604 research outputs found
Supporting the planning of a community fisheries monitoring and evaluation database: a collaborative project undertaken by CFDO, FLD, STREAM, VSO and AYAD
Cambodia is one of the poorest countries in the world; much of its population live in rural areas and many live below the local poverty line. The management of common property aquatic resources is of over-riding importance to food security and sustainable rural development in Cambodia. Aquatic resources are utilized principally by subsistence fishers and the landless, for whom aquatic resource use is an important livelihood activity.
Subsistence fishers access mainly the rivers, lakes and inundated forests in Tonle Sap provinces, the lower Mekong and Bassac regions and the upper part of the Mekong.
Freshwater capture fisheries probably contribute more to national food security and the national economy in Cambodia than in any other country in the world. (PDF contains 52 pages
The Galactic O-Star Spectroscopic Survey (GOSSS). II. Bright Southern Stars
We present the second installment of GOSSS, a massive spectroscopic survey of
Galactic O stars, based on new homogeneous, high signal-to-noise ratio, R ~
2500 digital observations from both hemispheres selected from the Galactic
O-Star Catalog (GOSC). In this paper we include bright stars and other objects
drawn mostly from the first version of GOSC, all of them south of delta = -20
degrees, for a total number of 258 O stars. We also revise the northern sample
of paper I to provide the full list of spectroscopically classified Galactic O
stars complete to B = 8, bringing the total number of published GOSSS stars to
448. Extensive sequences of exceptional objects are given, including the early
Of/WN, O Iafpe, Ofc, ON/OC, Onfp, Of?p, and Oe types, as well as
double/triple-lined spectroscopic binaries. The new spectral subtype O9.2 is
also discussed. The magnitude and spatial distributions of the observed sample
are analyzed. We also present new results from OWN, a multi-epoch
high-resolution spectroscopic survey coordinated with GOSSS that is assembling
the largest sample of Galactic spectroscopic massive binaries ever attained.
The OWN data combined with additional information on spectroscopic and visual
binaries from the literature indicate that only a very small fraction (if any)
of the stars with masses above 15-20 M_Sol are born as single systems. In the
future we will publish the rest of the GOSSS survey, which is expected to
include over 1000 Galactic O stars.Comment: 110 pages, 16 figures, accepted for publication in ApJS. Some figures
have low quality due to arXiv file size limitations, alternative version
available at http://jmaiz.iaa.es/files/Sotaetal14.pd
Spectroscopic and photometric analysis of the early-type spectroscopic binary HD 161853 in the centre of an H II region
We study the O-type star HD 161853, which has been noted as a probable
double-lined spectroscopic binary system. We secured high-resolution spectra of
HD 161853 during the past nine years. We separated the two components in the
system and measured their respective radial velocities for the first time. We
confirm that HD 161853 is an 1 Ma old binary system consisting of an O8 V
star ( M) and a B1--3 V star ( M) at about 1.3 kpc. From the radial velocity curve, we measure an
orbital period = 2.667650.00001 d and an eccentricity =
0.1210.007. Its -band light curve is constant within 0.014 mag and does
not display eclipses, from which we impose a maximum orbital inclination
deg. HD 161853 is probably associated with an H II region and a poorly
investigated very young open cluster. In addition, we detect a compact emission
region at 50 arcsec to HD 161853 in 22m-WISE and 24m-Spitzer images,
which may be identified as a dust wave piled up by the radiation pressure of
the massive binary system.Comment: 5 pages, 4 figures, to appear in A&
The tale of two centres
We study motion in the field of two fixed centres described by a family of
Einstein-dilaton-Maxwell theories. Transitions between regular and chaotic
motion are observed as the dilaton coupling is varied.Comment: 20 pages, RevTeX, 7 figures included, TeX format change
On the multiplicity of the zero-age main-sequence O star Herschel 36
We present the analysis of high-resolution optical spectroscopic observations
of the zero-age main-sequence O star Herschel 36 spanning six years. This star
is definitely a multiple system, with at least three components detected in its
spectrum. Based on our radial-velocity (RV) study, we propose a picture of a
close massive binary and a more distant companion, most probably in wide orbit
about each other. The orbital solution for the binary, whose components we
identify as O9 V and B0.5 V, is characterized by a period of 1.5415 +/- 0.0006
days. With a spectral type O7.5 V, the third body is the most luminous
component of the system and also presents RV variations with a period close to
498 days. Some possible hypotheses to explain the variability are briefly
addressed and further observations are suggested.Comment: 6 pages, 2 figure
Departure from the constant-period ephemeris for the transiting exoplanet WASP-12 b
Most hot Jupiters are expected to spiral in towards their host stars due to
transfering of the angular momentum of the orbital motion to the stellar spin.
Their orbits can also precess due to planet-star interactions. Calculations
show that both effects could be detected for the very-hot exoplanet WASP-12 b
using the method of precise transit timing over a timespan of the order of 10
yr. We acquired new precise light curves for 29 transits of WASP-12 b,
spannning 4 observing seasons from November 2012 to February 2016. New
mid-transit times, together with literature ones, were used to refine the
transit ephemeris and analyse the timing residuals. We find that the transit
times of WASP-12 b do not follow a linear ephemeris with a 5 sigma confidence
level. They may be approximated with a quadratic ephemeris that gives a rate of
change in the orbital period of -2.56 +/- 0.40 x 10^{-2} s/yr. The tidal
quality parameter of the host star was found to be equal to 2.5 x 10^5 that is
comparable to theoretical predictions for Sun-like stars. We also consider a
model, in which the observed timing residuals are interpreted as a result of
the apsidal precession. We find, however, that this model is statistically less
probable than the orbital decay.Comment: Accepted for publication in A&A Letter
Chaos in Static Axisymmetric Spacetimes I : Vacuum Case
We study the motion of test particle in static axisymmetric vacuum spacetimes
and discuss two criteria for strong chaos to occur: (1) a local instability
measured by the Weyl curvature, and (2) a tangle of a homoclinic orbit, which
is closely related to an unstable periodic orbit in general relativity. We
analyze several static axisymmetric spacetimes and find that the first
criterion is a sufficient condition for chaos, at least qualitatively. Although
some test particles which do not satisfy the first criterion show chaotic
behavior in some spacetimes, these can be accounted for the second criterion.Comment: More comments for the quantitative estimation of chaos are added, and
some inappropriate terms are changed. This will appear on Class. Quant. Gra
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