2,119 research outputs found
Acoustic spectral analysis and testing techniques
Subjects covered in four reports are described including: (1) mathematical techniques for combining decibel levels of octaves or constant bandwidth: (2) techniques for determining equation for power spectral density function; (3) computer program to analyze acoustical test data; and (4) computer simulation of horn responses utilizing hyperbolic horn theory
Modelling spectral line profiles of wind-wind shock emissions from massive binary systems
One of the most intriguing spectral features of WR binary stars is the
presence of time-dependent line profiles. Long term observations of several
systems revealed the periodicity of this variability, synchronized with the
orbital movement. Several partially successful models have been proposed to
reproduce the observed data. The most promising assume that the origin of the
emission is the wind-wind interaction zone. In this scenario, two high velocity
and dense winds produce a strong shock layer, responsible for most of the
X-rays observed from these systems. As the secondary star moves along its
orbital path, the shock region of conical shape, changes its position with
relation to the line of sight. As a consequence, the stream measured Doppler
shift presents time variations resulting in position changes of the spectral
line. In our work, we present an alternative model, introducing turbulence in
the shock layer to account for the line broadening and opacity effects for the
asymmetry in the line profiles. We showed that the gas turbulence avoids the
need of an unnaturally large contact layer thickness to reproduce line
broadening. Also, we demonstrated that if the emission from the opposing cone
surface is absorbed, the result is a single peaked profile. This result fully
satisfies the recent data obtained from massive binary systems, and can help on
the determination of both winds and orbital parameters. We successfully applied
this model to the Br22 system and determined its orbital parameters.Comment: To appear in the MNRA
Polarization and kinematics in Cygnus A
From optical spectropolarimetry of Cygnus A we conclude that the scattering
medium in the ionization cones in Cygnus A is moving outward at a speed of
170+-34 km/s, and that the required momentum can be supplied by the radiation
pressure of an average quasar. Such a process could produce a structure
resembling the observed ionization cones, which are thought to result from
shadowing by a circumnuclear dust torus. We detect a polarized red wing in the
[O III] emission lines arising from the central kiloparsec of Cygnus A. This
wing is consistent with line emission created close to the boundary of the
broad-line region.Comment: 5 pages, accepted for publication in MNRAS letter
The Rich Mid-Infrared Environments of Two Highly-Obscured X-ray Binaries: Spitzer Observations of IGR J16318-4848 and GX 301-2
We present the results of Spitzer mid-infrared spectroscopic observations of
two highly-obscured massive X-ray binaries: IGR J16318-4848 and GX301-2. Our
observations reveal for the first time the extremely rich mid-infrared
environments of this type of source, including multiple continuum emission
components (a hot component with T > 700 K and a warm component with T ~ 180 K)
with apparent silicate absorption features, numerous HI recombination lines,
many forbidden ionic lines of low ionization potentials, and pure rotational H2
lines. This indicates that both sources have hot and warm circumstellar dust,
ionized stellar winds, extended low-density ionized regions, and
photo-dissociated regions. It appears difficult to attribute the total optical
extinction of both sources to the hot and warm dust components, which suggests
that there could be an otherwise observable colder dust component responsible
for the most of the optical extinction and silicate absorption features. The
observed mid-infrared spectra are similar to those from Luminous Blue
Variables, indicating that the highly-obscured massive X-ray binaries may
represent a previously unknown evolutionary phase of X-ray binaries with
early-type optical companions. Our results highlight the importance and utility
of mid-infrared spectroscopy to investigate highly-obscured X-ray binaries.Comment: To appear in ApJ Letter
The peculiar B-type supergiant HD327083
Coude spectroscopic data of a poorly-studied peculiar supergiant, HD327083,
are presented. Halpha and Hbeta line profiles have been fitted employing a
non-LTE code adequate for spherically expanding atmospheres. Line fits lead to
estimates of physical parameters. These parameters suggest that HD327083 may be
close to the Luminous Blue Variable phase but it is also possible that it could
be a B[e] Supergiant.Comment: 4 pages, 4 figures, Accepted for publication in A&A Lette
Signature of wide-spread clumping in B supergiant winds
We seek to establish additional observational signatures of the effects of
clumping in OB star winds. The action of clumping on strategic wind-formed
spectral lines is tested to steer the development of models for clumped winds
and thus improve the reliability of mass-loss determinations for massive
stars.The SiIV 1400 resonance line doublets of B0 to B5 supergiants are
analysed using empirical line-synthesis models. The focus is on decoding
information on wind clumping from measurements of ratios of the radial optical
depths (tau_(rad)(w)) of the red and blue components of the SiIV doublet. We
exploit in particular the fact that the two doublet components are decoupled
and formed independently for targets with relatively low wind terminal
velocities. Line-synthesis analyses reveal that the mean ratio of tau_(rad)(w)
of the blue to red SiIV components are rarely close to the canonical value of ~
2 (expected from atomic constants), and spread instead over a range of values
between ~1 and 2. These results are interpreted in terms of a photosphere that
is partially obscured by optically thick structures in the outflowing gas.The
spectroscopic signatures established in this study demonstrate the wide-spread
existence of wind clumping in B supergiants. The additional information in
unsaturated doublet profiles provides a means to quantify the porosity of the
winds.Comment: Accepted for publication in A&A Letter
Compositional dynamics of multilevel innovation platforms in agricultural research for development
Article purchasedInnovation platforms (IPs) form a popular vehicle in agricultural research for development (AR4D) to facilitate stakeholder interaction, agenda setting, and collective action toward sustainable agricultural development. In this article, we analyze multilevel stakeholder engagement in fulfilling seven key innovation system functions. Data are gathered from experiences with interlinked community and (sub)national IPs established under a global AR4D program aimed at stimulating sustainable agricultural development in Central Africa. Our findings show that all innovation systems functions required multilevel action, but that fulfillment of specific functions demands for strategic involvement of specific stakeholders at specific levels. We observed that a research- and dissemination-oriented sequence in the functions was prioritized in AR4D IPs and argue that such a sequence may be different in other types of (business) IPs. Our findings provide an incentive to think function oriented about compositional dynamics (stakeholder groups * levels) in innovation processes, rather than striving for equal stakeholder participation
Astrophysical parameters of 14 open clusters projected close to the Galactic plane
Astrophysical parameters (\textit{age, reddening, distance, core and cluster
radii}) of 14 open clusters (OCs) projected close to the Galactic plane are
derived with 2MASS photometry. The OCs are Be 63, Be 84, Cz 6, Cz 7, Cz 12, Ru
141, Ru 144, Ru 172, FSR 101, FSR 1430, FSR 1471, FSR 162, FSR 178 and FSR 198.
The OCs Be 63, Be 84, Ru 141, Ru 144, and Ru 172 are studied in more detail
than in previous works, while the others have astrophysical parameters derived
for the first time. The open clusters of the sample are located at
kpc from the Sun and at Galactocentric distances
kpc, with age in the range 10 Myr to 1.5 Gyr and reddening in the
range mag. The core and cluster radii are in the range
pc and pc, respectively. Cz 6 and FSR 198 are the youngest OCs of
this sample, with a population of pre-main sequence (PMS) stars, while FSR 178
is the oldest cluster.Comment: 11 pages, 14 figures - accepted by A&
XMM-Newton observations of a superbubble in N 158 in the LMC
Aims: We study the diffuse X-ray emission observed in the field of view of
the pulsar B 0540-69 in the Large Magellanic Cloud (LMC) by XMM-Newton. We want
to understand the nature of this soft diffuse emission, which coincides with
the superbubble in the HII region N 158, and improve our understanding of the
evolution of superbubbles. Methods: We analyse the XMM-Newton spectra of the
diffuse emission. Using the parameters obtained from the spectral fit, we
perform calculations of the evolution of the superbubble. The mass loss and
energy input rates are based on the initial mass function (IMF) of the observed
OB association inside the superbubble. Results: The analysis of the spectra
shows that the soft X-ray emission arises from hot shocked gas surrounded by a
thin shell of cooler, ionised gas. We show that the stellar winds alone cannot
account for the energy inside the superbubble, but the energy release of 2 - 3
supernova explosions in the past ~1 Myr provides a possible explanation.
Conclusions: The combination of high sensitivity X-ray data, allowing spectral
analysis, and analytical models for superbubbles bears the potential to reveal
the evolutionary state of interstellar bubbles, if the stellar content is
known.Comment: 7 pages. Accepted for publication in A&
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