Sampling

Settings that change how the initial binary population is sampled

sampling_method

Select which models to use to generate an initial sample of binary parameters at Zero Age Main Sequence

Default: independent

Option details

  • independent: Initialize binaries with independent parameter distributions for the primary mass, mass ratio, eccentricity, separation, and binary fraction
  • multidim: Initialize binaries with multidimensional parameter distributions according to Moe & Di Stefano 2017

primary_model

Model for sampling primary masses
[Only used when sampling_method = independent]

Default: kroupa01

Option details

  • salpeter55: Use the Salpeter 1955 IMF
  • kroupa93: Use the Kroupa 1993 IMF
  • kroupa01: Use the Kroupa 2001 IMF

porb_model

Model for sampling orbital periods
[Only used when sampling_method = independent]

Default: sana12

Option details

  • sana12: Sample from power law orbital period between 0.15 < log(P/day) < 5.5 following Sana+2012
  • log_uniform: Sample semi-major axis flat in log space from RRLO < 0.5 up to \(10^{5} {\rm R_{\odot}}\) according to Abt (1983) and consistent with Dominik+2012,2013 - then convert to orbital period in days using Kepler's third law.
  • renzo19: Uses sana12 for massive binaries (\(m_1 > 15 {\rm M_{\odot}}\)) and flat in log otherwise (following Renzo+19).
  • raghavan10: Sample log normal orbital periods in days with mean_logP = 4.9 and sigma_logP = 2.3 between \(0 < \log_{10}(P / {\rm day}) < 9\) following Raghavan+2010
  • moe19: As raghavan10 but with different close binary fractions following Moe+2019
  • custom: Sample from a custom power law. The user provides a dictionary of min, max and slope values for the power law.

ecc_model

Model for sampling eccentricity
[Only used when sampling_method = independent]

Default: sana12

Option details

  • thermal: Samples from a thermal eccentricity distribution following Heggie (1975)
  • uniform: Samples from a uniform eccentricity distribution
  • sana12: Samples from the eccentricity distribution from Sana+2012
  • circular: Assumes zero eccentricity for all systems

qmin

Minimum mass ratio for sampling the secondary mass
[Only used when sampling_method = independent]

Default: -1

Option details

The assumed mass ratio distribution is flat in \(q \equiv m_2 / m_1\). NOTE: only one of qmin and m2_min should be specified.

  • values in [0, 1]: Sets the minimum mass ratio
  • -1: Set the minimum mass ratio such that the pre-MS lifetime of the secondary is not longer than the full lifetime of the primary if it were to evolve as a single star

m2_min

Minimum secondary mass for sampling
[Only used when sampling_method = independent]

Default: 0.1

Option details

NOTE: only one of qmin and m2_min should be specified.

  • positive values: Sample the secondary mass uniformly between m2_min and mass_1
  • 0.1: Default value

binfrac_model

Model for sampling binary fraction
[Only used when sampling_method = independent]

Default: 0.5

Option details

  • values between [0, 1]: Fixed binary fraction
  • vanHaaften: Primary mass dependent binary fraction following van Haaften+05
  • offner22: Primary mass dependent binary fraction following Offner+22
  • 0.5: Default value

SF_start

Sets the time in the past when star formation initiates in Myr.

Default: 13700.0

Option details

  • positive values: Start time of star formation in Myr
  • 13700.0: For example, this specifies a start time at the beginning of a Hubble time

SF_duration

Sets the duration of constant star formation from ``SF_start`` in Myr.

Default: 0.0

Option details

  • positive values: Duration of star formation in Myr
  • 0.0: A single burst of star formation
  • 13700.0: For example, this specifies a constant star formation rate over a Hubble time

metallicity

Sets the metallicity of the stellar population.

Default: 0.02

Option details

COSMIC expects an absolute metallicity (i.e., NOT units of zsun)

  • positive values: Absolute metallicity
  • 0.02: For example, this sets the metallicity to approximately solar metallicity