14,545 research outputs found
Snake eels (Ophichthidae) of the remote St. Peter and St. Paul’s Archipelago (Equatorial Atlantic) : Museum records after 37 years of shelf life
Despite of its major zoogeographical interest, the biological diversity of central Atlantic oceanic islands are still poorly known because of its remoteness. Incomplete species inventories are a hindrance to macroecology and conservation because knowledge on species distribution are important for identifying patterns and processes in biodiversity and for conservation planning. Records of the snake-eel family Ophichthidae for the St. Peter and St. Paul’s Archipelago, Brazil, are presented for the first time after revision of material collected and deposited in a museum collection 37 yrs ago. Specimens of Apterichtus kendalli and Herpetoichthys regius were collected using rotenone on sand bottoms and one Myrichthys sp. was observed and photographed swimming over a rocky reef. Remarkably, these species were not seen or collected in the St. Peter and St. Paul’s Archipelago ever since despite the substantial increase of biological expeditions over the past two decades, suggesting that the unjustified rotenone sampling prohibition in Brazil is hindering advancement of the nation’s biological diversity knowledge.info:eu-repo/semantics/publishedVersio
Atmospheric NLTE-Models for the Spectroscopic Analysis of Blue Stars with Winds. III. X-ray emission from wind-embedded shocks
X-rays/EUV radiation emitted from wind-embedded shocks in hot, massive stars
can affect the ionization balance in their outer atmospheres, and can be the
mechanism responsible for the production of highly ionized species. To allow
for these processes in the context of spectral analysis, we have implemented
such emission into our unified, NLTE model atmosphere/spectrum synthesis code
FASTWIND.
The shock structure and corresponding emission is calculated as a function of
user-supplied parameters. We account for a temperature and density
stratification inside the post-shock cooling zones, calculated for radiative
and adiabatic cooling in the inner and outer wind, respectively. The
high-energy absorption of the cool wind is considered by adding important
K-shell opacities, and corresponding Auger ionization rates have been included
into the NLTE network.
We tested and verified our implementation carefully against corresponding
results from various alternative model atmosphere codes, and studied the
effects from shock emission for important ions from He, C, N, O, Si, and P.
Surprisingly, dielectronic recombination turned out to play an essential role
for the ionization balance of OIV/OV around Teff = 45,000 K. Finally, we
investigated the behavior of the mass absorption coefficient, kappa_nu(r),
important in the context of X-ray line formation in massive star winds.
In almost all considered cases, direct ionization is of major influence, and
Auger ionization significantly affects only NVI and OVI. The approximation of a
radially constant kappa_nu is justified for r > 1.2 Rstar and lambda < 18 A,
and also for many models at longer wavelengths. To estimate the actual value of
this quantity, however, the HeII opacities need to be calculated from detailed
NLTE modeling, at least for wavelengths longer than 18 to 20 A, and information
on the individual CNO abundances has to be present.Comment: accepted by A&
Carbon line formation and spectroscopy in O-type stars
The determination of chemical abundances constitutes a fundamental
requirement for obtaining a complete picture of a star. Particularly in massive
stars, CNO abundances are of prime interest, due to the nuclear CNO-cycle and
various mixing processes which bring these elements to the surface.
We aim at enabling a reliable carbon spectroscopy for our unified NLTE
atmosphere code FASTWIND.
We develop a new carbon model atom including CII/III/IV/V, and discuss
problems related to carbon spectroscopy in O-type stars. We describe different
tests to examine the reliability of our implementation, and investigate which
mechanisms influence the carbon ionization balance. By comparing with
high-resolution spectra from six O-type stars, we check in how far
observational constraints can be reproduced by our new carbon line synthesis.
Carbon lines are even more sensitive to a variation of temperature, gravity,
and mass-loss rate, than hydrogen/helium lines. We are able to reproduce most
of the observed lines from our stellar sample, and to estimate those specific
carbon abundances which bring the lines from different ions into agreement. For
hot dwarfs and supergiants earlier than O7, X-rays from wind-embedded shocks
can impact the synthesized line strengths, particularly for CIV, potentially
affecting the abundance determination.
We have demonstrated our capability to derive realistic carbon abundances by
means of FASTWIND, using our recently developed model atom. We found that
complex effects can have a strong influence on the carbon ionization balance in
hot stars. For a further understanding, the UV range needs to be explored as
well. By means of detailed nitrogen and oxygen model atoms available to use, we
will be able to perform a complete CNO abundance analysis for larger samples of
massive stars, and to provide constraints on corresponding evolutionary models
and aspects.Comment: 22 pages, 16 figures, 6 table
Local solutions in Sobolev spaces with negative indices for the "good" Boussinesq equation
We study the local well-posedness of the initial-value problem for the
nonlinear "good" Boussinesq equation with data in Sobolev spaces \textit{}
for negative indices of .Comment: Referee comments incorporate
Using Fractionalization Indexes: deriving methodological principles for growth studies from time series evidence
Recent cross country growth studies have found that ethnolinguistic fractionalization is an important explanatory variable of long-run growth performance. This paper highlights some limitations of cross country studies by focusing on the time series evidence for South Africa. In presenting variation over time in a number of social, political and economic dimensions, this paper adds longitudinal evidence on a range of dimensions that have been linked to long run economic development. Given South Africa’s history of ethnic and racial politics, it constitutes a useful case study to explore the dynamics of the possible effects of ethnolinguistic fractionalization on growth. We introduce three new sets of fractionalization indicators for South Africa and one set of political indicators. The results of this study provide important nuance to the existing body of evidence, for the use of fractionalization indices in growth studies.
- …