2,821 research outputs found
Spectro-Morphology of Galaxies
We present a quantitative method to classify galaxies, based on
multi-wavelength data and elaborated from the properties of nearby galaxies.
Our objective is to define an evolutionary method that can be used for low and
high redshift objects. We estimate the concentration of light (C) at the galaxy
center and the 180 degree-rotational asymmetry (A), computed at several
wavelengths, from ultraviolet (UV) to I-band. The variation of the indices of
concentration and asymmetry with the wavelength reflects the proportion and the
distribution of young and old stellar populations in galaxies. In general C is
found to decrease from optical to UV, and A is found to increase from optical
to UV: the patchy appearance of galaxies in UV with no bulge is often very
different from their counterpart at optical wavelengths, with prominent bulges
and more regular disks. The variation of C and A with the wavelength is
quantified. By this way, we are able to distinguish five types of galaxies that
we call spectro-morphological types: compact, ringed, spiral, irregular and
central-starburst galaxies, which can be differentiated by the repartition of
their stellar populations. We discuss in detail the morphology of galaxies of
the sample, and describe the morphological characteristics of each
spectro-morphological type. We apply spectro-morphology to three objects at a
redshift z=1 in the Hubble Deep Field North, that gives encouraging results for
applications to large samples of high-redshift galaxies. This method of
morphological classification could be used to study the evolution of the
morphology with the redshift and is expected to bring observational constraints
on scenarios of galaxy evolution.Comment: Accepted for publication in Astronomy & Astrophysic
ESMO Minimum Clinical Recommendations for diagnosis, adjuvant treatment and follow-up of primary breast cancer
The "Twin Jet" Planetary Nebula M2-9
We present a model for the structure, temporal behavior, and evolutionary
status of the bipolar nebula M2-9. According to this model the system consists
of an AGB or post-AGB star and a hot white dwarf companion, with an orbital
period of about 120 years. The white dwarf has undergone a symbiotic nova
eruption about 1200 years ago, followed by a supersoft x-ray source phase. The
positional shift of the bright knots in the inner nebular lobes is explained in
terms of a revolving ionizing source. We show that the interaction between the
slow, AGB star's wind, and a collimated fast wind from the white dwarf clears a
path for the ionizing radiation in one direction, while the radiation is
attenuated in others. This results in the mirror-symmetric (as opposed to the
more common point-symmetric) shift in the knots. We show that M2-9 provides an
important evolutionary link among planetary nebulae with binary central stars,
symbiotic systems, and supersoft x-ray sources.Comment: 13 pages + 2 figures. Submitted to Ap
HST Imaging of Globular Clusters in the Edge--on Spiral Galaxies NGC 4565 and NGC 5907
We present a study of the globular cluster systems of two edge-on spiral
galaxies, NGC4565 and NGC5907, from WFPC2 images in the F450W and F814W
filters. The globular cluster systems of both galaxies appear to be similar to
the Galactic globular cluster system. In particular, we derive total numbers of
globular clusters of N_{GC}(4565)= 204+/-38 {+87}{-53} and
N_{GC}(5907)=170+/-41 {+47}{-72} (where the first are statistical, the second
potential systematic errors) for NGC4565 and NGC5907, respectively. This
determination is based on a comparison to the Milky Way system, for which we
adopt a total number of globular clusters of 180+/-20. The specific frequency
of both galaxies is S_N~0.6: indistinguishable from the value for the Milky
Way. The similarity in the globular cluster systems of the two galaxies is
noteworthy since they have significantly different thick disks and
bulge-to-disk ratios. This would suggest that these two components do not play
a major role in the building up of a globular cluster system around late-type
galaxies.Comment: Accepted for publication in the Astronomical Journal, 17 pages incl 5
figures, AAS style two columns. Also available at
http://www.eso.org/~mkissler, Color version of figure 1 only available at
http://www.eso.org/~mkissler (B/W version included
Severe malnutrition in children presenting to health facilities in an urban slum in Bangladesh
Ideally embedded space-times
Due to the growing interest in embeddings of space-time in higher-dimensional
spaces we consider a specific type of embedding. After proving an inequality
between intrinsically defined curvature invariants and the squared mean
curvature, we extend the notion of ideal embeddings from Riemannian geometry to
the indefinite case. Ideal embeddings are such that the embedded manifold
receives the least amount of tension from the surrounding space. Then it is
shown that the de Sitter spaces, a Robertson-Walker space-time and some
anisotropic perfect fluid metrics can be ideally embedded in a five-dimensional
pseudo-Euclidean space.Comment: layout changed and typos corrected; uses revtex
Vacuum spacetimes of embedding class two
Doubt is cast on the much quoted results of Yakupov that the torsion vector in embedding class two vacuum space-times is necessarily a gradient vector and that class 2 vacua of Petrov type III do not exist. The rst result is equivalent to the fact that the two second fundamental forms associated with the embedding necessarily commute and has been assumed in most later investigations of class 2 vacuum space-times. Yakupov stated the result without proof, but hinted that it followed purely algebraically from his identity: Rijkl Ckl = 0 where Cij is the commutator of the two second fundamental forms of the embedding.From Yakupov's identity, it is shown that the only class two vacua with non-zero commutator Cij must necessarily be of Petrov type III or N. Several examples are presented of non-commuting second fundamental forms that satisfy Yakupovs identity and the vacuum condition following from the Gauss equation; both Petrov type N and type III examples occur. Thus it appears unlikely that his results could follow purely algebraically. The results obtained so far do not constitute denite counter-examples to Yakupov's results as the non-commuting examples could turn out to be incompatible with the Codazzi and Ricci embedding equations. This question is currently being investigated
Teaching argumentative synthesis writing through deliberative dialogues: instructional practices in secondary education
Dialogical argumentation practice contributes positively to argumentative writing skills. Specifically, deliberative dialogues are effective in promoting argument and counterargument integration in students' essays. However, the potential of dialogic activities may be increased if they are combined with instructional practices. The primary objective of this research is to compare the impact of four intervention programs, aimed at improving argumentative synthesis writing from conflicting sources. The four programs resulted from the combination of two instructional components (Explicit Instruction through video modellingâEI, or a Procedural GuidelineâG), while Deliberative DialoguesâDDâwere a constant element. We conducted a pre-post quasi-experimental study in which 186 Spanish third grade secondary school students (aged 14â15) participated. We evaluated the quality of the syntheses by examining the level of argumentative coverage (the total number of arguments included in the synthesis) and the level of integration (the type and frequency of the argumentative strategies used in the syntheses). The results showed that the effectiveness of the instructional methods varies according to the synthesis quality indicator. Explicit instruction, in combination with deliberative dialogues, was especially helpful in improving the level of integration of syntheses. The procedural guideline, in combination with deliberative dialogues, contributed significantly to the coverage of arguments. The combination of these two elements did not favor the writing of synthesis as expected, probably due to the conditions in which the intervention was carried out. The findings of this study revealed that the coverage of arguments and integration processes are of different nature, follow different learning paths and require different instructional processes.pre-print875 K
Light Element Evolution and Cosmic Ray Energetics
Using cosmic-ray energetics as a discriminator, we investigate evolutionary
models of LiBeB. We employ a Monte Carlo code which incorporates the delayed
mixing into the ISM both of the synthesized Fe, due to its incorporation into
high velocity dust grains, and of the cosmic-ray produced LiBeB, due to the
transport of the cosmic rays. We normalize the LiBeB production to the integral
energy imparted to cosmic rays per supernova. Models in which the cosmic rays
are accelerated mainly out of the average ISM significantly under predict the
measured Be abundance of the early Galaxy, the increase in [O/Fe] with
decreasing [Fe/H] notwithstanding. We suggest that this increase could be due
to the delayed mixing of the Fe. But, if the cosmic-ray metals are accelerated
out of supernova ejecta enriched superbubbles, the measured Be abundances are
consistent with a cosmic-ray acceleration efficiency that is in very good
agreement with the current epoch data. We also find that neither the above
cosmic-ray origin models nor a model employing low energy cosmic rays
originating from the supernovae of only very massive progenitors can account
for the Li data at values of [Fe/H] below 2.Comment: latex 19 pages, 2 tables, 10 eps figures, uses aastex.cls natbib.sty
Submitted to the Astrophysical Journa
Constraints from Al Measurements on the Galaxy's Recent Global Star Formation Rate and Core Collapse Supernovae Rate
Gamma-rays from the decay of Al offer a stringent constraint on the
Galaxy's global star formation rate over the past million years, supplementing
other methods for quantifying the recent Galactic star formation rate, such as
equivalent widths of H emission. Advantages and disadvantages of using
Al gamma-ray measurements as a tracer of the massive star formation rate
are analyzed. Estimates of the Galactic Al mass derived from COMPTEL
measurements are coupled with a simple, analytical model of the Al
injection rate from massive stars and restrict the Galaxy's recent star
formation rate to \hbox{5 4 M\sun yr}. In addition, we show that
the derived Al mass implies a present day \hbox{Type II + Ib} supernovae
rate of 3.4 2.8 per century, which seems consistent with other
independent estimates of the Galactic core collapse supernova rate. If some
independent measure of the massive star initial mass function or star formation
rate or \hbox{Type II + Ib} supernovae rate were to become available (perhaps
through estimates of the Galactic Fe mass), then a convenient way to
restrain, or possibly determine, the other parameters is presented.Comment: 11 pages including 1 figure, ApJ in pres
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