SeBa is a software package to simulate the evolution of single and binary stars from the zero-age main-sequence up to and including remnant phases.It is valid for masses in the range 0.01-100 Msun with variable metallicity. SeBa includes prescriptions for mass loss by stellar winds, supernova and binary interactions.

This document contains following parts:

Compilation

Simple examples

Understanding the SeBa output

References

Compilation

SeBa can be compiled as following:

make clean
make
cd dstar 
make

Simple examples of runs

Single system

To evolve a single system with the parameters primary mass M=2 solar mass, secondary mass m=1 solar mass, eccentricy e=0.2, orbital separation a=200 solar radii, time T=13500 Myrs, metallicity z=0.001, you need to run:

./SeBa -M 2 -m 1 -e 0.2 -a 200 -T 13500 -z 0.001

Multiple systems with specified parameters

If you need to follow the binary stellar evolution for multiple systems with parameters which are already specified you can start SeBa multiple times, e.g.

./SeBa -M 2 -m 1 -e 0.2 -a 200 -T 13500 -z 0.001
./SeBa -M 2.5 -m 1.5 -e 0.5 -a 500 -T 500 -z 0.02

This is probably not handy for more than 5 systems. Although this can be added in e.g. a shell or Python script. For example a file named run.sh, should contain the lines for the example given above:

./SeBa -M 2 -m 1 -e 0.2 -a 200 -T 13500
./SeBa -M 2.5 -m 1.5 -e 0.5 -a 500 -T 500

Note:Check permissions of run.sh file; it should be executable by the owner. If not: type ' chmod 744 run.sh ' in command line. To run the shell script: ./run.sh

Another option is to use an input file:

./SeBa -I 'SeBa_input.txt'

which contains following information a e M m z, e.g.

200 0.2 2 1 0.001
500 0.5 2.5 1.5 0.02

Random population

Monte Carlo based approach

./SeBa -R -n 200
./SeBa -R -n 250000 -m 0.96 -M 11 -q 1e-4 -Q 1 -A 1e6 -f 4 -T 13500

with following parameters [default]:

-R SeBa generates randomly the initial parameters -n number of systems simulated
-m -M min/max primary mass [0.1,100]
-q -Q min/max mass ratio [0,1]
-e -E min/max eccentricity [0,1]
-a -A min/max orbital separation [0, 1e6]
-T time in Myr in the simulation of the binaries. Same time for all binaries [13500Myr]
-z metallicity of binary stars. All binaries have the same metallicity. [0.02]
   To vary the metallicity, multiple simulations should be run. 
-N initial ID number of first simulated binary [0]
(comes in handy for stitching together production runs)   

(Experimental)

-C Initial stellar type primary star [default is main_sequence]
-c Initial stellar type secondary star [default is main_sequence]
Starts at beginning of specified phase. Options are planet, brown_dwarf, main_sequence, hertzsprung_gap, sub_giant, horizontal_branch, super_giant, helium_star, helium_giant, hyper_giant, carbon_star, thorn_zytkow, helium_dwarf, carbon_dwarf, oxygen_dwarf, xray_pulsar, radio_pulsar, neutron_star, black_hole, Disintegrated

The initial parameters are drawn from distributions:

-x mass function exponent in case of power law [-2.35] 
-F/f mass function option: 
	0) Equal mass
	1) Power-law [default] 
	2) Miller & Scalo
	3) Scalo
	4) Kroupa

Option -F requires one of the following strings: (mf_Power_Law, Miller_Scalo, Scalo, Kroupa)
-f requires the appropriate interger (see mkmass.C)

-y exponent for a power-law distribution [0] (flat in log)
-G/g Semi major axis option: 
	0) Equal_sma 
	1) Power Law [default]
	2) Duquennoy & Mayor (1987) Option -G requires one of the following strings:
	(Equal_sma, sma_Power_Law, Duquennoy_Mayor) -g requires appropriate integer (see double_star.h)

-v exponent for a power-law distribution
-U/u eccentricity option: 
	0) Equal eccentricity
	1) Power Law
	2) Thermal distribution [default] Option -U requires one of the following strings:
	(Equal_ecc, ecc_Power_Law, Thermal_Distribution) -u requires appropriate interger (see double_star.h)

-w exponent for a power-law distribution
-P/p mass ratio option: 0) constant mass ratio
	1) Flat_q
	2) Power Law
	3) Hogeveen (1992)
Option -P requires one of the following strings: (Equal_q, Flat_q, qf_Power_Law, Hogeveen)
-p requires appropriate interger (see double_star.h)

Understanding the SeBa output

SeBa adds the evolutionary history of each binary in the SeBa.data file. Every line represents a moment in the evolution of the binary when something interesting happened, for example one of the star transitions from the main-sequence to the hertzsprung gap, or mass transfer starts or stops. The meaning of the columns is defined below. The first column represents a unique identifier for each binary.

Structure of SeBa.data file

columns (starting at column 1):
column 1 binary identity number 
column 2 binary type
column 3 mass transfer type
column 4 time
column 5 separation in Solar radii
column 6 eccentricity
column 7 & 13 stellar identity number (either 0 or 1)
column 8 & 14 star type
column 9 & 15 stellar mass in Solar mass
column 10 & 16 stellar radius in Solar radii
column 11 & 17 log of effective temperature
column 12 & 18 core mass in Solar mass

Binary types

2 detached
3 semi detached + stable mass transfer 
4 contact
5 CE (gamma)
6 double spiral-in
7 merged
8 disrupted
9 CE (alpha)

Mass transfer types

1 on nuclear time scale
2 on angular momentum loss timescale (either gravitational waves &
magnetic braking)
3 on thermal time scale
4 CE due to dynamics
5 CE due to Darwin Riemann instability

Stellar types

1 planet
2 brown dwarf
3 main sequence
5 hertzsprung gap
6 sub-giant
7 core helium burning star 
8 agb
10 helium star
11 helium giant
12 carbon-oxygen white dwarf 
13 helium white dwarf
14 oxygen-neon white dwarf 
18 neutron star
19 black hole
20 disintegrated

References

See the following publications:

• Portegies Zwart S.F. & Verbunt F., 1996, A&A, 309, 179: "Population synthesis of high-mass binaries"
• Toonen, S., Nelemans, G., Portegies Zwart S.F., 2012, A&A, 546A, 70T: "Supernova Type Ia progenitors from merging double white dwarfs. Using a new population synthesis model"