218 research outputs found
Pairing Reentrance Phenomenon in Heated Rotating Nuclei in the Shell Model Monte Carlo Approach
Rotational motion of heated 72-Ge is studied within the microscopic Shell
Model Monte Carlo approach. We investigate the the angular momentum alignment
and nuclear pairing correlations associated with J-pi Cooper pairs as a
function of the rotational frequency and temperature. The reentrance of pairing
correlations with temperature is predicted at high rotational frequencies. It
manifests itself through the anomalous behavior of specific heat and level
density.Comment: 4 pages; 4 figure
Modelling the Galactic Bar Using Red Clump Giants
The color-magnitude diagrams of stars obtained for 12
fields across the Galactic bulge with the OGLE project reveal a well-defined
population of bulge red clump giants. We find that the distributions of the
apparent magnitudes of the red clump stars are systematically fainter when
moving towards lower galactic fields. The most plausible explanation of
this distinct trend is that the Galactic bulge is a bar, whose nearest end lies
at positive galactic longitude. We model this Galactic bar by fitting for all
fields the observed luminosity functions in the red clump region of the
color-magnitude diagram. We find that almost regardless of the analytical
function used to describe the 3-D stars distribution of the Galactic bar, the
resulting models have the major axis inclined to the line of sight by
, with axis ratios corresponding to . This
puts a strong constraint on the possible range of the Galactic bar models.
Gravitational microlensing can provide us with additional constrains on the
structure of the Galactic bar.Comment: submitted to the New Astronomy, 27 pages, 11 figures; also available
at ftp://www.astro.princeton.edu/stanek/Barmodel and through WWW at
http://www.astro.princeton.edu/~library/prep.htm
Hartree-Fock-Bogoliubov Theory of Polarized Fermi Systems
Condensed Fermi systems with an odd number of particles can be described by
means of polarizing external fields having a time-odd character. We illustrate
how this works for Fermi gases and atomic nuclei treated by density functional
theory or Hartree-Fock-Bogoliubov (HFB) theory. We discuss the method based on
introducing two chemical potentials for different superfluid components,
whereby one may change the particle-number parity of the underlying
quasiparticle vacuum. Formally, this method is a variant of non-collective
cranking, and the procedure is equivalent to the so-called blocking. We present
and exemplify relations between the two-chemical-potential method and the
cranking approximation for Fermi gases and nuclei.Comment: 11 RevTeX pages, 4 figures, submitted to Physical Review A, extended
versio
Intermediate valence of CeNi2Al3 compound and its evidences: Theoretical and experimental approach
We present measurements of magnetic, transport and electronic properties obtained for polycrystalline CeNi2Al3
intermetallic compound. Magnetic susceptibility χ(T) was investigated in the range from 2 to 700 K, and its
behavior is characteristic of a compound with unstable valence, varying between Ce3þ and Ce4þ. In the temperature
range down to 2 K there was no trace of magnetic order, no anomalies in the temperature dependence of
the specific heat were found. The Sommerfeld coefficient extracted from the linear term of the heat capacity
takes a value of γ ¼ 21 mJ/(mol K2). The dependence of S(T) is linear up to about 25 K, which is symptomatic of
a thermopower in the Fermi’s liquid regime.
The structure of satellites in the Ce(3d) electron spectrum obtained by the X-ray photoelectron spectroscopy
(XPS) method indicates that the states of Ce(4f) are of mixed valence character. Analysis of Ce(3d) states based
on Gunnarsson-Sch€onhammer theory shows that the energy of hybridization of Ce(4f) states with a conduction
band is about 78 meV. For more detailed information about electronic states the fully relativistic band structure
was calculated within the density functional theory (DFT) for the first time. Below Fermi’s energy, the density of
states is mainly formed by Ni(3d) states hybridized with Ce(4f) ones
A gravitationally lensed quasar discovered in OGLE
Indexación: Scopus; Web of Science.We report the discovery of a new gravitationally lensed quasar (double) from the Optical Gravitational Lensing Experiment (OGLE) identified inside the ~670deg2 area encompassing the Magellanic Clouds. The source was selected as one of ~60 'red W1-W2' mid-infrared objects from WISE and having a significant amount of variability in OGLE for both two (or more) nearby sources. This is the first detection of a gravitational lens, where the discovery is made 'the other way around', meaning we first measured the time delay between the two lensed quasar images of -132 < tAB < -76 d (90 per cent CL), with the median tAB ~-102 d (in the observer frame), and where the fainter image B lags image A. The system consists of the two quasar images separated by 1.5 arcsec on the sky, with I ~20.0mag and I ~19.6mag, respectively, and a lensing galaxy that becomes detectable as I ~21.5 mag source, 1.0 arcsec from image A, after subtracting the two lensed images. Both quasar images show clear AGN broad emission lines at z=2.16 in the New Technology Telescope spectra. The spectral energy distribution (SED) fitting with the fixed source redshift provided the estimate of the lensing galaxy redshift of z ~0.9 ± 0.2 (90 per cent CL), while its type is more likely to be elliptical (the SED-inferred and lens-model stellar mass is more likely present in ellipticals) than spiral (preferred redshift by the lens model). © 2018 The Author(s). Published by Oxford University Press on behalf of the Royal Astronomical Society.https://academic.oup.com/mnras/article/476/1/663/483368
OGLE16aaa - a Signature of a Hungry Super Massive Black Hole
We present the discovery and first three months of follow-up observations of
a currently on-going unusual transient detected by the OGLE-IV survey, located
in the centre of a galaxy at redshift z=0.1655. The long rise to absolute
magnitude of -20.5 mag, slow decline, very broad He and H spectral features
make OGLE16aaa similar to other optical/UV Tidal Disruption Events (TDEs). Weak
narrow emission lines in the spectrum and archival photometric observations
suggest the host galaxy is a weak-line Active Galactic Nucleus (AGN), which has
been accreting at higher rate in the past. OGLE16aaa, along with SDSS J0748,
seems to form a sub-class of TDEs by weakly or recently active super-massive
black holes (SMBHs). This class might bridge the TDEs by quiescent SMBHs and
flares observed as "changing-look QSOs", if we interpret the latter as TDEs. If
this picture is true, the previously applied requirement for identifying a
flare as a TDE that it had to come from an inactive nucleus, could be leading
to observational bias in TDE selection, thus affecting TDE-rate estimations.Comment: Accepted in MNRAS Letter
WR 20a is an Eclipsing Binary: Accurate Determination of Parameters for an Extremely Massive Wolf-Rayet System
We present a high-precision I-band light curve for the Wolf-Rayet binary WR
20a, obtained as a sub-project of the Optical Gravitational Lensing Experiment.
Rauw et al. have recently presented spectroscopy for this system, strongly
suggesting extremely large minimum masses of 70.7 +/- 4.0 Mo and 68.8 +/- 3.8
Mo for the component stars of the system, with the exact values depending
strongly on the period of the system. We detect deep eclipses of about 0.4 mag
in the light curve of WR 20a, confirming and refining the suspected period of
P=3.686 days and deriving an inclination angle of i=74.5 +/- 2 deg. Using these
photometric data and the radial velocity data of Rauw et al., we derive the
masses for the two components of WR 20a to be 83.0 +/- 5.0 Mo and 82.0 +/- 5.0
Mo. Therefore, WR 20a is confirmed to consist of two extremely massive stars
and to be the most massive binary known with an accurate mass determination.Comment: 13 pages, 2 figures, 3 tables, accepted for publication in ApJ
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