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V733 Cep (Persson's Star): A New FU Orionis Object in Cepheus
Persson recently found that a faint star had appeared in a cloud inCepheus. A CCD image shows a R~17.3 nebulous star, now known as V733Cep, located in the L1216 = Cep F cloud at the apex of a cavity in thecloud. Infrared photometry indicates a modest infrared excess. Opticalspectroscopy shows a well-defined Li I λ6707 line, andblueshifted absorption troughs at the Hα and Na I D linesextending to at least 200 km s-1, indicative of a massivefast wind. An infrared 1-4 μm spectrum of V733 Cep shows the presenceof strong water vapor features, and is almost identical to a similar IRspectrum of FU Ori that is reddened by AV=8 mag. Assuming anintrinsic energy distribution similar to that of FU Ori, V733 Cep has aluminosity of about 135 Lsolar at the assumed distance of 800pc. The star was detected by the Midcourse Space Experiment satellite at8.3 μm, but not by IRAS. Nor is it detected at 850 μm, indicatingthat while the star possesses circumstellar material it is notsurrounded by a significant cool envelope. A 12CO(3-2) mapshows what appears to be a small molecular outflow along the same axisas the cavity seen in optical images. There is evidence for a limitedamount of other low- and medium-mass star formation in the Cep F cloud.The totality of the evidence strongly indicates that V733 Cep is a newFU Ori-type object that must have erupted sometime between 1953 and1984.
| Study of photon dominated regions in Cepheus B
Aims. The aim of the paper is to understand the emission from the photondominated regions in Cepheus B, estimate the column densities of neutralcarbon in bulk of the gas in Cepheus B and to derive constraints on thefactors which determine the abundance of neutral carbon relative toCO. Methods: .This paper presents 15 arcmin ×15 arcmin fullysampled maps of [C I] at 492 GHz and 12CO 4-3 observed withKOSMA at 1´ resolution. The new observations have been combinedwith the FCRAO 12CO 1-0, IRAM-30 m 13CO 2-1 andC18O 1-0 data, and far-infrared continuum data fromHIRES/IRAS. The KOSMA-τ spherical PDR model has been used tounderstand the [C I] and CO emission from the PDRs in Cepheus B and toexplain the observed variation of the relative abundances of bothC0 and CO. Results: .The emission from the PDRassociated with Cepheus B is primarily at V_LSR between -14 and -11 kms-1. We estimate about 23% of the observed [C II] emissionfrom the molecular hotspot is due to the ionized gas in the H II region.Over bulk of the material the C0 column density does notchange significantly, (2.0±1.4)×1017cm-2, although the CO column density changes by an order ofmagnitude. The observed C/CO abundance ratio varies between 0.06 and 4in Cepheus B. We find an anti-correlation of the observed C/CO abundanceratio with the observed hydrogen column density, which holds even whenall previous observations providing C/CO ratios are included. Here weshow that this observed variation of C/CO abundance with total columndensity can be explained only by clumpy PDRs consisting of an ensembleof clumps. At high H2 column densities high mass clumps, which exhibitlow C/CO abundance, dominate, while at low column densities, low massclumps with high C/CO abundance dominate.
| The relation between far-UV and visible extinctions
For directions of sufficient reddening (/E(B-V)>~0.25), there is asimple relation between the slope of the extinction curve in the far-UVand /E(B-V). Regardless of direction, the far-UV extinction curve isproportional to 1/λn e-2E(B-V)/λ(/λ in μm, /n=4), in accordance with the idea that reddenedstars spectra are contaminated by scattered light (Zagury, 2001b). Thisrelation is not compatible with the standard theory of extinction whichstates that far-UV and visible extinctions are due to different classesof particle. In that model the two (far-UV and visible) extinctions varythus independently according to the proportion of each type of particle.In preceding papers I have shown that the standard theory cannot explainUV observations of nebulae, and is contradicted by the UV spectra ofstars with very low reddening: for how long shall the standard theory beconsidered as the interpretation of the extinction curve?
| A Search for High-Velocity Be Stars
We present an analysis of the kinematics of Be stars based uponHipparcos proper motions and published radial velocities. We findapproximately 23 of the 344 stars in our sample have peculiar spacemotions greater than 40 km s-1 and up to 102 kms-1. We argue that these high-velocity stars are the resultof either a supernova that disrupted a binary or ejection by closeencounters of binaries in young clusters. Be stars spun up by binarymass transfer will appear as high-velocity objects if there wassignificant mass loss during the supernova explosion of the initiallymore massive star, but the generally moderate peculiar velocities of BeX-ray binaries indicate that the progenitors lose most of their massprior to the supernova (in accordance with model predictions). Binaryformation models for Be stars predict that most systems bypass thesupernova stage (and do not receive runaway velocities) to createultimately Be+white dwarf binaries. The fraction of Be stars spun up bybinary mass transfer remains unknown, since the post-mass transfercompanions are difficult to detect.
| Statistical analysis of intrinsic polarization, IR excess and projected rotational velocity distributions of classical Be stars
We present the results of statistical analyses of a sample of 627 Bestars. The parameters of intrinsic polarization (p*),projected rotational velocity (v sin i), and near IR excesses have beeninvestigated. The values of p* have been estimated for a muchlarger and more representative sample of Be stars (~490 objects) thanpreviously. We have confirmed that most Be stars of early spectral typehave statistically larger values of polarization and IR excesses incomparison with the late spectral type stars. It is found that thedistributions of p* diverge considerably for the differentspectral subgroups. In contrast to late spectral types (B5-B9.5), thedistribution of p* for B0-B2 stars does not peak at the valuep*=0%. Statistically significant differences in the meanprojected rotational velocities (/line{vsin i}) are found for differentspectral subgroups of Be stars in the sense that late spectral typestars (V luminosity class) generally rotate faster than early types, inagreement with previously published results. This behaviour is, however,not obvious for the III-IV luminosity class stars. Nevertheless, thecalculated values of the ratio vt/vc of the truerotational velocity, vt, to the critical velocity forbreak-up, vc, is larger for late spectral type stars of allluminosity classes. Thus, late spectral type stars appear to rotatecloser to their break-up rotational velocity. The distribution of nearIR excesses for early spectral subgroups is bi-modal, the position ofthe second peak displaying a maximum value E(V-L)~ 1 . m 3for O-B1.5 stars, decreasing to E(V-L)~0. m8 for intermediatespectral types (B3-B5). It is shown that bi-modality disappears for latespectral types (B6-B9.5). No correlations were found betweenp* and near IR excesses and between E(V-L) and vsin i for thedifferent subgroups of Be stars. In contrast to near IR excesses, arelation between p* and far IR excesses at 12 mu m is clearlyseen. A clear relation between p* and vsin i (as well asbetween p* and /line{vsin i}/vc) is found by thefact that plots of these parameters are bounded by a ``triangular"distribution of p*: vsin i, with a decrease of p*towards very small and very large vsin i (and /line{vsini}/vc) values. The latter behaviour can be understood in thecontext of a larger oblateness of circumstellar disks for the stars witha rapid rotation. From the analysis of correlations between differentobservational parameters we conclude that circumstellar envelopes forthe majority of Be stars are optically thin disks with the range of thehalf-opening angle of 10degr
| CO mapping and multi-line-analysis of Cepheus B
We present large scale (approx. 15x15 arcmin) on-the-fly maps of theCepheus B molecular cloud in the J=3-2 and 2-1 transitions of12CO, 13CO and C18O obtained with theKOSMA 3m-telescope. We use these maps to study the spatial variation ofthe excitation conditions of the molecular gas. Additional Ciobservations allow to refine our analysis. The gas temperature isdominated by UV radiation from identified adjacent and embedded sourcesplus additional heating by a hot core in the north-west of the cloud. Aspherical clump PDR model allows to reproduce the observed line ratiosat most positions. Only 12CO line ratios at the hot coreposition are inconsistent with this scenario and hence give evidence foradditional heating mechanisms. Local volume densities are ~ 2*104 cm-3 while the average volume density ofCepheus B is less than 103 cm-3; thus, Cepheus Bis highly clumped and the volume of these clumps fills only 2% to 4% ofthe whole cloud. Deep penetration of FUV radiation into the clumpymedium is consistent with the detection of [Ci] emission from within thecloud. Abundance ratios of atomic carbon to CO are >= 0.2. The13CO/C18O integrated line intensity ratio risessignificantly above the isotopic element ratio at the cloud edges whereC18O intensities are low. Possible explanations for thiscommon observation in terms of fractionation and selectivephotodissociation on clump surfaces in a clumpy cloud are discussed.
| Catalogue of H-alpha emission stars in the Northern Milky Way
The ``Catalogue of Stars in the Northern Milky Way Having H-alpha inEmission" appears in Abhandlungen aus der Hamburger Sternwarte, Band XIin the year 1997. It contains 4174 stars, range {32degr <= l() II< 214degr , -10degr < b() II < +10degr } having the Hαline in emission. HBH stars and stars of further 99 lists taken from theliterature till the end of 1994 were included in the catalogue. We givethe cross-identification of stars from all lists used. The catalogue isalso available in the Centre de Données, Strasbourg ftp130.79.128.5 or http://cdsweb.u-strasbg.fr and at the HamburgObservatory via internet.
| CS observations of the hotspot at the S 155/Cepheus B interface
We have used the IRAM 30-m telescope to map, in the J=2-1, J=3-2 andJ=5-4 rotational transitions of CS, the molecular hotspot locatedsouth-east of the Cepheus OB3 association, at the interface that dividesthe S 155 diffuse Hii region from the Cepheus B molecular cloud. We havealso used the FCRAO 13.7-m telescope to map the larger scale CS(2-1)emission. The $+/-imeq 1'\times 1'$ segment that has been mapped athigher spatial resolution with the 30-m telescope covers four radiocontinuum sources, one of which (source A) is a blister-type Hii region.By using the CS molecule we analyse: i) the molecular density at theinterface region and ii) the kinematics of the molecular gas at thefront. The observations confirm that the blister has created a cavity atthe edge of the molecular hotspot and is bounded on its sharp side by adense mlecular front in pressure equilibrium with the ionized gas. Thenear-IR star at the centre of the blister (A-NIR) is responsible for itsionization and for the heating of the hotspot.
| UBV beta Database for Case-Hamburg Northern and Southern Luminous Stars
A database of photoelectric UBV beta photometry for stars listed in theCase-Hamburg northern and southern Milky Way luminous stars surveys hasbeen compiled from the original research literature. Consisting of over16,000 observations of some 7300 stars from over 500 sources, thisdatabase constitutes the most complete compilation of such photometryavailable for intrinsically luminous stars around the Galactic plane.Over 5000 stars listed in the Case-Hamburg surveys still lackfundamental photometric data.
| Be stars in open clusters. II. Balmer line spectroscopy
We present Hα line profiles (R ~= 3x103, S/N ~=102 at continuum level, ~= 50 for some objects) for 58 starsin 8 northern open clusters and associations, complemented with Hβand Hγ profiles for 36 of them as well as Hdelta and Hepsilon for16 programme stars. Our observations, though lower in resolution, yieldresults which are in good agreement with those obtained in earlier worksbased mainly on field Be stars. Our data suggest a similar spectroscopicbehavior for both field and cluster Be stars. The line parameters (EW,FWHM, Delta vp) have been obtained for each line. Nearly thewhole set of stars have previously published quasi-simultaneousuvby\beta photometry, so a study of reliable correlations betweenphotometric and spectroscopic data can be undertaken. Based onobservations made at the German-Spanish Astronomical Center, Calar Alto,Spain which is operated by the Max Planck Institut fuer Astronomie,Heidelberg, jointly with the spanish National Commission for Astronomy.
| Catalogue of stars in the northern Milky Way having H-alpha in emission
Not Available
| Be stars in open clusters I. uvbyβ photometry.
We present uvbyβ photometry for Be stars in eight open clusters andtwo OB associations. It is shown that Be stars occupy anomalouspositions in the photometric diagrams, which can be explained in termsof the circumstellar continuum radiation contribution to the photometricindices. In the (b-y)_0_-M_V_ plane Be stars appear redder than the nonemission B stars, due to the additional reddening caused by the hydrogenfree-bound and free-free recombination in the circumstellar envelope. Inthe c_0_-M_V_ plane the earlier Be stars present lower c_0_ values thanabsorption-line B stars, which is caused by emission in the Balmerdiscontinuity, while the later Be stars deviate towards higher c_0_values, indicating absorption in the Balmer discontinuity ofcircumstellar origin.
| Derivation of the Galactic rotation curve using space velocities
We present rotation curves of the Galaxy based on the space-velocitiesof 197 OB stars and 144 classical cepheids, respectively, which rangeover a galactocentric distance interval of about 6 to 12kpc. Nosignificant differences between these rotation curves and rotationcurves based solely on radial velocities assuming circular rotation arefound. We derive an angular velocity of the LSR of{OMEGA}_0_=5.5+/-0.4mas/a (OB stars) and {OMEGA}_0_=5.4+/-0.5mas/a(cepheids), which is in agreement with the IAU 1985 value of{OMEGA}_0_=5.5mas/a. If we correct for probable rotations of the FK5system, the corresponding angular velocities are {OMEGA}_0_=6.0mas/a (OBstars) and {OMEGA}_0_=6.2mas/a (cepheids). These values agree betterwith the value of {OMEGA}_0_=6.4mas/a derived from the VLA measurementof the proper motion of SgrA^*^.
| UBVRI-CCD photometry of Cepheus OB3 association.
Johnson CCD photometry was performed in the two subgroups of theassociation Cepheus OB3, for selected fields each containing at leastone star with previous UBV photoelectric photometry. Photometry forabout 1000 stars down to visual magnitude 21 is provided, although thecompleteness tests show that the sample is complete down to V=19mag.Individual errors were assigned to the magnitude and colours for eachstar. Colour-colour and colour-magnitude diagrams are shown. Astrometricpositions of the stars are also given. Description of the reductionprocedure is fully detailed.
| 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.
| Sequential star formation in the Cepheus molecular cloud: the S 155/Cepheus B interface.
In this paper we present new radio and near-infrared observations of abright Hα knot located south-east of the Cepheus OB3 association,near the ionization front that divides the S 155 diffuse HII region fromthe Cepheus B molecular cloud. The arcsec resolution VLA radio continuumimages reveal that the previously unresolved radio source # 9,coincident with the Hα knot, is composed of four distinct sources:an extended RIDGE and three smaller diameter components. From the radiocontinuum spectrum and the general morphology it is possible to deducethat the RIDGE represents an ionization front in the northern part ofthe Hα knot. The larger of the small-diameter components is ablister-type compact HII region, still partly bounded by high densitymolecular gas. Another one of these components, which is very weak, isfound to be variable. The third source is definitely unresolved even at0.4 arcsec resolution and has a non-thermal spectral index. In thelatter two sources, the proximity to sources with strong NIR excess inthe field suggests that they are not background objects but, mostprobably, the non-thermal emission of PMS stars. Near-infrared J, H, andK observations of the same region with similar resolution have detectedseveral objects, either inside the Hα knot or deeply embedded inthe dust cloud/molecular clump to the south of it. Three red sources(previously undetected even in I-band) are found to be close to thepositions of the three small-diameter radio continuum sources. One ofthese is located at the center of the blister type HII region andclearly is produced by its highly obscured exciting star. This miniaturenear-infrared stellar cluster (in terms of total extension, if comparedto the size of the neighboring OB association or of the Cepheus Bmolecular cloud) may be the product of an outburst of star formationtriggered by the compression of the Cepheus B molecular cloud by theionization front produced by the brightest stars of theprevious-generation OB association. While the large-scale generalmorphology and the ionization balance of the S 155/Cepheus B molecularcloud is dictated by the brightest members of the OB association, theenergy for the far-IR emission from the region of the Hα knot andthe heating of the adjacent molecular hotspot may come entirely from thestars of the newly-formed cluster, without the need of external inputfrom the luminous stars of the OB association.
| Trapezium systems containing T tauri stars
The results of a spectroscopic investigation of four stars comprising aTrapezium system in the nebula Sh 155 are presented. The stars have anumber of emission lines typical of red emission stars and T Tau stars.This system is one of the 13 systems which we have found in the Palomaratlas. It is shown that all of these systems are members of OBassociations.
| Chemical transitions for interstellar C2 and CN in cloud envelopes
Observations were made of absorption from CH, C2, and CN towardmoderately reddened stars in Sco, OB2, Ceo OB3, and Taurus/Auriga. Forthese directions, most of the reddening is associated with a singlecloud complex, for example, the rho Ophiuchus molecular cloud, and as aresult, the observations probe moderately dense material. When combinedwith avaliable data for nearby directions, the survey provides the basisfor a comprehensive analysis of the chemistry for these species. Thechemical transitions affecting C2 and CN in cloud envelopes wereanalyzed. The depth into a cloud at which a transition takes place wascharacterized by tauuv, the grain optical depth at 1000 A.One transition at tauuv approx. = 2, which arises from, theconversion of C(+) into CO, affects the chemistries for both moleculesbecause of the key role this ion plays. A second one involvingproduction terms in the CN chemistry occurs at tauuv ofapprox. = 3; neutral reactions which C2 and CH is more important atlarger values for tauuv. The transition fromphotodissociation to chemical destruction takes place attauuv approx. = 4.5 for C2 and CN. The observational data forstars in Sco OB2, Cep OB3, and Taurus/Auriga were studied with chemicalrate equations containing the most important production and destructionmechanisms. Because the sample of stars in Sco OB2 includes sight lineswith Av ranging from 1-4 mag, sight lines dominated byphotochemistry could be analyzed separately from those controlled bygas-phase destruction. The analysis yielded values for two poorly knownrate constants for reactions involved in the production of CN; thereactions are C2 + N yields CN + C and C(+) + NH yields all products.The other directions were analyzed with the inferred values. Thepredicted column densities for C2 and CN agree with the observed valuesto better than 50%, and in most instances 20%. When combining theestimates for density and temperature derived from chemical modeling andmolecular excitation for a specific cloud, such as the rho Ophiuchusmolecular cloud, the portion of the cloud envelope probed by C2 and CNabsorption was found to be in pressure equilibrium.
| Tracing the Roots of Interstellar Mid Infrared Emission
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1993A&A...275..549J&db_key=AST
| Hα Interferometric Optical and Near Infrared Photometric Studies of Star Forming Regions - Part One - the Cepheus-B / SH:2-155 / CEPHEUS-OB3 Association Complex
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1993A&A...273..619M&db_key=AST
| Carbon monoxide and far-infrared observations of the S 155-Cepheus B region
We present maps of the CO J = 3-2 and (C-13)O J = 2-1 molecular line andmid- to far-infrared continuum emission of the interface between theCepheus B molecular cloud and the S155 H II region. Far-infrared dustcolor temperature and optical depth maps show the molecular cloud to beexternally heated and that the edge of the cloud is compressed by theexpansion of S155. The data are compared with current models, andvarious dust grain parameters are derived. A hotspot is observed in theCO J = 3-2 emission line, at a position coincident with the radiocontinuum and infrared emission peaks. The infrared, radio continuum,and molecular line emission from the hotspot are all consistent with itbeing a compact H II region, ionized by an embedded B1-B0.5 star. Theposition of the compact H II region, adjacent to the northwestern edgeof Cep B, suggests it is the product of a phase of sequential OB starformation.
| An Einstein Observatory SAO-based catalog of B-type stars
About 4000 X-ray images obtained with the Einstein Observatory are usedto measure the 0.16-4.0 keV emission from 1545 B-type SAO stars fallingin the about 10 percent of the sky surveyed with the IPC. Seventy-fourdetected X-ray sources with B-type stars are identified, and it isestimated that no more than 15 can be misidentified. Upper limits to theX-ray emission of the remaining stars are presented. In addition tosummarizing the X-ray measurements and giving other relevant opticaldata, the present extensive catalog discusses the reduction process andanalyzes selection effects associated with both SAO catalog completenessand IPC target selection procedures. It is concluded that X-rayemission, at the level of Lx not less than 10 exp 30 ergs/s, is quitecommon in B stars of early spectral types (B0-B3), regardless ofluminosity class, but that emission, at the same level, becomes lesscommon, or nonexistent, in later B-type stars.
| Galactic OB associations in the northern Milky Way Galaxy. I - Longitudes 55 deg to 150 deg
The literature on all OB associations was reviewed, and their IRAS pointsource content was studied, between galactic longitude 55 and 150 deg.Only one third of the 24 associations listed by Ruprecht et al. (1981)have been the subject of individual studies designed to identify thebrightest stars. Distances to all of these were recomputed using themethod of cluster fitting of the B main sequence stars, which makes itpoossible to reexamine the absolute magnitude calibration of the Ostars, as well as for the red supergiant candidate stars. Also examinedwas the composite HR diagram for these associations. Associations withthe best defined main sequences, which also tend to contain very youngclusters, referred to here as OB clusters, have extremely few evolved Band A or red supergiants. Associations with poorly defined mainsequences and few OB clusters have many more evolved stars. They alsoshow an effect in the upper HR diagram referred to as a ledge byFitzpatrick and Garmany (1990) in similar data for the Large MagellanicCloud. It is suggested that the differences in the associations are notjust observational selection effects but represent real differences inage and formation history.
| Extinction law survey based on UV ANS photometry
The paper presents an extensive survey of interstellar extinction curvesderived from the ANS photometric measurements of early type starsbelonging to our Galaxy. This survey is more extensive and deeper thanany other one, based on spectral data. The UV color excesses aredetermined with the aid of 'artificial standards', a new techniqueproposed by the authors which allows the special check of Sp/L match ofa target and the selected standard. The results indicate that extinctionlaw changes from place to place.
| Photoelectric photometry of OB stars in the Vilnius system
Not Available
| Infrared dust and millimeter-wave carbon monoxide emission in the Orion region
The far-infrared dust emission seen by the IRAS satellite in the Orionregion is analyzed as a function of the local radiation field intensity,and the dust temperature and opacity are compared with (C-12)O and(C-13)O emission. The infrared radiation is interpreted within theframework of a single-component large grain model and a multicomponentgrain model consisting of subpopulations of grains with size-dependenttemperatures. A strong dependence of the 100-micron optical depthderived is found using the large grain model on the averageline-of-sight dust temperature and radiation field. In the hotenvironment surrounding high-luminosity sources and H II regions, alldust along the line-of-sight radiates at 100 microns, and thedust-to-gas ratio, based on the 100-micron opacity and I(/C-13/O),appears to be in agreement with the standard value, about 1 percent bymass. A relationship is found between the inferred dust-to-gas ratio andthe radiation field intensity responsible for heating the dust which canbe used to estimate the gas column density from the dust opacity derivedfrom the 60- and 100-micron IRAS fluxes.
| Correlation between the very broad structure and the continuum in FUV extinction curves
There exists a correlation between the amount of the far UV extinctionand the relative strength of the very broad structure in the 500 to 600nm wavelength region of the interstellar extinction curves. For a givencolor excess E(B-V) values of the UV extinction large than averagecorrespond to larger strengths of the very broad structure (VBS) andvice versa. The VBS seems to be a common dust-related feature.
| Close binaries observed polarimetrically
Not Available
| Trapezium-type wide systems
On the basis of the Smithsonian Observatory Catalogues 15 Trapezium-typesystems are found. Photometric distances are determined for theTrapezium components. A conclusion is drawn on physical relations of thecomponents in the systems. The fact of existence of Trapezium-type largestellar systems confirms the existence of Trapezia with positive totalenergy.
| The interstellar 217 NM band - A third catalogue of equivalent widths
A catalog of equivalent widths of the 217 nm interstellar absorptionband as well as other parameters characterizing the extinction curve inthe ultraviolet has been compiled for 790 O and B stars. A relativelytight correlation between the equivalent width of the 217 nm band andE(B-V) indicates that the absorber of this band is connected with thepopulation of larger interstellar grains responsible for the visualextinction. The parameter characterizing the amount of extinction in thefar UV is only weakly correlated with E(B-V), a result in accord withthe assumption that a second population of very small grains causes therapid increase of the far-UV extinction.
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