Multicolor UBVRI polarimetry of NGC 4755 and the beta Cephei population

VEGA, E. I.; ORSATTI, A. M.; MARTINEZ, R. E.

REVISTA MEXICANA DE ASTRONOMíA Y ASTROFíSICA

UNIV NACIONAL AUTONOMA MEXICO

Lugar: México; Año: 2015 vol. 51 p. 73 - 88

0185-1101

We present UBVRI polarimetric observations of 66 stars in the direction of NGC 4755, including eleven β cephei stars. About half of these variables show indications of intrinsic polarization, but according to the theory neither radial nor non-radial pulsations could cause such polarizations. From the main characteristics of their P_{V} vs. λ_{V} curves we found as a possible origin, in some cases, scattering of light in extended atmospheres and suspected binarity, in some cases. The parameters of the interstellar medium towards the cluster are P_{V}=2.76± 0.13(%) and θ_{V}=76.6° ± 0.9°; the mean wavelength of maximum polarization amounts to 0.56± 0.04μ m. The value of polarization efficiency is higher than the mean, indicating a good alignment of the dust particles. A total of 25 stars were identified as members of NGC 4755; the identification task was improved through the use of polarimetric tools.