Estudio polarimétrico de cúmulos abiertos en la región de ARA OB1: Hogg 22 y NGC 6204

Vergne, M. M.; Martínez, R.; Feinstein, C.
Bibliographical reference

Boletín de la Asociación Argentina de Astronomía, vol.46, p.74

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2003
Number of authors
3
IAC number of authors
0
Citations
0
Refereed citations
0
Description
We present new (UBVRI) multicolor linear polarimetric data for 22 of the brightest stars in the area of the open clusters Hogg 22 and NGC 6204 with the aim of studying the properties of the ISM (interstellar medium) toward these clusters and between them. The new data were incorporated to our data set of previously taken observations (Waldhausen et al. 1999), resulting the total number of 28 observed stars in the region. Our data yield for NGC 6204 a mean polarization percentage of Pλ_max˜1.8%, close to the polarization value produced by the ISM with normal efficiency (Pλ_max ˜ 5 EB-V) with a color excess of EB-V =0.51. Meanwhile for Hogg 22, located behind NGC 6204, the mean polarization found is Pλ_max˜ 2.15%, lower than the expected value for the observed color excess of EB-V =0.68 (Forbes et al., 1996) and the average efficiency of polarization for the interstellar dust. The mean angle of the polarization vectors of Hogg 22 is θ=44o.9, which agrees quite well with the expected angle produce by dust particles aligned in the direction of the Galactic Plane (θ=48o), while for NGC 6204 a lower value θ=33o.7 was found. We believe that Hogg 22 is being depolarized by the composition of the polarimetric vectors in front and behind of NGC 6204, therefore a simple model of two different dust components with different orientation of the magnetic field can explain the observations of Hogg 22.