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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 (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/399/141
| The Photophysics of the Carrier of Extended Red Emission
Interstellar dust contains a component that reveals its presence byemitting a broad unstructured band of light in the 540-950 nm wavelengthrange, referred to as extended red emission (ERE). The presence ofinterstellar dust and ultraviolet photons are two necessary conditionsfor ERE to occur. This is the basis for suggestions that attribute EREto an interstellar dust component capable of photoluminescence. In thisstudy, we have collected all published ERE observations withabsolute-calibrated spectra for interstellar environments, where thedensity of ultraviolet photons can be estimated reliably. In each case,we determined the band-integrated ERE intensity, the wavelength of peakemission in the ERE band, and the efficiency with which absorbedultraviolet photons are contributing to the ERE. The data show thatradiation is not only driving the ERE, as expected for aphotoluminescence process, but is modifying the ERE carrier, asmanifested by a systematic increase in the ERE band's peak wavelengthand a general decrease in the photon conversion efficiency withincreasing densities of the prevailing exciting radiation. The overallspectral characteristics of the ERE and the observed high quantumefficiency of the ERE process are currently best matched by the recentlyproposed silicon nanoparticle (SNP) model. Using the experimentallyestablished fact that ionization of semiconductor nanoparticles quenchestheir photoluminescence, we proceeded to test the SNP model bydeveloping a quantitative model for the excitation and ionizationequilibrium of SNPs under interstellar conditions for a wide range ofradiation field densities. With a single adjustable parameter, the crosssection for photoionization, the model reproduces the observations ofERE intensity and ERE efficiency remarkably well. The assumption thatabout 50% of the ERE carriers are neutral under radiation conditionsencountered in the diffuse interstellar medium leads to a prediction ofthe single-photon ionization cross section of SNPs with average diameter3.5 nm of <=3.4×10-15 cm2. The shift ofthe ERE band's peak wavelength toward larger values with increasingradiation density requires a change of the size distribution of theactively luminescing ERE carriers through a gradual removal of thesmaller particles by size-dependent photofragmentation. We propose thatheat-assisted Coulomb decay of metastable, multiply charged SNPs is sucha process, which selectively removes the smaller components of anexisting SNP size distribution.
| Spectral variability of luminous early type stars. I. Peculiar supergiant HD199478
We have obtained time-series of high-quality Hα spectra with highresolution in wavelength (R = lambda /delta lambda of 15000 to 22000)and time (Delta t =1d) of the late-type B supergiant HD199478. Thespectra were analysed in terms of line-profile variability (lpv) usingcontemporary techniques of time-series analysis, such as TemporalVariance Spectrum and the 2d- Discrete Fourier Transform. The Hαprofile is found to consist of a highly variable emission core (between-280 and +150 km s-1) superimposed on almost constant,extended (+/-1000 km s-1) emission wings. Due to the lack ofstrong line-emission, the latter is attributed to electron-scattering indeep atmospheric layers. The Hα variability manifests itself byvariations in velocity and intensity of blue- and red-shifted emissionpeaks, which result in drastic alterations in the shape of the profilefrom almost symmetric and unshifted emission, with respect to thestellar rest frame, through blue- or red-shifted asymmetric emission, todouble-peaked emission or a reverse P Cygni-type profile. Significantvariations in total emissivity (i.e. EW) of the line are also noted, butthese variations do not appear to be obviously linked to changes in theline-profile shape. The pattern of variability resembles that inBe-stars - though on a much shorter time scale - and suggestsinterpretation in terms of an axially symmetric and perturbed stellarwind. Since the time-scale of the V/R variations is found to be 3 to 5times longer than the radial fundamental pulsation period but consistentwith rotational period, rotational modulation as a possible cause forthis variability is considered. Besides variations in Hα ,continuous changes in velocity (typical dispersion of sigma ~ 5 kms-1) and strength, i.e. EW, (up to 13% of the mean) of asample of three absorption lines (CII lambda lambda6583 , 6578 and HeIlambda6678 ) were also observed. The phenomenon observed is more likelyconnected to changes in velocity and temperature structures of thestellar photosphere. Pulsation instability as a possible cause ofphotospheric variability is suggested.
| 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
| Spectroscopy of extended red emission in reflection nebulae
This paper reports the results of a spectroscopic survey of reflectionnebulae, aimed at studying the characteristics of the broad emissionfeature responsible for the extended red emission (ERE) observed inthese objects. The ERE band was detected and its strength, centralwavelength, and width were measured in 12 nebulae, while upper limitswere recorded in 12 further objects. The maximum ERE band intensity wasfound to vary from object to object within an extremely narrow range,while the associated scattered light intensities differed by nearly twoorders of magnitude. The ERE band is interpreted as arising from thephotoluminescence of hydrogenated amorphous carbon (HAC) grains whichbecome rehydrogenated and gain luminescence efficiency in narrow H2photodissociation zones. These zones are probably thin shells around theexciting stars. Observed changes in the central wavelengths and widthsof the ERE bands detected in different parts of a given nebula, and fromnebula to nebula, support the HAC model and are explained as arisingfrom variations in the degree of hydrogenation to the solid grains.
| CO observations of galactic reflection nebulae
Carbon monoxide emission has been observed toward about 35 galacticreflection nebulae. The peaking of CO temperatures near the hotter starsindicates substantial local heating of the gas and dust by the embeddedstars. Wide low-level emission wings are seen on several of the (C-12)Oline profiles; these are most plausibly interpreted as due to cloudmaterial accelerated by such processes as radiation pressure from thenewborn stars.
| Untersuchungen über Reflexionsnebel am Palomar Sky Survey I. Verzeichnis von Reflexionsnebeln
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