7,427 research outputs found
MOST observations of the roAp stars HD 9289, HD 99563, and HD 134214
We report on the analysis of high-precision space-based photometry of the
roAp (rapidly oscillating Ap) stars HD 9289, HD 99563, and HD134214. All three
stars were observed by the MOST satellite for more than 25 days, allowing
unprecedented views of their pulsation. We find previously unknown candidate
frequencies in all three stars. We establish the rotation period of HD 9289
(8.5 d) for the first time and show that the star is pulsating in two modes
that show different mode geometries. We present a detailed analysis of HD
99563's mode multiplet and find a new candidate frequency which appears
independent of the previously known mode. Finally, we report on 11 detected
pulsation frequencies in HD 134214, 9 of which were never before detected in
photometry, and 3 of which are completely new detections. Thanks to the
unprecedentedly small frequency uncertainties, the p-mode spectrum of HD 134214
can be seen to have a well-defined large frequency spacing similar to the
well-studied roAp star HD 24712 (HR 1217).Comment: 11 pages, 12 figures, accepted for publication in A&
THE EFFECT OF A CHANGING MARKET MIX IN SEED CORN ON INVENTORY COSTS
Changing product characteristics are causing U.S. seed corn companies to reevaluate their inventory strategies. A simulation model based upon the Economic Order Quantity model is built in @Risk to reflect a shortened product life cycle and product proliferation. Inventory costs levels increase because of increased uncertainty of demand. Empirical results find that shortening the product life cycle and expanding the product line increases total inventory costs by 120.8%, increases the average inventory level (primarily due to added safety stock) by 56.2%, and increases the cost of carryover, stockout cost, and safety stock cost by 143, 165, and 119 %, respectively. To maintain higher levels of customer service with products displaying shorter life cycles, more safety stock must be held to guard against stockouts.Crop Production/Industries,
Cyclosporin A inhibits PGE2 release from vascular smooth muscle cells
The influence of the fungoid undecapeptide cyclosporin A (CyA) on PGE2 release from cultured rat aortic smooth muscle cells was investigated in this study. We found that CyA time and concentration dependently (ED50:500 ng/ml) inhibited PGE2 release from the cells. CyA attenuated both basal and PGE2 release evoked by angiotensin II (10(-10)-10(-6) M), arginine vasopressin (10(-10)-10(-6) M) and ionomycin (10(-9)-10(-6) M). CyA (1 microgram/ml) did not affect the conversion of exogenous arachidonic acid (1 microM) into PGE2. The inhibitory effect of CyA was neutralized by high concentrations of the calcium ionophore ionomycin (greater than 3 X 10(-6) M). Taken together our results indicate that CyA inhibits both basal and vasoconstrictor evoked PGE2 release from vascular smooth muscle by impairing the availability of free arachidonic acid rather than by inhibiting the conversion of arachidonic acid into PGE2
A Tight Upper Limit on Oscillations in the Ap star Epsilon Ursae Majoris from WIRE Photometry
Observations of Epsilon UMa obtained with the star tracker on the Wide Field
Infrared Explorer (WIRE) satellite during a month in mid-2000 are analyzed.
This is one of the most precise photometry of an Ap star. The amplitude
spectrum is used to set an upper limit of 75 parts per million for the
amplitude of stellar pulsations in this star unless it accidentally oscillates
with a single mode at the satellite orbit, its harmonics or their one day
aliases. This is the tightest limit put on the amplitude of oscillations in an
Ap star. As the rotation period of Epsilon UMa is relatively short (5.1 d), it
cannot be argued that the observations were made at a wrong rotational phase.
Our results thus support the idea that some Ap stars do not pulsate at all.Comment: 4 pages, 4 figures, 2 style files, accepted for publication in ApJ
On the understanding of pulsations in the atmosphere of roAp stars: phase diversity and false nodes
Studies based on high-resolution spectroscopic data of rapidly oscillating Ap
stars show a surprising diversity of pulsation behavior in the atmospheric
layers, pointing, in particular, to the co-existence of running and standing
waves. The correct interpretation of these data requires a careful modelling of
pulsations in these magnetic stars. In light of this, in this work we present a
theoretical analysis of pulsations in roAp stars, taking into account the
direct influence of the magnetic field. We derive approximate analytical
solutions for the displacement components parallel and perpendicular to the
direction of the magnetic field, that are appropriate to the outermost layer.
From these, we determine the expression for the theoretical radial velocity for
an observer at a general position, and compute the corresponding pulsation
amplitude and phase as function of height in the atmosphere. We show that the
integral for the radial velocity has contributions from three different types
of wave solutions, namely, running waves, evanescent waves, and standing waves
of nearly constant amplitude. We then consider a number of case studies to
illustrate the origin of the different pulsational behaviour that is found in
the observations. Concerning pulsation amplitude, we find that it generally
increases with atmospheric height. Pulsation phase, however, shows a diversity
of behaviours, including phases that are constant, increasing, or decreasing
with atmospheric height. Finally, we show that there are situations in which
the pulsation amplitude goes through a zero, accompanied by a phase jumps of
, and argue that such behaviour does not correspond to a pulsation node in
the outermost layers of the star, but rather to a visual effect, resulting from
the observers inability to resolve the stellar surface.Comment: 21 pages, 25 figure
The NASA Astrophysics Data System: Overview
The NASA Astrophysics Data System Abstract Service has become a key component
of astronomical research. It provides bibliographic information daily, or near
daily, to a majority of astronomical researchers worldwide.
We describe the history of the development of the system and its current
status.
We show several examples of how to use the ADS, and we show how ADS use has
increased as a function of time. Currently it is still increasing
exponentially, with a doubling time for number of queries of 17 months.
Using the ADS logs we make the first detailed model of how scientific
journals are read as a function of time since publication.
The impact of the ADS on astronomy can be calculated after making some simple
assumptions. We find that the ADS increases the efficiency of astronomical
research by 333 Full Time Equivalent (2000 hour) research years per year, and
that the value of the early development of the ADS for astronomy, compared with
waiting for mature technologies to be adopted, is 2332 FTE research years.
The ADS is available at http://adswww.harvard.edu/.Comment: 19 pages, 22 figure
Proper Motion of Pulsar B1800-21
We report high angular resolution, multi-epoch radio observations of the
young pulsar PSR B1800-21. Using two pairs of data sets, each pair spanning
approximately a ten year period, we calculate the proper motion of the pulsar.
We obtain a proper motion of mu_alpha=11.6 +- 1.8 mas/yr, mu_delta=14.8 +- 2.3
mas/yr, which clearly indicates a birth position at the extreme edge of the W30
supernova remnant. Although this does not definitively rule out an association
of W30 and PSR B1800-21, it does not support an association.Comment: 13 pages, 1 color figure. Replaced with version accepted for
publication in Astrophysical Journa
The NASA Astrophysics Data System: Data Holdings
Since its inception in 1993, the ADS Abstract Service has become an
indispensable research tool for astronomers and astrophysicists worldwide. In
those seven years, much effort has been directed toward improving both the
quantity and the quality of references in the database. From the original
database of approximately 160,000 astronomy abstracts, our dataset has grown
almost tenfold to approximately 1.5 million references covering astronomy,
astrophysics, planetary sciences, physics, optics, and engineering. We collect
and standardize data from approximately 200 journals and present the resulting
information in a uniform, coherent manner. With the cooperation of journal
publishers worldwide, we have been able to place scans of full journal articles
on-line back to the first volumes of many astronomical journals, and we are
able to link to current version of articles, abstracts, and datasets for
essentially all of the current astronomy literature. The trend toward
electronic publishing in the field, the use of electronic submission of
abstracts for journal articles and conference proceedings, and the increasingly
prominent use of the World Wide Web to disseminate information have enabled the
ADS to build a database unparalleled in other disciplines.
The ADS can be accessed at http://adswww.harvard.eduComment: 24 pages, 1 figure, 6 tables, 3 appendice
The Century Survey Galactic Halo Project II: Global Properties and the Luminosity Function of Field Blue Horizontal Branch Stars
We discuss a 175 deg^2 spectroscopic survey for blue horizontal branch (BHB)
stars in the Galactic halo. We use the Two Micron All Sky Survey (2MASS) and
the Sloan Digital Sky Survey (SDSS) to select BHB candidates, and find that the
2MASS and SDSS color-selection is 38% and 50% efficient, respectively, for BHB
stars. Our samples include one likely run-away B7 star 6 kpc below the Galactic
plane. The global properties of the BHB samples are consistent with membership
in the halo population: the median metallicity is [Fe/H]=-1.7, the velocity
dispersion is 108 km/s, and the mean Galactic rotation of the BHB stars
3<|z|<15 kpc is -4 +- 30 km/s. We discuss the theoretical basis of the Preston,
Shectman & Beers M_V-color relation for BHB stars, and conclude that intrinsic
shape of the BHB M_V-color relation results from the physics of stars on the
horizontal branch. We calculate the luminosity function for the field BHB star
samples using the Efstathiou, Ellis, & Peterson maximum-likelihood method which
is unbiased by density variations. The field BHB luminosity function exhibits a
steep rise at bright luminosities, a peak between 0.8 < M_V < 1.0, and a tail
at faint luminosities. We compare the field BHB luminosity functions with the
luminosity functions derived from sixteen different globular cluster BHBs.
Kolmogorov-Smirnov tests suggest that field BHB stars and BHB stars in globular
clusters share a common distribution of luminosities, with the exception of
globular clusters with extended BHBs.Comment: 14 pages, including 16 figures, accepted for publication in A
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