Optical polarization observations in the Scorpius region: NGC 6124

VERGNE, M.M.; FEINSTEIN, C.; MARTINEZ, R. E.; ORSATTI, A. M.; ALVAREZ, M.P.

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY

WILEY-BLACKWELL PUBLISHING, INC

Año: 2010 vol. 403 p. 2041 - 2052

0035-8711

We have obtained optical multicolour (UBVRI) linear polarimetric data for 46 of the brightest stars in the area of the open cluster NGC 6124 in order to investigate the properties of the interstellar medium (ISM) that lies along the line of sight toward the cluster. Our data yield a mean polarization efficiencyof  P_V/E_{B-V}=3.1 +/-0.62, i.e., a value lower than the polarization produced by the ISM with normal efficiency for an average color excess of  E_{B-V}=0.80 as that found for NGC 6124. Besides, the polarization shows an orientation of 8..1 degrees which is not parallel to the Galactic Disk, an effect that we think may be caused by the Lupus Cloud. Our analysis also indicates that the observed visual extinction in NGC 6124 is caused by the presence of three different absorption sheets located between the Sun and NGC 6124. The values of the internal dispersion of the polarization  (delta P_v= 1.3% )and of the colour excess (delta E_{B-V}= 0.29 mag) for the members of NGC6124 seem to be compatible with the presence of an intra-cluster dust component. Only six stars exhibit some evidence of intrinsic polarization. Ourwork also shows that polarimetry provides an excellent tool to distinguish between member and non-member stars of a cluster.