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Optical polarization study in the open cluster NGC 6250
We present (UBVRI) multicolour linear polarimetric data for 32 of thebrightest stars in the area of the open cluster NGC 6250, with the aimof studying the properties of the interstellar medium (ISM) towards thecluster. Our data yield a mean polarization per cent, close to thepolarization value produced by the ISM with normal efficiency for a meancolour excess of EB- V = 0.37. Our analysis indicates thatthe observed visual absorption in NGC 6250 is caused by a nearby dustlayer (within 300 pc) producing a polarization with an angle close tothe Galactic plane (?GP ~ 38°). In addition, thereare at least two more dust layers along the line of sight between theSun and the cluster producing a change in the observed polarization,making our results compatible with Neckel and Klare's results. Theobservations show differences between the orientation of the localmagnetic field of the nearby dust layer and the one that is polarizingalong the way to the cluster (??v = 20°).The internal dispersion of the polarization values for the members ofNGC 6250 seems to be compatible with the presence of intracluster dust.The majority of observed stars do not present evidence of intrinsicpolarization in their light. In this work, we also show (as in severalprevious papers) how polarimetry is an excellent technique foridentifying non-member stars.Based on observations obtained at Complejo Astronómico ElLeoncito (CASLEO), operated under agreement between the Conicet and theNational Universities of La Plata, Córdoba, and San Juan,Argentina.E-mail: cfeinstein@fcaglp.unlp.edu.ar
| Diffuse interstellar bands in RAVE survey spectra
We have used spectra of hot stars from the RAVE Survey in order toinvestigate the visibility and properties of five diffuse interstellarbands previously reported in the literature. The RAVE spectroscopicsurvey for Galactic structure and kinematics records CCD spectracovering the 8400-8800 Å wavelength region at 7500 resolvingpower. The spectra are obtained with the UK Schmidt at the AAO, equippedwith the 6dF multi-fiber positioner. The DIB at 8620.4 Å is by farthe strongest and cleanest of all DIBs occurring within the RAVEwavelength range, with no interference by underlying absorption stellarlines in hot stars. It correlates so tightly with reddening that itturns out to be a reliable tool to measure it, following the relationEB-V = 2.72 (± 0.03)× EW~(Å), validthroughout the general interstellar medium of our Galaxy. The presenceof a DIB at 8648 Å is confirmed. Its intensity appears unrelatedto reddening, in agreement with scanty and preliminary reports availablein the literature, and its measurability is strongly compromised bysevere blending with underlying stellar He I doublet at 8649 Å.The two weak DIBs at 8531 and 8572 Å do not appear real and shouldactually be blends of underlying stellar lines. The very weak DIB at8439 Å cannot be resolved within the profile of the much strongerunderlying hydrogen Paschen 18 stellar line.Table 1 is only available in electronic form at http://www.aanda.org
| Absolute proper motions of open clusters. I. Observational data
Mean proper motions and parallaxes of 205 open clusters were determinedfrom their member stars found in the Hipparcos Catalogue. 360 clusterswere searched for possible members, excluding nearby clusters withdistances D < 200 pc. Members were selected using ground basedinformation (photometry, radial velocity, proper motion, distance fromthe cluster centre) and information provided by Hipparcos (propermotion, parallax). Altogether 630 certain and 100 possible members werefound. A comparison of the Hipparcos parallaxes with photometricdistances of open clusters shows good agreement. The Hipparcos dataconfirm or reject the membership of several Cepheids in the studiedclusters. Tables 1 and 2 are only available in electronic form at theCDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/Abstract.html
| Extinction law in dust clouds and the young southern cluster NGC 6250 - Further evidence for high values of R
Abstract image available at:http://adsabs.harvard.edu/abs/1977AJ.....82..902H
| Photometric standard sequences in Norma iII = 320° - 340°
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