目录
图像
上传图像
DSS Images Other Images
相关文章
B-type supergiants in the Small Magellanic Cloud: rotational velocities and implications for evolutionary models
High-resolution spectra for 24 SMC and Galactic B-type supergiants havebeen analysed to estimate the contributions of both macroturbulence androtation to the broadening of their metal lines. Two differentmethodologies are considered, viz. goodness-of-fit comparisons betweenobserved and theoretical line profiles and identifying zeros in theFourier transforms of the observed profiles. The advantages andlimitations of the two methods are briefly discussed with the lattertechniques being adopted for estimating projected rotational velocities(v sin i) but the former being used to estimate macroturbulentvelocities. The projected rotational velocity estimates range fromapproximately 20 to 60 km s-1, apart from one SMC supergiant,Sk 191, with a v sin i ≃ 90 km s-1. Apart from Sk 191,the distribution of projected rotational velocities as a function ofspectral type are similar in both our Galactic and SMC samples withlarger values being found at earlier spectral types. There is marginalevidence for the projected rotational velocities in the SMC being higherthan those in the Galactic targets but any differences are only of theorder of 5-10 km s-1, whilst evolutionary models predictdifferences in this effective temperature range of typically 20 to 70 kms-1. The combined sample is consistent with a linearvariation of projected rotational velocity with effective temperature,which would imply rotational velocities for supergiants of 70 kms-1 at an effective temperature of 28 000 K (approximately B0spectral type) decreasing to 32 km s-1 at 12 000 K (B8spectral type). For all targets, the macroturbulent broadening wouldappear to be consistent with a Gaussian distribution (although otherdistributions cannot be discounted) with an 1/e half-width varying fromapproximately 20 km s-1 at B8 to 60 km s-1 at B0spectral types.
| Correlation patterns between 11 diffuse interstellar bands and ultraviolet extinction
We relate the equivalent widths of 11 diffuse interstellar bands,measured in the spectra of 49 stars, to different colour excesses in theultraviolet. We find that most of the observed bands correlatepositively with the extinction in the neighbourhood of the2175-Åbump. Correlation with colour excesses in other parts of theextinction curve is more variable from one diffuse interstellar band toanother; we find that some diffuse bands (5797, 5850 and 6376 Å)correlate positively with the overall slope of the extinction curve,while others (5780 and 6284 Å) exhibit negative correlation. Wediscuss the implications of these results on the links between thediffuse interstellar band carriers and the properties of theinterstellar grains.
| Cloud Structure and Physical Conditions in Star-forming Regions from Optical Observations. II. Analysis
To complement the optical absorption line survey of diffuse moleculargas in Paper I, we obtained and analyzed far-ultraviolet H2and CO data on lines of sight toward stars in Cep OB2 and Cep OB3.Possible correlations between column densities of different species forindividual velocity components, not total columns along a line of sightas in the past, were examined and were interpreted in terms of cloudstructure. The analysis reveals that there are two kinds of CH indiffuse molecular gas: CN-like CH and CH+-like CH. Evidenceis provided that CO is also associated with CN in diffuse molecularclouds. Different species are distributed according to gas density inthe diffuse molecular gas. Both calcium and potassium may be depletedonto grains in high-density gas, but with different dependencies onlocal gas density. Gas densities for components where CN was detectedwere inferred from a chemical model. Analysis of cloud structureindicates that our data are generally consistent with the large-scalestructure suggested by maps of CO millimeter-wave emission. On smallscales, the gas density is seen to vary by factors greater than 5.0 overscales of ~10,000 AU. The relationships between column densities of COand CH with that of H2 along a line of sight show similarslopes for the gas toward Cep OB2 and Cep OB3, but the CO/H2and CH/H2 ratios tend to differ, which we ascribe tovariation in average density along the line of sight.
| Profiles of Very Weak Diffuse Interstellar Bands around 6440 Å
Profiles of very weak diffuse interstellar bands (DIBs) between 6400 and6470 Å observed with high resolution and very high S/N aredemonstrated. We show that with the increasing quality of reddenedstellar spectra, the whole spectral range is covered with weak or veryweak DIBs-at least one every 2-3 Å. We also present the details ofthe profiles of a few stronger features; the presence of substructuresresembles the profiles of strong DIBs observed in high resolution duringthe last decade and supports the hypothesis of a molecular origin of atleast a majority of DIBs.
| On the massive stellar population of the super star cluster Westerlund 1
We present new spectroscopic and photometric observations of the youngGalactic open cluster Westerlund 1 (Wd 1) that reveala unique population of massive evolved stars. We identify ~200 clustermembers and present spectroscopic classifications for ~25% of these. Wefind that all stars so classified are unambiguously post-Main Sequenceobjects, consistent with an apparent lack of an identifiable MainSequence in our photometric data to V 20. We are able to identifyrich populations of Wolf Rayet stars, OB supergiants and short livedtransitional objects. Of these, the latter group consists of both hot(Luminous Blue Variable and extreme B supergiant) and cool (YellowHypergiant and Red Supergiant) objects - we find that half the knownGalactic population of YHGs resides within Wd 1. We obtain a meanV-MV ~ 25 mag from the cluster Yellow Hypergiants, implying aMain Sequence turnoff at or below MV =-5 (O7 V or later).Based solely on the masses inferred for the 53 spectroscopicallyclassified stars, we determine an absolute minimum mass of ~1.5 ×10^3~Mȯ for Wd 1. However, considering the completephotometrically and spectroscopically selected cluster population andadopting a Kroupa IMF we infer a likely mass for Wd 1 of~10^5~Mȯ, noting that inevitable source confusion andincompleteness are likely to render this an underestimate. As such, Wd 1is the most massive compact young cluster yet identified in the LocalGroup, with a mass exceeding that of Galactic Centre clusters such asthe Arches and Quintuplet. Indeed, the luminosity, inferred mass andcompact nature of Wd 1 are comparable with those of Super Star Clusters- previously identified only in external galaxies - and is consistentwith expectations for a Globular Cluster progenitor.
| The Optical Spectrum of an LBV Candidate in the Cyg OB2 Association
We have obtained the first high-spectral-resolution (R=15000 and 60000)optical spectra for the extremely luminous star No. 12, identified withthe IR source IRAS 20308+4104 in the Cyg OB2 association. We haveidentified about 200 spectral features at 4552 7939 Å, includingthe interstellar NaI, KI lines and numerous DIBs, which are thestrongest absorption lines in the spectrum, along with the HeI, CII, andSiII lines. A two-dimensional spectral classification indicates that thestar's spectral type is B5±0.5 Ia+. Our analysis of theradial-velocity pattern shows the presence of a radial-velocity gradientin the stellar atmosphere, due to the infall of matter onto the star.The strong Hα emission line displays broad Thompson wings andtime-variable core absorption, providing evidence that the stellar windis inhomogeneous, and a slightly blue-shifted P Cygni absorptionprofile. We conclude that the wind is time-variable.
| The Indo-US Library of Coudé Feed Stellar Spectra
We have obtained spectra for 1273 stars using the 0.9 m coudéfeed telescope at Kitt Peak National Observatory. This telescope feedsthe coudé spectrograph of the 2.1 m telescope. The spectra havebeen obtained with the no. 5 camera of the coudé spectrograph anda Loral 3K×1K CCD. Two gratings have been used to provide spectralcoverage from 3460 to 9464 Å, at a resolution of ~1 Å FWHMand at an original dispersion of 0.44 Å pixel-1. For885 stars we have complete spectra over the entire 3460 to 9464 Åwavelength region (neglecting small gaps of less than 50 Å), andpartial spectral coverage for the remaining stars. The 1273 stars havebeen selected to provide broad coverage of the atmospheric parametersTeff, logg, and [Fe/H], as well as spectral type. The goal ofthe project is to provide a comprehensive library of stellar spectra foruse in the automated classification of stellar and galaxy spectra and ingalaxy population synthesis. In this paper we discuss thecharacteristics of the spectral library, viz., details of theobservations, data reduction procedures, and selection of stars. We alsopresent a few illustrations of the quality and information available inthe spectra. The first version of the complete spectral library is nowpublicly available from the National Optical Astronomy Observatory(NOAO) via ftp and http.
| Cloud Structure and Physical Conditions in Star-forming Regions from Optical Observations. I. Data and Component Structure
We present high-resolution optical spectra (at ~0.6-1.8 kms-1) of interstellar CN, CH, CH+, Ca I, K I, andCa II absorption toward 29 lines of sight in three star-forming regions,ρ Oph, Cep OB2, and Cep OB3. The observations and data reduction aredescribed. The agreement between earlier measurements of the totalequivalent widths and our results is quite good. However, our higherresolution spectra reveal complex structure and closely blendedcomponents in most lines of sight. The velocity component structure ofeach species is obtained by analyzing the spectra of the six species fora given sight line together. The tabulated column densities and Dopplerparameters of individual components are determined by using the methodof profile fitting. Total column densities along lines of sight arecomputed by summing results from profile fitting for individualcomponents and are compared with column densities from the apparentoptical depth method. A more detailed analysis of these data and theirimplications will be presented in a companion paper.
| Toward an adequate method to isolate spectroscopic families of diffuse interstellar bands
We divide some of the observed diffuse interstellar bands (DIBs) intofamilies that appear to have the spectral structure of single species.Three different methods are applied to separate such families, exploringthe best approach for future investigations of this type. Starting witha statistical treatment of the data, we found that statistical methodsby themselves give insufficient results. Two other methods of dataanalysis (`averaging equivalent widths' and `investigating the figureswith arranged spectrograms') were found to be more useful as tools forfinding the spectroscopic families of DIBs. On the basis of thesemethods, we suggest some candidates as `relatives' of 5780- and5797-Å bands.
| High-Resolution Observations of Interstellar Ca I Absorption-Implications for Depletions and Electron Densities in Diffuse Clouds
We present high-resolution (FWHM~0.3-1.5 km s-1) spectra,obtained with the AAT UHRF, the McDonald Observatory 2.7 m coudéspectrograph, and/or the KPNO coudé feed, of interstellar Ca Iabsorption toward 30 Galactic stars. Comparisons of the column densitiesof Ca I, Ca II, K I, and other species-for individual componentsidentified in the line profiles and also when integrated over entirelines of sight-yield information on relative electron densities anddepletions (dependent on assumptions regarding the ionizationequilibrium). There is no obvious relationship between the ratio N(CaI)/N(Ca II) [equal to ne/(Γ/αr) forphotoionization equilibrium] and the fraction of hydrogen in molecularform f(H2) (often taken to be indicative of the local densitynH). For a smaller sample of sight lines for which thethermal pressure (nHT) and local density can be estimated viaanalysis of the C I fine-structure excitation, the average electrondensity inferred from C, Na, and K (assuming photoionizationequilibrium) seems to be independent of nH andnHT. While the electron density (ne) obtained fromthe ratio N(Ca I)/N(Ca II) is often significantly higher than the valuesderived from other elements, the patterns of relative nederived from different elements show both similarities and differencesfor different lines of sight-suggesting that additional processesbesides photoionization and radiative recombination commonly andsignificantly affect the ionization balance of heavy elements in diffuseinterstellar clouds. Such additional processes may also contribute tothe (apparently) larger than expected fractional ionizations(ne/nH) found for some lines of sight withindependent determinations of nH. In general, inclusion of``grain-assisted'' recombination does reduce the inferred ne,but it does not reconcile the ne estimated from differentelements; it may, however, suggest some dependence of ne onnH. The depletion of calcium may have a much weakerdependence on density than was suggested by earlier comparisons with CHand CN. Two appendices present similar high-resolution spectra of Fe Ifor a few stars and give a compilation of column density data for Ca I,Ca II, Fe I, and S I.
| A Method for Simultaneous Determination of AV and R and Applications
A method for the simultaneous determination of the interstellarextinction (AV) and of the ratio of total to selectiveextinction (R), derived from the 1989 Cardelli, Clayton, & Mathisfitting of the interstellar extinction law, is presented and applied toa set of 1900 color excesses derived from observations of stars inUBVRIJHKL. The method is used to study the stability of AVand R within selected regions in Perseus, Scorpius, Monoceros, Orion,Sagittarius, Ophiuchus, Carina, and Serpens. Analysis shows that R isapproximately constant and peculiar to each sector, with mean valuesthat vary from 3.2 in Perseus to 5.6 in Ophiuchus. These results aresimilar to published values by Aiello et al., He et al., Vrba &Rydgren, O'Donnell, and Cardelli, Clayton, & Mathis.
| Some Diffuse Interstellar Bands Related to Interstellar C2 Molecules
We have investigated the correlations between the equivalent widths of21 selected diffuse interstellar bands (DIBs) and the correspondinginterstellar column densities N(C2), N(CN), and N(CH), toward53 stars with color excesses 0.11<=E(B-V)<=1.99. The observationaldata were derived primarily from echelle spectra acquired at R=38,000 aspart of our extensive, continuing survey of the bands. All but six ofthe 53 final spectra show signal-to-noise ratios >=800 at 5780Å. The principal result presented here is that seven of the 21bands prove to be examples of ``the C2 DIBs,'' a class ofweak, narrow bands whose normalized equivalent widthsWλ(X)/Wλ (λ6196) are wellcorrelated specifically with N(C2)/E(B-V) via power laws. Incontrast, the similarly normalized equivalent widths of the 14 other,well-known DIBs analyzed here are uncorrelated, or weaklyanticorrelated, with N(C2)/E(B-V), to within theobservational uncertainties. Thus, the polyatomic molecule(s) presumedto cause these seven C2 DIBs may bear a direct chemicalrelation to C2 that is not shared by the polyatomic moleculesputatively responsible for the other 14 bands. The C2 DIBsalso show positive correlations with N(CN)/E(B-V) and N(CH)/E(B-V) inour particular sample of light paths, although generally with shallowerslopes in the case of N(CN) and with greater scatter in the case ofN(CH). Eleven additional C2 DIBs are also identified but arenot analyzed here. Among the 18 C2 DIBs identified, fourapparently have not been previously detected. The λ4963 band isgenerally the strongest of the 18 C2 DIBs, while theλ4734 band shows the most sensitive correlation withN(C2).Based on observations obtained with the Apache Point Observatory 3.5 mtelescope, which is owned and operated by the Astrophysical ResearchConsortium.
| The total-to-selective extinction ratio determined from near IR photometry of OB stars
The paper presents an extensive list of the total to selectiveextinction ratios R calculated from the infrared magnitudes of 597 O andB stars using the extrapolation method. The IR magnitudes of these starswere taken from the literature. The IR colour excesses are determinedwith the aid of "artificial standards" - Wegner (1994). The individualand mean values of total to selective extinction ratios R differ in mostcases from the average value R=3.10 +/-0.05 - Wegner (1993) in differentOB associations. The relation between total to selective extinctionratios R determined in this paper and those calculated using the "methodof variable extinction" and the Cardelli et al. (1989) formulae isdiscussed. The R values presented in this paper can be used to determineindividual absolute magnitudes of reddened OB stars with knowntrigonometric parallaxes.
| Macroturbulent and rotational broadening in the spectra of B-type supergiants
The absorption-line spectra of early B-type supergiants show significantbroadening that implies that an additional broadening mechanism(characterized here as `macroturbulence') is present in addition torotational broadening. Using high-resolution spectra withsignal-to-noise ratios of typically 500, we have attempted to quantifythe relative contributions of rotation and macroturbulence, but evenwith data of this quality significant problems were encountered.However, for all our targets, a model where macroturbulence dominatesand rotation is negligible is acceptable; the reverse scenario leads topoor agreement between theory and observation. Additionally, there ismarginal evidence for the degree of broadening increasing with linestrength, possibly a result of the stronger lines being formed higher inthe atmosphere. Acceptable values of the projected rotational velocityare normally less than or equal to 50 km s-1, which may alsobe a typical upper limit for the rotational velocity. Our best estimatesfor the projected rotational velocity are typically 10-20 kms-1 and hence compatible with this limit. These values arecompared with those predicted by single star evolutionary models, whichare initially rapidly rotating. It is concluded that either these modelsunderestimate the rate of rotational breaking or some of the targets maybe evolving through a blue loop or are binaries.
| 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.
| The Spectral Components of SS 433
We present results from new optical and UV spectroscopy of the unusualbinary system SS 433, and we discuss the relationship of the particularspectral components that we observe to the properties of the binary.These spectral components include1. The continuum spectrum, which weassociate with flux from the super-Eddington accretion disk and thedense part of its wind. A far-UV spectrum from the Hubble SpaceTelescope Space Telescope Imaging Spectrograph made during the edge-onorientation of the disk places an upper limit on the temperature of anequivalent blackbody source (T<21,000 K for AV=7.8) whencombined with near-UV and optical fluxes. The continuum source has aneffective projected radius of approximately half the binary separation,so that the source may be larger than the Roche radius of the compactstar.2. Hα moving components, whichare formed far from the binary orbital plane in the relativistic jets.We confirm that these emission features appear as ``bullets'' at a fixedwavelength and may last for a few days. We present a contemporary radialvelocity curve for the precessional motion of the jets that includes thenodding motion caused by tidal interaction with the opticalstar.3. Hα and He I ``stationary''emission lines, which we suggest are formed in the disk wind in a volumelarger than the dimensions of the binary. These lines vary on alltimescales and sometimes appear as P Cygni lines. We suggest that theirradial velocity curves (which show greatest redshift at inferiorconjunction of the optical star) result from an evacuation of the diskwind surrounding the optical star (caused by physical blockage, heating,or colliding winds). We argue that the wake of this interaction regioncauses an extended eclipse of the X-ray source (as seen in Rossi X-RayTiming Explorer All-Sky Monitor light curves).4.A weak ``stationary'' emission feature, which we identify as a CII λλ7231, 7236 blend that attains maximum radial velocityat the orbital quadrature of disk recession (like the velocity curve ofHe II λ4686). This is probably formed in outflow from the centralregion of the disk near the compact star.5.Absorption and emission features from outflowing clumps in thedisk wind (seen most clearly in an episode of blueshifted Na Iemission).6. We found no clear evidence ofthe absorption-line spectrum of the optical star, although we point outthe presence of He I absorption features (blended with the stationaryemission) with the expected radial velocity trend at the orbital andprecessional phases when the star might best beseen.7. A rich interstellar absorptionspectrum of diffuse interstellar bands.The resultssuggest that the binary is embedded in an expanding thick disk (detectedin recent radio observations) that is fed by the wind from thesuper-Eddington accretion disk.
| An upper limit to the interstellar C5 abundance in translucent clouds
We have analyzed high resolution spectra of several slightly tomoderately reddened stars collected at two observatories: ESO (La Silla)and Terskol (Northern Caucasia), to estimate the abundance of theC5 molecule in the interstellar medium. We confirm thepresence of a feature near 4975 Å which appears to be a weak DIBrather than the predicted C5 band since the origin band near5109 Å remains invisible even in spectra of high signal-to-noiseratio ( ~ 2500) and spectral resolution (R ~ 220 000). This confirmsthat the C5 abundance in translucent interstellar clouds isvery low. We estimate its limit as low as 1011cm-2 in the scale E(B-V)=0.35 for ``zeta" type objects thatis two times lower than that of Maier et al. (2002). Based on datacollected at the ESO 3.6 m telescope operated on La Silla Observatory,Chile and 2-m telescope of the Terskol Observatory, Russia.
| Discovery of spectral variation in the optical counterpart of IRAS 01005+7910
We present a study of the high-resolution spectroscopic data for theproto-planetary nebula candidate IRAS 01005+7910. For the first time acareful spectral line identification is carried out, and a significantvariability of the optical spectrum is detected. We found absorptionlines of C II/III, N II, O II, Al III, Si III, and Mg II (lambda4481Å), as well as emission lines of Si II and [Fe II]. Bothabsorption and emission components are present in the Balmer lines, Na Iresonance D1,2 lines, He I, and Fe III lines. The He I lineprofiles vary from straight to inverse P Cyg-type on a timescale of daysto months. The resonance Na I lines show 5 absorption components at aresolution of R=60 000. Additionally, the Na I D2 lineexhibits a variable emission component with a width comparable to thatof the Balmer line emission components. Using the model atmospheresmethod within the LTE-approximation, the effective temperature(Teff ~21 500 K), the metallicity [Fe/H]sun=-0.31,and the ratio C/O>1 is reported. Finally, we suggest that IRAS01005+7910 is a carbon-rich post-AGB star with a luminosity log(L/Lsun)=3.6 at a distance about 3 kpc.
| The ISO-SWS post-helium atlas of near-infrared stellar spectra
We present an atlas of near-infrared spectra (2.36 mu m-4.1 mu m) of ~300 stars at moderate resolution (lambda /delta lambda ~ 1500-2000). Thespectra were recorded using the Short-Wavelength Spectrometer aboard theInfrared Space Observatory (ISO-SWS). The bulk of the observations wereperformed during a dedicated observation campaign after the liquidhelium depletion of the ISO satellite, the so-called post-heliumprogramme. This programme was aimed at extending the MK-classificationto the near-infrared. Therefore the programme covers a large range ofspectral types and luminosity classes. The 2.36 mu m-4.05 mu m region isa valuable spectral probe for both hot and cool stars. H I lines(Bracket, Pfund and Humphreys series), He I and He II lines, atomiclines and molecular lines (CO, H2O, NH, OH, SiO, HCN,C2H2, ...) are sensitive to temperature, gravityand/or the nature of the outer layers of the stellar atmosphere(outflows, hot circumstellar discs, etc.). Another objective of theprogramme was to construct a homogeneous dataset of near-infraredstellar spectra that can be used for population synthesis studies ofgalaxies. At near-infrared wavelengths these objects emit the integratedlight of all stars in the system. In this paper we present the datasetof post-helium spectra completed with observations obtained during thenominal operations of the ISO-SWS. We discuss the calibration of the SWSdata obtained after the liquid helium boil-off and the data reduction.We also give a first qualitative overview of how the spectral featuresin this wavelength range change with spectral type. The dataset isscrutinised in two papers on the quantitative classification ofnear-infrared spectra of early-type stars ({Lenorzer} et al.\cite{lenorzer:2002a}) and late-type stars (Vandenbussche et al., inprep). Based on observations with ISO, an ESA project with instrumentsfunded by ESA Members States (especially the PI countries France,Germany, the Netherlands and the United Kingdom) and with theparticipation of ISAS and NASA. The full atlas is available inelectronic form at www.edpsciences.org Table 1 is only available inelectronic form at the CDS via anonymous ftp to cdsarc.u-strasbg.fr(130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?/A+A/390/1033
| An atlas of 2.4 to 4.1 mu m ISO/SWS spectra of early-type stars
We present an atlas of spectra of O- and B-type stars, obtained with theShort Wavelength Spectrometer (SWS) during the Post-Helium program ofthe Infrared Space Observatory (ISO). This program is aimed at extendingthe Morgan & Keenan classification scheme into the near-infrared.Later type stars will be discussed in a separate publication. Theobservations consist of 57 SWS Post-Helium spectra from 2.4 to 4.1 μm, supplemented with 10 spectra acquired during the nominal mission witha similar observational setting. For B-type stars, this sample providesample spectral coverage in terms of subtype and luminosity class. ForO-type stars, the ISO sample is coarse and therefore is complementedwith 8 UKIRT Larcmin -band observations. In terms of the presence ofdiagnostic lines, the Larcmin -band is likely the most promising of thenear-infrared atmospheric windows for the study of the physicalproperties of B stars. Specifically, this wavelength interval containsthe Bralpha , Pfgamma , and other Pfund lines which are probes ofspectral type, luminosity class and mass loss. Here, we present simpleempirical methods based on the lines present in the 2.4 to 4.1 mu minterval that allow the determination of i) the spectral type of Bdwarfs and giants to within two subtypes; ii) the luminosity class of Bstars to within two classes; iii) the mass-loss rate of O stars and Bsupergiants to within 0.25 dex. Based on observations with ISO, an ESAproject with instruments funded by ESA Member States (especially the PIcountries: France, Germany, The Netherlands and the UK) and with theparticipation of ISAS and NASA. The appendix is only available inelectronic form at the CDS via anonymous ftp to cdsarc.u-strasbg.fr(130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin.qcat?J/A+A/384/473
| Far-ultraviolet extinction and diffuse interstellar bands
We relate the equivalent widths of the major diffuse interstellar bands(DIBs) near 5797 and 5780Å with different colour excesses,normalized by E(B-V), which characterize the growth of interstellarextinction in different wavelength ranges. It is demonstrated that thetwo DIBs correlate best with different parts of the extinction curve,and the ratio of these diffuse bands is best correlated with thefar-ultraviolet (UV) rise. A number of peculiar lines of sight are alsofound, indicating that the carriers of some DIBs and the far-UVextinction can be separated in certain environments, e.g. towards thePer OB2 association.
| On the detection of the linear C5 molecule in the interstellar medium
An upper limit of the column density of the C5 linearmolecule in translucent interstellar clouds is estimated fromhigh-resolution (R=80000) and very high signal-to-noise ratio (~1000)echelle spectra. It is 1012cm-2 per E(B-V)=1 (twoorders of magnitude lower than that of C2).
| Profiles of blue and infrared diffuse interstellar bands
The paper presents a survey of profiles of reasonably strong diffuseinterstellar bands (DIBs) based on the extensive set of high-resolutionspectra acquired with the aid of echelle spectrographs installed at the2-m Terskol, 2-m Pic du Midi and 1-m SAO telescopes. The surveyeddiffuse interstellar bands cover the spectral ranges of blue andnear-infrared, i.e the DIBs not surveyed by Krełowski &Schmidt. The possible modifications caused by stellar and telluric linesare discussed. The very broad features such as 4430 are not discussedbecause the shapes of their profiles, extracted from echelle spectra,are very uncertain. The signal-to-noise (S/N) ratios of the spectra arenot high enough to enable discussion of the profiles of numerous weakinterstellar features discovered recently.
| A High-Resolution Survey of Interstellar K I Absorption
We present high-resolution (FWHM ~0.4-1.8 km s-1) spectra,obtained with the AAT UHRF, the McDonald Observatory 2.7 m coudéspectrograph, and/or the KPNO coudé feed, of interstellar K Iabsorption toward 54 Galactic stars. These new K I spectra revealcomplex structure and narrow, closely blended components in many linesof sight. Multicomponent fits to the line profiles yield estimates forthe column densities, line widths, and velocities for 319 individualinterstellar cloud components. The median component width (FWHM) and thetrue median separation between adjacent components are both <~1.2 kms-1. The median and maximum individual component K I columndensities, about 4×1010 and 1012cm-2, correspond to individual component hydrogen columndensities of about 2×1020 and 1021cm-2 and E(B-V)~0.03 and 0.17, respectively. If T istypically ~100 K, then at least half the individual components havesubsonic internal turbulent velocities. We also reexamine therelationships between the column densities of K I, Na I, C I, Li I,Htot, H2, and CH. The four trace neutral speciesexhibit essentially linear relationships with each other over wideranges in overall column density. If C is uniformly depleted by 0.4 dex,then Li, Na, and K are each typically depleted by 0.6-0.7 dex. The totalline of sight values for N(K I) and N(Na I) show roughly quadraticdependences on N(Htot), but the relationships for theensemble of individual clouds could be significantly steeper. Thesequadratic (or steeper) dependences appear to rule out significantcontributions to the ionization from cosmic rays, X-rays, and/or chargeexchange with C II in most cases. Charge exchange with negativelycharged large molecules may often be more important than radiativerecombination in neutralizing most singly ionized atomic species in coolH I clouds, however-suggesting that the true ne,nH, and thermal pressures may be significantly smaller thanthe values estimated by considering only radiative recombination. BothN(CH) and N(H2) are nearly linearly proportional to N(K I)and N(Na I) [except for 1015cm-2<~N(H2)<~1019cm-2, over which H2 makes the transition to theself-shielded regime]. Those relationships appear also to hold for manyindividual components and component groups, suggesting thathigh-resolution spectra of K I and Na I can be very useful forinterpreting lower resolution molecular data. The scatter about allthese mean relationships is generally small (<~0.1-0.2 dex), ifcertain consistently ``discrepant'' sight lines are excluded-suggestingthat both the relative depletions and the relative ionization of Li, C,Na, and K are generally within factors of 2 of their mean values.Differences noted for sight lines in Sco-Oph, in the Pleiades, near theOrion Trapezium, and in the LMC and SMC may be due to differences in thestrength and/or shape of the ambient radiation fields, perhaps amplifiedby the effects of charge transfer with large molecules.
| The problem of C7- as source of diffuse interstellar bands revisited
We used spectra of several bright, reddened stars, most of them likelyto be obscured by individual interstellar clouds, to examine theproposition that C7- may carry several diffuseinterstellar bands (DIBs) (Tulej et al. 1998). To search for the broadfeatures of the C7- B <- X system we used lowresolution, very high S/N spectra, but even in heavily reddened objectsthe predicted bands remain undetectable. High resolution (R=80 000)spectra prove that the diffuse bands, found in close vicinity of narrowlines belonging to the A <- X system, show variable strength ratiosfrom object to object which proves that they are not of the same origin.The paper brings thus evidence that the C7-molecule does not cause any of the detected DIBs.
| A possible sets of diffuse bands originating at the same carrier
This paper discusses measurements of eight selected diffuse interstellarbands (DIBs): lambda lambda 5793, 5809, 5819, 5828, 6196, 6397, 6614 and6660 performed in high resolution, high S/N spectra of 41 reddenedstars. Central depths, considered less error-prone than equivalentwidths, are measured and mutual correlations between the selected DIBsare analyzed. Tight correlations between the DIBs: 5809, 6196, 6614 and6660 may suggest their common origin despite their widths differing by afactor of up to 2. The performed simulations prove that this fact doesnot preclude a common, molecular carrier of such features.
| Multicomponent radiatively driven stellar winds. II. Gayley-Owocki heating in multitemperature winds of OB stars
We show that the so-called Gayley-Owocki (Doppler) heating is importantfor the temperature structure of the wind of main sequence stars coolerthan the spectral type O6. The formula for Gayley-Owocki heating isderived directly from the Boltzmann equation as a direct consequence ofthe dependence of the driving force on the velocity gradient. SinceGayley-Owocki heating deposits heat directly on the absorbing ions, wealso investigated the possibility that individual components of theradiatively driven stellar wind have different temperatures. This effectis negligible in the wind of O stars, whereas a significant temperaturedifference takes place in the winds of main sequence B stars for starscooler than B2. Typical temperature differences between absorbing ionsand other flow components for such stars is of the order 103K. However, in the case when the passive component falls back onto thestar, the absorbing component reaches temperatures of order106 K, which allows for emission of X-rays. Moreover, wecompare our computed terminal velocities with the observed ones. Wefound quite good agreement between predicted and observed terminalvelocities. The systematic difference coming from the using of the socalled ``cooking formula'' has been removed.
| 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.
| Sixth Catalogue of Fundamental Stars (FK6). Part III. Additional fundamental stars with direct solutions
The FK6 is a suitable combination of the results of the HIPPARCOSastrometry satellite with ground-based data, measured over a longinterval of time and summarized mainly in the FK5. Part III of the FK6(abbreviated FK6(III)) contains additional fundamental stars with directsolutions. Such direct solutions are appropriate for single stars or forobjects which can be treated like single stars. Part III of the FK6contains in total 3272 stars. Their ground-based data stem from thebright extension of the FK5 (735 stars), from the catalogue of remainingSup stars (RSup, 732 stars), and from the faint extension of the FK5(1805 stars). From the 3272 stars in Part III, we have selected 1928objects as "astrometrically excellent stars", since their instantaneousproper motions and their mean (time-averaged) ones do not differsignificantly. Hence most of the astrometrically excellent stars arewell-behaving "single-star candidates" with good astrometric data. Thesestars are most suited for high-precision astrometry. On the other hand,354 of the stars in Part III are Δμ binaries in the sense ofWielen et al. (1999). Many of them are newly discovered probablebinaries with no other hitherto known indication of binarity. The FK6gives, besides the classical "single-star mode" solutions (SI mode),other solutions which take into account the fact that hidden astrometricbinaries among "apparently single-stars" introduce sizable "cosmicerrors" into the quasi-instantaneously measured HIPPARCOS proper motionsand positions. The FK6 gives, in addition to the SI mode, the "long-termprediction (LTP) mode" and the "short-term prediction (STP) mode". TheseLTP and STP modes are on average the most precise solutions forapparently single stars, depending on the epoch difference with respectto the HIPPARCOS epoch of about 1991. The typical mean error of anFK6(III) proper motion in the single-star mode is 0.59 mas/year. This isa factor of 1.34 better than the typical HIPPARCOS errors for thesestars of 0.79 mas/year. In the long-term prediction mode, in whichcosmic errors are taken into account, the FK6(III) proper motions have atypical mean error of 0.93 mas/year, which is by a factor of about 2better than the corresponding error for the HIPPARCOS values of 1.83mas/year (cosmic errors included).
|
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
