#format wiki
#language en
#acl ValdTeamGroup:read,write,delete All:read
= Stellar model atmospheres =

An ''Extract Stellar'' request computes line strengths in a model atmosphere,
and the request has to name one. The form offers two grids and an upload:

 * '''ATLAS9 (Castelli & Kurucz)''' - the default
 * '''MARCS'''
 * '''Upload own model atmosphere...''' - your own `.krz` file

This page describes which models each choice can actually reach, since neither
grid fills the Teff x log g box its endpoints suggest.

<<TableOfContents(2)>>

== What each choice resolves to ==

Both grids live in `$VALD_HOME/MODELS/STELLAR`, which holds far more than the
two families below: seven Castelli/ATLAS9 metallicity families (`am20` `am15`
`am10` `am05` `ap00` `ap02` `ap05`) and some 2400 MARCS models over ten
metallicities and four alpha/CNO patterns. A grid choice maps to exactly '''one'''
metallicity family. Were a choice to span several, the metallicity of the
atmosphere you got would depend on filename sort order.

||'''Choice'''||'''Filenames used'''||'''Composition'''||'''Nodes'''||
||ATLAS9||`castelli_ap00k2_T<Teff>G<10 log g>.krz`||[M/H] = 0.0 (`ap00`), microturbulence 2 km/s (`k2`)||476||
||MARCS||`p<Teff>_g<log g>_m0.0_t01_st_z+0.00_a+0.00_c+0.00_n+0.00_o+0.00_r+0.00_s+0.00.krz`||z, alpha, C, N, O, r and s all +0.00; microturbulence 1 km/s (`t01`)||173||

Note the two different conventions for log g in the filename: ATLAS9 writes
10 x log g as two digits (`G45` = 4.5), MARCS writes a signed decimal (`g+4.5`).

The MARCS models offered here are the '''plane-parallel''' ones (the `p` prefix).
The line selection cannot use a spherical model: an uploaded MARCS model with
`MODEL TYPE= 3` in its header is rejected, and must be converted to
plane-parallel geometry first.

== You always get a model, even outside the grid ==

A request whose Teff and log g fall outside the grid - or between its nodes - is
'''not''' an error. The nearest node is used instead, by the distance

{{{
    dist = |dTeff| + 100 x |d(10 log g)|
}}}

so 0.1 dex in log g weighs the same as 100 K in Teff, and Teff is followed in
preference to gravity. Nothing in the result file announces this. The model that
was actually used is shown as '''Model atmosphere''' on the request's own status
page - worth a glance whenever the parameters sit near an edge of the coverage
below.

The nodes of the other grid are never considered: they are named by a pattern
this grid does not recognise, so a MARCS request can never be answered with an
ATLAS9 atmosphere merely because it lies nearer in Teff.

== Coverage ==

'''●''' a model is present, '''○''' the combination does not exist.

=== ATLAS9 (Castelli & Kurucz), [M/H] = 0.0 ===

476 models: Teff 3500-50000 K at 76 values (250 K apart up to 13000 K,
1000 K apart above it) x log g 0.0-5.0 in steps of 0.5. That is 57% of the
76 x 11 box: the grid is a staircase, because low gravities are not
computed for hot models. Above 40000 K only log g >= 4.5 exists, and at
50000 K only log g = 5.0.

||'''Teff ↓ / log g →'''||'''0.0'''||'''0.5'''||'''1.0'''||'''1.5'''||'''2.0'''||'''2.5'''||'''3.0'''||'''3.5'''||'''4.0'''||'''4.5'''||'''5.0'''||
||'''3500'''||●||●||●||●||●||●||●||●||●||●||●||
||'''3750'''||●||●||●||●||●||●||●||●||●||●||●||
||'''4000'''||●||●||●||●||●||●||●||●||●||●||●||
||'''4250'''||●||●||●||●||●||●||●||●||●||●||●||
||'''4500'''||●||●||●||●||●||●||●||●||●||●||●||
||'''4750'''||●||●||●||●||●||●||●||●||●||●||●||
||'''5000'''||●||●||●||●||●||●||●||●||●||●||●||
||'''5250'''||●||●||●||●||●||●||●||●||●||●||●||
||'''5500'''||●||●||●||●||●||●||●||●||●||●||●||
||'''5750'''||●||●||●||●||●||●||●||●||●||●||●||
||'''6000'''||●||●||●||●||●||●||●||●||●||●||●||
||'''6250'''||○||●||●||●||●||●||●||●||●||●||●||
||'''6500'''||○||●||●||●||●||●||●||●||●||●||●||
||'''6750'''||○||●||●||●||●||●||●||●||●||●||●||
||'''7000'''||○||●||●||●||●||●||●||●||●||●||●||
||'''7250'''||○||●||●||●||●||●||●||●||●||●||●||
||'''7500'''||○||●||●||●||●||●||●||●||●||●||●||
||'''7750'''||○||○||●||●||●||●||●||●||●||●||●||
||'''8000'''||○||○||●||●||●||●||●||●||●||●||●||
||'''8250'''||○||○||●||●||●||●||●||●||●||●||●||
||'''8500'''||○||○||○||●||●||●||●||●||●||●||●||
||'''8750'''||○||○||○||●||●||●||●||●||●||●||●||
||'''9000'''||○||○||○||●||●||●||●||●||●||●||●||
||'''9250'''||○||○||○||○||●||●||●||●||●||●||●||
||'''9500'''||○||○||○||○||●||●||●||●||●||●||●||
||'''9750'''||○||○||○||○||●||●||●||●||●||●||●||
||'''10000'''||○||○||○||○||●||●||●||●||●||●||●||
||'''10250'''||○||○||○||○||●||●||●||●||●||●||●||
||'''10500'''||○||○||○||○||●||●||●||●||●||●||●||
||'''10750'''||○||○||○||○||●||●||●||●||●||●||●||
||'''11000'''||○||○||○||○||●||●||●||●||●||●||●||
||'''11250'''||○||○||○||○||●||●||●||●||●||●||●||
||'''11500'''||○||○||○||○||●||●||●||●||●||●||●||
||'''11750'''||○||○||○||○||●||●||●||●||●||●||●||
||'''12000'''||○||○||○||○||○||●||●||●||●||●||●||
||'''12250'''||○||○||○||○||○||●||●||●||●||●||●||
||'''12500'''||○||○||○||○||○||●||●||●||●||●||●||
||'''12750'''||○||○||○||○||○||●||●||●||●||●||●||
||'''13000'''||○||○||○||○||○||●||●||●||●||●||●||
||'''14000'''||○||○||○||○||●||●||●||●||●||●||●||
||'''15000'''||○||○||○||○||○||●||●||●||●||●||●||
||'''16000'''||○||○||○||○||○||●||●||●||●||●||●||
||'''17000'''||○||○||○||○||○||●||●||●||●||●||●||
||'''18000'''||○||○||○||○||○||●||●||●||●||●||●||
||'''19000'''||○||○||○||○||○||●||●||●||●||●||●||
||'''20000'''||○||○||○||○||○||○||●||●||●||●||●||
||'''21000'''||○||○||○||○||○||○||●||●||●||●||●||
||'''22000'''||○||○||○||○||○||○||●||●||●||●||●||
||'''23000'''||○||○||○||○||○||○||●||●||●||●||●||
||'''24000'''||○||○||○||○||○||○||●||●||●||●||●||
||'''25000'''||○||○||○||○||○||○||●||●||●||●||●||
||'''26000'''||○||○||○||○||○||○||●||●||●||●||●||
||'''27000'''||○||○||○||○||○||○||○||●||●||●||●||
||'''28000'''||○||○||○||○||○||○||○||●||●||●||●||
||'''29000'''||○||○||○||○||○||○||○||●||●||●||●||
||'''30000'''||○||○||○||○||○||○||○||●||●||●||●||
||'''31000'''||○||○||○||○||○||○||○||●||●||●||●||
||'''32000'''||○||○||○||○||○||○||○||○||●||●||●||
||'''33000'''||○||○||○||○||○||○||○||○||●||●||●||
||'''34000'''||○||○||○||○||○||○||○||○||●||●||●||
||'''35000'''||○||○||○||○||○||○||○||○||●||●||●||
||'''36000'''||○||○||○||○||○||○||○||○||●||●||●||
||'''37000'''||○||○||○||○||○||○||○||○||●||●||●||
||'''38000'''||○||○||○||○||○||○||○||○||●||●||●||
||'''39000'''||○||○||○||○||○||○||○||○||●||●||●||
||'''40000'''||○||○||○||○||○||○||○||○||○||●||●||
||'''41000'''||○||○||○||○||○||○||○||○||○||●||●||
||'''42000'''||○||○||○||○||○||○||○||○||○||●||●||
||'''43000'''||○||○||○||○||○||○||○||○||○||●||●||
||'''44000'''||○||○||○||○||○||○||○||○||○||●||●||
||'''45000'''||○||○||○||○||○||○||○||○||○||●||●||
||'''46000'''||○||○||○||○||○||○||○||○||○||●||●||
||'''47000'''||○||○||○||○||○||○||○||○||○||●||●||
||'''48000'''||○||○||○||○||○||○||○||○||○||●||●||
||'''49000'''||○||○||○||○||○||○||○||○||○||●||●||
||'''50000'''||○||○||○||○||○||○||○||○||○||○||●||

=== MARCS, plane-parallel, z+0.00 ===

173 models: Teff 2500-8000 K (100 K steps to 4000 K, 250 K above it)
x log g 3.0-5.5. 90% filled - much closer to a full box than ATLAS9,
but note that it starts at log g 3.0, so '''MARCS has no giants''' here, and that
log g 5.5 exists only for the coolest dwarfs.

||'''Teff ↓ / log g →'''||'''3.0'''||'''3.5'''||'''4.0'''||'''4.5'''||'''5.0'''||'''5.5'''||
||'''2500'''||●||●||●||●||●||●||
||'''2600'''||●||●||●||●||●||●||
||'''2700'''||●||●||●||●||●||●||
||'''2800'''||●||●||●||●||●||●||
||'''2900'''||●||●||●||●||●||●||
||'''3000'''||●||●||●||●||●||●||
||'''3100'''||●||●||●||●||●||●||
||'''3200'''||●||●||●||●||●||●||
||'''3300'''||●||●||●||●||●||●||
||'''3400'''||●||●||●||●||●||●||
||'''3500'''||●||●||●||●||●||●||
||'''3600'''||●||●||●||●||●||●||
||'''3700'''||●||●||●||●||●||●||
||'''3800'''||●||●||●||●||●||●||
||'''3900'''||●||●||●||●||●||●||
||'''4000'''||●||●||●||●||●||○||
||'''4250'''||●||●||●||●||●||○||
||'''4500'''||●||●||●||●||●||○||
||'''4750'''||●||●||●||●||●||○||
||'''5000'''||●||●||●||●||●||○||
||'''5250'''||●||●||●||●||●||○||
||'''5500'''||●||●||●||●||●||○||
||'''5750'''||●||●||●||●||●||○||
||'''6000'''||●||●||●||●||●||○||
||'''6250'''||●||●||●||●||●||○||
||'''6500'''||●||●||●||●||●||○||
||'''6750'''||●||●||●||●||●||○||
||'''7000'''||●||●||●||●||●||○||
||'''7250'''||●||●||●||●||●||○||
||'''7500'''||●||●||●||●||●||○||
||'''7750'''||●||●||●||○||●||○||
||'''8000'''||○||●||●||●||●||○||

== Choosing between them ==

 * '''Teff above 8000 K''': ATLAS9 is the only choice. MARCS stops at 8000 K.
 * '''Giants and supergiants''' (log g < 3.0): ATLAS9 only.
 * '''Cool dwarfs below 3500 K''': MARCS only, which reaches down to 2500 K.
 * '''Where both apply''' (roughly 3500-8000 K, log g 3.0-5.0), the grids differ in
   physics, not just in sampling: MARCS uses a more complete treatment of
   molecular opacity, which matters most for the coolest stars. The two also
   differ in microturbulence, 2 km/s for this ATLAS9 family against 1 km/s for
   MARCS.
 * Anything else - a different metallicity, a different microturbulence, a
   spherical or interpolated model - has to be uploaded as a `.krz` file.

== Uploading your own model atmosphere ==

Choosing ''Upload own model atmosphere...'' on the stellar form replaces the
grid entirely: the file you send is the atmosphere the line selection runs in,
and the Teff and log g shown on the request are read out of its header rather
than taken from the form. Use it for a metallicity, a microturbulence or an
interpolated node the two grids above do not have.

The file must be in '''krz''' format - the condensed Kurucz-style model
`select5` reads. The format is documented at
[[https://marcs.astro.uu.se/docs.html#krzform|marcs.astro.uu.se/docs.html]], and
every file in the VALD grid is an example of it.

=== Layout ===

||'''Line'''||'''Contents'''||
||1||A title. Free text, not interpreted.||
||2||The parameter line: `T EFF=`, `GRAV`, `MODEL TYPE=`, `WLSTD=`.||
||3||20 continuous-opacity switches, Kurucz convention, whole numbers.||
||4-13||99 abundances, then the number of depth points as the 100th number.||
||rest||One row per depth point: RHOX, T, XNE, XNA, RHO.||

The head of a grid model, which is the shape to copy:

{{{
TITLE  [0.0] VTURB=2  L/H=1.25 NOVER NEW ODF
T EFF= 5750. GRAV= 4.5  MODEL TYPE= 0 WLSTD= 5000.
 1 1 1 1 1 1 1 1 1 1 1 1 1 0 1 0 0 0 0 0 - Opacity switches
  0.920  -1.11 -10.94 -10.64  -9.49  -3.52  -4.12  -3.21  -7.48  -3.96
  ... eight more lines of ten ...
 -20.00 -12.54 -20.00 -20.00 -20.00 -20.00 -20.00 -20.00 -20.00 72
 5.561746900E-04,   3628.5, 2.86500E+09, 3.51119E+13, 7.35900E-11,
}}}

The last number of the abundance block (`72` above) is the depth-point count,
not an abundance. Abundances and that count are a single list-directed read, so
they may be spread over any number of lines; the grid files use ten lines of ten.

=== Rules that are easy to break ===

 * '''`MODEL TYPE=` must be 0.''' Type 3 is spherical, and the line selection
   cannot use a spherical atmosphere. Most of the MARCS grid is spherical and
   has to be converted to plane-parallel geometry first. A spherical file also
   carries a sixth column, the height above the reference radius, which is not
   read here.
 * '''The four keywords must appear in the order above''', and within the first
   256 characters of line 2. Each value is taken as the text between one keyword
   and the next rather than looked up by name, so a keyword out of order
   silently scrambles all four values. (`GRAV` is listed without its `=` because
   that is the bare word the reader searches for.)
 * '''Abundances are number fractions, not the A(X)=12 dex scale.''' A value at
   or above zero is used as N_atom/N_all; a negative value is read as its log10.
   Both conventions appear in real files - a MARCS model writes helium as 0.078,
   an ATLAS9 model writes -1.110, and those are the same abundance. But an
   abundance table on the dex scale, where iron is 7.50, is not rejected by the
   Fortran: it is read as a number fraction of 7.5 and the result is quietly
   wrong. If your file is on that scale, subtract 12.04 from every value. The
   upload check refuses any value above 1 for exactly this reason.
 * '''Use -20.00, not 0.00, for an element you have no abundance for.''' The
   abundances are written back into the result header as log10, so an exact zero
   becomes -Infinity there. The grid models floor at -20.00.
 * '''Whole numbers must be written as whole numbers.''' The opacity switches,
   `MODEL TYPE=` and the depth-point count are read into Fortran INTEGERs, which
   refuse `0.` and `7.2E1` outright. That is an error there, not a rounding.
 * '''3 to 100 depth points.''' `select5` sizes its arrays for 100 and rejects
   more.
 * '''Plain text, at most 512 kB.''' A 100-layer model is about 12 kB.

=== What happens to the file ===

The upload is checked before the job starts, and a file that would not read is
refused with a message naming the line - the checks are deliberately no stricter
than the Fortran, so anything accepted here runs. The bytes are then stored and
run '''unchanged''' rather than rewritten into a canonical form, so the file that
produced a result is the file you sent.

The filename is kept too, reduced to letters, digits and `. _ + -` and truncated
to fit - `select5` holds the whole path in 120 characters. It is printed into the
result header and carried into every exported format, so it is worth sending a
name that says what the model is: `marcs_p5750_g45_m-0.5.krz` rather than
`model.krz`.