125 research outputs found
NLTE 1.5D Modeling of Red Giant Stars
Spectra for 2D stars in the 1.5D approximation are created from synthetic
spectra of 1D non-local thermodynamic equilibrium (NLTE) spherical model
atmospheres produced by the PHOENIX code. The 1.5D stars have the spatially
averaged Rayleigh-Jeans flux of a K3-4 III star, while varying the temperature
difference between the two 1D component models (),
and the relative surface area covered. Synthetic observable quantities from the
1.5D stars are fitted with quantities from NLTE and local thermodynamic
equilibrium (LTE) 1D models to assess the errors in inferred
values from assuming horizontal homogeneity and LTE. Five different quantities
are fit to determine the of the 1.5D stars: UBVRI
photometric colors, absolute surface flux SEDs, relative SEDs, continuum
normalized spectra, and TiO band profiles. In all cases except the TiO band
profiles, the inferred value increases with increasing
. In all cases, the inferred value
from fitting 1D LTE quantities is higher than from fitting 1D NLTE quantities
and is approximately constant as a function of
within each case. The difference between LTE and NLTE for the TiO bands is
caused indirectly by the NLTE temperature structure of the upper atmosphere, as
the bands are computed in LTE. We conclude that the difference between
values derived from NLTE and LTE modelling is relatively
insensitive to the degree of the horizontal inhomogeneity of the star being
modeled, and largely depends on the observable quantity being fit.Comment: 46 pages, 14 figures, 7 tables, accepted for publication in ApJ on
April 5, 201
The ChromaStar+ modelling suite and the VALD line list
We present Version 2023-02-04 (ISO) of the Chroma+ atmospheric, spectrum, and
transit light-curve modelling suite, which incorporates the VALD atomic line
list. This is a major improvement as the previous versions used the much
smaller NIST line list. The NIST line list is still available in Chroma+ for
those projects requiring speed over completeness of line opacity. We describe a
procedure for exploiting the ''Array job'' capability of the slurm workload
manager on multi-cpu machines to compute broadband high resolution spectra with
the VALD line list quickly using the Java version of the code (ChromaStarServer
(CSS)). The inclusion of a much larger line list more completely allows for the
many weaker lines that over-blanket the blue band in late-type stars and has
allowed us to reduce the amount of additional ad hoc continuous opacity needed
to fit the solar spectral energy distribution (SED). The additional line
opacity exposed a subtle bug in the spectrum synthesis procedure that was
causing residual blue line wing opacity to accumulate at shorter wavelengths.
We present our latest fits to the observed solar SED and to the observed
rectified high resolution visible band spectra of the Sun and the standard
stars Arcturus and Vega. We also introduce the fully automated Burke-Gaffney
Observatory (BGO) at Saint Mary's University (SMU) and compare our synthetic
spectra to low resolution spectra obtained with our grism spectrograph that is
available to students. The fully automated BGO, the spectrograph, and the BGO
spectrum reduction procedure are fully described in a companion paper. All
codes are available from the OpenStars www site: www.ap.smu.ca/OpenStars.Comment: 26 pages, 13 figure
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