1,686 research outputs found
The British Contribution to the Hydrography of Canada
Almost inevitably, the starting point for an account of “The British Contribution to the Hydrographic Surveying of Canada” must start with Captain Cook. B.C. — or before Cook — most other British visitors to Canadian waters had produced “maps” rather than “ charts” . It is harder to decide on a finishing point : although the Canadian Parliament attained authority in 1867 over certain navigational matters and the Canadian Hydrographic Office was formed in 1883, it was not until 1908 that the first Canadian ship Lilloet was available to take over the surveying task and HM ships continued to survey off British Columbia until 1910, off Newfoundland till 1912 — indeed, HMS Challenger was surveying off Labrador from 1932 to 1934. The paper considers the subject in the four sections of Canada’s roughly rectangular boundaries
Contract Hydrographic Surveys
National hydrographers — with responsibility for surveying to the accuracy needed for navigational safety — have been under pressure to keep pace with the rapidly increased draught of tankers, operating along new routes to new ports and offshore terminals, and accepting reduced underkeel clearances, at a time when offshore hydrocarbon and other new marine resource activities have called for extensive data collection, interpretation and presentation of quite different sets of parameters. The paper describes how contract surveys have been used to increase the surveying carried out for the safety of navigation in British waters
The On The Fly Imaging Technique
The On-The-Fly (OTF) imaging technique enables single-dish radio telescopes
to construct images of small areas of the sky with greater efficiency and
accuracy. This paper describes the practical application of the OTF imaging
technique. By way of example the implementation of the OTF imaging technique at
the NRAO 12 Meter Telescope is described. Specific requirements for data
sampling, image formation, and Doppler correction are discussed.Comment: 10 pages, 13 figures, accepted A&
A Search for Sub-Millisecond Pulsars
We have conducted a search of 19 southern Galactic globular clusters for
sub-millisecond pulsars at 660 MHz with the Parkes 64-m radio telescope. To
minimize dispersion smearing we used the CPSR baseband recorder, which samples
the 20 MHz observing band at the Nyquist rate. By possessing a complete
description of the signal we could synthesize an optimal filterbank in
software, and in the case of globular clusters of known dispersion measure,
much of the dispersion could be removed using coherent techniques. This allowed
for very high time resolution (25.6 us in most cases), making our searches in
general sensitive to sub-millisecond pulsars with flux densities greater than
about 3 mJy at 50 cm. No new pulsars were discovered, placing important
constraints on the proportion of pulsars with very short spin periods in these
clusters.Comment: 8 pages, 3 figures, to appear in Ap
Discovery of 35 New Supernova Remnants in the Inner Galaxy
We report the discovery of up to 35 new supernova remnants (SNRs) from a 42
arcsec resolution 90cm multi-configuration Very Large Array survey of the
Galactic plane covering 4.5 deg< l <22.0 deg and |b| < 1.25 deg. Archival 20cm,
11cm, and 8 micron data have also been used to identify the SNRs and constrain
their properties. The 90cm image is sensitive to SNRs with diameters 2.5 arcmin
to 50 arcmin and down to a surface brightness limit of about 10^{-21} W m^{-2}
Hz^{-1} sr^{-1}. This survey has nearly tripled the number of SNRs known in
this part of the Galaxy, and represents an overall 15% increase in the total
number of Galactic SNRs. These results suggest that further deep low frequency
surveys of the inner Galaxy will solve the discrepancy between the expected
number of Galactic SNRs and the significantly smaller number of currently known
SNRs.Comment: 5 pages; Accepted to ApJL, high resolution figures available from
http://www.ifa.hawaii.edu/~cbrogan/high_res
The radio SNR G65.1+0.6 and its associated pulsar J1957+2831
New images of the radio Supernova Remnant (SNR) G65.1+0.6 are presented,
based on the 408 MHz and 1420 MHz continuum emission and the HI-line emission
data of the Canadian Galactic Plane Survey (CGPS). A large shell-like structure
seen in the 2695 MHz Effelsberg map appears to have nonthermal spectral index.
HI observations show structures associated with the SNR G65.1+0.6 in the radial
velocity range of -20 to -26 kms and suggest a distance of 9.2 kpc for the
SNR. The estimated Sedov age for G65.1+0.6 is 4 - 14 x10E4 yr. The pulsar (PSR)
J1957+2831 is possibly associated with G65.1+0.6, with consistent distance and
kinematic age estimate, but different characteristic age than the SNR. The
EGRET source 3EG J1958+2909 and gamma-ray source 2CG 065+00 are also near the
eastern edge of the SNR but do not agree in position with the pulsar and are
likely not associated with the SNR. The SNR's flux densities at 408 MHz
(8.6+-0.8 Jy), 1420 MHz (4.9+-0.5 Jy) and 2695 MHz (3.3+-0.5 Jy) have been
corrected for flux densities from compact sources within the SNR. The
integrated flux density based spectral index between 1420 MHz and 408 MHz is
0.45+-0.11 and agrees with the T-T plot spectral index of 0.34+-0.20. The
nearby SNR DA495 has a T-T plot spectral index of 0.50+-0.01.Comment: 7pages, 5 pictures and tables, will appear in A&
Radio Spectrum and Distance of the SNR HB9
New images are presented of the supernova remnant (SNR) HB9 based on 408 MHz
and 1420 MHz continuum emission and HI-line emission data of the Canadian
Galactic Plane Survey (CGPS) by the Dominion Radio Astrophysical Observatory
(DRAO). Two methods of spectral index analysis for HB9 are presented and
compared: one removes compact sources at both frequencies but is limited to the
resolution of the 408 MHz image; the other removes compact sources only in the
1420 MHz image so is effective at higher spatial resolution. The second allows
more detailed spectral index variation studies than the first. The two T-T plot
methods and new integrated flux densities give spectral index
(S_{\nu}\propto\nu^{-alpha}) for the whole of HB9 of 0.48+-0.03; and
0.47+-0.06, respectively. These are lower than previous spectral index for HB9
(alpha=0.61). Spatial variations of spectral index are derived using the second
method and yield a steeper spectral index for interior regions than for the
rim. This can be explained by a standard curved interstellar electron energy
spectrum combined with lower interior magnetic field compared to that near the
outer shock, which results in a larger proportion of steep spectrum emission
for lines-of-sight through the central body of the SNR. HI observations show
structures probably associated with the SNR in the radial velocity range -3 to
-9 km/s and suggest a distance of 0.8+-0.4 kpc for the SNR. This is consistent
with the distance to the radio pulsar 0458+46, offset from the center of HB9 by
23'. However the pulsar spindown and kinematic ages are significantly greater
than estimates of the SNR age: the Sedov age for HB9 is 6600 yr and the
evaporative cloud model yields ages of 4000-7,000 yr.Comment: 8 pages, 6 figures, 1 table, accepted by A&
A Limit on the Polarized Anisotropy of the Cosmic Microwave Background at Subdegree Angular Scales
A ground-based polarimeter, PIQUE, operating at 90 GHz has set a new limit on
the magnitude of any polarized anisotropy in the cosmic microwave background.
The combination of the scan strategy and full width half maximum beam of 0.235
degrees gives broad window functions with average multipoles, l = 211+294-146
and l = 212+229-135 for the E- and B-mode window functions, respectively. A
joint likelihood analysis yields simultaneous 95% confidence level flat band
power limits of 14 and 13 microkelvin on the amplitudes of the E- and B-mode
angular power spectra, respectively. Assuming no B-modes, a 95% confidence
limit of 10 microkelvin is placed on the amplitude of the E-mode angular power
spectrum alone.Comment: 4 pages, 3 figures, submitted to Astrophysical Journal Letter
G55.0+0.3: A Highly Evolved Supernova Remnant
Multi-frequency analysis has revealed the presence of a new supernova
remnant, G55.0+0.3, in the Galactic plane. A kinematic distance of 14 kpc has
been measured from HI spectral line data. The faint, clumpy half-shell is
non-thermal and has a physical radius of 70 pc. Using an evolutionary model,
the age of the remnant is estimated to be on the order of one million years,
which exceeds conventional limits by a factor of five. The remnant may be
associated with the nearby pulsar J1932+2020, which has a spin-down age of 1.1
million years. This work implies that the radiative lifetimes of remnants could
be much longer than previously suggested.Comment: 27 pages, 7 figures in 9 files (figures 1 and 2 require 2 files
each), Accepted for publication in The Astrophysical Journal (Jan. 20, 1998
volume
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