1,333 research outputs found
Investigation of serendipitious WFC sources
The serendipitious WFC sources under investigation, i.e., those which just happened to lie in the field of view while another object was being studied, were disappointing. The integration times were chosen to suit the primary target not the serendipitous targets. UX UMa, CZ Ori, BI Ori, WX Cet and AR And were not detected. A long (approximately 17 ksec) pointed observation of UX Uma (PI Wood) has since been carried out (February 1993) and the data is expected shortly. The other observations were much more successful. V471 Tau was observed with the WFC for 6.5 hrs with the S1 filter and 1.1 hrs with the S2b filter. It was easily detected with a count rate of 0.03 cps in the S1 filter and 0.15 cps in the S2b filter. The oscillations were seen, even before the data was folded, as was expected from preliminary results from the survey (Barstow et al. 1992). The pointed observations provide a much better phase coverage of the oscillations than did the survey data where the coverage was sparse. These data will be presented in a paper with the PSPC data (PI's Robinson and Shipman) and the pulse profiles in the different wavelengths will be compared
Effects of Rotationally-Induced Mixing in Compact Binary Systems with Low-Mass Secondaries and in Single Solar-Type Stars
Many population synthesis and stellar evolution studies have addressed the
evolution of close binary systems in which the primary is a compact remnant and
the secondary is filling its Roche lobe, thus triggering mass transfer.
Although tidal locking is expected in such systems, most studies have neglected
the rotationally-induced mixing that may occur. Here we study the possible
effects of mixing in the mass-losing stars for a range in secondary star masses
and metallicities. We find that tidal locking can induce rotational mixing
prior to contact and thus affect the evolution of the secondary star if the
effects of the Spruit-Tayler dynamo are included both for angular momentum and
chemical transport. Once contact is made, the effect of mass transfer tends to
be more rapid than the evolutionary time scale, so the effects of mixing are no
longer directly important, but the mass transfer strips matter to inner layers
that may have been affected by the mixing. These effects are enhanced for
secondaries of 1-1.2 Msun and for lower metallicities. We discuss the possible
implications for the paucity of carbon in the secondaries of the cataclysmic
variable SS Cyg and the black hole candidate XTE J1118+480 and for the
progenitor evolution of Type Ia supernovae. We also address the issue of the
origin of blue straggler stars in globular and open clusters. We find that for
models that include rotation consistent with that observed for some blue
straggler stars, evolution is chemically homogeneous. This leads to tracks in
the HR diagram that are brighter and bluer than the non-rotating main-sequence
turn-off point. Rotational mixing could thus be one of the factors that
contribute to the formation of blue stragglers.Comment: 46 pages, 18 figure
Strong [O III] Objects Among SDSS Broad-Line Active Galaxies
We present the results of a spectral principal component analysis on 9046
broad-line AGN from the Sloan Digital Sky Survey. We examine correlations
between spectral regions within various eigenspectra (e.g., between Fe II
strength and H width) and confirm that the same trends are apparent in
spectral measurements, as validation of our technique. Because we found that
our sample had a large range in the equivalent width of [O III] 5007,
we divided the data into three subsets based on [O III] strength. Of these,
only in the sample with the weakest equivalent width of [O III] were we able to
recover the known correlation between [O III] strength and full width at half
maximum of H and their anticorrelation with Fe II strength. At the low
luminosities considered here ( of erg
s), interpretation of the principal components is considerably
complicated particularly because of the wide range in [O III] equivalent width.
We speculate that variations in covering factor are responsible for this wide
range in [O III] strength.Comment: 26 pages, 11 figures, published in Ap
Long-Term Optical Observations Of Two Lmxbs: Uw Crb (=Ms 1603+260) And V1408 Aql (=4U 1957+115)
We present new optical photometry of two low-mass X-ray binary stars, UW CrB (MS 1603+260) and V1408 Aql (4U 1957+115). UW CrB is an eclipsing binary and we refine its eclipse ephemeris and measure an upper limit to the rate of change of its orbital period, vertical bar P vertical bar < 4.2 x 10(-11) (unitless). The light curve of UW CrB shows optical counterparts of type I X-ray bursts. We tabulate the times, orbital phases, and fluences of 33 bursts and show that the optical flux in the bursts comes primarily from the accretion disk, not from the secondary star. The new observations are consistent with a model in which the accretion disk in UW CrB is asymmetric and precesses in the prograde direction with a period of similar to 5.5 days. The light curve of V1408 Aql has a low-amplitude modulation at its 9.33 hr orbital period. The modulation remained a nearly pure sine curve in the new data as it was in 1984 and 2008, but its mean amplitude was lower, 18% against 23% in the earlier data. A model in which the orbital modulation is caused by the varying aspect of the heated face of the secondary star continues to give an excellent fit to the light curve. We derive a much improved orbital ephemeris for the system.NSF 0958783Astronom
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Time Resolved Spectroscopy Of Cataclysmic Variables - SS Cygni
NSF AST76-23882, AST 79-06340McDonald Observator
Applying genetic algorithms to convoy scheduling
We present the results of our work on applying genetic algorithms combined with a discrete event simulation to the problem of convoy scheduling. We show that this approach can automatically remove conflicts from a convoy schedule thereby providing to the human operator the ability to search for better solutions after an initial conflict free schedule is obtained. We demonstrate that it is feasible to find a conflict free schedule for realistic problems in a few minutes on a common workstation or laptop. The system is currently being integrated into a larger Transportation Information System that regulates highway movement for the militaryIFIP International Conference on Artificial Intelligence in Theory and Practice - Industrial Applications of AIRed de Universidades con Carreras en Informática (RedUNCI
Applying genetic algorithms to convoy scheduling
We present the results of our work on applying genetic algorithms combined with a discrete event simulation to the problem of convoy scheduling. We show that this approach can automatically remove conflicts from a convoy schedule thereby providing to the human operator the ability to search for better solutions after an initial conflict free schedule is obtained. We demonstrate that it is feasible to find a conflict free schedule for realistic problems in a few minutes on a common workstation or laptop. The system is currently being integrated into a larger Transportation Information System that regulates highway movement for the militaryIFIP International Conference on Artificial Intelligence in Theory and Practice - Industrial Applications of AIRed de Universidades con Carreras en Informática (RedUNCI
Ion bombardment experiments suggesting an origin for organic particles in pre-cometary and cometary ices
During the Giotto and Vega encounters with Comet Halley both organic particles called CHON and energetic ions were detected. The acceleration of ions to hundreds of keV in the vicinity of the bow shock and near the nucleus may be a demonstration of a situation occurring in the early solar system (perhaps during the T Tauri stage) that led to the formation of organic particles only now released. Utilizing a Van de Graaff accelerator and a target chamber having cryogenic and mass spectrometer capabilities, frozen gases were bombarded at 10 K with 175 keV protons with the result that fluffy solid material remains after sublimation of the ice. Initial experiments were carried out with a gas mixture in parts of 170 carbon monoxide, 170 argon, 25 water, 20 nitrogen, and 15 methane formulated to reflect an interstellar composition in experiments involving the freezing out of the products of a plasma. The plasma experiments resulted in a varnish-like film residue that exhibited luminescence when excited with ultraviolet radiation, while the ion bombardment created particulate material that was not luminescent
Effects of Digitization and JPEG Compression on Land Cover Classification Using Astronaut-Acquired Orbital Photographs
Studies that utilize astronaut-acquired orbital photographs for visual or digital classification require high-quality data to ensure accuracy. The majority of images available must be digitized from film and electronically transferred to scientific users. This study examined the effect of scanning spatial resolution (1200, 2400 pixels per inch [21.2 and 10.6 microns/pixel]), scanning density range option (Auto, Full) and compression ratio (non-lossy [TIFF], and lossy JPEG 10:1, 46:1, 83:1) on digital classification results of an orbital photograph from the NASA - Johnson Space Center archive. Qualitative results suggested that 1200 ppi was acceptable for visual interpretive uses for major land cover types. Moreover, Auto scanning density range was superior to Full density range. Quantitative assessment of the processing steps indicated that, while 2400 ppi scanning spatial resolution resulted in more classified polygons as well as a substantially greater proportion of polygons < 0.2 ha, overall agreement between 1200 ppi and 2400 ppi was quite high. JPEG compression up to approximately 46:1 also did not appear to have a major impact on quantitative classification characteristics. We conclude that both 1200 and 2400 ppi scanning resolutions are acceptable options for this level of land cover classification, as well as a compression ratio at or below approximately 46:1. Auto range density should always be used during scanning because it acquires more of the information from the film. The particular combination of scanning spatial resolution and compression level will require a case-by-case decision and will depend upon memory capabilities, analytical objectives and the spatial properties of the objects in the image
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