目录
图像
上传图像
DSS Images Other Images
相关文章
An Extended FUSE Survey of Diffuse O VI Emission in the Interstellar Medium
We present a survey of diffuse O VI emission in the interstellar medium(ISM) obtained with the Far Ultraviolet Spectroscopic Explorer (FUSE).Spanning 5.5 yr of FUSE observations, from launch through 2004 December,our data set consists of 2925 exposures along 183 sight lines, includingall of those with previously published O VI detections. The data wereprocessed using an implementation of CalFUSE version 3.1 modified tooptimize the signal-to-noise ratio and velocity scale of spectra from anaperture-filling source. Of our 183 sight lines, 73 show O VIλ1032 emission, 29 at >3 σ significance. Six of the 3σ features have velocities |vLSR|>120 kms-1, while the others have |vLSR|<=50 kms-1. Measured intensities range from 1800 to 9100 LU (lineunit; 1 photon cm-2 s-1 sr-1), with amedian of 3300 LU. Combining our results with published O VI absorptiondata, we find that an O VI-bearing interface in the local ISM yields anelectron density ne=0.2-0.3 cm-3 and a path lengthof 0.1 pc, while O VI-emitting regions associated with high-velocityclouds in the Galactic halo have densities an order of magnitude lowerand path lengths 2 orders of magnitude longer. Although the O VIintensities along these sight lines are similar, the emission isproduced by gas with very different properties.Based on observations made with the NASA-CNES-CSA Far UltravioletSpectroscopic Explorer. FUSE is operated for NASA by Johns HopkinsUniversity under NASA contract NAS5-32985.
| The Homogeneity of Interstellar Elemental Abundances in the Galactic Disk
We present interstellar elemental abundance measurements derived fromSpace Telescope Imaging Spectrograph echelle observations of 47 sightlines extending up to 6.5 kpc through the Galactic disk. These pathsprobe a variety of interstellar environments, covering ranges of nearly4 orders of magnitude in molecular hydrogen fraction f(H2)and more than 2 in mean hydrogen sight-line density. Coupling the current data with Goddard HighResolution Spectrograph data from 17 additional sight lines and thecorresponding Far Ultraviolet Spectroscopic Explorer and Copernicusobservations of H2 absorption features, we explore magnesium,phosphorus, manganese, nickel, copper, and germanium gas-phase abundancevariations as a function of : density-dependentdepletion is noted for each element, consistent with a smooth transitionbetween two abundance plateaus identified with warm and cold neutralinterstellar medium depletion levels. The observed scatter with respectto an analytic description of these transitions implies that totalelemental abundances are homogeneous on length scales of hundreds ofparsecs, to the limits of abundance measurement uncertainty. Theprobable upper limit we determine for intrinsic variability at any is 0.04 dex, aside from an apparent 0.10 dexdeficit in copper (and oxygen) abundances within 800 pc of the Sun.Magnesium dust abundances are shown to scale with the amount of siliconin dust, and in combination with a similar relationship between iron andsilicon, these data appear to favor the young F and G star values ofSofia & Meyer as an elemental abundance standard for the Galaxy.Based on observations with the NASA/ESA.
| Supernova remnant S 147 and its associated neutron star(s)
The supernova remnant S 147 harbors the pulsar PSRJ 0538+2817 whose characteristic age is more than an order ofmagnitude greater than the kinematic age of the system (inferred fromthe angular offset of the pulsar from the geometric center of thesupernova remnant and the pulsar proper motion). To reconcile thisdiscrepancy we propose that PSR J 0538+2817 could be the stellarremnant of the first supernova explosion in a massive binary system andtherefore could be as old as its characteristic age. Our proposalimplies that S 147 is the diffuse remnant of the second supernovaexplosion (that disrupted the binary system) and that a much youngersecond neutron star (not necessarily manifesting itself as a radiopulsar) should be associated with S 147. We use the existingobservational data on the system to suggest that the progenitor of thesupernova that formed S 147 was a Wolf-Rayet star (so that thesupernova explosion occurred within a wind bubble surrounded by amassive shell) and to constrain the parameters of the binary system. Wealso restrict the magnitude and direction of the kick velocity receivedby the young neutron star at birth and find that the kick vector shouldnot strongly deviate from the orbital plane of the binary system.
| An Analysis of the Shapes of Ultraviolet Extinction Curves. IV. Extinction without Standards
In this paper we present a new method for deriving UV through IRextinction curves, based on the use of stellar atmosphere models toprovide estimates of the intrinsic (i.e., unreddened) stellar spectralenergy distributions (SEDs), rather than unreddened (or lightlyreddened) standard stars. We show that this ``extinction withoutstandards'' technique greatly increases the accuracy of the derivedextinction curves and allows realistic estimations of the uncertainties.An additional benefit of the technique is that it simultaneouslydetermines the fundamental properties of the reddened stars themselves,making the procedure valuable for both stellar and interstellar studies.Given the physical limitations of the models we currently employ, thetechnique is limited to main-sequence and mildly evolved B stars.However, in principle, it can be adapted to any class of star for whichaccurate model SEDs are available and for which the signatures ofinterstellar reddening can be distinguished from those of the stellarparameters. We demonstrate how the extinction without standards curvesmake it possible to (1) study the uniformity of curves in localizedspatial regions with unprecedented precision, (2) determine therelationships between different aspects of curve morphology, (3) producehigh-quality extinction curves from low color excess sight lines, and(4) derive reliable extinction curves for mid to late B stars, therebyincreasing spatial coverage and allowing the study of extinction in openclusters and associations dominated by such stars. The application ofthis technique to the available database of UV through IR SEDs, and tofuture observations, will provide valuable constraints on the nature ofinterstellar grains and on the processes that modify them, and it willenhance our ability to remove the multiwavelength effects of extinctionfrom astronomical energy distributions.
| B Star Rotational Velocities in h and χ Persei: A Probe of Initial Conditions during the Star Formation Epoch?
Projected rotational velocities (vsini) have been measured for 216 B0-B9stars in the rich, dense h and χ Persei double cluster and comparedwith the distribution of rotational velocities for a sample of fieldstars having comparable ages (t~12-15 Myr) and masses (M~4-15Msolar). For stars that are relatively little evolved fromtheir initial locations on the zero-age main sequence (ZAMS) (those withmasses M~4-5 Msolar), the mean vsini measured for the h andχ Per sample is slightly more than 2 times larger than the meandetermined for field stars of comparable mass, and the cluster and fieldvsini distributions differ with a high degree of significance. Forsomewhat more evolved stars with masses in the range 5-9Msolar, the mean vsini in h and χ Per is 1.5 times thatof the field; the vsini distributions differ as well, but with a lowerdegree of statistical significance. For stars that have evolvedsignificantly from the ZAMS and are approaching the hydrogen exhaustionphase (those with masses in the range 9-15 Msolar), thecluster and field star means and distributions are only slightlydifferent. We argue that both the higher rotation rates and the patternof rotation speeds as a function of mass that differentiatemain-sequence B stars in h and χ Per from their field analogs werelikely imprinted during the star formation process rather than a resultof angular momentum evolution over the 12-15 Myr cluster lifetime. Wespeculate that these differences may reflect the effects of the higheraccretion rates that theory suggests are characteristic of regions thatgive birth to dense clusters, namely, (1) higher initial rotationspeeds; (2) higher initial radii along the stellar birth line, resultingin greater spin-up between the birth line and the ZAMS; and (3) a morepronounced maximum in the birth line radius-mass relationship thatresults in differentially greater spin-up for stars that become mid- tolate-B stars on the ZAMS.
| The Homogeneity of Interstellar Oxygen in the Galactic Disk
We present an analysis of high-resolution Hubble Space Telescope (HST)Space Telescope Imaging Spectrograph (STIS) observations of O Iλ1356 and H I Lyα absorption in 36 sight lines that probe avariety of Galactic disk environments and include paths that range overnearly 4 orders of magnitude in f(H2), over 2 orders ofmagnitude in , and that extend up to 6.5 kpc inlength. Since the majority of these sight lines have also been observedby the Far Ultraviolet Spectroscopic Explorer (FUSE), we have undertakenthe study of gas-phase O/H abundance ratio homogeneity using the currentsample and previously published Goddard High Resolution Spectrograph(GHRS) results. Two distinct trends are identified in the 56 sight linesample: an apparent decrease in gas-phase oxygen abundance withincreasing mean sight-line density () and a gapbetween the mean O/H ratio for sight lines shorter and longer than about800 pc. The first effect is a smooth transition between two depletionlevels associated with large mean density intervals; it is centered near=1.5cm-3 and is similar to trendsevident in gas-phase abundances of other elements. Paths less dense thanthe central value exhibit a mean O/H ratio of log10(O/H)=-3.41+/-0.01 (or 390+/-10ppm), which is consistent with averages determined for several longlow-density paths observed by STIS (André et al. 2003) and shortlow-density paths observed by FUSE (Moos et al. 2002). Sight lines ofhigher mean density exhibit an average O/H value of log10(O/H)=-3.55+/-0.02 (284+/-12ppm). The data points for low- paths are scatteredmore widely than those for denser sight lines, because O/H ratios forsuch paths shorter than 800 pc are generally about 0.10 dex lower thanthe values for longer ones. Scenarios that would be consistent withthese results include a recent infall of metal-poor gas onto the localGalactic disk and an interstellar environment toward Orion that isconducive to reducing the apparent gas-phase oxygen abundance.Based on observations with the NASA/ESA Hubble Space Telescope (HST) andthe NASA-CNES-CSA Far Ultraviolet Spectroscopic Explorer (FUSE). HSTspectra were obtained at the Space Telescope Science Institute, which isoperated by the Association of Universities for Research in Astronomy,Inc., under NASA contract NAS5-26555 FUSE is operated for NASA by theJohns Hopkins University under NASA contract NAS5-32985.
| Stars with ISM Polarization Observed with HPOL. II
Polarization data are given for stars whose polarizations are mostlyinterstellar which were observed with the University of Wisconsinspectropolarimeter (HPOL) during 1995-2003. Several cases are found forwhich K in the Serkowski Law for ISM polarization is higher than allowedby published formulas.
| Intermediate-velocity gas observed towards the Shajn 147 SNR
We present high-resolution spectra (R 3 km s-1) of theinterstellar Na I and Ca II interstellar absorption lines observedtowards 3 early-type stars with distances of 360 to 1380 pc along theline-of-sight towards the 800 pc distant Shajn 147 (S147) SupernovaRemnant (SNR). These data are supplemented with far-UV (912-1180Å) aborption spectra of HD 36665 andHD 37318 recorded with the NASA Far UltravioletSpectroscopic Explorer (FUSE) satellite. The observations revealintermediate-velocity (IV) absorption features at Vhelio =+92 km s-1 towards HD 37318 and atVhelio = -65 and -52 km s-1 towards HD36665, in addition to several other gas cloud components withlower velocity. These IV components can be associated with the expansionof the SNR that has disrupted the surrounding interstellar gas. The IVcomponent at V = +92 km s-1 seen towards HD37318 was detected only in the far-UV lines of Fe II and N II,suggesting that it is composed mainly of warm and ionized gas. The twoIV components observed towards HD 36665 were detectedin Na I, Ca II, N I, N II, O I and Fe II, indicating that it is composedof both neutral and ionized gas shells. Highly ionized gas was detectedin the O VIλ 1032 Å absorption line at V +40 kms-1 towards both stars. This hot and highly ionized gascomponent is characterized by a columnn density ratio of N(C IV)/N(O VI)< 0.27, which is consistent with that predicted by current models ofevolved SNRs. However, we cannot preclude its origin in the interstellarmedium in line-of-sight to S147. Column-density ratios of [Mg/Fe],[Al/Si],[Si/Fe], [N/Fe], [O/Fe] and [Na/Ca] have been derived for the IVgas components detected towards S147. Similar ratios have also beenderived for fast-moving gas observed towards two other SNRs in order togain some insight into the behavior of element abundances in thedisturbed interstellar gas associated with these regions. In all casesexcept for Na and Ca, these elements appear to be present withnear-solar abundance ratios.
| The Homogeneity of Interstellar Krypton in the Galactic Disk
We present an analysis of high-resolution Hubble Space Telescope SpaceTelescope Imaging Spectrograph (STIS) observations of Kr I λ1236absorption in seven sight lines that probe a variety of interstellarenvironments. In combination with krypton and hydrogen column densitiesderived from current and archival STIS and Far-Ultraviolet SpectroscopicExplorer data, the number of sight lines with reliable Kr/H ISMabundance ratios has been increased by 50% to 26-including paths thatsample a range of nearly 5 orders of magnitude in f(H2) andover 2 orders of magnitude in , and extend up to4.8 kpc in length. For sight lines contained entirely within the localspiral arm (the Orion spur), the spread of Kr/H ratios about the mean oflog10[N(Kr)/N(H)]ISM=-9.02+/-0.02is remarkably tight (0.06 dex), less than the typical data-pointuncertainty. Intriguingly, the only two sight lines that extend throughneighboring structures, in particular gas associated with theCarina/Sagittarius arm, exhibit relatively large, near-solar kryptonabundances (log10[N(Kr)/N(H)]combined=-8.75+0.09-0.11).Although these deviations are only measured at the 2 σ level, theysuggest the possibility that krypton abundances beyond the Orion spurmay differ from the local value.Based on observations with the NASA/ESA Hubble Space Telescope (HST) andthe NASA-CNES-CSA Far-Ultraviolet Spectroscopic Explorer (FUSE). HSTspectra were obtained at the Space Telescope Science Institute, which isoperated by the Association of Universities for Research in Astronomy,Inc. under NASA contract NAS5-26555 FUSE is operated for NASA by theJohns Hopkins University under NASA contract NAS-32985.
| 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?
| Rotational Velocities of B Stars
We measured the projected rotational velocities of 1092 northern B starslisted in the Bright Star Catalogue (BSC) and calibrated them againstthe 1975 Slettebak et al. system. We found that the published values ofB dwarfs in the BSC average 27% higher than those standards. Only 0.3%of the stars have rotational velocities in excess of two-thirds of thebreakup velocities, and the mean velocity is only 25% of breakup,implying that impending breakup is not a significant factor in reducingrotational velocities. For the B8-B9.5 III-V stars the bimodaldistribution in V can be explained by a set of slowly rotating Ap starsand a set of rapidly rotating normal stars. For the B0-B5 III-V starsthat include very few peculiar stars, the distributions in V are notbimodal. Are the low rotational velocities of B stars due to theoccurrence of frequent low-mass companions, planets, or disks? Therotational velocities of giants originating from late B dwarfs areconsistent with their conservation of angular momentum in shells.However, we are puzzled by why the giants that originate from the earlyB dwarfs, despite having 3 times greater radii, have nearly the samerotational velocities. We find that all B-type primaries in binarieswith periods less than 2.4 days have synchronized rotational and orbitalmotions; those with periods between 2.4 and 5.0 days are rotating withina factor 2 of synchronization or are ``nearly synchronized.'' Thecorresponding period ranges for A-type stars are 4.9 and 10.5 days, ortwice as large. We found that the rotational velocities of the primariesare synchronized earlier than their orbits are circularized. The maximumorbital period for circularized B binaries is 1.5 days and for Abinaries is 2.5 days. For stars of various ages from 107.5 to1010.2 yr the maximum circularized periods are a smoothexponential function of age.
| Catalogue of Apparent Diameters and Absolute Radii of Stars (CADARS) - Third edition - Comments and statistics
The Catalogue, available at the Centre de Données Stellaires deStrasbourg, consists of 13 573 records concerning the results obtainedfrom different methods for 7778 stars, reported in the literature. Thefollowing data are listed for each star: identifications, apparentmagnitude, spectral type, apparent diameter in arcsec, absolute radiusin solar units, method of determination, reference, remarks. Commentsand statistics obtained from CADARS are given. The Catalogue isavailable in electronic form at the CDS via anonymous ftp tocdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcar?J/A+A/367/521
| Classification and properties of UV extinction curves
The catalog of Savage et al. (\cite{ref27}) reporting colour excesses of1415 stars from ANS photometry offers the opportunity to deeplyinvestigate the characteristics of UV extinction curves which differfrom the standard extinction of the diffuse interstellar medium. To thisaim we have selected a sample of 252 curves, which have been comparedwith the relations derived by Cardelli et al. (\cite{ref4}; CCM in thefollowing) for a variety of R_V values in the range 2.4-5 and have beenclassified as normal if they fit at least one of the CCM curves oranomalous otherwise. We find that normal curves with small R_V are justas numerous as those with large R_V. The anomalous objects are arrangedinto two groups according to the strength of the bump at 0.217 mu . Fora given value of c_2 this increases along the sequence: type Aanomalous, normals and type B anomalous, suggesting that this sequenceshould correspond to an increase of the amount of small grains along thesightline. Considerations concerning the environmental characteristicsindicate that the anomalous behaviour is not necessarily tied to theexistence of dense gas clouds along the line of sight.
| The 74th Special Name-list of Variable Stars
We present the Name-list introducing GCVS names for 3153 variable starsdiscovered by the Hipparcos mission.
| 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.
| A survey of vacuum-ultraviolet extinction curves based on International Ultraviolet Explorer spectra
This paper presents the interstellar extinction curves derived from theIUE spectra with the aid of the already published 'artificialstandards'. The variety of possible shapes of the curves, demonstratedearlier on spectra from the TD/1 satellite, is fully confirmed.
| The Identification of Diffuse Bands
Not Available
| The ROSAT all-sky survey catalogue of optically bright OB-type stars.
For the detailed statistical analysis of the X-ray emission of hot starswe selected all stars of spectral type O and B listed in the Yale BrightStar Catalogue and searched for them in the ROSAT All-Sky Survey. Inthis paper we describe the selection and preparation of the data andpresent a compilation of the derived X-ray data for a complete sample ofbright OB stars.
| Diffuse interstellar bands: resolved rotational band structure at 5850A.
The only candidate of what may be a resolved rotational vibrational bandin the DIB Survey of Jenniskens & Desert (1994), the triplet ofbands at 5844, 5850 and 5852 A, is examined in detail in order toestablish the nature of these DIBs. We find that superposed on the broadλ5844 are four weak features, reminiscent of substructure foundon top of the broad λ5778. The relative band strength of DIBsλ5844 and λ5850 correlates with the rotational temperaturein the J=0 and J=1 levels of molecular hydrogen. However, we do not findvariations in band shape that are consistent with substructure of aresolved rotational band profile. Instead, the narrow λ5850 isfound to have a shoulder on the red and blue side of the main band,which can imply that this band itself is an unresolved rovib band withP, Q and R branches.
| 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.
| Diffuse interstellar bands and UV extinction curves. The missing link.
The connection between diffuse interstellar bands and components of theinterstellar ultraviolet extinction curve, decomposed according to theFitzpatrick & Massa scheme, is analysed from new observations ofseveral DIBs in the line of sight to 28 stars measured by IUE. We findthat the strength of the 217.5nm bump positively correlates with DIBstrength, whereas correlations with a negative slope exist with the FUVnon-linear rise and the width of the bump. There is no correlation withlinear rise. The relation of bump height versus DIB strength does notpass through zero. The results are interpreted within the polycyclicaromatic hydrocarbon (PAH) framework. They strengthen the hypothesisthat the FUV non-linear rise is produced by neutral PAHs, whereas DIBcarriers are found among some ionised or radical PAHs.
| The interstellar extinction curve
The history of the study of interstellar extinction is brieflydiscussed. The methods used to determine the extinction law arepresented and compared, and the main difficulties involving theapplication of certain methods are shown. This paper emphasizes thenecessity of investigating single-cloud extinction curves instead ofill-defined long-distance means.
| Three known and twenty-two new variable stars of early spectral type
Photoelectric photometry is reported of three known and 22 newvariables, all brighter than V = 7.5 mag. The three known ones are: theellipsoidal variable 42 (V467) Per, the Beta Cep-type star HR 6684 =V2052 Oph, and the eclipsing variable HR 8854 = V649 Cas. The newvariable stars are listed. They include two Beta Cep candidates, oneeclipsing and three ellipsoidal variables, a 'mid-B' variable, anAlpha(2) CVn variable, and two Lambda Eri stars. The twelve remainingnew variables could not be classified because of insufficient data. TheLambda Eri variables found in the present investigation, together withsome examples from the literature, indicate that rotational modulationoccurs not only in Be, but also in normal B stars.
| 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
| Complex Structure in Two Diffuse Interstellar Bands
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1993A&A...274..465J&db_key=AST
| Environment Dependence of Interstellar Extinction Curves
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1993A&A...274..439J&db_key=AST
| Far UV nonlinear rise extinction in relation to CH and CH(+) abundances
The amount of FUV nonlinear rise in the interstellar extinction curve isfound to be proportional to the CH abundance in the line of sight. TheCH(+) abundance shows, if any, a negative trend with the FUV nonlinearrise. Implications for the carrier of the FUV nonlinear rise arediscussed.
| Atlas of extinction curves derived from ultraviolet spectra of the TD-1 satellite
The collection of 166 extinction curves derived from the publishedlow-resolution spectra acquired with the aid of the spectrometer onboard the TD-1 satellite is presented. The observed variety ofextinction laws is apparently due to the varied physical parameters ofinterstellar clouds; for example, the bright stars, included in thesample of TD-1 material, are very likely to be obscured by single clouds(interstellar or circumstellar). The system of standards constructedwith the aid of a special procedure allowing the possible effects ofspectral mismatch to be avoided and making possible the derivation ofextinction curves even in cases of very small E(B-V)S, was applied. Thecurves are presented in the form of plots, normalized to E(B-V) = 1.
| 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.
| Close binaries observed polarimetrically
Not Available
|
提交文章
相关链接
提交链接
下列团体成员
|
观测天体数据
目录:
|
INHABITED SKY
