====== GC2: Challenge 3 ======

===== Simulated observations and biases =====

**PI**: Antonio Sollima\\
**Other participants**: Eduardo Balbinot, Mark Gieles, Alice Zocchi, Anna Lisa Varri, Vincent Henault-Brunet


Questions to address:

  - How different are the fits when considering: 1) all stars and 2) only visible stars?
  - Is it better to consider luminosity weighted profiles, or number density profiles?
  - How much can we do with 2 velocity components instead of 1 (i.e. with Gaia data)?

Snapshots from [[:tests:collision:mock_data|Sections C and D of the Mock data page]] can be used for this challenge.

==== Including GAIA realistic errors ====

Using PyGaia 0.6 and the NBODY snapshots in [[:tests:collision:mock_data|Sections B]].

Method:
  - Assume a position for the cluster in the Galaxy (X,Y,Z taken from Harris catalogue)
  - Transform phase-space coordinates to observed ones (''pygaia.astrometry.vectorastrometry.phaseSpaceToAstrometry'')
  - Compute errors using ''parallaxErrorSkyAvg'' and ''parallaxErrorSkyAvg''
  - Back to phase-space with ´''astrometryToPhaseSpace''

On the plots bellow the red dots are computed using error free data and the black dots using the GAIA error model. The quantity shown is the on-sky velocity dispersion versus the distance to the cluster centre.

Cluster @ 3kpc
{{:tests:3kpc_sky_disp.png?400|}}

Cluster @ 5kpc
{{:tests:5kpc_sky_disp.png?400|}}

Cluster @ 8kpc
{{:tests:8kpc_sky_disp.png?400|}}

Cluster @ 10kpc
{{:tests:10kpc_sky_disp.png?400|}}


Other plots:

CMD in GAIA photometric system for stars in the snapshot (in this example the cluster is at 3kpc)
{{:tests:cmd.png?400|}}

Observed three component velocities (black) and real ones (red) as a function of observed GAIA BP magnitude
{{:tests:vel_mag.png?400|}}