29,128 research outputs found
C and N Abundances in Stars At the Base of the Red Giant Branch in M5
We present an analysis of a large sample of moderate resolution Keck LRIS
spectra of subgiant (V \sim 17.2) and fainter stars in the Galactic globular
cluster M5 (NGC 5904) with the goal of deriving C and N abundances.
Star-to-star stochastic variations with significant range in both [C/Fe] and
[N/Fe] are found at all luminosities extending to the bottom of the RGB at M_V
\sim +3. Similar variations in CH appear to be present in the main sequence
turnoff spectra. There is no sign of a change in the behavior of C and N with
evolutionary stage over the full range in luminosity of the RGB and SGB. The C
and N abundances appear strongly anti-correlated, as would be expected from the
CN-cycle processing of stellar material. Yet the present stars are considerably
fainter than the RGB bump, the point at which deep mixing is believed to set
in. On this basis, while the observed abundance pattern is consistent with
proton capture nucleosynthesis, we infer that the site of the reactions is
likely not within the present sample, but rather in a population of more
massive (2 -- 5 M(Sun)) now defunct stars. The range of variation of the N
abundances is very large and the sum of C+N increases as C decreases. To
reproduce this requires the incorporation not only of CN but also of
ON-processed material. Furthermore, the existence of this correlation is quite
difficult to reproduce with an external mechanism such as ``pollution'' with
material processed in a more massive AGB star, which mechanism is fundamentally
stochastic in nature. We therefore suggest that although the internal mixing
hypothesis has serious flaws,new theoretical insights are needed and it should
not be ruled out yet. (abridged)Comment: Slightly updated version to conform to that accepted by the A
Cygnus X-3 in outburst : quenched radio emission, radiation losses and variable local opacity
We present multiwavelength observations of Cygnus X-3 during an extended
outburst in 1994 February - March. Intensive radio monitoring at 13.3, 3.6 &
2.0 cm is complemented by observations at (sub)millimetre and infrared
wavelengths, which find Cyg X-3 to be unusually bright and variable, and
include the first reported detection of the source at 0.45 mm. We report the
first confirmation of quenched radio emission prior to radio flaring
independent of observations at Green Bank. The observations reveal evidence for
wavelength-dependent radiation losses and gradually decreasing opacity in the
environment of the radio jet. We find that the radiation losses are likely to
be predominantly inverse Compton losses experienced by the radio-emitting
electrons in the strong radiation field of a luminous companion to the compact
object. We interpret the decreasing opacity during the flare sequence as
resulting from a decreasing proportion of thermal electrons entrained in the
jet, reflecting a decreasing density in the region of jet formation. We
present, drawing in part on the work of other authors, a model based upon
mass-transfer rate instability predicting gamma-ray, X-ray, infrared and radio
trends during a radio flaring sequence.Comment: LaTeX, 11 pages, 6 figures. Submitted to MNRA
Aspects of short range correlations in a relativistic model
In the present work short range correlations are introduced for the first
time in a relativistic approach to the equation of state of the infinite
nuclear matter in the framework of the Hartree-Fock approximation using an
effective Hamiltonian derived from the Walecka model. The
unitary correlation method is used to introduce short range correlations. The
effect of the correlations in the ground state properties of the nuclear matter
is discussed.Comment: 7 pages, 3 figure
A Survey of Merger Remnants II: The Emerging Kinematic and Photometric Correlations
This paper is the second in a series exploring the properties of 51 {\it
optically} selected, single-nuclei merger remnants. Spectroscopic data have
been obtained for a sub-sample of 38 mergers and combined with previously
obtained infrared photometry to test whether mergers exhibit the same
correlations as elliptical galaxies among parameters such as stellar luminosity
and distribution, central stellar velocity dispersion (), and
metallicity. Paramount to the study is to test whether mergers lie on the
Fundamental Plane. Measurements of have been made using the
Ca triplet absorption line at 8500 {\AA} for all 38 mergers in the sub-sample.
Additional measurements of were made for two of the mergers
in the sub-sample using the CO absorption line at 2.29 \micron. The results
indicate that mergers show a strong correlation among the parameters of the
Fundamental Plane but fail to show a strong correlation between
and metallicity (Mg). In contrast to earlier studies,
the of the mergers are consistent with objects which lie
somewhere between intermediate-mass and luminous giant elliptical galaxies.
However, the discrepancies with earlier studies appears to correlate with
whether the Ca triplet or CO absorption lines are used to derive
, with the latter almost always producing smaller values.
Finally, the photometric and kinematic data are used to demonstrate for the
first time that the central phase-space density of mergers are equivalent to
elliptical galaxies. This resolves a long-standing criticism of the merger
hypothesis.Comment: Accepted Astronomical Journal (to appear in January 2006
Numerical Models of Viscous Accretion Flows Near Black Holes
We report on a numerical study of viscous fluid accretion onto a black hole.
The flow is axisymmetric and uses a pseudo-Newtonian potential to model
relativistic effects near the event horizon. The numerical method is a variant
of the ZEUS code. As a test of our numerical scheme, we are able to reproduce
results from earlier, similar work by Igumenshchev and Abramowicz and Stone et
al. We consider models in which mass is injected onto the grid as well as
models in which an initial equilibrium torus is accreted. In each model we
measure three ``eigenvalues'' of the flow: the accretion rate of mass, angular
momentum, and energy. We find that the eigenvalues are sensitive to r_{in}, the
location of the inner radial boundary. Only when the flow is always supersonic
on the inner boundary are the eigenvalues insensitive to small changes in
r_{in}. We also report on the sensitivity of the results to other numerical
parameters.Comment: 14 pages, 4 figures, 2 tables, to appear in v573 n2 pt1 ApJ July 10,
200
A tight Tsirelson inequality for infinitely many outcomes
We present a novel tight bound on the quantum violations of the CGLMP
inequality in the case of infinitely many outcomes. Like in the case of
Tsirelson's inequality the proof of our new inequality does not require any
assumptions on the dimension of the Hilbert space or kinds of operators
involved. However, it is seen that the maximal violation is obtained by the
conjectured best measurements and a pure, but not maximally entangled, state.
We give an approximate state which, in the limit where the number of outcomes
tends to infinity, goes to the optimal state for this setting. This state might
be potentially relevant for experimental verifications of Bell inequalities
through multi-dimenisonal entangled photon pairs.Comment: 5 pages, 2 figures; improved presentation, change in title, as
published
The Status of the Wave Function in Dynamical Collapse Models
The idea that in dynamical wave function collapse models the wave function is
superfluous is investigated. Evidence is presented for the conjecture that, in
a model of a field theory on a 1+1 lightcone lattice, knowing the field
configuration on the lattice back to some time in the past, allows the wave
function or quantum state at the present moment to be calculated, to arbitrary
accuracy so long as enough of the past field configuration is known.Comment: 35 pages, 11 figures, LaTex, corrected typos, some modifications
made. to appear in Found. of Phys. Lett. Vol. 18, Nbr 6, Nov 2005, 499-51
Improved Color-Temperature Relations and Bolometric Corrections for Cool Stars
We present new grids of colors and bolometric corrections for F-K stars
having 4000 K < Teff < 6500 K, 0.0 < log g < 4.5 and -3.0 < [Fe/H] < 0.0. A
companion paper extends these calculations into the M giant regime. Colors are
tabulated for Johnson U-V and B-V; Cousins V-R and V-I; Johnson-Glass V-K, J-K
and H-K; and CIT/CTIO V-K, J-K, H-K and CO. We have developed these
color-temperature (CT) relations by convolving synthetic spectra with
photometric filter-transmission-profiles. The synthetic spectra have been
computed with the SSG spectral synthesis code using MARCS stellar atmosphere
models as input. Both of these codes have been improved substantially,
especially at low temperatures, through the incorporation of new opacity data.
The resulting synthetic colors have been put onto the observational systems by
applying color calibrations derived from models and photometry of field stars
which have Teffs determined by the infrared-flux method. The color calibrations
have zero points and slopes which change most of the original synthetic colors
by less than 0.02 mag and 5%, respectively. The adopted Teff scale (Bell &
Gustafsson 1989) is confirmed by the extraordinary agreement between the
predicted and observed angular diameters of the field stars. We have also
derived empirical CT relations from the field-star photometry. Except for the
coolest dwarfs (Teff < 5000 K), our calibrated, solar-metallicity model colors
are found to match these and other empirical relations quite well. Our
calibrated, 4 Gyr, solar-metallicity isochrone also provides a good match to
color-magnitude diagrams of M67. We regard this as evidence that our calibrated
colors can be applied to many astrophysical problems, including modelling the
integrated light of galaxies. (abridged)Comment: To appear in the March 2000 issue of the Astronomical Journal. 72
pages including 16 embedded postscript figures (one page each) and 6 embedded
postscript tables (18 pages total
Non-local correlations as an information theoretic resource
It is well known that measurements performed on spatially separated entangled
quantum systems can give rise to correlations that are non-local, in the sense
that a Bell inequality is violated. They cannot, however, be used for
super-luminal signalling. It is also known that it is possible to write down
sets of ``super-quantum'' correlations that are more non-local than is allowed
by quantum mechanics, yet are still non-signalling. Viewed as an information
theoretic resource, super-quantum correlations are very powerful at reducing
the amount of communication needed for distributed computational tasks. An
intriguing question is why quantum mechanics does not allow these more powerful
correlations. We aim to shed light on the range of quantum possibilities by
placing them within a wider context. With this in mind, we investigate the set
of correlations that are constrained only by the no-signalling principle. These
correlations form a polytope, which contains the quantum correlations as a
(proper) subset. We determine the vertices of the no-signalling polytope in the
case that two observers each choose from two possible measurements with d
outcomes. We then consider how interconversions between different sorts of
correlations may be achieved. Finally, we consider some multipartite examples.Comment: Revtex. 12 pages, 6 figure
Angular momentum dependent friction slows down rotational relaxation under non-equilibrium conditions
It has recently been shown that relaxation of the rotational energy of hot
non-equlibrium photofragments (i) slows down significantly with the increase of
their initial rotational temperature and (ii) differs dramatically from the
relaxation of the equilibrium rotational energy correlation function,
manifesting thereby breakdown of the linear response description [Science 311,
1907 (2006)]. We demonstrate that this phenomenon may be caused by the angular
momentum dependence of rotational friction. We have developed the generalized
Fokker-Planck equation whose rotational friction depends upon angular momentum
algebraically. The calculated rotational correlation functions correspond well
to their counterparts obtained via molecular dynamics simulations in a broad
range of initial non-equilibrium conditions. It is suggested that the angular
momentum dependence of friction should be taken into account while describing
rotational relaxation far from equilibrium
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