1,901 research outputs found
Quantitative Estimates of Environmental Effects on the Star Formation Rate of Disk Galaxies in Clusters of Galaxies
A simple model is constructed to evaluate the change of star formation rate
of a disk galaxy due to environmental effects in clusters of galaxies. Three
effects, (1) tidal force from the potential well of the cluster, (2) increase
of external pressure when the galaxy plows into the intracluster medium, (3)
high-speed encounters between galaxies, are investigated. General analysis
indicates that the star formation rate increases significantly when the
pressure of molecular clouds rises above in yr. The tidal force from the potential well of the cluster increases
pressures of molecular clouds in a disk galaxy infalling towards the cluster
center. Before the galaxy reaches the cluster center, the star formation rate
reaches a maximum. The peak is three to four times larger than the initial
value. If this is the main mechanism of the Butcher-Oemler effect, blue
galaxies are expected to be located within kpc from the center of
the cluster. However this prediction is inconsistent with the recent
observations. The increase of external pressure when the galaxy plows into the
intracluster medium does not change star formation rate of a disk galaxy
significantly. The velocity perturbation induced by a single high-speed
encounter between galaxies is too small to affect star formation rate of a disk
galaxy, while successive high-speed encounters (galaxy harassment) trigger star
formation activity because of the accumulation of gas in the galaxy center.
Therefore, the galaxy harassment remains as the candidate for a mechanism of
the Butcher-Oemler effect.Comment: 12 pages, 13 figures. To be published in Ap
Different Modes of Anion Response Cause Circulatory Phase Transfer of a Coordination Cage with Controlled Directionality
Controlled directional transport of molecules is essential to complex natural systems, exemplified by cellular transport up to organismal circulatory systems. In contrast to these natural systems, synthetic systems that enable transport of molecules between several spatial locations on the macroscopic scale, when external stimuli are applied, remain to be explored. Here we report the transfer of a supramolecular cage with controlled directionality between three phases, based on the cage that responds reversibly in two distinct ways to different anions. Notably, circulatory phase transfer of the cage was demonstrated based on a system where the three layers of solvent are arranged within a circular track. The direction of circulation between solvent phases depended upon the order of addition of anions.European Research Council (695009),
UK Engineering and Physical Sciences Research Council (EPSRC, EP/P027067/1
Comparison among HB-inspired algorithms for continuous-spin systems and gauge fields
We propose a new local algorithm for the thermalization of n-vector spin
models, which can also be used in the numerical simulation of SU(N) lattice
gauge theories. The algorithm combines heat-bath (HB) and micro-canonical
updates in a single step -- as opposed to the hybrid overrelaxation method,
which alternates between the two kinds of update steps -- while preserving
ergodicity. We test our proposed algorithm in the case of the one-dimensional
4-vector spin model and compare its performance with the standard HB algorithm
and with other HB-inspired algorithms.Comment: 6 pages, 4 figures. Work presented at the IV Brazilian Meeting on
Simulational Physics -- Ouro Preto - MG/Brazil, August 200
V0332+53 in the outburst of 2004--2005: luminosity dependence of the cyclotron line and pulse profile
We present results of observations of the transient X-ray pulsar V0332+53
performed during a very powerful outburst in Dec, 2004 -- Feb, 2005 with the
INTEGRAL and RXTE observatories in a wide (3-100 keV) energy band. A cyclotron
resonance scattering line at an energy of ~26 keV has been detected in the
source spectrum together with its two higher harmonics at ~50 and ~73 keV,
respectively. We show that the energy of the line is not constant but linearly
changes with the source luminosity. Strong pulse profile variations, especially
near the cyclotron line, are revealed for different levels of the source
intensity. We discuss the obtained results in terms of the theoretical models
of X-ray pulsars.Comment: Accepted for publication in MNRAS. 10 pages, 9 figure
Numerical Study of the Ghost-Gluon Vertex in Landau gauge
We present a numerical study of the ghost-gluon vertex and of the
corresponding renormalization function \widetilde{Z}_1(p^2) in minimal Landau
gauge for SU(2) lattice gauge theory. Data were obtained for three different
lattice volumes (V = 4^4, 8^4, 16^4) and for three lattice couplings \beta =
2.2, 2.3, 2.4. Gribov-copy effects have been analyzed using the so-called
smeared gauge fixing. We also consider two different sets of momenta (orbits)
in order to check for possible effects due to the breaking of rotational
symmetry. The vertex has been evaluated at the asymmetric point (0;p,-p) in
momentum-subtraction scheme. We find that \widetilde{Z}_1(p^2) is approximately
constant and equal to 1, at least for momenta p > ~ 1 GeV. This constitutes a
nonperturbative verification of the so-called nonrenormalization of the Landau
ghost-gluon vertex. Finally, we use our data to evaluate the running coupling
constant \alpha_s(p^2).Comment: 19 pages, 6 figures, 9 tables, using axodraw.sty; minor modifications
in the abstract, introduction and conclusion
ASCA Observations of the Composite Warm Absorber in NGC 3516
We obtained X-ray spectra of the Seyfert 1 galaxy NGC~3516 in March 1995
using ASCA. Simultaneous far-UV observations were obtained with HUT on the
Astro-2 shuttle mission. The ASCA spectrum shows a lightly absorbed power law
of energy index 0.78. The low energy absorbing column is significantly less
than previously seen. Prominent O~vii and O~viii absorption edges are visible,
but, consistent with the much lower total absorbing column, no Fe K absorption
edge is detectable. A weak, narrow Fe~K emission line from cold
material is present as well as a broad Fe~K line. These features are
similar to those reported in other Seyfert 1 galaxies. A single warm absorber
model provides only an imperfect description of the low energy absorption. In
addition to a highly ionized absorber with ionization parameter and
a total column density of , adding a lower
ionization absorber with and a total column of significantly improves the fit. The contribution of
resonant line scattering to our warm absorber models limits the Doppler
parameter to at 90\% confidence. Turbulence at the sound
speed of the photoionized gas provides the best fit. None of the warm absorber
models fit to the X-ray spectrum can match the observed equivalent widths of
all the UV absorption lines. Accounting for the X-ray and UV absorption
simultaneously requires an absorbing region with a broad range of ionization
parameters and column densities.Comment: 14 pages, 4 Postscript figures, uses aaspp4.sty To appear in the
August 20, 1996, issue of The Astrophysical Journa
Discovery of a flux-related change of the cyclotron line energy in Her X-1
We present the results of ten years of repeated measurements of the Cyclotron
Resonance Scattering Feature (CRSF) in the spectrum of the binary X-ray pulsar
Her X-1 and report the discovery of a positive correlation of the centroid
energy of this absorption feature in pulse phase averaged spectra with source
luminosity.Our results are based on a uniform analysis of observations bythe
RXTE satellite from 1996 to 2005, using sufficiently long observations of 12
individual 35-day Main-On states of the source. The mean centroid energy E_c of
the CRSF in pulse phase averaged spectra of Her X-1 during this time is around
40 keV, with significant variations from one Main-On state to the next. We find
that the centroid energy of the CRSF in Her X-1 changes by ~5% in energy for a
factor of 2 in luminosity. The correlation is positive, contrary to what is
observed in some high luminosity transient pulsars. Our finding is the first
significant measurement of a positive correlation between E_c and luminosity in
any X-ray pulsar. We suggest that this behaviour is expected in the case of
sub-Eddington accretion and present a calculation of a quantitative estimate,
which is very consistent with the effect observed in Her X-1.We urge that Her
X-1 is regularly monitored further and that other X-ray pulsars are
investigated for a similar behaviour.Comment: 4 pages, 2 figures, accepted by A&A Letter
Near-infrared Observations of Be/X-ray Binary Pulsar A0535+262
We present results obtained from an extensive near-infrared spectroscopic and
photometric observations of the Be/X-ray binary A0535+262/HDE 245770 at
different phases of its ~111 day orbital period. This observation campaign is a
part of the monitoring programme of selective Be/X-ray binary systems aimed at
understanding the X-ray and near-IR properties at different orbital phases,
especially during the periastron passage of the neutron star. The near-IR
observations were carried out using the 1.2 m telescope at Mt. Abu IR
observatory. Though the source was relatively faint for spectroscopic
observations with 1.2 m telescope, we monitored the source during the 2011
February--March giant outburst to primarily investigate whether any drastic
changes in the near-IR JHK spectra take place at the periastron passage.
Changes of such a striking nature were expected to be detectable in our
spectra. Photometric observations of the Be star show a gradual and systematic
fading in the JHK light curves since the onset of the X-ray outburst that could
suggest a mild evacuation/truncation of the circumstellar disc of the Be
companion. Near-IR spectroscopy of the object shows that the JHK spectra are
dominated by the emission lines of hydrogen Brackett and Paschen series and HeI
lines at 1.0830, 1.7002 and 2.0585 micron. The presence of all hydrogen
emission lines in the JHK spectra, along with the absence of any significant
change in the continuum of the Be companion during X-ray quiescent and X-ray
outburst phases suggest that the near-IR line emitting regions of the disc are
not significantly affected during the X-ray outburst.Comment: 10 Pages, 5 Figures, Accepted for publication in Res. in Astronomy
and Astrophysic
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