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Abstract: We present polarimetric observations in the UBVRI bands of 72 stars locatedin the direction of the medium age open cluster NGC 5617. Our intention is touse polarimetry as a tool membership identification, by building on previousinvestigations intended mainly to determine the cluster-s generalcharacteristics rather than provide membership suitable for studies such asstellar content and metallicity, as well as study the characteristics of thedust lying between the Sun and the cluster. The obsevations were carried outusing the five-channel photopolarimeter of the Torino Astronomical Observatoryattached to the 2.15m telescope at the Complejo Astron\-omico El LeoncitoCASLEO; Argentina. We are able to add 32 stars to the list of members of NGC5617, and review the situation for others listed in the literature. Inparticular, we find that five blue straggler stars in the region of the clusterare located behind the same dust as the member stars are and we confirm themembership of two red giants. The proposed polarimetric memberships arecompared with those derived by photometric and kinematical methods, withexcellent results. Among the observed stars, we identify 10 with intrinsicpolarization in their light. NGC 5617 can be polarimetrically characterizedwith $P {max}= 4.40%$ and $ \theta {v}= 73^\circ.1$. The spread in polarizationvalues for the stars observed in the direction of the cluster seems to becaused by the uneven distribution of dust in front of the cluster-s face.Finally, we find that in the direction of the cluster, the interstellar mediumis apparently free of dust, from the Sun-s position up to theCarina-Sagittarius arm, where NGC 5617 seems to be located at its farthestborder.

Author: Ana Maria Orsatti, Carlos Feinstein, M. Marcela Vergne, Ruben E. Martinez, E. Irene Vega

Source: https://arxiv.org/

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