103 research outputs found
A Near-Infrared Template Derived from I Zw 1 for the FeII Emission in Active Galaxies
In AGN spectra, a series of FeII multiplets form a pseudo-continuum that
extends from the ultraviolet to the near-infrared (NIR). This emission is
believed to originate in the Broad Line Region (BLR), and it has been known for
a long time that pure photoionization fails to reproduce it in the most extreme
cases, as does the collisional-excitation alone. The most recent models by
Sigut & Pradhan (2003) include details of the FeII ion microphysics and cover a
wide range in ionization parameter log U_ion= (-3.0 -> -1.3) and density log
n_H = (9.6 -> 12.6). With the aid of such models and a spectral synthesis
approach, we study for the first time in detail the NIR emission of I Zw 1. The
main goals are to confirm the role played by Ly\alpha-fluorescence mechanisms
in the production of the FeII spectrum and to construct the first
semi-empirical NIR FeII template that best represents this emission and can be
used to subtract it in other sources. A good overall match between the observed
FeII+MgII features with those predicted by the best fitted model is obtained,
corroborating the Ly\alpha-fluorescence as a key process to understand the FeII
spectrum. The best model is then adjusted by applying a deconvolution method on
the observed FeII+MgII spectrum. The derived semi-empirical template is then
fitted to the spectrum of Ark 564, suitably reproducing its observed FeII+MgII
emission. Our approach extends the current set of available FeII templates into
the NIR region.Comment: 47 pages, 5 tables, 12 figures. Accepted for publication in The
Astrophysical Journa
Inclination Angles for Be Stars Determined Using Machine Learning
We test the viability of training machine learning algorithms with synthetic
H alpha line profiles to determine the inclination angles of Be stars (the
angle between the central B star's rotation axis and the observer's line of
sight) from a single observed medium-resolution, moderate S/N, spectrum. The
performance of three different machine learning algorithms were compared:
neural networks tasked with regression, neural networks tasked with
classification, and support vector regression. Of these three algorithms,
neural networks tasked with regression consistently outperformed the other
methods with a RMSE error of 7.6 degrees on an observational sample of 92
galactic Be stars with inclination angles known from direct H alpha profile
fitting, from the spectroscopic signature of gravitational darkening, and, in a
few cases, from interferometric observations that resolved the disk. The
trained neural networks enable a quick and useful determination of the
inclination angles of observed Be stars which can be used to search for
correlated spin axes in young open clusters or to extract an equatorial
rotation velocity from a measurement of v sin(i).Comment: 14 pages, 7 figure
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
- …