342 research outputs found
Detection of high-velocity material from the wind-wind collision zone of Eta Carinae across the 2009.0 periastron passage
We report near-IR spectroscopic observations of the Eta Carinae massive
binary system during 2008-2009 using VLT/CRIRES. We detect a strong, broad
absorption wing in He I 10833 extending up to -1900 km/s across the 2009.0
spectroscopic event. Archival HST/STIS ultraviolet and optical data shows a
similar high-velocity absorption (up to -2100 km/s) in the UV resonance lines
of Si IV 1394, 1403 across the 2003.5 event. UV lines from low-ionization
species, such as Si II 1527, 1533 and C II 1334, 1335, show absorption up to
-1200 km/s, indicating that the absorption with v from -1200 to -2100 km/s
originates in a region markedly faster and more ionized than the nominal wind
of the primary star. Observations obtained at the OPD/LNA during the last 4
spectroscopic cycles (1989-2009) also display high-velocity absorption in He I
10833 during periastron. Based on the OPD/LNA dataset, we determine that
material with v < -900 km/s is present in the phase range 0.976 < phi < 1.023
of the spectroscopic cycle, but absent in spectra taken at phi < 0.947 and phi
> 1.049. Therefore, we constrain the duration of the high-velocity absorption
to be 95 to 206 days (or 0.047 to 0.102 in phase). We suggest that the
high-velocity absorption originates from shocked gas in the wind-wind collision
zone, at distances of 15 to 45 AU in the line-of-sight to the primary star.
Using 3-D hydrodynamical simulations of the wind-wind collision zone, we find
that the dense high-velocity gas is in the line-of-sight to the primary star
only if the binary system is oriented in the sky so that the companion is
behind the primary star during periastron, corresponding to a longitude of
periastron of omega ~ 240 to 270 degrees. We study a possible tilt of the
orbital plane relative to the Homunculus equatorial plane and conclude that our
data are broadly consistent with orbital inclinations in the range i=40 to 60
degrees.Comment: 18 pages, 15 figures, accepted for publication in A&A;
high-resolution PDF version available also at
http://www.mpifr.de/staff/jgroh/etacar.htm
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Semantic fluency in deaf children who use spoken and signed language, in comparison to hearing peers
Background
Deafness has an adverse impact on childrenâs ability to acquire spoken languages. Signed languages offer a more accessible input for deaf children, but because the vast majority are born to hearing parents who do not sign, their early exposure to sign language is limited. Deaf children as a whole are therefore at high risk of language delays.
Aims
We compared deaf and hearing childrenâs performance on a semantic fluency task. Optimal performance on this task requires a systematic search of the mental lexicon, the retrieval of words within a subcategory, and, when that subcategory is exhausted, switching to a new subcategory. We compared retrieval patterns between groups, and also compared the responses of deaf children who used British Sign Language (BSL) to those who used spoken English. We investigated how semantic fluency performance related to childrenâs expressive vocabulary and executive function skills, and also re-tested semantic fluency in the majority of the children nearly two years later, in order to investigate how much progress they had made in that time.
Methods and procedures
Participants were deaf children aged 6-11 years (N=106, comprising 69 users of spoken English, 29 users of BSL and 8 users of Sign Supported English) compared to hearing children (N=120) of the same age who used spoken English. Semantic fluency was tested for the category âanimalsâ. We coded for errors, clusters (e.g., âpetsâ, âfarm animalsâ) and switches. Participants also completed the Expressive One-Word Picture Vocabulary Test and a battery of six non-verbal executive function tasks. In addition, we collected follow-up semantic fluency data for 70 deaf and 74 hearing children, nearly 2 years after they were first tested.
Outcomes and results
Deaf children, whether using spoken or signed language, produced fewer items in the semantic fluency task than hearing children, but they showed similar patterns of responses for items most commonly produced, clustering of items into subcategories and switching between subcategories. Both vocabulary and executive function scores predicted the number of correct items produced. Follow-up data from deaf participants showed continuing delays relative to hearing children two years later.
Conclusions and implications
We conclude that semantic fluency can be used experimentally to investigate lexical organisation in deaf children, and that it potentially has clinical utility across the heterogeneous deaf population. We present normative data to aid clinicians who wish to use this task with deaf children
Polychromatic solitons in a quadratic medium
We introduce the simplest model to describe parametric interactions in a
quadratically nonlinear optical medium with the fundamental harmonic containing
two components with (slightly) different carrier frequencies [which is a direct
analog of wavelength-division multiplexed (WDM) models, well known in media
with cubic nonlinearity]. The model takes a closed form with three different
second-harmonic components, and it is formulated in the spatial domain. We
demonstrate that the model supports both polychromatic solitons (PCSs), with
all the components present in them, and two types of mutually orthogonal simple
solitons, both types being stable in a broad parametric region. An essential
peculiarity of PCS is that its power is much smaller than that of a simple
(usual) soliton (taken at the same values of control parameters), which may be
an advantage for experimental generation of PCSs. Collisions between the
orthogonal simple solitons are simulated in detail, leading to the conclusion
that the collisions are strongly inelastic, converting the simple solitons into
polychromatic ones, and generating one or two additional PCSs. A collision
velocity at which the inelastic effects are strongest is identified, and it is
demonstrated that the collision may be used as a basis to design a simple
all-optical XOR logic gate.Comment: 9 pages, 8 figures, accepted to Phys. Rev.
Precession and Nutation in the eta Carinae binary system: Evidences from the X-ray light curve
It is believed that eta Carinae is actually a massive binary system, with the
wind-wind interaction responsible for the strong X-ray emission. Although the
overall shape of the X-ray light curve can be explained by the high
eccentricity of the binary orbit, other features like the asymmetry near
periastron passage and the short quasi-periodic oscillations seen at those
epochs, have not yet been accounted for. In this paper we explain these
features assuming that the rotation axis of eta Carinae is not perpendicular to
the orbital plane of the binary system. As a consequence, the companion star
will face eta Carinae on the orbital plane at different latitudes for different
orbital phases and, since both the mass loss rate and the wind velocity are
latitude dependent, they would produce the observed asymmetries in the X-ray
flux. We were able to reproduce the main features of the X-ray light curve
assuming that the rotation axis of eta Carinae forms an angle of 29 degrees
with the axis of the binary orbit. We also explained the short quasi-periodic
oscillations by assuming nutation of the rotation axis, with amplitude of about
5 degrees and period of about 22 days. The nutation parameters, as well as the
precession of the apsis, with a period of about 274 years, are consistent with
what is expected from the torques induced by the companion star.Comment: 9 pages, 8 figures, MNRAS accepte
The first X-ray survey of Galactic Luminous Blue Variables
Aims: The X-ray emission of massive stars has been studied when these objects
are in their main-sequence phase, as well as in their Wolf-Rayet phase.
However, the X-ray properties of the transitional Luminous Blue Variable (LBV)
phase remain unknown. Methods: Using a dedicated but limited XMM survey as well
as archival XMM and Chandra observations, we performed the first X-ray survey
of LBVs: about half of the known LBVs or candidate LBVs are studied. Results:
Apart from the well known X-ray sources eta Car and Cyg OB2 #12, four
additional LBVs are detected in this survey, though some doubt remains on the
association with the X-ray source for two of these. For the other LBVs, upper
limits on the flux were derived, down to for
PCyg. This variety in the strength of the X-ray emission is discussed, with
particular emphasis on the potential influence of binarity.Comment: 13 pages, 2 figures, accepted by A&
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