M. Marcela Vergne

Revisiting the area of the open cluster Stock¿16

Deep CCD UBV(RI)C photometry has been carried out in the area of the open cluster Stock 16. The different photo- metric diagrams indicate the presence of three superimposed stellar groups, all composed of early type stars. The first of them, the cluster Stock 16, suffers from slightly variable reddening with a mean color excessEB−V � = 0.51 . The second group, reddened byEB−V � = 0.84 , includes the Wolf-Rayet star WR 50 (a WC7+OB), and the third one, with a meanEB−V � = 1.18 , also includes another Wolf-Rayet star, WR 51 (a WN4+OB?). Our results confirm the distance and reddening already stated for Stock 16 but include new members. Concerning the other two highly reddened groups, we show that the first one - located at a distance of 3600 pc - is probably related to an anonymous OB association behind Cen OB1 also at 3600 pc already mentioned in the literature; the other seems to be a distant OB association - at more than 9000 pc - which may belong to the Scutum-Crux spiral arm. In these two groups we find evidence that the absorption law, AV /EB−V = R amounts to 4.0 approximately. The ages of the different star populations in the zone range from 5 × 10 6 yr to 6.4 × 10 6 yr for Stock 16, 8 × 10 6 for the second most reddened group and 5 × 10 6 for the probable association in Scutum-Crux. A determination of the IMF slope of Stock 16 was also carried out for stars in the mass range 1.8 < M < 14 M� , giving a normal value x = 1.3.

Optical Polarization Observations of NGC 6231: Evidence for a Past Supernova Fingerprint*

We present the first linear multicolor polarization observations for a sample of 35 stars in the direction of the Galactic cluster NGC 6231. We have found a complex pattern in the angles of the polarimetric vectors. Near the core of this cluster the structure shows a semicircular pattern that we have interpreted as a reorientation of the dust particles showing the morphology of the magnetic field. We propose that a supernova event occurred some time ago and produced a shock on the local ISM. We discuss in this paper independent confirmations of this event, both from the studies on the diffuse interstellar absorptions and the results of the pre-main-sequence stars. We also show that a supernova is supported by the evolutionary status of the cluster.

Optical polarization observations in the region of Stock 16

We present ( UBVRI ) multicolor linear polarimetric data for 26 of the brightest stars in the area of the open cluster Stock 16 that were considered to study the properties of the ISM (interstellar medium) towards the cluster. Our data yield a mean polarization percentage of

On the Effect of Chaotic Orbits on Dynamical Friction

P\sim2.5\%

Optical multicolor polarization observations in the region of the open cluster NGC 5749

, close to the polarization value produced by the ISM with normal efficiency (

Optical polarization observations in the Scorpius region: NGC 6124★

P_{\lambda_{\rm max}} \sim 5 E_{B-V}

Tidal stripping and accretion in clusters of galaxies with smoothly distributed missing mass

) undergoing a color excess of

How accurate is common wisdom on dynamical friction

E_{B-V} =0.51

Orbital decay of galactic satellites as a result of dynamical friction

. The mean angle of the polarization vectors,

Optical polarization observations in Hogg 22 and NGC 6204

\theta= 74\fdg9