go-orbits

Binary orbits after asymmetric momentum kick

Compute binary orbits after an asymmetry in a core collapse of a massive star using linear momentum conservation as presented in Kalogera et al. 1996 and Kalogera 2000

Installation

The code is written purely in Go so its installation requires go to be installed in your system.

First, clone this code into your computer

git clone git@github.com:asimazbunzel/go-orbits.git

(in case ssh is not available, clone it with the HTTPS URL).

Then, the module must be initialized with

go mod init github.com/asimazbunzel/go-orbits

Once this is done, the following command will get you all the libraries needed for the code to work

go mod tidy

Finally, to compile the code run

make build

(which needs the command make available, always present in a GNU/Linux distribution).

This last command will generate a binary called orbits located in the bin folder. This is the program that will be called to compute the distribution of kicks.

Usage

All the necessary options are controlled via a configuration file in YAML format. There is an example in this repository called config.yaml. In it, there is an explanation for the utility of each of the options.

In order to run the code, change directory into the bin folder and run

./orbits -C path/to/config/file

For example, in the example given with the config.yaml file, the command would look like this

./orbits -C ../config.yaml

Some comments about the options

• m1, m2, separation and period are the conditions of the binary just before the core collapse.

• compact_object_mass is the mass of the newly born compact object.

• kick_distribution and kick_direction are the distributions for the asymmetric kick. The kick_distribution options are either Maxwell or Uniform for a Maxwellian or a Uniform distribution of the strength of the kick. While kick_direction has not other available option as of now (maybe in the future could be changed).

• reduce_by_fallback applies a function that reduces the strength of the kick by (1 - f) with f being the fraction of mass that falls back to the compact object at core collapse.

• kick_sigma is used when kick_distribution is Maxwell. While min_kick_value and max_kick_value are used when kick_distribution is Uniform.

• min_phi and max_phi are options for the angle in the orbital plane of the binary. Do not change it, for now.

• seed is the number used by the random number generator method.

• number_of_cases represents the number of draws for the different kicks.

• log_level option for the amount of terminal output. Options are debug or info.

• save_kicks and kicks_filename are self explanatory.

• save_bounded_orbits and bounded_orbits_filename are used to store the binaries that survive the kick.

• save_grid_of_orbits and grid_of_orbits_filename are used to store a grid of binaries with a probability above a threshold of minimum_probability_for_grid.

• period_quantile_min, period_quantile_max, eccentricity_quantile_min, eccentricity_quantile_max, number_of_periods and number_of_eccentricities are controls for the creation of the grid. Do not change them, for now.

Output

The code will create 3 different files (according to some controls shown above). One of the files will contain info on the strength and direction of the kick (kicks_filename), another will have info on the binaries that survive the kick (bounded_orbits_filename). The last file will create a grid of orbital parameters assuming that the 2D plane of (period, eccentricity) can be divided into a rectangular grid in which, each of the rectangles will have associated a probability according to how many binaries are within its boundaries (grid_of_orbits_filename).