Differences between revisions 1 and 5 (spanning 4 versions)

Stellar model atmospheres

An Extract Stellar request needs a model atmosphere. The request form offers two grids of solar-metallicity models, or you can upload your own.

Contents

Stellar model atmospheres

The two grids

ATLAS9 (default): 476 models, Teff 3500-50000 K, log g 0.0-5.0, [M/H] = 0.0, microturbulence 2 km/s. These are the Castelli & Kurucz grid with new opacity distribution functions, from kurucz.harvard.edu/grids.html.

Castelli, F. & Kurucz, R. L. 2003, IAU Symp. 210, Modelling of Stellar Atmospheres, poster A20 - ADS

MARCS: 173 plane-parallel models, Teff 2500-8000 K, log g 3.0-5.5, standard composition with [M/H] = 0.0, microturbulence 1 km/s, from marcs.astro.uu.se.

Gustafsson, B., Edvardsson, B., Eriksson, K. et al. 2008, A&A 486, 951 - ADS

Which model you get

VALD does not interpolate. It uses the grid model nearest to the requested Teff and log g, where 100 K in Teff counts the same as 0.1 dex in log g. A request outside the grid, or in one of its gaps, is therefore not rejected but answered with the nearest edge model. The model actually used is shown as Model atmosphere on the request's status page; check it if your parameters are near the edge of the coverage below.

ATLAS9 coverage

● model present, ○ not in the grid. Low gravities are missing for hot models.

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 coverage

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	○	●	●	●	●	○

In short: use ATLAS9 above 8000 K and for giants (log g < 3.0), MARCS below 3500 K. Where both grids apply, MARCS has the more complete molecular opacities, which matters most for cool stars.

Uploading your own model

For any other metallicity, microturbulence or an interpolated model, choose Upload own model atmosphere... on the form. The file must be in krz format, described at marcs.astro.uu.se/docs.html, and must be plane-parallel (MODEL TYPE= 0); spherical models are rejected. Teff and log g are then taken from the file header. The file name appears in the output header, so a descriptive one (e.g. marcs_p5750_g45_m-0.5.krz) helps.

-  ⇤ ← Revision 1 as of 2026-09-15 10:04:56 → 
  Size: 11325
  Editor: ThomasMarquart
  Comment: ATLAS9/MARCS coverage
+   ← Revision 5 as of 2026-09-23 18:17:43 → ⇥
  Size: 9622
  Editor: ThomasMarquart
  Comment: Restore full coverage grids
-Deletions are marked like this.
+Additions are marked like this.
 Line 6:
-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.
+An ''Extract Stellar'' request needs a model atmosphere. The request form offers
two grids of solar-metallicity models, or you can upload your own.
-Line 18:
+Line 11:
-== What each choice resolves to ==
+== The two grids ==
-Line 20:
+Line 13:
-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.
+'''ATLAS9''' (default): 476 models, Teff 3500-50000 K, log g 0.0-5.0,
[M/H] = 0.0, microturbulence 2 km/s. These are the Castelli & Kurucz grid with new
opacity distribution functions, from
[[http://kurucz.harvard.edu/grids.html|kurucz.harvard.edu/grids.html]].
-Line 27:
+Line 18:
-||'''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||
+ . Castelli, F. & Kurucz, R. L. 2003, IAU Symp. 210, ''Modelling of Stellar Atmospheres'', poster A20 -
 [[https://ui.adsabs.harvard.edu/abs/2003IAUS..210P.A20C/abstract|ADS]]
-Line 31:
+Line 21:
-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`).
+'''MARCS''': 173 plane-parallel models, Teff 2500-8000 K, log g 3.0-5.5,
standard composition with [M/H] = 0.0, microturbulence 1 km/s, from
[[https://marcs.astro.uu.se|marcs.astro.uu.se]].
-Line 34:
+Line 25:
-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.
+ . Gustafsson, B., Edvardsson, B., Eriksson, K. et al. 2008, A&A 486, 951 -
 [[https://ui.adsabs.harvard.edu/abs/2008A&A...486..951G/abstract|ADS]]
-Line 39:
+Line 28:
-== You always get a model, even outside the grid ==
+== Which model you get ==
-Line 41:
+Line 30:
-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
+VALD does not interpolate. It uses the grid model nearest to the requested Teff
and log g, where 100 K in Teff counts the same as 0.1 dex in log g. A request
outside the grid, or in one of its gaps, is therefore not rejected but answered
with the nearest edge model. The model actually used is shown as
'''Model atmosphere''' on the request's status page; check it if your parameters
are near the edge of the coverage below.
-Line 44:
+Line 37:
-{{{
    dist = |dTeff| + 100 x |d(10 log g)|
}}}
+=== ATLAS9 coverage ===
-Line 48:
+Line 39:
-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.
+'''●''' model present, '''○''' not in the grid. Low gravities are missing for
hot models.
-Line 148:
+Line 120:
-=== 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.
+=== MARCS coverage ===
-Line 189:
+Line 156:
-== Choosing between them ==
+In short: use ATLAS9 above 8000 K and for giants (log g < 3.0), MARCS below
3500 K. Where both grids apply, MARCS has the more complete molecular
opacities, which matters most for cool stars.
-Line 191:
+Line 160:
- * '''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 ==

For any other metallicity, microturbulence or an interpolated model, choose
''Upload own model atmosphere...'' on the form. The file must be in '''krz'''
format, described at
[[https://marcs.astro.uu.se/docs.html#krzform|marcs.astro.uu.se/docs.html]], and
must be '''plane-parallel''' (`MODEL TYPE= 0`); spherical models are rejected.
Teff and log g are then taken from the file header. The file name appears in the
output header, so a descriptive one (e.g. `marcs_p5750_g45_m-0.5.krz`) helps.