1,300 research outputs found
Archetypal analysis of galaxy spectra
Archetypal analysis represents each individual member of a set of data
vectors as a mixture (a constrained linear combination) of the pure types or
archetypes of the data set. The archetypes are themselves required to be
mixtures of the data vectors. Archetypal analysis may be particularly useful in
analysing data sets comprising galaxy spectra, since each spectrum is,
presumably, a superposition of the emission from the various stellar
populations, nebular emissions and nuclear activity making up that galaxy, and
each of these emission sources corresponds to a potential archetype of the
entire data set. We demonstrate archetypal analysis using sets of composite
synthetic galaxy spectra, showing that the method promises to be an effective
and efficient way to classify spectra. We show that archetypal analysis is
robust in the presence of various types of noise.Comment: 6 pages, 5 figures, 1 style-file. Accepted for publication by MNRA
VLA Observations of the "Eye of the Tornado"- the High Velocity \HII Region G357.63-0.06
The unusual supernova remnant candidate G357.7-0.1 and the compact source
G357.63-0.06 have been observed with the Very Large Array at 1.4 and 8.3 GHz.
The H92 line (8.3 GHz) was detected from the compact source with a
surprising velocity of about -210 km/s indicating that this source is an \HII
region, is most likely located at the Galactic center, and is unrelated to the
SNR. The \HI absorption line (1.4 GHz) data toward these sources supports this
picture and suggests that G357.7-0.1 lies farther away than the Galactic
center.Comment: Latex, 14 pages including 4 figures. Accepted to A
Supramolecular Complexation of Carbon Nanostructures by Crown Ethers
Since their discovery, crown ethers as well as the most recent carbon nanostructures, namely fullerenes, carbon nanotubes, and graphene, have received a lot of attention from the chemical community. Merging these singular chemical structures by noncovalent forces has provided a large number of unprecedented supramolecular assemblies with new geometric and electronic properties whose more representative examples are presented in this Synopsis organized according to the different nature of the carbon nanostructures
The Molonglo Galactic Plane Survey: I. Overview and Images
The first epoch Molonglo Galactic Plane Survey (MGPS1) is a radio continuum
survey made using the Molonglo Observatory Synthesis Telescope (MOST) at 843
MHz with a resolution of 43" X 43" cosec |delta|. The region surveyed is 245
deg < l < 355 deg, |b| < 1.5 deg. The thirteen 9 deg X 3 deg mosaic images
presented here are the superposition of over 450 complete synthesis
observations, each taking 12 h and covering 70' X 70' cosec |delta|. The
root-mean-square sensitivity over much of the mosaiced survey is 1-2 mJy/beam
(1 sigma), and the positional accuracy is approximately 1" X 1" cosec |delta|
for sources brighter than 20 mJy. The dynamic range is no better than 250:1,
and this also constrains the sensitivity in some parts of the images. The
survey area of 330 sq deg contains well over 12,000 unresolved or barely
resolved objects, almost all of which are extra-galactic sources lying in the
Zone of Avoidance. In addition a significant fraction of this area is covered
by extended, diffuse emission associated with thermal complexes, discrete H II
regions, supernova remnants, and other structures in the Galactic interstellar
medium.Comment: Paper with 3 figures and 1 table + Table 2 + 7 jpg grayscales for Fig
4. Astrophysical Journal Supplement (in press) see also
http://www.astrop.physics.usyd.edu.au/MGP
A high-resolution radio survey of the Vela supernova remnant
This paper presents a high-resolution radio continuum (843 MHz) survey of the
Vela supernova remnant. The contrast between the structures in the central
pulsar-powered nebula of the remnant and the synchrotron radiation shell allows
the remnant to be identified morphologically as a member of the composite
class. The data are the first of a composite remnant at spatial scales
comparable with those available for the Cygnus Loop and the Crab Nebula, and
make possible a comparison of radio, optical and soft X-ray emission from the
resolved shell filaments. The survey, made with the Molonglo Observatory
Synthesis Telescope, covers an area of 50 square degrees at a resolution of
43'' x 60'', while imaging structures on scales up to 30'.Comment: 18 pages, 7 jpg figures (version with ps figures at
http://astro.berkeley.edu/~dbock/papers/); AJ, in pres
The Source of Three-minute Magneto-acoustic Oscillations in Coronal Fans
We use images of high spatial, spectral and temporal resolution, obtained
using both ground- and space-based instrumentation, to investigate the coupling
between wave phenomena observed at numerous heights in the solar atmosphere.
Intensity oscillations of 3 minutes are observed to encompass photospheric
umbral dot structures, with power at least three orders-of-magnitude higher
than the surrounding umbra. Simultaneous chromospheric velocity and intensity
time series reveal an 87 \pm 8 degree out-of-phase behavior, implying the
presence of standing modes created as a result of partial wave reflection at
the transition region boundary. An average blue-shifted Doppler velocity of
~1.5 km/s, in addition to a time lag between photospheric and chromospheric
oscillatory phenomena, confirms the presence of upwardly-propagating slow-mode
waves in the lower solar atmosphere. Propagating oscillations in EUV intensity
are detected in simultaneous coronal fan structures, with a periodicity of 172
\pm 17 s and a propagation velocity of 45 \pm 7 km/s. Numerical simulations
reveal that the damping of the magneto-acoustic wave trains is dominated by
thermal conduction. The coronal fans are seen to anchor into the photosphere in
locations where large-amplitude umbral dot oscillations manifest. Derived
kinetic temperature and emission measure time-series display prominent
out-of-phase characteristics, and when combined with the previously established
sub-sonic wave speeds, we conclude that the observed EUV waves are the coronal
counterparts of the upwardly-propagating magneto-acoustic slow-modes detected
in the lower solar atmosphere. Thus, for the first time, we reveal how the
propagation of 3 minute magneto-acoustic waves in solar coronal structures is a
direct result of amplitude enhancements occurring in photospheric umbral dots.Comment: Accepted into ApJ (13 pages and 10 figures
Extended HI Rotation Curve and Mass Distribution of M31
New HI observations of Messier 31 (M31) obtained with the Effelsberg and
Green Bank 100-m telescopes make it possible to measure the rotation curve of
that galaxy out to ~35 kpc. Between 20 and 35 kpc, the rotation curve is nearly
flat at a velocity of ~226 km/s. A model of the mass distribution shows that at
the last observed velocity point, the minimum dark-to-luminous mass ratio is
\~0.5 for a total mass of 3.4 10^11 Msol at R < 35 kpc. This can be compared to
the estimated MW mass of 4.9 10^11 Msol for R < 50 kpc.Comment: 4 pages, 2 figures, accepted for publication in ApJ Letter
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