Interstellar polarization and extinction towards the young open cluster NGC 1502
Department of Physics and Astronomy, Virginia Military Institute,
2 Department of Physics and Astronomy, University of Wisconsin Oshkosh, 800 Algoma Blvd., Oshkosh, WI 54901, USA
3 Department of Theoretical Physics and Astrophysics, Masaryk University, Kotlářská 2, 611 37 Brno, Czech Republic
Accepted: 6 March 2018
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 uvbyβ 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 uvbyβ 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 pmax and λmax 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 AV = 2.14 ± 0.16 mag. Using 11 stars with uvbyβ 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.
Key words: stars: early type / open clusters and associations: individual: NGC 1502
© ESO 2018