24,033 research outputs found
Spot activity of the RS CVn star {\sigma} Geminorum
We model the photometry of RS CVn star Geminorum to obtain new
information on the changes of the surface starspot distribution, i.e., activity
cycles, differential rotation and active longitudes. We use the previously
published Continuous Periods Search-method (CPS) to analyse V-band differential
photometry obtained between the years 1987 and 2010 with the T3 0.4 m Automated
Telescope at the Fairborn Observatory. The CPS-method divides data into short
subsets and then models the light curves with Fourier-models of variable orders
and provides estimates of the mean magnitude, amplitude, period and light curve
minima. These light curve parameters are then analysed for signs of activity
cycles, differential rotation and active longitudes. We confirm the presence of
two previously found stable active longitudes, synchronised with the orbital
period d and find eight events where the active longitudes
are disrupted. The epochs of the primary light curve minima rotate with a
shorter period d than the orbital motion. If the
variations in the photometric rotation period were to be caused by differential
rotation, this would give a differential rotation coefficient of . The presence of two slightly different periods of active regions may
indicate a superposition of two dynamo modes, one stationary in the orbital
frame and the other one propagating in the azimuthal direction. Our estimate of
the differential rotation is much higher than previous results. However,
simulations show that this can be caused by insufficient sampling in our data.Comment: 10 pages, 6 figures. Submitted to A&
Schwarzchild Black Holes in Matrix Theory II
We present a crude Matrix Theory model for Schwarzchild black holes in
uncompactified dimension greater than . The model accounts for the size,
entropy, and long range state interactions of black holes. The key feature of
the model is a Boltzmann gas of D0 branes, a concept which depends on certain
qualitative features of Matrix Theory which have not previously been utilized
in studies of black holes.Comment: 20 pages,harvmac,big, Some Typos corrected, 1 reference adde
Discovery of Griffiths phase in itinerant magnetic semiconductor Fe_{1-x}Co_xS_2
Critical points that can be suppressed to zero temperature are interesting
because quantum fluctuations have been shown to dramatically alter electron gas
properties. Here, the metal formed by Co doping the paramagnetic insulator
FeS, FeCoS, is demonstrated to order ferromagnetically at
where we observe unusual transport, magnetic, and
thermodynamic properties. We show that this magnetic semiconductor undergoes a
percolative magnetic transition with distinct similarities to the Griffiths
phase, including singular behavior at and zero temperature.Comment: 10 pages, 4 figure
Lensing Effects on the Protogalaxy Candidate cB58 and their Implications for the Cosmological Constant
The amplification of the protogalaxy candidate cB58 due to gravitational
lensing by the foreground cluster of galaxies MS1512.4+3647 is quantified based
on recent ROSAT and ASCA X-ray observations. It is found that the amplification
is at most 25 for any reasonable cosmological model with or without
cosmological constant. It is also argued that the system may be used to place
new constraints on the value of the cosmological constant. The gas mass
fraction for this cluster is found to be about 0.2.Comment: LaTex, 9 pages, 9 figures, uses aas2pp4.sty, Accepted for publication
in Ap
Quantum Monte Carlo method using phase-free random walks with Slater determinants
We develop a quantum Monte Carlo method for many fermions that allows the use
of any one-particle basis. It projects out the ground state by random walks in
the space of Slater determinants. An approximate approach is formulated to
control the phase problem with a trial wave function . Using
plane-wave basis and non-local pseudopotentials, we apply the method to Si
atom, dimer, and 2, 16, 54 atom (216 electrons) bulk supercells. Single Slater
determinant wave functions from density functional theory calculations were
used as with no additional optimization. The calculated binding
energy of Si2 and cohesive energy of bulk Si are in excellent agreement with
experiments and are comparable to the best existing theoretical results.Comment: 5 pages, Latex, with 1 fi
The LyAlpha Line Profiles of Ultraluminous Infrared Galaxies: Fast Winds and Lyman Continuum Leakage
We present new Hubble Space Telescope Cosmic Origins Spectrograph
far-ultraviolet (far-UV) spectroscopy and Keck Echellete optical spectroscopy
of 11 ultraluminous infrared galaxies (ULIRGs), a rare population of local
galaxies experiencing massive gas inflows, extreme starbursts, and prominent
outflows. We detect H Lyman alpha emission from 8 ULIRGs and the companion to
IRAS09583+4714. In contrast to the P Cygni profiles often seen in galaxy
spectra, the H Lyman alpha profiles exhibit prominent, blueshifted emission out
to Doppler shifts exceeding -1000 km/s in three HII-dominated and two
AGN-dominated ULIRGs. To better understand the role of resonance scattering in
shaping the H Lyman alpha line profiles, we directly compare them to
non-resonant emission lines in optical spectra. We find that the line wings are
already present in the intrinsic nebular spectra, and scattering merely
enhances the wings relative to the line core. The H Lyman alpha attenuation (as
measured in the COS aperture) ranges from that of the far-UV continuum to over
100 times more. A simple radiative transfer model suggests the H Lyman alpha
photons escape through cavities which have low column densities of neutral
hydrogen and become optically thin to the Lyman continuum in the most advanced
mergers. We show that the properties of the highly blueshifted line wings on
the H Lyman alpha and optical emission-line profiles are consistent with
emission from clumps of gas condensing out of a fast, hot wind. The luminosity
of the H Lyman alpha emission increases non-linearly with the ULIRG bolometric
luminosity and represents about 0.1 to 1% of the radiative cooling from the hot
winds in the HII-dominated ULIRGs.Comment: Submitted to Ap
Investigation of DC-8 nacelle modifications to reduce fan-compressor noise in airport communities. Part 2 - Design studies and duct-lining investigations, May 1967 - October 1969
Modifications to reduce fan-compressor noise level of DC-8 aircraft - Part
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