34,604 research outputs found
HST-FOS Observations of M87: Ly-a Emission from the Active Galactic Nucleus
The Faint Object Spectrograph on the Hubble Space Telescope was used to
obtain spectra of the central region of M87. These spectra cover the wavelength
range 1140 - 1606 Angstrom and have a resolution of about 1 Angstrom. The
nuclear continuum is clearly visible in the spectra. The only strong line that
is observed is Ly-alpha, which has a velocity width of about 3000 km/sec. There
is also a marginal detection of C IV 1549. The ratio of Ly-alpha to C IV in the
nuclear spectrum is at least a factor of 2 higher than in a spectrum taken at a
position on the disk about 0.6" away from the nucleus by Dopita et al. This
enhancement of Ly-alpha at the nucleus could point to significant differences
in the properties of the emitting gas and/or the excitation mechanism between
the outer and inner disk regions. The strength of the observed Ly-alpha places
limits on the properties of the absorbing gas present within M87. For instance,
if the hydrogen column at the systemic velocity of M87 is greater than about
10^18 cm^{-2} then it can cover only a small fraction of the line emitting
region. Spectra separated by 5 days show a 60% difference in the Ly-alpha flux,
but the same continuum level. This could be due to either a displacement
between the aperture positions for the two sets of observations, or it could be
due to intrinsic variability of the source. The current observations do not
strongly favor either of these alternatives. The observations do show, however,
that the Ly-alpha line is a useful tracer of kinematics in the M87 nucleus.Comment: 14 pages + 5 figures. LaTeX uses aaspp4.sty. Accepted for publication
in the Astrophysical Journa
A high excitation HII region in the faint dwarf elliptical galaxy A0951+68
We present the results of BVRI imaging and optical spectroscopy of the dwarf
galaxy A0951+68. The images reveal that, although this galaxy is classified as
a dwarf elliptical, it has some properties that are similar to dwarf irregular
galaxies. It contains two bright knots of emission, one of which is red and
unresolved and the other blue and resolved. The blue knot also shows a high
excitation emission line spectrum. The observed line ratios indicate that this
is an HII region, although with some line ratios that are border-line with
those in AGN. The emission line luminosity is consistent with ionisation by a
single, very luminous O star, or several smaller O stars, but the extended blue
light in the knot shows that this has occurred as part of a substantial recent
star formation event. We find that the metal abundance, while low compared to
typical large galaxies, actually seems to be high for such a low luminosity
dwarf. The position of A0951 in the literature is incorrect and we provide the
correct value.Comment: 8 pages, Latex, 4 encapsulated postscript figures included, 1
separate JPEG figure; to be published in Monthly Notice
Symplectic structure for elastic and chiral conducting cosmic string models
This article is based on the covariant canonical formalism and corresponding
symplectic structure on phase space developed by Witten, Zuckerman and others
in the context of field theory. After recalling the basic principles of this
procedure, we construct the conserved bilinear symplectic current for generic
elastic string models. These models describe current carrying cosmic strings
evolving in an arbitrary curved background spacetime. Particular attention is
paid to the special case of the chiral string for which the worldsheet current
is null. Different formulations of the chiral string action are discussed in
detail, and as a result the integrability property of the chiral string is
clarified.Comment: 18 page
Entrainment coefficient and effective mass for conduction neutrons in neutron star crust: II Macroscopic treatment
Phenomena such as pulsar frequency glitches are believed to be attributable
to differential rotation of a current of ``free'' superfluid neutrons at
densities above the ``drip'' threshold in the ionic crust of a neutron star.
Such relative flow is shown to be locally describable by adaption of a
canonical two fluid treatment that emphasizes the role of the momentum
covectors constructed by differentiation of action with respect to the
currents, with allowance for stratification whereby the ionic number current
may be conserved even when the ionic charge number Z is altered by beta
processes. It is demonstrated that the gauge freedom to make different choices
of the chemical basis determining which neutrons are counted as ``free'' does
not affect their ``superfluid'' momentum covector, which must locally have the
form of a gradient (though it does affect the ``normal'' momentum covector
characterising the protons and those neutrons that are considered to be
``confined'' in the nuclei). It is shown how the effect of ``entrainment''
(whereby the momentum directions deviate from those of the currents) is
controlled by the (gauge independent) mobility coefficient K, estimated in
recent microscopical quantum mechanical investigations, which suggest that the
corresponding (gauge dependent) ``effective mass'' m* of the free neutrons can
become very large in some layers. The relation between this treatment of the
crust layers and related work (using different definitions of ``effective
mass'') intended for the deeper core layers is discussed.Comment: 21 pages Latex. Part II of article whose Part I (Simple microscopic
models) is given by nucl-th/0402057. New version extended to include figure
A single-board preprocessor and pulse generator
The Aeronomy Lab. of NOAA has designed and built a single board, programmable radar controller for use with VHF ST (stratosphere troposphere) radars. The controller consists of a coherent integrator preprocessor and a radar pulse generator, both of which are described, as well as interfaces to an antenna beam switch and a receiver bandwidth switch. The controller occupies a single slot in a Data General Nova of Eclipse computer. The integrator and pulse generator take advantage of high density, dual port FIFO chips such as the 512 x 9 Mostek MK 4501. These FIFOs have separate input and output ports and independent read and write cycles with cycle times of less than 200 ns, making them very fast and easy to interface. A simple block diagram of the coherent integrator is shown. The integrator is designed to handle inputs from one receiver (2 channels) with 1 sec sample spacing. The pulse generator is based on controllers designed by R. F. Woodman for the Arecibo and SOUSY radars us a recirculating memory scheme
New concept in brazing metallic honeycomb panels
Aluminum oxide coating provides surface which will not be wetted by brazing alloy and which stops metallic diffusion welding of tooling materials to part being produced. This method eliminates loss of tooling materials and parts from braze wetting and allows fall-apart disassembly of tooling after brazing
KIC 2856960: the impossible triple star
KIC 2856960 is a star in the Kepler field which was observed by Kepler for 4
years. It shows the primary and secondary eclipses of a close binary of 0.258d
as well as complex dipping events that last for about 1.5d at a time and recur
on a 204d period. The dips are thought to result when the close binary passes
across the face of a third star. In this paper we present an attempt to model
the dips. Despite the apparent simplicity of the system and strenuous efforts
to find a solution, we find that we cannot match the dips with a triple star
while satisfying Kepler's laws. The problem is that to match the dips the
separation of the close binary has to be larger than possible relative to the
outer orbit given the orbital periods. Quadruple star models can get round this
problem but require the addition of a so-far undetected intermediate period of
order 5 -- 20d that has be a near-perfect integer divisor of the outer 204d
period. Although we have no good explanation for KIC 2856960, using the full
set of Kepler data we are able to update several of its parameters. We also
present a spectrum showing that KIC 2856960 is dominated by light from a K3- or
K4-type star.Comment: 11 pages, 13 figures, accepted for publication in MNRAS August 21,
201
Poly-essential and general Hyperelastic World (brane) models
This article provides a unified treatment of an extensive category of
non-linear classical field models whereby the universe is represented (perhaps
as a brane in a higher dimensional background) in terms of a structure of a
mathematically convenient type describable as hyperelastic, for which a
complete set of equations of motion is provided just by the energy-momentum
conservation law. Particular cases include those of a perfect fluid in
quintessential backgrounds of various kinds, as well as models of the elastic
solid kind that has been proposed to account for cosmic acceleration. It is
shown how an appropriately generalised Hadamard operator can be used to
construct a symplectic structure that controles the evolution of small
perturbations, and that provides a characteristic equation governing the
propagation of weak discontinuities of diverse (extrinsic and extrinsic) kinds.
The special case of a poly-essential model - the k-essential analogue of an
ordinary polytropic fluid - is examined and shown to be well behaved (like the
fluid) only if the pressure to density ratio is positive.Comment: 16 pages Latex, Contrib. to 10th Peyresq Pysics Meeting, June 2005:
Micro and Macro Structures of Spacetim
Principles and Practice of Artificial Insemination in Turkeys
Low fertility is one of the most common and most costly problems in turkey breeder flocks. As a partial solution to this problem, there has been a growing interest in artificial insemination of turkeys. Artificial insemination is a practical solution to infertility due to inactive toms, Inefficient toms and nonreceptive hens, but is not a solution to infertility due to poor management
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