The Pleiades Reflection Nebula. II. Simple Model Constraints on Dust Properties and Scattering Geometry
We have used wide-field ultraviolet, optical, and far-infraredphotometric images of Pleiades reflection nebulosity to analyze dustproperties and the three-dimensional nebular geometry. Scattered lightdata were taken from 1650 and 2200 Å Wide-Field Imaging SurveyPolarimeter images and a large 4400 Å mosaic of Burrell SchmidtCCD frames. Dust thermal emission maps were extracted from IRAS data.The scattering geometry analysis is complicated by the blending of lightfrom many stars and the likely presence of more than one scatteringlayer. Despite these complications, we conclude that most of thescattered light comes from dust in front of the stars in at least twoscattering layers, one far in front and extensive, the other nearer thestars and confined to areas of heavy nebulosity. The first layer can beapproximated as an optically thin, foreground slab whose line-of-sightseparation from the stars averages ~0.7 pc. The second layer is alsooptically thin in most locations and may lie at less than half theseparation of the first layer, perhaps with some material among orbehind the stars. The association of nebulosities peripheral to the maincondensation around the brightest stars is not clear. Models withstandard grain properties cannot account for the faintness of thescattered UV light relative to the optical. Some combination ofsignificant changes in grain model albedo and phase function asymmetryvalues is required. Our best-performing model has a UV albedo of0.22+/-0.07 and a scattering asymmetry of 0.74+/-0.06. Hypotheticaloptically thick dust clumps missed by interstellar sight linemeasurements have little effect on the nebular colors but might shiftthe interpretation of our derived scattering properties from individualgrains to the bulk medium.
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The Pleiades and alpha Persei Clusters
The upper-main-sequence members of the Pleiades and alpha Perseiclusters, considered as members of the Local Association, yield meanparallaxes that are only 4% larger than the mean values from Hipparcosobservations. The (log T_eff, M_V) diagram reveals that in thetemperature range from 6000 to 8000 K, the Hyades and alpha Perseimain-sequence members are nearly identical and several tenths of amagnitude brighter than similar stars on the Pleiades main sequence. Thedeparture of the Pleiades main sequence cannot be traced to either ageor heavy-element abundance differences in the range thought to apply tothese clusters. A 50% increase in the helium abundance of Pleiades overHyades stars could account for the luminosity difference. Alternativeexplanations are that the Pleiades cluster is rejected from superclustermembership and/or that the Hipparcos parallax results for the Pleiadesare in error by some 10%.
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Vitesses radiales. Catalogue WEB: Wilson Evans Batten. Subtittle: Radial velocities: The Wilson-Evans-Batten catalogue.
We give a common version of the two catalogues of Mean Radial Velocitiesby Wilson (1963) and Evans (1978) to which we have added the catalogueof spectroscopic binary systems (Batten et al. 1989). For each star,when possible, we give: 1) an acronym to enter SIMBAD (Set ofIdentifications Measurements and Bibliography for Astronomical Data) ofthe CDS (Centre de Donnees Astronomiques de Strasbourg). 2) the numberHIC of the HIPPARCOS catalogue (Turon 1992). 3) the CCDM number(Catalogue des Composantes des etoiles Doubles et Multiples) byDommanget & Nys (1994). For the cluster stars, a precise study hasbeen done, on the identificator numbers. Numerous remarks point out theproblems we have had to deal with.
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X-ray studies of coeval star samples. II - The Pleiades cluster as observed with the Einstein Observatory
Coronal X-ray emission of the Pleiades stars is investigated, andmaximum likelihood, integral X-ray luminosity functions are computed forPleiades members in selected color-index ranges. A detailed search isconducted for long-term variability in the X-ray emission of those starsobserved more than once. An overall comparison of the survey resultswith those of previous surveys confirms the ubiquity of X-ray emissionin the Pleiades cluster stars and its higher rate of emission withrespect to older stars. It is found that the X-ray emission from dA andearly dF stars cannot be proven to be dissimilar to that of Hyades andfield stars of the same spectral type. The Pleiades cluster members showa real rise of the X-ray luminosity from dA stars to early dF stars.X-ray emission for the young, solarlike Pleiades stars is about twoorders of magnitude more intense than for the nearby solarlike stars.
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A VBLUW photometric survey of the Pleiades cluster
Photometric data are presented for 390 known or suspected members of thePleiades cluster. The data were obtained in 1979 at ESO using theWalraven VBLUW photometer and the Dutch 91-cm telescope. A comparisonwas made with subsets obtained with the same telescope andinstrumentation at the former Leiden Southern Station at the SAAO annexduring 1976 and 1977, and with data obtained at ESO during 1980 and1981. The much improved performance of the telescope and the photometerat their new site is obvious from these comparisons. The stars measuredcomprise the selection of possible members by Hertzsprung (1947)brighter than m(pg) = 14.5 and a selection of possible members in theouter region of the cluster by Pels et al. (1975). Of the starsselected, 66 were found not to be members. A few of these are possiblyescaping members. The present data set provides a well determined mainsequence over the range K2V to B9V, as well as data on some of theprobably premain-sequence K2-to-K5 and postmain-sequence B8-to-B6 stars.Finding charts for the stars selected by Pels are presented in anappendix.
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A spectroscopic investigation of the Pleiades.
Not Available
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Photoelectric photometry of stars in the system UPXYZVS with glass filters. V. Pleiades.
Not Available
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Photoelectric Studies.IV. Color-Luminosity Array for Stars in the Region of the Sun.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1950ApJ...112..141E&db_key=AST
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Photoelectric Studies. II. Color-Luminosity Array for Members of the Pleiades Cluster.
Abstract image available at:http://adsabs.harvard.edu/abs/1950ApJ...111...81E
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Spectrophotometric methods for determining stellar luminosity.
Not Available
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The physical members of the Pleiades group
Not Available
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