## BANYAN: Bayesian Analysis for Nearby Young AssociatioNs

# Calculation of the membership probability of stars (without photometry information)

# (Version 1.0)

**BANYAN is a Bayesian analysis tool to determine the membership probability of candidate stars to nearby young kinematic groups. The membership criteria are common space velocities (UVW) and Galactic positions (ZYZ). Only young co-moving groups within 100 pc listed below are considered. Based on a set of observables, minimally sky position and proper motion but ideally combined with radial velocity and parallax information, Bayesian inference is used to determine the membership probabilities of a candidate star along with the predicted radial velocity for all associations considered. If the parallax is unknown, BANYAN returns the most probable (« statistical ») distance. If known, the trigonometric distance is used as a « prior » to condition the probably density functions. In general, you should find a very good agreement between the trigonometric parallax and the predicted statistical distance. The details of this method are described in Malo et al. (2013).**

The results of this tool should be interpreted with

__caution__.

**1)**We stress that a high probability in one of the associations considered here does not necessarily imply that the candidate star is young. Space velocity and Galactic position is only one of the many criteria that a star should satisfy to be declared genuinely young. It is on the onus of the user to show that the candidate star shows a number of youth indicators (e.g. appropriate position in the HR diagram, appropriate Li EW, variability, x-rays and UV activities, high vsin i, evidence for debris disk, etc). Conversely, a high probability in « field (old) » does not necessarily imply that the star is old; it simply means that it is less likely to be a member of the young associations considered here compared to the « field (old) » which is of course inclusive of other young associations not included in the analysis.

**2)**In general, the more observables you have, the more trustworthy are the membership probabilities but note

**#1**still applies!

**3)**For some targets, results obtained with BANYAN may differ from those published in Malo et al. as the latter uses a very similar analysis but with more observables (I,J photometry). Significant differences between membership probabilities with/without photometry is suggestive that more information (e.g. radial velocity and ultimately parallax) is needed to assess the membership of the candidate with more confidence.

**Please note that the information entered on this web page is not stored on our server.**

Name | Age (Myr) | U (km/s) | σ U | V (km/s) | σ V | W (km/s) | σ W | X (pc) | σ X (pc) | Y (pc) | σ Y (pc) | Z (pc) | σ Z (pc) | #star |
---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|

βPictoris | 12-22 | -10.94 | 2.06 | -16.25 | 1.30 | -9.27 | 1.54 | 9.27 | 31.71 | -5.96 | 15.19 | -13.59 | 8.22 | 39 |

TW Hydrae | 8-20 | -9.95 | 4.02 | -17.91 | 1.75 | -4.65 | 2.57 | 12.49 | 7.08 | -42.28 | 7.33 | 21.55 | 4.20 | 10 |

Tucana-Horologium | 10-40 | -9.88 | 1.51 | -20.70 | 1.87 | -0.90 | 1.31 | 11.39 | 19.29 | -21.21 | 9.17 | -35.40 | 5.39 | 44 |

Columba | 10-40 | -12.24 | 1.03 | -21.32 | 1.18 | -5.58 | 0.89 | -27.44 | 13.79 | -31.32 | 20.55 | -27.97 | 15.09 | 21 |

Carina | 10-40 | -10.34 | 1.28 | -22.31 | 0.58 | -5.91 | 0.11 | 15.55 | 5.66 | -58.53 | 16.69 | -22.95 | 2.74 | 5 |

Argus | 30-50 | -21.78 | 1.32 | -12.08 | 1.97 | -4.52 | 0.50 | 14.60 | 18.60 | -24.67 | 19.06 | -6.72 | 11.43 | 11 |

AB Doradus | 50-120 | -7.12 | 1.39 | -27.31 | 1.31 | -13.81 | 2.16 | -2.37 | 20.03 | 1.48 | 18.83 | -15.62 | 16.59 | 47 |

Field (old) | -10.92 | 23.22 | -13.35 | 13.44 | -6.79 | 8.97 | -0.18 | 53.29 | 2.10 | 51.29 | 3.27 | 50.70 | 10097 |