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|Abundance Variations Within Globular Clusters|
Abundance variations within globular clusters (GCs), and of GC starswith respect to field stars, are important diagnostics of a variety ofphysical phenomena, related to the evolution of individual stars, masstransfer in binary systems, and chemical evolution in high densityenvironments. The broad astrophysical implications of GCs as buildingblocks of our knowledge of the Universe make a full understanding oftheir history and evolution basic in a variety of astrophysical fields.We review the current status of the research in this field, comparingthe abundances in GCs with those obtained for field stars, discussing indepth the evidence for H-burning at high temperatures in GC stars,describing the process of self-enrichment in GCs with particularreference to the case of the most massive Galactic GC ( Cen), anddiscussing various classes of cluster stars with abundance anomalies.Whereas the overall pattern might appear very complex at first sight,exciting new scenarios are opening where the interplay between GCdynamical and chemical properties are closely linked with each other.
|Merged catalogue of reflection nebulae|
Several catalogues of reflection nebulae are merged to create a uniformcatalogue of 913 objects. It contains revised coordinates,cross-identifications of nebulae and stars, as well as identificationswith IRAS point sources.The catalogue is only available in electronic form at the CDS viaanonymous ftp to cdsarc.u-strasbg.fr (220.127.116.11) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/399/141
|Rocket Observations of Far-Ultraviolet Dust Scattering in NGC 2023|
The reflection nebula NGC 2023 was observed by a rocket-borne long-slitimaging spectrograph in the 900-1400 Å bandpass on 2000 February11. A spectrum of the star, as well as that of the nebular scatteredlight, was recorded. Through the use of a Monte Carlo modeling process,the scattering properties of the dust were derived. The albedo is low,0.2-0.4, and decreasing toward shorter wavelengths, while the phasefunction asymmetry parameter is consistent with highlyforward-scattering grains, g~0.85. The decrease in albedo, while theoptical depth increases to shorter wavelengths, implies that the far-UVrise in the extinction curve is due to an increase in absorptionefficiency.
|Barnard's Merope Nebula Revisited: New Observational Results|
IC 349 is a small, fan-shaped reflection nebula located only 30" from 23Tau; its nucleus is, by a factor 15, the brightest area of the Pleiadesnebulosity. We propose that IC 349 is a fragment of the Taurus-Aurigamolecular cloud that has been encountered by the Pleiades in thatcluster's southward motion and is being illuminated and shaped by theradiation field of 23 Tau. New Hubble Space Telescope multicolor imageryand the structure, colors, and surface brightness of IC 349 arediscussed in terms of that hypothesis. What is known of the propermotion of the nebula, what can be inferred of the properties of thenebula from its color, and what is expected from radiation pressuretheory appear to be compatible with this cloudlet-encounter hypothesis.
|The UV spectrum of nebulae|
This paper presents an analysis of the UV spectrum of some nebulae withclearly identified illuminating stars, all observed by the IUEsatellite.The data show remarkable properties of the UV spectrum of thenebulae. Each spectrum is the product of the star spectrum and a linearfunction of 1/lambda. There is no peculiar behaviour in the spectrums at2200 A: no bump created in the spectrum of a nebula and no excess ofscattering. When moving away from the star, the surface brightness of anebula decreases as the inverse of the square of the angular distance tothe star.These results can logically be interpreted in terms ofscattering of starlight. They imply constant properties of theinterstellar grains in the UV and in the directions of space sampled bythe nebulae, and probably a strong forward scattering phase function.There is no evidence for any particular type of grain which wouldspecifically extinguish starlight at 2200 A. Concerning the UV spectrumof a star, this may imply a revisal of the traditional interpretation ofthe 2200 A bump.
|Distribution of gas, dust and the lambda 6613 Å DIB carrier in the Perseus OB2 association|
We present a study of the spatial distribution of the lambda 6613 ÄDIB carrier in the Perseus OB2 association based on high resolutionobservations toward lines of sight representing different interstellarenvironments. We determined that in the studied region, the lambda 6613Ä DIB carrier is concentrated in two distinct clouds withvelocities of 1.4 (+/- 0.4) and 12.0 (+/- 0.9) km s(-1) . We comparedthe lambda 6613 Ä DIB carrier's velocity with the Na I velocitydistribution derived from our survey measurements, as well as with CO,OH, H I and Ca Ii measurements from the literature. We conclude that thebehaviour of the carrier of the lambda 6613 Ä DIB follows theoverall expansion motion of the gas in the association. The DIB velocityis directly linked to that of Ca Ii and H I. The DIB total columndensity is proportional to the total column density of Ca Ii and H Imaking those atoms good tracers of the lambda 6613 Ä DIB carrier.Those new results support the assumption that the lambda 6613 Ä DIBwould arise from a gas phase molecule, possibly single-ionized(Sonnentrucker et al. 1997). We also conclude that the DIB carrier isdistributed in shell structures over the whole association. We finallyshow from the DIB velocity structure that the DIB carrier, gas and dustare well mixed toward the association but that the DIB shells have anangular extent twice larger than that of the dust. Based on observationswith OHP 1.52m Telescope and Aurelie spectrograph.
|Photodissociated H I in NGC 2023|
We report the detection of photodissociated H I toward the reflectionnebula NGC 2023. The Very Large Array observations reveal compact (~ 0.3pc) emission associated with the source. The observed spectrum has adouble-peaked profile that we believe is caused by absorbing foregroundneutral gas. We corrected the observed spectrum for the absorption, anddetermined with this absorption-corrected profile an H I column densityand mass of 1.7 ×1021 cm-2 and 1.2Modot, respectively. This column density agrees well withtheoretical model predictions. The H I 21 cm map shows a morphology verysimilar to that present in the images of [C II] at 158 μm, HIRES 60μm IRAS, and POSS optical.
|A Survey of Near-Infrared Emission in Visual Reflection Nebulae|
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1996ApJS..102..369S&db_key=AST
|Briefly noted: Irish astronomy (poem)|
|Le secret des Pleiades.|
|The albedo and scattering phase function of interstellar dust and the diffuse background at far-ultraviolet wavelengths|
The diffuse FUV background in a variety of targets has been observedwith a nebular spectrometer designed specifically to eliminate potentialsources of contamination. The intensity of the background near theGalactic plane is found to be much lower than previously published. Thedata are analyzed using a radiative transfer model with a limited set offree parameters, including those which describe the scatteringproperties of the interstellar dust. Strong evidence is presented thatscattering of starlight by Galactic dust associated with neutralhydrogen produces the major part of the FUV diffuse background. Fewassumptions are necessary to conclude that the albedo of the grains islow in the FUV. The grains, at least at high latitude, scatter fairlyisotropically in the FUV. The low FUV albedo and the usual phase factorg are not consistent with predictions of standard models for the sizedistribution and composition of interstellar grains.
|IRAS Surface Brightness Images of Reflection Nebulae in the Pleiades|
|Colors of reflection nebulae. I - Phase function effects in the Merope nebula|
The subject of color differences between reflection nebulae and theirilluminating stars is reexamined in the light of developments ofobservational techniques, permitting accurate surface-brightnessphotometry over an expanded spectral region from the UV to the IR.Color-color diagrams for reflection nebulae can yield useful informationabout the wavelength dependence of the scattering properties of nebulardust without excessive sensitivity to the specific nebular geometry orthe presence of multiple scattering, resulting in considerable savingsin computational efforts. As an illustration, the color-differencemethod was applied to existing data for the Merope nebula, covering thespectral region 1550-5500 A. Strong evidence for a monotonicallychanging phase function of scattering at wavelengths less than or equalto 3500 A is found. The result is interpreted in the context of aplausible geometry for the Merope environment as providing support for abimodal size distribution of nebular dust grains.
|La constel-lacio de Tauro.|
|The surface brightness of reflection nebulae - NGC 1432 and the 17 Tauri nebulosity|
New photoelectric surface brightness measurements of the reflectionnebulae near 20 Tau and 17 Tau are reported for intermediate widthbandpasses centered near 3500, 4100, 4700, and 5500 A. The derivedsurface brightness distributions have been used to set limits on thedensity and the spatial extent of the dust clouds near these stars. NGC1432 (20 Tau) can be represented successfully by either an inclinedplane-parallel dust slab with the star in front or by an extended,optically thin spherical shell surrounding 20 Tau. The 17 Tau nebulosityis most easily modelled by an extended spherical cloud of low uniformdensity. A comparison of the absolute surface brightness of fourreflection nebulae, NGC 7023, NGC 1435, NGC 1432, and the 17 Taunebulosity, shows the latter two to be relatively inefficient producersof scattered light.
|IUE observations of reflection nebulae|
Low-resolution IUE spectra in the SWP and LWR ranges were obtained ofseveral reflection nebulae in the vicinity of their respectiveilluminating stars. Data for NGC 7023 (HD200775), NGC 1435 (Merope, 23Tau), NGC 1432 (Maia, 20 Tau) and the Electra (17 Tau) nebula were foundto display significant differences in the shape of their normalizednebular spectra. If the dust in these nebulae is similar from one objectto the next, these differences can be most readily explained bydifferences in the line-of-sight dust distribution, coupled with awavelength-dependent phase function, changing from a strongly forwardthrowing form (g = 0.6-0.7) in the visible to a more nearly isotropicshape (g approximately 0.25) at 1400A.
|Studies of bright diffuse galactic nebulae with special regard to their spatial distribution.|
|Measures of Barnard's new Merope nebula.|
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