OCAAT: automated analysis of star cluster colour-magnitude diagrams for gauging the local distance scale

G.I. PERREN; R.A. VÁZQUEZ; A.E. PIATTI; A. MOITIHNO

Proceedings of the IAU

IAU

Año: 2014 vol. 10 p. 298 - 300

1743-9213

Star clusters are among the fundamental astrophysical objects usedin setting the local distance scale. Despite its crucial importance,the accurate determination of the distances to the Magellanic Clouds(SMC/LMC) remains a fuzzy step in the cosmological distance ladder. Theexquisite astrometry of the recently launched ESA Gaia mission isexpected to deliver extremely accurate statistical parallaxes, and thusdistances, to the SMC/LMC. However, an independent SMC/LMC distancedetermination via main sequence fitting of star clusters provides animportant validation check point for the Gaia distances. This has beena valuable lesson learnt from the famous Hipparcos Pleiades distancediscrepancy problem. Current observations will allow hundreds ofLMC/SMC clusters to be analyzed in this light.Today, the mostcommon approach for star cluster main sequence fitting is still by eye.The process is intrinsically subjective and affected by largeuncertainties, especially when applied to poorly populated clusters. Itis also, clearly, not an efficient route for addressing the analysis ofhundreds, or thousands, of star clusters. These concerns, together witha new attitude towards advanced statistical techniques in astronomy andthe availability of powerful computers, have led to the emergence ofsoftware packages designed for analyzing star cluster photometry. Witha few rare exceptions, those packages are not publicly available.Herewe present OCAAT (Open Cluster Automated Analysis Tool), a suite ofpublicly available open source tools that fully automatises clusterisochrone fitting. The code will be applied to a large set of hundredsof open clusters observed in the Washington system, located in theMilky Way and the Magellanic Clouds. This will allow us to generate anobjective and homogeneous catalog of distances up to ~ 60 kpc alongwith its associated reddening, ages and metallicities and uncertaintyestimates.