2,306 research outputs found
SuperWASP observations of pulsating Am stars
We have studied over 1600 Am stars at a photometric precision of 1 mmag with SuperWASP photometric data. Contrary to previous belief, we find that around 200 Am stars are pulsating δ Sct and γ Dor stars, with low amplitudes that have been missed in previous, less extensive studies. While the amplitudes are generally low, the presence of pulsation in Am stars places a strong constraint on atmospheric convection, and may require the pulsation to be laminar. While some pulsating Am stars have been previously found to be δ Sct stars, the vast majority of Am stars known to pulsate are presented in this paper. They will form the basis of future statistical studies of pulsation in the presence of atomic diffusion
Effects of environmental changes on marsh vegetation with special reference to salinity
A literature survey primarily concerned with brackish and salt marshes located along the eastern coast of North America and the Gulf Coast was presented. The review concentrated upon the vegetation of the marshes, particularly in regard to distribution, composition, succession, and productivity. Special efforts were made to include major works concerned with the Louisiana and Mississipi coastal marshes. It appears that spring to early summer (weeks 18-34 of the year; April - mid-July) is the best period of time to categorize the communities. It is during this time of the year that the communities appear most stable in regard to species composition. This allows a strong correlation to be drawn between the salinity of the region and the dominant species of the community. As such, this would seem to be best period in which to sample the marsh via air or land for differences in vegetation and salinity
Eclipsing binaries in open clusters
Accurate physical parameters have been determined for two early-type detached
eclipsing binaries in the open cluster h Persei (NGC 869). Masses accurate to
1.5% are derived from high-resolution spectroscopy and radii accurate to 4--6%
have been obtained from fitting the existing light curves. The four stars are
placed in the mass radius plane and compared to the theoretical stellar models
of the Granada Group. The best-fitting models have a low metallicity of
approximately Z=0.01 and a high helium abundance of Y=0.34. This is the first
determination of the bulk metallicity of the Perseus Double Cluster. Recent
studies have assumed a solar metallicity so their results should be reviewed.Comment: 4 pages, 5 figures. To appear in Spectroscopically and Spatially
Resolving the Components of Close Binary Stars, ASP Conf. Series, 200
Absolute dimensions of detached eclipsing binaries. III. The metallic-lined system YZ Cassiopeiae
The bright binary system YZ Cassiopeiae is a remarkable laboratory for
studying the Am phenomenon. It consists of a metallic-lined A2 star and an F2
dwarf on a circular orbit, which undergo total and annular eclipses. We present
an analysis of 15 published light curves and 42 new high-quality echelle
spectra, resulting in measurements of the masses, radii, effective temperatures
and photospheric chemical abundances of the two stars. The masses and radii are
measured to 0.5% precision: M_A = 2.263 +/- 0.012 Msun, M_B = 1.325 +/- 0.007
Msun, R_A = 2.525 +/- 0.011 Rsun and R_B = 1.331 +/- 0.006 Rsun. We determine
the abundance of 20 elements for the primary star, of which all except scandium
are super-solar by up to 1 dex. The temperature of this star (9520 +/- 120 K)
makes it one of the hottest Am stars. We also measure the abundances of 25
elements for its companion (Teff = 6880 +/- 240 K), finding all to be solar or
slightly above solar. The photospheric abundances of the secondary star should
be representative of the bulk composition of both stars. Theoretical stellar
evolutionary models are unable to match these properties: the masses, radii and
temperatures imply a half-solar chemical composition (Z = 0.009 +/- 0.003) and
an age of 490-550 Myr. YZ Cas therefore presents a challenge to stellar
evolutionary theory.Comment: Accepted for publication in MNRAS. 15 pages, 9 tables, 7 figure
Synthesis of the Beryllium 3131A Spectral Region
The Beryllium spectral region of the Sun, Procyon and 4 stars in the open
cluster NGC6633 up to Teff = 7500K have been synthesised using ATLAS9 model
atmospheres and the MOOG spectral synthesis program.
The line list used for these syntheses has been modified from the ATLAS9 line
list to improve the quality of the fits in light of the improved opacities in
the new version of the MOOG code.
Significant changes have been made to the Mn I line at ATLAS9 wavelength
3131.037A and an OH line has been added at 3131.358A. In addition there are a
number of minor changes to gf-values throughout the synthesised region thus
improving the fit for the spectra across the temperature range considerably.Comment: 4 pages, 3 figures. To appear in the proceedings of the Workshop
"ATLAS 12 and related codes", Trieste, July 11-15, 200
Subsynchronous vibrations in a high pressure centrifugal compressor: A case history
Two distinct aerodynamically excited vibrations in a high pressure low flow centrifugal compressor are documented. A measured vibration near 21% of running speed was identified as a nonresonant forced vibration which results from rotating stall in the diffuser; a measured vibration near 50% of running speed was identified as a self excited vibration sustained by cross coupling forces acting at the compressor wheels. The dependence of these characteristics on speed, discharge pressure, and changes in bearing design are shown. The exciting mechanisms of diffuser stall and aerodynamic cross coupling are evidenced. It is shown how the rotor characteristics are expected to change as a result of modifications. The operation of the compressor after the modifications is described
Spectrum Analysis of Bright Kepler late B- to early F- Stars
The Kepler satellite mission delivers single band-pass light curves of a huge
number of stars observed in the Cygnus-Lyra region opening a new window for
asteroseismology. In order to accomplish one of the preconditions for the
asteroseismic modelling of the stars, we aim to derive fundamental parameters
and individual abundances for a sample of 18 Gamma Dor (GD)/Delta Sct (DSct)
and 8 SPB/beta Cep candidate stars in the Kepler satellite field of view. We
use the spectral synthesis method to model newly obtained, high-resolution
spectra of 26 stars in order to derive their fundamental parameters and
individual abundances. The stars are then placed into the log(Teff)-log(g)
diagram and the obtained spectroscopic classification is compared to the
existing photometric one. For hot stars, the KIC temperatures appear to be
systematically underestimated, in agreement with previous findings. We also
find that the temperatures derived from our spectra agree reasonably well with
those derived from the SED fitting. According to their position in the
log(Teff)-log(g) diagram, two stars are expected GD stars, four stars are
expected DSct stars, and four stars are possibly DSct stars at the blue edge of
the instability strip. Two stars are confirmed SPB variables, and one star
falls into the SPB instability region but its parameters might be biased by
binarity. Two of the four stars that fall into the DSct instability region show
GD-type oscillation in their light curves implying that GD-like oscillations
are much more common among the DSct stars than is theoretically expected.
Moreover, one of the stars located at the hot border of the DSct instability
strip is classified as DSct-GD hybrid pulsator from its light curve analysis.
Given that these findings are fully consistent with recent investigations, we
conclude that a revision of the GD and DSct instability strips is essential.Comment: 14 pages, 14 figures, 6 tables; accepted for publication in MNRA
The Habitable Zone Gallery
The Habitable Zone Gallery (www.hzgallery.org) is a new service to the
exoplanet community which provides Habitable Zone (HZ) information for each of
the exoplanetary systems with known planetary orbital parameters. The service
includes a sortable table with information on the percentage of orbital phase
spent within the HZ, planetary effective temperatures, and other basic
planetary properties. In addition to the table, we also plot the period and
eccentricity of the planets with respect to their time spent in the HZ. The
service includes a gallery of known systems which plot the orbits and the
location of the HZ with respect to those orbits. Also provided are animations
which aid in orbit visualization and provide the changing effective temperature
for those planets in eccentric orbits. Here we describe the science motivation,
the under-lying calculations, and the structure of the web site.Comment: 6 pages, 3 figures, accepted for publication in PAS
\u3ci\u3eDendroctonus Valens\u3c/i\u3e and \u3ci\u3eHylastes Porculus\u3c/i\u3e (Coleoptera: Scolytidae): Vectors of Pathogenic Fungi (Ophiostomatales) Associated With Red Pine Decline Disease.
A study was conducted to determine whether Dendroctonus valens and Hylastes porculus could vector their commonly associated fungi to red pine. Field collected adult D. valens transmitted Leptographium terebrantis, Leptographium procerum and Ophiostoma ips into 45%, 30%, and 5%, respectively of the wounded red pine roots onto which they were caged. Field collected H. porculus transmitted L. terebrantis, L. procerum and O. ips into 55%, 40%, and 5%, respectively, of the wounded red pine roots onto which beetles were caged. None of the control roots, which were mechanically wounded only, were found to contain O. ips, whereas only one control root contained L. terebrantis and only one control root contained L. procerum. This work demonstrates that D. valens and H. porculus can vector their associated Leptographium fungi to red pine trees and that these organisms are likely involved in red pine decline disease
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