779 research outputs found
Evidence for large superhumps in TX Col and V4742 Sgr
Since the discovery of the largest positive superhump period in TV Col, we
have started a program to search for superhumps in CVs with large orbital
periods. Here, we summarize preliminary results of TX Col and V4742 Sgr. TX Col
is an intermediate polar with a 5.7-h orbital period. V4742 Sgr is a recent
nova with no known periods. CCD unfiltered continuous photometry of these 2
objects was carried out during 56 nights in 2002-3. In TX Col, in addition to
the orbital period of 5.7 h, we found peaks at 7.1 h and 5.0 h. These are
interpreted as positive and negative superhumps correspondingly, although the
effects of the quasi-periodic oscillations at about 2 h were not taken into
consideration. In the light curve of V4742 Sgr 2 long periods are detected --
6.1 and 5.4 h as well as a short-term period at 1.6 h. This result suggests
that V4742 Sgr is an intermediate polar candidate and a permanent superhump
system with a large orbital period (5.4 h) and a superhump period excess of 13
percent. If these results are confirmed, TX Col, V4742 Sgr and TV Col form a
group of intermediate polars with extremely large superhump periods. There
seems to be now growing evidence that superhumps can occur in intermediate
polars with long orbital periods, which is very likely inconsistent with the
theoretical prediction that superhumps can only occur in systems with mass
ratios below 0.33. Alternatively, if the mass ratio in these systems is
nevertheless below the theoretical limit, they should harbour undermassive
secondaries and massive white dwarfs, near the Chandrasekhar limit, which would
make them excellent candidates for progenitors of supernovae type Ia.Comment: 9 pages, 8 figures, 3 sty files, To appear in the proceedings of IAU
JD5, `White Dwarfs: Galactic and Cosmological Probes', eds. Ed Sion, Stephane
Vennes and Harry Shipman, Full abstract in pape
Antiferromagnetism in the Exact Ground State of the Half Filled Hubbard Model on the Complete-Bipartite Graph
As a prototype model of antiferromagnetism, we propose a repulsive Hubbard
Hamiltonian defined on a graph \L={\cal A}\cup{\cal B} with and bonds connecting any element of with all the
elements of . Since all the hopping matrix elements associated with
each bond are equal, the model is invariant under an arbitrary permutation of
the -sites and/or of the -sites. This is the Hubbard model
defined on the so called -complete-bipartite graph,
() being the number of elements in (). In this
paper we analytically find the {\it exact} ground state for at
half filling for any ; the repulsion has a maximum at a critical
-dependent value of the on-site Hubbard . The wave function and the
energy of the unique, singlet ground state assume a particularly elegant form
for N \ra \inf. We also calculate the spin-spin correlation function and show
that the ground state exhibits an antiferromagnetic order for any non-zero
even in the thermodynamic limit. We are aware of no previous explicit analytic
example of an antiferromagnetic ground state in a Hubbard-like model of
itinerant electrons. The kinetic term induces non-trivial correlations among
the particles and an antiparallel spin configuration in the two sublattices
comes to be energetically favoured at zero Temperature. On the other hand, if
the thermodynamic limit is taken and then zero Temperature is approached, a
paramagnetic behavior results. The thermodynamic limit does not commute with
the zero-Temperature limit, and this fact can be made explicit by the analytic
solutions.Comment: 19 pages, 5 figures .ep
Charge Form Factor and Cluster Structure of Li Nucleus
The charge form factor of Li nucleus is considered on the basis of its
cluster structure. The charge density of Li is presented as a
superposition of two terms. One of them is a folded density and the second one
is a sum of He and the deuteron densities. Using the available
experimental data for He and deuteron charge form factors, a good
agreement of the calculations within the suggested scheme is obtained with the
experimental data for the charge form factor of Li, including those in
the region of large transferred momenta.Comment: 12 pages 5 figure
Investigate the origins of COVID-19
On 30 December 2019, the Program for Monitoring Emerging Diseases notified the world about a pneumonia of unknown cause in Wuhan, China. Since then, scientists have made remarkable progress in understanding the causative agent, severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), its transmission, pathogenesis, and mitigation by vaccines, therapeutics, and non-pharmaceutical interventions. Yet more investigation is still needed to determine the origin of the pandemic. Theories of accidental release from a lab and zoonotic spillover both remain viable. Knowing how COVID-19 emerged is critical for informing global strategies to mitigate the risk of future outbreaks
Low Frequency Flickering of TT Arietis:Hard and Soft X-ray Emission Region
Using archival ASCA observations of TT Arietis, X-ray energy spectra and
power spectra of the intensity time series are presented for the first time.
The energy spectra are well-fitted by a two continuum plasma emission model
with temperatures around 1 keV and 10 keV. A coherent feature at about 0.643
mHz appeared in the power spectra during the observation.Comment: 9 pages in PostScript including figures, accepted for publication in
Astrophysics and Space Science, available at
http://astroa.physics.metu.edu.tr/preprints.htm
Production and Decay of D_1(2420)^0 and D_2^*(2460)^0
We have investigated and final states and
observed the two established charmed mesons, the with mass
MeV/c and width MeV/c and
the with mass MeV/c and width
MeV/c. Properties of these final states, including
their decay angular distributions and spin-parity assignments, have been
studied. We identify these two mesons as the doublet predicted
by HQET. We also obtain constraints on {\footnotesize } as a function of the cosine of the relative phase of the two
amplitudes in the decay.Comment: 15 pages in REVTEX format. hardcopies with figures can be obtained by
sending mail to: [email protected]
Measurement of the branching fraction for
We have studied the leptonic decay of the resonance into tau
pairs using the CLEO II detector. A clean sample of tau pair events is
identified via events containing two charged particles where exactly one of the
particles is an identified electron. We find . The result is consistent with
expectations from lepton universality.Comment: 9 pages, RevTeX, two Postscript figures available upon request, CLNS
94/1297, CLEO 94-20 (submitted to Physics Letters B
Study of the B^0 Semileptonic Decay Spectrum at the Upsilon(4S) Resonance
We have made a first measurement of the lepton momentum spectrum in a sample
of events enriched in neutral B's through a partial reconstruction of B0 -->
D*- l+ nu. This spectrum, measured with 2.38 fb**-1 of data collected at the
Upsilon(4S) resonance by the CLEO II detector, is compared directly to the
inclusive lepton spectrum from all Upsilon(4S) events in the same data set.
These two spectra are consistent with having the same shape above 1.5 GeV/c.
From the two spectra and two other CLEO measurements, we obtain the B0 and B+
semileptonic branching fractions, b0 and b+, their ratio, and the production
ratio f+-/f00 of B+ and B0 pairs at the Upsilon(4S). We report b+/b0=0.950
(+0.117-0.080) +- 0.091, b0 = (10.78 +- 0.60 +- 0.69)%, and b+ = (10.25 +- 0.57
+- 0.65)%. b+/b0 is equivalent to the ratio of charged to neutral B lifetimes,
tau+/tau0.Comment: 14 page, postscript file also available at
http://w4.lns.cornell.edu/public/CLN
Measurement of the Decay Asymmetry Parameters in and
We have measured the weak decay asymmetry parameters (\aLC ) for two \LC\
decay modes. Our measurements are \aLC = -0.94^{+0.21+0.12}_{-0.06-0.06} for
the decay mode and \aLC = -0.45\pm 0.31 \pm
0.06 for the decay mode . By combining these
measurements with the previously measured decay rates, we have extracted the
parity-violating and parity-conserving amplitudes. These amplitudes are used to
test models of nonleptonic charmed baryon decay.Comment: 11 pages including the figures. Uses REVTEX and psfig macros. Figures
as uuencoded postscript. Also available as
http://w4.lns.cornell.edu/public/CLNS/1995/CLNS95-1319.p
Observation of the Charmed Baryon Decays to , , and
We have observed two new decay modes of the charmed baryon into
and using data collected with the
CLEO II detector. We also present the first measurement of the branching
fraction for the previously observed decay mode . The branching fractions for these three modes relative to
are measured to be , , and , respectively.Comment: 12 page uuencoded postscript file, postscript file also available
through http://w4.lns.cornell.edu/public/CLN
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