ChemistryStats

This is an extension module design to perform chemistry statistics on GEAR outputs.

General concepts

The goal of the module is to trace the succession of chemical events (supernova explosions) that lead to the chemical properties (abundances of atomic elements) of a stellar particle.

Quick destription of GEAR

Storage of chemical informations

In GEAR, a gas particle (i) store its chemical properties in two variables (arrays) : Metal (SphP[i].Metal) and MetalNS (SphP[i].MetalNS). Both variable have a dimension NELEMENTS where NELEMENTS is the number of atomic elements considered in the code.

Every time the ejecta of a star touches a gas particle, the ejecta are added in the MetalNS in the slot of the corresponding element. Thus, MetalNS contains the direct pollution of stars without any mixing process.

On the contrary, the Metal variable is obtained by convolving the values stored in MetalNS of nearby neighbouring particles. It is a smoothed variable. This convolution is performed at every time a gas particle is active (i.e, at every of its timestep).

\[\texttt{SphP[i].Metal[k]} = \frac{1}{\rho_i}\,\Sigma_j{w_{ij}\,m_j\,\texttt{SphP[j].MetalNS[k]}}\]

Weights

We define the weight \(\alpha_{ij}\) as:

\[\alpha_{ij} = \frac{w_{ij}\,m_j}{\rho_i}\]

We define \(\alpha_{Z,ij}\) as:

\[\alpha_{Z,ij} = \frac{Z_j\,w_{ij}\,m_j}{\rho_i}\]

Note that in the code : \(Z_j=\texttt{SphP[j].MetalNS[METALS]}\).

Snapshots

Booth Metal and MetalNS may be saved in hdf5 snapshots for gas particle only. For stellar particles only the variable Metal is stored for the moment.

Star formation

In GEAR, a star particle forms out of a gas particle and inherit its chemical properties stored in the array Metal, i.e., the abundances that have been smoothed.

chimie log files

Three types of chimie log files are generated:

chimie.txt_Gas.* : These log files record every time any gas particle receive ejecta from a stellar particle. It contains the time of the event, the ID of both the gas and the stellar particle and the mass of each ejecta. The ejecta are provided by the variable MetalNS and thus, they are not smoothed.

chimie.txt_SNs.* : These log files record every time a stellar particle generate one or several supernova explosion. It provides the time, the ID of the stellar particle its mass, the number of SNIa and SNII exploded and their mean mass 1.

chimie.txt_Star.* : These log files record every time a stellar particle is formed. It records the time when the particle is formed, the ID of the stellar particle and its mass, the ID of the progenitor gas particle and its mass, and a list of all gas particles that contributed the most to the last metals mixing event, i.e., that contributed to SphP[i].Metal through the convolution defined above. In this list, we provide the ID, the weight of the contribution both in term of mass (\(\alpha_{ij}\)) and metals (\(\alpha_{Z,ij}\)), and the mass of the particle. The list is limited to the contributors with the largest \(\alpha_{Z,ij}\).

The information stored in those files is thus always obtained via the MetalNS. This ensure to get an access to un-mixed abundances, allowing to trace the direct pollution (no mixing/smoothing) of gas by stars.

GEAR flags (compilation options)

Both CHIMIE_STATS and CHIMIE_KEEP_TRACE_OF_LAST_SMOOTH_METALS must be enabled.

Tracing the chemical history of one stellar particle

To trace the chemical history of one stellar particle, we first have to find its progenitor gas particle. The progenitor gas particle contains chemical information that results from a smooth metallicity mixing. The GEAR log files stores the IDs of the gas particles that contributed to the last mixing this particle suffers, before forming the stars. Knowing each of these gas particles we can then follow each of them individually and retrieve each chemical event that contributed to the enrichment of these gas particles. We record the information in term of mass and metallicity of the progenitor stars that exploded as a supernova, but also the time of the explosion and the mass of each element that the gas particle received.

ChemistryStats data structure

In the ChemistryStats module, data from the chimie.txt_Gas.* and chimie.txt_Star.* files are stored in dictionaries data_Gas and data_Star.

data_Gas

The dictionary keys are IS of gas particles found in the logs. Each key is linked to another dictionary with each entry corresponding to an event, i.e., a time in the simulation when the gas particle received ejecta from a stellar particle.

data_Gas[ID]["TimeStep"]	Timestep of the event
data_Gas[ID]["Time"]	Simulation time of the event
data_Gas[ID]["IDStar"]	ID of the stellar particle at the origin of the event
data_Gas[ID]["StarMeanMass"]	mean of the SNe progenitor star
data_Gas[ID]["StarFeH"]	[Fe/H] of the SNe progenitor star
data_Gas[ID]["aij"]	fraction of the ejecta of the stellar particle received by the gas particle
data_Gas[ID]["Mass_0"]	mass of the particle before receiving the ejecta
data_Gas[ID]["Fe_0"]	Fe mass of the particle before receiving the ejecta
data_Gas[ID]["Mg_0"]	Mg mass of the particle before receiving the ejecta
data_Gas[ID]["Mass_1"]	mass of the particle after receiving the ejecta
data_Gas[ID]["Fe_1"]	Fe mass of the particle after receiving the ejecta
data_Gas[ID]["Mg_1"]	Mg mass of the particle after receiving the ejecta

Note that only Fe and Mg are considered for the moment. Other elements can be easily added.

data_Star

The dictionary keys are IS of all the stellar particles found. Each key is linked to another dictionary with the following entries:

data_Star[ID]["TimeStep"]	timestep of formation time of the stellar particle
data_Star[ID]["Time"]	formation time of the stellar particle
data_Star[ID]["IDprog"]	ID of the progenitor gas particle
data_Star[ID]["flagToStar"]	flag indicating if a the gas particle as turned into a stellar particle or not
data_Star[ID]["IDs"]	the list of ID of gas particles that contributed to the smooting of the progenitor gas particle
data_Star[ID]["aij"]	the list of corresponding weights (\(\alpha_{ij}\))
data_Star[ID]["Zaij"]	the list of corresponding Z weights (\(\alpha_{Z,ij}\))
data_Star[ID]["mass"]	the list of masses

Examples of available python scripts

Convert GEAR log files stored in snap into the chemistrystats.pkl pickle file:

chemistryStats2pickle ./snap -o chemistrystats.pkl

Get the enrichment history of the stellar particle with ID 1984264:

chemistryStats_getStarEnrichment chemistrystats.pkl --ID 1984264

Plot the distribution of the number of SNe that contributed to the chemical enrichment of stellar particles:

chemistryStats_getStarsDistribution chemistrystats.pkl --xmin 1 --xmax 100

Plot the distribution of the number of SNe that contributed to the chemical enrichment of stellar particles excluding SNe that contributed through the smoothed metallicity:

chemistryStats_getStarsDistribution chemistrystats.pkl --xmin 1 --xmax 100 --NoSmooth

Plot the number of SNe a stellar particle has been enriched from, as a function of [Fe/H] vs [Mg/Fe]:

chemistryStats_getStarsDistribution_FevsMgFe chemistrystats.pkl  snap/snapshot_0200.hdf5 --xmin -6 --xmax 0.5 --ymin -1 --ymax 1.5

The same but considering only progenitor stars more massive than 140 solar masses:

chemistryStats_getStarsDistribution_FevsMgFe chemistrystats.pkl  snap/snapshot_0200.hdf5 --xmin -6 --xmax 0.5 --ymin -1 --ymax 1.5 --minMass 140

The same but considering only direct pollution and not pollution via smoothing:

chemistryStats_getStarsDistribution_FevsMgFe chemistrystats.pkl  snap/snapshot_0200.hdf5 --xmin -6 --xmax 0.5 --ymin -1 --ymax 1.5 --NoSmooth

Footnotes

1

The mean mass is defined as 0.5*(Mmax+Mmin) where Mmax is the mass of the star exploding just at the beginning of one timestep (the one with the shortest lifetime for this timestep) and Mmin is the mass of the star exploding just at the end of the timestep (the one with the largest lifetime for this timestep). For technical reason, we assume that all masses formed during the timestep have this mean mass. As the timesteps are very small, Mmin and Mmax are very similar.