116 research outputs found
Be Star Disk Models in Consistent Vertical Hydrostatic Equilibrium
A popular model for the circumstellar disks of Be stars is that of a
geometrically thin disk with a density in the equatorial plane that drops as a
power law of distance from the star. It is usually assumed that the vertical
structure of such a disk (in the direction parallel to the stellar rotation
axis) is governed by the hydrostatic equilibrium set by the vertical component
of the star's gravitational acceleration. Previous radiative equilibrium models
for such disks have usually been computed assuming a fixed density structure.
This introduces an inconsistency as the gas density is not allowed to respond
to temperature changes and the resultant disk model is not in vertical,
hydrostatic equilibrium. In this work, we modify the {\sc bedisk} code of
\citet{sig07} so that it enforces a hydrostatic equilibrium consistent with the
temperature solution. We compare the disk densities, temperatures, H
line profiles, and near-IR excesses predicted by such models with those
computed from models with a fixed density structure. We find that the fixed
models can differ substantially from the consistent hydrostatic models when the
disk density is high enough that the circumstellar disk develops a cool
(K) equatorial region close to the parent star. Based on
these new hydrostatic disks, we also predict an approximate relation between
the (global) density-averaged disk temperature and the of the
central star, covering the full range of central Be star spectral types.Comment: 25 pages; 11 figure
Sign and speech share partially overlapping conceptual representations
Conceptual knowledge is fundamental to human cognition. Yet the extent to which it is influenced by language is unclear. Studies of semantic processing show that similar neural patterns are evoked by the same concepts presented in different modalities (e.g. spoken words and pictures or text) [1–3]. This suggests that conceptual representations are ‘modality independent’. However, an alternative possibility is that the similarity reflects retrieval of common spoken language representations. Indeed, in hearing spoken language users, text and spoken language are co-dependent [4,5] and pictures are encoded via visual and verbal routes [6]. A parallel approach investigating semantic cognition, shows that bilinguals activate similar patterns for the same words in their different languages [7,8]. This suggests that conceptual representations are ‘language independent’. However, this has only been tested in spoken language bilinguals. If different languages evoke different conceptual representations, this should be most apparent comparing languages that differ greatly in structure. Hearing people with signing deaf parents are bilingual in sign and speech: languages conveyed in different modalities. Here we test the influence of modality and bilingualism on conceptual representation by comparing semantic representations elicited by spoken British English and British Sign Language in hearing early, sign-speech bilinguals. We show that representations of semantic categories are shared for sign and speech, but not for individual spoken words and signs. This provides evidence for partially shared representations for sign and speech, and shows that language acts as a subtle filter through which we understand and interact with the world
Lyman Alpha Fluorescent Excitation of FeII in Active Galactic Nuclei
We have calculated FeII emission line strengths for Active Galactic Nuclei
Broad-Line Regions using precise radiative transfer and Iron Project atomic
data. We improve the treatment of all previously considered excitation
mechanisms for the FeII emission, continuum fluorescence, collisional
excitation, fluorescence by self-overlap among the iron lines, and fluorescent
excitation by Lyman-alpha. We demonstrate that Lyman-alpha fluorescence is of
fundamental importance in determining the strength of the FeII emission. In
addition to enhancing the ultraviolet and optical FeII flux, Lyman-alpha
fluorescence also results in significant near-infrared FeII emission in the
8500-9500 Angstrom wavelength range. New observations are suggested to probe
this effect in strong FeII emitting quasars.Comment: 12 pages, 2 encapsulated Postscript figures. To be Published in The
Astrophysical Journal Letter
Emission Lines in the Spectrum of the 3He Star 3 Cen A
Emission in the 4d - 4f transitions of MnII (multiplet 13, 6122-6132 Ang), in
the 4f - 6g transitions of PII, and in 6149.5 Ang of HgII has been detected in
the spectrum of the helium weak star 3 Centauri A (B5 III-IVp). Weaker emission
from the same MnII multiplet is also seen in the hot, mild HgMn star 46 Aquila
(B9 III).It is suggested that the emission is of photospheric origin and may be
evidence for the stratification of manganese, phosphorus and mercury in the
photosphere of 3 CenA, and of manganese in 46Aql.Comment: 16 pages, 3 figure
A Parameter Study of Classical Be Star Disk Models Constrained by Optical Interferometry
We have computed theoretical models of circumstellar disks for the classical
Be stars Dra, Psc, and Cyg. Models were constructed
using a non-LTE radiative transfer code developed by \citet{sig07} which
incorporates a number of improvements over previous treatments of the disk
thermal structure, including a realistic chemical composition. Our models are
constrained by direct comparison with long baseline optical interferometric
observations of the H emitting regions and by contemporaneous H
line profiles. Detailed comparisons of our predictions with H
interferometry and spectroscopy place very tight constraints on the density
distributions for these circumstellar disks.Comment: 10 figures,28 pages, accepted by Ap
The Thermal Structure of the Circumstellar Disk Surrounding the Classical Be Star gamma Cassiopeia
We have computed radiative equilibrium models for the gas in the
circumstellar envelope surrounding the hot, classical Be star Cassiopeia. This calculation is performed using a code that incorporates a
number of improvements over previous treatments of the disk's thermal structure
by \citet{mil98} and \citet{jon04}; most importantly, heating and cooling rates
are computed with atomic models for H, He, CNO, Mg, Si, Ca, & Fe and their
relevant ions. Thus, for the first time, the thermal structure of a Be disk is
computed for a gas with a solar chemical composition as opposed to assuming a
pure hydrogen envelope. We compare the predicted average disk temperature, the
total energy loss in H, and the near-IR excess with observations and
find that all can be accounted for by a disk that is in vertical hydrostatic
equilibrium with a density in the equatorial plane of to
. We also discuss the changes in
the disk's thermal structure that result from the additional heating and
cooling processes available to a gas with a solar chemical composition over
those available to a pure hydrogen plasma.Comment: 11 pages, 8 figures high resolution figures available at
http://inverse.astro.uwo.ca/sig_jon07.htm
Predicted FeII Emission-Line Strengths from Active Galactic Nuclei
We present theoretical FeII emission line strengths for physical conditions
typical of Active Galactic Nuclei with Broad-Line Regions. The FeII line
strengths were computed with a precise treatment of radiative transfer using
extensive and accurate atomic data from the Iron Project. Excitation mechanisms
for the FeII emission included continuum fluorescence, collisional excitation,
self-fluorescence amoung the FeII transitions, and fluorescent excitation by
Lyman-alpha and Lyman-beta. A large FeII atomic model consisting of 827 fine
structure levels (including states to E ~ 15 eV) was used to predict fluxes for
approximately 23,000 FeII transitions, covering most of the UV, optical, and IR
wavelengths of astrophysical interest. Spectral synthesis for wavelengths from
1600 Angstroms to 1.2 microns is presented. Applications of present theoretical
templates to the analysis of observations are described. In particular, we
discuss recent observations of near-IR FeII lines in the 8500 Angstrom -- 1
micron region which are predicted by the Lyman-alpha fluorescence mechanism. We
also compare our UV spectral synthesis with an empirical iron template for the
prototypical, narrow-line Seyfert galaxy I Zw 1. The theoretical FeII template
presented in this work should also applicable to a variety of objects with FeII
spectra formed under similar excitation conditions, such as supernovae and
symbiotic stars.Comment: 33 pages, 15 postscript figure
- …