  This study presents structural and fundamental astrophysical parameters of
poorly studied open cluster NGC 2509. We used the third photometric and
astrometric data release of the Gaia (Gaia DR3) to perform analyses. By taking
into account the Gaia DR3 astrometric data, we calculated the membership
probabilities of the stars in the region of NGC 2509. As a result of the
membership analysis, 244 stars with membership probabilities $P\geq50$% were
determined as the physical members of the cluster. The colour excess, distance
and age were obtained simultaneously by fitting solar metallicity PARSEC
isochrones to $G\times G_{\rm BP}-G_{\rm RP}$ colour-magnitude diagram. We
considered the most likely cluster member stars during the fitting procedure
and calculated the colour excess, distance and age of the NGC 2509 as $E(G_{\rm
BP}-G_{\rm RP})=0.100\pm0.015$ mag, $d=2518\pm667$ pc and $t=1.5\pm 0.1$ Gyr,
respectively.

Astrophysics of Galaxies