Summer Research Fellowship Programme of India's Science Academies

Binary stellar population in the open star clusters of our Galaxy

Naman Joshi

IISER Bhopal, Bhauri, Bhopal Bypass Road, Bhopal, Madhya Pradesh 462066

Dr. Annapurni Subramanian

Indian Institute of Astrophysics, II Block, Koramangala, Bangalore, Karnataka 560034


Binary Star Fraction is important to understand the dynamics and evolution of a star cluster. The main objective of this project is to calculate the binary fraction of stars in open clusters of our galaxy. We use photometric data from European Space Agency GAIA Survey (GAIA Data Release 2) for a number of open clusters and construct their Colour Magnitude Diagram (CMDs). We fitted theoretical isochrones to the cluster CMDs using TOPCAT tools and programs in Python, after accounting for various parameters such as distance modulus, metallicity, extinction and reddening. We identified binaries based on their location on the CMDs and estimated the binary fraction (BF) for 15 clusters. We then converted the observed fraction to the total fraction, and the average value of BF was estimated to be 0.53. The estimation of binary fraction was possible due to the identification of the cluster members by GAIA. We further studied its correlation with other cluster parameters and found a weak correlation with integrated cluster magnitude and no correlation with age and metallicity.

Keywords : binary fraction, GAIA, Isochrone fitting, CMD, TOPCAT

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