3,452 research outputs found
Regular Oscillation Sub-spectrum of Rapidly Rotating Stars
We present an asymptotic theory that describes regular frequency spacings of
pressure modes in rapidly rotating stars. We use an asymptotic method based on
an approximate solution of the pressure wave equation constructed from a stable
periodic solution of the ray limit. The approximate solution has a Gaussian
envelope around the stable ray, and its quantization yields the frequency
spectrum. We construct semi-analytical formulas for regular frequency spacings
and mode spatial distributions of a subclass of pressure modes in rapidly
rotating stars. The results of these formulas are in good agreement with
numerical data for oscillations in polytropic stellar models. The regular
frequency spacings depend explicitly on internal properties of the star, and
their computation for different rotation rates gives new insights on the
evolution of mode frequencies with rotation.Comment: 14 pages, 10 figure
Insect (Arthropoda: Insecta) Composition in the Diet of Ornate Box Turtles (Terrapene ornata ornata) in Two Western Illinois Sand Prairies, with a New State Record for Cyclocephala (Coleoptera: Scarabaeidae)
A study of fecal samples collected over a two-year period from juvenile ornate box turtles (Terrapene ornata ornata Agassiz) revealed diets consisting of six orders of insects representing 19 families. Turtles were reared in captivity from eggs harvested from local, wild populations, and released at two remnant prairies. Identifiable insect fragments were found in 94% of samples in 2013 (n=33) and 96% in 2014 (n=25). Frequency of occurrence of insects in turtle feces is similar to results reported in previous studies of midwestern Terrapene species. A comparison of insect composition presented no significant difference between release sites. There is no significant difference in consumed insect species between turtles released into or outside of a fenced enclosure at the same site. Specimens of Cyclocephala longula LeConte collected during this study represent a new state record for Illinois
Mode identification in rapidly rotating stars
Context: Recent calculations of pulsation modes in rapidly rotating polytropic models and models based on the Self-Consistent Field method have shown that the frequency spectrum of low degree pulsation modes can be described by an empirical formula similar to Tassoul's asymptotic formula, provided that the underlying rotation profile is not too differential.
Aims: Given the simplicity of this asymptotic formula, we investigate whether it can provide a means by which to identify pulsation modes in rapidly rotating stars.
Methods: We develop a new mode identification scheme which consists in scanning a multidimensional parameter space for the formula coefficients which yield the best-fitting asymptotic spectra. This mode identification scheme is then tested on artificial spectra based on the asymptotic formula, on random frequencies and on spectra based on full numerical eigenmode calculations for which the mode identification is known beforehand. We also investigate the effects of adding random frequencies to mimic the effects of chaotic modes which are also expected to show up in such stars.
Results: In the absence of chaotic modes, it is possible to accurately find a correct mode identification for most of the observed frequencies provided these frequencies are sufficiently close to their asymptotic values. The addition of random frequencies can very quickly become problematic and hinder correct mode identification. Modifying the mode identification scheme to reject the worst fitting modes can bring some improvement but the results still remain poorer than in the case without chaotic modes
Self-trapping at the liquid vapor critical point
Experiments suggest that localization via self-trapping plays a central role
in the behavior of equilibrated low mass particles in both liquids and in
supercritical fluids. In the latter case, the behavior is dominated by the
liquid-vapor critical point which is difficult to probe, both experimentally
and theoretically. Here, for the first time, we present the results of
path-integral computations of the characteristics of a self-trapped particle at
the critical point of a Lennard-Jones fluid for a positive particle-atom
scattering length. We investigate the influence of the range of the
particle-atom interaction on trapping properties, and the pick-off decay rate
for the case where the particle is ortho-positronium.Comment: 12 pages, 3 figures, revtex4 preprin
BVRI Surface Photometry of Isolated Spiral Galaxies
A release of multicolor broad band (BVRI) photometry for a subsample of 44
isolated spirals drawn from the Catalogue of Isolated Galaxies (CIG) is
presented. Total magnitudes and colors at various circular apertures, as well
as some global structural/morphological parameters are estimated. Morphology is
reevaluated through optical and sharp/filtered R band images, (B-I) color index
maps, and archive near-IR JHK images from the Two-Micron Survey. The CAS
structural parameters (Concentration, Asymmetry, and Clumpiness) were
calculated from the images in each one of the bands. The fraction of galaxies
with well identified optical/near-IR bars (SB) is 63%, while a 17% more shows
evidence of weak or suspected bars (SAB). The sample average value of the
maximum bar ellipticity is 0.4. Half of the galaxies in the sample shows rings.
We identify two candidates for isolated galaxies with disturbed morphology. The
structural CAS parameters change with the observed band, and the tendencies
they follow with the morphological type and global color are more evident in
the redder bands. In any band, the major difference between our isolated
spirals and a sample of interacting spirals is revealed in the A-S plane. A
deep and uniformly observed sample of isolated galaxies is intended for various
purposes including (i) comparative studies of environmental effects, (ii)
confronting model predictions of galaxy evolution and (iii) evaluating the
change of galaxy properties with redshift.Comment: 44 pages, 9 figures and 7 tables included. To appear in The
Astronomical Journal. For the 43 appendix figures 4.1-4.43 see
http://www.astroscu.unam.mx/~avila/Figs4.1_4.43.tar.gz (7.2 Mb tar.gz file
Pulsation modes in rapidly rotating stellar models based on the Self-Consistent Field method
Context: New observational means such as the space missions CoRoT and Kepler
and ground-based networks are and will be collecting stellar pulsation data
with unprecedented accuracy. A significant fraction of the stars in which
pulsations are observed are rotating rapidly.
Aims: Our aim is to characterise pulsation modes in rapidly rotating stellar
models so as to be able to interpret asteroseismic data from such stars.
Methods: The pulsation code developed in Ligni\`eres et al. (2006) and Reese
et al. (2006) is applied to stellar models based on the self-consistent field
(SCF) method (Jackson et al. 2004, 2005, MacGregor et al. 2007).
Results: Pulsation modes in SCF models follow a similar behaviour to those in
uniformly rotating polytropic models, provided that the rotation profile is not
too differential. Pulsation modes fall into different categories, the three
main ones being island, chaotic, and whispering gallery modes, which are
rotating counterparts to modes with low, medium, and high l-|m| values,
respectively. The frequencies of the island modes follow an asymptotic pattern
quite similar to what was found for polytropic models. Extending this
asymptotic formula to higher azimuthal orders reveals more subtle behaviour as
a function of m and provides a first estimate of the average advection of
pulsation modes by rotation. Further calculations based on a variational
principle confirm this estimate and provide rotation kernels that could be used
in inversion methods. When the rotation profile becomes highly differential, it
becomes more and more difficult to find island and whispering gallery modes at
low azimuthal orders. At high azimuthal orders, whispering gallery modes, and
in some cases island modes, reappear.Comment: 16 pages, 11 figures, accepted for publication in A&
Insect (Arthropoda: Insecta) Composition in the Diet of Ornate Box Turtles (Terrapene ornata ornata) in Two Western Illinois Sand Prairies, with a New State Record for Cyclocephala (Coleoptera: Scarabaeidae)
A study of fecal samples collected over a two-year period from juvenile ornate box turtles (Terrapene ornata ornata Agassiz) revealed diets consisting of six orders of insects representing 19 families. Turtles were reared in captivity from eggs harvested from local, wild populations, and released at two remnant prairies. Identifiable insect fragments were found in 94% of samples in 2013 (n=33) and 96% in 2014 (n=25). Frequency of occurrence of insects in turtle feces is similar to results reported in previous studies of midwestern Terrapene species. A comparison of insect composition presented no significant difference between release sites. There is no significant difference in consumed insect species between turtles released into or outside of a fenced enclosure at the same site. Specimens of Cyclocephala longula LeConte collected during this study represent a new state record for Illinois
Photometric Decomposition of Barred Galaxies
We present a non-parametric method for decomposition of the light of disk
galaxies into disk, bulge and bar components. We have developed and tested the
method on a sample of 68 disk galaxies for which we have acquired I-band
photometry. The separation of disk and bar light relies on the single
assumption that the bar is a straight feature with a different ellipticity and
position angle from that of the projected disk. We here present the basic
method, but recognise that it can be significantly refined. We identify bars in
only 47% of the more nearly face-on galaxies in our sample. The fraction of
light in the bar has a broad range from 1.3% to 40% of the total galaxy light.
If low-luminosity galaxies have more dominant halos, and if halos contribute to
bar stability, the luminosity functions of barred and unbarred galaxies should
differ markedly; while our sample is small, we find only a slight difference of
low significance.Comment: Accepted to appear in AJ, 36 pages, 9 figures, full on-line figures
available at http://www.physics.rutgers.edu/~sellwood/Reese.htm
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