1,415 research outputs found
Inhomogeneous molecular ring around the B[e] supergiant LHA 120-S 73
We aim to improve our knowledge on the structure and dynamics of the
circumstellar disk of the LMC B[e] supergiant LHA 120-S 73. High-resolution
optical and near-IR spectroscopic data were obtained over a period of 16 and 7
years, respectively. The spectra cover the diagnostic emission lines from
[CaII] and [OI], as well as the CO bands. These features trace the disk at
different distances from the star. We analyzed the kinematics of the individual
emission regions by modeling their emission profiles. A low-resolution
mid-infrared spectrum was obtained as well, which provides information on the
composition of the dusty disk. All diagnostic emission features display
double-peaked line profiles, which we interpret as due to Keplerian rotation.
We find that LHA 120-S 73 is surrounded by at least four individual rings of
material with alternating densities (or by a disk with strongly non-monotonic
radial density distribution). Moreover, we find that the molecular ring must
have gaps or at least strong density inhomogeneities, or in other words, a
clumpy structure. The mid-infrared spectrum displays features of oxygen- and
carbon-rich grain species, which indicates a long-lived, stable dusty disk. We
cannot confirm the previously reported high value for the stellar rotation
velocity. The line profile of HeI 5876 A is strongly variable in both width and
shape and resembles of those seen in non-radially pulsating stars. A proper
determination of the real underlying stellar rotation velocity is hence not
possible. The existence of multiple stable and clumpy rings of alternating
density recalls ring structures around planets. Although there is currently
insufficient observational evidence, it is tempting to propose a scenario with
one (or more) minor bodies or planets revolving around LHA 120-S 73 and
stabilizing the ring system, in analogy to the shepherd moons in planetary
systems.Comment: 14 pages, 13 figure, accepted for pulication in A&
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
Spectral Variations of Of?p Oblique Magnetic Rotator Candidates in the Magellanic Clouds
Optical spectroscopic monitoring has been conducted of two O stars in the
Small and one in the Large Magellanic Cloud, the spectral characteristics of
which place them in the Of?p category, which has been established in the Galaxy
to consist of oblique magnetic rotators. All of these Magellanic stars show
systematic spectral variations typical of the Of?p class, further strengthening
their magnetic candidacy to the point of virtual certainty. The spectral
variations are related to photometric variations derived from OGLE data by Naze
et al. (2015) in a parallel study, which yields rotational periods for two of
them. Now circular spectropolarimetry is required to measure their fields, and
ultraviolet spectroscopy to further characterize their low-metallicity,
magnetically confined winds, in support of hydrodynamical analyses.Comment: 18 pages, 6 figures, accepted for publication by A
Influence of ultrasound-assisted par-frying on crust formation and browning during the production of French fries
Frying is a key processing step during the production of French fries and important for
end product quality and sensory attributes. It is governed by heat and mass transfer
between the frying oil and the potato strips. Crust and color of the French fries are key
quality parameters and important in consumer perception. Crust formation is a result of
combined heat and mass transfer effects. Convective heat transfer from frying oil to
potato strips and heat conduction within the tissue cause water evaporation. Mass
transfer occurs in the form of water vapor release to the frying oil and oil absorption in
the outer layers of the potato strips. Browning of French fries is related to Maillard
reactions between reducing sugars and amino acids. High contents of reducing sugars
are often related to an undesired dark color and bitter taste of French fries.
High-intensity ultrasound transmitted to liquid media causes cavitation and microstreaming,
which can influence boundary layers and cell structures and result in
improved heat and mass transfer.
The influence of an ultrasound treatment of potato strips during the par-frying step was
investigated in order to determine the effect on the resulting changes in product quality.
Improved heat transfer at the product surface due to micro-streaming in the oil and a
facilitated release of vapor from the product surface was observed. A faster crust
formation was found at the initial phase of frying but the crust was found to become
softer at longer sonication times due to persistent mechanical ultrasound effects. French
fries from ultrasound assisted par-frying had a lighter color after finish-frying in
comparison to the conventionally par-fried samples due to an improved release of
reducing sugars from the tissue.
Ultrasound-assisted par-frying showed to be effective in modifying heat and mass
transfer with an impact on crust formation and browning of French fries. Further work
is required regarding the optimization of parameters and sonication times
Spectral classification and properties of the O Vz stars in the Galactic O-Star Spectroscopic Survey (GOSSS)
On the basis of the Galactic O-Star Spectroscopic Survey (GOSSS), a detailed
systematic investigation of the O Vz stars is presented. The currently used
spectral classification criteria are rediscussed, and the Vz phenomenon is
recalibrated through the addition of a quantitative criterion based on the
equivalent widths of the He I 4471, He II 4542, and He II 4686 spectral lines.
The GOSSS O Vz and O V populations resulting from the newly adopted spectral
classification criteria are comparatively analyzed. The locations of the O Vz
stars are probed, showing a concentration of the most extreme cases toward the
youngest star forming regions. The occurrence of the Vz spectral peculiarity in
a solar-metallicity environment, as predicted by the fastwind code, is also
investigated, confirming the importance of taking into account several
processes for the correct interpretation of the phenomenon.Comment: Accepted for publication in The Astronomical Journa
IGR J08408--4503: a new recurrent Supergiant Fast X-ray Transient
The supergiant fast X-ray transient IGR J08408-4503 was discovered by
INTEGRAL on May 15, 2006, during a bright flare. The source shows sporadic
recurrent short bright flares, reaching a peak luminosity of 10^36 erg s^-1
within less than one hour. The companion star is HD 74194, an Ob5Ib(f)
supergiant star located at 3 kpc in the Vela region. We report the light curves
and broad-band spectra (0.1-200 keV) of all the three flares of IGR J08408-4503
detected up to now based on INTEGRAL and Swift data. The flare spectra are well
described by a power-law model with a high energy cut-off at ~15 keV. The
absorption column density during the flares was found to be ~10^21 cm^-2,
indicating a very low matter density around the compact object. Using the
supergiant donor star parameters, the wind accretion conditions imply an
orbital period of the order of one year, a spin period of the order of hours
and a magnetic field of the order of 10^13 G.Comment: 5 pages, 2 figures, accepted for publication in Astrophysical Journal
Letter
Varieties of capitalism and resilience clusters: an exploratory approach to European regions
Regions around the world suffered asymmetric effects with the global economic crisis of the last decade. European regions were not different, and a myriad of impacts with varied magnitudes was felt. This article, inspired by the literature of varieties of capitalism (VoC), presents statistical and econometric evidence about the differences of regional resilience, measured by the variation of economic product, unemployment and R&D across regions in European Union during the economic downturn. An exploratory approach analyses the socio‐economic resilience between different member states, and VoC ideal‐types (liberal market economies, the continental capitalism, the social‐democrat economies, the Mediterranean capitalism, and the Eastern economies). The study presents a typology of resilience clusters in European regions. There were found six types of profiles concerning resilience: great performers, fast growth, intermediate position, R&D reduction, regions in divergence, and Mediterranean regions in big trouble. The study identifies key aspects for resilience, providing policy implications for regional economic policies. The comparison of the resilience clusters and the original VoC categorization has implications for this branch of literature as it does not completely address the variety of regional answers to the shocks.info:eu-repo/semantics/acceptedVersio
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