk porosities of 11 Parthenope (12±4%) and 16 Psyche (46±16%) are smaller than previously-reported values. Empirical expressions modeling bulk density as a function of mean radius are presented for the C and S taxonomic classes. To accurately model the forces on these asteroids during the mass determination process, we created an integrated ephemeris of the 300 large asteroids used in preparing the DE-405 planetary ephemeris; this new BC-405 integrated asteroid ephemeris also appears useful in other high-accuracy applications.

Galaxy simulations in the Gaia era

NASA Astrophysics Data System (ADS)

Minchev, Ivan

2018-04-01

We live in an age where an enormous amount of astrometric, photometric, asteroseismic, and spectroscopic data of Milky Way stars are being acquired, many orders of magnitude larger than about a decade ago. Thanks to the Gaia astrometric mission and followup ground-based spectroscopic surveys in the next 5-10 years about 10-20 Million stars will have accurate 6D kinematics and chemical composition measurements. KEPLER-2, PLATO, and TESS will provide asteroseismic ages for a good fraction of those. In this article we outline some outstanding problems concerning the formation and evolution of the Milky Way and argue that, due to the complexity of physical processes involved in the formation of disk galaxies, numerical simulations in the cosmological context are needed for the interpretation of Milky Way observations. We also discuss in some detail the formation of the Milky Way thick disk, chemodynamical models, and the effects of radial migration.

Mesoscale modeling of vacancy-mediated Si segregation near an edge dislocation in Ni under irradiation

NASA Astrophysics Data System (ADS)

Li, Zebo; Trinkle, Dallas R.

2017-04-01

We use a continuum method informed by transport coefficients computed using self-consistent mean field theory to model vacancy-mediated diffusion of substitutional Si solutes in FCC Ni near an a/2 [1 1 ¯0 ] (111 ) edge dislocation. We perform two sequential simulations: first under equilibrium boundary conditions and then under irradiation. The strain field around the dislocation induces heterogeneity and anisotropy in the defect transport properties and determines the steady-state vacancy and Si distributions. At equilibrium both vacancies and Si solutes diffuse to form Cottrell atmospheres with vacancies accumulating in the compressive region above the dislocation core while Si segregates to the tensile region below the core. Irradiation raises the bulk vacancy concentration, driving vacancies to flow into the dislocation core. The out-of-equilibrium vacancy fluxes drag Si atoms towards the core, causing segregation to the compressive region, despite Si being an oversized solute in Ni.

Porous metal oxide particles and their methods of synthesis

DOEpatents

Chen, Fanglin; Liu, Qiang

2013-03-12

Methods are generally disclosed for synthesis of porous particles from a solution formed from a leaving agent, a surfactant, and a soluble metal salt in a solvent. The surfactant congregates to form a nanoparticle core such that the metal salt forms about the nanoparticle core to form a plurality of nanoparticles. The solution is heated such that the leaving agent forms gas bubbles in the solution, and the plurality of nanoparticles congregate about the gas bubbles to form a porous particle. The porous particles are also generally disclosed and can include a particle shell formed about a core to define an average diameter from about 0.5 .mu.m to about 50 .mu.m. The particle shell can be formed from a plurality of nanoparticles having an average diameter of from about 1 nm to about 50 nm and defined by a metal salt formed about a surfactant core.

Wormhole at the core of an infinite cosmic string

NASA Astrophysics Data System (ADS)

Aros, Rodrigo O.; Zamorano, Nelson

1997-11-01

We study a solution of Einstein's equations that describes a straight cosmic string with a variable angular deficit, starting with a 2π deficit at the core. We show that the coordinate singularity associated with this defect can be interpreted as a traversable wormhole lodging at the core of the string. A negative energy density gradually decreases the angular deficit as the distance from the core increases, ending, at radial infinity, in a Minkowski spacetime. The negative energy density can be confined to a small transversal section of the string by gluing to it an exterior Gott-like solution that freezes the angular deficit existing at the matching border. The equation of state of the string is such that any massive particle may stay at rest anywhere in this spacetime. In this sense this is a 2+1 spacetime solution. A generalization that includes the existence of two interacting parallel wormholes is displayed. These wormholes are not traversable. Finally, we point out that a similar result, flat at infinity and with a 2π defect (or excess) at the core, has been recently published by Dyer and Marleau. Even though theirs is a local string fully coupled to gravity, our toy model captures important aspects of this solution.

Methotrexate diethyl ester-loaded lipid-core nanocapsules in aqueous solution increased antineoplastic effects in resistant breast cancer cell line.

PubMed

Yurgel, Virginia C; Oliveira, Catiuscia P; Begnini, Karine R; Schultze, Eduarda; Thurow, Helena S; Leon, Priscila M M; Dellagostin, Odir A; Campos, Vinicius F; Beck, Ruy C R; Guterres, Silvia S; Collares, Tiago; Pohlmann, Adriana R; Seixas, Fabiana K

2014-01-01

Breast cancer is the most frequent cancer affecting women. Methotrexate (MTX) is an antimetabolic drug that remains important in the treatment of breast cancer. Its efficacy is compromised by resistance in cancer cells that occurs through a variety of mechanisms. This study evaluated apoptotic cell death and cell cycle arrest induced by an MTX derivative (MTX diethyl ester [MTX(OEt)2]) and MTX(OEt)2-loaded lipid-core nanocapsules in two MTX-resistant breast adenocarcinoma cell lines, MCF-7 and MDA-MB-231. The formulations prepared presented adequate granulometric profile. The treatment responses were evaluated through flow cytometry. Relying on the mechanism of resistance, we observed different responses between cell lines. For MCF-7 cells, MTX(OEt)2 solution and MTX(OEt)2-loaded lipid-core nanocapsules presented significantly higher apoptotic rates than untreated cells and cells incubated with unloaded lipid-core nanocapsules. For MDA-MB-231 cells, MTX(OEt)2-loaded lipid-core nanocapsules were significantly more efficient in inducing apoptosis than the solution of the free drug. S-phase cell cycle arrest was induced only by MTX(OEt)2 solution. The drug nanoencapsulation improved apoptosis induction for the cell line that presents MTX resistance by lack of transport receptors.

Methotrexate diethyl ester-loaded lipid-core nanocapsules in aqueous solution increased antineoplastic effects in resistant breast cancer cell line

PubMed Central

Yurgel, Virginia C; Oliveira, Catiuscia P; Begnini, Karine R; Schultze, Eduarda; Thurow, Helena S; Leon, Priscila MM; Dellagostin, Odir A; Campos, Vinicius F; Beck, Ruy CR; Guterres, Silvia S; Collares, Tiago; Pohlmann, Adriana R; Seixas, Fabiana K

2014-01-01

Breast cancer is the most frequent cancer affecting women. Methotrexate (MTX) is an antimetabolic drug that remains important in the treatment of breast cancer. Its efficacy is compromised by resistance in cancer cells that occurs through a variety of mechanisms. This study evaluated apoptotic cell death and cell cycle arrest induced by an MTX derivative (MTX diethyl ester [MTX(OEt)2]) and MTX(OEt)2-loaded lipid-core nanocapsules in two MTX-resistant breast adenocarcinoma cell lines, MCF-7 and MDA-MB-231. The formulations prepared presented adequate granulometric profile. The treatment responses were evaluated through flow cytometry. Relying on the mechanism of resistance, we observed different responses between cell lines. For MCF-7 cells, MTX(OEt)2 solution and MTX(OEt)2-loaded lipid-core nanocapsules presented significantly higher apoptotic rates than untreated cells and cells incubated with unloaded lipid-core nanocapsules. For MDA-MB-231 cells, MTX(OEt)2-loaded lipid-core nanocapsules were significantly more efficient in inducing apoptosis than the solution of the free drug. S-phase cell cycle arrest was induced only by MTX(OEt)2 solution. The drug nanoencapsulation improved apoptosis induction for the cell line that presents MTX resistance by lack of transport receptors. PMID:24741306

New Method for Astrometric Measurements in Space Mission, JASMINE.

NASA Astrophysics Data System (ADS)

Yano, T.; Gouda, N.; Yamada, Y.

2006-08-01

We present a new method for measuring positions of stars in the Milky Way Galaxy by astrometric satellite, JASMINE, which is in progress at the National Astronomical Observatory of Japan. JASMINE is the acronym of the Japan Astrometry Satellite Mission for Infrared (z-band : 0.9 micron) Exploration, and is planned to be launched around 2015 The main objective of JASMINE is to study the fundamental structure and evolution of the bulge components of the Milky Way Galaxy. In order to accomplish these objectives, JASMINE will measure trigonometric parallaxes, positions and proper motions of about a few million stars during the observational program, with the precision of 10 microarcsec at z =14mag. The telescope of JASMINE has just one field of view, which is different from other astrometric satellites like Hipparcos and GAIA, that have two fields of view with large angle. These satellites, Hipparcos and GAIA, scan along the great circle with the spin axis perpendicular to both two fields of view to estimate the relative positions of stars on the great circle. They scan many different great circles to observe all the sky. On the other hand, JASMINE will take overlapping fields of view without any gaps to survey an area of about 20deg*10deg. Accordingly survey area covers the region of about 20deg*10deg in the bulge component. JASMINE will continue the above procedure for observing the area during the mission life. As a consequence, JASMINE will observe the restricted regions around the Galactic bulge and sweep repeatedly. The mission life is planned to be 5 years.

A detector interferometric calibration experiment for high precision astrometry

NASA Astrophysics Data System (ADS)

Crouzier, A.; Malbet, F.; Henault, F.; Léger, A.; Cara, C.; LeDuigou, J. M.; Preis, O.; Kern, P.; Delboulbe, A.; Martin, G.; Feautrier, P.; Stadler, E.; Lafrasse, S.; Rochat, S.; Ketchazo, C.; Donati, M.; Doumayrou, E.; Lagage, P. O.; Shao, M.; Goullioud, R.; Nemati, B.; Zhai, C.; Behar, E.; Potin, S.; Saint-Pe, M.; Dupont, J.

2016-11-01

Context. Exoplanet science has made staggering progress in the last two decades, due to the relentless exploration of new detection methods and refinement of existing ones. Yet astrometry offers a unique and untapped potential of discovery of habitable-zone low-mass planets around all the solar-like stars of the solar neighborhood. To fulfill this goal, astrometry must be paired with high precision calibration of the detector. Aims: We present a way to calibrate a detector for high accuracy astrometry. An experimental testbed combining an astrometric simulator and an interferometric calibration system is used to validate both the hardware needed for the calibration and the signal processing methods. The objective is an accuracy of 5 × 10-6 pixel on the location of a Nyquist sampled polychromatic point spread function. Methods: The interferometric calibration system produced modulated Young fringes on the detector. The Young fringes were parametrized as products of time and space dependent functions, based on various pixel parameters. The minimization of function parameters was done iteratively, until convergence was obtained, revealing the pixel information needed for the calibration of astrometric measurements. Results: The calibration system yielded the pixel positions to an accuracy estimated at 4 × 10-4 pixel. After including the pixel position information, an astrometric accuracy of 6 × 10-5 pixel was obtained, for a PSF motion over more than five pixels. In the static mode (small jitter motion of less than 1 × 10-3 pixel), a photon noise limited precision of 3 × 10-5 pixel was reached.

Astrometry in the globular cluster M13. II. Membership probabilities from old proper motions

DOE Office of Scientific and Technical Information (OSTI.GOV)

Cudworth, K.

Astrometric cluster membership probabilities have been derived from proper motions measured by other authors for stars in the region of the globular cluster M13. Several stars of individual interest are discussed.

The Caviar software package for the astrometric reduction of Cassini ISS images: description and examples

NASA Astrophysics Data System (ADS)

Cooper, N. J.; Lainey, V.; Meunier, L.-E.; Murray, C. D.; Zhang, Q.-F.; Baillie, K.; Evans, M. W.; Thuillot, W.; Vienne, A.

2018-02-01

Aims: Caviar is a software package designed for the astrometric measurement of natural satellite positions in images taken using the Imaging Science Subsystem (ISS) of the Cassini spacecraft. Aspects of the structure, functionality, and use of the software are described, and examples are provided. The integrity of the software is demonstrated by generating new measurements of the positions of selected major satellites of Saturn, 2013-2016, along with their observed minus computed (O-C) residuals relative to published ephemerides. Methods: Satellite positions were estimated by fitting a model to the imaged limbs of the target satellites. Corrections to the nominal spacecraft pointing were computed using background star positions based on the UCAC5 and Tycho2 star catalogues. UCAC5 is currently used in preference to Gaia-DR1 because of the availability of proper motion information in UCAC5. Results: The Caviar package is available for free download. A total of 256 new astrometric observations of the Saturnian moons Mimas (44), Tethys (58), Dione (55), Rhea (33), Iapetus (63), and Hyperion (3) have been made, in addition to opportunistic detections of Pandora (20), Enceladus (4), Janus (2), and Helene (5), giving an overall total of 287 new detections. Mean observed-minus-computed residuals for the main moons relative to the JPL SAT375 ephemeris were - 0.66 ± 1.30 pixels in the line direction and 0.05 ± 1.47 pixels in the sample direction. Mean residuals relative to the IMCCE NOE-6-2015-MAIN-coorb2 ephemeris were -0.34 ± 0.91 pixels in the line direction and 0.15 ± 1.65 pixels in the sample direction. The reduced astrometric data are provided in the form of satellite positions for each image. The reference star positions are included in order to allow reprocessing at some later date using improved star catalogues, such as later releases of Gaia, without the need to re-estimate the imaged star positions. The Caviar software is available for free download from: ftp://ftp://ftp.imcce.fr/pub/softwares/caviar.Full Tables 1 and 5 are only available at the CDS via anonymous ftp to http://cdsarc.u-strasbg.fr (http://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/610/A2

Astrometry of Solar System Objects with Gaia

NASA Astrophysics Data System (ADS)

Hestroffer, Daniel J.; Arenou, Frederic; Desmars, Josselin; Robert, Vincent; Thuillot, William; Arlot, Jean-Eudes; Carry, Benoit; David, Pedro; Eggl, Siegfried; Fabricius, Claus; Kudryashova, Maria; Lainey, Valery; Spoto, Federica; Tanga, Paolo; Gaia DPAC

2016-10-01

The Gaia ESA space mission will provide astrometric observations of a large number of celestial bodies, with unprecedented accuracy, and in an homogenous reference frame (to become the optical ICRF). The Gaia satellite is monitoring regularly the whole celestial sphere, with one complete scan in about 6month, down to approximately magnitude V≤20.7. It will provide after its nominal lifetime, (5 years, 2014-2019) about 70 astrometric points for several hundred thousands of solar system objects, asteroids from the Near-Earth region to Centaurs and bright TNOs, as well as planetary satellites and comets. The highly precise astrometric and photometric data is bound to lead to huge advances in the science of small Small Solar System Bodies (e.g. Tanga et al. 2016 P\\&SS, Hestroffer et al. 2014 COSPAR #40 ; Mignard et al. 2007 EMP).The first Gaia data release (GDR#1) is foreseen for Q3-2016 and will provide highly precise positions of selected stars down to mag V≈20. While solar system objets data is foreseen for the next data release (in 2017), science of Solar System will also highly benefit from the Gaia stellar catalogue. We will present the status of the satellite and Gaia mission, and details on the stellar data that will be published in this GDR#1. We discuss the catalogue content, number of stars, parameters and precisions, and the process of cross-matching and validation. We also touch upon the construction of combined Tycho-Gaia TGAS catalogue.A Gaia data daily processing is devoted to the identification of Solar System Objects. During this process the detection of new (or critical) objects arises and leads to the triggering of scientific alerts to be found on the web gaiafunsso.imcce.fr. We have also set up an international follow-up network called Gaia-FUN-SSO to validate the detection in space. For this goal, in case of detection the observational data must be sent to the MPC by the observers. Besides, Gaia should benefit for the classical astrometric reduction, for future as well as for past observations, which is part of the NAROO project (Robert et al. 2015 A&A). We will also touch upon the next releases steps, and the SSO data from Gaia observations that will be published.

Resolved astrometric orbits of ten O-type binaries

NASA Astrophysics Data System (ADS)

Le Bouquin, J.-B.; Sana, H.; Gosset, E.; De Becker, M.; Duvert, G.; Absil, O.; Anthonioz, F.; Berger, J.-P.; Ertel, S.; Grellmann, R.; Guieu, S.; Kervella, P.; Rabus, M.; Willson, M.

2017-05-01

Aims: Our long-term aim is to derive model-independent stellar masses and distances for long period massive binaries by combining apparent astrometric orbit with double-lined radial velocity amplitudes (SB2). Methods: We followed-up ten O+O binaries with AMBER, PIONIER and GRAVITY at the VLTI. Here, we report on 130 astrometric observations over the last seven years. We combined this dataset with distance estimates to compute the total mass of the systems. We also computed preliminary individual component masses for the five systems with available SB2 radial velocities. Results: Nine of the ten binaries have their three-dimensional orbit well constrained. Four of them are known to be colliding wind, non-thermal radio emitters, and thus constitute valuable targets for future high angular resolution radio imaging. Two binaries break the correlation between period and eccentricity tentatively observed in previous studies. This suggests either that massive star formation produces a wide range of systems, or that several binary formation mechanisms are at play. Finally, we found that the use of existing SB2 radial velocity amplitudes can lead to unrealistic masses and distances. Conclusions: If not understood, the biases in radial velocity amplitudes will represent an intrinsic limitation for estimating dynamical masses from SB2+interferometry or SB2+Gaia. Nevertheless, our results can be combined with future Gaia astrometry to measure the dynamical masses and distances of the individual components with an accuracy of 5 to 15%, completely independently of the radial velocities. Based on observations collected with the PIONIER/VLTI, AMBER/VLTI and GRAVITY/VLTI instruments at the European Southern Observatory, Paranal, under programs 087.C-0458, 087.D-0150, 087.D-0264, 090.D-0036, 090.D-0291, 090.D-0600, 091.D-0087, 091.D-0334, 092.C-0243, 092.C-0542, 092.D-0015, 092.D-0366, 092.D-0590, 092.D-0647, 093.C-0503, 093.D-0039, 093.D-0040, 093.D-0673, 094.C-0397, 094.C-0884, 189.C-0644, 60.A-9168, 096.D-0114.The list of astrometric positions is only available at the CDS via anonymous ftp to http://cdsarc.u-strasbg.fr (http://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/601/A34

Conductive cable fibers with insulating surface prepared by co-axial electrospinning of multi-walled nanotubes and cellulose

PubMed Central

Miyauchi, Minoru; Miao, Jianjun; Simmons, Trevor J.; Lee, Jong-Won; Doherty, Thomas V.; Dordick, Jonathan S.; Linhardt, Robert J.

2010-01-01

A core-sheath of multi-walled carbon nanotube (MWNT)-cellulose fibers of diameters from several hundreds nm to several µm were prepared by co-axial electrospinning from a non-valatile, non-flammable ionic liquid (IL) solvent, 1-methyl-3-methylimidazolium acetate ([EMIM][Ac]). MWNTs were dispersed in IL to form a gel solution. This gel core solution was electrospun surrounded by a sheath solution of cellulose disolved in the same IL. Electrospun fibers were collected in a coagulation bath containing ethanol-water to completely remove the IL and dried to form a core-sheath MWNT-cellulose fibers having a cable structure with a conductive core and insulating sheath. Enzymatic treatment of a portion of a mat of these fibers with cellulase selectively removed the cellulose sheath exposing the MWNT core for connection to an electrode. These MWNT-cellulose fiber mats demonstrated excellent conductivity due to a conductive pathway of bundleled MWNTs. Fiber mat conductivity increased with increasing ratio of MWNT in the fibers with a maximum conductivity of 10.7 S/m obtained at 45 wt% MWNT loading. PMID:20690644

Conductive cable fibers with insulating surface prepared by coaxial electrospinning of multiwalled nanotubes and cellulose.

PubMed

Miyauchi, Minoru; Miao, Jianjun; Simmons, Trevor J; Lee, Jong-Won; Doherty, Thomas V; Dordick, Jonathan S; Linhardt, Robert J

2010-09-13

Core-sheath multiwalled carbon nanotube (MWNT)-cellulose fibers of diameters from several hundreds of nanometers to several micrometers were prepared by coaxial electrospinning from a nonvolatile, nonflammable ionic liquid (IL) solvent, 1-methyl-3-methylimidazolium acetate ([EMIM][Ac]). MWNTs were dispersed in IL to form a gel solution. This gel core solution was electrospun surrounded by a sheath solution of cellulose dissolved in the same IL. Electrospun fibers were collected in a coagulation bath containing ethanol-water to remove the IL completely and dried to form core-sheath MWNT-cellulose fibers having a cable structure with a conductive core and insulating sheath. Enzymatic treatment of a portion of a mat of these fibers with cellulase selectively removed the cellulose sheath exposing the MWNT core for connection to an electrode. These MWNT-cellulose fiber mats demonstrated excellent conductivity because of a conductive pathway of bundled MWNTs. Fiber mat conductivity increased with increasing ratio of MWNT in the fibers with a maximum conductivity of 10.7 S/m obtained at 45 wt % MWNT loading.

On the Possibilities of Predicting Geomagnetic Secular Variation with Geodynamo Modeling

NASA Technical Reports Server (NTRS)

Kuang, Wei-Jia; Tangborn, Andrew; Sabaka, Terrance

2004-01-01

We use our MoSST core dynamics model and geomagnetic field at the core-mantle boundary (CMB) continued downward from surface observations to investigate possibilities of geomagnetic data assimilation, so that model results and current geomagnetic observations can be used to predict geomagnetic secular variation in future. As the first attempt, we apply data insertion technique to examine evolution of the model solution that is modified by geomagnetic input. Our study demonstrate that, with a single data insertion, large-scale poloidal magnetic field obtained from subsequent numerical simulation evolves similarly to the observed geomagnetic variation, regardless of the initial choice of the model solution (so long it is a well developed numerical solution). The model solution diverges on the time scales on the order of 60 years, similar to the time scales of the torsional oscillations in the Earth's core. Our numerical test shows that geomagnetic data assimilation is promising with our MoSST model.

DASTCOM5: A Portable and Current Database of Asteroid and Comet Orbit Solutions

NASA Astrophysics Data System (ADS)

Giorgini, Jon D.; Chamberlin, Alan B.

2014-11-01

A portable direct-access database containing all NASA/JPL asteroid and comet orbit solutions, with the software to access it, is available for download (ftp://ssd.jpl.nasa.gov/pub/xfr/dastcom5.zip; unzip -ao dastcom5.zip). DASTCOM5 contains the latest heliocentric IAU76/J2000 ecliptic osculating orbital elements for all known asteroids and comets as determined by a least-squares best-fit to ground-based optical, spacecraft, and radar astrometric measurements. Other physical, dynamical, and covariance parameters are included when known. A total of 142 parameters per object are supported within DASTCOM5. This information is suitable for initializing high-precision numerical integrations, assessing orbit geometry, computing trajectory uncertainties, visual magnitude, and summarizing physical characteristics of the body. The DASTCOM5 distribution is updated as often as hourly to include newly discovered objects or orbit solution updates. It includes an ASCII index of objects that supports look-ups based on name, current or past designation, SPK ID, MPC packed-designations, or record number. DASTCOM5 is the database used by the NASA/JPL Horizons ephemeris system. It is a subset exported from a larger MySQL-based relational Small-Body Database ("SBDB") maintained at JPL. The DASTCOM5 distribution is intended for programmers comfortable with UNIX/LINUX/MacOSX command-line usage who need to develop stand-alone applications. The goal of the implementation is to provide small, fast, portable, and flexibly programmatic access to JPL comet and asteroid orbit solutions. The supplied software library, examples, and application programs have been verified under gfortran, Lahey, Intel, and Sun 32/64-bit Linux/UNIX FORTRAN compilers. A command-line tool ("dxlook") is provided to enable database access from shell or script environments.

Astrometria diferencial de precision con VLBI el triangulo de Draco (y estudios de SN1993J)

NASA Astrophysics Data System (ADS)

Ros, E.

1997-11-01

The Very Long Baseline Interferometry (VLBI) technique provides unprecedented resolutions in astronomy. In this PhD we show progress in the study of high precision phase-delay differential astrometry through observations of the radio source triangle formed by the BL-Lac objects 1803+784 and 2007+777, and the QSO 1928+738, in the Northern constellation of Draco (the Dragon), from observations carried out on 20/21 November 1991 with an intercontinental interferometric array simultaneously at the frequencies of 2.3 and 8.4 GHz. We have determined the angular separations among the three radio sources with submilliarcsecond accuracy from a weighted least squares analysis of the differential phase delay from the three celestial bodies. Our present work introduces important advances with respect to previous astrometric studies, carried out over radio source pairs separated by smaller angular distances. We have consistently modeled the parameters involved in an astrometric VLBI observation, in order to reproduce the differential phase observed for radio sources separated by almost 7o on the sky. We have demonstrated the possibility of phase-connection over these angular distances at 8.4 GHz, even at an epoch of a maximum in the solar activity. After the phase-connection we have corrected the effects of the extended structure of the radio source and of the ionosphere. This last correction is one of the main technical achievements of this thesis: it is possible to remove the ionospheric contribution with independent measurements of the ionosphere total electron content obtained at Global Positioning Systems (GPS) sites the VLBI observing stations. The triangular geometry introduces constraints in parameter space that allow a better estimation of the angular separations among the radio sources. It is possible to test the consistency of the astrometric results through the Sky-Closure, defined as the circular sum of the angular separations of the three radio sources, determined pairwise and independently. In our case it is consistent with zero, and verifies satisfactorily the data process followed. The comparison of the measurements of the separations of the pair 1928+738/2007+777 (1991 data) with previous measurements (data from 1985 and 1988), carried out with the same technique, allows us to register adequately the absolute position of 1928+738 relative to 2007+777. We estimate the proper motion of components in 1928+738, and also identify the position of the radio source core. We confirm the superluminal motion of the components of 1928+738. The comparison of our results with those obtained by Eubanks (USNO) from group delay measurements (without structure correction) show the incorrectness of the latter. We also include succinctly in this PhD my colaboration in the work on the radio supernova SN 1993J, in galaxy M81. We have discovered a shell-like structure of the radio emission of SN 1993J which exploded on March 1993. We have also elaborated a movie of its evolution, by monitoring the shell structure for different epochs, and determined the deceleration of its expansion.

Test Scheduling for Core-Based SOCs Using Genetic Algorithm Based Heuristic Approach

NASA Astrophysics Data System (ADS)

Giri, Chandan; Sarkar, Soumojit; Chattopadhyay, Santanu

This paper presents a Genetic algorithm (GA) based solution to co-optimize test scheduling and wrapper design for core based SOCs. Core testing solutions are generated as a set of wrapper configurations, represented as rectangles with width equal to the number of TAM (Test Access Mechanism) channels and height equal to the corresponding testing time. A locally optimal best-fit heuristic based bin packing algorithm has been used to determine placement of rectangles minimizing the overall test times, whereas, GA has been utilized to generate the sequence of rectangles to be considered for placement. Experimental result on ITC'02 benchmark SOCs shows that the proposed method provides better solutions compared to the recent works reported in the literature.

The direct identification of core-collapse supernova progenitors.

PubMed

Van Dyk, Schuyler D

2017-10-28

To place core-collapse supernovae (SNe) in context with the evolution of massive stars, it is necessary to determine their stellar origins. I describe the direct identification of SN progenitors in existing pre-explosion images, particularly those obtained through serendipitous imaging of nearby galaxies by the Hubble Space Telescope I comment on specific cases representing the various core-collapse SN types. Establishing the astrometric coincidence of a SN with its putative progenitor is relatively straightforward. One merely needs a comparably high-resolution image of the SN itself and its stellar environment to perform this matching. The interpretation of these results, though, is far more complicated and fraught with larger uncertainties, including assumptions of the distance to and the extinction of the SN, as well as the metallicity of the SN environment. Furthermore, existing theoretical stellar evolutionary tracks exhibit significant variations one from the next. Nonetheless, it appears fairly certain that Type II-P (plateau) SNe arise from massive stars in the red supergiant phase. Many of the known cases are associated with subluminous Type II-P events. The progenitors of Type II-L (linear) SNe are less established. Among the stripped-envelope SNe, there are now a number of examples of cool, but not red, supergiants (presumably in binaries) as Type IIb progenitors. We appear now finally to have an identified progenitor of a Type Ib SN, but no known example yet for a Type Ic. The connection has been made between some Type IIn SNe and progenitor stars in a luminous blue variable phase, but that link is still thin, based on direct identifications. Finally, I also describe the need to revisit the SN site, long after the SN has faded, to confirm the progenitor identification through the star's disappearance and potentially to detect a putative binary companion that may have survived the explosion.This article is part of the themed issue 'Bridging the gap: from massive stars to supernovae'. © 2017 The Author(s).

MPACT Standard Input User s Manual, Version 2.2.0

DOE Office of Scientific and Technical Information (OSTI.GOV)

Collins, Benjamin S.; Downar, Thomas; Fitzgerald, Andrew

The MPACT (Michigan PArallel Charactistics based Transport) code is designed to perform high-fidelity light water reactor (LWR) analysis using whole-core pin-resolved neutron transport calculations on modern parallel-computing hardware. The code consists of several libraries which provide the functionality necessary to solve steady-state eigenvalue problems. Several transport capabilities are available within MPACT including both 2-D and 3-D Method of Characteristics (MOC). A three-dimensional whole core solution based on the 2D-1D solution method provides the capability for full core depletion calculations.

Shape sensing using multi-core fiber optic cable and parametric curve solutions.

PubMed

Moore, Jason P; Rogge, Matthew D

2012-01-30

The shape of a multi-core optical fiber is calculated by numerically solving a set of Frenet-Serret equations describing the path of the fiber in three dimensions. Included in the Frenet-Serret equations are curvature and bending direction functions derived from distributed fiber Bragg grating strain measurements in each core. The method offers advantages over prior art in that it determines complex three-dimensional fiber shape as a continuous parametric solution rather than an integrated series of discrete planar bends. Results and error analysis of the method using a tri-core optical fiber is presented. Maximum error expressed as a percentage of fiber length was found to be 7.2%.

DISTRIBUTION COEFICIENTS (KD) GENERATED FROM A CORE SAMPLE COLLECTED FROM THE SALTSTONE DISPOSAL FACILITY

DOE Office of Scientific and Technical Information (OSTI.GOV)

Almond, P.; Kaplan, D.

Core samples originating from Vault 4, Cell E of the Saltstone Disposal Facility (SDF) were collected in September of 2008 (Hansen and Crawford 2009, Smith 2008) and sent to SRNL to measure chemical and physical properties of the material including visual uniformity, mineralogy, microstructure, density, porosity, distribution coefficients (K{sub d}), and chemical composition. Some data from these experiments have been reported (Cozzi and Duncan 2010). In this study, leaching experiments were conducted with a single core sample under conditions that are representative of saltstone performance. In separate experiments, reducing and oxidizing environments were targeted to obtain solubility and Kd valuesmore » from the measurable species identified in the solid and aqueous leachate. This study was designed to provide insight into how readily species immobilized in saltstone will leach from the saltstone under oxidizing conditions simulating the edge of a saltstone monolith and under reducing conditions, targeting conditions within the saltstone monolith. Core samples were taken from saltstone poured in December of 2007 giving a cure time of nine months in the cell and a total of thirty months before leaching experiments began in June 2010. The saltstone from Vault 4, Cell E is comprised of blast furnace slag, class F fly ash, portland cement, and Deliquification, Dissolution, and Adjustment (DDA) Batch 2 salt solution. The salt solution was previously analyzed from a sample of Tank 50 salt solution and characterized in the 4QCY07 Waste Acceptance Criteria (WAC) report (Zeigler and Bibler 2009). Subsequent to Tank 50 analysis, additional solution was added to the tank solution from the Effluent Treatment Project as well as from inleakage from Tank 50 pump bearings (Cozzi and Duncan 2010). Core samples were taken from three locations and at three depths at each location using a two-inch diameter concrete coring bit (1-1, 1-2, 1-3; 2-1, 2-2, 2-3; 3-1, 3-2, 3-3) (Hansen and Crawford 2009). Leaching experiments were conducted with a section of core sample 3-2. All cores from location 3 were drilled without using water. Core sample 3-2 was drilled from approximately six inches to a depth of approximately 13 inches. Approximately six inches of the core was removed but it broke into two pieces during removal from the bit. At the time of drilling, core material appeared olive green in color (Smith 2008). The fact that the samples were cored as olive green and were received after storage with a gray outer layer is indicative that some oxidation had occurred prior to leaching studies.« less

Torque Balances on the Taylor Cylinders in the Geomagnetic Data Assimilation

NASA Technical Reports Server (NTRS)

Kuang, Weijia; Tangborn, Andrew

2004-01-01

In this presentation we report on our continuing effort in geomagnetic data assimilation, aiming at understanding and predicting geomagnetic secular variation on decadal time scales. In particular, we focus on the effect of the torque balances on the cylindrical surfaces in the core co-axial with the Earth's rotation axis (the Taylor cylinders) on the time evolution of assimilated solutions. We use our MoSST core dynamics,model and observed geomagnetic field at the Earth's surface derived via Comprehensive Field Model (CFM) for the geomagnetic data assimilation. In our earlier studies, a model solution is selected randomly from our numerical database. It is then assimilated with the observations such that the poloidal field possesses the same field tomography on the core-mantel boundary (CMB) continued downward from surface observations. This tomography change is assumed to be effective through out the outer core. While this approach allows rapid convergence between model solutions and the observations, it also generates sevee numerical instabilities: the delicate balance between weak fluid inertia and the magnetic torques on the Taylor cylinders are completely altered. Consequently, the assimilated solution diverges quickly (in approximately 10% of the magnetic free-decay time in the core). To improve the assimilation, we propose a partial penetration of the assimilation from the CMB: The full-scale modification at the CMB decreases linearly and vanish at an interior radius r(sub a). We shall examine from our assimilation tests possible relationships between the convergence rate of the model solutions to observations and the cut-off radius r(sub a). A better assimilation shall serve our nudging tests in near future.

Torque Balances on the Taylor Cylinders in the Geomagnetic Data Assimilation

NASA Astrophysics Data System (ADS)

Kuang, W.; Tangborn, A.

2004-05-01

In this presentation we report on our continuing effort in geomagnetic data assimilation, aiming at understanding and predicting geomagnetic secular variation on decadal time scales. In particular, we focus on the effect of the torque balances on the cylindrical surfaces in the core co-axial with the Earth's rotation axis (the Taylor cylinders) on the time evolution of assimilated solutions. We use our MoSST core dynamics model and observed geomagnetic field at the Earth's surface derived via Comprehensive Field Model (CFM) for the geomagnetic data assimilation. In our earlier studies, a model solution is selected randomly from our numerical database. It is then assimilated with the observations such that the poloidal field possesses the same field tomography on the core-mantel boundary (CMB) continued downward from surface observations. This tomography change is assumed to be effective through out the outer core. While this approach allows rapid convergence between model solutions and the observations, it also generates sever numerical instabilities: the delicate balance between weak fluid inertia and the magnetic torques on the Taylor cylinders are completely altered. Consequently, the assimilated solution diverges quickly (in approximately 10% of the magnetic free-decay time in the core). To improve the assimilation, we propose a partial penetration of the assimilation from the CMB: The full-scale modification at the CMB decreases linearly and vanish at an interior radius ra. We shall examine from our assimilation tests possible relationships between the convergence rate of the model solutions to observations and the cut-off radius ra. A better assimilation shall serve our nudging tests in near future.

Determination of Hydraulic and Transport Parameters of Organic Chemical and Inorganic Anions Solutes for Unfractured Cores of Berea Sandstone Using a Hydraulic Coreholder

NASA Astrophysics Data System (ADS)

Blanford, W. J.; Neil, L.

2017-12-01

To better evaluate the potential for toxic organic chemicals to migrate upward through the rock strata from hydraulic fracturing zones and into groundwater resources, a series of miscible displacement solute transport studies of cores of Berea Sandstone have been conducted using hydrostatic core holder. These tests involved passing aqueous solutions with natural background level of salts using a high pressure LC pump through 2 in wide by 3 in long unfractured cores held within the holder. Relative solute transport of 100 to 500ml pulses of target solutes including a series of chlorinated solvents and methylated benzenes was measured through in-line UV and fluorescence detectors and manual sampling and analysis with GCMS. The results found these sandstones to result in smooth ideal shaped breakthrough curves. Analysis with 1D transport models (CXTFIT) of the results found strong correlation with chemical parameters (diffusion coefficients, aqueous solubility, and octanol-water partitioning coefficients) showing that these parameter and QSPR relationships can be used to make accurate predictions for such a system. In addition to the results of the studies, lessons learned from this novel use of a coreholder for evaluation of porosity, water-saturated permeability, and solute transport of these sandstones (K = 1.5cm/day) and far less permeable sandstones samples (K = 0.15 cm/yr) from a hydraulic fracturing site in central Pennsylvania will be presented.

Influence of internal composition on physicochemical properties of alginate aqueous-core capsules.

PubMed

Ben Messaoud, Ghazi; Sánchez-González, Laura; Probst, Laurent; Desobry, Stéphane

2016-05-01

To enhance physicochemical properties of alginate aqueous-core capsules, conventional strategies were focused in literature on designing composite and coated capsules. In the present study, own effect of liquid-core composition on mechanical and release properties was investigated. Capsules were prepared by dripping a CaCl2 solution into an alginate gelling solution. Viscosity of CaCl2 solution was adjusted by adding cationic, anionic and non-ionic naturally derived polymers, respectively chitosan, xanthan gum and guar gum. In parallel, uniform alginate hydrogels were prepared by different methods (pouring, in situ forming and mixing). Mechanical stability of capsules and plane hydrogels were respectively evaluated by compression experiments and small amplitude oscillatory shear rheology and then correlated. Capsules permeability was evaluated by monitoring diffusion of encapsulated cochineal dye, riboflavin and BSA. The core-shell interactions were investigated by ATR-FTIR. Results showed that inner polymer had an impact on membrane stability and could act as an internal coating or provide mechanical reinforcement. Mechanical properties of alginate capsules were in a good agreement with rheological behavior of plane hydrogels. Release behavior of the entrapped molecules changed considerably. This study demonstrated the importance of aqueous-core composition, and gave new insights for possible adjusting of microcapsules physicochemical properties by modulating core-shell interactions. Copyright © 2016 Elsevier Inc. All rights reserved.

Radiation Hardened DDR2 SDRAM Solution

NASA Astrophysics Data System (ADS)

Wang, Pierre-Xiao; Sellier, Charles

2016-08-01

The Radiation Hardened (RH) DDR2 SDRAM Solution is a User's Friendly, Plug-and-Play and Radiation Hardened DDR2 solution, which includes the radiation tolerant stacking DDR2 modules and a radiation intelligent memory controller (RIMC) IP core. It provides a high speed radiation hardened by design DRAM solution suitable for all space applications such as commercial or scientific geo-stationary missions, earth observation, navigation, manned space vehicles and deep space scientific exploration. The DDR2 module has been guaranteed with SEL immune and TID > 100Krad(Si), on the other hand the RIMC IP core provides a full protection against the DDR2 radiation effects such as SEFI and SEU.

New interpretation of data of the Earth's solid core

NASA Astrophysics Data System (ADS)

Guliyev, H. H.

2017-06-01

The commonly accepted scientific opinions on the inner core as the deformable solid globe are based on the solution of the problem on the distribution of elastic parameters in the inner structures of the Earth. The given solution is obtained within the necessary integral conditions on its self-weight, moment of inertia concerning the axes of rotation and periods of free oscillations of the Earth. It is shown that this solution does not satisfy the mechanics of the deformable solid body with sufficient local conditions following from basic principles concerning the strength, stability and actuality of velocities of propagation of elastic waves. The violation of local conditions shows that the inner core cannot exist in the form of the deformable solid body within the commonly accepted elastic parameters.

Precision Orbit of δ Delphini and Prospects for Astrometric Detection of Exoplanets

NASA Astrophysics Data System (ADS)

Gardner, Tyler; Monnier, John D.; Fekel, Francis C.; Williamson, Mike; Duncan, Douglas K.; White, Timothy R.; Ireland, Michael; Adams, Fred C.; Barman, Travis; Baron, Fabien; ten Brummelaar, Theo; Che, Xiao; Huber, Daniel; Kraus, Stefan; Roettenbacher, Rachael M.; Schaefer, Gail; Sturmann, Judit; Sturmann, Laszlo; Swihart, Samuel J.; Zhao, Ming

2018-03-01

Combining visual and spectroscopic orbits of binary stars leads to a determination of the full 3D orbit, individual masses, and distance to the system. We present a full analysis of the evolved binary system δ Delphini using astrometric data from the MIRC and PAVO instruments on the CHARA long-baseline interferometer, 97 new spectra from the Fairborn Observatory, and 87 unpublished spectra from the Lick Observatory. We determine the full set of orbital elements for δ Del, along with masses of 1.78 ± 0.07 M ⊙ and 1.62 ± 0.07 M ⊙ for each component, and a distance of 63.61 ± 0.89 pc. These results are important in two contexts: for testing stellar evolution models and for defining the detection capabilities for future planet searches. We find that the evolutionary state of this system is puzzling, as our measured flux ratios, radii, and masses imply a ∼200 Myr age difference between the components, using standard stellar evolution models. Possible explanations for this age discrepancy include mass transfer scenarios with a now-ejected tertiary companion. For individual measurements taken over a span of two years, we achieve <10 μas precision on the differential position with 10 minute observations. The high precision of our astrometric orbit suggests that exoplanet detection capabilities are within reach of MIRC at CHARA. We compute exoplanet detection limits around δ Del and conclude that, if this precision is extended to wider systems, we should be able to detect most exoplanets >2 M J on orbits >0.75 au around individual components of hot binary stars via differential astrometry.

Astrometry for Astrophysics

NASA Astrophysics Data System (ADS)

van Altena, William F.

Part I. Astrometry in the Twenty-First Century: 1. Opportunities and challenges for astrometry in the twenty-first century M. Perryman; 2. Astrometric satellites L. Lindegren; 3. Ground-based opportunities for astrometry N. Zacharias; Part II. Relativistic Foundations of Astrometry and Celestial Mechanics: 4. Vectors in astrometry, an introduction L. Lindegren; 5. Relativistic principles of astrometry and celestial mechanics S. Klioner; 6. Celestial mechanics of the N-body problem S. Klioner; 7. Celestial coordinate systems and positions N. Capitaine and M. Stavinschi; 8. Fundamental algorithms for celestial coordinates and positions P. Wallace; Part III. Observing through the Atmosphere: 9. The Earth's atmosphere: refraction, turbulence, delays and limitations to astrometic precision W. van Altena and E. Fomalont; 10. Astrometry with ground-based diffraction-limited imaging A. Ghez; 11. Optical interferometry A. Glindermann; 12. Radio interferometry E. Fomalont; Part VI. From Detected Photons to the Celestial Sphere: 13. Geometrical optics and astrometry D. Schroeder; 14. CCD imaging detectors S. Howell; 15. Using CCDs in the time-delayed integration mode D. Rabinowitz; 16. Statistical astronomy A. Brown; 17. Analyzing poorly-sampled images: HST imaging astrometry J. Anderson; 18. Image deconvolution J. Nuñez; 19. From measures to celestial coordinates Z. H. Tang and W. van Altena; 20. Astrometric catalogs: concepts, history and necessity C. López; 21. Trigonometric parallaxes F. Benedict and B. McArthur; Part V. Applications of Astrometry to Topics in Astrophysics: 22. Galactic structure astrometry R. Méndez; 23. Binary and multiple stars E. Horch; 24. Binaries: HST, Hipparcos and Gaia D. Pourbaix; 25. Star clusters I. Platais; 26. Solar System astrometry F. Mignard; 27. Extrasolar planets A. Sozzetti; 28. Astrometric measurement and cosmology R. Easther; Appendices; Index.

Astrometry for Astrophysics

NASA Astrophysics Data System (ADS)

van Altena, William F.

2012-11-01

Part I. Astrometry in the Twenty-First Century: 1. Opportunities and challenges for astrometry in the twenty-first century M. Perryman; 2. Astrometric satellites L. Lindegren; 3. Ground-based opportunities for astrometry N. Zacharias; Part II. Relativistic Foundations of Astrometry and Celestial Mechanics: 4. Vectors in astrometry, an introduction L. Lindegren; 5. Relativistic principles of astrometry and celestial mechanics S. Klioner; 6. Celestial mechanics of the N-body problem S. Klioner; 7. Celestial coordinate systems and positions N. Capitaine and M. Stavinschi; 8. Fundamental algorithms for celestial coordinates and positions P. Wallace; Part III. Observing through the Atmosphere: 9. The Earth's atmosphere: refraction, turbulence, delays and limitations to astrometic precision W. van Altena and E. Fomalont; 10. Astrometry with ground-based diffraction-limited imaging A. Ghez; 11. Optical interferometry A. Glindermann; 12. Radio interferometry E. Fomalont; Part VI. From Detected Photons to the Celestial Sphere: 13. Geometrical optics and astrometry D. Schroeder; 14. CCD imaging detectors S. Howell; 15. Using CCDs in the time-delayed integration mode D. Rabinowitz; 16. StaStatistical astronomy A. Brown; 17. Analyzing poorly-sampled images: HST imaging astrometry J. Anderson; 18. Image deconvolution J. Nuñez; 19. From measures to celestial coordinates Z. H. Tang and W. van Altena; 20. Astrometric catalogs: concepts , history and necessity C. Löpez; 21. Trigonometric parallaxes F. Benedict and B. McArthur; Part V. Applications of Astrometry to Topics in Astrophysics: 22. Galactic structure astrometry R. Méndez; 23. Binary and multiple stars E. Horch; 24. Binaries: HST, Hipparcos and Gaia D. Pourbaix; 25. Star clusters I. Platais; 26. Solar System astrometry F. Mignard; 27. Extrasolar planets A. Sozzetti; 28. Astrometric measurement and cosmology R. Easther; Appendices; Index.

Astrometrically registered simultaneous observations of the 22 GHz H{sub 2}O and 43 GHz SiO masers toward R Leonis Minoris using KVN and source/frequency phase referencing

DOE Office of Scientific and Technical Information (OSTI.GOV)

Dodson, Richard; Rioja, María J.; Jung, Tae-Hyun

2014-11-01

Oxygen-rich asymptotic giant branch (AGB) stars can be intense emitters of SiO (v = 1 and 2, J = 1 → 0) and H{sub 2}O maser lines at 43 and 22 GHz, respectively. Very long baseline interferometry (VLBI) observations of the maser emission provide a unique tool to probe the innermost layers of the circumstellar envelopes in AGB stars. Nevertheless, the difficulties in achieving astrometrically aligned H{sub 2}O and v = 1 and v = 2 SiO maser maps have traditionally limited the physical constraints that can be placed on the SiO maser pumping mechanism. We present phase-referenced simultaneous spectral-linemore » VLBI images for the SiO v = 1 and v = 2, J = 1 → 0, and H{sub 2}O maser emission around the AGB star R LMi, obtained from the Korean VLBI Network (KVN). The simultaneous multi-channel receivers of the KVN offer great possibilities for astrometry in the frequency domain. With this facility, we have produced images with bona fide absolute astrometric registration between high-frequency maser transitions of different species to provide the positions of the H{sub 2}O maser emission and the center of the SiO maser emission, hence reducing the uncertainty in the proper motions for R LMi by an order of magnitude over that from Hipparcos. This is the first successful demonstration of source frequency phase referencing for millimeter VLBI spectral-line observations and also where the ratio between the frequencies is not an integer.« less

PARSEC's Astrometry - The Risky Approach

NASA Astrophysics Data System (ADS)

Andrei, A. H.

2015-10-01

Parallaxes - and hence the fundamental establishment of stellar distances - rank among the oldest, most direct, and hardest of astronomical determinations. Arguably amongst the most essential too. The direct approach to obtain trigonometric parallaxes, using a constrained set of equations to derive positions, proper motions, and parallaxes, has been labelled as risky. Properly so, because the axis of the parallactic apparent ellipse is smaller than one arcsec even for the nearest stars, and just a fraction of its perimeter can be followed. Thus the classical approach is of linearizing the description by locking the solution to a set of precise positions of the Earth at the instants of observation, rather than to the dynamics of its orbit, and of adopting a close examination of the few observations available. In the PARSEC program the parallaxes of 143 brown dwarfs were planned. Five years of observation of the fields were taken with the WFI camera at the ESO 2.2m telescope in Chile. The goal is to provide a statistically significant number of trigonometric parallaxes for BD sub-classes from L0 to T7. Taking advantage of the large, regularly spaced, quantity of observations, here we take the risky approach to fit an ellipse to the observed ecliptic coordinates and derive the parallaxes. We also combine the solutions from different centroiding methods, widely proven in prior astrometric investigations. As each of those methods assess diverse properties of the PSFs, they are taken as independent measurements, and combined into a weighted least-squares general solution. The results obtained compare well with the literature and with the classical approach.

New Astrometric Reduction of the USNO Photographic Plates of Planetary Satellites

NASA Astrophysics Data System (ADS)

de Cuyper, J.-P.; Winter, L.; de Decker, G.; Zacharias, N.; Pascu, D.; Arlot, J.-E.; Robert, V.; Lainey, V.

2009-09-01

An international collaboration has been set up between the US Naval Observatory (USNO) in Washington DC, the IMCCE of Paris Observatory (OBSPM) and the Royal Observatory of Belgium (ROB) to make a new astrometric reduction of the USNO archival photographic plates of planetary satellites. In order to obtain a better knowledge of their orbital motions these photographic plates are digitized with the new generation DAMIAN digitizer at the ROB, providing a geometric stability of better than 0.1 μm on the plates. We focus here on a subset of a few hundred photographic plates of the Galilean satellites, taken with the McCormick and the USNO 26-inch refractors between 1967 and 1998. Specific procedures and algorithms are used to obtain highly accurate positions using the Tycho2, UCAC2 (20 - 30 mas) and later the UCAC3 (10 - 20 mas) catalogues. A comparison with the MAMA digitizer of the Paris Observatory is made through the results obtained from digital mosaic images of the plates.

Absolute Nuv magnitudes of Gaia DR1 astrometric stars and a search for hot companions in nearby systems

NASA Astrophysics Data System (ADS)

Makarov, V. V.

2017-10-01

Accurate parallaxes from Gaia DR1 (TGAS) are combined with GALEX visual Nuv magnitudes to produce absolute Mnuv magnitudes and an ultraviolet HR diagram for a large sample of astrometric stars. A functional fit is derived of the lower envelope main sequence of the nearest 1403 stars (distance <40 pc), which should be reddening-free. Using this empirical fit, 50 nearby stars are selected with significant Nuv excess. These are predominantly late K and early M dwarfs, often associated with X-ray sources, and showing other manifestations of magnetic activity. The sample may include systems with hidden white dwarfs, stars younger than the Pleiades, or, most likely, tight interacting binaries of the BY Dra-type. A separate collection of 40 stars with precise trigonometric parallaxes and Nuv-G colors bluer than 2 mag is presented. It includes several known novae, white dwarfs, and binaries with hot subdwarf (sdOB) components, but most remain unexplored.

Space Astrometry Science with Gaia

NASA Astrophysics Data System (ADS)

Mignard, Francois

2009-05-01

The European Space Agency has formally approved in spring 2006 the overall funding of its next space astrometry mission Gaia scheduled for a launch in spring 2012. The mission will create an extraordinarily precise three-dimensional map of about one billion stars throughout our Galaxy and beyond from repeated astrometric and photometric observations over about five years. End-of-mission expected accuracies in wide angle astrometry fall in the 7-25 muas range for start brighter than 15 mag and sub-mas at the faint end (20 mag). The science covered by Gaia is broad and extends from galactic and stellar astrophysics to solar systems dynamics and physics and the construction of an inertial frame in the visible with extragalactic sources. Fundamental physics with general relativity testing will also be a major product of the mission. In the presentation I will overview the Gaia science case, stressing more specifically the astrometric side of the expected results and provide few hints on the overall organisation of the data analysis entrusted to the Data Processing and Analysis Consortium (DPAC).

Clarification of the formation process of the super massive black hole by Infrared astrometric satellite, Small-JASMINE

NASA Astrophysics Data System (ADS)

Yano, Taihei; JASMINE-WG

2018-04-01

Small-JASMINE (hearafter SJ), infrared astrometric satellite, will measure the positions and the proper motions which are located around the Galactic center, by operating at near infrared wave-lengths. SJ will clarify the formation process of the super massive black hole (hearafter SMBH) at the Galactic center. In particular, SJ will determine whether the SMBH was formed by a sequential merging of multiple black holes. The clarification of this formation process of the SMBH will contribute to a better understanding of merging process of satellite galaxies into the Galaxy, which is suggested by the standard galaxy formation scenario. A numerical simulation (Tanikawa and Umemura, 2014) suggests that if the SMBH was formed by the merging process, then the dynamical friction caused by the black holes have influenced the phase space distribution of stars. The phase space distribution measured by SJ will make it possible to determine the occurrences of the merging process.

A 1.3 giga pixels focal plane for GAIA

NASA Astrophysics Data System (ADS)

Laborie, Anouk; Pouny, Pierre; Vetel, Cyril; Collados, Emmanuel; Rougier, Gilles; Davancens, Robert; Zayer, Igor; Perryman, Michael; Pace, Oscar

2004-06-01

The astrometric mission GAIA is a cornerstone mission of the European Space Agency, due for launch in the 2010 time frame. Requiring extremely demanding performance GAIA calls for the development of an unprecedented large focal plane featuring innovative technologies. For securing the very challenging GAIA development, a significant number of technology activities have been initiated by ESA through a competitive selection process. In this context, an industrial consortium led by EADS-Astrium (France) with e2v technologies (UK) as major subcontractor was selected for the GAIA CCD and Focal Plane Technology Demonstrators programme, which is by far the most significant and the most critical GAIA pre-development for all aspects: science performance, development schedule and cost. This programme has started since August 2002 and will end early 2005 prior to commencement of the GAIA Phase B. While the GAIA payload will host three instruments and related focal planes, the major mission objectives are assigned to the Astrometric (ASTRO) Focal Plane, which is the subject of this presentation.

Application of the Allan Variance to Time Series Analysis in Astrometry and Geodesy: A Review.

PubMed

Malkin, Zinovy

2016-04-01

The Allan variance (AVAR) was introduced 50 years ago as a statistical tool for assessing the frequency standards deviations. For the past decades, AVAR has increasingly been used in geodesy and astrometry to assess the noise characteristics in geodetic and astrometric time series. A specific feature of astrometric and geodetic measurements, as compared with clock measurements, is that they are generally associated with uncertainties; thus, an appropriate weighting should be applied during data analysis. In addition, some physically connected scalar time series naturally form series of multidimensional vectors. For example, three station coordinates time series X, Y, and Z can be combined to analyze 3-D station position variations. The classical AVAR is not intended for processing unevenly weighted and/or multidimensional data. Therefore, AVAR modifications, namely weighted AVAR (WAVAR), multidimensional AVAR (MAVAR), and weighted multidimensional AVAR (WMAVAR), were introduced to overcome these deficiencies. In this paper, a brief review is given of the experience of using AVAR and its modifications in processing astrogeodetic time series.

VizieR Online Data Catalog: HST FGS-1r parallaxes for 8 metal-poor stars (Chaboyer+, 2017)

NASA Astrophysics Data System (ADS)

Chaboyer, B.; McArthur, B. E.; O'Malley, E.; Benedict, G. F.; Feiden, G. A.; Harrison, T. E.; McWilliam, A.; Nelan, E. P.; Patterson, R. J.; Sarajedini, A.

2017-08-01

Each program star was observed with the HST Advanced Camera for Surveys-Wide Field Camera (ACS/WFC) in the F606W and F814W filters. The CTE-corrected ACS/WFC images for the program stars were retrieved from MAST. These instrumental magnitudes were corrected for exposure time, matched to form colors, and calibrated to the VEGAMag and ground-based VI systems using the Sirianni+ (2005PASP..117.1049S) photometric transformations. Ground based photometry for all of our program stars were obtained using the New Mexico State University (NMSU) 1m telescope, the MDM 1.3m telescope, and the SMARTS 0.9m telescope. See appendix A1 for further details. We used HST FGS-1r, a two-axis interferometer, to make the astrometric observations. Eighty-nine orbits of HST astrometric observations were made between 2008 December and 2013 June. Every orbit contained several observations of the target and surrounding reference stars. (4 data files).

Astrometry with the VLT Interferometer

NASA Astrophysics Data System (ADS)

Quirrenbach, Andreas

The VLTI was originally conceived as an imaging instrument, providing a resolution of a few milliarcseconds at near-infrared wavelengths for studies of stars, circumstellar matter, and extragalactic objects. However, following the pioneering work on interferometric narrow-angle astrometry by Shao and Colavita (1992) and Colavita (1994), it was proposed that the VLTI could also be used for astrometric planet detection (Quirrenbach 1995). It was envisaged that the astrometric mode of the VLTI could be implemented by taking advantage of the large unvignetted field-of-view foreseen at that time (von der Lühe, Quirrenbach, & Koehler 1995). The idea of using the VLTI for narrowangle astrometry was embraced by ESO's Interferometry Science Advisory Committee (Paresce et al. 1996), but the technical concept for the delay lines has changed. The current plan for narrow-angle astrometry is based on dual star feeds at the telescopes and comprehensive internal laser metrology, as described in the PRIMA (Phase-Referenced Imaging and Microarcsecond Astrometry) study (Quirrenbach et al. 1998).

Observing exoplanet populations with high-precision astrometry

NASA Astrophysics Data System (ADS)

Sahlmann, Johannes

2012-06-01

This thesis deals with the application of the astrometry technique, consisting in measuring the position of a star in the plane of the sky, for the discovery and characterisation of extra-solar planets. It is feasible only with a very high measurement precision, which motivates the use of space observatories, the development of new ground-based astronomical instrumentation and of innovative data analysis methods: The study of Sun-like stars with substellar companions using CORALIE radial velocities and HIPPARCOS astrometry leads to the determination of the frequency of close brown dwarf companions and to the discovery of a dividing line between massive planets and brown dwarf companions; An observation campaign employing optical imaging with a very large telescope demonstrates sufficient astrometric precision to detect planets around ultra-cool dwarf stars and the first results of the survey are presented; Finally, the design and initial astrometric performance of PRIMA, ! a new dual-feed near-infrared interferometric observing facility for relative astrometry is presented.

Astrometric Telescope Facility preliminary systems definition study. Volume 1: Executive summary

NASA Technical Reports Server (NTRS)

Sobeck, Charlie

1987-01-01

The Astrometric Telescope Facility (ATF) is a spaceborne observatory proposed for use on the Space Station (SS) as an Initial Operating Capability (IOC) payload. The primary objective of the ATF will be the search for extrasolar planetary systems and a detailed investigation of any discovered systems. In addition, it will have the capability of conducting other astrophysics investigations; e.g., measuring precise distances and motions of stars within our galaxy. The purposes of the study were to: (1) define mission and system requirements; (2) define a strawman system concept for the facility at the Prephase A level; (3) define the need for additional trade studies or technology development; and (4) estimate program cost for the strawman concept. It has been assumed for the study that the ATF will be a SS payload, will use a SS-provided Coarse Pointing System (CPS), will meet SS constraints, and will make maximum use of existing flight qualified designs or designs to be qualified by the SS program for general SS use.

WFC3 Micro-arcsecond astrometry of the possible SNIa progenitor BPM 71214

NASA Astrophysics Data System (ADS)

Debes, John

2012-10-01

We propose to use the newly commissioned scanning mode on WFC3 to obtain astrometric measurements of the ~0.008 AU WD/M dwarf binary BPM 71214. This system is a fascinating mystery for post-common envelope binary evolution and may be a SN1a progenitor. COS spectra of the WD in the system shows that it is rapidly rotating with a vsin i of 200 km/s, implying that it has already accreted significant mass from its companion, but mass transfer has since stopped. The COS spectra imply a near Chandrasekar mass for the WD, while optical spectroscopy suggests a mass of 0.8 M_Sun. We propose to take four orbits of WFC3 observations in scanning mode to obtain astrometric measurements of this system at a per-measurement precision of ~30~micro-arcseconds. Such measurements will definitively constrain the mass of the WD and fully solve for both masses in the binary.

CCD astrometric observations of Saturnian satellites

NASA Astrophysics Data System (ADS)

Veiga, C. H.; Vieira Martins, R.; Vienne, A.; Thuillot, W.; Arlot, J.-E.

2003-03-01

Astrometric positions of the first eight largest Saturnian satellites and the Lagrangian satellites Helene, Telesto and Calypso are presented from 493 CCD frames taken at the oppositions in 1995 through 1999. The images were obtained over 27 nights. Observed positions are compared with the calculated ones from Vienne and Duriez TASS 1.7 for the large satellites and from JPL positions for the Lagrangian satellites. The rms is about 0farcs 12 for the former but 0farcs 20 for Iapetus and 0farcs 28 for Hyperion. For the Lagrangian satellites it is about 0farcs 21 for Helene, 2farcs 02 for Telesto and 0farcs 60 for Calypso. The catalog (Full Table \\ref{tab4}) is only available in electronic form at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/400/1095 Based on observations made at Laboratório Nacional de Astrofísica/MCT-Itajubá-Brazil.

Atronomical CCD observations of the main Saturn's satellites at Pulkovo Observatory in 2004-2007

NASA Astrophysics Data System (ADS)

Khrutskaya, E. V.; Kiseleva, T. P.; Izmailov, I. S.; Khovrichev, M. Yu.; Berezhnoy, A. A.

2009-08-01

The results of astrometric observations of Saturn’s satellites (S1-S8) obtained using a 26-inch refractor and a normal astrograph at Pulkovo Observatory in 2004-2007 are given. High-accuracy equatorial coordinates of Saturn’s satellites in the system of the UCAC2 reference catalog and the relative “satellite-satellite” positions suitable for specifying their motion theories are obtained. The observations are compared with the DE405 + TASS1.7 and INPOP06 + TASS1.7 theories of motion. The root-mean-square errors of the obtained satellite positions lie within the range of 10-50 mas, as far as the intrinsic convergence is concerned, and 20-70 mas, as far as the extrinsic one is concerned. The observation results are included into the astrometrical database of the Pulkovo Observatory ( www.puldb.ru ).

A Strong Radio Brightening at the Jet Base of M 87 during the Elevated Very High Energy Gamma-Ray State in 2012

NASA Astrophysics Data System (ADS)

Hada, K.; Giroletti, M.; Kino, M.; Giovannini, G.; D'Ammando, F.; Cheung, C. C.; Beilicke, M.; Nagai, H.; Doi, A.; Akiyama, K.; Honma, M.; Niinuma, K.; Casadio, C.; Orienti, M.; Krawczynski, H.; Gómez, J. L.; Sawada-Satoh, S.; Koyama, S.; Cesarini, A.; Nakahara, S.; Gurwell, M. A.

2014-06-01

We report our intensive, high angular resolution radio monitoring observations of the jet in M 87 with the VLBI Exploration of Radio Astrometry (VERA) and the European VLBI Network (EVN) from 2011 February to 2012 October, together with contemporaneous high-energy (100 MeV 100 GeV) γ rays by VERITAS. We detected a remarkable (up to ~70%) increase of the radio flux density from the unresolved jet base (radio core) with VERA at 22 and 43 GHz coincident with the VHE activity. Meanwhile, we confirmed with EVN at 5 GHz that the peculiar knot, HST-1, which is an alternative favored γ-ray production site located at gsim120 pc from the nucleus, remained quiescent in terms of its flux density and structure. These results in the radio bands strongly suggest that the VHE γ-ray activity in 2012 originates in the jet base within 0.03 pc or 56 Schwarzschild radii (the VERA spatial resolution of 0.4 mas at 43 GHz) from the central supermassive black hole. We further conducted VERA astrometry for the M 87 core at six epochs during the flaring period, and detected core shifts between 22 and 43 GHz, a mean value of which is similar to that measured in the previous astrometric measurements. We also discovered a clear frequency-dependent evolution of the radio core flare at 43, 22, and 5 GHz the radio flux density increased more rapidly at higher frequencies with a larger amplitude, and the light curves clearly showed a time-lag between the peaks at 22 and 43 GHz, the value of which is constrained to be within ~35-124 days. This indicates that a new radio-emitting component was created near the black hole in the period of the VHE event, and then propagated outward with progressively decreasing synchrotron opacity. By combining the obtained core shift and time-lag, we estimated an apparent speed of the newborn component propagating through the opaque region between the cores at 22 and 43 GHz. We derived a sub-luminal speed (less than ~0.2c) for this component. This value is significantly slower than the super-luminal (~1.1c) features that appeared from the core during the prominent VHE flaring event in 2008, suggesting that stronger VHE activity can be associated with the production of a higher Lorentz factor jet in M 87.

A Strong Radio Brightening At The Jet Base Of M 87 During The Elevated Very High Energy Gamma-Ray State In 2012

DOE PAGES

Hada, K.; Giroletti, M.; Kino, M.; ...

2014-06-04

We report our intensive, high-angular-resolution radio monitoring observations of the jet in M 87 with the VLBI Exploration of Radio Astrometry (VERA) and the European VLBI Network (EVN) from February 2011 to October 2012, together with contemporaneous high-energy (HE; 100 MeV< E <100 GeV) -ray light curves obtained by the Fermi Large Area Telescope (LAT). During this period (specifically from February 2012 to March 2012), an elevated level of the M 87 flux is reported at very-high-energy (VHE; E > 100 GeV) -rays by VERITAS. We detected a remarkable (up to ~70%) increase of the radio flux density from themore » unresolved jet base (radio core) with VERA at 22 and 43 GHz coincident with the VHE activity. Meanwhile, we confirmed with EVN at 5 GHz that the peculiar knot HST-1, which is an alternative favored -ray production site located at &120 pc from the nucleus, remained quiescent in terms of its flux density and structure. These results in the radio bands strongly suggest that the VHE -ray activity in 2012 originates in the jet base within 0.03 pc or 56 Schwarzschild radii (the VERA spatial resolution of 0.4 mas at 43 GHz) from the central supermassive black hole. We further conducted VERA astrometry for the M 87 core at six epochs during the flaring period, and detected core shifts between 22 and 43 GHz, a mean value of which is similar to that measured in the previous astrometric measurements. We also discovered a clear frequency-dependent evolution of the radio core flare at 43, 22 and 5 GHz; the radio flux density increased more rapidly at higher frequencies with a larger amplitude, and the light curves clearly showed a time-lag between the peaks at 22 and 43 GHz, the value of which is constrained to be within ~ 35 - 124 days. This indicates that a new radio-emitting component was created near the black hole in the period of the VHE event, and then propagated outward with progressively decreasing synchrotron opacity. By combining the obtained core shift and time-lag, we estimated an apparent speed of the newborn component propagating through the opaque region between the cores at 22 and 43 GHz. We derived a sub-luminal speed (less than ~0.2c) for this component. This value is significantly slower than the super-luminal (~1.1c) features that appeared from the core during the prominent VHE flaring event in 2008, suggesting that the stronger VHE activity can be associated with the production of the higher Lorentz factor jet in M 87.« less

Flow Field and Acoustic Predictions for Three-Stream Jets

NASA Technical Reports Server (NTRS)

Simmons, Shaun Patrick; Henderson, Brenda S.; Khavaran, Abbas

2014-01-01

Computational fluid dynamics was used to analyze a three-stream nozzle parametric design space. The study varied bypass-to-core area ratio, tertiary-to-core area ratio and jet operating conditions. The flowfield solutions from the Reynolds-Averaged Navier-Stokes (RANS) code Overflow 2.2e were used to pre-screen experimental models for a future test in the Aero-Acoustic Propulsion Laboratory (AAPL) at the NASA Glenn Research Center (GRC). Flowfield solutions were considered in conjunction with the jet-noise-prediction code JeNo to screen the design concepts. A two-stream versus three-stream computation based on equal mass flow rates showed a reduction in peak turbulent kinetic energy (TKE) for the three-stream jet relative to that for the two-stream jet which resulted in reduced acoustic emission. Additional three-stream solutions were analyzed for salient flowfield features expected to impact farfield noise. As tertiary power settings were increased there was a corresponding near nozzle increase in shear rate that resulted in an increase in high frequency noise and a reduction in peak TKE. As tertiary-to-core area ratio was increased the tertiary potential core elongated and the peak TKE was reduced. The most noticeable change occurred as secondary-to-core area ratio was increased thickening the secondary potential core, elongating the primary potential core and reducing peak TKE. As forward flight Mach number was increased the jet plume region decreased and reduced peak TKE.

VizieR Online Data Catalog: The VLBA Extragalactic Proper Motion Catalog (Truebenbach+, 2017)

NASA Astrophysics Data System (ADS)

Truebenbach, A. E.; Darling, J.

2017-11-01

We created our catalog of extragalactic radio proper motions using the 2017a Goddard VLBI global solution. The 2017a solution is computed from more than 30 years of dual-band VLBI observations --1979 August 3 to 2017 March 27. We also observed 28 objects with either no redshift or a "questionable" Optical Characteristic of Astrometric Radio Sources (OCARS; Malkin 2016ARep...60..996M) redshift at the Apache Point Observatory (APO) 3.5m telescope and/or at Gemini North. We conducted observations on the 3.5m telescope at Apache Point Observatory with the Dual Imaging Spectrograph (DIS) from 2015 April 18 to 2016 June 30. We chose two objects for additional observations with the Gemini Multi-Object Spectrograph-North (GMOS-N) at Gemini North Observatory. 2021+317 was observed on 2016 June 26 and 28, while 0420+417 was observed on 2016 November 8 and 26. We also observed 42 radio sources with the Very Long Baseline Array (VLBA) in the X-band (3.6cm/8.3GHz). Our targets had all been previously observed by VLBI. Our VLBA observations were conducted in two campaigns from 2015 September to 2016 January and 2016 October to November. The final extragalactic proper motion catalog (created primarily from archival Goddard VLBI data, with redshifts obtained from OCARS) contains 713 proper motions with average uncertainties of 24μas/yr. (5 data files).

Synthesis of Au/TiO2 Core-Shell Nanoparticles from Titanium Isopropoxide and Thermal Resistance Effect of TiO2 Shell

NASA Astrophysics Data System (ADS)

Kwon, Hyun-Woo; Lim, Young-Min; Tripathy, Suraj Kumar; Kim, Byoung-Gyu; Lee, Min-Sang; Yu, Yeon-Tae

2007-04-01

On the synthesis of Au/TiO2 core-shell structure nanoparticles, the effect of the concentration of Ti4+ on the morphology and optical property of Au/TiO2 core-shell nanoparticles was examined. A gold colloid was prepared by mixing HAuCl4\\cdot4H2O and C6H5Na3\\cdot2H2O. Titanium stock solution was prepared by mixing solutions of titanium(IV) isopropoxide (TTIP) and triethanolamine (TEOA). The concentration of the Ti4+ stock solution was adjusted to 0.01-0.3 mM, and then the gold colloid was added to the Ti4+ stock solution. Au/TiO2 core-shell structure nanoparticles could be prepared by the hydrolysis of the Ti4+ stock solution at 80 °C. The size of the as-prepared Au nanoparticles was 15 nm. The thickness of the TiO2 shell on the surface of gold particles was about 10 nm. The absorption peak of the Au/TiO2 core-shell nanoparticles shifted towards the red end of the spectrum by about 3 nm because of the formation of the TiO2 shell on the surface of the gold particles. The crystal structure of the TiO2 shell showed an anatase phase. The increase in the Au crystallite size of the Au/TiO2 nanoparticles with increasing heat treatment temperature is smaller than that in the pure Au nanoparticles. This may be due to the encapsulation of Au particles with the TiO2 shell that prevents the growth of the nanoparticle nucleation.

Thermo-optical characterization of cadmium selenide/zinc sulfide (CdSe/ZnS) quantum dots embedded in biocompatible materials.

PubMed

Pilla, Viviane; Alves, Leandro P; Iwazaki, Adalberto N; Andrade, Acácio A; Antunes, Andrea; Munin, Egberto

2013-09-01

Cadmium selenide/zinc sulfide (CdSe/ZnS) core-shell quantum dots (QDs) embedded in biocompatible materials were thermally and optically characterized with a thermal lens (TL) technique. Transient TL measurements were performed with a mode-mismatched, dual-beam (excitation and probe) configuration. A thermo-optical study of the CdSe/ZnS QDs was performed for different core diameters (3.5, 4.0, 5.2, and 6.6 nm) in aqueous solution and synthetic saliva, and three different core diameters (2.4, 2.9, and 4.1 nm) embedded in restorative dental resin (0.025% by mass). The thermal diffusivity results are characteristic of the biocompatible matrices. The radiative quantum efficiencies for aqueous solution and biofluid materials are dependent on the core size of the CdSe/ZnS core-shell QDs. The results obtained from the fluorescence spectral measurements for the biocompatible materials support the TL results.

Single axis controlled hybrid magnetic bearing for left ventricular assist device: hybrid core and closed magnetic circuit.

PubMed

da Silva, Isaias; Horikawa, Oswaldo; Cardoso, Jose R; Camargo, Fernando A; Andrade, Aron J P; Bock, Eduardo G P

2011-05-01

In previous studies, we presented main strategies for suspending the rotor of a mixed-flow type (centrifugal and axial) ventricular assist device (VAD), originally presented by the Institute Dante Pazzanese of Cardiology (IDPC), Brazil. Magnetic suspension is achieved by the use of a magnetic bearing architecture in which the active control is executed in only one degree of freedom, in the axial direction of the rotor. Remaining degrees of freedom, excepting the rotation, are restricted only by the attraction force between pairs of permanent magnets. This study is part of a joint project in development by IDPC and Escola Politecnica of São Paulo University, Brazil. This article shows advances in that project, presenting two promising solutions for magnetic bearings. One solution uses hybrid cores as electromagnetic actuators, that is, cores that combine iron and permanent magnets. The other solution uses actuators, also of hybrid type, but with the magnetic circuit closed by an iron core. After preliminary analysis, a pump prototype has been developed for each solution and has been tested. For each prototype, a brushless DC motor has been developed as the rotor driver. Each solution was evaluated by in vitro experiments and guidelines are extracted for future improvements. Tests have shown good results and demonstrated that one solution is not isolated from the other. One complements the other for the development of a single-axis-controlled, hybrid-type magnetic bearing for a mixed-flow type VAD. © 2011, Copyright the Authors. Artificial Organs © 2011, International Center for Artificial Organs and Transplantation and Wiley Periodicals, Inc.

Tracing the young massive high-eccentricity binary system θ^1Orionis C through periastron passage

NASA Astrophysics Data System (ADS)

Kraus, S.; Weigelt, G.; Balega, Y. Y.; Docobo, J. A.; Hofmann, K.-H.; Preibisch, T.; Schertl, D.; Tamazian, V. S.; Driebe, T.; Ohnaka, K.; Petrov, R.; Schöller, M.; Smith, M.

2009-04-01

Context: The nearby high-mass star binary system θ^1Ori C is the brightest and most massive of the Trapezium OB stars at the core of the Orion Nebula Cluster, and it represents a perfect laboratory to determine the fundamental parameters of young hot stars and to constrain the distance of the Orion Trapezium Cluster. Aims: By tracing the orbital motion of the θ^1Ori C components, we aim to refine the dynamical orbit of this important binary system. Methods: Between January 2007 and March 2008, we observed θ^1Ori C with VLTI/AMBER near-infrared (H- and K-band) long-baseline interferometry, as well as with bispectrum speckle interferometry with the ESO 3.6 m and the BTA 6 m telescopes (B'- and V'-band). Combining AMBER data taken with three different 3-telescope array configurations, we reconstructed the first VLTI/AMBER closure-phase aperture synthesis image, showing the θ^1Ori C system with a resolution of ˜ 2 mas. To extract the astrometric data from our spectrally dispersed AMBER data, we employed a new algorithm, which fits the wavelength-differential visibility and closure phase modulations along the H- and K-band and is insensitive to calibration errors induced, for instance, by changing atmospheric conditions. Results: Our new astrometric measurements show that the companion has nearly completed one orbital revolution since its discovery in 1997. The derived orbital elements imply a short-period (P ≈ 11.3 yr) and high-eccentricity orbit (e ≈ 0.6) with periastron passage around 2002.6. The new orbit is consistent with recently published radial velocity measurements, from which we can also derive the first direct constraints on the mass ratio of the binary components. We employ various methods to derive the system mass (M_system = 44 ± 7 M⊙) and the dynamical distance (d = 410 ± 20 pc), which is in remarkably good agreement with recently published trigonometric parallax measurements obtained with radio interferometry. Based on observations made with ESO telescopes at the La Silla Paranal Observatory under the OT and VISA-MPG GTO programme IDs 078.C-0360(A), 080.C-0541(A,B,C,D), 080.D-0225(B), and 080.C-0388(A).

Dynamic Voltage-Frequency and Workload Joint Scaling Power Management for Energy Harvesting Multi-Core WSN Node SoC

PubMed Central

Li, Xiangyu; Xie, Nijie; Tian, Xinyue

2017-01-01

This paper proposes a scheduling and power management solution for energy harvesting heterogeneous multi-core WSN node SoC such that the system continues to operate perennially and uses the harvested energy efficiently. The solution consists of a heterogeneous multi-core system oriented task scheduling algorithm and a low-complexity dynamic workload scaling and configuration optimization algorithm suitable for light-weight platforms. Moreover, considering the power consumption of most WSN applications have the characteristic of data dependent behavior, we introduce branches handling mechanism into the solution as well. The experimental result shows that the proposed algorithm can operate in real-time on a lightweight embedded processor (MSP430), and that it can make a system do more valuable works and make more than 99.9% use of the power budget. PMID:28208730

Dynamic Voltage-Frequency and Workload Joint Scaling Power Management for Energy Harvesting Multi-Core WSN Node SoC.

PubMed

Li, Xiangyu; Xie, Nijie; Tian, Xinyue

2017-02-08

This paper proposes a scheduling and power management solution for energy harvesting heterogeneous multi-core WSN node SoC such that the system continues to operate perennially and uses the harvested energy efficiently. The solution consists of a heterogeneous multi-core system oriented task scheduling algorithm and a low-complexity dynamic workload scaling and configuration optimization algorithm suitable for light-weight platforms. Moreover, considering the power consumption of most WSN applications have the characteristic of data dependent behavior, we introduce branches handling mechanism into the solution as well. The experimental result shows that the proposed algorithm can operate in real-time on a lightweight embedded processor (MSP430), and that it can make a system do more valuable works and make more than 99.9% use of the power budget.

Electrophoretic extraction of proteins from two-dimensional electrophoresis gel spots

DOEpatents

Zhang, Jian-Shi; Giometti, C.S.; Tollaksen, S.L.

1987-09-04

After two-dimensional electrophoresis of proteins or the like, resulting in a polyacrylamide gel slab having a pattern of protein gel spots thereon, an individual protein gel spot is cored out from the slab, to form a gel spot core which is placed in an extraction tube, with a dialysis membrane across the lower end of the tube. Replicate gel spots can be cored out from replicate gel slabs and placed in the extraction tube. Molten agarose gel is poured into the extraction tube where the agarose gel hardens to form an immobilizing gel, covering the gel spot cores. The upper end portion of the extraction tube is filled with a volume of buffer solution, and the upper end is closed by another dialysis membrane. Upper and lower bodies of a buffer solution are brought into contact with the upper and lower membranes and are provided with electrodes connected to the positive and negative terminals of a dc power supply, thereby producing an electrical current which flows through the upper membrane, the volume of buffer solution, the agarose, the gel spot cores and the lower membrane. The current causes the proteins to be extracted electrophoretically from the gel spot cores, so that the extracted proteins accumulate and are contained in the space between the agarose gel and the upper membrane. 8 figs.

Coaxial Electrospinning and Characterization of Core-Shell Structured Cellulose Nanocrystal Reinforced PMMA/PAN Composite Fibers

PubMed Central

Li, Chao; Li, Qingde; Ni, Xiaohui; Liu, Guoxiang; Cheng, Wanli; Han, Guangping

2017-01-01

A modified coaxial electrospinning process was used to prepare composite nanofibrous mats from a poly(methyl methacrylate) (PMMA) solution with the addition of different cellulose nanocrystals (CNCs) as the sheath fluid and polyacrylonitrile (PAN) solution as the core fluid. This study investigated the conductivity of the as-spun solutions that increased significantly with increasing CNCs addition, which favors forming uniform fibers. This study discussed the effect of different CNCs addition on the morphology, thermal behavior, and the multilevel structure of the coaxial electrospun PMMA + CNCs/PAN composite nanofibers. A morphology analysis of the nanofibrous mats clearly demonstrated that the CNCs facilitated the production of the composite nanofibers with a core-shell structure. The diameter of the composite nanofibers decreased and the uniformity increased with increasing CNCs concentrations in the shell fluid. The composite nanofibrous mats had the maximum thermal decomposition temperature that was substantially higher than electrospun pure PMMA, PAN, as well as the core-shell PMMA/PAN nanocomposite. The BET (Brunauer, Emmett and Teller) formula results showed that the specific surface area of the CNCs reinforced core-shell composite significantly increased with increasing CNCs content. The specific surface area of the composite with 20% CNCs loading rose to 9.62 m2/g from 3.76 m2/g for the control. A dense porous structure was formed on the surface of the electrospun core-shell fibers. PMID:28772933

VLBI Phase-Referenced Observations on Southern Hemisphere HIPPARCOS Radio Start

NASA Technical Reports Server (NTRS)

Guirado, J. C.; Preston, R. A.; Jones, D. L.; Lestrade, J. F.; Reynolds, J. E.; Jauncey, D. L.; Tzioumis, A. K.; Ferris, R. H.; King, E. A.; Lovell, J. E. J.;

Core-Sheath Paraffin-Wax-Loaded Nanofibers by Electrospinning for Heat Storage.

PubMed

Lu, Yuan; Xiao, Xiudi; Zhan, Yongjun; Huan, Changmeng; Qi, Shuai; Cheng, Haoliang; Xu, Gang

2018-04-18

Paraffin wax (PW) is widely used for smart thermoregulation materials due to its good thermal performance. However, the leakage and low thermal conductivity of PW hinder its application in the heat storage field. Accordingly, developing effective methods to address these issues is of great importance. In this study, we explored a facile approach to obtain PW-loaded core-sheath structured flexible nanofibers films via coaxial electrospinning technique. The PW as the core layer was successfully encapsulated by the sheath-layer poly(methyl methacrylate). The diameter of the fiber core increased from 395 to 848 nm as the core solution speed rate increased from 0.1 to 0.5 mL/h. In addition, it can be seen that higher core solution speed rate could lead to higher PW encapsulation efficiency according to the transmission electron microscopy results. The core-sheath nanofiber films, moreover, possessed the highest latent heat of 58.25 J/g and solidifying enthalpy of -56.49 J/g. In addition, we found that after 200 thermal cycles, there was little change in latent heat, which demonstrated that it is beneficial for the PW-loaded core-sheath structure to overcome the leakage issue and enhance thermal stability properties for the thermoregulation film.

VizieR Online Data Catalog: 2007.5 to 2010.4 HST astrometry of HD 202206 (Benedict+, 2017)

NASA Astrophysics Data System (ADS)

Benedict, G. F.; Harrison, T. E.

2017-08-01

For this study astrometric measurements came from Fine Guidance Sensor 1r (FGS 1r), an upgraded FGS installed in 1997 during the second Hubble Space Telescope (HST) servicing mission. It provided superior fringes from which to obtain target and reference star positions (McArthur et al. 2003hstc.conf..373M). We utilized only the fringe tracking mode (POS mode) in this investigation. POS mode observations of a star have a typical duration of 60s, during which over 2000 individual position measures are collected. The astrometric centroid is estimated by choosing the median measure, after filtering large outliers (caused by cosmic-ray hits and particles trapped by the Earth's magnetic field). The standard deviation of the measures provides a measurement error. We refer to the aggregate of astrometric centroids of each star secured during one visibility period as an "orbit". Because one of the pillars of the scientific method involves reproducibility, we present a complete ensemble of time-tagged HD202206 and reference star astrometric measurements, Optical Field Angle Distortion (OFAD; McArthur et al. 2006hstc.conf..396M) and intra-orbit-drift-corrected, in Table2, along with calculated parallax factors in R.A. and decl. These data, collected from 2007.5 to 2010.4, in addition to providing material for confirmation of our results, might ultimately be combined with Gaia measures, significantly extending the time baseline of astrometry, thereby improving proper motion and perturbation characterization. Our band passes for reference star photometry include: BVRI photometry of the reference stars from the NMSU 1m telescope located at Apache Point Observatory and JHK (from 2MASS; see Cutri et al. 2003, Cat. II/246). Table4 lists the visible and infrared photometry for the HD202206 reference stars. To establish spectral type and luminosity class, the reference frame stars were observed on 2009 December 9 using the RCSPEC on the Blanco 4m telescope at Cerro Tololo Inter-American Observatory (CTIO). We used the KPGL1 grating to give a dispersion of 0.95Å/pix. Classifications used a combination of template matching and line ratios. We determine the spectral types for the higher S/N stars to within ±1 subclass. Classifications for the lower S/N stars have ±2 subclass uncertainty. Table5 lists the spectral types and luminosity classes for our reference stars. (6 data files).

Pluto: improved astrometry from 19 years of observations

NASA Astrophysics Data System (ADS)

Benedetti-Rossi, G.; Vieira Martins, R.; Camargo, J. I. B.; Assafin, M.; Braga-Ribas, F.

2014-10-01

Context. We present astrometric positions of Pluto, consistent with the International Celestial Reference System, from 4412 CCD frames observed over 120 nights with three telescopes at the Observatório do Pico dos Dias in Brazil, covering a time span from 1995 to 2013, and also 145 frames observed over 11 nights in 2007 and 2009 with the ESO/MPG 2.2m telescope equipped with the Wide Field Imager (WFI). Aims: Our aim is to contribute to the study and improvement of the orbit of Pluto with new astrometric methods and positions. Methods: All astrometric positions of Pluto were reduced with the Platform for Reduction of Astronomical Images Automatically (PRAIA), using the USNO CCD Astrograph Catalogue 4 (UCAC4) as the reference catalog. We also used the planetary ephemeris DE421+plu021 for comparisons. The positions were corrected for differential chromatic refraction. The (x, y) center of Pluto was determined from corrections to the measured photocenter, which was contaminated by Charon. The corrections were obtained with an original procedure based on analytical expressions derived from a two-dimensional Gaussian function i.e. the point spread function PSF fitted to the images to derive the (x, y) measurements. Results: We obtained mean values of 4 mas and 37 mas for right ascension and declination, and standard deviations of σα = 45 mas and σδ = 49 mas, for the offsets in the sense observed minus ephemeris position, after the corrections. We confirm the presence of a linear drift in the ephemeris declinations from 2005 on, also obtained from stellar occultations. Conclusions: We present astrometric positions of Pluto for 19 years of observations in Brazil. The positions, corrected for differential chromatic refraction and Pluto/Charon photocenter effects, presented the same behavior as obtained from stellar occultations, with a drift in declinations of about 100 mas since 2005. The results indicate that the DE421 Pluto ephemeris used in this work need to be corrected. Full Table 4 is only available in electronic form at the CDS via anonymous ftp to http://cdsarc.u-strasbg.fr (ftp://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/570/A86Based on observations made at Laboratório Nacional de Astrofísica (LNA), Itajubá-MG, Brazil.Partially based on observations through the ESO runs 079.A-9202(A), 075.C-0154, 077.C-0283, and 079.C-0345.

The LEECH Exoplanet Imaging Survey. Further constraints on the planet architecture of the HR 8799 system

NASA Astrophysics Data System (ADS)

Maire, A.-L.; Skemer, A. J.; Hinz, P. M.; Desidera, S.; Esposito, S.; Gratton, R.; Marzari, F.; Skrutskie, M. F.; Biller, B. A.; Defrère, D.; Bailey, V. P.; Leisenring, J. M.; Apai, D.; Bonnefoy, M.; Brandner, W.; Buenzli, E.; Claudi, R. U.; Close, L. M.; Crepp, J. R.; De Rosa, R. J.; Eisner, J. A.; Fortney, J. J.; Henning, T.; Hofmann, K.-H.; Kopytova, T. G.; Males, J. R.; Mesa, D.; Morzinski, K. M.; Oza, A.; Patience, J.; Pinna, E.; Rajan, A.; Schertl, D.; Schlieder, J. E.; Su, K. Y. L.; Vaz, A.; Ward-Duong, K.; Weigelt, G.; Woodward, C. E.

2015-04-01

Context. Astrometric monitoring of directly imaged exoplanets allows the study of their orbital parameters and system architectures. Because most directly imaged planets have long orbital periods (>20 AU), accurate astrometry is challenging when based on data acquired on timescales of a few years and usually with different instruments. The LMIRCam camera on the Large Binocular Telescope is being used for the LBT Exozodi Exoplanet Common Hunt (LEECH) survey to search for and characterize young and adolescent exoplanets in L' band (3.8 μm), including their system architectures. Aims: We first aim to provide a good astrometric calibration of LMIRCam. Then, we derive new astrometry, test the predictions of the orbital model of 8:4:2:1 mean motion resonance proposed for the system, and perform new orbital fitting of the HR 8799 bcde planets. We also present deep limits on a putative fifth planet inside the known planets. Methods: We use observations of HR 8799 and the Θ1 Ori C field obtained during the same run in October 2013. Results: We first characterize the distortion of LMIRCam. We determine a platescale and a true north orientation for the images of 10.707 ± 0.012 mas/pix and -0.430 ± 0.076°, respectively. The errors on the platescale and true north orientation translate into astrometric accuracies at a separation of 1'' of 1.1 mas and 1.3 mas, respectively. The measurements for all planets agree within 3σ with a predicted ephemeris. The orbital fitting based on the new astrometric measurements favors an architecture for the planetary system based on 8:4:2:1 mean motion resonance. The detection limits allow us to exclude a fifth planet slightly brighter or more massive than HR 8799 b at the location of the 2:1 resonance with HR 8799 e (~9.5 AU) and about twice as bright as HR 8799 cde at the location of the 3:1 resonance with HR 8799 e (~7.5 AU). The LBT is an international collaboration among institutions in the United States, Italy, and Germany. LBT Corporation partners are: The University of Arizona on behalf of the Arizona university system; Istituto Nazionale di Astrofisica, Italy; LBT Beteiligungsgesellschaft, Germany, representing the Max-Planck Society, the Astrophysical Institute Potsdam, and Heidelberg University; The Ohio State University, and The Research Corporation, on behalf of The University of Notre Dame, University of Minnesota, and University of Virginia.

Near-Earth Asteroids Astrometry with Gaia and Beyond

NASA Astrophysics Data System (ADS)

Bancelin, D.; Hestroffer, D.; Thuillot, W.

2010-05-01

Gaia is an astrometric mission from the European Space Agency (ESA) that will be launched in Spring 2012. The Gaia telescope and spectrometer will operate in the visible wavelength scanning the whole sky during 5 years (nominal mission duration). It will observe about one billion stars and QSOs but also a large number of solar system bodies, mainly asteroids, and a few comets and planetary satellites. The unprecedented accuracy of the measures both astrometric and photometric (note that the spectroscopic observations are of little scientific value for Solar System objects science) will enable to significantly improve the knowledge of the dynamics and physical properties for a large number of asteroids. With a relatively limiting magnitude somewhat reduced to V≤20 (compared to other future or ongoing surveys) Gaia will mainly oserve main-belt asteroids (MBAs), and very few TNOs or Centaurs. The Gaia telescope will also be able to observe several thousands of Near- Earth Objects (NEOs) down to low solar elongation (observation of solar system objects are performed with elongation 45° ≤ L ≤ 135°). Gaia will not be a ''big'' NEO discover, however it can possibly discover inner-Earth orbiting objects (IEOs) or sub-Atens, from atmosphereless low solar-elongation observations. In the case of discovering a new NEO target, ground-based observations in network could be needed to avoid confusion in identifying the object in the database, or loss of the target. We are aiming to generate VO-alert for such eventuality. Ground-based observations of NEOs would also more generally enter into the operational centre in construction at the IMCCE that will deal with data mining, astrometric reduction, orbit computation, alerts, etc. On the other hand, in the framework of ESA Space Situational Awareness (SSA), ground-based astrometry, possibly complemented by Gaia data, is needed to refine the orbits and collision assessment of PHAs. High accuracy astrometric and colour-photometry observations of NEOs will provide information on their taxonomy, spin state and shape, and detailed information of their orbits. Small effects acting on their dynamics can then be measured; these include link of reference frame (kinematically non rotating and dynamically non rotating one), local tests of the General Relativity and measure of the solar quadrupole J2 basically from the drift of the perihelion, test of the variation of the constant of gravity dG/dt, and detection of non gravitational effect such as the thermal Yarkovsky effect and cometary activity. Dedicated ground-based observations can be used on specific targets to complement the limited wavelength, time resolution and imaging capabilities of the Gaia telescope.

The LCOGT NEO Follow-up Network

NASA Astrophysics Data System (ADS)

Lister, Tim; Greenstreet, Sarah; Gomez, Edward; Christensen, Eric J.; Larson, Stephen M.

2016-10-01

The LCOGT NEO Follow-up Network is using the telescopes of the Las Cumbres Observatory Global Telescope Network (LCOGT) and a web-based target selection, scheduling and data reduction system to confirm NEO candidates and characterize radar-targeted known NEOs. Starting in July 2014, the LCOGT NEO Follow-up Network has observed over 3,500 targets and reported more than 16,000 astrometric and photometric measurements to the Minor Planet Center (MPC).The LCOGT NEO Follow-up Network's main aims are to perform confirming follow-up of the large number of NEO candidates and to perform characterization measurements of radar targets to obtain light curves and rotation rates. The NEO candidates come from the NEO surveys such as Catalina, PanSTARRS, ATLAS, NEOWISE and others. In particular, we are targeting objects in the Southern Hemisphere, where the LCOGT NEO Follow-up Network is the largest resource for NEO observations.LCOGT has completed the first phase of the deployment with the installation and commissioning of the nine 1-meter telescopes at McDonald Observatory (Texas), Cerro Tololo (Chile), SAAO (South Africa) and Siding Spring Observatory (Australia). The telescope network has been fully operational since 2014 May, and observations are being executed remotely and robotically. Future expansion to a site at Ali Observatory, Tibet is planned for 2017-2018.We have developed web-based software called NEOexchange which automatically downloads and aggregates NEO candidates from the Minor Planet Center's NEO Confirmation Page, the Arecibo and Goldstone radar target lists and the NASA ARM list. NEOexchange allows the planning and scheduling of observations on the LCOGT Telescope Network and the tracking of the resulting blocks and generated data. We have recently extended the NEOexchange software to include automated data reduction to re-compute the astrometric solution, determine the photometric zeropoint and find moving objects and present these results to the user via the website.We will present results from the LCOGT NEO Follow-up Network and from the development of the NEOexchange software which is used to schedule, analyze and report observations taken with the LCOGT Network.

Strong Constraints to the Putative Planet Candidate around VB 10 Using Doppler Spectroscopy

NASA Astrophysics Data System (ADS)

Anglada-Escudé, Guillem; Shkolnik, Evgenya L.; Weinberger, Alycia J.; Thompson, Ian B.; Osip, David J.; Debes, John H.

2010-03-01

We present new radial velocity (RV) measurements of the ultra-cool dwarf VB 10, which was recently announced to host a giant planet detected with astrometry. The new observations were obtained using optical spectrographs (MIKE/Magellan and ESPaDOnS/CFHT) and cover 65% of the reported period of 270 days. The nominal precision of the new Doppler measurements is about 150 m s-1 while their standard deviation is 250 m s-1. However, there are indications that such a larger variation is due to uncontrolled systematic errors. We apply least-squares periodograms to identify the most significant signals and evaluate their false alarm probabilities (FAPs). We show that this method is the proper generalization to astrometric data because (1) it mitigates the coupling of the orbital parameters with the parallax and proper motion, and (2) it permits a direct generalization to include nonlinear Keplerian parameters in a combined fit to astrometry and RV data. Our analysis of the astrometry alone uncovers the reported 270 day period and an even stronger signal at ~50 days. We estimate the uncertainties in the parameters using a Markov chain Monte Carlo approach. Although the new data alone cannot rule out the presence of a candidate, when combined with published RV measurements, the FAPs of the best solutions grow to unacceptable levels strongly suggesting that the observed astrometric wobble is not due to an unseen companion. The new measurements put an upper limit of m sin i ~ 2.5 m jup for a companion with a period shorter than one year and moderate eccentricities. Based on observations collected with the 6.5 m Magellan Telescopes located at Las Campanas Observatory, Chile, at the W. M. Keck Observatory, and the Canada-France-Hawaii Telescope (CFHT). The Keck Observatory is operated as a scientific partnership between the California Institute of Technology, the University of California, and NASA, and was made possible by the generous financial support of the W. M. Keck Foundation. CFHT is operated by the National Research Council of Canada, the Institut National des Sciences de l'Univers of the Centre National de la Recherche Scientique of France, and the University of Hawaii.

The focusing effect of P-wave in the Moon's and Earth's low-velocity core. Analytical solution

NASA Astrophysics Data System (ADS)

Fatyanov, A. G.; Burmin, V. Yu

2018-04-01

The important aspect in the study of the structure of the interiors of planets is the question of the presence and state of core inside them. While for the Earth this task was solved long ago, the question of whether the core of the Moon is in a liquid or solid state up to the present is debatable up to present. If the core of the Moon is liquid, then the velocity of longitudinal waves in it should be lower than in the surrounding mantle. If the core is solid, then most likely, the velocity of longitudinal waves in it is higher than in the mantle. Numerical calculations of the wave field allow us to identify the criteria for drawing conclusions about the state of the lunar core. In this paper we consider the problem of constructing an analytical solution for wave fields in a layered sphere of arbitrary radius. A stable analytic solution is obtained for the wave fields of longitudinal waves in a three-layer sphere. Calculations of the total wave fields and rays for simplified models of the Earth and the Moon with real parameters are presented. The analytical solution and the ray pattern showed that the low-velocity cores of the Earth and the Moon possess the properties of a collecting lens. This leads to the emergence of a wave field focusing area. As a result, focused waves of considerable amplitude appear on the surface of the Earth and the Moon. In the Earth case, they appear before the first PKP-wave arrival. These are so-called "precursors", which continue in the subsequent arrivals of waves. At the same time, for the simplified model of the Earth, the maximum amplitude growth is observed in the 147-degree region. For the Moon model, the maximum amplitude growth is around 180°.

Fabrication of metal nanoshells

NASA Technical Reports Server (NTRS)

Kim, Jae-Woo (Inventor); King, Glen C. (Inventor); Lillehei, Peter T. (Inventor); Park, Yeonjoon (Inventor); Elliott, Jr., James R. (Inventor); Choi, Sang H. (Inventor); Chu, Sang-Hyon (Inventor)

2012-01-01

Metal nanoshells are fabricated by admixing an aqueous solution of metal ions with an aqueous solution of apoferritin protein molecules, followed by admixing an aqueous solution containing an excess of an oxidizing agent for the metal ions. The apoferritin molecules serve as bio-templates for the formation of metal nanoshells, which form on and are bonded to the inside walls of the hollow cores of the individual apoferritin molecules. Control of the number of metal atoms which enter the hollow core of each individual apoferritin molecule provides a hollow metal nonparticle, or nanoshell, instead of a solid spherical metal nanoparticle.

A Study on the Plasmonic Properties of Silver Core Gold Shell Nanoparticles: Optical Assessment of the Particle Structure

NASA Astrophysics Data System (ADS)

Mott, Derrick; Lee, JaeDong; Thi Bich Thuy, Nguyen; Aoki, Yoshiya; Singh, Prerna; Maenosono, Shinya

2011-06-01

This paper reports a qualitative comparison between the optical properties of a set of silver core, gold shell nanoparticles with varying composition and structure to those calculated using the Mie solution. To achieve this, silver nanoparticles were synthesized in aqueous phase from a silver hydroxide precursor with sodium acrylate as dual reducing-capping agent. The particles were then coated with a layer of gold with controllable thickness through a reduction-deposition process. The resulting nanoparticles reveal well defined optical properties that make them suitable for comparison to ideal calculated results using the Mie solution. The discussion focuses on the correlation between the synthesized core shell nanoparticles with varying Au shell thickness and the Mie solution results in terms of the optical properties. The results give insight in how to design and synthesize silver core, gold shell nanoparticles with controllable optical properties (e.g., SPR band in terms of intensity and position), and has implications in creating nanoparticle materials to be used as biological probes and sensing elements.

Multi level optimization of burnable poison utilization for advanced PWR fuel management

NASA Astrophysics Data System (ADS)

Yilmaz, Serkan

The objective of this study was to develop an unique methodology and a practical tool for designing burnable poison (BP) pattern for a given PWR core. Two techniques were studied in developing this tool. First, the deterministic technique called Modified Power Shape Forced Diffusion (MPSFD) method followed by a fine tuning algorithm, based on some heuristic rules, was developed to achieve this goal. Second, an efficient and a practical genetic algorithm (GA) tool was developed and applied successfully to Burnable Poisons (BPs) placement optimization problem for a reference Three Mile Island-1 (TMI-1) core. This thesis presents the step by step progress in developing such a tool. The developed deterministic method appeared to perform as expected. The GA technique produced excellent BP designs. It was discovered that the Beginning of Cycle (BOC) Kinf of a BP fuel assembly (FA) design is a good filter to eliminate invalid BP designs created during the optimization process. By eliminating all BP designs having BOC Kinf above a set limit, the computational time was greatly reduced since the evaluation process with reactor physics calculations for an invalid solution is canceled. Moreover, the GA was applied to develop the BP loading pattern to minimize the total Gadolinium (Gd) amount in the core together with the residual binding at End-of-Cycle (EOC) and to keep the maximum peak pin power during core depletion and Soluble boron concentration at BOC both less than their limit values. The number of UO2/Gd2O3 pins and Gd 2O3 concentrations for each fresh fuel location in the core are the decision variables and the total amount of the Gd in the core and maximum peak pin power during core depletion are in the fitness functions. The use of different fitness function definition and forcing the solution movement towards to desired region in the solution space accelerated the GA runs. Special emphasize is given to minimizing the residual binding to increase core lifetime as well as minimizing the total Gd amount in the core. The GA code developed many good solutions that satisfy all of the design constraints. For these solutions, the EOC soluble boron concentration changes from 68.9 to 97.2 ppm. It is important to note that the difference of 28.3 ppm between the best and the worst solution in the good solutions region represent the potential of 12.5 Effective-Full-Power-Day (EPFD) savings in cycle length. As a comparison, the best BP loading design has 97.2 ppm soluble boron concentration at EOC while the BP loading with available vendors' U/Gd FA designs has 94.4 ppm SOB at EOC. It was estimated that the difference of 2.8 ppm reflected the potential savings of 1.25 EFPD in cycle length. Moreover, the total Gd amount was reduced by 6.89% in mass that provided extra savings in fuel cost compared to the BP loading pattern with available vendor's U/Gd FA designs. (Abstract shortened by UMI.)

Stabilization of Pt monolayer catalysts under harsh conditions of fuel cells

DOE PAGES

Zhang, Xiaoming; Liu, Ping; Yu, Shansheng; ...

2015-05-21

We employed density functional theory (DFT) to explore the stability of core (M = Cu, Ru, Rh, Pd, Ag, Os, Ir, Au)-shell (Pt) catalysts under harsh conditions, including solutions and reaction intermediates involved in the oxygen reduction reaction (ORR) in fuel cells. A pseudomorphic surface alloy (PSA) with a Pt monolayer (Pt 1ML) supported on an M surface, Pt 1ML/M(111) or (001), was considered as a model system. Different sets of candidate M cores were identified to achieve a stable Pt 1ML shell depending on the conditions. In vacuum conditions, the Pt 1ML shell can be stabilized on the mostmore » of M cores except Cu, Ag, and Au. The situation varies under various electrochemical conditions. Depending on the solutions and the operating reaction pathways of the ORR, different M should be considered. Pd and Ir are the only core metals studied, being able to keep the Pt ML shell intact in perchloric acid, sulfuric acid, phosphoric acid, and alkaline solutions as well as under the ORR conditions via different pathways. Ru and Os cores should also be paid attention, which only fall during the ORR via the *OOH intermediate. Rh core works well as long as the ORR does not undergo the pathway via *O intermediate. Our results show that PSAs can behave differently from the near surface alloy, Pt 1ML/M 1ML/Pt(111), highlighting the importance of considering both chemical environments and the atomic structures in rational design of highly stable core-shell nanocatalysts. Finally, the roles that d-band center of a core M played in determining the stability of supported Pt 1ML shell were also discussed.« less

Stabilization of Pt monolayer catalysts under harsh conditions of fuel cells

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zhang, Xiaoming; Yu, Shansheng; Zheng, Weitao, E-mail: wtzheng@jlu.edu.cn, E-mail: pingliu3@bnl.gov

2015-05-21

We employed density functional theory to explore the stability of core (M = Cu, Ru, Rh, Pd, Ag, Os, Ir, Au)-shell (Pt) catalysts under harsh conditions, including solutions and reaction intermediates involved in the oxygen reduction reaction (ORR) in fuel cells. A pseudomorphic surface alloy (PSA) with a Pt monolayer (Pt{sub 1ML}) supported on an M surface, Pt{sub 1ML}/M(111) or (001), was considered as a model system. Different sets of candidate M cores were identified to achieve a stable Pt{sub 1ML} shell depending on the conditions. In vacuum conditions, the Pt{sub 1ML} shell can be stabilized on the most ofmore » M cores except Cu, Ag, and Au. The situation varies under various electrochemical conditions. Depending on the solutions and the operating reaction pathways of the ORR, different M should be considered. Pd and Ir are the only core metals studied, being able to keep the Pt{sub ML} shell intact in perchloric acid, sulfuric acid, phosphoric acid, and alkaline solutions as well as under the ORR conditions via different pathways. Ru and Os cores should also be paid attention, which only fall during the ORR via the *OOH intermediate. Rh core works well as long as the ORR does not undergo the pathway via *O intermediate. Our results show that PSAs can behave differently from the near surface alloy, Pt{sub 1ML}/M{sub 1ML}/Pt(111), highlighting the importance of considering both chemical environments and the atomic structures in rational design of highly stable core-shell nanocatalysts. Finally, the roles that d-band center of a core M played in determining the stability of supported Pt{sub 1ML} shell were also discussed.« less

Space Mirror Alignment System

NASA Technical Reports Server (NTRS)

Jau, Bruno M.; McKinney, Colin; Smythe, Robert F.; Palmer, Dean L.

2011-01-01

An optical alignment mirror mechanism (AMM) has been developed with angular positioning accuracy of +/-0.2 arcsec. This requires the mirror s linear positioning actuators to have positioning resolutions of +/-112 nm to enable the mirror to meet the angular tip/tilt accuracy requirement. Demonstrated capabilities are 0.1 arc-sec angular mirror positioning accuracy, which translates into linear positioning resolutions at the actuator of 50 nm. The mechanism consists of a structure with sets of cross-directional flexures that enable the mirror s tip and tilt motion, a mirror with its kinematic mount, and two linear actuators. An actuator comprises a brushless DC motor, a linear ball screw, and a piezoelectric brake that holds the mirror s position while the unit is unpowered. An interferometric linear position sensor senses the actuator s position. The AMMs were developed for an Astrometric Beam Combiner (ABC) optical bench, which is part of an interferometer development. Custom electronics were also developed to accommodate the presence of multiple AMMs within the ABC and provide a compact, all-in-one solution to power and control the AMMs.

Studying the Pair WDS 01487+7528 = HJ 2075 AB Using the GAIA-DR1 Data

NASA Astrophysics Data System (ADS)

Romero, Francisco Rica

2018-01-01

In September 2016, the European Space Agency (ESA) released GAIA-DR1. ESA also published TGAS, a subset of Gaia source comprising those stars in the Hipparcos and Tycho-2 catalogs for which a full 5-parameters astrometric solution have been achieved. After publication of TGAS, the author decided to use the parallaxes and proper motions to review the double stars studied by LIADA’s Double Star Section during 2003. This year LIADA measured and studied 103 pairs of which only 10 have both stellar components listed in TGAS. Of those 10 pairs, 80% (8 double stars) are optical and only 2 are physical (with common parallaxes and proper motions).The main object of this work is a new study of HJ 2075 AB (WDS 01487+7528), located at 60 pc and composed of stars of 10.0 and 11.3 magnitudes with spectral types G8V and K4V separated by 31". This is a physical pair according to TGAS data (common parallaxes and proper motions).

TIMING OF FIVE MILLISECOND PULSARS DISCOVERED IN THE PALFA SURVEY

DOE Office of Scientific and Technical Information (OSTI.GOV)

Scholz, P.; Kaspi, V. M.; Ferdman, R. D.

2015-02-20

We present the discovery of five millisecond pulsars (MSPs) from the PALFA Galactic plane survey using Arecibo. Four of these (PSRs J0557+1551, J1850+0244, J1902+0300, and J1943+2210) are binary pulsars whose companions are likely white dwarfs, and one (PSR J1905+0453) is isolated. Phase-coherent timing solutions, ranging from ∼1 to ∼3 yr in length, and based on observations from the Jodrell Bank and Arecibo telescopes, provide precise determinations of spin, orbital, and astrometric parameters. All five pulsars have large dispersion measures (>100 pc cm{sup –3}, within the top 20% of all known Galactic field MSPs) and are faint (1.4 GHz flux densitymore » ≲0.1 mJy, within the faintest 5% of all known Galactic field MSPs), illustrating PALFA's ability to find increasingly faint, distant MSPs in the Galactic plane. In particular, PSR J1850+0244 has a dispersion measure of 540 pc cm{sup –3}, the highest of all known MSPs. Such distant, faint MSPs are important input for accurately modeling the total Galactic MSP population.« less

RAVE-Gaia and the impact on Galactic archeology

NASA Astrophysics Data System (ADS)

Kunder, Andrea

2018-04-01

The new data release (DR5) of the RAdial Velocity Experiment (RAVE) includes radial velocities of 520,781 spectra of 457,588 individual stars, of which 215,590 individual stars are released in the Tycho-Gaia astrometric solution (TGAS) in Gaia DR1. Therefore, RAVE contains the largest TGAS overlap of the recent and ongoing Milky Way spectroscopic surveys. Most of the RAVE stars also contain stellar parameters (effective temperature, surface gravity, overall metallicity), as well as individual abundances for Mg, Al, Si, Ca, Ti, Fe, and Ni. Combining RAVE with TGAS brings the uncertainties in space velocities down by a factor of 2 for stars in the RAVE volume - 10 km s-1 uncertainties in space velocities are now able to be derived for the majority (70%) of the RAVE-TGAS sample, providing a powerful platform for chemo-dynamic analyses of the Milky Way. Here we discuss the RAVE-TGAS impact on Galactic archaeology as well as how the Gaia parallaxes can be used to break degeneracies within the RAVE spectral regime for an even better return in the derivation of stellar parameters and abundances.

Interplanetary gas. XX - Does the radial solar wind speed increase with latitude

NASA Technical Reports Server (NTRS)

Brandt, J. C.; Harrington, R. S.; Roosen, R. G.

1975-01-01

The astrometric technique used to derive solar wind speeds from ionic comet-tail orientations has been used to test the suggestion that the radial solar wind speed is higher near the solar poles than near the equator. We find no evidence for the suggested latitude variation.

Erratum: Retraction Note to: "The Second Version of the OCARS Catalog of Optical Characteristics of Astrometric Radio Sources" [Astronomy Reports 60, 996 (2016)

NASA Astrophysics Data System (ADS)

Malkin, Z. M.

2018-04-01

The Editor-in-Chief is retracting this article [1] because data from the RFC catalog, http://astrogeo.org/rfc, were used without permission from the copyright holder. The author admitted the decision to retract.

Observations of Spacecraft Targets, Unusual Asteroids, and Targets of Opportunity

NASA Technical Reports Server (NTRS)

Tholen, David J.

1998-01-01

Obtain physical and astrometric observations of: (1) spacecraft targets to support mission operations; (2) known asteroids with unusual orbits to help determine their origin; and (3) newly discovered minor planets (including both asteroids and comets) that represent a particular opportunity to add significant new knowledge of the Solar System.

NASA's future plans for space astronomy and astrophysics

NASA Technical Reports Server (NTRS)

Kaplan, Mike

1992-01-01

A summary is presented of plans for the future NASA astrophysics missions called SIRTF (Space Infrared Telescope Facility), SOFIA (Stratospheric Observatory for Infrared Astronomy), SMIM (Submillimeter Intermdiate Mission), and AIM (Astrometric Interferometry Mission), the Greater Observatories, and MFPE (Mission From Planet Earth). Technology needs for these missions are briefly described.

Washington Correlator

NASA Technical Reports Server (NTRS)

Hall, David M.; Boboltz, David

2013-01-01

This report summarizes the activities of the Washington Correlator for 2012. The Washington Correlator provides up to 80 hours of attended processing per week plus up to 40 hours of unattended operation, primarily supporting Earth Orientation and astrometric observations. In 2012, the major programs supported include the IVS-R4, IVS-INT, APSG, and CRF observing sessions.

Searching for New Double Stars with a Computer

NASA Astrophysics Data System (ADS)

Bryant, T. V.

2015-04-01

The advent of computers with large amounts of RAM memory and fast processors, as well as easy internet access to large online astronomical databases, has made computer searches based on astrometric data practicable for most researchers. This paper describes one such search that has uncovered hitherto unrecognized double stars.

Misfit stresses in a composite core-shell nanowire with an eccentric parallelepipedal core subjected to one-dimensional cross dilatation eigenstrain

NASA Astrophysics Data System (ADS)

Krasnitckii, S. A.; Kolomoetc, D. R.; Smirnov, A. M.; Gutkin, M. Yu

2017-03-01

We present an analytical solution to the boundary-value problem in the classical theory of elasticity for a core-shell nanowire with an eccentric parallelepipedal core of an arbitrary rectangular cross section. The core is subjected to one-dimensional cross dilatation eigenstrain. The misfit stresses are found in a concise and transparent closed form which is convenient for practical use in theoretical modeling of misfit relaxation processes.

Intrinsic Aniostropic Anelasticity of Hcp Iron Due to Light Element Solute Atoms

NASA Astrophysics Data System (ADS)

Redfern, S. A. T.

2014-12-01

Earth's inner core is elastically anisotropic, with seismology showing faster wave propagation along the polar axis compared to the equatorial plane. Some inner core studies report anisotropic seismic attenuation. Attenuation of body-waves has, previously, been postulated to be due to scattering by anisotropic microstructure, but recent normal mode studies also show strong anisotropic attenuation (Mäkinen et al. 2014). This suggests that the anisotropic attenuation is a result of the intrinsic (and anisotropic) anelastic properties of the solid iron alloy forming Earth's inner core. Here, I consider the origins of inner core anisotropic attenuation. Possibilities include grain boundary relaxation, dislocation bowing/glide, or point defect (alloying element) relaxations. The inner core is an almost perfect environment for near-equilibrium crystallisation, with very low temperature gradients across the inner core, low gravity, and slow crystallisation rates. It is assumed that grain sizes may be of the order of hundreds of metres. This implies vanishingly small volumes of grain boundary, and insignificant grain boundary relaxation. The very high homologous temperature and the absence of obvious deviatoric stress, also leads one to conclude that dislocation densities are low. On the other hand, estimates for light element concentrations are of the order of a few % with O, S, Si, C and H at various times being suggested as candidate elements. Light element solutes in hcp metals contribute to intrinsic anelastic attenuation if they occur in sufficient concentrations to pair and form elastic dipoles. Switching of dipoles under the stress of a passing seismic wave will result in anelastic mechanical loss. Such attenuation has been measured in hcp metals in the lab, and is anisotropic due to the intrinsic elastic anisotropy of the host lattice. Such solute pair relaxations result in a "Zener effect", which is suggested here to be responsible for observed anisotropic seismic attenuation. Zener relaxation magnitude scales with solute concentrationand is consistent with around 5% loght element. Variations in attenuation are expected in a core with spatially varying concentrations of light element, and attenuation tomography of the inner core could, therefore, be employed to map chemical heterogeneity.

A fiber-optic sensor based on no-core fiber and Faraday rotator mirror structure

NASA Astrophysics Data System (ADS)

Lu, Heng; Wang, Xu; Zhang, Songling; Wang, Fang; Liu, Yufang

2018-05-01

An optical fiber sensor based on the single-mode/no-core/single-mode (SNS) core-offset technology along with a Faraday rotator mirror structure has been proposed and experimentally demonstrated. A transverse optical field distribution of self-imaging has been simulated and experimental parameters have been selected under theoretical guidance. Results of the experiments demonstrate that the temperature sensitivity of the sensor is 0.0551 nm/°C for temperatures between 25 and 80 °C, and the correlation coefficient is 0.99582. The concentration sensitivity of the device for sucrose and glucose solutions was found to be as high as 12.5416 and 6.02248 nm/(g/ml), respectively. Curves demonstrating a linear fit between wavelength shift and solution concentration for three different heavy metal solutions have also been derived on the basis of experimental results. The proposed fiber-optic sensor design provides valuable guidance for the measurement of concentration and temperature.

Assembly of Modified Ferritin Proteins on Carbon Nanotubes and its Electrocatalytic Activity for Oxygen Reduction

NASA Technical Reports Server (NTRS)

Kim, Jae-Woo; Lillehei, Peter T.; Park, Cheol

2012-01-01

Highly effective dispersions of carbon nanotubes (CNTs) can be made using a commercially available buffer solution. Buffer solutions of 3-(N-morpholino)-propanesulfonic acid (MOPS), which consists of a cyclic ring with nitrogen and oxygen heteroatoms, a charged group, and an alkyl chain greatly enhance the dispersibility and stability of CNTs in aqueous solutions. Additionally, the ability of biomolecules, especially cationized Pt-cored ferritins, to adhere onto the well-dispersed CNTs in the aqueous buffer solution is also improved. This was accomplished without the use of surfactant molecules, which are detrimental to the electrical, mechanical, and other physical properties of the resulting products. The assembled Pt-cored ferritin proteins on the CNTs were used as an electrocatalyst for oxygen reduction

Dissipative soliton vortices and tropical cyclones

NASA Astrophysics Data System (ADS)

Chefranov, S. G.; Chefranov, A. G.

2017-10-01

We have obtained a new exact steady-state solution to the hydrodynamic equation for a viscous incompressible liquid, which is a generalization of the well-known Sullivan solution (1959), taking into account additionally the external (Eckman) friction and rotation of the system as a single whole. In contrast to the radial structure of a Sullivan vortex, different circulation directions of velocity field tangential component are possible in the new solution in the inner and outer cells. We have considered the correspondence of this solution to the radial vortex structure observed in tropical cyclones, where the precisely anticyclonic circulation always exists in the inner core (typhoon, hurricane eye), which is associated with descending vertical currents for the cyclonic direction of rotation (as well as ascending currents) outside this core.

A revised estimate of the distance to the clouds in the Chamaeleon complex using the Tycho-Gaia Astrometric Solution

NASA Astrophysics Data System (ADS)

Voirin, Jordan; Manara, Carlo F.; Prusti, Timo

2018-03-01

Context. The determination of the distance to dark star-forming clouds is a key parameter to derive the properties of the cloud itself and of its stellar content. This parameter is still loosely constrained even in nearby star-forming regions. Aim. We want to determine the distances to the clouds in the Chamaeleon-Musca complex and explore the connection between these clouds and the large-scale cloud structures in the Galaxy. Methods: We used the newly estimated distances obtained from the parallaxes measured by the Gaia satellite and included in the Tycho-Gaia Astrometric Solution catalog. When known members of a region are included in this catalog we used their distances to infer the distance to the cloud. Otherwise, we analyzed the dependence of the color excess on the distance of the stars and looked for a turn-on of this excess, which is a proxy of the position of the front-edge of the star-forming cloud. Results: We are able to measure the distance to the three Chamaeleon clouds. The distance to Chamaeleon I is 179-10-10+11+11 pc, where the quoted uncertainties are statistical and systematic uncertainties, respectively, 20 pc further away than previously assumed. The Chamaeleon II cloud is located at the distance of 181-5-10+6+11 pc, which agrees with previous estimates. We are able to measure for the first time a distance to the Chamaeleon III cloud of 199-7-11+8+12 pc. Finally, the distance of the Musca cloud is smaller than 603-70-92+91+133 pc. These estimates do not allow us to distinguish between the possibility that the Chamaeleon clouds are part of a sheet of clouds parallel to the Galactic plane, or perpendicular to it. Conclusions: We measured a larger distance to the Chamaeleon I cloud than assumed in the past, confirmed the distance to the Chamaeleon II region, and measured for the first time the distance to the Chamaleon III cloud. These values are consistent with the scenario in which the three clouds are part of a single large-scale structure. Gaia Data Release 2 will allow us to put more stringent constraints on the distances to these clouds by giving us access to parallax measurements for a larger number of members of these regions. Tables 3-6 are only available at the CDS via anonymous ftp to http://cdsarc.u-strasbg.fr (http://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/610/A64

Registration of H2O and SiO masers in the Calabash Nebula to confirm the planetary nebula paradigm

NASA Astrophysics Data System (ADS)

Dodson, R.; Rioja, M.; Bujarrabal, V.; Kim, J.; Cho, S. H.; Choi, Y. K.; Youngjoo, Y.

2018-05-01

We report on the astrometric registration of very long baseline interferometry images of the SiO and H2O masers in OH 231.8+4.2, the iconic proto-planetary nebula also known as the Calabash nebula, using the Korean VLBI Network and source frequency phase referencing. This, for the first time, robustly confirms the alignment of the SiO masers, close to the asymptotic giant branch star, driving the bilobe structure with the water masers in the outflow. We are able to trace the bulk motions for the H2O masers over the last few decades to be 19 km s-1 and deduce that the age of this expansion stage is 38 ± 2 yr. The combination of this result with the distance allows a full 3D reconstruction and confirms that the H2O masers lie on and expand along the known large-scale symmetry axis and that the outflow is only a few decades old, so mass loss is almost certainly ongoing. Therefore, we conclude that the SiO emission marks the stellar core of the nebular, the H2O emission traces the expansion, and there must be multiple epochs of ejection to drive the macro-scale structure.

Radial velocities of stars in the globular cluster M4 and the cluster distance

NASA Technical Reports Server (NTRS)

Peterson, R. C.; Rees, Richard F.; Cudworth, Kyle M.

1995-01-01

The internal stellar velocity distribution of the globular cluster M4 is evaluated from nearly 200 new radial velocity measurements good to 1 km/s and a rederivation of existing proper motions. The mean radial velocity of the cluster is 70.9 +/- 0.6 km/s. The velocity dispersion is 3.5 +/- 0.3 km/s at the core, dropping marginally towards the outskirts. Such a low internal dispersion is somewhat at odds with the cluster's orbit, for which the perigalacticon is sufficiently close to the galactic center that the probability of cluster disruption is high; a tidal radius two-thirds the currently accepted value would eliminate the discrepancy. The cluster mass-to-light ratio is also small, M/L(sub V) = 1.0 +/- 0.4 in solar units. M4 thus joins M22 as a cluster of moderate and concentration with a mass-to-light ratio among the lowest known. The astrometric distance to the cluster is also smaller than expected, 1.72 +/- 0.14 kpc. This is only consistent with conventional estimates of the luminosity of horizontal branch stars provided an extinction law R = A(sub V)/E(B-V) approximately 4 is adopted, as has been suggested recently by several authors.

NPOI: recent technology and science

NASA Astrophysics Data System (ADS)

Benson, James A.; Hutter, Donald J.; Johnston, Kenneth J.; Zavala, Robert T.; White, Nathaniel M.; Pauls, Thomas A.; Gilbreath, G. C.; Armstrong, J. T.; Hindsley, Robert B.

2004-10-01

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.

Optical Imagers | CTIO

Science.gov Websites

DECam SAM 0.9-m CCD Goodman SOI Optical Spectrographs CHIRON COSMOS Goodman Filters Telescopes Blanco 4 magnitudes, astrometric, and spectral properties Filters Filter Overview Filter list (all filters up to and including 4x4-inch, sorted by wavelength) Filters - 3 & 4 inch (for SOAR, Schmidt, 0.9-m imaging

VizieR Online Data Catalog: Infrared excesses of Hipparcos stars (McDonald+, 2012)

NASA Astrophysics Data System (ADS)

McDonald, I.; Zijlstra, A. A.; Boyer, M. L.

2013-08-01

The new Hipparcos (Hp)/Tycho (BT, VT) reduction (van Leeuwen 2007. Cat. I/311) was used as the primary astrometric and photometric catalogue, to which the other catalogues were matched. Additional data were sourced from SDSS DR8, DENIS, 2MASS, MSX, AKARI, IRAS and Wide surveys. (1 data file).

Asteroid Lightcurve Analysis at Isaac Aznar Observatory Aras De Los Olmos, Valencia, Spain

NASA Astrophysics Data System (ADS)

Macias, Amadeo Aznar

2015-01-01

The Isaac Aznar Observatory conducts astrometric and photometric studies of asteroids. This paper contains the photometric results of four asteroids obtained from 2014 April to August. These asteroids were selected from the Collaborative Asteroid Lightcurve Link (CALL) web site: 1088 Mitaka, 2956 Yeomans, 3894 Williamcooke, and (4555) 1974QL.

Statistical description of tectonic motions

NASA Technical Reports Server (NTRS)

Agnew, Duncan Carr

1993-01-01

This report summarizes investigations regarding tectonic motions. The topics discussed include statistics of crustal deformation, Earth rotation studies, using multitaper spectrum analysis techniques applied to both space-geodetic data and conventional astrometric estimates of the Earth's polar motion, and the development, design, and installation of high-stability geodetic monuments for use with the global positioning system.

Astrometric surveys in the Gaia era

NASA Astrophysics Data System (ADS)

Zacharias, Norbert

2018-04-01

The Gaia first data release (DR1) already provides an almost error free optical reference frame on the milli-arcsecond (mas) level allowing significantly better calibration of ground-based astrometric data than ever before. Gaia DR1 provides positions, proper motions and trigonometric parallaxes for just over 2 million stars in the Tycho-2 catalog. For over 1.1 billion additional stars DR1 gives positions. Proper motions for these, mainly fainter stars (G >= 11.5) are currently provided by several new projects which combine earlier epoch ground-based observations with Gaia DR1 positions. These data are very helpful in the interim period but will become obsolete with the second Gaia data release (DR2) expected in April 2018. The era of traditional, ground-based, wide-field astrometry with the goal to provide accurate reference stars has come to an end. Future ground-based astrometry will fill in some gaps (very bright stars, observations needed at many or specific epochs) and mainly will go fainter than the Gaia limit, like the PanSTARRS and the upcoming LSST surveys.

Distance to VY Canis Majoris with VERA

NASA Astrophysics Data System (ADS)

Choi, Yoon Kyung; Hirota, Tomoya; Honma, Mareki; Kobayashi, Hideyuki; Bushimata, Takeshi; Imai, Hiroshi; Iwadate, Kenzaburo; Jike, Takaaki; Kameno, Seiji; Kameya, Osamu; Kamohara, Ryuichi; Kan-Ya, Yukitoshi; Kawaguchi, Noriyuki; Kijima, Masachika; Kim, Mi Kyoung; Kuji, Seisuke; Kurayama, Tomoharu; Manabe, Seiji; Maruyama, Kenta; Matsui, Makoto; Matsumoto, Naoko; Miyaji, Takeshi; Nagayama, Takumi; Nakagawa, Akiharu; Nakamura, Kayoko; Oh, Chung Sik; Omodaka, Toshihiro; Oyama, Tomoaki; Sakai, Satoshi; Sasao, Tetsuo; Sato, Katsuhisa; Sato, Mayumi; Shibata, Katsunori M.; Tamura, Yoshiaki; Tsushima, Miyuki; Yamashita, Kazuyoshi

2008-10-01

We report on astrometric observations of H2O masers around the red supergiant VY Canis Majoris carried out with VLBI Exploration of Radio Astrometry (VERA). Based on astrometric monitoring for 13 months, we successfully measured a trigonometric parallax of 0.88±0.08 mas, corresponding to a distance of 1.14+0.11-0.09kpc. This is the most accurate determined distance to VY CMa and the first one based on an annual parallax measurement. The luminosity of VY CMa has been overestimated due to a previously accepted distance. With our result, we re-estimated the luminosity of VY CMa to be (3±0.5) × 105Lodot using the bolometric flux integrated over optical and IR wavelengths. This improved luminosity value makes the location of VY CMa on the Hertzsprung-Russell (HR) diagram much closer to the theoretically allowable zone (i.e. the left side of the Hayashi track) than previous ones, though the uncertainty in the effective temperature of the stellar surface still does not permit us to make a final conclusion.

The future of Astrometry in Space

NASA Astrophysics Data System (ADS)

Vallenari, Antonella

2018-04-01

This contribution focuses on the importance of astrometry and on its future developments. Over the centuries astrometry has greatly contributed to the advance of the knowledge of the Universe. Nowadays a major breakthrough is on the way due to astrometric sky surveys from space. ESA space missions Hipparcos first and then Gaia point out the outstanding contribution that space astrometry can provide to our knowledge in many fields of astrophysics, going from the Milky Way formation and evolution, to stellar astrophysics, extra-galactic astrophysics, and fundamental physics. We briefly outline the properties of Gaia first and second data release, and the accuracies expected end-of-mission. The next big advance in space astrometry would be either to improve the astrometric accuracy of one order of magnitude, or to move to a different wavelength domain. While both options have the potential to bring us in a new era of discovery, they have to face enormous issues. We summarize the future directions in space astrometry that are proposed or under investigation by the scientific community, their main challenges and the expected outcome.

Astrometric Masses of 21 Asteroids, and an Integrated Asteroid Ephemeris

NASA Astrophysics Data System (ADS)

Baer, James J.; Chesley, S. R.

2007-07-01

We apply the technique of astrometric mass determination to measure the masses of 21 main-belt asteroids; the masses of 6 Hebe (7.59 +/- 1.42 x 10-12 SM), 9 Metis (1.03 +/- 0.24 x 10-11 SM), 17 Thetis (6.17 +/- 0.64 x 10-13 SM), 19 Fortuna (5.41 +/- 0.76 x 10-12 SM), and 189 Phthia (1.87 +/- 0.64 x 10-14 SM) appear to be new. The resulting bulk porosities of 11 Parthenope (12%) and 16 Psyche (45%) are smaller than previous values; while the bulk porosities of 52 Europa (41%) and 189 Phthia (64%) are significant. The variations in density within the C- and S-classes are consistent with either heteorogenous mineralogical compositions within each class, significant variations in porosity, or both. To accurately model the forces on these asteroids during the mass determination process, we created an integrated ephemeris of the 300 large asteroids used in preparing the DE-405 planetary ephemeris; this new BC-405 integrated asteroid ephemeris also appears useful in other high-accuracy applications.

Mitigation of Angle Tracking Errors Due to Color Dependent Centroid Shifts in SIM-Lite

NASA Technical Reports Server (NTRS)

Nemati, Bijan; An, Xin; Goullioud, Renaud; Shao, Michael; Shen, Tsae-Pyng; Wehmeier, Udo J.; Weilert, Mark A.; Wang, Xu; Werne, Thomas A.; Wu, Janet P.;

Understanding Fomalhaut as a Cooper pair

NASA Astrophysics Data System (ADS)

Feng, F.; Jones, H. R. A.

2018-03-01

Fomalhaut is a nearby stellar system and has been found to be a triple based on astrometric observations. With new radial velocity and astrometric data, we study the association between Fomalhaut A, B, and C in a Bayesian framework, finding that the system is gravitationally bound or at least associated. Based on simulations of the system, we find that Fomalhaut C can be easily destabilized through combined perturbations from the Galactic tide and stellar encounters. Considering that observing the disruption of a triple is probably rare in the solar neighbourhood, we conclude that Fomalhaut C is a so-called `gravitational pair' of Fomalhaut A and B. Like the Cooper pair mechanism in superconductors, this phenomenon only appears once the orbital energy of a component becomes comparable with the energy fluctuations caused by the environment. Based on our simulations, we find (1) an upper limit of 8 km s-1 velocity difference is appropriate when selecting binary candidates, and (2) an empirical formula for the escape radius, which is more appropriate than tidal radius when measuring the stability of wide binaries.

The Gaia–WISE Extragalactic Astrometric Catalog

NASA Astrophysics Data System (ADS)

Paine, Jennie; Darling, Jeremy; Truebenbach, Alexandra

2018-06-01

The Gaia mission has detected a large number of active galactic nuclei (AGNs) and galaxies, but these objects must be identified among the thousandfold more numerous stars. Extant astrometric AGN catalogs do not have the uniform sky coverage required to detect and characterize the all-sky, low-multipole proper motion signals produced by the barycenter motion, gravitational waves, and cosmological effects. To remedy this, we present an all-sky sample of 567,721 AGNs in Gaia Data Release 1, selected using WISE two-color criteria. The catalog has fairly uniform sky coverage beyond the Galactic plane, with a mean density of 12.8 AGNs per square degree. The objects have magnitudes ranging from G = 8.8 down to Gaia’s magnitude limit, G = 20.7. The catalog is approximately 50% complete but suffers from low stellar contamination, roughly 0.2%. We predict that the end-of-mission Gaia proper motions for this catalog will enable detection of the secular aberration drift to high significance (23σ) and will place an upper limit on the anisotropy of the Hubble expansion of about 2%.

GIER: A Danish computer from 1961 with a role in the modern revolution of astronomy - II

NASA Astrophysics Data System (ADS)

Høg, Erik

2018-04-01

A Danish computer, GIER, from 1961 played a vital role in the development of a new method for astrometric measurement. This method, photon counting astrometry, ultimately led to two satellites with a significant role in the modern revolution of astronomy. A GIER was installed at the Hamburg Observatory in 1964 where it was used to implement the entirely new method for the measurement of stellar positions by means of a meridian circle, at that time the fundamental instrument of astrometry. An expedition to Perth in Western Australia with the instrument and the computer was a success. This method was also implemented in space in the first ever astrometric satellite Hipparcos launched by ESA in 1989. The Hipparcos results published in 1997 revolutionized astrometry with an impact in all branches of astronomy from the solar system and stellar structure to cosmic distances and the dynamics of the Milky Way. In turn, the results paved the way for a successor, the one million times more powerful Gaia astrometry satellite launched by ESA in 2013. Preparations for a Gaia successor in twenty years are making progress.

Astrometric Telescope Facility isolation and pointing study

NASA Technical Reports Server (NTRS)

Hibble, William; Allen, Terry; Jackson, Louis; Medbery, James; Self, Richard

1988-01-01

The Astrometric Telescope Facility (ATF), an optical telescope designed to detect extrasolar planetary systems, is scheduled to be a major user of the Space Station's Payload Pointing System (PPS). However, because the ATF has such a stringent pointing stability specification and requires + or - 180 deg roll about its line of sight, mechanisms to enhance the basic PPS capability are required. The ATF pointing performance achievable by the addition of a magnetic isolation and pointing system (MIPS) between the PPS upper gimbal and the ATF, and separately, by the addition of a passive isolation system between the Space Station and the PPS base was investigated. The candidate MIPS can meet the ATF requirements in the presence of a 0.01 g disturbance. It fits within the available annular region between the PPS and the ATF while meeting power and weight limitations and providing the required roll motion, payload data and power services. By contrast, the passive base isolator system must have an unrealistically low isolation bandwidth on all axes to meet ATF pointing requirements and does not provide roll about the line of sight.

Electrophoretic extraction of proteins from two-dimensional electrophoresis gel spots

DOEpatents

Zhang, Jian-Shi; Giometti, Carol S.; Tollaksen, Sandra L.

1989-01-01

After two-dimensional electrophoresis of proteins or the like, resulting in a polyacrylamide gel slab having a pattern of protein gel spots thereon, an individual protein gel spot is cored out from the slab, to form a gel spot core which is placed in an extraction tube, with a dialysis membrane across the lower end of the tube. Replicate gel spots can be cored out from replicate gel slabs and placed in the extraction tube. Molten agarose gel is poured into the extraction tube where the agarose gel hardens to form an immobilizing gel, covering the gel spot cores. The upper end portion of the extraction tube is filled with a volume of buffer solution, and the upper end is closed by another dialysis membrane. Upper and lower bodies of a buffer solution are brought into contact with the upper and lower membranes and are provided with electrodes connected to the positive and negative terminals of a DC power supply, thereby producing an electrical current which flows through the upper membrane, the volume of buffer solution, the agarose, the gel spot cores and the lower membrane. The current causes the proteins to be extracted electrophoretically from the gel spot cores, so that the extracted proteins accumulate and are contained in the space between the agarose gel and the upper membrane. A high percentage extraction of proteins is achieved. The extracted proteins can be removed and subjected to partial digestion by trypsin or the like, followed by two-dimensional electrophoresis, resulting in a gel slab having a pattern of peptide gel spots which can be cored out and subjected to electrophoretic extraction to extract individual peptides.

26. SOME CORES, SUCH AS THESE IN THE BRASS FOUNDRY ...

Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

26. SOME CORES, SUCH AS THESE IN THE BRASS FOUNDRY CA.1950, ARE DIPPED INTO A SOLUTION PRIOR TO BEING BAKED IN THE CORE OVEN BEHIND, TO SET THE RESIN AND CREATE A STRUCTURE STRONG ENOUGH TO HOLD UP AGAINST MOLTEN METAL. - Stockham Pipe & Fittings Company, 4000 Tenth Avenue North, Birmingham, Jefferson County, AL

Final Research Performance Report - Small Molecular Associative Carbon Dioxide (CO 2) Thickeners for Improved Mobility Control

DOE Office of Scientific and Technical Information (OSTI.GOV)

Enick, Robert M.

The initial objective of this project was to promote the application of a CO 2 thickener for improved mobility control during CO 2 EOR based on solubility tests, viscosity tests, and core floods. Ultimately, it was demonstrated that the CO 2-soluble polymeric thickeners are much better suited for use a CO 2-soluble conformance control agents for diverting the flow of CO 2 away from thief zones. Our team generated several effective small molecule CO 2 thickeners with ARPA-e funding. Unfortunately, none of these small molecule thickeners could dissolve in CO 2 without the addition of unacceptably large amounts of hexanemore » or toluene as a co-solvent Therefore none were viable candidates for the core flooding studies associated with NETL award. Therefore during the entire core flood testing program associated with this NETL award, our team used only the most promising polymeric CO 2 thickener, a polyfluoroacrylate (PFA). In order to produce an environmentally benign polymer, the monomer used to make the new polymers used in this study was a fluoroacrylate that contains only six fluorinated carbons. We verified CO 2 solubility with a phase behavior cell. The thickening potential of all polymer samples was substantiated with a falling ball viscometer and a falling cylinder viscometer at Pitt. Two different viscometers were used to determine the increase in CO 2 viscosity that could be achieved via the dissolution of PFA. Praxair, which has an interest in thickening CO 2 for pilot EOR projects and for waterless hydraulic fracturing, agreed to measure the viscosity of CO 2-PFA solutions at no cost to the project. Falling cylinder viscometery was conducted at Pitt in our windowed high pressure phase behavior cell. Both apparatuses indicated that at very low shear rates the CO 2 viscosity increased by a factor of roughly 3.5 when 1wt% PFA was dissolved in the CO 22. Our team also planned thickener concentrations and compositions at Pitt for the core tests that were conducted at Special Core Analysis Laboratories, Inc., (SCAL) in Midland, TX, where the ability for PFA to reduce CO 2 mobility in a core was then tested. During the beginning of these tests, the PFA polymer was then shown to impart reasonable improvements in mobility control during the SCAL core tests; as the CO 2-PFA solution displaced CO 2 from the core at a constant volumetric flow rate, the pressure drop increased as expected. However, as the test progressed, there was clear and surprising evidence of dramatic reductions in core permeability due to PFA adsorption, especially for sandstones. For example, as the CO 2-PFA solution displaced pure CO 2 from sandstone and limestone cores, the pressure drop increased by factors of multiple hundreds to over a thousand. It was subsequently demonstrated that the PFA injected into the core either (a) adsorbed strongly and irreversibly onto the rock surfaces, (b) deposited/precipitated within the rock, thereby blocking pores in a manner that could be dislodged by large changes in flow rate or flow direction, or (c) remained in solution and passed completely through the core. The loss of PFA to the porous media and the unacceptably large increases in pressure drop both indicated that PFA was inappropriate for CO 2 EOR mobility control, where thickener adsorption must be minimized and mobility reductions of only 10-100-fold are typically required. However, we realized that because the CO 2-PFA solution could greatly reduce the permeability of porous media, it could serve as a near wellbore conformance control agent for blocking “thief zones”, where adsorption is acceptable and dramatic increases in pressure drop are desirable. These effects were more dramatic for sandstone than for limestone. Therefore, these PFA fluoroacrylate polymers can serve as a CO 2-soluble conformance control agent for CO 2-EOR, especially in sandstone formations. This injection of a single phase solution of CO 2-PFA for permeability reduction is (to the best of our knowledge) the first report of a CO 2-soluble conformance control additive. We also demonstrated that the optimal strategy for using CO 2-PFA solutions for conformance control is analogous to the application of water-based polymeric gels; the CO 2-PFA solution should first be injected only in an isolated thief zone to induce dramatic reductions in permeability only in that thief zone, and then CO 2 should be injected into all of the zones. Finally, it was noted that given the propensity of PFA to adsorb onto sandstone, the adsorption of PFA from CO 2-PFA solutions onto cement surfaces promote the sealing of extremely fine cracks in casing cement.« less

A Model for Astrometric Detection and Characterization of Multi-Exoplanet Systems

NASA Astrophysics Data System (ADS)

April Thompson, Maggie; Spergel, David N.

2017-01-01

In this thesis, we develop an approximate linear model of stellar motion in multi- planet systems as an aid to observers using the astrometric method to detect and characterize exoplanets. Recent and near-term advances in satellite and ground-based instruments are on the threshold of achieving sufficient (~10 micro-arcsecond) angular accuracies to allow astronomers to measure and analyze the transverse mo- tion of stars about the common barycenter in single- and multi-planet systems due to the gravitational influence of companion planets. Given the emerging statistics of extrasolar planetary systems and the long observation periods required to assess exoplanet influences, astronomers should find an approximate technique for preliminary estimates of multiple planet numbers, masses and orbital parameters useful in determining the most likely stellar systems for follow-up studies. In this paper, we briefly review the history of astrometry and discuss its advantages and limitations in exoplanet research. In addition, we define the principal astrometric signature and describe the main variables affecting it, highlighting astrometry’s complementary role to radial velocity and photometric transit exoplanet detection techniques. We develop and test a Python computer code using actual data and projections of the Sun’s motion due to the influence of the four gas giants in the solar system. We then apply this model to over 50 hypothetical massive two- and three-exoplanet systems to discover useful general patterns by employing a heuristic examination of key aspects of the host star’s motion over long observation intervals. Finally, we modify the code by incorporating an inverse least-squares fit program to assess its efficiency in identifying the main characteristics of multi-planet systems based on observational records over 5-, 10- and 20-year periods for a variety of actual and hypothetical exoplanetary systems. We also explore the method’s sensitivity to measurement frequencies, intervals and errors.

NEAT: a spatial telescope to detect nearby exoplanets using astrometry

NASA Astrophysics Data System (ADS)

Crouzier, Antoine

2015-01-01

With the present state of exoplanet detection techniques, none of the rocky planets of the Solar System would be discovered, yet their presence is a very strong constraint on the scenarios of formation of planetary systems. Astrometry, by measuring the reflex effect of planets on their central host stars, lead us to the mass of planets and to their orbit determination. This technique is used frequently and is very successful to determine the masses and the orbits of binary stars. From space, it is possible to use differential astrometry around nearby Solar-type stars to detect exoplanets down to one Earth mass in habitable zone, where the sensitivity of the technique is optimal. Finding habitable Earths in the Solar neighborhood would be a major step forward for exoplanet detection and these planets would be prime targets for attempting to find life outside of the Solar System, by searching for bio-markers in their atmospheres. A scientific consortium has formed to promote this kind of astrometric space mission. A mission called NEAT (Nearby Earth Astrometric Telescope) has been proposed to ESA in 2010. A laboratory testbed called NEAT-demo was assembled at IPAG, its main goal is to demonstrate CCD detector calibration to the required accuracy. During my PhD, my activities were related to astrophysical aspects as well as instrumental aspects of the mission. Regarding the scientific case, I compiled a catalog of mission target stars and reference stars (needed for the differential astrometric measurements) and I estimated the scientific return of NEAT-like missions in terms of number of detected exoplanets and their parameter distributions. The second aspect of the PhD is relative to the testbed, which mimics the NEAT telescope configuration. I am going to present the testbed itself, the data analysis methods and the results. An accuracy of 3e-4 pixel was obtained for the relative positions of artificial stars and we have determined that measures of pixel positions by the metrology is currently limited by stray light.

Mass of the Local Group from Proper Motions of Distant Dwarf Galaxies

NASA Astrophysics Data System (ADS)

van der Marel, Roeland

2010-09-01

The Local Group and its two dominant spirals, the Milky Way and M31, have become the benchmark for testing many aspects of cosmological and galaxy formation theories, due to many exciting new discoveries in the past decade. However, it is difficult to put results in a proper cosmological context, because our knowledge of the mass M of the Local Group remains uncertain by a factor 4. In units of 10^{12} solar masses, a spherical infall model for the zero-velocity surface gives M 1.3; the sum of estimates for the Milky Way and M31 masses gives M 2.6; and the Local Group Timing argument for the M31 orbit gives M 5.6. It is possible to discriminate between the proposed masses by calculating the orbits of galaxies at the edge of the Local Group, which requires knowledge of transverse velocity components. We therefore propose to use ACS/WFC to determine the proper motions of the 4 dwarf galaxies near the edge of the Local Group {Cetus, Leo A, Tucana, Sag DIG} for which deep first epoch data {with 5-7 year time baselines} already exist in the HST Archive. Our team has extensive expertise with HST astrometric science, and our past/ongoing work for, e.g., Omega Cen, LMC/SMC and M31 show that the necessary astrometric accuracy is within the reach of HST's demonstrated capabilities. We have developed, tested, and published a new technique that uses compact background galaxies as astrometric reference sources, and we have already reduced the first epoch data. The final predicted transverse velocity accuracy, 36 km/s when averaged over the sample, will be sufficient to discriminate between each of the proposed Local Group masses at 2-sigma significance {4-sigma between the most extreme values}. Our project will yield the most accurate Local Group mass determination to date, and only HST can achieve the required accuracy.

An Astrometric Facility For Planetary Detection On The Space Station

NASA Astrophysics Data System (ADS)

Nishioka, Kenji; Scargle, Jeffrey D.; Givens, John J.

1987-09-01

An Astrometric Telescope Facility (ATF) for planetary detection is being studied as a potential Space Station initial operating capability payload. The primary science objective of this mission is the detection and study of planetary systems around other stars. In addition, the facility will be capable of other astrometric measurements such as stellar motions of other galaxies and highly precise direct measurement of stellar distances within the Milky Way Galaxy. This paper summarizes the results of a recently completed ATF preliminary systems definition study. Results of this study indicate that the preliminary concept for the facility is fully capable of meeting the science objectives without the development of any new technologies. This preliminary systems study started with the following basic assumptions: 1) the facility will be placed in orbit by a single Shuttle launch, 2) the Space Station will provide a coarse pointing system , electrical power, communications, assembly and checkout, maintenance and refurbishment services, and 3) the facility will be operated from a ground facility. With these assumptions and the science performance requirements a preliminary "strawman" facility was designed. The strawman facility design with a prime-focus telescope of 1.25-m aperture, f-ratio of 13 and a single prime-focus instrument was chosen to minimize random and systemmatic errors. Total facility mass is 5100 kg and overall dimensions are 1.85-m diam by 21.5-m long. A simple straightforward operations approach has been developed for ATF. A real-time facility control is not normally required, but does maintain a near real-time ground monitoring capability for facility and science data stream on a full-time basis. Facility observational sequences are normally loaded once a week. In addition, the preliminary system is designed to be fail-safe and single-fault tolerant. Routine interactions by the Space Station crew with ATF will not be necessary, but onboard controls are provided for crew override as required for emergencies and maintenance.

Analysis of the Bayesian Cramér-Rao lower bound in astrometry. Studying the impact of prior information in the location of an object

NASA Astrophysics Data System (ADS)

Echeverria, Alex; Silva, Jorge F.; Mendez, Rene A.; Orchard, Marcos

2016-10-01

Context. The best precision that can be achieved to estimate the location of a stellar-like object is a topic of permanent interest in the astrometric community. Aims: We analyze bounds for the best position estimation of a stellar-like object on a CCD detector array in a Bayesian setting where the position is unknown, but where we have access to a prior distribution. In contrast to a parametric setting where we estimate a parameter from observations, the Bayesian approach estimates a random object (I.e., the position is a random variable) from observations that are statistically dependent on the position. Methods: We characterize the Bayesian Cramér-Rao (CR) that bounds the minimum mean square error (MMSE) of the best estimator of the position of a point source on a linear CCD-like detector, as a function of the properties of detector, the source, and the background. Results: We quantify and analyze the increase in astrometric performance from the use of a prior distribution of the object position, which is not available in the classical parametric setting. This gain is shown to be significant for various observational regimes, in particular in the case of faint objects or when the observations are taken under poor conditions. Furthermore, we present numerical evidence that the MMSE estimator of this problem tightly achieves the Bayesian CR bound. This is a remarkable result, demonstrating that all the performance gains presented in our analysis can be achieved with the MMSE estimator. Conclusions: The Bayesian CR bound can be used as a benchmark indicator of the expected maximum positional precision of a set of astrometric measurements in which prior information can be incorporated. This bound can be achieved through the conditional mean estimator, in contrast to the parametric case where no unbiased estimator precisely reaches the CR bound.

A statistical study of radio-source structure effects on astrometric very long baseline interferometry observations

NASA Technical Reports Server (NTRS)

Ulvestad, J. S.

1989-01-01

Errors from a number of sources in astrometric very long baseline interferometry (VLBI) have been reduced in recent years through a variety of methods of calibration and modeling. Such reductions have led to a situation in which the extended structure of the natural radio sources used in VLBI is a significant error source in the effort to improve the accuracy of the radio reference frame. In the past, work has been done on individual radio sources to establish the magnitude of the errors caused by their particular structures. The results of calculations on 26 radio sources are reported in which an effort is made to determine the typical delay and delay-rate errors for a number of sources having different types of structure. It is found that for single observations of the types of radio sources present in astrometric catalogs, group-delay and phase-delay scatter in the 50 to 100 psec range due to source structure can be expected at 8.4 GHz on the intercontinental baselines available in the Deep Space Network (DSN). Delay-rate scatter of approx. 5 x 10(exp -15) sec sec(exp -1) (or approx. 0.002 mm sec (exp -1) is also expected. If such errors mapped directly into source position errors, they would correspond to position uncertainties of approx. 2 to 5 nrad, similar to the best position determinations in the current JPL VLBI catalog. With the advent of wider bandwidth VLBI systems on the large DSN antennas, the system noise will be low enough so that the structure-induced errors will be a significant part of the error budget. Several possibilities for reducing the structure errors are discussed briefly, although it is likely that considerable effort will have to be devoted to the structure problem in order to reduce the typical error by a factor of two or more.

Low temperature grown ZnO@TiO{sub 2} core shell nanorod arrays for dye sensitized solar cell application

DOE Office of Scientific and Technical Information (OSTI.GOV)

Goh, Gregory Kia Liang; Le, Hong Quang, E-mail: lehq@imre.a-star.edu.sg; Huang, Tang Jiao

High aspect ratio ZnO nanorod arrays were synthesized on fluorine-doped tin oxide glasses via a low temperature solution method. By adjusting the growth condition and adding polyethylenimine, ZnO nanorod arrays with tunable length were successfully achieved. The ZnO@TiO{sub 2} core shells structures were realized by a fast growth method of immersion into a (NH{sub 4}){sub 2}·TiF{sub 6} solution. Transmission electron microscopy, X-ray Diffraction and energy dispersive X-ray measurements all confirmed the existence of a titania shell uniformly covering the ZnO nanorod's surface. Results of solar cell testing showed that addition of a TiO{sub 2} shell to the ZnO nanorod significantlymore » increased short circuit current (from 4.2 to 5.2 mA/cm{sup 2}), open circuit voltage (from 0.6 V to 0.8 V) and fill factor (from 42.8% to 73.02%). The overall cell efficiency jumped from 1.1% for bare ZnO nanorod to 3.03% for a ZnO@TiO{sub 2} core shell structured solar cell with a 18–22 nm shell thickness, a nearly threefold increase. - Graphical abstract: The synthesis process of coating TiO{sub 2} shell onto ZnO nanorod core is shown schematically. A thin, uniform, and conformal shell had been grown on the surface of the ZnO core after immersing in the (NH{sub 4}){sub 2}·TiF{sub 6} solution for 5–15 min. - Highlights: • ZnO@TiO{sub 2} core shell nanorod has been grown on FTO substrate using low temperature solution method. • TEM, XRD, EDX results confirmed the existing of titana shell, uniformly covered rod's surface. • TiO{sub 2} shell suppressed recombination, demonstrated significant enhancement in cell's efficiency. • Core shell DSSC's efficiency achieved as high as 3.03%, 3 times higher than that of ZnO nanorods.« less

Saturn gravity results obtained from Pioneer 11 tracking data and earth-based Saturn satellite data

NASA Technical Reports Server (NTRS)

Null, G. W.; Lau, E. L.; Biller, E. D.; Anderson, J. D.

1981-01-01

Improved gravity coefficients for Saturn, its satellites and rings are calculated on the basis of a combination of Pioneer 11 spacecraft Doppler tracking data and earth-based determinations of Saturn natural satellite apse and node rates. Solutions are first obtained separately from the coherent Doppler tracking data obtained for the interval from August 20 to September 4, surrounding the time of closest approach, with the effects of solar plasma on radio signal propagation taken into account, and from secular rates for Mimas, Enceladus, Tethys, Dione, Rhea and Titan determined from astrometric data by Kozai (1957, 1976) and Garcia (1972). Combination of the data by the use of the Pioneer solution and corresponding unadjusted covariance matrix as a priori information for a secular rate analysis results in values for the total ring mass of essentially zero at a standard error level of 1.7 x 10 to the -6th Saturn masses, a ratio of solar mass to that of the Saturn system of 3498.09 + or - 0.22, masses of Rhea, Titan and Iapetus of 4.0 + or - 0.9, 238.8 + or - 3, and 3.4 + or - 1.3 x 10 to the -6th Saturn masses, respectively, and second and fourth zonal harmonics of 16,479 + or - 18 and -937 + or - 38, respectively. The harmonic coefficients are noted to be important as boundary conditions in the modeling of the Saturn interior.

Massive parallelization of a 3D finite difference electromagnetic forward solution using domain decomposition methods on multiple CUDA enabled GPUs

NASA Astrophysics Data System (ADS)

Schultz, A.

2010-12-01

3D forward solvers lie at the core of inverse formulations used to image the variation of electrical conductivity within the Earth's interior. This property is associated with variations in temperature, composition, phase, presence of volatiles, and in specific settings, the presence of groundwater, geothermal resources, oil/gas or minerals. The high cost of 3D solutions has been a stumbling block to wider adoption of 3D methods. Parallel algorithms for modeling frequency domain 3D EM problems have not achieved wide scale adoption, with emphasis on fairly coarse grained parallelism using MPI and similar approaches. The communications bandwidth as well as the latency required to send and receive network communication packets is a limiting factor in implementing fine grained parallel strategies, inhibiting wide adoption of these algorithms. Leading Graphics Processor Unit (GPU) companies now produce GPUs with hundreds of GPU processor cores per die. The footprint, in silicon, of the GPU's restricted instruction set is much smaller than the general purpose instruction set required of a CPU. Consequently, the density of processor cores on a GPU can be much greater than on a CPU. GPUs also have local memory, registers and high speed communication with host CPUs, usually through PCIe type interconnects. The extremely low cost and high computational power of GPUs provides the EM geophysics community with an opportunity to achieve fine grained (i.e. massive) parallelization of codes on low cost hardware. The current generation of GPUs (e.g. NVidia Fermi) provides 3 billion transistors per chip die, with nearly 500 processor cores and up to 6 GB of fast (DDR5) GPU memory. This latest generation of GPU supports fast hardware double precision (64 bit) floating point operations of the type required for frequency domain EM forward solutions. Each Fermi GPU board can sustain nearly 1 TFLOP in double precision, and multiple boards can be installed in the host computer system. We describe our ongoing efforts to achieve massive parallelization on a novel hybrid GPU testbed machine currently configured with 12 Intel Westmere Xeon CPU cores (or 24 parallel computational threads) with 96 GB DDR3 system memory, 4 GPU subsystems which in aggregate contain 960 NVidia Tesla GPU cores with 16 GB dedicated DDR3 GPU memory, and a second interleved bank of 4 GPU subsystems containing in aggregate 1792 NVidia Fermi GPU cores with 12 GB dedicated DDR5 GPU memory. We are applying domain decomposition methods to a modified version of Weiss' (2001) 3D frequency domain full physics EM finite difference code, an open source GPL licensed f90 code available for download from www.OpenEM.org. This will be the core of a new hybrid 3D inversion that parallelizes frequencies across CPUs and individual forward solutions across GPUs. We describe progress made in modifying the code to use direct solvers in GPU cores dedicated to each small subdomain, iteratively improving the solution by matching adjacent subdomain boundary solutions, rather than iterative Krylov space sparse solvers as currently applied to the whole domain.

Nanocrystalline p-hydroxyacetanilide (paracetamol) and gold core-shell structure as a model drug deliverable organic-inorganic hybrid nanostructure

NASA Astrophysics Data System (ADS)

Das, Subhojit; Paul, Anumita; Chattopadhyay, Arun

2013-09-01

We report on the generation of core-shell nanoparticles (NPs) having an organic nanocrystal (NC) core coated with an inorganic metallic shell, being dispersed in aqueous medium. First, NCs of p-hydroxyacetanilide (pHA)--known also as paracetamol--were generated in an aqueous medium. Transmission electron microscopy (TEM) and powder X-ray diffraction (XRD) evidenced the formation of pHA NCs and of their crystalline nature. The NCs were then coated with Au to form pHA@Au core-shell NPs, where the thickness of the Au shell was on the order of nanometers. The formation of Au nanoshell--surrounding pHA NC--was confirmed from its surface plasmon resonance (SPR) band in the UV/Vis spectrum and by TEM measurements. Further, on treatment of the core-shell particles with a solution comprising NaCl and HCl (pH < 3), the Au shell could be dissolved, subsequently releasing pHA molecules. The dissolution of Au shell was marked by a gradual diminishing of its SPR band, while the release of pHA molecules in the solution was confirmed from TEM and FTIR studies. The findings suggest that the core-shell NP could be hypothesized to be a model for encapsulating drug molecules, in their crystalline forms, for slow as well as targeted release.We report on the generation of core-shell nanoparticles (NPs) having an organic nanocrystal (NC) core coated with an inorganic metallic shell, being dispersed in aqueous medium. First, NCs of p-hydroxyacetanilide (pHA)--known also as paracetamol--were generated in an aqueous medium. Transmission electron microscopy (TEM) and powder X-ray diffraction (XRD) evidenced the formation of pHA NCs and of their crystalline nature. The NCs were then coated with Au to form pHA@Au core-shell NPs, where the thickness of the Au shell was on the order of nanometers. The formation of Au nanoshell--surrounding pHA NC--was confirmed from its surface plasmon resonance (SPR) band in the UV/Vis spectrum and by TEM measurements. Further, on treatment of the core-shell particles with a solution comprising NaCl and HCl (pH < 3), the Au shell could be dissolved, subsequently releasing pHA molecules. The dissolution of Au shell was marked by a gradual diminishing of its SPR band, while the release of pHA molecules in the solution was confirmed from TEM and FTIR studies. The findings suggest that the core-shell NP could be hypothesized to be a model for encapsulating drug molecules, in their crystalline forms, for slow as well as targeted release. Electronic supplementary information (ESI) available: See DOI: 10.1039/c3nr03566b

Challenges Regarding IP Core Functional Reliability

NASA Technical Reports Server (NTRS)

Berg, Melanie D.; LaBel, Kenneth A.

2017-01-01

For many years, intellectual property (IP) cores have been incorporated into field programmable gate array (FPGA) and application specific integrated circuit (ASIC) design flows. However, the usage of large complex IP cores were limited within products that required a high level of reliability. This is no longer the case. IP core insertion has become mainstream including their use in highly reliable products. Due to limited visibility and control, challenges exist when using IP cores and subsequently compromise product reliability. We discuss challenges and suggest potential solutions to critical application IP insertion.

Solution softening in magnesium alloys: the effect of solid solutions on the dislocation core structure and nonbasal slip.

PubMed

Tsuru, T; Udagawa, Y; Yamaguchi, M; Itakura, M; Kaburaki, H; Kaji, Y

2013-01-16

There is a pressing need to improve the ductility of magnesium alloys so that they can be applied as lightweight structural materials. In this study, a mechanism for enhancing the ductility of magnesium alloys has been pursued using the atomistic method. The generalized stacking fault (GSF) energies for basal and prismatic planes in magnesium were calculated by using density functional theory, and the effect of the GSF energy on the dislocation core structures was examined using a semidiscrete variational Peierls-Nabarro model. Yttrium was found to have an anomalous influence on the solution softening owing to a reduction in the GSF energy gradient.

Free energy change of a dislocation due to a Cottrell atmosphere

DOE PAGES

Sills, R. B.; Cai, W.

2018-03-07

The free energy reduction of a dislocation due to a Cottrell atmosphere of solutes is computed using a continuum model. In this work, we show that the free energy change is composed of near-core and far-field components. The far-field component can be computed analytically using the linearized theory of solid solutions. Near the core the linearized theory is inaccurate, and the near-core component must be computed numerically. The influence of interactions between solutes in neighbouring lattice sites is also examined using the continuum model. We show that this model is able to reproduce atomistic calculations of the nickel–hydrogen system, predictingmore » hydride formation on dislocations. The formation of these hydrides leads to dramatic reductions in the free energy. Lastly, the influence of the free energy change on a dislocation’s line tension is examined by computing the equilibrium shape of a dislocation shear loop and the activation stress for a Frank–Read source using discrete dislocation dynamics.« less

Free energy change of a dislocation due to a Cottrell atmosphere

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sills, R. B.; Cai, W.

The free energy reduction of a dislocation due to a Cottrell atmosphere of solutes is computed using a continuum model. In this work, we show that the free energy change is composed of near-core and far-field components. The far-field component can be computed analytically using the linearized theory of solid solutions. Near the core the linearized theory is inaccurate, and the near-core component must be computed numerically. The influence of interactions between solutes in neighbouring lattice sites is also examined using the continuum model. We show that this model is able to reproduce atomistic calculations of the nickel–hydrogen system, predictingmore » hydride formation on dislocations. The formation of these hydrides leads to dramatic reductions in the free energy. Lastly, the influence of the free energy change on a dislocation’s line tension is examined by computing the equilibrium shape of a dislocation shear loop and the activation stress for a Frank–Read source using discrete dislocation dynamics.« less

Double-gap Alfvén eigenmodes: revisiting eigenmode interaction with the alfvén continuum.

PubMed

Gorelenkov, N N

2005-12-31

A new type of global shear Alfvén eigenmode is found in tokamak plasmas where the mode localization is in the region intersecting the Alfvén continuum. The eigenmode is formed by the coupling of two solutions from two adjacent gaps (akin to potential wells) in the shear Alfvén continuum. For tokamak plasmas with reversed magnetic shear, it is shown that the toroidicity-induced solution tunnels through the continuum to match the ellipticity-induced Alfvén eigenmode so that the resulting solution is continuous at the point of resonance with the continuum. The existence of these double-gap Alfvén eigenmodes allows for potentially new ways of coupling edge fields to the plasma core in conditions where the core region is conventionally considered inaccessible. Implications include new approaches to heating and current drive in fusion plasmas as well as its possible use as a core diagnostic in burning plasmas.

Free energy change of a dislocation due to a Cottrell atmosphere

NASA Astrophysics Data System (ADS)

Sills, R. B.; Cai, W.

2018-06-01

The free energy reduction of a dislocation due to a Cottrell atmosphere of solutes is computed using a continuum model. We show that the free energy change is composed of near-core and far-field components. The far-field component can be computed analytically using the linearized theory of solid solutions. Near the core the linearized theory is inaccurate, and the near-core component must be computed numerically. The influence of interactions between solutes in neighbouring lattice sites is also examined using the continuum model. We show that this model is able to reproduce atomistic calculations of the nickel-hydrogen system, predicting hydride formation on dislocations. The formation of these hydrides leads to dramatic reductions in the free energy. Finally, the influence of the free energy change on a dislocation's line tension is examined by computing the equilibrium shape of a dislocation shear loop and the activation stress for a Frank-Read source using discrete dislocation dynamics.

The earth's C21 and S21 gravity coefficients and the rotation of the core

NASA Technical Reports Server (NTRS)

Wahr, John M.

1987-01-01

Observational results for the earth's C21 and S21 gravity coefficients can be used to constrain the mean equatorial rotation of the core with respect to the mantle. Current satellite gravity solutions suggest the equatorial rotation rate is no larger than 1 x 10 to the -7th times the earth's diurnal spin rate, a limit more than one order of magnitude smaller than the polar rotation rate inferred from the westward drift of the earth's magnetic field. The next generation gravity solutions should improve this constraint by more than one order of magnitude. Implications for the fluid pressure at the core-mantle boundary and for the shape of that boundary are discussed.

Association of a multifunctional ionic block copolymer in a selective solvent

DOE PAGES

Etampawala, Thusitha N.; Aryal, Dipak; Osti, Naresh C.; ...

2016-11-14

The self-assembly of multiblock copolymers in solutions is controlled by a delicate balance between inherent phase segregation due to incompatibility of the blocks and the interaction of the individual blocks with the solvent. The current study elucidates the association of pentablock copolymers in a mixture of selective solvents which are good for the hydrophobic segments and poor for the hydrophilic blocks using small angle neutron scattering (SANS). The pentablock consists of a center block of randomly sulfonated polystyrene, designed for transport, tethered to poly-ethylene-r-propylene and end-capped by poly-t-butyl styrene, for mechanical stability. We find that the pentablock forms ellipsoidal core-shellmore » micelles with the sulfonated polystyrene in the core and Gaussian decaying chains of swollen poly-ethylene-r-propylene and poly-t-butyl styrene tertiary in the corona. With increasing solution concentration, the size of the micelle, the thickness of the corona, and the aggregation number increase, while the solvent fraction in the core decreases. As a result, in dilute solution the micelle increases in size as the temperature is increased, however, temperature effects dissipate with increasing solution concentration.« less

Tuning the synthesis of platinum-copper nanoparticles with a hollow core and porous shell for the selective hydrogenation of furfural to furfuryl alcohol

NASA Astrophysics Data System (ADS)

Huang, Shuangshuang; Yang, Nating; Wang, Shibin; Sun, Yuhan; Zhu, Yan

2016-07-01

Pt-Cu nanoparticles constructed with a hollow core and porous shell have been synthesized in which Pt-Cu cages with multiporous outermost shells are formed at the initial stage and then the Pt and Cu atoms in solution continuously fed these hollow-core of cages by passing through the porous tunnels of the outermost shells, finally leading to the formation of hollow structures with different sizes. Furthermore, these hollow-core Pt-Cu nanoparticles are more effective than the solid-core Pt-Cu nanoparticles for the catalytic hydrogenation of furfural toward furfuryl alcohol. The former can achieve almost 100% conversion of furfural with 100% selectivity toward the alcohol.Pt-Cu nanoparticles constructed with a hollow core and porous shell have been synthesized in which Pt-Cu cages with multiporous outermost shells are formed at the initial stage and then the Pt and Cu atoms in solution continuously fed these hollow-core of cages by passing through the porous tunnels of the outermost shells, finally leading to the formation of hollow structures with different sizes. Furthermore, these hollow-core Pt-Cu nanoparticles are more effective than the solid-core Pt-Cu nanoparticles for the catalytic hydrogenation of furfural toward furfuryl alcohol. The former can achieve almost 100% conversion of furfural with 100% selectivity toward the alcohol. Electronic supplementary information (ESI) available. See DOI: 10.1039/c6nr03894h

Bench-to-bedside review: Dealing with increased intensive care unit staff turnover: a leadership challenge

PubMed Central

Laporta, Denny P; Burns, Judy; Doig, Chip J

2005-01-01

Critical care leaders frequently must face challenging situations requiring specific leadership and management skills for which they are, not uncommonly, poorly prepared. Such a fictitious scenario was discussed at a Canadian interdisciplinary critical care leadership meeting, whereby increasing intensive care unit (ICU) staff turnover had led to problems with staff recruitment. Participants discussed and proposed solutions to the scenario in a structured format. The results of the discussion are presented. In situations such as this, the ICU leader should first define the core problem, its complexity, its duration and its potential for reversibility. These factors often reside within workload and staff support issues. Some examples of core problems discussed that are frequently associated with poor retention and recruitment are a lack of a positive team culture, a lack of a favorable ICU image, a lack of good working relationships between staff and disciplines, and a lack of specific supportive resources. Several tools or individuals (typically outside the ICU environment) are available to help determine the core problem. Once the core problem is identified, specific solutions can be developed. Such solutions often require originality and flexibility, and must be planned, with specific short-term, medium-term and long-term goals. The ICU leader will need to develop an implementation strategy for these solutions, in which partners who can assist are identified from within the ICU and from outside the ICU. It is important that the leader communicates to all stakeholders frequently as the process moves forward. PMID:16277732

Effects of Salinity and Confining Pressure on Hydration-Induced Fracture Propagation and Permeability of Mancos Shale

NASA Astrophysics Data System (ADS)

Zhang, Shifeng; Sheng, James J.

2017-11-01

Low-salinity water imbibition was considered an enhanced recovery method in shale oil/gas reservoirs due to the resulting hydration-induced fractures, as observed at ambient conditions. To study the effect of confining pressure and salinity on hydration-induced fractures, time-elapsed computerized tomography (CT) was used to obtain cross-sectional images of shale cores. Based on the CT data of these cross-sectional images, cut faces parallel to the core axial in the middle of the core and 3D fracture images were also reconstructed. To study the effects of confining pressure and salinity on shale pore fluid flowing, shale permeability was measured with Nitrogen (N2), distilled water, 4% KCl solution, and 8% KCl solution. With confining pressures increased to 2 MPa or more, either in distilled water or in KCl solutions of different salinities, fractures were observed to close instead to propagate at the end of the tests. The intrinsic permeabilities of #1 and #2 Mancos shale cores were 60.0 and 7000 nD, respectively. When tested with distilled water, the permeability of #1 shale sample with 20.0 MPa confining pressure loaded, and #2 shale sample with 2.5 MPa confining pressure loaded, decreased to 0.45 and 15 nD, respectively. Using KCl can partly mitigate shale permeability degradation. Compared to 4% KCl, 8% KCl can decrease more permeability damage. From this point of view, high salinity KCl solution should be required for the water-based fracturing fluid.

Bench-to-bedside review: dealing with increased intensive care unit staff turnover: a leadership challenge.

PubMed

Laporta, Denny P; Burns, Judy; Doig, Chip J

2005-10-05

Critical care leaders frequently must face challenging situations requiring specific leadership and management skills for which they are, not uncommonly, poorly prepared. Such a fictitious scenario was discussed at a Canadian interdisciplinary critical care leadership meeting, whereby increasing intensive care unit (ICU) staff turnover had led to problems with staff recruitment. Participants discussed and proposed solutions to the scenario in a structured format. The results of the discussion are presented. In situations such as this, the ICU leader should first define the core problem, its complexity, its duration and its potential for reversibility. These factors often reside within workload and staff support issues. Some examples of core problems discussed that are frequently associated with poor retention and recruitment are a lack of a positive team culture, a lack of a favorable ICU image, a lack of good working relationships between staff and disciplines, and a lack of specific supportive resources. Several tools or individuals (typically outside the ICU environment) are available to help determine the core problem. Once the core problem is identified, specific solutions can be developed. Such solutions often require originality and flexibility, and must be planned, with specific short-term, medium-term and long-term goals. The ICU leader will need to develop an implementation strategy for these solutions, in which partners who can assist are identified from within the ICU and from outside the ICU. It is important that the leader communicates to all stakeholders frequently as the process moves forward.

Nano-JASMINE and small-JASMINE data analysis

NASA Astrophysics Data System (ADS)

Yamada, Yoshiyuki; Shirasaki, Yuji; Nishi, Ryoichi

2018-04-01

Space astrometry missions Nano-JASMINE and small-JASMINE are planned in Japan. Data analysis tasks are performed under Gaia-JASMINE collaboration in long time. We expected to achieve 3 mas accuracy in Nano-JASMINE, and 20 micro arcsec in small-JASMINE of astrometric performance. Gaia DR1 publication and instruction is done from NAOJ and Niigata University.

Using NCAR Yellowstone for PhotoVoltaic Power Forecasts with Artificial Neural Networks and an Analog Ensemble

NASA Astrophysics Data System (ADS)

Cervone, G.; Clemente-Harding, L.; Alessandrini, S.; Delle Monache, L.

2016-12-01

A methodology based on Artificial Neural Networks (ANN) and an Analog Ensemble (AnEn) is presented to generate 72-hour deterministic and probabilistic forecasts of power generated by photovoltaic (PV) power plants using input from a numerical weather prediction model and computed astronomical variables. ANN and AnEn are used individually and in combination to generate forecasts for three solar power plant located in Italy. The computational scalability of the proposed solution is tested using synthetic data simulating 4,450 PV power stations. The NCAR Yellowstone supercomputer is employed to test the parallel implementation of the proposed solution, ranging from 1 node (32 cores) to 4,450 nodes (141,140 cores). Results show that a combined AnEn + ANN solution yields best results, and that the proposed solution is well suited for massive scale computation.

In-fiber refractive index sensor based on single eccentric hole-assisted dual-core fiber.

PubMed

Yang, Jing; Guan, Chunying; Tian, Peixuan; Yuan, Tingting; Zhu, Zheng; Li, Ping; Shi, Jinhui; Yang, Jun; Yuan, Libo

2017-11-01

We propose a novel and simple in-fiber refractive index sensor based on resonant coupling, constructed by a short section of single eccentric hole-assisted dual-core fiber (SEHADCF) spliced between two single-mode fibers. The coupling characteristics of the SEHADCF are calculated numerically. The strong resonant coupling occurs when the fundamental mode of the center core phase-matches to that of the suspended core in the air hole. The effective refractive index of the fundamental mode of the suspended core can be obviously changed by injecting solution into the air hole. The responses of the proposed devices to the refractive index and temperature are experimentally measured. The refractive index sensitivity is 627.5 nm/refractive index unit in the refractive index range of 1.335-1.385. The sensor without solution filling is insensitive to temperature in the range of 30-90°C. The proposed refractive index sensor has outstanding advantages, such as simple fabrication, good mechanical strength, and excellent microfluidic channel, and will be of importance in biological detection, chemical analysis, and environment monitoring.

Fabrication of quantum dot/silica core-shell particles immobilizing Au nanoparticles and their dual imaging functions

NASA Astrophysics Data System (ADS)

Kobayashi, Yoshio; Matsudo, Hiromu; Li, Ting-ting; Shibuya, Kyosuke; Kubota, Yohsuke; Oikawa, Takahiro; Nakagawa, Tomohiko; Gonda, Kohsuke

2016-03-01

The present work proposes preparation methods for quantum dot/silica (QD/SiO2) core-shell particles that immobilize Au nanoparticles (QD/SiO2/Au). A colloid solution of QD/SiO2 core-shell particles with an average size of 47.0 ± 6.1 nm was prepared by a sol-gel reaction of tetraethyl orthosilicate in the presence of the QDs with an average size of 10.3 ± 2.1 nm. A colloid solution of Au nanoparticles with an average size of 17.9 ± 1.3 nm was prepared by reducing Au3+ ions with sodium citrate in water at 80 °C. Introduction of amino groups to QD/SiO2 particle surfaces was performed using (3-aminopropyl)-triethoxysilane (QD/SiO2-NH2). The QD/SiO2/Au particles were fabricated by mixing the Au particle colloid solution and the QD/SiO2-NH2 particle colloid solution. Values of radiant efficiency and computed tomography for the QD/SiO2/Au particle colloid solution were 2.23 × 107 (p/s/cm2/sr)/(μW/cm2) at a QD concentration of 8 × 10-7 M and 1180 ± 314 Hounsfield units and an Au concentration of 5.4 × 10-2 M. The QD/SiO2/Au particle colloid solution was injected into a mouse chest wall. Fluorescence emitted from the colloid solution could be detected on the skin covering the chest wall. The colloid solution could also be X-ray-imaged in the chest wall. Consequently, the QD/SiO2/Au particle colloid solution was found to have dual functions, i.e., fluorescence emission and X-ray absorption in vivo, which makes the colloid solution suitable to function as a contrast agent for dual imaging processes.

Continuations of the nonlinear Schrödinger equation beyond the singularity

NASA Astrophysics Data System (ADS)

Fibich, G.; Klein, M.

2011-07-01

We present four continuations of the critical nonlinear Schrödinger equation (NLS) beyond the singularity: (1) a sub-threshold power continuation, (2) a shrinking-hole continuation for ring-type solutions, (3) a vanishing nonlinear-damping continuation and (4) a complex Ginzburg-Landau (CGL) continuation. Using asymptotic analysis, we explicitly calculate the limiting solutions beyond the singularity. These calculations show that for generic initial data that lead to a loglog collapse, the sub-threshold power limit is a Bourgain-Wang solution, both before and after the singularity, and the vanishing nonlinear-damping and CGL limits are a loglog solution before the singularity, and have an infinite-velocity expanding core after the singularity. Our results suggest that all NLS continuations share the universal feature that after the singularity time Tc, the phase of the singular core is only determined up to multiplication by eiθ. As a result, interactions between post-collapse beams (filaments) become chaotic. We also show that when the continuation model leads to a point singularity and preserves the NLS invariance under the transformation t → -t and ψ → ψ*, the singular core of the weak solution is symmetric with respect to Tc. Therefore, the sub-threshold power and the shrinking-hole continuations are symmetric with respect to Tc, but continuations which are based on perturbations of the NLS equation are generically asymmetric.

Origins of anisotropic seismic attenuation of the inner core - intrinsic anelasticity of hcp iron alloy

NASA Astrophysics Data System (ADS)

Redfern, Simon

2015-04-01

Earth's inner core is elastically anisotropic, with seismology showing faster wave propagation along the polar axis compared to the equatorial plane. Some inner core studies report anisotropic seismic attenuation. Attenuation of body-waves has, previously, been postulated to be due to scattering by anisotropic microstructure, but recent normal mode studies also show strong anisotropic attenuation (Mäkinen et al. 2014). This suggests that the anisotropic attenuation is a result of the intrinsic (and anisotropic) anelastic properties of the solid iron alloy forming Earth's inner core. Here, I consider the origins of inner core anisotropic attenuation. Possibilities include grain boundary relaxation, dislocation bowing/glide, or point defect (alloying element) relaxations. The inner core is an almost perfect environment for near-equilibrium crystallisation, with very low temperature gradients across the inner core, low gravity, and slow crystallisation rates. It is assumed that grain sizes may be of the order of hundreds of metres. This implies vanishingly small volumes of grain boundary, and insignificant grain boundary relaxation. The very high homologous temperature and the absence of obvious deviatoric stress, also leads one to conclude that dislocation densities are low. On the other hand, estimates for light element concentrations are of the order of a few % with O, S, Si, C and H at various times being suggested as candidate elements. Light element solutes in hcp metals contribute to intrinsic anelastic attenuation if they occur in sufficient concentrations to pair and form elastic dipoles. Switching of dipoles under the stress of a passing seismic wave will result in anelastic mechanical loss. Such attenuation has been measured in hcp metals in the lab, and is anisotropic due to the intrinsic elastic anisotropy of the host lattice. Such solute pair relaxations result in a "Zener effect", which is suggested here to be responsible for observed anisotropic seismic attenuation. Zener relaxation magnitude scales with solute concentration and is consistent with around 5% light element. Variations in attenuation are expected in a core with spatially varying concentrations of light element, and attenuation tomography of the inner core could, therefore, be employed to map chemical heterogeneity.

The effect of operational parameters on the photocatalytic degradation of Congo red organic dye using ZnO-CdS core-shell nano-structure coated on glass by Doctor Blade method.

PubMed

Habibi, Mohammad Hossein; Rahmati, Mohammad Hossein

2015-02-25

Photocatalytic degradation of Congo red was investigated using ZnO-CdS core-shell nano-structure coated on glass by Doctor Blade method in aqueous solution under irradiation. Field-emission scanning electron microscopy (FESEM) and X-ray diffraction (XRD) techniques were used for the morphological and structural characterization of ZnO-CdS core-shell nanostructures. XRD results showed diffractions of wurtzite zinc oxide core and wurtzite cadmium sulfide shell. FESEM results showed that nanoparticles are nearly hexagonal with an average diameter of about 50 nm. The effect of catalyst loading, UV-light irradiation time and solution pH on photocatalytic degradation of Congo red was studied and optimized values were obtained. Results showed that the employment of efficient photocatalyst and selection of optimal operational parameters may lead to complete decolorization of dye solutions. It was found that ZnO-CdS core-shell nano-structure is more favorable for the degradation of Congo red compare to pure ZnO or pure CdS due to lower electron hole recombination. The results showed that the photocatalytic degradation rate of Congo red is enhanced with increasing the content of ZnO up to ZnO(0.2 M)/CdS(0.075 M) which is reached 88.0% within 100 min irradiation. Copyright © 2014 Elsevier B.V. All rights reserved.

The effect of acidified sample storage time on the determination of trace element concentration in ice cores by ICP-SFMS

NASA Astrophysics Data System (ADS)

Uglietti, C.; Gabrielli, P.; Lutton, A.; Olesik, J.; Thompson, L. G.

2012-12-01

Trace elements in micro-particles entrapped in ice cores are a valuable proxy of past climate and environmental variations. Inductively coupled plasma sector field mass spectrometry (ICP-SFMS) is generally recognized as a sensitive and accurate technique for the quantification of ultra-trace element concentrations in ice cores. Usually, ICP-SFMS analyses of ice core samples are performed by melting and acidifying aliquots. Acidification is important to transfer trace elements from particles into solution by partial and/or complete dissolution. Only elements in solution and in sufficiently small particles will be vaporized and converted to elemental ions in the plasma for detection by ICP-SFMS. However, experimental results indicate that differences in acidified sample storage time at room temperature may lead to the recovery of different trace element fractions. Moreover, different lithologies of the relatively abundant crustal material entrapped in the ice matrix could also influence the fraction of trace elements that are converted into elemental ions in the plasma. These factors might affect the determination of trace elements concentrations in ice core samples and hamper the comparison of results obtained from ice cores from different locations and/or epochs. In order to monitor the transfer of elements from particles into solution in acidified melted ice core samples during storage, a test was performed on sections from nine ice cores retrieved from low latitude drilling sites around the world. When compared to ice cores from polar regions, these samples are characterized by a relative high content of micro-particles that may leach trace elements into solution differently. Of the nine ice cores, five are from the Tibetan Plateau (Dasuopu, Guliya, Naimonanyi, Puruogangri and Dunde), two from the Andes (Quelccaya and Huascaran), one from Africa (Kilimanjaro) and one from the Eastern Alps (Ortles). These samples were decontaminated by triple rinsing, melted and stored in pre-cleaned low-density polyethylene bottles, and kept frozen until acidification (2% v/v ultra-pure HNO3). Determination of twenty trace elements (Ag, Al, As, Bi, Cd, Co, Cr, Cu, Fe, Mn, Mo, Pb, Rb, Sb, Sn, Ti, Tl, U, V, and Zn) was repeated at different times after acidification using the same aliquot. Analyses show a mean increase of 40-50% in trace element concentration in all the samples during the first 15 days of storage after acidification, except Al, Fe, V and Cr, which show a larger increase (90-100%). After 15 days the trace element concentrations reach generally stable values (with small increases within measurement uncertainty), except for the Naimonanyi and Kilimanjaro samples which continue to increase. In contrast, Ag concentration decreases after one week, likely due to its low stability in the acidified solution that may depend on the Cl- concentration. We froze the samples 43 days after the acidification. After two weeks the samples were melted and re-analyzed by ICP-SFMS in two different laboratories as an inter-calibration exercise. The results show a good correspondence between the measured concentrations determined by the two instruments and a consistent additional increase of 20-30% of measured trace element concentrations in almost all samples.

Carboxyl-functionalized nanoparticles with magnetic core and mesopore carbon shell as adsorbents for the removal of heavy metal ions from aqueous solution.

PubMed

Wang, Hui; Yu, Yi-Fei; Chen, Qian-Wang; Cheng, Kai

2011-01-21

This communication demonstrates superparamagnetic nanosized particles with a magnetic core and a porous carbon shell (thickness of 11 nm), which can remove 97% of Pb(2+) ions from an acidic aqueous solution at a Pb(2+) ion concentration of 100 mg L(-1). It is suggested that a weak electrostatic force of attraction between the heavy metal ions and the nanoparticles and the heavy metal ions adsorption on the mesopore carbon shell contribute most to the superior removal property.

Quantum mechanics/molecular mechanics modeling of photoelectron spectra: the carbon 1s core-electron binding energies of ethanol-water solutions.

PubMed

Löytynoja, T; Niskanen, J; Jänkälä, K; Vahtras, O; Rinkevicius, Z; Ågren, H

2014-11-20

Using ethanol-water solutions as illustration, we demonstrate the capability of the hybrid quantum mechanics/molecular mechanics (QM/MM) paradigm to simulate core photoelectron spectroscopy: the binding energies and the chemical shifts. An integrated approach with QM/MM binding energy calculations coupled to preceding molecular dynamics sampling is adopted to generate binding energies averaged over the solute-solvent configurations available at a particular temperature and pressure and thus allowing for a statistical assessment with confidence levels for the final binding energies. The results are analyzed in terms of the contributions in the molecular mechanics model-electrostatic, polarization, and van der Waals-with atom or bond granulation of the corresponding MM charge and polarizability force-fields. The role of extramolecular charge transfer screening of the core-hole and explicit hydrogen bonding is studied by extending the QM core to cover the first solvation shell. The results are compared to those obtained from pure electrostatic and polarizable continuum models. Particularly, the dependence of the carbon 1s binding energies with respect to the ethanol concentration is studied. Our results indicate that QM/MM can be used as an all-encompassing model to study photoelectron binding energies and chemical shifts in solvent environments.

Fusion splicing small-core photonic crystal fibers and single-mode fibers by repeated arc discharges.

PubMed

Xiao, Limin; Jin, Wei; Demokan, M S

2007-01-15

We demonstrate a novel method for low-loss splicing small-core photonic crystal fibers (PCFs) and single-mode fibers (SMFs) by repeated arc discharges using a conventional fusion splicer. An optimum mode field match at the interface of PCF-SMF and an adiabatic mode field variation in the longitudinal direction of the small-core PCF can be achieved by repeated arc discharges applied over the splicing joint to gradually collapse the air holes of the small-core PCF. This method is simple and offers a practical solution for light coupling between small-core PCFs and SMFs.

Fusion splicing small-core photonic crystal fibers and single-mode fibers by repeated arc discharges

NASA Astrophysics Data System (ADS)

Xiao, Limin; Jin, Wei; Demokan, M. S.

2007-01-01

We demonstrate a novel method for low-loss splicing small-core photonic crystal fibers (PCFs) and single-mode fibers (SMFs) by repeated arc discharges using a conventional fusion splicer. An optimum mode field match at the interface of PCF-SMF and an adiabatic mode field variation in the longitudinal direction of the small-core PCF can be achieved by repeated arc discharges applied over the splicing joint to gradually collapse the air holes of the small-core PCF. This method is simple and offers a practical solution for light coupling between small-core PCFs and SMFs.

Decisive role of magnetism in the interaction of chromium and nickel solute atoms with 1/2$$\\langle$$111$$\\rangle$$-screw dislocation core in body-centered cubic iron

DOE PAGES

Odbadrakh, Kh.; Samolyuk, G.; Nicholson, D.; ...

2016-09-13

Resistance to swelling under irradiation and a low rate of corrosion in high temperature environments make Fe-Cr and Fe-Cr-Ni alloys promising structural materials for energy technologies. In this paper we report the results obtained using a combination of density functional theory (DFT) techniques: plane wave basis set solutions for pseudo-potentials and multiple scattering solutions for all electron potentials. We have found a very strong role of magnetism in the stability of screw dislocation cores in pure Fe and their interaction with Cr and Ni magnetic impurities. In particular, the screw dislocation quadrupole in Fe is stabilized only in the presencemore » of ferromagnetism. In addition, Ni atoms, who's magnetic moment is oriented along the magnetization direction of the Fe matrix, prefer to occupy in core positions whereas Cr atoms, which couple anti-ferromagnetically with the Fe matrix, prefer out of the dislocation core positions. In effect, Ni impurities are attracted to, while Cr impurities are repelled by the dislocation core. Moreover, we demonstrate that this contrasting behavior can be explained only by the nature of magnetic coupling of the impurities to the Fe matrix. In addition, Cr interaction with the dislocation core mirrors that of Ni if the Cr magnetic moment is constrained to be along the direction of Fe matrix magnetization. In addition, we have shown that the magnetic contribution can affect the impurity-impurity interaction at distances up to a few Burgers vectors. In particular, the distance between Cr atoms in Fe matrix should be at least 3–4 lattice parameters in order to eliminate finite size effects.« less

An integrated outsourcing solution at York Central Hospital.

PubMed

Marr, Jo-Anne; Tam, Richard; Simms, Stephen; Bacchus, Feria

2011-01-01

Canadian hospitals struggle to balance the need to increase and improve operational services and quality with diminishing resources. Many realize that sustaining their organization depends on how well they focus their resources and talents on their core business, clinical care delivery. Outsourcing of non-core, non-clinical support services is a solution for many organizations. Most often, this is put into action one service provider at a time. In 2007, however, York Central Hospital (YCH) implemented Sodexo's integrated Comprehensive Service Solutions (CSS) for all its support service functions. In doing so, YCH achieved significant improvements in patient and staff satisfaction rates, substantial cost savings through improved operational efficiency from process improvements and leveraging technology investments, and increased retail food revenue.

Theoretical prediction on corrugated sandwich panels under bending loads

NASA Astrophysics Data System (ADS)

Shu, Chengfu; Hou, Shujuan

2018-05-01

In this paper, an aluminum corrugated sandwich panel with triangular core under bending loads was investigated. Firstly, the equivalent material parameters of the triangular corrugated core layer, which could be considered as an orthotropic panel, were obtained by using Castigliano's theorem and equivalent homogeneous model. Secondly, contributions of the corrugated core layer and two face panels were both considered to compute the equivalent material parameters of the whole structure through the classical lamination theory, and these equivalent material parameters were compared with finite element analysis solutions. Then, based on the Mindlin orthotropic plate theory, this study obtain the closed-form solutions of the displacement for a corrugated sandwich panel under bending loads in specified boundary conditions, and parameters study and comparison by the finite element method were executed simultaneously.

Speckle Interferometry at SOAR in 2014

NASA Astrophysics Data System (ADS)

Tokovinin, Andrei; Mason, Brian D.; Hartkopf, William I.; Mendez, Rene A.; Horch, Elliott P.

2015-08-01

The results of speckle interferometric observations at the Southern Astrophysical Research Telescope (SOAR) telescope in 2014 are given. A total of 1641 observations were taken, yielding 1636 measurements of 1218 resolved binary and multiple stars and 577 non-resolutions of 441 targets. We resolved for the first time 56 pairs, including some nearby astrometric or spectroscopic binaries and ten new subsystems in previously known visual binaries. The calibration of the data is checked by linear fits to the positions of 41 wide binaries observed at SOAR over several seasons. The typical calibration accuracy is 0.°1 in angle and 0.3% in pixel scale, while the measurement errors are on the order of 3 mas. The new data are used here to compute 194 binary star orbits, 148 of which are improvements on previous orbital solutions and 46 are first-time orbits. Based on observations obtained at the Southern Astrophysical Research (SOAR) telescope, which is a joint project of the Ministério da Ciência, Tecnologia, e Inovação (MCTI) da República Federativa do Brasil, the U.S. National Optical Astronomy Observatory (NOAO), the University of North Carolina at Chapel Hill (UNC), and Michigan State University (MSU).

The Uncertain Nature of Cometary Motions

NASA Technical Reports Server (NTRS)

Yeomans, Donald K.

1997-01-01

The number of active short- and long-periodic comets crossing the Earth's orbit each year is less than 10 percent of the corresponding number of asteroids crossing the Earth's orbit. However, the higher relative velocities of comets with respect to the Earth and the uncertainties associated with accurately computing their future trajectories can cause considerable problems when assessing the risks of Earth-crossing objects. Unlike asteroids, the motions of active comets are often affected by so-called nongravitational (outgassing) forces that are imperfectly modeled. In addition, the astrometric optical observations that are used to refine a comet's orbit are often imprecise because a comet's center of mass can be hidden by atmospheric gas and dust. For long-period comets, there is the additional problem of having to base orbital solutions on relatively short observational data intervals. Long-term numerical integrations extending two centuries into the future have been carried out to investigate upcoming Earth-close approaches by known periodic comets. Error analyses and impact probabilities have been computed for those comets that will pass closest to the Earth. Although there are no known comets that will make dangerously close Earth approaches in the next two centuries, there are a few objects that warrant future monitoring.

Astrometry of the Orcus/Vanth occultation on UT 7 March 2017

NASA Astrophysics Data System (ADS)

Bosh, Amanda S.; Zuluaga, Carlos; Levine, Stephen; Sickafoose, Amanda A.; Genade, Anja; Schindler, Karsten; Lister, Tim; Person, Michael J.

2017-10-01

On UT 7 March 2017, Orcus was predicted to occult a star with m=14.3. Observations were made at five observatories: the 0.6-m Astronomical Telescope of the University of Stuttgart (ATUS) at Sierra Remote Observatories (SRO), California; Las Cumbres Observatory’s 1-m telescope (ELP) at McDonald Observatory, Fort Davis, Texas; NASA’s 3-m InfraRed Telescope Facility (IRTF) on Mauna Kea, Hawaii; the 4.1-m Southern Astrophysical Research telescope (SOAR) on Cerro Pachón, Chile; and the 0.6-m Southeastern Association for Research in Astronomy telescope (SARA-CT) at Cerro Tololo, Chile. While observations at all sites were successful, only two—ELP and IRTF—observed solid-body occultation signatures. We will discuss the various predictions for this event and the reasons for the differences among them, including an offset of 130 mas for the star position from the position in the Gaia catalog. The sum of the positive and negative detections place constraints on the geometry of the Orcus/Vanth system, and we present our astrometric results for the geometric solution for this occultation. The implications of the light curve analyses are presented by Sickafoose et al., this conference.

An efficient framework for Java data processing systems in HPC environments

NASA Astrophysics Data System (ADS)

Fries, Aidan; Castañeda, Javier; Isasi, Yago; Taboada, Guillermo L.; Portell de Mora, Jordi; Sirvent, Raül

2011-11-01

Java is a commonly used programming language, although its use in High Performance Computing (HPC) remains relatively low. One of the reasons is a lack of libraries offering specific HPC functions to Java applications. In this paper we present a Java-based framework, called DpcbTools, designed to provide a set of functions that fill this gap. It includes a set of efficient data communication functions based on message-passing, thus providing, when a low latency network such as Myrinet is available, higher throughputs and lower latencies than standard solutions used by Java. DpcbTools also includes routines for the launching, monitoring and management of Java applications on several computing nodes by making use of JMX to communicate with remote Java VMs. The Gaia Data Processing and Analysis Consortium (DPAC) is a real case where scientific data from the ESA Gaia astrometric satellite will be entirely processed using Java. In this paper we describe the main elements of DPAC and its usage of the DpcbTools framework. We also assess the usefulness and performance of DpcbTools through its performance evaluation and the analysis of its impact on some DPAC systems deployed in the MareNostrum supercomputer (Barcelona Supercomputing Center).

Parallax Results from URAT Epoch Data

NASA Astrophysics Data System (ADS)

Finch, Charlie T.; Zacharias, Norbert

2016-06-01

We present 1103 trigonometric parallaxes and proper motions from the United States Naval Observatory Robotic Astrometric Telescope (URAT) observations taken at the Naval Observatory Flagstaff Station (NOFS) over a three-year period from 2012 April to 2015 June covering the entire sky north of about -10^\\circ decl. We selected two samples: previously suspected nearby stars from known photometric distances and stars showing a large, significant parallax signature in URAT epoch data without any prior selection criteria. All systems presented in this paper have an observed parallax ≥40 mas with no previous published trigonometric parallax. The formal errors on these weighted parallax solutions are mostly between 4 and 10 mas. This sample gives a significant (of the order of 50%) increase to the number of known systems having a trigonometric parallax to be within 25 pc of the Sun (without applying Lutz-Kelker bias corrections). A few of these are found to be within 10 pc. Many of these new nearby stars display a total proper motion of less than 200 mas yr-1. URAT parallax results have been verified against Hipparcos and Yale data for stars in common. The publication of all signifigant parallax observations from URAT data is in preparation for CDS.

Mass Redistribution in the Core and Time-varying Gravity at the Earth's Surface

NASA Technical Reports Server (NTRS)

Kuang, Wei-Jia; Chao, Benjamin F.; Fang, Ming

2003-01-01

The Earth's liquid outer core is in convection, as suggested by the existence of the geomagnetic field in much of the Earth's history. One consequence of the convection is the redistribution of mass resulting from relative motion among fluid parcels with slightly different densities. This time dependent mass redistribution inside the core produces a small perturbation on the gravity field of the Earth. With our numerical dynamo solutions, we find that the mass redistribution (and the resultant gravity field) symmetric about the equator is much stronger than that anti-symmetric about the equator. In particular, J(sub 2) component is the strongest. In addition, the gravity field variation increases with the Rayleigh number that measures the driving force for the geodynamo in the core. With reasonable scaling from the current dynamo solutions, we could expect that at the surface of the Earth, the J(sub 2) variation from the core is on the order of l0(exp -16)/year relative to the mean (i.e. spherically symmetric) gravity field of the Earth. The possible shielding effect due to core-mantle boundary pressure variation loading is likely much smaller and is therefore negligible. Our results suggest that time-varying gravity field perturbation due to core mass redistribution may be measured with modem space geodetic observations, which will result a new means of detecting dynamical processes in the Earth's deep interior.

Preelectroplating Treatment Of Titanium Honeycomb Core

NASA Technical Reports Server (NTRS)

Kelly, Michael L.; Harvey, James S.

1992-01-01

New technique used to treat titanium honeycomb core electrochemically by applying conversion coat to keep honeycomb active and receptive to electroplating with solution of sodium bichromate and hydrofluoric acid. Maskant permits electroplating of controlled amount of filler metal on edge of honeycomb. Eliminates excess copper filler.

Stability and accuracy of 3D neutron transport simulations using the 2D/1D method in MPACT

DOE Office of Scientific and Technical Information (OSTI.GOV)

Collins, Benjamin, E-mail: collinsbs@ornl.gov; Stimpson, Shane, E-mail: stimpsonsg@ornl.gov; Kelley, Blake W., E-mail: kelleybl@umich.edu

2016-12-01

A consistent “2D/1D” neutron transport method is derived from the 3D Boltzmann transport equation, to calculate fuel-pin-resolved neutron fluxes for realistic full-core Pressurized Water Reactor (PWR) problems. The 2D/1D method employs the Method of Characteristics to discretize the radial variables and a lower order transport solution to discretize the axial variable. This paper describes the theory of the 2D/1D method and its implementation in the MPACT code, which has become the whole-core deterministic neutron transport solver for the Consortium for Advanced Simulations of Light Water Reactors (CASL) core simulator VERA-CS. Several applications have been performed on both leadership-class and industry-classmore » computing clusters. Results are presented for whole-core solutions of the Watts Bar Nuclear Power Station Unit 1 and compared to both continuous-energy Monte Carlo results and plant data.« less

Stability and accuracy of 3D neutron transport simulations using the 2D/1D method in MPACT

DOE PAGES

Collins, Benjamin; Stimpson, Shane; Kelley, Blake W.; ...

2016-08-25

We derived a consistent “2D/1D” neutron transport method from the 3D Boltzmann transport equation, to calculate fuel-pin-resolved neutron fluxes for realistic full-core Pressurized Water Reactor (PWR) problems. The 2D/1D method employs the Method of Characteristics to discretize the radial variables and a lower order transport solution to discretize the axial variable. Our paper describes the theory of the 2D/1D method and its implementation in the MPACT code, which has become the whole-core deterministic neutron transport solver for the Consortium for Advanced Simulations of Light Water Reactors (CASL) core simulator VERA-CS. We also performed several applications on both leadership-class and industry-classmore » computing clusters. Results are presented for whole-core solutions of the Watts Bar Nuclear Power Station Unit 1 and compared to both continuous-energy Monte Carlo results and plant data.« less

MODEST - JPL GEODETIC AND ASTROMETRIC VLBI MODELING AND PARAMETER ESTIMATION PROGRAM

NASA Technical Reports Server (NTRS)

Sovers, O. J.

1994-01-01

Observations of extragalactic radio sources in the gigahertz region of the radio frequency spectrum by two or more antennas, separated by a baseline as long as the diameter of the Earth, can be reduced, by radio interferometry techniques, to yield time delays and their rates of change. The Very Long Baseline Interferometric (VLBI) observables can be processed by the MODEST software to yield geodetic and astrometric parameters of interest in areas such as geophysical satellite and spacecraft tracking applications and geodynamics. As the accuracy of radio interferometry has improved, increasingly complete models of the delay and delay rate observables have been developed. MODEST is a delay model (MOD) and parameter estimation (EST) program that takes into account delay effects such as geometry, clock, troposphere, and the ionosphere. MODEST includes all known effects at the centimeter level in modeling. As the field evolves and new effects are discovered, these can be included in the model. In general, the model includes contributions to the observables from Earth orientation, antenna motion, clock behavior, atmospheric effects, and radio source structure. Within each of these categories, a number of unknown parameters may be estimated from the observations. Since all parts of the time delay model contain nearly linear parameter terms, a square-root-information filter (SRIF) linear least-squares algorithm is employed in parameter estimation. Flexibility (via dynamic memory allocation) in the MODEST code ensures that the same executable can process a wide array of problems. These range from a few hundred observations on a single baseline, yielding estimates of tens of parameters, to global solutions estimating tens of thousands of parameters from hundreds of thousands of observations at antennas widely distributed over the Earth's surface. Depending on memory and disk storage availability, large problems may be subdivided into more tractable pieces that are processed sequentially. MODEST is written in FORTRAN 77, C-language, and VAX ASSEMBLER for DEC VAX series computers running VMS. It requires 6Mb of RAM for execution. The standard distribution medium for this package is a 1600 BPI 9-track magnetic tape in DEC VAX BACKUP format. It is also available on a TK50 tape cartridge in DEC VAX BACKUP format. Instructions for use and sample input and output data are available on the distribution media. This program was released in 1993 and is a copyrighted work with all copyright vested in NASA.

High Precision Optical Observations of Space Debris in the Geo Ring from Venezuela

NASA Astrophysics Data System (ADS)

Lacruz, E.; Abad, C.; Downes, J. J.; Casanova, D.; Tresaco, E.

2018-01-01

We present preliminary results to demonstrate that our method for detection and location of Space Debris (SD) in the geostationary Earth orbit (GEO) ring, based on observations at the OAN of Venezuela is of high astrometric precision. A detailed explanation of the method, its validation and first results is available in (Lacruz et al. 2017).

ExoSOFT: Exoplanet Simple Orbit Fitting Toolbox

NASA Astrophysics Data System (ADS)

Mede, Kyle; Brandt, Timothy D.

2017-08-01

ExoSOFT provides orbital analysis of exoplanets and binary star systems. It fits any combination of astrometric and radial velocity data, and offers four parameter space exploration techniques, including MCMC. It is packaged with an automated set of post-processing and plotting routines to summarize results, and is suitable for performing orbital analysis during surveys with new radial velocity and direct imaging instruments.

Error Sources in Asteroid Astrometry

NASA Technical Reports Server (NTRS)

Owen, William M., Jr.

2000-01-01

Asteroid astrometry, like any other scientific measurement process, is subject to both random and systematic errors, not all of which are under the observer's control. To design an astrometric observing program or to improve an existing one requires knowledge of the various sources of error, how different errors affect one's results, and how various errors may be minimized by careful observation or data reduction techniques.

Multiple Shells Around Wolf-Rayet Stars: Space Based Astrometric Observing

NASA Technical Reports Server (NTRS)

Marston, Anthony P.

1995-01-01

The completion of a complementary optical emission-line survey of the nebulae associated with Wolf-Rayet stars in the southern sky is reported, along with the completion of a survey the large-scale environments of Wolf-Rayet stars using IRAS Skyflux data. HIRES IRAS maps in the four IRAS wavebands for appoximately half of all galactic Wolf-Rayet stars are created.

Optical/IR Products - Naval Oceanography Portal

Science.gov Websites

are here: Home › USNO › Astrometry › Optical/IR Products USNO Logo USNO Navigation Optical/IR VLBI-based Products Astrometry Information Center Info Optical/IR Products Access to astrometric 2012. A poster paper describing the progress of URAT was presented at the April 2014 DDA meeting in

Gaiaverse: the Gaia's outreach portal

NASA Astrophysics Data System (ADS)

Masana, E.

2017-03-01

Gaiaverse (http://gaiaverse.eu) is a dissemination portal on the ESA Gaia's mission developed within the GENIUS project, an European project funded by the European Commission to boost the impact of the next European breakthrough in astrophysics, the Gaia astrometric mission. The portal was opened in July 2015. Gaiaverse is administrated by the Universitat de Barcelona (UB) and the Consorci de Serveis Universitaris de Catalunya (CSUC).

16 febbraio 2004. 121 Hermione occulta la stella TYC 1905-00864-1 in Gemini

NASA Astrophysics Data System (ADS)

Corbisiero, Massimo

2005-04-01

On 16 February 2004, the asteroid 121 Hermione occulted the star TYC 1905-00864-1 in Gemini: new astrometric observations and duplicity of the asteroid lead the UAI Occultation Section to launch a call for observations throughout Italy. Interesting results have been obtained along with new dimensions of the asteroid derived from positive observations.

Precision optical interferometry in space

NASA Technical Reports Server (NTRS)

Reasenberg, Robert D.

1993-01-01

POINTS, an astrometric Optical interferometer with a nominal measurement accuracy of 5 microarcseconds for the angle between a pair of stars separated by about 90 deg, is presently under consideration by two divisions of NASA-OSSA. It will be a powerful new multi-disciplinary tool for astronomical research. If chosen as the TOPS-1 (Toward Other Planetary Systems) instrument by the Solar-System Exploration Division, it will perform a definitive search for extra-solar planetary systems, either finding and characterizing a large number of them or showing that they are far less numerous than now believed. If chosen as the AIM (Astrometric Interferometry Mission) by the Astrophysics Division, POINTS will open new areas of astrophysical research and change the nature of the questions being asked in some old areas. In either case. it will be the first of a new class of powerful instruments in space and will prove the technology for the larger members of that class to follow. Based on a preliminary indication of the observational needs of the two missions, we find that a single POINTS mission will meet the science objectives of both TOPS-1 and AIM. The instrument detects dispersed fringe (channel led spectrum) and therefore can tolerate large pointing errors.

Cassini ISS astrometry of the Saturnian satellites: Tethys, Dione, Rhea, Iapetus, and Phoebe 2004-2012

NASA Astrophysics Data System (ADS)

Tajeddine, R.; Lainey, V.; Cooper, N. J.; Murray, C. D.

2015-03-01

Context. The Cassini spacecraft has been orbiting Saturn since 2004 and has returned images of satellites with an astrometric resolution as high as a few hundred meters per pixel. Aims: We used the images taken by the Narrow Angle Camera (NAC) of the Image Science Subsystem (ISS) instrument on board Cassini, for the purpose of astrometry. Methods: We applied the same method that was previously developed to reduce Cassini NAC images of Mimas and Enceladus. Results: We provide 5463 astrometric positions in right ascension and declination (α, δ) of the satellites: Tethys, Dione, Rhea, Iapetus, and Phoebe, using images that were taken by Cassini NAC between 2004 and 2012. the mean residuals compared to the JPL ephemeris SAT365 are of the order of hundreds of meters with standard deviations of the order of a few kilometers. The frequency analysis of the residuals shows the remaining unmodelled effects of satellites on the dynamics of other satellites. Full Table 1 is only available at the CDS via anonymous ftp to http://cdsarc.u-strasbg.fr (ftp://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/575/A73

THE CELESTIAL REFERENCE FRAME AT 24 AND 43 GHz. I. ASTROMETRY

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lanyi, G. E.; Jacobs, C. S.; Naudet, C. J.

2010-05-15

We present astrometric results for compact extragalactic objects observed with the Very Long Baseline Array at radio frequencies of 24 and 43 GHz. Data were obtained from ten 24 hr observing sessions made over a five-year period. These observations were motivated by the need to extend the International Celestial Reference Frame (ICRF) to higher radio frequencies to enable improved deep space navigation after 2016 and to improve state-of-the-art astrometry. Source coordinates for 268 sources were estimated at 24 GHz and for 131 sources at 43 GHz. The median formal uncertainties of right ascension and declination at 24 GHz are 0.08more » and 0.15 mas, respectively. Median formal uncertainties at 43 GHz are 0.20 and 0.35 mas, respectively. Weighted root-mean-square differences between the 24 and 43 GHz positions and astrometric positions based on simultaneous 2.3 and 8.4 GHz Very Long Baseline Interferometry observations, such as the ICRF, are less than about 0.3 mas in both coordinates. With observations over five years we have achieved a precision at 24 GHz approaching that of the ICRF but unaccounted systematic errors limit the overall accuracy of the catalogs.« less

Analysis of Error Sources in STEP Astrometry

NASA Astrophysics Data System (ADS)

Liu, S. Y.; Liu, J. C.; Zhu, Z.

2017-11-01

The space telescope Search for Terrestrial Exo-Planets (STEP) employed a method of sub-pixel technology which ensures that the astrometric accuracy of telescope on the focal plane is at the order of 1 μas. This kind of astrometric precision is promising to detect earth-like planets beyond the solar system. In this paper, we analyze the influence of some key factors, including errors in the stellar proper motions, parallax, the optical center of the system, and the velocities and positions of the satellite, on the detection of exo-planets. We propose a relative angular distance method to evaluate the non-linear terms in stellar distance caused by possibly existing exo-planets. This method could avoid the direct influence of measured errors of the position and proper motion of the reference stars. Supposing that there are eight reference stars in the same field of view and a star with a planet system, we simulate their five-year observational data, and use the least square method to get the parameters of the planet orbit. Our results show that the method is robust to detect terrestrial planets based on the 1 μas precision of STEP.

Optimal Compression Methods for Floating-point Format Images

NASA Technical Reports Server (NTRS)

Pence, W. D.; White, R. L.; Seaman, R.

2009-01-01

We report on the results of a comparison study of different techniques for compressing FITS images that have floating-point (real*4) pixel values. Standard file compression methods like GZIP are generally ineffective in this case (with compression ratios only in the range 1.2 - 1.6), so instead we use a technique of converting the floating-point values into quantized scaled integers which are compressed using the Rice algorithm. The compressed data stream is stored in FITS format using the tiled-image compression convention. This is technically a lossy compression method, since the pixel values are not exactly reproduced, however all the significant photometric and astrometric information content of the image can be preserved while still achieving file compression ratios in the range of 4 to 8. We also show that introducing dithering, or randomization, when assigning the quantized pixel-values can significantly improve the photometric and astrometric precision in the stellar images in the compressed file without adding additional noise. We quantify our results by comparing the stellar magnitudes and positions as measured in the original uncompressed image to those derived from the same image after applying successively greater amounts of compression.

Astrometry of Pluto from 1930-1951 observations: The Lampland plate collection

DOE Office of Scientific and Technical Information (OSTI.GOV)

Buie, Marc W.; Folkner, William M., E-mail: buie@boulder.swri.edu, E-mail: william.m.folkner@jpl.nasa.gov

We present a new analysis of 843 photographic plates of Pluto taken by Carl Lampland at Lowell Observatory from 1930–1951. This large collection of plates contains useful astrometric information that improves our knowledge of Pluto's orbit. This improvement provides critical support to the impending flyby of Pluto by New Horizons. New Horizons can do inbound navigation of the system to improve its targeting. This navigation is capable of nearly eliminating the sky-plane errors but can do little to constrain the time of closest approach. Thus the focus on this work was to better determine Pluto's heliocentric distance and to determinemore » the uncertainty on that distance with a particular eye to eliminating systematic errors that might have been previously unrecognized. This work adds 596 new astrometric measurements based on the USNO CCD Astrograph Catalog 4. With the addition of these data the uncertainty of the estimated heliocentric position of Pluto in Developmental Ephemerides 432 (DE432) is at the level of 1000 km. This new analysis gives us more confidence that these estimations are accurate and are sufficient to support a successful flyby of Pluto by New Horizons.« less

VizieR Online Data Catalog: Solar neighborhood. XXXII. L and M dwarfs (Dieterich+, 2014)

NASA Astrophysics Data System (ADS)

Dieterich, S. B.; Henry, T. J.; Jao, W.-C.; Winters, J. G.; Hosey, A. D.; Riedel, A. R.; Subasavage, J. P.

2015-01-01

We obtained VRI photometry for all targets in our sample using the Cerro Tololo Inter-American Observatory (CTIO) 0.9m telescope for the brighter targets and the SOuthern Astrophysical Research (SOAR) Optical Imager camera on the SOAR 4.1m telescope for fainter targets. SOAR observations were conducted between 2009 September and 2010 December during six observing runs comprising NOAO programs 2009B-0425, 2010A-0185, and 2010B-0176. A total of 17 nights on SOAR were used for optical photometry. Table 1 shows the photometry in the photometric system used by the telescope with which the measurements were taken (Johnson-Kron-Cousins for the CTIO 0.9m telescope and Bessell for SOAR). Astrometric observations are based in part on observations obtained via the Cerro Tololo Inter-American Observatory Parallax Investigation (CTIOPI), at the Cerro Tololo 0.9m telescope. CTIOPI is a large and versatile astrometric monitoring program targeting diverse types of stellar and substellar objects in the solar neighborhood. Observations are taken using the CTIO 0.9m telescope and its sole instrument, a 2048*2048 Tektronix imaging CCD detector with a plate scale of 0.401''/pixel. (4 data files).

On the accuracy of mass measurement for microlensing black holes as seen by Gaia and OGLE

NASA Astrophysics Data System (ADS)

Rybicki, Krzysztof A.; Wyrzykowski, Łukasz; Klencki, Jakub; de Bruijne, Jos; Belczyński, Krzysztof; Chruślińska, Martyna

2018-05-01

We investigate the impact of combining Gaia astrometry from space with precise, high cadence OGLE photometry from the ground. For the archival event OGLE3-ULENS-PAR-02, which is likely a black hole, we simulate a realistic astrometric time series of Gaia measurements and combine it with the real photometric data collected by the OGLE project. We predict that at the end of the nominal 5 yr of the Gaia mission, for the events brighter than G ≈ 15.5 mag at the baseline, caused by objects heavier than 10 M⊙, it will be possible to unambiguously derive masses of the lenses, with accuracy between a few and 15 per cent. We find that fainter events (G < 17.5) can still have their lens masses determined, provided that they are heavier than 30 M⊙. We estimate that the rate of astrometric microlensing events caused by the stellar-origin black holes is ≈ 4 × 10- 7 yr- 1, which implies, that after 5 yr of Gaia operation and ≈5 × 106 bright sources in Gaia, it will be possible to identify few such events in the Gaia final catalogues.

Compatibility of a Diffractive Pupil and Coronagraphic Imaging

NASA Technical Reports Server (NTRS)

Bendek, Eduardo; Belikov, Rusian; Pluzhnyk, Yevgeniy; Guyon, Olivier

2013-01-01

Detection and characterization of exo-earths require direct-imaging techniques that can deliver contrast ratios of 10(exp 10) at 100 milliarc-seconds or smaller angular separation. At the same time, astrometric data is required to measure planet masses and can help detect planets and constrain their orbital parameters. To minimize costs, a single space mission can be designed using a high efficiency coronograph to perform direct imaging and a diffractive pupil to calibrate wide-field distortions to enable high precision astrometric measurements. This paper reports the testing of a diffractive pupil on the high-contrast test bed at the NASA Ames Research Center to assess the compatibility of using a diffractive pupil with coronographic imaging systems. No diffractive contamination was found within our detectability limit of 2x10(exp -7) contrast outside a region of 12lambda/D and 2.5x10(exp -6) within a region spanning from 2 to 12lambda/D. Morphology of the image features suggests that no contamination exists even beyond the detectability limit specified or at smaller working angles. In the case that diffractive contamination is found beyond these stated levels, active wavefront control would be able to mitigate its intensity to 10(exp -7) or better contrast.

UCAC3: ASTROMETRIC REDUCTIONS

DOE Office of Scientific and Technical Information (OSTI.GOV)

Finch, Charlie T.; Zacharias, Norbert; Wycoff, Gary L., E-mail: finch@usno.navy.mi

2010-06-15

Presented here are the details of the astrometric reductions from the x, y data to mean right ascension (R.A.), declination (decl.) coordinates of the third U.S. Naval Observatory CCD Astrograph Catalog (UCAC3). For these new reductions we used over 216,000 CCD exposures. The Two-Micron All-Sky Survey (2MASS) data are used extensively to probe for coordinate and coma-like systematic errors in UCAC data mainly caused by the poor charge transfer efficiency of the 4K CCD. Errors up to about 200 mas have been corrected using complex look-up tables handling multiple dependences derived from the residuals. Similarly, field distortions and sub-pixel phasemore » errors have also been evaluated using the residuals with respect to 2MASS. The overall magnitude equation is derived from UCAC calibration field observations alone, independent of external catalogs. Systematic errors of positions at the UCAC observing epoch as presented in UCAC3 are better corrected than in the previous catalogs for most stars. The Tycho-2 catalog is used to obtain final positions on the International Celestial Reference Frame. Residuals of the Tycho-2 reference stars show a small magnitude equation (depending on declination zone) that might be inherent in the Tycho-2 catalog.« less

Astrometry of Pluto from 1930-1951 Observations: the Lampland Plate Collection

NASA Astrophysics Data System (ADS)

Buie, Marc W.; Folkner, William M.

2015-01-01

We present a new analysis of 843 photographic plates of Pluto taken by Carl Lampland at Lowell Observatory from 1930-1951. This large collection of plates contains useful astrometric information that improves our knowledge of Pluto's orbit. This improvement provides critical support to the impending flyby of Pluto by New Horizons. New Horizons can do inbound navigation of the system to improve its targeting. This navigation is capable of nearly eliminating the sky-plane errors but can do little to constrain the time of closest approach. Thus the focus on this work was to better determine Pluto's heliocentric distance and to determine the uncertainty on that distance with a particular eye to eliminating systematic errors that might have been previously unrecognized. This work adds 596 new astrometric measurements based on the USNO CCD Astrograph Catalog 4. With the addition of these data the uncertainty of the estimated heliocentric position of Pluto in Developmental Ephemerides 432 (DE432) is at the level of 1000 km. This new analysis gives us more confidence that these estimations are accurate and are sufficient to support a successful flyby of Pluto by New Horizons.

Observations of the Natural Planetary Satellites for Dynamical and Physical Purpose

NASA Astrophysics Data System (ADS)

Arlot, J. E.; Thuillot, W.; Fienga, A.; Bec-Borsenberger, A.; Baron, N.; Berthier, J.; Colas, F.; Descamps, P.

1999-12-01

At the Institut de mecanique celeste-Bureau des longitudes, we started several programs of observation of the natural planetary satellites. First, we took the opportunity of the transit of the Earth and the Sun in the equatorial plane of Jupiter to observe the mutual phenomena of the Galilean satellites. These observations provide astrometric data of high accuracy useful for dynamical studies of the motions of the satellites and photometric data allowing to characterize the surfaces of the satellites. A campaign was organized leading to 400 light curves made throughout the world in about 40 countries. Second, we started astrometric CCD observations of the faint satellites of Jupiter JVI to JXIII and of the satellite of Saturn Phoebe (SIX) for dynamical purpose at Observatoire de Haute Provence using the 120cm-telescope. PPM, Hipparcos and USNO A.2 catalogue were used for calibration in order to get absolute J2000 R.A. and declination of these objects. In August and December, 1998, CCD observations provided 43 absolute positions of JVI, 23 of JVII, 53 of JVIII, 35 of JIX, 29 of JX, 27 of JXI, 18 of JXII, 16 of JXIII and 135 of SIX (Phoebe). A campaign will also take place in 1999.

Core-Shell Composite Fibers for High-Performance Flexible Supercapacitor Electrodes.

PubMed

Lu, Xiaoyan; Shen, Chen; Zhang, Zeyang; Barrios, Elizabeth; Zhai, Lei

2018-01-31

Core-shell nanofibers containing poly(acrylic acid) (PAA) and manganese oxide nanoparticles as the core and polypyrrole (PPy) as the shell were fabricated through electrospinning the solution of PAA and manganese ions (PAA/Mn 2+ ). The obtained nanofibers were stabilized by Fe 3+ through the interaction between Fe 3+ ions and carboxylate groups. Subsequent oxidation of Mn 2+ by KMnO 4 produced uniform manganese dioxide (MnO 2 ) nanoparticles in the fibers. A PPy shell was created on the fibers by immersing the fibers in a pyrrole solution where the Fe 3+ ions in the fiber polymerized the pyrrole on the fiber surfaces. In the MnO 2 @PAA/PPy core-shell composite fibers, MnO 2 nanoparticles function as high-capacity materials, while the PPy shell prevents the loss of MnO 2 during the charge/discharge process. Such a unique structure makes the composite fibers efficient electrode materials for supercapacitors. The gravimetric specific capacity of the MnO 2 @PAA/PPy core-shell composite fibers was 564 F/g based on cyclic voltammetry curves at 10 mV/s and 580 F/g based on galvanostatic charge/discharge studies at 5 A/g. The MnO 2 @PAA/PPy core-shell composite fibers also present stable cycling performance with 100% capacitance retention after 5000 cycles.

Rotational modes of a simple Earth model

NASA Astrophysics Data System (ADS)

Seyed-Mahmoud, B.; Rochester, M. G.; Rogister, Y. J. G.

2017-12-01

We study the tilt-over mode (TOM), the spin-over mode (SOM), the free core nutation (FCN), and their relationships to each other using a simple Earth model with a homogeneous and incompressible liquid core and a rigid mantle. Analytical solutions for the periods of these modes as well as that of the Chandler wobble is found for the Earth model. We show that the FCN is the same mode as the SOM of a wobbling Earth. The reduced pressure, in terms of which the vector momentum equation is known to reduce to a scalar second order differential equation (the so called Poincaŕe equation), is used as the independent variable. Analytical solutions are then found for the displacement eigenfucntions in a meridional plane of the liquid core for the aforementioned modes. We show that the magnitude of motion in the mantle during the FCN is comparable to that in the liquid core, hence very small. The displacement eigenfunctions for these aforementioned modes as well as those for the free inner core nutation (FICN), computed numerically, are also given for a three layer Earth model which also includes a rigid but capable of wobbling inner core. We will discuss the slow convergence of the period of the FICN in terms of the characteristic surfaces of the Poincare equation.

A novel heterogeneous algorithm to simulate multiphase flow in porous media on multicore CPU-GPU systems

NASA Astrophysics Data System (ADS)

McClure, J. E.; Prins, J. F.; Miller, C. T.

2014-07-01

Multiphase flow implementations of the lattice Boltzmann method (LBM) are widely applied to the study of porous medium systems. In this work, we construct a new variant of the popular "color" LBM for two-phase flow in which a three-dimensional, 19-velocity (D3Q19) lattice is used to compute the momentum transport solution while a three-dimensional, seven velocity (D3Q7) lattice is used to compute the mass transport solution. Based on this formulation, we implement a novel heterogeneous GPU-accelerated algorithm in which the mass transport solution is computed by multiple shared memory CPU cores programmed using OpenMP while a concurrent solution of the momentum transport is performed using a GPU. The heterogeneous solution is demonstrated to provide speedup of 2.6 × as compared to multi-core CPU solution and 1.8 × compared to GPU solution due to concurrent utilization of both CPU and GPU bandwidths. Furthermore, we verify that the proposed formulation provides an accurate physical representation of multiphase flow processes and demonstrate that the approach can be applied to perform heterogeneous simulations of two-phase flow in porous media using a typical GPU-accelerated workstation.

Silicon Nanophotonics for Many-Core On-Chip Networks

NASA Astrophysics Data System (ADS)

Mohamed, Moustafa

Number of cores in many-core architectures are scaling to unprecedented levels requiring ever increasing communication capacity. Traditionally, architects follow the path of higher throughput at the expense of latency. This trend has evolved into being problematic for performance in many-core architectures. Moreover, the trends of power consumption is increasing with system scaling mandating nontraditional solutions. Nanophotonics can address these problems, offering benefits in the three frontiers of many-core processor design: Latency, bandwidth, and power. Nanophotonics leverage circuit-switching flow control allowing low latency; in addition, the power consumption of optical links is significantly lower compared to their electrical counterparts at intermediate and long links. Finally, through wave division multiplexing, we can keep the high bandwidth trends without sacrificing the throughput. This thesis focuses on realizing nanophotonics for communication in many-core architectures at different design levels considering reliability challenges that our fabrication and measurements reveal. First, we study how to design on-chip networks for low latency, low power, and high bandwidth by exploiting the full potential of nanophotonics. The design process considers device level limitations and capabilities on one hand, and system level demands in terms of power and performance on the other hand. The design involves the choice of devices, designing the optical link, the topology, the arbitration technique, and the routing mechanism. Next, we address the problem of reliability in on-chip networks. Reliability not only degrades performance but can block communication. Hence, we propose a reliability-aware design flow and present a reliability management technique based on this flow to address reliability in the system. In the proposed flow reliability is modeled and analyzed for at the device, architecture, and system level. Our reliability management technique is superior to existing solutions in terms of power and performance. In fact, our solution can scale to thousand core with low overhead.

General relativistic effects on the orbit of the S2 star with GRAVITY

NASA Astrophysics Data System (ADS)

Grould, M.; Vincent, F. H.; Paumard, T.; Perrin, G.

2017-12-01

Context. The first observations of the GRAVITY instrument obtained in 2016, have shown that it should become possible to probe the spacetime close to the supermassive black hole Sagittarius A* (Sgr A*) at the Galactic center by using accurate astrometric positions of the S2 star. Aims: The goal of this paper is to investigate the detection by GRAVITY of different relativistic effects affecting the astrometric and/or spectroscopic observations of S2 such as the transverse Doppler shift, the gravitational redshift, the pericenter advance and higher-order general relativistic (GR) effects, in particular the Lense-Thirring effect due to the angular momentum of the black hole. Methods: We implement seven stellar-orbit models to simulate both astrometric and spectroscopic observations of S2 beginning near its next pericenter passage in 2018. Each model takes into account a certain number of relativistic effects. The most accurate one is a fully GR model and is used to generate the mock observations of the star. For each of the six other models, we determine the minimal observation times above which it fails to fit the observations, showing the effects that should be detected. These threshold times are obtained for different astrometric accuracies as well as for different spectroscopic errors. Results: Transverse Doppler shift and gravitational redshift can be detected within a few months by using S2 observations obtained with pairs of accuracies (σA,σV) = (10-100 μas, 1-10 km s-1) where σA and σV are the astrometric and spectroscopic accuracies, respectively. Gravitational lensing can be detected within a few years with (σA,σV) = (10 μas, 10 km s-1). Pericenter advance should be detected within a few years with (σA,σV) = (10 μas, 1-10 km s-1). Cumulative high-order photon curvature contributions, including the Shapiro time delay, affecting spectroscopic measurements can be observed within a few months with (σA,σV) = (10 μas, 1 km s-1). By using a stellar-orbit model neglecting relativistic effects on the photon path except the major contribution of gravitational lensing, S2 observations obtained with accuracies (σA,σV) = (10 μas, 10 km s-1), and a black hole angular momentum (a,i',Ω') = (0.99,45°,160°), the 1σ error on the spin parameter a is of about 0.4, 0.2, and 0.1 for a total observing run of 16, 30, and 47 yr, respectively. The 1σ errors on the direction of the angular momentum reach σi' ≈ 25° and σΩ' ≈ 40° when considering the three orbital periods run. We found that the uncertainties obtained with a less spinning black hole (a = 0.7) are similar to those evaluated with a = 0.99. Conclusions: The combination of S2 observations obtained with the GRAVITY instrument and the spectrograph SINFONI (Spectrograph for INtegral Field Observations in the Near Infrared) also installed at the VLT (Very Large Telescope) will lead to the detection of various relativistic effects. Such detections will be possible with S2 monitorings obtained within a few months or years, depending on the effect. Strong constraints on the angular momentum of Sgr A* (e.g., at 1σ = 0.1) with the S2 star will be possible with a simple stellar-orbit model without using a ray-tracing code but with approximating the gravitational lensing effect. However, long monitorings are necessary, and we thus must rely on the discovery of closer-in stars near Sgr A* if we want to efficiently constrain the black hole parameters with stellar orbits in a short time, or monitor the flares if they orbit around the black hole.

VizieR Online Data Catalog: OCARS catalog second version (Malkin, 2016)

NASA Astrophysics Data System (ADS)

Malkin, Z. M.

2016-11-01

Unlike the first version, supported in 2007-2015, the second version of the OCARS catalog includes three files: ocars.txt is the main file containing the source coordinates, source types, redshifts, and approximate magnitudes, together with commentary; this file corresponds to the first version of the OCARS catalog; ocars_m.txt contains photometric data in the 13 uUBgV rRiIzJHK bands; ocars_n.txt contains a table of corresponding source names in various catalogs; currently, only cross-identifications with IVS programs4 and the LQAC catalog [9] are included; The list of objects included in the OCARS catalog is formed from various astrometric and geodeticVLBI programs and catalogs in the following order: - sources in the ICRF2 [2]; - other sources observed in the framework of IVS programs; - sources from the NASA Goddard VLBI group catalog5 ; - sources from the RFC catalog,6 which is the most complete astrometric catalog of radio sources, is updated each quarter, and contributed more than half the OCARS objects; the latest version of OCARS used the RFC-2016a catalog based on observations obtained in 1980-2015 as part of IVS and other radio astrometric programs [19-31]; - sources from the literature. Optical Characteristics of Astrometric Radio Sources (OCARS) ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Last revised: 27-NOV-2016 Latest update: - removed 30+ RFC sources not identified in NED and optics - removed rather long detailed statistics table, which seems to be not interested for most of users; it is always available on request - a few additions and amendments E-mail alerts about updates are available on request. URL of this file is http://www.gao.spb.ru/english/as/ac_vlbi/ocars.txt Supplement files: Optical and IR magnitudes: http://www.gao.spb.ru/english/as/acvlbi/ocarsm.txt Cross-identification table: http://www.gao.spb.ru/english/as/acvlbi/ocarsn.txt OCARS catalog in CSV format: http://www.gao.spb.ru/english/as/ac_vlbi/ocars.csv Please send comments and requests to Zinovy Malkin, malkin(at)gao.spb.ru ---------------------------------------------------------------------------- The Second Version of the OCARS Catalog of Optical Characteristics of Astrometric Radio Sources. Astronomy Reports, 2016, Vol. 60, No. 11, pp. 996-1005. DOI: 10.1134/S1063772916110032 If you use OCARS catalog in your work, please cite this publication. ---------------------------------------------------------------------- Brief OCARS statistics (detailed statistics is available on request) ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Total number of sources 11375 +30...+90 3320 ( 29.2%) -30...+30 6233 ( 54.8%) -90...-30 1822 ( 16.0%) Number of sources with known type 6284 ( 55.2%) AGN 4704 ( 74.9%) quasars 3027 ( 64.3%) BL Lac 992 ( 21.1%) Seyfert 384 ( 8.2%) blazars 89 ( 1.9%) radio galaxies 1580 ( 25.1%) Number of sources with redshift info 5845 ( 51.4%) +30...+90 1803 ( 30.8%) -30...+30 3329 ( 57.0%) -90...-30 713 ( 12.2%) unreliable 868 ( 14.9%) Number of sources with known magnitude 8133 ( 71.5%) +30...+90 2380 ( 29.3%) -30...+30 4481 ( 55.1%) -90...-30 1272 ( 15.6%) Number of sources with both z and magnitude info 5803 ( 51.0%) (3 data files).

Interpretation of well logs in a carbonate aquifer

USGS Publications Warehouse

MacCary, L.M.

1978-01-01

This report describes the log analysis of the Randolph and Sabial core holes in the Edwards aquifer in Texas, with particular attention to the principles that can be applied generally to any carbonate system. The geologic and hydrologic data were obtained during the drilling of the two holes, from extensive laboratory analysis of the cores, and from numerous geophysical logs run in the two holes. Some logging methods are inherently superiors to others for the analysis of limestone and dolomite aquifers. Three such systems are the dentistry, neutron, and acoustic-velocity (sonic) logs. Most of the log analysis described here is based on the interpretation of suites of logs from these three systems. In certain instances, deeply focused resistivity logs can be used to good advantage in carbonate rock studies; this technique is used to computer the water resistivity in the Randolph core hole. The rocks penetrated by the Randolph core hole are typical of those carbonates that have undergone very little solution by recent ground-water circulation. There are few large solutional openings; the water is saline; and the rocks are dark, dolomitic, have pore space that is interparticle or intercrystalline, and contain unoxidized organic material. The total porosity of rocks in the saline zone is higher than that of rocks in the fresh-water aquifer; however, the intrinsic permeability is much less in the saline zone because there are fewer large solutional openings. The Sabinal core hole penetrates a carbonate environment that has experienced much solution by ground water during recent geologic time. The rocks have high secondary porosities controlled by sedimentary structures within the rock; the water is fresh; and the dominant rock composition is limestone. The relative percentages of limestone and dolomite, the average matrix (grain) densities of the rock mixtures , and the porosity of the rock mass can be calculated from density, neutron, and acoustic logs. With supporting data from resistivity logs, the formation water quality can be estimated, as well as the relative cementation or tortuosity of the rock. Many of these properties calculated from logs can be verified by analysis of the core available from test holes drilled in the saline and fresh water zones.

Method for PE Pipes Fusion Jointing Based on TRIZ Contradictions Theory

NASA Astrophysics Data System (ADS)

Sun, Jianguang; Tan, Runhua; Gao, Jinyong; Wei, Zihui

The core of the TRIZ theories is the contradiction detection and solution. TRIZ provided various methods for the contradiction solution, but all that is not systematized. Combined with the technique system conception, this paper summarizes an integration solution method for contradiction solution based on the TRIZ contradiction theory. According to the method, a flowchart of integration solution method for contradiction is given. As a casestudy, method of fusion jointing PE pipe is analysised.

Dislocation core structures of tungsten with dilute solute hydrogen

NASA Astrophysics Data System (ADS)

Wang, Yinan; Li, Qiulin; Li, Chengliang; Shu, Guogang; Xu, Ben; Liu, Wei

2017-12-01

In this paper, a combination of quantum mechanical and interatomic potential-based atomistic calculations are used to predict the core structures of screw and edge dislocations in tungsten in the presence of a particular concentration of hydrogen atoms. These configurations of the core structures are the results of two competing energies: the interaction between the partial dislocations and the corresponding generalized stacking fault energy in between the two partial dislocations, which are presented in this work. With this, we can precisely predict the configurations of the hydrogen-doped dislocation core structures.