378 research outputs found
The Ecosystem Approach to Fisheries: Issues, Terminology, Principles, Institutional Foundations, Implementation and Outlook
Ecosystems are complex and dynamic natural units that produce goods and services beyond those of benefit to fisheries. Because fisheries have a direct impact on the ecosystem, which is also impacted by other human activities, they need to be managed in an ecosystem context. The meaning of the terms 'ecosystem management', 'ecosystem based management', 'ecosystem approach to fisheries'(EAF), etc., are still not universally defined and progressively evolving. The justification of EAF is evident in the characteristics of an exploited ecosystem and the impacts resulting from fisheries and other activities. The rich set of international agreements of relevance to EAF contains a large number of principles and conceptual objectives. Both provide a fundamental guidance and a significant challenge for the implementation of EAF. The available international instruments also provide the institutional foundations for EAF. The FAO Code of Conduct for Responsible Fisheries is particularly important in this respect and contains provisions for practically all aspects of the approach. One major difficulty in defining EAF lies precisely in turning the available concepts and principles into operational objectives from which an EAF management plan would more easily be developed. The paper discusses these together with the types of action needed to achieve them. Experience in EAF implementation is still limited but some issues are already apparent, e.g. in added complexity, insufficient capacity, slow implementation, need for a pragmatic approach, etc. It is argued, in conclusion, that the future of EAF and fisheries depends on the way in which the two fundamental concepts of fisheries management and ecosystem management, and their respective stakeholders, will join efforts or collide
The outburst of an embedded low-mass YSO in L1641
Strong outbursts in very young and embedded protostars are rare and not yet
fully understood. They are believed to originate from an increase of the mass
accretion rate onto the source. We report the discovery of a strong outburst in
a low-mass embedded young stellar object (YSO), namely 2MASS-J05424848-0816347
or [CTF93]216-2, as well as its photometric and spectroscopic follow-up. Using
near- to mid-IR photometry and NIR low-resolution spectroscopy, we monitor the
outburst, deriving its magnitude, duration, as well as the enhanced accretion
luminosity and mass accretion rate. [CTF93]216-2 increased in brightness by
~4.6, 4.0, 3.8, and 1.9 mag in the J, H, Ks bands and at 24 um, respectively,
corresponding to an L_bol increase of ~20 L_sun. Its early spectrum, probably
taken soon after the outburst, displays a steep almost featureless continuum,
with strong CO band heads and H_2O broad-band absorption features, and Br gamma
line in emission. A later spectrum reveals more absorption features, allowing
us to estimate T_eff~3200 K, M~0.25 M_sun, and mass accretion rate~1.2x10^{-6}
M_sun yr^{-1}. This makes it one of the lowest mass YSOs with a strong outburst
so far discovered.Comment: To be published in A&A letter; 5 pages, 4 figure
A spectroscopic study of southern (candidate) gamma Doradus stars. I. Time series analysis
We present results of a spectroscopic study of 37 southern (candidate) gamma
Doradus stars based on echelle spectra. The observed spectra were
cross-correlated with the standard template spectrum of an F0-type star for an
easier detection of binary and intrinsic variations. We identified 15 objects
as spectroscopic binaries, including 7 new ones, and another 3 objects are
binary suspects. At least 12 objects show composite spectra. We could determine
the orbital parameters for 9 binaries, of which 4 turn out to be ellipsoidal
variables. For 6 binaries, we estimated the expected time-base of the orbital
variations. Clear profile variations are observed for 17 objects, pointing
towards stellar pulsation. For 8 of them, we have evidence that the main
spectroscopic and photometric periods coincide. Our results, in combination
with prior knowledge from the literature, lead to the classification of 10
objects as new bona-fide gamma Doradus stars, 1 object as new bona-fide delta
Scuti star, and 8 objects as constant stars. Finally, we determined the
projected rotational velocity with two independent methods. The resulting vsini
values range from 3 to 135 km/s. For the bona-fide gamma Doradus stars, the
majority has vsini below 60 km/s.Comment: 13 pages (+ 10 pages online material), 10 (+16) figures. Accepted for
publication by A&
The Centurion 18 telescope of the Wise Observatory
We describe the second telescope of the Wise Observatory, a 0.46-m Centurion
18 (C18) installed in 2005, which enhances significantly the observing
possibilities. The telescope operates from a small dome and is equipped with a
large-format CCD camera. In the last two years this telescope was intensively
used in a variety of monitoring projects.
The operation of the C18 is now automatic, requiring only start-up at the
beginning of a night and close-down at dawn. The observations are mostly
performed remotely from the Tel Aviv campus or even from the observer's home.
The entire facility was erected for a component cost of about 70k$ and a labor
investment of a total of one man-year.
We describe three types of projects undertaken with this new facility: the
measurement of asteroid light variability with the purpose of determining
physical parameters and binarity, the following-up of transiting extrasolar
planets, and the study of AGN variability. The successful implementation of the
C18 demonstrates the viability of small telescopes in an age of huge
light-collectors, provided the operation of such facilities is very efficient.Comment: 16 pages, 13 figures, some figures quality was degraded, accepted for
publication in Astrophysics and Space Scienc
A possible architecture of the planetary system HR 8799
HR8799 is a nearby A-type star with a debris disk and three planetary
candidates recently imaged directly. We undertake a coherent analysis of
various portions of observational data on all known components of the system.
The goal is to elucidate the architecture and evolutionary status of the
system. We try to further constrain the age and orientation of the system,
orbits and masses of the companions, as well as the location of dust. From the
high luminosity of debris dust and dynamical constraints, we argue for a rather
young system's age of <50Myr. The system must be seen nearly, but not exactly,
pole-on. Our analysis of the stellar rotational velocity yields an inclination
of 13-30deg, whereas i>20deg is needed for the system to be dynamically stable,
which suggests a probable inclination range of 20-30deg. The spectral energy
distribution is naturally reproduced with two dust rings associated with two
planetesimal belts. The inner "asteroid belt" is located at ~10AU inside the
orbit of the innermost companion and a "Kuiper belt" at >100AU is just exterior
to the orbit of the outermost companion. The dust masses in the inner and outer
ring are estimated to be ~1E-05 and 4E-02 M_earth, respectively. We show that
all three planetary candidates may be stable in the mass range suggested in the
discovery paper by Marois et al. 2008 (between 5 and 13 Jupiter masses), but
only for some of all possible orientations. Stable orbits imply a double
(4:2:1) mean-motion resonance between all three companions. We finally show
that in the cases where the companions themselves are orbitally stable, the
dust-producing planetesimal belts are also stable against planetary
perturbations.Comment: 12 pages, 14 figures, 4 tables, accepted to be published in Astronomy
& Astrophysics (May 20, 2009
GRB 070311: a direct link between the prompt emission and the afterglow
We present prompt gamma-ray, early NIR/optical, late optical and X-ray
observations of the peculiar GRB 070311 discovered by INTEGRAL, in order to
gain clues on the mechanisms responsible for the prompt gamma-ray pulse as well
as for the early and late multi-band afterglow of GRB 070311. We fitted with
empirical functions the gamma-ray and optical light curves and scaled the
result to the late time X-rays. The H-band light curve taken by REM shows two
pulses peaking 80 and 140 s after the peak of the gamma-ray burst and possibly
accompanied by a faint gamma-ray tail. Remarkably, the late optical and X-ray
afterglow underwent a major rebrightening between 3x10^4 and 2x10^5 s after the
burst with an X-ray fluence comparable with that of the prompt emission
extrapolated in the same band. Notably, the time profile of the late
rebrightening can be described as the combination of a time-rescaled version of
the prompt gamma-ray pulse and an underlying power law. This result supports a
common origin for both prompt and late X-ray/optical afterglow rebrightening of
GRB 070311 within the external shock scenario. The main fireball would be
responsible for the prompt emission, while a second shell would produce the
rebrightening when impacting the leading blastwave in a refreshed shock
(abridged).Comment: 14 pages, 11 figures, 4 tables, accepted to A&
Elliptic and hyperelliptic magnetohydrodynamic equilibria
The present study is a continuation of a previous one on "hyperelliptic"
axisymmetric equilibria started in [Tasso and Throumoulopoulos, Phys. Plasmas
5, 2378 (1998)].
Specifically, some equilibria with incompressible flow nonaligned with the
magnetic field and restricted by appropriate side conditions like "isothermal"
magnetic surfaces, "isodynamicity" or P + B^2/2 constant on magnetic surfaces
are found to be reducible to elliptic integrals. The third class recovers
recent equilibria found in [Schief, Phys. Plasmas 10, 2677 (2003)]. In contrast
to field aligned flows, all solutions found here have nonzero toroidal magnetic
field on and elliptic surfaces near the magnetic axis.Comment: 9 page
Exoplanet Science with the European Extremely Large Telescope. The Case for Visible and Near-IR Spectroscopy at High Resolution
Exoplanet science is booming. In 20 years our knowledge has expanded
considerably, from the first discovery of a Hot Jupiter, to the detection of a
large population of Neptunes and super-Earths, to the first steps toward the
characterization of exoplanet atmospheres. Between today and 2025, the field
will evolve at an even faster pace with the advent of several space-based
transit search missions, ground-based spectrographs, high-contrast imaging
facilities, and the James Webb Space Telescope. Especially the ESA M-class
PLATO mission will be a game changer in the field. From 2024 onwards, PLATO
will find transiting terrestrial planets orbiting within the habitable zones of
nearby, bright stars. These objects will require the power of Extremely Large
Telescopes (ELTs) to be characterized further. The technique of ground-based
high-resolution spectroscopy is establishing itself as a crucial pathway to
measure chemical composition, atmospheric structure and atmospheric circulation
in transiting exoplanets. A high-resolution spectrograph covering the visible
and near-IR domains, mounted on the European ELT, will be able to detect
molecules such as water vapour, carbon dioxide and oxygen in the atmospheres of
habitable planets under favourable circumstances. E-ELT HiRES is the perfect
ground-based match to the PLATO space mission and represents a unique
opportunity for Europe to lead the world into the era of exploration of
exoplanets with habitable conditions. HiRES will also be extremely
complementary to other E-ELT planned instruments specialising in different
kinds of planets, such as METIS and EPICS
Discovery and analysis of p-mode and g-mode oscillations in the A-type primary of the eccentric binary HD 209295
We have discovered both intermediate-order gravity mode and low-order
pressure mode pulsation in the same star, HD 209295. It is therefore both a
Gamma Doradus and a Delta Scuti star, which makes it the first pulsating star
to be a member of two classes.
The star is a single-lined spectroscopic binary with an orbital period of
3.10575 d and an eccentricity of 0.352. Weak pulsational signals are found in
both the radial velocity and line-profile variations, allowing us to show that
the two highest-amplitude Gamma Doradus pulsation modes are consistent with l=1
and |m|=1.
In our 280 h of BVI multi-site photometry we detected ten frequencies in the
light variations, one in the Delta Scuti regime and nine in the Gamma Doradus
domain. Five of the Gamma Doradus frequencies are exact integer multiples of
the orbital frequency. This observation leads us to suspect they are tidally
excited. Results of theoretical modeling (stability analysis, tidal excitation)
were consistent with the observations.
We could not detect the secondary component of the system in infrared
photometry, suggesting that it may not be a main-sequence star. Archival data
of HD 209295 show a strong ultraviolet excess, the origin of which is not
known. The orbit of the primary is consistent with a secondary mass of M > 1.04
Msun indicative of a neutron star or a white dwarf companion.Comment: 18 pages, 18 figures, accepted for publication in MNRAS, shortened
abstrac
GRB 080319B: A Naked-Eye Stellar Blast from the Distant Universe
Long duration gamma-ray bursts (GRBs) release copious amounts of energy
across the entire electromagnetic spectrum, and so provide a window into the
process of black hole formation from the collapse of a massive star. Over the
last forty years, our understanding of the GRB phenomenon has progressed
dramatically; nevertheless, fortuitous circumstances occasionally arise that
provide access to a regime not yet probed. GRB 080319B presented such an
opportunity, with extraordinarily bright prompt optical emission that peaked at
a visual magnitude of 5.3, making it briefly visible with the naked eye. It was
captured in exquisite detail by wide-field telescopes, imaging the burst
location from before the time of the explosion. The combination of these unique
optical data with simultaneous gamma-ray observations provides powerful
diagnostics of the detailed physics of this explosion within seconds of its
formation. Here we show that the prompt optical and gamma-ray emissions from
this event likely arise from different spectral components within the same
physical region located at a large distance from the source, implying an
extremely relativistic outflow. The chromatic behaviour of the broadband
afterglow is consistent with viewing the GRB down the very narrow inner core of
a two-component jet that is expanding into a wind-like environment consistent
with the massive star origin of long GRBs. These circumstances can explain the
extreme properties of this GRB.Comment: 43 pages, 18 figures, 3 tables, submitted to Nature May 11, 200
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