958 research outputs found
Kinematic Orbits and the Structure of the Internal Space for Systems of Five or More Bodies
The internal space for a molecule, atom, or other n-body system can be
conveniently parameterised by 3n-9 kinematic angles and three kinematic
invariants. For a fixed set of kinematic invariants, the kinematic angles
parameterise a subspace, called a kinematic orbit, of the n-body internal
space. Building on an earlier analysis of the three- and four-body problems, we
derive the form of these kinematic orbits (that is, their topology) for the
general n-body problem. The case n=5 is studied in detail, along with the
previously studied cases n=3,4.Comment: 38 pages, submitted to J. Phys.
A new clue to the transition mechanism between optical high and low states of the supersoft X-ray source RX J0513.9-6951, implied from the recurrent nova CI Aquilae 2000 outburst model
We have found a new clue to the transition mechanism between optical
high/X-ray off and optical low/X-ray on states of the LMC supersoft X-ray
source RX J0513.9-6951. A sharp ~1 mag drop is common to the CI Aql 2000
outburst. These drops are naturally attributed to cessation of optically thick
winds on white dwarfs. A detailed light-curve analysis of CI Aql indicates that
the size of a disk drastically shrinks when the wind stops. This causes ~1-2
mag drop in the optical light curve. In RX J0513.9-6951, the same mechanism
reproduces sharp ~1 mag drop from optical high to low states. We predict this
mechanism also works on the transition from low to high states. Interaction
between the wind and the companion star attenuates the mass transfer and drives
full cycles of low and high states.Comment: 9 pages including 5 figures, to appear in the Astrophysical Journa
Phase equilibrium modelling of the amphibolite to granulite facies transition in metabasic rocks (Ivrea Zone, NW Italy)
The development of thermodynamic models for tonalitic melt and the updated clinopyroxene and amphibole models now allow the use of phase equilibrium modelling to estimate PâT conditions and melt production for anatectic mafic and intermediate rock types at highâtemperature conditions.
The Permian midâlower crustal section of the Ivrea Zone preserves a metamorphic field gradient from mid amphibolite facies to granulite facies, and thus records the onset of partial melting in metabasic rocks. Interlayered metabasic and metapelitic rocks allows the direct comparison of PâT estimates and partial melting between both rock types with the same metamorphic evolution. Pseudosections for metabasic compositions calculated in the Na2OâCaOâK2OâFeOâMgOâAl2O3âSiO2âH2OâTiO2âO (NCKFMASHTO) system are presented and compared with those of metapelitic rocks calculated with consistent endmember data and aâx models. The results presented in this study show that PâT conditions obtained by phase equilibria modelling of both metabasic and metapelitic rocks give consistent results within uncertainties, allowing integration of results obtained for both rock types. In combination, the calculations for both metabasic and metapelitic rocks allows an updated and more precisely constrained metamorphic field gradient for Val Strona di Omegna to be defined. The new field gradient has a slightly lower dP/dT which is in better agreement with the onset of crustal thinning of the Adriatic margin during the Permian inferred in recent studies
The ROSAT Galactic Plane Survey: analysis of a low latitude sample area in Cygnus
We present the analysis of the point source content of a low galactic
latitude region selected from the ROSAT all-sky survey. The test field is
centered at l = 90deg, b = 0deg and has an area of 64.5 deg2. A total of 128
soft X-ray sources are detected above a maximum likelihood of 8. Catalogue
searches and optical follow-up observations show that in this direction of the
galactic plane, 85% of the sources brighter than 0.03 PSPC cts/s are identified
with active coronae. F-K type stars represent 67% (+/-13%) of the stellar
identifications and M type stars account for 19% (+/- 6%). These results
together with those of similar optical campaigns demonstrate that the soft
X-ray population of the Milky Way is largely dominated by active stars. The
modelling of this population suggests that most of the stars detected by ROSAT
in this direction are younger than 1 Gyr. The small number of unidentified
sources at low X-ray flux put rather strong constraints on the hypothetical
X-ray emission from old neutron stars accreting from the interstellar medium.
Our observations clearly rule out models which assume no dynamical heating for
this population and a total number of Nns = 10^9 neutron stars in the Galaxy.
If accretion on polar caps is the dominant mode then our upper limit may imply
Nns ~ 10^8.Comment: 27 pages, 22 figures, Latex. Full resolution PostScript available at
ftp://cdsarc.u-strasbg.fr/pub/xray/rgps_cygnus.ps.gz To be published in
Astronomy & Astrophysics, Main Journa
Testing Mode-Coupling Theory for a Supercooled Binary Lennard-Jones Mixture II: Intermediate Scattering Function and Dynamic Susceptibility
We have performed a molecular dynamics computer simulation of a supercooled
binary Lennard-Jones system in order to compare the dynamical behavior of this
system with the predictions of the idealized version of mode-coupling theory
(MCT). By scaling the time by the temperature dependent -relaxation
time , we find that in the -relaxation regime and
, the coherent and incoherent intermediate scattering functions, for
different temperatures each follows a -dependent master curve as a function
of scaled time. We show that during the early part of the -relaxation,
which is equivalent to the late part of the -relaxation, these master
curves are well approximated by the master curve predicted by MCT for the
-relaxation. This part is also fitted well by a power-law, the so-called
von Schweidler law. We show that the effective exponent of this power-law
depends on the wave vector if is varied over a large range. The early
part of the -relaxation regime does not show the critical decay
predicted by MCT. The -dependence of the nonergodicity parameter for
and are in qualitative agreement with MCT. On the time
scale of the late -relaxation the correlation functions show a
Kohlrausch-Williams-Watt behavior (KWW). The KWW exponent is
significantly different from the effective von Schweidler exponent . At low
temperatures the -relaxation time shows a power-law behavior
with a critical temperature that is the same as the one found previously for
the diffusion constant [Phys. Rev. Lett. {\bf 73}, 1376 (1994)]. The critical
exponent of this power-law and the von Schweidler exponent fulfill the
connection proposed by MCT between these two quantities. We also show that theComment: 28 Pages of REVTEX, Figures available from W. Ko
Identification of selected sources from the ROSAT Galactic Plane Survey - I
We report on optical searches in the error circles of 93 ROSAT survey sources
located at low galactic latitudes (|b| < 20 deg). These sources were extracted
from the ROSAT Galactic Plane Survey using various selection criteria on
hardness ratio, X-ray and optical brightness and integrated galactic absorption
in the direction of the source. We find optical identifications in 76 cases,
among which are 25 new AGN, 6 new CVs and a new Be/X-ray binary. In order to
illustrate the relevance of the source selections applied here, we
cross-correlated the ROSAT all-sky survey bright source list with SIMBAD.
Different classes of X-ray emitters populate distinct regions of a multi
dimensional parameter space involving flux ratios, galactic latitude and Nh.
This relatively good segregation offers the possibility to build source samples
with enhanced probability of identification with a given class. Complete
optical identification of such subsamples could eventually be used to compute
meaningful probabilities of identification for all sources using as basis a
restricted set of multi-wavelength information.Comment: 18 pages, 7 figures, Postscript. Optical spectra and finding charts
available at ftp://cdsarc.u-strasbg.fr/pub/xray/rgps_idI.ps.gz Submitted to
Astronomy & Astrophysics, Supplement Serie
Disk instability and the spectral evolution of the 1992 outburst of the intermediate polar GK Persei
The disk instability model can explain the previous history of dwarf-nova-like outbursts in the intermediate polar GK Per, which occur about once every three years. Disk models that reproduce the recurrence time and outburst light curves suggest that GK Per has a large effective inner disk radius (approx. 30-40 white dwarf radii) truncated by a strong magnetic field (10(exp 7) G). In this context, the effective radius is that of the portion of the disk that participates in the disk thermal instability. The radius derived is larger than the corotation radius, which must be an upper limit on the true dynamical inner radius of the disk. Disk instability models with this large effective inner radius predict that the ultraviolet continuum should be rather flat. Here we compare the predictions of the disk instability model to IUE observations of the 1981 outburst and to IUE and ROSAT observations of the recent 1992 outburst of GK Per. The model disk continuum spectral evolution is consistent with the observed UV and optical spectra, especially at maximum and in the early decay phase of the outburst. The consistency of the model with the observed UV spectra suggests that the effective inner radius of the disk is almost constant, independent of mass accretion rate, and that whatever structure lies between the effective inner radius and the corotation radius neither participates in the disk instability nor radiates substantially in the UV. The related physics of the inner disk region will be briefly discussed
RX J0513.9-6951: The first example of accretion wind evolution, a key evolutionary process to Type Ia supernovae
A new self-sustained model for long-term light curve variations of RX
J0513.9-6951 is proposed based on an optically thick wind model of
mass-accreting white dwarfs (WDs). When the mass accretion rate to a WD exceeds
the critical rate of \sim 1 x 10^{-6} M_\sun yr^{-1}, optically thick strong
winds begin to blow from the WD so that a formation of common envelope is
avoided. The WD can accrete and burn hydrogen-rich matter atop the WD at the
critical rate. The excess matter transferred to the WD above the critical rate
is expelled by winds. This is called the accretion wind evolution. This
ejection process, however, occurs intermittently because the mass transfer is
attenuated by strong winds: the strong winds collide with the secondary surface
and strip off the very surface layer of the secondary. The matter stripped-off
is lost from the binary system. Properly formulating this mass stripping effect
and the ensuing decay of mass transfer rate, we are able to reproduce, in a
self-sustained manner, the transition between the optical high/X-ray off and
optical low/X-ray on states of RX J0513.9-6951. Thus RX J0513.9-6951 is the
first example of the accretion wind evolution, which is a key evolutionary
process in a recently developed evolutionary path to Type Ia supernovae.Comment: 22 pages including 13 figures, to appear in the Astrophysical Journa
Moyal star product approach to the Bohr-Sommerfeld approximation
The Bohr-Sommerfeld approximation to the eigenvalues of a one-dimensional
quantum Hamiltonian is derived through order (i.e., including the
first correction term beyond the usual result) by means of the Moyal star
product. The Hamiltonian need only have a Weyl transform (or symbol) that is a
power series in , starting with , with a generic fixed point in
phase space. The Hamiltonian is not restricted to the kinetic-plus-potential
form. The method involves transforming the Hamiltonian to a normal form, in
which it becomes a function of the harmonic oscillator Hamiltonian.
Diagrammatic and other techniques with potential applications to other normal
form problems are presented for manipulating higher order terms in the Moyal
series.Comment: 27 pages, no figure
A limit cycle model for long-term optical variations of V Sagittae: The second example of accretion wind evolution
V Sagittae shows quasi-periodic optical high (soft X-ray off) and low (soft
X-ray on) states with the total period of ~300 days. A binary model is
presented to explain orbital light curves both for the high and low states as
well as the transition mechanism between them. The binary model consists of a
white dwarf (WD), a disk around the WD, and a lobe-filling main-sequence (MS)
companion. In the optical high state, the mass transfer rate to the WD exceeds
the critical rate of ~1 x 10^{-6} Msun/yr, and the WD blows an optically thick,
massive wind. Surface layers of the disk are blown in the wind and the disk
surface extends to the companion or over. As a result, optical luminosity of
the disk increases by a magnitude because of its large irradiation effect. The
massive wind completely obscures soft X-rays. This corresponds to the optical
high/soft X-ray off state. The transition between optical high and low states
is driven by an attenuation of the mass transfer from the secondary. As the
mass supply stops, the WD wind weakens and eventually stops. The disk shrinks
to a Roche lobe size and the optical magnitude drops. This phase corresponds to
the optical low/soft X-ray on state. This cycle is repeated like a limit cycle.
The WD can grow in mass at the critical rate and eventually reach the
Chandrasekhar mass limit. This process is called ``accretion wind evolution,''
which is a key evolutionary process in a recently developed evolutionary
scenario of Type Ia supernovae. This evolutionary process was first confirmed
in the LMC supersoft X-ray source RX J0513.96951. Thus, V Sge is the second
example of accretion wind evolution.Comment: to appear in ApJ, 33 pages including figure
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