MESA Binary Inputs Information

Below, you can find information about all the input parameters and outputs for MESA binary. MESA documentation can be found here; most of the information here can be found on the controls or binary controls pages.

In addition to the controls that we've given users the ability to modify, we've also included some additional controls in each simulation. They have largely been omitted from the list of controls users can modify because they are either relatively universal or allowing users to edit all of them would clutter the simulation inputs page. To list all of them here would be quite lengthy; you can find them in the inlists. If you wish to have any one added as a control, please contact us.

Basic Parameters

Mass of star

Initial mass of either star, in solar masses. Must be between [0.08, 100].

Metallicity of star

Initial metallicity of either star, expressed as a decimal fraction. Default is 0.012, or the metallicity of the sun. Must be between [0, 0.04].

Insert condition

MESA Binary works by first running individual simulations for each star with the above masses and metallicities to a given stopping condition, then inserting both stars into a binary simulation (this is done to allow for users to control the metallicities; running binary MESA simulations by default does not allow for this option). The default is to stop the individual evolution when the stars reach the ZAMS. When inserted into the binary simulation, they will be inserted with a distance equal to the orbital separation. Keep in mind a given combination of masses and metallicities may reach every condition. Stars given an unreachable stopping condition will never generate a final model, causing the binary simulation to fail, as there is no model to load into the binary evolution. Constraints exist to enforce limits on the insert conditions for a given mass, e.g., a 1 solar mass star will never reach carbon burning. The constraining conditions were taken from Dr. Siobahn Morgan's website and have been given significant wiggle room to account for other metallicities. However, there are certainly edge cases that went unaccounted for; if you encounter such, please contact us with the details of the simulation.

• PreMS - Before the main sequence. Defined as the point where the log10 of the center temperature is greater than 5.
• ZAMS - Zero age main sequence, or the point at which a star begins the main sequence. Defined as the point where
• IAMS - Intermediate age main sequence, defined as the point where the central h1 abundance is less than 0.3.
• TAMS - Terminal age main sequence, or the point at which a star ends the main sequence. Defined as the point where the central h1 abundance is less than1e-6
• He Burn - Helium burning. Defined as the point where the luminosity (in solar luminosities) from the triple alpha process exceeds 100.
• ZACHeB - Zero age helium core burning. Defined as the point where the central energy generation rate from the triple alpha rate exceeds 100erg/g/s.
• TACHeB - Terminal age helium core burning. Defined as the point where the central helium abundance is less than 0.0001.
• TP AGP - Thermally pulsating asymptotic giant branch. Defined as the point where central helium abundance is less than 0.0001, the mass of the helium shell is less than 0.1, and there is a convective region that is burning helium.

Orbital separation

Initial orbital separation of both stars, in days. Must be larger than 0.001, but large values may result in failure as stars are too far apart to interact. Also keep in mind that the simulation may fail if the initial orbital separation is too small.

Model star 2 as a point mass

Models star 2 as an un-evolving point with mass as set above. This is useful for modeling compact objects like white dwarfs, neutron stars, or black holes in binaries where you are not studying the compact object.

Mass Transfer Parameters

Mass transfer scheme

• Ritter. As per Ritter (1988). For semi-detached binaries; when only one star is filling its Roche lobe and transferring mass.
• Kolb - Optically thick overflow, as per Kolb & Ritter (1990).
• Roche lobe - Such that the donor remains inside its Roche lobe.
• Contact - Extends Roche lobe to include contact systems.

Mass transfer efficiency α, β, and δ

α, β, and δ govern fractions, expressed as decimals less than 1, of mass loss during mass transfer. Total transfer efficiency is given by 1 - α - β - δ. Their sum must be less than or equal to 1.

• α - Fraction of mass lost from the donor as wind
• β - Fraction of mass lost from the accretor as wind
• δ - Fraction of mass lost from coplanar toroid

Binary Interaction Parameters

Magnetic braking

Accounts for the magnetic field interactions of each of the stars. These interactions work to carry away angular momentum. In binary systems, this is important because it works to decrease the orbital separation, potentially bringing the stars close enough to interact.

Magnetic braking gamma

Controls the strength of the effects of magnetic braking. 3 and 4 are commonplace values. A larger value means stronger magnetic braking at the same distance.

Gravitational wave radiation

Accounts for the gravitational wave radiation produced by two orbiting masses. Like magnetic braking, this radiation works to decrease the orbital separation.

Mass loss

Accounts for the angular momentum lost due to the loss of mass from the system.

Hot wind scheme

Turn on a hot wind scheme when surface temperature is above a specified threshold.

• (blank) - For no wind.
• Vink - For O and B supergiant stars, as per Vink, J.S., de Koter, A., & Lamers, H.J.G.L.M., (2001).
• Bjorklund - For hot, massive stars, as per Björklund, R., Sundqvist, J.O., Puls, J., & Najarro, F., (2021).
• Dutch - Works as both a hot and cold wind scheme. For massive stars, combines the results from several papers published by Dutch authors.

RGB/AGB cold wind scheme

Turn on a cold wind scheme when surface temperature is below a specified threshold.

• (blank) - For no wind.
• Reimers - Mass loss for red giants, as per D. Reimers "Problems in Stellar Atmospheres and Envelopes” (1975).
• Blöcker - Mass loss for AGB stars, as per T. Blocker “Stellar evolution of low and intermediate-mass stars”. (1995).
• de Jager - As per de Jager, C., Nieuwenhuijzen, H., & van der Hucht, K. A. (1988).
• van Loon - As per van Loon et al. (2005).
• Nieuwenhuijzen - As per Nieuwenhuijzen, H.; de Jager, C. (1990 ).
• Dutch - Works as both a hot and cold wind scheme. For massive stars, combines the results from several papers published by Dutch authors.

Hot wind fully on at

Above this temperature, only use the hot wind scheme.

Cold wind fully on at

Below this temperature, only use the cold wind scheme.

Simulation Resolution Controls

Mesh delta coefficient

Temporal resolution coefficient. A larger value means larger steps between each time interval; the opposite is true for a smaller value.

Variance control target

Spatial resolution coefficient. A larger value means a smaller number of grid points, decreasing the spatial resolution; the opposite is true for a smaller value.

History & profile recording interval:

A higher value corresponds to lower temporal resolution and smaller file size; the opposite is true for smaller values. Must be between [5, 100].

Stopping Conditions

Many of these stopping conditions come with warnings, but not strictly enforced limits. The warnings exist to let users know where unphysical conditions are given based on the initial condition of each star; say for example if the initial mass of star 1 is 1 solar mass and the stopping condition is carbon burning. Such a star will never reach carbon burning in isolation, but may do so if it accretes enough mass from a companion. Please keep these in mind while running simulations.

Terminate at phase

End the simulation once the given star reaches this evolutionary phase.

• Helium burning
• Carbon burning
• Neon burning
• Oxygen burning
• Silicon burning

Terminate at abundance fraction

End the simulation once the given star reaches the given abundance conditions, expressed as a fraction of the given region.

• Central hydrogen lower limit
• Central helium upper and lower limit
• Central carbon upper and lower limit
• Central oxygen upper and lower limit
• Central neon upper and lower limit
• Central silicon upper and lower limit
• Central iron upper and lower limit

Terminate at mass

End the simulation once the given mass criteria is reached. Limits are not enforced, but keep in mind how the interplay between these parameters and the starting masses.

• Star minimum mass - Must be lower than the initial mass, for the case where mass is lost
• Star maximum mass - Must be higher than the initial mass, for the case where mass is gained
• Envelope maximum mass - Envelope mass is defined as the star mass - the helium core mass
• Helium core maximum mass
• Carbon-oxygen core maximum mass
• Iron core maximum mass

Terminate at log quantity

End the simulation once the given star reaches the given log (base 10) quantity.

• Upper & lower central density, in g/cm³
• Upper & lower central temperature, in Kelvin
• Upper & lower surface temperature, in Kelvin
• Upper & lower radius, in solar radii

Terminate if initial overflow

Terminate if the first model has Roche lobe overflow. Corresponds to an initial system with an orbital period too small to be physical.

Accretor overflow

Terminate if the accretor radius is larger than its Roche lobe, expressed as relative error. Set to 0 to allow for no overflow.

Maximum model number

The maximum number of models. Set to 1,000 by default. Keep in mind the interaction with the history & profile recording interval. For example, setting a maximum model number of 1000 and a recording interval of 100 will result in only 10 history & profile files being created, resulting in low data resolution. Must be between [1, 5,000].

Maximum simulation age

Maximum simulation age, measured in years. First number is the multiplying factor, second number is the exponent. For example, 5e6 is 5,000,000 (5 million) years.

MESA Binary Output Information

Below, you can find information about all the possible outputs for MESA Binary. If you wish to include output data not listed here, please contact us.
Note that to generate some plots included in the MESA Binary package, specific quantities are needed. Those are:

• Kippenhahn: include gradr (radiative gradient) and grada (adiabatic gradient). Found in profile columns.
• Abundances: include all desired elements/isotopes. Found in profile columns.

Data Outputs

Profile columns

For each profile, MESA divides the star into zones. Each selected quantity here will be recorded for every zone. Please keep in mind that MESA will record for each quantity in each zone for every profile; the amount of data can add up quickly. Thus, keep in mind that adding more parameters can increase the simulation run and download time.

• Defaults:
• zone - numerically ordered zone, with 1 being the surface zone and the last entry being the central zone
• mass - mass coordinate of outer boundary, in M _☉
• logR - log10 radius at outer boundary, in R _☉
• logT - log10 temperature at center, in K.
• logRho - log10 density at center, in g/cm³
• logP - log10 pressure at center, in Bayres
• x_mass_fraction_H - fraction comprised of Hydrogen
• y_mass_fraction_He - fraction comprised of Heliun
• z_mass_fraction_metals - fraction comprised of metals
• Log quantities:
• logPgas - log10 gas pressure at center, in Bayres
• log_g - log10 graviational acceleration, in cm/sec²
• logE - log10 specific internal energy, in erg/g
• logS - log10 specific entropy, in erg/g·K
• Grad quantities:
• grada - adiabatic gradient
• gradr - radiative gradient
• gradT - temperature gradient
• Miscellaneous:
• csound - speed of sound, in cm/s
• luminosity - in L _☉
• eta - electron degeneracy parameter. eta >> 1 for significant degeneracy
• opacity
• tau - optical depth
• Nuclear energy generation:
• pp - energy production from the pp reaction
• cno - energy production from cno reactions
• tri_alpha - energy production from triple alpha reactions
• eps_nuc - net energy production from nuclear reactions, including losses to reaction neutrinos in ergs·s/g
• Elemental & isotopic abundances:
• h1 - decimal abundance of ¹H
• he3 - decimal abundance of ³He
• he4 - decimal abundance of ⁴He
• c12 - decimal abundance of ¹²C
• n14 - decimal abundance of ¹⁴N
• o16 - decimal abundance of ¹⁶O
• ne20 - decimal abundance of ²⁰Ne
• mg24 - decimal abundance of ²⁴Mg
• si28 - decimal abundance of ²⁸Si
• s32 - decimal abundance of ³²S
• ar36 - decimal abundance of ³⁶Ar
• ca40 - decimal abundance of ⁴⁰Ca
• fe56 - decimal abundance of ⁵⁶Fe

History columns

History data is stored at each recording interval for the whole star or particular regions in the star. For example, total stellar mass or the mass of the core.

• Defaults:
  • model_number - model number, counting from the start of the run
  • star_age - elapsed time from start of simulation, in years
  • star_mass - total mass of the star, in M _☉
  • log_Teff - log10 effective temperature at the surface, in K
  • log_L - log10 of the luminosity, in L _☉
  • log_R - log10 of the radius, in R _☉
  • log_center_T - log10 of the central temperature, in K
  • log_center_Rho - log10 of the central density, in g/cm³
  • log_center_P - log10 of the central pressure, in Bayres
  • log_g - log10 of the surface gravity, in dynes
• Log quantities:
• log_abs_mdot - log10 of the absolute value of the change in mass, in M _☉/year
• log_Lneu - log10 power emitted as neutrinos, both nuclear and thermal, in units of L _☉
• log_Lneu_nuc - log10 power emitted as nuclear neutrinos, in units of L _☉
• Mass quantities:
• envelope_mass - defined as (star mass - helium core mass), in M _☉
• he_core_mass - mass of the helium core, in M _☉
• co_core_mass - mass of the carbon-oxygen core, M _☉
• one_core_mass - mass of the oxygen-neon core, M _☉
• fe_core_mass - mass of the iron core, M _☉
• Timescales:
• dynamic_timescale - orbital period around a star, in s
• kh_timescale - time needed to radiate away all energy as thermal energy, in s (Kelvin–Helmholtz timescale)
• nuc_timescale - characteristic timescale of nuclear abundance changes, in s (Nuclear timescale)

Binary history columns

Exact same as history columns, but for data regarding the system, not each star.

• Defaults:
• model_number - model number, counting from the start of the run
• age - age of the donor star, starting at the beginning of the simulation. Set so that both stars have roughly the same age
• period_days - orbital period, in days
• binary_separation - distance between stars, measured in R _☉. All orbits areth circular
• star_1/2_mass - mass of each star. Enabled only to still allow for generating plots dependent on mass even when doing point mass evolution, in M _☉
• Mass quantities:
• lg_wind_mdot_1/2 - log10 of the absolute magnitude of a respective stars mass transfer rate due to wind, in M _☉/yr
• lg_mstar_dot_1/2 - log10 of the absolute magnitude of a respective stars mass transfer rate, in M _☉/yr
• lg_system_mdot_1/2 - log10 of the absolute magnitude of the mass lost from the system due to inefficient mass transfer around a respective star, in M _☉/yr
• Angular momentum
• J_orb - orbital angular momentum, in g·cm²/s
• J_spin_1/2 - spin angular momentum of a r ective star, in g·cm²/s
• Jdot - time derivative of J_orb, in g·cm²/s²
• jdot_mb - time derivative of J due to magnetic braking
• jdot_gr - time derivative of J due to gravitational wave radiation
• jdot_ml - time derivative of J due to mass loss