Abundance#

sme.abund stores the elemental abundance pattern, while sme.monh stores the global metallicity offset.

In PySME, the abundance used in synthesis is:

A(X) = pattern(X) + monh

for elements heavier than He. Hydrogen and helium are not shifted by monh.

Recommended explicit abundance views#

PySME provides explicit abundance-scale views so you can choose which quantity you want to read or write:

sme.abund.A["Ti"]          # absolute abundance used in synthesis, H=12 scale
sme.abund.xh["Ti"]         # [Ti/H]
sme.abund.xm["Ti"]         # [Ti/M]_PySME = [Ti/H] - sme.monh
sme.abund.pattern["Ti"]    # current internal SME pattern before adding monh
sme.abund.reference["Ti"]  # fixed abundance reference pattern
sme.abund.solar["Ti"]      # alias to reference for built-in solar patterns

Here M in xm means PySME’s global metallicity parameter sme.monh, not a recomputed total metal mass fraction Z.

Legacy direct assignment#

Legacy direct assignment is still supported:

sme.abund["Ti"] = 5.105

but this is ambiguous because it writes the internal SME pattern, not the abundance used in synthesis. New code should prefer:

sme.abund.A["Ti"] = 3.909

or, if you intentionally want to set the internal pattern directly:

sme.abund.pattern["Ti"] = 5.105

Practical examples#

from pysme.abund import Abund

sme.abund = Abund(pattern="asplund2021", monh=-0.20)

1. Set a target absolute abundance used in synthesis#

If you want final A(Mg) = 7.40:

sme.abund.A["Mg"] = 7.40

2. Set a scaled-solar abundance offset relative to H#

If you want [Mg/H] = -0.15 relative to the reference pattern:

sme.abund.xh["Mg"] = -0.15

3. Set an element enhancement at fixed metallicity#

If you want [Mg/M]_PySME = +0.30 at the current monh:

sme.abund.xm["Mg"] = 0.30

For the common case where Fe follows monh, this is equivalent to the usual idea of [Mg/Fe]. PySME does not add a dedicated xfe view in this first API.

4. Work directly with the internal SME pattern#

If you want to inspect or set the underlying pattern before monh is applied:

current_pattern = dict(sme.abund.pattern)
sme.abund.pattern["Mg"] = 7.60

5. Inspect the fixed abundance reference#

The reference pattern remains fixed even after you modify the current pattern:

ref_ti = sme.abund.reference["Ti"]

If the abundance object was initialized from a built-in solar pattern, the same value is also available through:

sme.abund.solar["Ti"]

For custom user-provided abundance patterns, use reference instead of solar.

Abundance

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