22,769 research outputs found
New Fe II energy levels from stellar spectra
The spectra of B-type and early A-type stars show numerous unidentified lines
in the whole optical range, especially in the 5100 - 5400 A interval. Because
Fe II transitions to high energy levels should be observed in this region, we
used semiempirical predicted wavelengths and gf-values of Fe II to identify
unknown lines. Semiempirical line data for Fe II computed by Kurucz are used to
synthesize the spectrum of the slow-rotating, Fe-overabundant CP star HR 6000.
We determined a total of 109 new 4f levels for Fe II with energies ranging from
122324 cm^-1 to 128110 cm^-1. They belong to the Fe II subconfigurations
3d^6(^3P)4f (10 levels), 3d^6(^3H)4f (36 levels), 3d^6(^3F)4f (37 levels), and
3d^6(^3G)4f (26 levels). We also found 14 even levels from 4d (3 levels), 5d (7
levels), and 6d (4 levels) configurations. The new levels have allowed us to
identify more than 50% of the previously unidentified lines of HR 6000 in the
wavelength region 3800-8000 A. Tables listing the new energy levels are given
in the paper; tables listing the spectral lines with loggf>/=-1.5 that are
transitions to the 4f energy levels are given in the Online Material. These new
levels produce 18000 lines throughout the spectrum from the ultraviolet to the
infrared.Comment: Paper accepted by A&A for publicatio
A study of the apsidal angle and a proof of monotonicity in the logarithmic potential case
This paper concerns the behaviour of the apsidal angle for orbits of central
force system with homogenous potential of degree and
logarithmic potential. We derive a formula for the apsidal angle as a fixed-end
points integral and we study the derivative of the apsidal angle with respect
to the angular momentum . The monotonicity of the apsidal angle as
function of is discussed and it is proved in the logarithmic potential
case.Comment: 24 pages, 1 figur
Oscillating waves and optimal smoothing effect for one-dimensional nonlinear scalar conservation laws
Lions, Perthame, Tadmor conjectured in 1994 an optimal smoothing effect for
entropy solutions of nonlinear scalar conservations laws . In this short paper
we will restrict our attention to the simpler one-dimensional case. First,
supercritical geometric optics lead to sequences of solutions
uniformly bounded in the Sobolev space conjectured. Second we give continuous
solutions which belong exactly to the suitable Sobolev space. In order to do so
we give two new definitions of nonlinear flux and we introduce fractional
spaces
Existence and instability of steady states for a triangular cross-diffusion system: a computer-assisted proof
In this paper, we present and apply a computer-assisted method to study
steady states of a triangular cross-diffusion system. Our approach consist in
an a posteriori validation procedure, that is based on using a fxed point
argument around a numerically computed solution, in the spirit of the
Newton-Kantorovich theorem. It allows us to prove the existence of various non
homogeneous steady states for different parameter values. In some situations,
we get as many as 13 coexisting steady states. We also apply the a posteriori
validation procedure to study the linear stability of the obtained steady
states, proving that many of them are in fact unstable
Rigorous numerics for NLS: bound states, spectra, and controllability
In this paper it is demonstrated how rigorous numerics may be applied to the
one-dimensional nonlinear Schr\"odinger equation (NLS); specifically, to
determining bound--state solutions and establishing certain spectral properties
of the linearization. Since the results are rigorous, they can be used to
complete a recent analytical proof [6] of the local exact controllability of
NLS.Comment: 30 pages, 2 figure
A refined analysis of the remarkable Bp star HR 6000
UVES spectra of the very young (~10^7 years) peculiar B-type star HR 6000
were analyzed in the near-UV and visual spectral regions (3050-9460 A) with the
aim to extend to other spectral ranges the study made previously in the UV
using IUE spectra. Stellar parameters Teff=12850K, logg=4.10, and xi=0km/s, as
determined from H_beta, H_gamma, H_delta Balmer profiles and from the Fe I, Fe
II ionization equilibrium, were used to compute an individual abundances
ATLAS12 model. We identified spectral peculiarities and obtained final stellar
abundances by comparing observed and computed equivalent widths and line
profiles. The adopted model fails to reproduce the (b-y) and c color indices.
The spectral analysis has revealed: the presence of emission lines for Mn II,
Cr II, and Fe II; isotopic anomalies for Hg, Ca; the presence of interstellar
lines of Na I at lambda lambda 3302.3, 3302.9, 5890, 5896 A, and of K I at
7665, 7699 A; the presence of a huge quantity of unidentified lines, which we
presume to be mostly due to Fe II transitions owing to the large Fe
overabundance amounting to [+0.7]. The main chemical peculiarities are an
extreme overabundance of Xe, followed by those of Hg, P, Y, Mn, Fe, Be, and Ti.
The most underabundant element is Si, followed by C, N, Al, S, Mg, V, Sr, Co,
Cl, Sc, and Ni. The silicon underabundance [-2.9] is the lowest value for Si
ever observed in any HgMn star. The observed lines of He I can not be
reproduced by a single value of the He abundance, but they require values
ranging from [-0.8] to [-1.6]. Furthermore, when the observed and computed
wings of He I lines are fitted, the observed line cores are much weaker than
the computed ones. From the present analysis we infer the presence of vertical
abundance stratification for He, Mn, and possibly also P.Comment: 14 pages, 8 figures, 6 tables, accepted for publication in A&
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