EDP Sciences
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Volume 408, Number 1, September II 2003
Page(s) 135 - 140
Section Stellar clusters and associations
DOI http://dx.doi.org/10.1051/0004-6361:20030919

A&A 408, 135-140 (2003)
DOI: 10.1051/0004-6361:20030919

Pismis 20: One or two clusters?

A. M. Orsatti1, 2, E. I. Vega1, 3 and H. G. Marraco1

1  Facultad de Ciencias Astronómicas y Geofísicas, Universidad Nacional de La Plata, Paseo del Bosque s/n, 1900 La Plata, Argentina
2  Instituto de Astrofísica de La Plata, (IALP, CONICET), Paseo del Bosque s/n, 1900 La Plata, Argentina
3  Instituto de Astronomía y Física del Espacio, C. C. 67 Suc. 28, 1428 Buenos Aires, Argentina

(Received 30 December 2002 / Accepted 16 May 2003)

We present UBVRI polarimetric observations of stars in the direction of the open cluster Pismis 20 and WR 67 . It is found that the observed members segregate polarimetrically into two groups, with different associated mean $P_{\max}$ (4.31 and 6.08% respectively). Although in the literature these stars are considered as members of the same cluster, the polarized light from these groups clearly differs. There are two possible explanations: very efficient polarizing dust particles exists between certain members of the cluster; or else Pismis 20 is composed of different groupings superimposed along the line of sight. WR 67 belongs to the group more affected by the dust.

Key words: ISM: dust, extinction -- open clusters and associations: individual: Pis20 -- stars: individual: WR67 -- technique: polarimetric

Offprint request: H. G. Marraco, hmarraco@fcaglp.unlp.edu.ar

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