1,436 research outputs found
Propeller propulsion integration, phase 1
A bibliography was compiled of all readily available sources of propeller analytical and experimental studies conducted during the 1930 through 1960 period. A propeller test stand was developed for the measurement of thrust and torque characteristics of full scale general aviation propellers and installed in the LaRC 30 x 60 foot full scale wind tunnel. A tunnel entry was made during the January through February 1980 period. Several propellers were tested, but unforseen difficulties with the shaft thrust torque balance severely degraded the data quality
Deceleration of Relativistic Radio Components and the morphologies of Gigahertz Peaked Spectrum Sources
A relativistic radio component, which moves in a direction close to the sky
plane, will increase in flux density when it decelerates. This effect is the
basis for the qualitative model for GPS galaxies we present in this paper,
which can explain their low-variability convex spectrum, their compact double
or compact symmetric morphology, and the lack of GPS quasars at similar
redshifts. Components are expelled from the nucleus at relativistic speeds at a
large angle to the line of sight, and are decelerated (eg. by ram-pressure or
entrainment of the external gas) before contributing to a mini-lobe. The young
components are Doppler boosted in the direction of motion but appear fainter
for the observer. The non-relativistic mini-lobes dominate the structure and
are responsible for the low variability in flux density and the convex radio
spectrum as well as the compact double angular morphology. Had the same source
been orientated at a small angle to the line of sight, the young components
would be boosted in the observer's direction resulting in a flat and variable
radio spectrum at high frequencies. Hence the characteristic convex spectrum of
a GPS source would not be seen. These sources at small angles to the line of
sight are probably identified with quasars, and are not recognized as GPS
sources, but are embedded in the large population of flat spectrum variable
quasars and BL Lac objects. This leads to a deficiency in GPS/CSOs identified
with quasars.Comment: 11 pages, LaTeX, accepted by A&A 26/Jan/199
PKS 1004+13: A High-Inclination, Highly-Absorbed Radio-Loud QSO -- The First Radio-Loud BAL QSO at Low Redshift?
The existence of BAL outflows in only radio-quiet QSOs was thought to be an
important clue to mass ejection and the radio-loud - radio-quiet dichotomy.
Recently a few radio-loud BAL QSOs have been discovered at high redshift. We
present evidence that PKS 1004+13 is a radio-loud BAL QSO. It would be the
first known at low-redshift (z = 0.24), and one of the most radio luminous. For
PKS 1004+13, there appear to be broad absorption troughs of O VI, N V, Si IV,
and C IV, indicating high-ionization outflows up to about 10,000 km/s. There
are also two strong, broad (~500 km/s), high-ionization, associated absorption
systems that show partial covering of the continuum source. The strong UV
absorption we have detected suggests that the extreme soft-X-ray weakness of
PKS 1004+13 is primarily the result of absorption. The large radio-lobe
dominance indicates BAL and associated gas at high inclinations to the central
engine axis, perhaps in a line-of-sight that passes through an accretion disk
wind.Comment: To appear in Ap.J. Letters, 1999 (June or July); 4 pages, 5 figure
A new luminosity component in 3C 48
The infrared emission from the quasar 3C 48 has a luminosity L ≃ 5 x 10^(12) L_☉ and dominates the power output of the quasar system. It is shown that the infrared emission, unlike that of most radio-loud quasars, is most likely not an extension of the radio emission of the quasar. It is argued that the infrared emission in 3C 48 is probably thermal radiation arising in a highly luminous galaxy surrounding the quasar
VLA radio continuum observations of a new sample of high redshift radio galaxies
We present new deep multi-frequency radio-polarimetric images of a sample of
high redshift radio galaxies (HzRGs), having redshift between 1.7 and 4.1. The
radio data at 4.7 and 8.2 GHz were taken with the Very Large Array in the A
configuration and provide a highest angular resolution of 0.2''. Maps of total
intensity, radio spectral index, radio polarization and internal magnetic field
are presented for each source. The morphology of most objects is that of
standard FRII double radio sources, but several contain multiple hot-spots in
one or both lobes. Compared to similar samples of HzRGs previously imaged,
there is a higher fraction (29%) of compact steep spectrum sources (i.e.
sources with a projected linear size less than 20 kpc). Radio cores are
identified in about half of the sample and tend to have relatively steep
spectra (alpha < -1). Polarization is detected in all but 4 sources, with
typical polarization at 8.2 GHz of around 10-20%. The Faraday rotation can be
measured in most of the radio galaxies: the observed rotation measure (RM) of 8
radio sources exceeds 100 rad m^{-2} in at least one of the lobes, with large
gradients between the two lobes. We find no dependence of Faraday rotation with
other properties of the radio sources. If the origin of the Faraday rotation is
local to the sources, as we believe, then the intrinsic RM is more than a 1000
rad m^{-2}. Because low redshift radio galaxies residing at the center of
clusters usually show extreme RMs, we suggest that the high-z large RM sources
also lie in very dense environments. Finally, we find that the fraction of
powerful radio galaxies with extreme Faraday rotation increases with redshift,
as would be expected if their average environment tends to become denser with
decreasing cosmic epoch.Comment: Accepted for publication in A&A Supplemen
A search for high redshift clusters associated with radio galaxies at 2 < z < 4
High redshift radio galaxies are amongst the most massive galaxies in the
early Universe and have properties expected from central galaxies in forming
clusters. We are carrying out an observational programme on the VLT to find and
study galaxy proto clusters around radio galaxies at redshifts 2 < z < 4.
First, we use narrow band imaging to select candidate galaxies which show
excess Lyman alpha emission at redshifts similar to the central radio galaxy.
Then, we use multi object spectroscopy to confirm the redshifts of these
candidates and measure the velocity dispersion of the cluster members. Our goal
is to observe a sample of about 10 targets and investigate galaxy overdensities
as a function of redshift. Here, we report on the current progress of the
programme and show some preliminary results which include the discovery of a
structure of galaxies at redshift 4.1.Comment: 4 pages, 3 figures, Sesto conference proceeding 'Probing cosmic
evolution with galaxy clusters
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