Observations of Internal Dynamics of Globular Clusters

Details Observations of Internal Dynamics of Globular Clusters Observations of Internal Dynamics of Globular Clusters

Aug 2006

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2006iaujd..14e...3b&link_type=abstract

Modelling Dense Stellar Systems, 26th meeting of the IAU, Joint Discussion 14, 22-23 August 2006, Prague, Czech Republic, JD14,

Astronomy and Astrophysics

Astronomy

Scientific paper

In preparation for the first simulation of a real globular cluster with a few 10^5 particles, possible by the advent of the new GRAPE-8, the MODEST community charged our group to provide all the needed observational inputs. The selected clusters for this experiment were M4 and NGC6397. We present the status of the project. The requested observational inputs are: cluster membership, internal proper motion, internal line of sight velocities, distance, mass function, mass segregation, anisotropy, binary fraction (and properties), spatial distribution of stars, white dwarf (WD) counts, tidal tail distribution, and absolute proper motion and radial velocities (to characterize the orbit). To obtain these observational quantities, we started an extensive observational campaign in order to get high precision photometry and astrometry with both HST --from space-- and with wide-field-imagers --from ground. In addition to this, for the third component of the motions (along the line of sight) we got time at FLAMES@VLT8m multifiber-spectroscoper. Furthermore, our exquisite photometry from the tip of the RGB to the bottom of the WD cooling sequence allows: (i) to obtain local present day mass functions (down to the hydrogen burning limit) at different distances from the cluster center, and cleaned from contamination of foreground/background, objects, (ii) to study the WDs down to the cooling sequence end, (iii) estimate the photometric binaries. Comparison of internal proper motions with line of sight velocities for thousands of stars provide geometric determination of the cluster distance with uncertainties of a few percents. The internal proper motions and radial velocities provide information on the stellar kinematics inside the cluster. High precision astrometry and photometry also allows us to disentangle blends from real binaries, for which we can now provide an estimate on their (present day) number, and radial distribution. A FLAMES@VLT project born inside MODEST to determine the spectroscopic binary fraction in M4 has been recently approved.

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