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Optical polarization observations in Hogg 22 and NGC 6204
We present new (UBVRI) multicolor linear polarimetric data for 22 of thebrightest stars in the area of the open clusters Hogg 22 and NGC 6204 tostudy the properties of the ISM (interstellar medium) toward theseclusters and between them. The new data were incorporated in our dataset of previous observations (Waldhausen et al. \cite{waldhausen}),resulting in 28 observed stars in the region. Our data yield for NGC6204 a mean polarization percentage ofPλ_max1.8%, close to the polarization valueproduced 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 isPλ_max 2.15%, lower than the expected value forthe 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=44.9°, which agrees with the expected angle produce by dust particlesaligned in the direction of the Galactic Plane(θ=48°), while for NGC 6204 a lower value,θ=33.7 °, was found. Therefore, we believe that Hogg 22 isdepolarized by the same dust that is polarizing NGC 6204, due todifferent orientations of the dust particles (and magnetic fields) thatpolarize the starlight.Based on observations obtanined at Complejo Astronómico ElLeoncito (CASLEO), operated under agreement between the CONICET and theNational Universities of La Plata, Córdoba, and San Juan,Argentina.
| 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
| NGC 6204 and HOGG 22: The Odd Couple
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1996AJ....111.1609F&db_key=AST
| The Henry Draper Extension Charts: A catalogue of accurate positions, proper motions, magnitudes and spectral types of 86933 stars
The Henry Draper Extension Charts (HDEC), published in the form offinding charts, provide spectral classification for some 87000 starsmostly between 10th and 11th magnitude. This data, being highlyvaluable, as yet was practically unusable for modern computer-basedastronomy. An earlier pilot project (Roeser et al. 1991) demonstrated apossibility to convert this into a star catalogue, using measurements ofcartesian coordinates of stars on the charts and positions of theAstrographic Catalogue (AC) for subsequent identification. We presenthere a final HDEC catalogue comprising accurate positions, propermotions, magnitudes and spectral classes for 86933 stars of the HenryDraper Extension Charts.
| Analysis of the results of MK classification of 176 stars in 37 southern open clusters
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1979A&AS...37..345F&db_key=AST
| Southern open stars clusters. III. UBV-Hbeta photometry of 28 clusters between galactic longitudes 297d and 353d
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1973A&AS...10..135M&db_key=AST
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