snapdragons (Barcelona flavour)

Snapdragons is a population synthesis & mock survey data generation code - it creates synthetic stars from an N-body simulation of a galaxy. Please cite the Snapdragons paper (Hunt et al. 2015, MNRAS, 450, 2132) if you use it for publication.

This version is used in some of the hands-on session for the Gaia-COST school in Barcelona . It differs only in some superficial respects from the original code. Main contributors of this version (apart from Jason Hunt) are Santi Roca and Mercé Romero.

How does this work?

It's that simple: From the input:

• N-body model (with positions, masses, ages, and metallicities)
• isochrone tables
• (2D/3D) extinction model
• initial mass function
• limiting magnitude
• Gaia error model snapdragons creates the output:
• Synthetic stellar data

The code is in written in fortran. It has a Makefile in the main directory, which compiles the source code in src. To compile just type 'make' in the main directory. The main module is called src/PopSynth.F, several options can be specified in Mockinioptions.h

You must dowload the extinction maps separately from https://1drv.ms/u/s!AnMgd4KLTt9j6HtlSWaRd9kP5Rem?e=QcCqax and place them in the ini folder (not inside UBV)

Getting started

Clone this repository to a place you like:

git clone https://github.com/fjaellet/Snapdragons

Get familiar with the file structure. To compile snapdragons, you will need the gfortran compiler (or modify the Makefile to satisfy your own architechture). From the top-level directory, you should then be able to run

make
./snapdragons

• which in a few seconds will create you a mock observation of the default input simulation (ini/input.dat).

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Changing input parameters

Input simulation

The input file needs to be an ascii table with the following structure: * x, y, z(kpc), vx, vy, vz(km/s), metallicity(z), age(Gyr), mass(solar) [, other columns] The name of the input file is hidden in PopSynth.F - so it might be easiest to replace the default input file (ini/input.dat) manually/using a python wrapper program.

Input parameters

Mockinioptions.h lets you choose some basic things:

• magnitude limit (in the V band): ChosenLim=14.0d0
• whether to convolve the results with the Gaia error model: error=1
• whether to output an ascii or a binary file: Binary=0

Don't forget to recompile before rerunning.

Output

The default snapdragons output is stored in output/ as ascii or binary file without header.. There is, however, a python script in py/ that will convert this output to standard FITS file in the same directory:

cd py
python snapdragons2fits.py

Output columns in the ascii/binary version are:

• 1 true ra
• 2 true dec
• 3 true parallax
• 4 true pmra
• 5 true pmdec
• 6 true rv
• 7 observed ra
• 8 observed dec
• 9 observed parallax
• 10 observed pmra
• 11 observed pmdec
• 12 observed rv
• 13 ra standard deviation
• 14 dec standard deviation
• 15 parallax standard deviation
• 16 pmra standard deviation
• 17 pmdec standard deviation
• 18 rv standard deviation
• 19 G Magnitude
• 20 G_bp - G_rp
• 21 observed G Magnitude
• 22 observed G_bp - G_rp
• 23 G Magnitude Gaia standard deviation
• 24 G_bp - G_rp Gaia standard deviation
• 25 apparent V mag
• 26 distance from sun
• 27 x
• 28 y
• 29 z
• 30 vx
• 31 vy
• 32 vz
• 33 mass (solar mass)
• 34 G_RVS
• 35 V-I
• 36 extinction
• 37 absolute V mag
• 38 absolute V-i
• 39 metallicity z*10^6
• 40 Age (log10years)
• 41 observed distance
• 42 observed x
• 43 observed y
• 44 observed z
• 45 observed vx
• 46 observed vy
• 47 observed vz
• 48 observed galactocentric vr
• 49 observed vrot
• 50 galactocentric radius
• 51 galactocentric vr
• 52 vrot
• 53 observed galactocentric radius
• 54 pmra (km/s)
• 55 pmdec (km/s)
• 56 observed pmra (km/s)
• 57 observed pmdec (km/s)