20,028 research outputs found
Study of optimum discrete estimators in measurement analysis
Study of statistical techniques for obtaining estimates of true data parameters uses discrete measured quantities containing random error. These techniques develop estimation procedures as an iterative algorithm for digital computation in real time
Methods for injection error analysis and their comparison Scientific report no. 13
Formulation of direct and adjoint methods of trajectory injection error in vector matrix notation and compariso
The APM Survey for Cool Carbon Stars in the Galactic Halo - II The Search for Dwarf Carbon Stars
We present proper motion measurements for carbon stars found during the APM
Survey for Cool Carbon Stars in the Galactic Halo (Totten & Irwin, 1998).
Measurements are obtained using a combination of POSSI, POSSII and UKST survey
plates supplemented where necessary by CCD frames taken at the Isaac Newton
Telescope. We find no significant proper motion for any of the new APM
colour-selected carbon stars and so conclude that there are no dwarf carbon
stars present within this sample. We also present proper motion measurements
for three previously known dwarf carbon stars and demonstrate that these
measurements agree favourably with those previously quoted in the literature,
verifying our method of determining proper motions. Results from a
complimentary program of JHK photometry obtained at the South African
Astronomical Observatory are also presented. Dwarf carbon stars are believed to
have anomalous near-infrared colours, and this feature is used for further
investigation of the nature of the APM carbon stars. Our results support the
use of JHK photomtery as a dwarf/giant discriminator and also reinforce the
conclusion that none of the new APM-selected carbon stars are dwarfs. Finally,
proper motion measurements combined with extant JHK photometry are presented
for a sample of previously known Halo carbon stars, suggesting that one of
these stars, CLS29, is likely to be a previously unrecognised dwarf carbon
star.Comment: 13 pages, 5 figures, accepted for publication in MNRAS, Also
available at http://www.astro.keele.ac.uk/~ejt/publications.htm
SCUBA Observations of NGC 1275
Deep SCUBA observations of NGC 1275 at 450 micron and 850 micron along with
the application of deconvolution algorithms have permitted us to separate the
strong core emission in this galaxy from the fainter extended emission around
it. The core has a steep spectral index and is likely due primarily to the AGN.
The faint emission has a positive spectral index and is clearly due to extended
dust in a patchy distribution out to a radius of 20 kpc from the
nucleus. These observations have now revealed that a large quantity of dust,
6 10 , 2 orders of magnitude larger than that
inferred from previous optical absorption measurements, exists in this galaxy.
We estimate the temperature of this dust to be 20 K (using an emissivity
index of = 1.3) and the gas/dust ratio to be 360. These values are
typical of spiral galaxies. The dust emission correlates spatially with the hot
X-ray emitting gas which may be due to collisional heating of broadly
distributed dust by electrons. Since the destruction timescale is short, the
dust cannot be replenished by stellar mass loss and must be externally
supplied, either via the infalling galaxy or the cooling flow itself.Comment: 13 pages, 4 figures. Figure 4 is colou
APM z>4 QSO Survey: Distribution and Evolution of High Column Density HI Absorbers
Eleven candidate damped Lya absorption systems were identified in 27 spectra
of the quasars from the APM z>4 survey covering the redshift range
2.83.5). High resolution echelle spectra (0.8A FWHM)
have been obtained for three quasars, including 2 of the highest redshift
objects in the survey. Two damped systems have confirmed HI column densities of
N(HI) >= 10^20.3 atoms cm^-2, with a third falling just below this threshold.
We have discovered the highest redshift damped Lya absorber known at z=4.383 in
QSO BR1202-0725. The APM QSOs provide a substantial increase in the redshift
path available for damped surveys for z>3. We combine this high redshift sample
with other quasar samples covering the redshift range 0.008 < z < 4.7 to study
the redshift evolution and the column density distribution function for
absorbers with log N(HI)>=17.2. In the HI column density distribution
f(N)=kN^-beta we find evidence for breaks in the power law, flattening for
17.221.2. The column density
distribution function for the data with log N(HI)>=20.3 is better fit with the
form f(N)=(f*/N*)(N/N*)^-beta exp(-N/N*). Significant redshift evolution in the
number density per unit redshift is evident in the higher column density
systems with an apparent decline in N(z) for z>3.5.Comment: To appear in MNRAS. Latex file (10 pages of text) plus 14 separate
postscript figure files. Requires mn.sty. Postscript version with figures
embedded is available at http://www.ociw.edu/~lisa/publications.htm
Evolution of Neutral Gas at High Redshift -- Implications for the Epoch of Galaxy Formation
Though observationally rare, damped Lya absorption systems dominate the mass
density of neutral gas in the Universe. Eleven high redshift damped Lya systems
covering 2.84 QSO Survey,
extending these absorption system surveys to the highest redshifts currently
possible. Combining our new data set with previous surveys we find that the
cosmological mass density in neutral gas, omega_g, does not rise as steeply
prior to z~2 as indicated by previous studies. There is evidence in the
observed omega_g for a flattening at z~2 and a possible turnover at z~3. When
combined with the decline at z>3.5 in number density per unit redshift of
damped systems with column densities log N(HI)>21 atoms cm^-2, these results
point to an epoch at z>3 prior to which the highest column density damped
systems are still forming. We find that over the redshift range 2<z<4 the total
mass in neutral gas is marginally comparable with the total visible mass in
stars in present day galaxies. However, if one considers the total mass visible
in stellar disks alone, ie excluding galactic bulges, the two values are
comparable. We are observing a mass of neutral gas comparable to the mass of
visible disk stars. Lanzetta, Wolfe & Turnshek (1995) found that omega_g(z~3.5)
was twice omega_g(z~2), implying a much larger amount of star formation must
have taken place between z=3.5 and z=2 than is indicated by metallicity
studies. This created a `cosmic G-dwarf problem'. The more gradual evolution of
omega_g we find alleviates this. These results have profound implications for
theories of galaxy formation.Comment: To appear in MNRAS. Latex file (4 pages of text) plus 3 separate
postscript figure files. Requires mn.sty. Postscript version with figures
embedded is available at http://www.ociw.edu/~lisa/publications.htm
Sagittarius: The Nearest Dwarf Galaxy
We have discovered a new Galactic satellite galaxy in the constellation of
Sagittarius. The Sagittarius dwarf galaxy is the nearest galaxy known, subtends
an angle of degrees on the sky, lies at a distance of 24 \kpc from the
Sun, \sim 16 \kpc from the centre of the Milky Way. Itis comparable in size
and luminosity to the largest dwarf spheroidal, has a well populated red
horizontal branch with a blue HB extension; a substantial carbon star
population; and a strong intermediate age stellar component with evidence of a
metallicity spread. Isodensity maps show it to be markedly elongated along a
direction pointing towards the Galactic centre and suggest that it has been
tidally distorted. The close proximity to the Galactic centre, the
morphological appearance and the radial velocity of 140 km/s indicate that this
system must have undergone at most very few close orbital encounters with the
Milky Way. It is currently undergoing strong tidal disruption prior to being
integrated into the Galaxy. Probably all of the four globular clusters, M54,
Arp 2, Ter 7 and Ter 8, are associated with the Sagittarius dwarf galaxy, and
will probably share the fate of their progenitor.Comment: MNRAS in press, 22pp uuencoded PS file, 26 printed figures available
on request from [email protected]
Stereoscopic computer graphics display system
Handbook was published on study which describes relative merits of two general-purpose, steroscopic display systems. Both systems are adaptable to most small data processing facilities and, with minimal hardware development, greatly enhance user ability to interact with computer and to interpret data output. Section also describes digital-to-analog converters designed for use with system
Two monopoles of one type and one of another
The metric on the moduli space of charge (2,1) SU(3)
Bogomolny-Prasad-Sommerfield monopoles is calculated and investigated. The
hyperKahler quotient construction is used to provide an alternative derivation
of the metric. Various properties of the metric are derived using the
hyperKahler quotient construction and the correspondence between BPS monopoles
and rational maps. Several interesting limits of the metric are also
considered.Comment: 48 pages, LaTeX, 2 figures. Typos corrected. Version in JHE
Complex regional pain syndrome with associated chest wall dystonia: a case report
Patients with complex regional pain syndrome (CRPS) often suffer from an array of associated movement disorders, including dystonia of an affected limb. We present a case of a patient with long standing CRPS after a brachial plexus injury, who after displaying several features of the movement disorder previously, developed painful dystonia of chest wall musculature. Detailed neurologic examination found palpable sustained contractions of the pectoral and intercostal muscles in addition to surface allodynia. Needle electromyography of the intercostal and paraspinal muscles supported the diagnosis of dystonia. In addition, pulmonary function testing showed both restrictive and obstructive features in the absence of a clear cardiopulmonary etiology. Treatment was initiated with intrathecal baclofen and the patient had symptomatic relief and improvement of dystonia. This case illustrates a novel form of the movement disorder associated with CRPS with response to intrathecal baclofen treatment
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