207 research outputs found
Morpho-kinematic analysis of the point-symmetric, bipolar planetary nebulae Hb 5 and K 3-17, a pathway to poly-polarity
The kinematics of the bipolar planetary nebulae Hb~5 and K 3-17 are
investigated in detail by means of a comprehensive set of spatially resolved
high spectral resolution, long-slit spectra. Both objects share particularly
interesting characteristics, such as a complex filamentary, rosette-type
nucleus, axial point-symmetry and very fast bipolar outflows. The kinematic
information of Hb~5 is combined with {\it HST} imagery to construct a detailed
3D model of the nebula using the code SHAPE. The model shows that the large
scale lobes are growing in a non-homologous way. The filamentary loops in the
core are proven to actually be secondary lobes emerging from what appears to be
a randomly punctured, dense, gaseous core and the material that forms the point
symmetric structure flows within the lobes with a distinct kinematic pattern
and its interaction with the lobes has had a shaping effect on them. Hb~5 and
K~3-17 may represent a class of fast evolving planetary nebulae that will
develop poly-polar characteristics once the nebular core evolves and expands.Comment: 19 pages, 8 figures. To appear in The Astrophysical Journa
Some Like It Fat: Comparative Ultrastructure of the Embryo in Two Demosponges of the Genus Mycale (Order Poecilosclerida) from Antarctica and the Caribbean
0000-0002-7993-1523© 2015 Riesgo et al. This is an open access article distributed under the terms of the Creative Commons Attribution License [4.0], which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. The attached file is the published version of the article
Adaptable Security in Wireless Sensor Networks by Using Reconfigurable ECC Hardware Coprocessors
Specific features of Wireless Sensor Networks (WSNs) like the open accessibility to nodes, or the easy observability of radio communications, lead to severe security challenges. The application of traditional security schemes on sensor nodes is limited due to the restricted computation capability, low-power availability, and the inherent low data rate. In order to avoid dependencies on a compromised level of security, a WSN node with a microcontroller and a Field Programmable Gate Array (FPGA) is used along this work to implement a state-of-the art solution based on ECC (Elliptic Curve Cryptography). In this paper it is described how the reconfiguration possibilities of the system can be used to adapt ECC parameters in order to increase or reduce the security level depending on the application scenario or the energy budget. Two setups have been created to compare the software- and hardware-supported approaches. According to the results, the FPGA-based ECC implementation requires three orders of magnitude less energy, compared with a low power microcontroller implementation, even considering the power consumption overhead introduced by the hardware reconfiguratio
Study of star-forming galaxies in SDSS up to redshift 0.4 II. Evolution from the fundamental parameters: mass, metallicity & SFR
To understand the formation and evolution of galaxies, it is important to
have a full comprehension of the role played by the metallicity, star formation
rate (SFR), morphology, and color. The interplay of these parameters at
different redshifts will substantially affect the evolution of galaxies and, as
a consequence, the evolution of them will provide important clues and
constraints on the galaxy evolution models. In this work we focus on the
evolution of the SFR, metallicity of the gas, and morphology of galaxies at low
redshift in search of signs of evolution. We use the S2N2 diagnostic diagram as
a tool to classify star--forming, composite, and AGN galaxies. We analyzed the
evolution of the three principal BPT diagrams, estimating the SFR and specific
SFR (SSFR) for our samples of galaxies, studying the luminosity and
mass-metallicity relations, and analyzing the morphology of our sample of
galaxies through the g-r color, concentration index, and SSFR. We found that
the S2N2 is a reliable diagram to classify star--forming, composite, and AGNs
galaxies. We demonstrate that the three principal BPT diagrams show an
evolution toward higher values of [OIII]5007/Hb due to a metallicity decrement.
We found an evolution in the mass-metallicity relation of ~ 0.2 dex for the
redshift range 0.3 < z < 0.4 compared to our local one. From the analysis of
the evolution of the SFR and SSFR as a function of the stellar mass and
metallicity, we discovered a group of galaxies with higher SFR and SSFR at all
redshift samples, whose morphology is consistent with those of late-type
galaxies. Finally, the comparison of our local (0.04<z<0.1) with our higher
redshift sample (0.3<z<0.4), show that the metallicity, the SFR and morphology,
evolve toward lower values of metallicity, higher SFRs, and late--type
morphologies for the redshift range 0.3<z<0.4Comment: 16 pages, 15 figures. Accepted for publication in A&
Bright Planetary Nebulae and their Progenitors in Galaxies Without Star Formation
We present chemical abundances for planetary nebulae in M32, NGC 185, and NGC
205 based upon spectroscopy obtained at the Canada-France-Hawaii Telescope
using the Multi-Object Spectrograph. From these and similar data compiled from
the literature for other Local Group galaxies, we consider the origin and
evolution of the stellar progenitors of bright planetary nebulae in galaxies
where star formation ceased long ago. The ratio of neon to oxygen abundances in
bright planetary nebulae is either identical to that measured in the
interstellar medium of star-forming dwarf galaxies or at most changed by a few
percent, indicating that neither abundance is significantly altered as a result
of the evolution of their stellar progenitors. Several planetary nebulae appear
to have dredged up oxygen, but these are the exception, not the rule. The
progenitors of bright planetary nebulae typically enhance their original helium
abundances by less than 50%. In contrast, nitrogen enhancements can reach
factors of 100. However, nitrogen often shows little or no enhancement,
suggesting that nitrogen enrichment is a random process. The helium, oxygen,
and neon abundances argue that the typical bright planetary nebulae in all of
the galaxies considered here are the progeny of stars with initial masses of
approximately 1.5 Msun or less, based upon the nucleosynthesis predictions of
current theoretical models. These models, however, are unable to explain the
nitrogen enrichment or its scatter. Similar conclusions hold for the bright
planetary nebulae in galaxies with ongoing star formation. Thus, though
composition varies significantly, there is unity in the sense that the
progenitors of typical bright planetary nebulae appear to have undergone
similar physical processes. (Abridged)Comment: accepted for publication in the Astrophysical Journa
The kinematics of the large western knot in the halo of the young planetary nebula NGC 6543
A detailed analysis is presented of the dominant ionised knot in the halo of
the planetary nebula NGC 6543. Observations were made at high spectral and
spatial resolution of the [OIII] 5007 line using the Manchester echelle
spectrometer combined with the 2.1-m San Pedro Martir Telescope. A 20-element
multislit was stepped across the field to give almost complete spatial coverage
of the knot and surrounding halo. The spectra reveal, for the first time, gas
flows around the kinematically inert knot. The gas flows are found to have
velocities comparable to the sound speed as gas is photo-evaporated off an
ionised surface. No evidence is found of fast wind interaction with the knot
and we find it likely that the fast wind is still contained in a
pressure-driven bubble in the core of the nebula. This rules out the
possibility of the knot having its origin in instabilities at the interface of
the fast and AGB winds. We suggest that the knot is embedded in the slowly
expanding Red Giant wind and that its surfaces are being continually
photoionised by the central star.Comment: 13 pages, 11 figures (all eps format). To be published in MNRAS,
accepted on 6/7/0
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