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Interstellar polarization and extinction towards the young open cluster NGC 1502



Druh Článek v odborném periodiku
Fakulta / Pracoviště MU

Přírodovědecká fakulta

Klíčová slova stars: early type; open clusters and associations: individual: NGC 1502
Popis Aims. NGC 1502 is located at the periphery of the Cam OB1 association and probably within the Orion Spur, with published distance estimates varying between 0.7 and 1.5 kpc. We combine new polarimetric observations and existing uvby beta and UBV photometries to provide new estimates of the cluster's parameters. Methods. We present new multi-wavelength polarization observations of 22 stars in the direction of the cluster and, using the wavelength of maximum polarization, calculate the total-to-selective extinction ratio for each of these stars. These are combined with homogenized uvby beta and UBV photometries to obtain the individual stellar distances and study the structure of the field. Results. We found no evidence of significant extinction variation across the cluster and obtained an average color excess E(b - y) = 0.56 +/- 0.02 mag, corresponding to E(B V) = 0.76 mag. Given the uniformity of both p(max) and lambda(max) toward the cluster and the distribution of the color excess with distance, it seems likely that the polarization in this region arises from aligned dust grains in the foreground of the cluster, not farther than 500-600 pc. Based on 20 stars located beyond 500 pc within the studied field of view, we obtained an average polarization-based total-to-selective extinction ratio R = 2.83 +/- 0.14 yielding visual absorption A(V) = 2.14 +/- 0.16 mag. Using 11 stars with uvby beta data that represent the main sequence of the cluster, we calculated a photometric distance of 1117(-89)(+96) pc. This estimate is fully supported by the UBV-based analysis and the new individual membership probabilities that we derive. Assuming a solar metallicity yields an age of 5 Myr. Our analysis yields controversial results regarding the membership of the stars associated with the SZ Cam system (HD 25638 and HD 25639) to the cluster.
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