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Imaging dense globular clusters like M3 and M15
Deep Space Exploration Society
Strikis Iakovos - MariosHellenic Amateur Astronomy AssociationElizabeth Observatory of Athens
Ido Bareketמצפה הכוכבים ברקת במכביםhttp://www.bareket-astro.comBareket observatory, Israel
Stouraitis DimitriosHellenic Amateur Astronomy AssociationGalilaio Astronomical Observatory
Amateur Astronomers have no consistent way of defining the core of a globular cluster, thus differentiating the core from the periphery. This segregation is important for characterizing the gravitational dynamics of the cluster, particularly in the core.
The periods of RR Lyrae variable stars introduce segregation errors due to their inherent variation. Current core sizing is a function of the luminosity versus distance from the core center. However, once in the core, the variations in the RR Lyrae stars introduce significant error in the luminosity determination. Hence, by characterizing the RR Lyrae quantities and oscillation periods, we can reduce the core dimension error.
Can Period/Luminosity flux density distributions help
determine the core from outer regions?
Not sure I'm saying this right, but it would be something like this: there is a P/L ratio difference between core and outer region, which would be a Bayesian prior, which would inform the decision to describe the core region.
For example: when the core's P/L ratio is negative at some slope, large enough to be significant when compared to the positive P/L ratio slope for the outer region's RR Lyrae stars, then this difference in slope of the P/L ratio would help inform the algorithm used to describe the core, and we could be confident we've identified the core, in-part because of the difference in the slope of the P/L ratios?That way whether or not we use some B - V color relationship to define the P/L ratio, or a flux density period/luminosity ratio over time (multiple images), we could still determine a significant change of the P/L slopes between core and outer region? Such that, where there is a 'significant' change in these slopes, which identifies the core.This all depends on the idea that the P/L ratio of the core RR Lyrae stars is less than the P/L ratio of the outer region's RR Lyrae stars.
Iakovos writes: “As for the decrease of the flux density of the M15 core ... I also think it is not real, and I believe that it is caused from the camera stabilization .... All cameras need about 1+1/2 hours to be thermal stabilized... If I start to image before that time the linearity of the camera (and sensitivity) are going to be changed until the camera gets thermal stabilized “...
Photo from home page of Natalia Dziourkevitch: http://www.aip.de/~nsd