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Subsections
To generate tables of Rosseland mean (RM) opacities the user should specify a few
input parameters,
namely: 1) the
grid of the state variables, and 2) the
chemical mixture.
Please refer to the original paper by
Marigo & Aringer (2009, A&A, 508, 1539)
for all the details.
Below one finds practical indications on how to proceed.
For a given chemical mixture, one RM opacity table is
arranged as a rectangular matrix of dimension
,
where

is the number of nodes of

is the number of nodes of
.
The lower and upper limits of
and
and their grid spacing should be defined.
The default values are given in Table 1.1.
parameter 
min value 
max value 
grid spacing (dex) 

3.2 
4.5 
0.01
for




0.05 for


8.0 
1.0 
0.50 for

The user can specify different limits of the state variables,
provided that
and
;
and
.
Also the grid spacing
,
,
can be
freely defined.
It is specified by the user in terms of the following quantities:
It can be chosen among various options, listed in Table 1. Click on the bibliograpghic reference to view
the corresponding compilation of the individual metal abundances and the total metallicity, both in mass fractions and in number fractions.
Table 1:
Compilations of the solar chemical composition

corresponds to the total abundance (in mass fraction) of metals, i.e. elements with
atomic number
, of the reference mixture (see Sect. 2.5).
It can be freely chosen as a nonnegative quantity,
.
It is expressed in mass fraction,
, and can be freely chosen in the interval
.
The user can define a sequence of increasing
values, starting from
up to
,
with a step
. This corresponds to compute a set of
opacity tables. To calculate one table, just set
.
The elemental abundances can be expressed either in mass fractions,
,
or in number fractions,
, according to:

(1) 
where
the number of elements,
is the number density of nuclei of type
with atomic mass
, and
is the
total number density of all atomic species (hydrogen, helium and metals).
In both cases the
normalization condition must hold, i.e.
and
.
The user should choose the preferred formalism,
and express the abundance variation factors of metals consistently
(see Sects 2.5 and 2.6).
For instance, if one wants to double the abundance of carbon with respects to its reference value,
it is necessary that ÆSOPUS knows whether the user's adopted abundance is in mass fraction, i.e.
or in number fraction,
.
For those ones interested in metalfree mixtures (with
), having a
primordial
chemical composition produced by the BigBang nucleosynthesis, it is possible to specify the
abundance
of lithium, expressed by the ratio Li/H.
The
default configuration assumes
as predicted by the standard BigBang nucleosynthesis in accordance with the
WMAP results (Coc et al. 2004).
2.6
Reference mixture
Please refer to Sects. 3.1 and 4.3 in
Marigo & Aringer (2009, A&A submitted)
for more details and applications to
enhanced mixtures.
By construction the reference mixture has a metallicity
, previously selected by the user.
The reference abundances of the metals,
or
are defined by the ratios (in dex):

(2) 
or

(3) 
which should be specified in the interactive mask. For each selected species the ratio can be set either
positive
(corresponding to
supersolar ratios), or
negative (corresponding to
subsolar ratios).
The
default configuration assumes
for all metals, i.e. the reference mixture
consists of
scaledsolar abundances.
Once specified the
ratios for the
selected elements, the user should decide
how the reference mixture is constructed in order to preserve the reference metallicity, namely:

Mixture
The total abundance variation of the
selected metals is balanced by the
abundance variation of
all other metals.

Mixture
The total abundance variation of the
selected metals is balanced by the
abundance variation of
irongroup elements.
Frequent applications of this setting section likely deal with
enhanced mixtures, i.e. with supersolar ratios
of
elements (O, Ne, Mg, Si, S, Ca, and Ti).
2.7
Additional chemical pattern
Finally, superimposed to the reference chemical mixture it is also possible to specify an additional chemical pattern,
defined by the
abundance enhancement/depression factor
or
of each metal species (heavier than helium),
with respect to its reference abundance.

(4) 
In the webmask the user should specify the decimal logarithm of the variation factors:
or
The
default configuration assumes
or
for all metals, i.e. the final mixture coincides with the reference mixture.
Where the variations factors of the
selected elements are set
(or
), then the actual metallicity
,
i.e. the enhancement/depression factors
of the selected elements
produce a net increase/depletion of total metal content
relative to the reference metallicity
.
In this case all
variation factors
can be freely specified without any additional constrain.
These optional settings should be of particular interest to researchers dealing with
the
atmospheres of TPAGB stars, as their C/O ratio,
as well as the absolute C, N, and O abundances, may be significantly altered by the occurrence
of the third dregdgeup and hotbottom burning.
For the three composition parameters, the user can define a few values (in dex),
each sequence corresponding to a grid of opacity tables.
For instance, let us suppose that the selected normalization of the abundances is in number fraction, then
one can choose the variation factors defined as:
Note that, by construction, the variation factors for O are given by
.
Filling in these fields will supersede
the variations factors for C, N, and O set in the previous mask
(see Sect. 2.6).
The maximum allowed numbers of values are:
;
;
ÆSOPUS computes RM opacity tables for
all combinations of
,
, and
.
It follows that the
total number of tables (for given
)
is
.
Pay attention that the resulting number of tables may become quite high!
Next: About this document ...
Up: Notes on the interactive
Previous: Notes on the interactive
Paola Marigo
20090626