4,586 research outputs found
Haro15: Is it actually a low metallicity galaxy?
We present a detailed study of the physical properties of the nebular
material in multiple knots of the blue compact dwarf galaxy Haro 15. Using long
slit and echelle spectroscopy, obtained at Las Campanas Observatory, we study
the physical conditions (electron density and temperature), ionic and total
chemical abundances of several atoms, reddening and ionization structure. The
latter was derived by comparing the oxygen and sulphur ionic ratios to their
corresponding observed emission line ratios (the eta and eta' plots) in
different regions of the galaxy. Applying direct and empirical methods for
abundance determination, we perform a comparative analysis between these
regions.Comment: (Poster paper) 2 pages, 2 figure
Leptonic emission from microquasar jets: from radio to very high-energy gamma-rays
Microquasars are sources of very high-energy gamma-rays and, very probably,
high-energy gamma-ray emitters. We propose a model for a jet that can allow to
give accurate observational predictions for jet emission at different energies
and provide with physical information of the object using multiwavelength data.Comment: 2 pages, 1 figure. Proceedings of the conference: "International
Astronomical Union Symposium No. 230: Populations of High Energy Sources in
Galaxies". Edited by Evert J.A. Meurs & Giuseppina Fabbian
Internal kinematic and physical properties in a BCD galaxy: Haro 15 in detail
We present a detailed study of the kinematic and physical properties of the
ionized gas in multiple knots of the blue compact dwarf galaxy Haro 15. Using
echelle and long slit spectroscopy data, obtained with different instruments at
Las Campanas Observatory, we study the internal kinematic and physical
conditions (electron density and temperature), ionic and total chemical
abundances of several atoms, reddening and ionization structure. Applying
direct and empirical methods for abundance determination, we perform a
comparative analysis between these regions and in their different components.
On the other hand, our echelle spectra show complex kinematics in several
conspicuous knots within the galaxy. To perform an in-depth 2D spectroscopic
study we complete this work with high spatial and spectral resolution
spectroscopy using the Integral Field Unit mode on the Gemini Multi-Object
Spectrograph instrument at the Gemini South telescope. With these data we are
able to resolve the complex kinematical structure within star forming knots in
Haro 15 galaxy.Comment: 6 pages, 2 figures, IX Scientific Meeting of the Spanish Astronomical
Society held on September 13-17, 2010, in Madrid, Spai
Radiation from matter entrainment in astrophysical jets: the AGN case
Jets are found in a variety of astrophysical sources, from young stellar
objects to active galactic nuclei. In all the cases the jet propagates with a
supersonic velocity through the external medium, which can be inhomogeneous,
and inhomogeneities could penetrate into the jet. The interaction of the jet
material with an obstacle produces a bow shock in the jet in which particles
can be accelerated up to relativistic energies and emit high-energy photons. In
this work, we explore the active galactic nuclei scenario, focusing on the
dynamical and radiative consequences of the interaction at different jet
heights. We find that the produced high-energy emission could be detectable by
the current gamma-ray telescopes. In general, the jet-clump interactions are a
possible mechanism to produce (steady or flaring) high-energy emission in many
astrophysical sources in which jets are present.Comment: 4 pages, 2 figures. Accepted for publication in the Proceedings of
the 275 IAU Symposium: "Jets at all Scales", held in Buenos Aires, September
13-17, 201
High velocity blue-shifted FeII absorption in the dwarf star-forming galaxy PHL293B: Evidence for a wind driven supershell?
X-shooter and ISIS WHT spectra of the starforming galaxy PHL 293B also known
as A2228-00 and SDSS J223036.79-000636.9 are presented in this paper.
We find broad (FWHM = 1000km/s) and very broad (FWZI = 4000km/s) components
in the Balmer lines, narrow absorption components in the Balmer series
blueshifted by 800km/s, previously undetected FeII multiplet (42) absorptions
also blueshifted by 800km/s, IR CaII triplet stellar absorptions consistent
with [Fe/H] < -2.0 and no broad components or blushifted absorptions in the HeI
lines. Based on historical records, we found no optical variability at the 5
sigma level of 0.02 mag between 2005 and 2013 and no optical variability at the
level of 0.1mag for the past 24 years.
The lack of variability rules out transient phenomena like luminous blue
variables or SN IIn as the origin of the blue shifted absorptions of HI and
FeII. The evidence points to either a young and dense expanding supershell or a
stationary cooling wind, in both cases driven by the young cluster wind.Comment: Accepted for publication in MNRAS; 15 pages, 10 figure
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Systems thinkers think About systems education under the April 2010 (volcanic ash) clouds of Austria
The fragmented nature of systems education with multiple traditions expressed in very different ways at different institutions with ultimate confusing effects on the community of learners (students, managers, policy makers, etc), led to a group of Systems Thinkers to discuss and create generic curricula for education and learning about systems for the generalist and specialist tracks. An active network of systems educators and stakeholders who can benefit from enhanced systems education in having to deal with complex issues, was also explored. In this presentation some guidelines for designing introductory and advanced courses will be discussed. The Introduction to Systemic Thinking and Practice course is intended as an introductory course for students from all disciplines. The Advanced Systemic Thinking and Practice course is intended as a more advanced course for students who are faced with complex issues that require a trans-disciplinary and integrated approach. The designs contain a set of key systems concepts and frameworks relevant to the appropriate level, along with some indicative tools and methods which will enable students to explore the concepts. The value of a Global Network of Systems Educators will also be discussed and how this network could help to fulfil the needs of managers, policy makers and society in general. An example will be given of how the integration of this network with the UQ-UNESCO/MAB Global Learning Laboratories NET could lead to more people (decision-and policy makers in Governments, managers, businesses, etc.) having the ability to practice systems thinking – all of these contributing to Systems Thinking becoming a more mainstream part of a sustainable society
Leptonic secondary emission in a hadronic microquasar model
Context: It has been proposed that the origin of the very high-energy photons
emitted from high-mass X-ray binaries with jet-like features, so-called
microquasars (MQs), is related to hadronic interactions between relativistic
protons in the jet and cold protons of the stellar wind. Leptonic secondary
emission should be calculated in a complete hadronic model that include the
effects of pairs from charged pion decays inside the jets and the emission from
pairs generated by gamma-ray absorption in the photosphere of the system. Aims:
We aim at predicting the broadband spectrum from a general hadronic microquasar
model, taking into account the emission from secondaries created by charged
pion decay inside the jet. Methods: The particle energy distribution for
secondary leptons injected along the jets is consistently derived taking the
energy losses into account. We also compute the spectral energy distribution
resulting from these leptons is calculated after assuming different values of
the magnetic field inside the jets. The spectrum of the gamma-rays produced by
neutral pion-decay and processed by electromagnetic cascades under the stellar
photon field. Results: We show that the secondary emission can dominate the
spectral energy distribution at low energies (~1 MeV). At high energies, the
production spectrum can be significantly distorted by the effect of
electromagnetic cascades. These effects are phase-dependent, and some
variability modulated by the orbital period is predicted.Comment: 8 pages, 5 figures. Accepted for publication in Astronomy &
Astrophysic
High-energy emission from jet-clump interactions in microquasars
High-mass microquasars are binary systems consisting of a massive star and an
accreting compact object from which relativistic jets are launched. There is
considerable observational evidence that winds of massive stars are clumpy.
Individual clumps may interact with the jets in high-mass microquasars to
produce outbursts of high-energy emission. Gamma-ray flares have been detected
in some high-mass X-ray binaries, such as Cygnus X-1, and probably in LS 5039
and LS I+61 303. We predict the high-energy emission produced by the
interaction between a jet and a clump of the stellar wind in a high-mass
microquasar. Assuming a hydrodynamic scenario for the jet-clump interaction, we
calculate the spectral energy distributions produced by the dominant
non-thermal processes: relativistic bremsstrahlung, synchrotron and inverse
Compton radiation, for leptons, and for hadrons, proton-proton collisions.
Significant levels of emission in X-rays (synchrotron), high-energy gamma rays
(inverse Compton), and very high-energy gamma rays (from the decay of neutral
pions) are predicted, with luminosities in the different domains in the range ~
10^{32}-10^{35} erg/s. The spectral energy distributions vary strongly
depending on the specific conditions. Jet-clump interactions may be detectable
at high and very high energies, and provide an explanation for the fast TeV
variability found in some high-mass X-ray binary systems.
Our model can help to infer information about the properties of jets and
clumpy winds by means of high-sensitivity gamma-ray astronomy.Comment: Accepted for publication in A&A (10 pages, 8 figures
Gamma-ray emission from massive young stellar objects
Massive stars form in dense and massive molecular cores. The exact formation
mechanism is unclear, but it is possible that some massive stars are formed by
processes similar to those that produce the low-mass stars, with
accretion/ejection phenomena occurring at some point of the evolution of the
protostar. This picture seems to be supported by the detection of a collimated
stellar wind emanating from the massive protostar IRAS 16547-4247. A triple
radio source is associated with the protostar: a compact core and two radio
lobes. The emission of the southern lobe is clearly non-thermal. Such emission
is interpreted as synchrotron radiation produced by relativistic electrons
locally accelerated at the termination point of a thermal jet. Since the
ambient medium is determined by the properties of the molecular cloud in which
the whole system is embedded, we can expect high densities of particles and
infrared photons. Because of the confirmed presence of relativistic electrons,
inverse Compton and relativistic Bremsstrahlung interactions are unavoidable.
Proton-proton collision should also occur, producing an injection of neutral
pions. In this paper we aim at making quantitative predictions of the spectral
energy distribution of the non-thermal spots generated by massive young stellar
objects, with emphasis on the particular case of IRAS 16547-4247. We present
spectral energy distributions for the southern lobe of this source, for a
variety of conditions. We show that high-energy emission might be detectable
from this object in the gamma-ray domain (MeV to TeV). The source may also be
detectable at X-rays through long exposures with current X-ray instruments.Comment: 8 pages, 6 figures, accepted for publication in A&
Spectral energy distribution of the gamma-ray microquasar LS 5039
The microquasar LS 5039 has recently been detected as a source of very high
energy (VHE) -rays. This detection, that confirms the previously
proposed association of LS 5039 with the EGRET source 3EG~J18241514, makes
of LS 5039 a special system with observational data covering nearly all the
electromagnetic spectrum. In order to reproduce the observed spectrum of LS
5039, from radio to VHE -rays, we have applied a cold matter dominated
jet model that takes into account accretion variability, the jet magnetic
field, particle acceleration, adiabatic and radiative losses, microscopic
energy conservation in the jet, and pair creation and absorption due to the
external photon fields, as well as the emission from the first generation of
secondaries. The radiative processes taken into account are synchrotron,
relativistic Bremsstrahlung and inverse Compton (IC). The model is based on a
scenario that has been characterized with recent observational results,
concerning the orbital parameters, the orbital variability at X-rays and the
nature of the compact object. The computed spectral energy distribution (SED)
shows a good agreement with the available observational data.Comment: 8 pages, 3 figures, submitted to A&A, revised vesion accounting for
referee comments, small improvements of the results due to better
calculation
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