1,363 research outputs found
A three-dimensional view of the remnant of Nova Persei 1901 (GK Per)
We present a kinematical study of the optical ejecta of GK Per. It is based
on proper motions measurements of 282 knots from ~20 images spanning 25 years.
Doppler-shifts are also computed for 217 knots. The combination of proper
motions and radial velocities allows a unique 3-D view of the ejecta to be
obtained. The main results are: (1) the outflow is a thick shell in which knots
expand with a significant range of velocities, mostly between 600 and 1000
km/s; (2) kinematical ages indicate that knots have suffered only a modest
deceleration since their ejection a century ago; (3) no evidence for anisotropy
in the expansion rate is found; (4) velocity vectors are generally aligned
along the radial direction but a symmetric pattern of non-radial velocities is
also observed at specific directions; (5) the total Halpha+[NII] flux has been
linearly decreasing at a rate of 2.6 % per year in the last decade. The Eastern
nebular side is fading at a slower rate than the Western one. Some of the knots
displayed a rapid change of brightness during the 2004-2011 period. Over a
longer timescale, a progressive circularization and homogenization of the
nebula is taking place; (6) a kinematic distance of 400+-30 pc is determined.
These results raise some problems to the previous interpretations of the
evolution of GK Per. In particular, the idea of a strong interaction of the
outflow with the surrounding medium in the Southwest quadrant is not supported
by our data.Comment: Accepted for publication in The Astrophysical Journal (19 pages, 17
figures). Higher resolution version of this article (2.5 MB) is available at
http://www.aai.ee/~sinope/ApJ89291_liimets.pd
Lagrangian Formalism for nonlinear second-order Riccati Systems: one-dimensional Integrability and two-dimensional Superintegrability
The existence of a Lagrangian description for the second-order Riccati
equation is analyzed and the results are applied to the study of two different
nonlinear systems both related with the generalized Riccati equation. The
Lagrangians are nonnatural and the forces are not derivable from a potential.
The constant value of a preserved energy function can be used as an
appropriate parameter for characterizing the behaviour of the solutions of
these two systems. In the second part the existence of two--dimensional
versions endowed with superintegrability is proved. The explicit expressions of
the additional integrals are obtained in both cases. Finally it is proved that
the orbits of the second system, that represents a nonlinear oscillator, can be
considered as nonlinear Lissajous figuresComment: 25 pages, 7 figure
Momentum-resolved evolution of the Kondo lattice into 'hidden-order' in URu2Si2
We study, using high-resolution angle-resolved photoemission spectroscopy,
the evolution of the electronic structure in URu2Si2 at the Gamma, Z and X
high-symmetry points from the high-temperature Kondo-screened regime to the
low-temperature `hidden-order' (HO) state. At all temperatures and symmetry
points, we find structures resulting from the interaction between heavy and
light bands, related to the Kondo lattice formation. At the X point, we
directly measure a hybridization gap of 11 meV already open at temperatures
above the ordered phase. Strikingly, we find that while the HO induces
pronounced changes at Gamma and Z, the hybridization gap at X does not change,
indicating that the hidden-order parameter is anisotropic. Furthermore, at the
Gamma and Z points, we observe the opening of a gap in momentum in the HO
state, and show that the associated electronic structure results from the
hybridization of a light electron band with the Kondo-lattice bands
characterizing the paramagnetic state.Comment: Updated published version. Mansucript + Supplemental Material (8
pages, 9 figures). Submitted 16 September 201
New insights into the outflows from R Aquarii
R Aquarii is a symbiotic binary surrounded by a large and complex nebula with
a prominent curved jet. It is one of the closest known symbiotic systems, and
therefore offers a unique opportunity to study the central regions of these
systems and the formation and evolution of astrophysical jets. We studied the
evolution of the central jet and outer nebula of R Aqr taking advantage of a
long term monitoring campaign of optical imaging, as well as of high-resolution
integral field spectroscopy. Narrow-band images acquired over a period of more
than 21 years are compared in order to study the expansion and evolution of all
components of the R Aqr nebula. The magnification method is used to derive the
kinematic ages of the features that appear to expand radially. Integral field
spectroscopy of the OIII 5007A emission is used to study the velocity structure
of the central regions of the jet. New extended features, further out than the
previously known hourglass nebula, are detected. The kinematic distance to R
Aqr is calculated to be 178 pc using the expansion of the large hourglass
nebula. This nebula of R Aqr is found to be roughly 650 years old, while the
inner regions have ages ranging from 125 to 290 years. The outer nebula is
found to be well described by a ballistic expansion, while for most components
of the jet strong deviations from such behaviour are found. We find that the
Northern jet is mostly red-shifted while its Southern part is blue-shifted,
apparently at odds with findings from previous studies but almost certainly a
consequence of the complex nature of the jet and variations in ionisation and
illumination between observations.Comment: 13 pages, 8 figures, accepted for publication in A&
Central potentials on spaces of constant curvature: The Kepler problem on the two-dimensional sphere and the hyperbolic plane
The Kepler problem is a dynamical system that is well defined not only on the
Euclidean plane but also on the sphere and on the Hyperbolic plane. First, the
theory of central potentials on spaces of constant curvature is studied. All
the mathematical expressions are presented using the curvature \k as a
parameter, in such a way that they reduce to the appropriate property for the
system on the sphere , or on the hyperbolic plane , when
particularized for \k>0, or \k<0, respectively; in addition, the Euclidean
case arises as the particular case \k=0. In the second part we study the main
properties of the Kepler problem on spaces with curvature, we solve the
equations and we obtain the explicit expressions of the orbits by using two
different methods: first by direct integration and second by obtaining the
\k-dependent version of the Binet's equation. The final part of the article,
that has a more geometric character, is devoted to the study of the theory of
conics on spaces of constant curvature.Comment: 37 pages, 7 figure
Trigonometry of 'complex Hermitian' type homogeneous symmetric spaces
This paper contains a thorough study of the trigonometry of the homogeneous
symmetric spaces in the Cayley-Klein-Dickson family of spaces of 'complex
Hermitian' type and rank-one. The complex Hermitian elliptic CP^N and
hyperbolic CH^N spaces, their analogues with indefinite Hermitian metric and
some non-compact symmetric spaces associated to SL(N+1,R) are the generic
members in this family. The method encapsulates trigonometry for this whole
family of spaces into a single "basic trigonometric group equation", and has
'universality' and '(self)-duality' as its distinctive traits. All previously
known results on the trigonometry of CP^N and CH^N follow as particular cases
of our general equations. The physical Quantum Space of States of any quantum
system belongs, as the complex Hermitian space member, to this parametrised
family; hence its trigonometry appears as a rather particular case of the
equations we obtain.Comment: 46 pages, LaTe
Model-Independent Sum Rule Analysis Based on Limited-Range Spectral Data
Partial sum rules are widely used in physics to separate low- and high-energy
degrees of freedom of complex dynamical systems. Their application, though, is
challenged in practice by the always finite spectrometer bandwidth and is often
performed using risky model-dependent extrapolations. We show that, given
spectra of the real and imaginary parts of any causal frequency-dependent
response function (for example, optical conductivity, magnetic susceptibility,
acoustical impedance etc.) in a limited range, the sum-rule integral from zero
to a certain cutoff frequency inside this range can be safely derived using
only the Kramers-Kronig dispersion relations without any extra model
assumptions. This implies that experimental techniques providing both active
and reactive response components independently, such as spectroscopic
ellipsometry in optics, allow an extrapolation-independent determination of
spectral weight 'hidden' below the lowest accessible frequency.Comment: 5 pages, 3 figure
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