9,098 research outputs found
Rotating Globular Clusters
Internal rotation is considered to play a major role in the dynamics of some
globular clusters. However, in only few cases it has been studied by
quantitative application of realistic and physically justified global models.
Here we present a dynamical analysis of the photometry and three-dimensional
kinematics of omega Cen, 47 Tuc, and M15, by means of a recently introduced
family of self-consistent axisymmetric rotating models. The three clusters,
characterized by different relaxation conditions, show evidence of differential
rotation and deviations from sphericity. The combination of line-of-sight
velocities and proper motions allows us to determine their internal dynamics,
predict their morphology, and estimate their dynamical distance. The
well-relaxed cluster 47 Tuc is very well interpreted by our model; internal
rotation is found to explain the observed morphology. For M15, we provide a
global model in good agreement with the data, including the central behavior of
the rotation profile and the shape of the ellipticity profile. For the
partially relaxed cluster omega Cen, the selected model reproduces the complex
three-dimensional kinematics; in particular the observed anisotropy profile,
characterized by a transition from isotropy, to weakly-radial anisotropy, and
then to tangential anisotropy in the outer parts. The discrepancy found for the
steep central gradient in the observed line-of-sight velocity dispersion
profile and for the ellipticity profile is ascribed to the condition of only
partial relaxation of this cluster and the interplay between rotation and
radial anisotropy.Comment: 19 pages, 14 figures, accepted for publication in the Astrophysical
Journa
Kinematic fingerprint of core-collapsed globular clusters
Dynamical evolution drives globular clusters toward core collapse, which
strongly shapes their internal properties. Diagnostics of core collapse have so
far been based on photometry only, namely on the study of the concentration of
the density profiles. Here we present a new method to robustly identify
core-collapsed clusters based on the study of their stellar kinematics. We
introduce the \textit{kinematic concentration} parameter, , the ratio
between the global and local degree of energy equipartition reached by a
cluster, and show through extensive direct -body simulations that clusters
approaching core collapse and in the post-core collapse phase are strictly
characterized by . The kinematic concentration provides a suitable
diagnostic to identify core-collapsed clusters, independent from any other
previous methods based on photometry. We also explore the effects of incomplete
radial and stellar mass coverage on the calculation of and find that our
method can be applied to state-of-art kinematic datasets.Comment: Accepted for publication in MNRAS Lette
The “medico-pedagogical institutes” and the failure of the collaboration between psychiatry and pedagogy (1889– 1978)
SBV Regularity for Genuinely Nonlinear, Strictly Hyperbolic Systems of Conservation Laws in one space dimension
We prove that if is the entropy
solution to a strictly hyperbolic system of conservation laws with
genuinely nonlinear characteristic fields then up to a
countable set of times the function is in
, i.e. its distributional derivative is a measure with no
Cantorian part.
The proof is based on the decomposition of into waves belonging to
the characteristic families and the balance
of the continuous/jump part of the measures in regions bounded by
characteristics. To this aim, a new interaction measure \mu_{i,\jump} is
introduced, controlling the creation of atoms in the measure .
The main argument of the proof is that for all where the Cantorian part
of is not 0, either the Glimm functional has a downward jump, or there is
a cancellation of waves or the measure is positive
Global Structure of Admissible BV Solutions to Piecewise Genuinely Nonlinear, Strictly Hyperbolic Conservation Laws in One Space Dimension
The paper describes the qualitative structure of an admissible BV solution to a strictly hyperbolic system of conservation laws whose characteristic families are piecewise genuinely nonlinear. More precisely, we prove that there are a countable set of points \u398 and a countable family of Lipschitz curves T{script} such that outside T{script} 2a \u398 the solution is continuous, and for all points in T{script}{set minus}\u398 the solution has left and right limit. This extends the corresponding structural result in [7] for genuinely nonlinear systems. An application of this result is the stability of the wave structure of solution w.r.t. -convergence. The proof is based on the introduction of subdiscontinuities of a shock, whose behavior is qualitatively analogous to the discontinuities of the solution to genuinely nonlinear systems
V4743 Sgr, a magnetic nova?
Two XMM Newton observations of Nova V4743 Sgr (Nova Sgr 2002) were performed
shortly after it returned to quiescence, 2 and 3.5 years after the explosion.
The X-ray light curves revealed a modulation with a frequency of ~0.75 mHz,
indicating that V4743 Sgr is most probably an intermediate polar (IP). The
X-ray spectra have characteristics in common with known IPs, with a hard
thermal plasma component that can be fitted only assuming a partially covering
absorber. In 2004 the X-ray spectrum had also a supersoft blackbody-like
component, whose temperature was close to that of the white dwarf (WD) in the
supersoft X-ray phase following the outburst, but with flux by at least two
orders of magnitude lower. In quiescent IPs, a soft X-ray flux component
originates at times in the polar regions irradiated by an accretion column, but
the supersoft component of V4743 Sgr disappeared in 2006, indicating a possible
origin different from accretion. We suggest that it may have been due to an
atmospheric temperature gradient on the WD surface, or to continuing localized
thermonuclear burning at the bottom of the envelope, before complete turn-off.
An optical spectrum obtained with SALT 11.5 years after the outburst showed a
prominent He II 4686A line and the Bowen blend, which reveal a very hot region,
but with peak temperature shifted to the ultraviolet (UV) range. V4743 Sgr is
the third post-outburst nova and IP candidate showing a low-luminosity
supersoft component in the X-ray flux a few years after the outburst.Comment: 9 pages, 5 figures, accepted to MNRA
A uniqueness result for the decomposition of vector fields in Rd
Given a vector field \u3c1(1,b) 08Lloc1(R+
7Rd,Rd+1) such that divt,x(\u3c1(1,b)) is a measure, we consider the problem of uniqueness of the representation \u3b7 of \u3c1(1 , b) Ld+1 as a superposition of characteristics \u3b3:(t\u3b3-,t\u3b3+)\u2192Rd, \u3b3\u2d9 (t) = b(t, \u3b3(t)). We give conditions in terms of a local structure of the representation \u3b7 on suitable sets in order to prove that there is a partition of Rd+1 into disjoint trajectories \u2118a, a 08 A, such that the PDE divt,x(u\u3c1(1,b)) 08M(Rd+1),u 08L 1e(R+
7Rd),can be disintegrated into a family of ODEs along \u2118a with measure r.h.s. The decomposition \u2118a is essentially unique. We finally show that b 08Lt1(BVx)loc satisfies this local structural assumption and this yields, in particular, the renormalization property for nearly incompressible BV vector fields
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