Садржај
Слике
Уплоадјуј своје слике
DSS Images Other Images
Везани чланци
Caroline Herschel's catalogue of nebulae
Not Available
| The Ultraviolet and Optical Spectra of Luminous B-Type Stars in the Small Magellanic Cloud
We present ultraviolet spectra from the Space Telescope ImagingSpectrograph (STIS) of 12 early B-type stars in the Small MagellanicCloud (SMC), composed of nine supergiants and three giants. Amorphological comparison with Galactic analogs is made using archivaldata from the International Ultraviolet Explorer (IUE). In general, theintensity of the P Cygni emission in the UV resonance lines is greaterand is seen to later spectral types in the Galactic spectra than intheir metal-deficient SMC counterparts. We attribute these effects asmost likely arising from weaker stellar winds in the SMC targets, aspredicted by radiatively driven wind theory. We also include unpublishedSTIS observations of two late O-type stars in the SMC. In combinationwith published O-type STIS data, we now have an extensive ultravioletspectral library of metal-deficient stars to use in the study ofunresolved starbursts and high-redshift star-forming galaxies. In thiscontext, we present empirical measurements for the B-type spectra of thenew ``1978 index'' suggested by Rix et al. as a probe of metallicity insuch systems.
| 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.
| Observations of Rotationally Resolved C3 in Translucent Sight Lines
The rotationally resolved spectrum of theA1Πu<--X1Σ+g000-000 transition of C3, centered at 4051.6 Å, hasbeen observed along 10 translucent lines of sight. To interpret thesespectra, a new method for the determination of column densities andanalysis of excitation profiles involving the simulation and fitting ofobserved spectra has been developed. The populations of lower rotationallevels (J<=14) in C3 are best fitted by thermaldistributions that are consistent with the kinetic temperaturesdetermined from the excitation profile of C2. Just as in thecase of C2, higher rotational levels (J>14) ofC3 show increased nonthermal population distributions inclouds that have been determined to have total gas densities below ~500cm-3.
| 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.
| 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.
| 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
| The proper motions of fundamental stars. I. 1535 stars from the Basic FK5
A direct combination of the positions given in the HIPPARCOS cataloguewith astrometric ground-based catalogues having epochs later than 1939allows us to obtain new proper motions for the 1535 stars of the BasicFK5. The results are presented as the catalogue Proper Motions ofFundamental Stars (PMFS), Part I. The median precision of the propermotions is 0.5 mas/year for mu alpha cos delta and 0.7mas/year for mu delta . The non-linear motions of thephotocentres of a few hundred astrometric binaries are separated intotheir linear and elliptic motions. Since the PMFS proper motions do notinclude the information given by the proper motions from othercatalogues (HIPPARCOS, FK5, FK6, etc.) this catalogue can be used as anindependent source of the proper motions of the fundamental stars.Catalogue (Table 3) is only available at the CDS via anonymous ftp tocdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strastg.fr/cgi-bin/qcat?J/A+A/365/222
| The Normal Energy Distributions in Stellar Spectra: Giants and Supergiants
We have derived the normal spectral energy distributions for thoseearly-type subgiants, giants, and supergiants that were not investigatedin our earlier studies, which were in most cases also not included inthe studies of Sviderskiene. Color indices computed using our normalenergy distributions are in good agreement with normal colors derivedfrom observations in the Vilnius photometric system. The reliability ofour distribution curves is also demonstrated by comparisons of observedand computed (W-B)-(B-V) two-color diagrams in the WBVR system. Normalcolor indices for the photometric WBVR system are derived.
| An analysis of Almagest magnitudes for the study of stellar evolution.
Not Available
| Galactic B-supergiants: A non-LTE model atmosphere analysis to estimate atmospheric parameters and chemical compositions
A non-LTE model atmosphere analysis of moderate resolution (R ~ 5 000)spectra of 46 Galactic B-type supergiants is presented. Standardtechniques are adopted, viz. plane-parallel geometry and radiative andhydrostatic equilibrium. Spectroscopic atmospheric parameters (T_eff,log g & v_turb) and chemical abundances (He, C, N, O, Mg & Si)are estimated, both as a test of the validity of such an approach and inan attempt to provide consistent results for supergiants covering asignificant range of spectral types. The values of the estimatedatmospheric parameters and their dependence on the physics adopted inthe model atmospheres calculations are discussed. The absolute metalabundances are compared to those of main sequence B-type stars and, ingeneral, their chemical compositions appear to be similar. Theabundances for He, C, N & O are considered in some detail and arediscussed in the context of possible evolutionary histories for thisstellar sample. Specifically, it is found that the supergiant sample canbe subdivided into a number of evolutionarily distinct groups. The lowermass objects are predominantly chemically near-normal i.e. theirphotospheres show little or no evidence for chemical processing, whereasthe higher mass supergiants have CNO ratios which are indicative of CNand possibly NO-cycle burning. An attempt is made to quantify thedifference in nitrogen and carbon abundances between the high and lowmass targets but this is hampered by theoretical uncertainties. Thepossibilities that the most highly processed supergiants may have eitherlarger rotational velocities or have undergone mass transfer within abinary system are discussed.
| 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.
| Near-Infrared H-Band Features in Late O and B Stars
We examine the spectral characteristics of normal OB stars withhigh-signal-to-noise ratio (>120) H-band (1.6 μm) spectra at aresolution of 2000. We find that several atomic lines vary smoothly withstellar temperature, as first shown by Blum et al. However, we find apreviously unreported, significant variation in the strength of some ofthese lines with stellar luminosity. B supergiant stars show stronger Hei and weaker Br 11 as compared with low-luminosity B dwarf stars of thesame spectral class. It is for this reason that luminosity class mustalso be determined to obtain an accurate spectral type for a given starusing H-band spectra. We suggest a method for estimating the spectraltype and luminosity of an OB star over the wavelength range from 1.66 to1.72 μm using hydrogen Br 11 at 1.681 mum, He i at 1.700 mum, and Heii at 1.693 mum. The use of the near-infrared spectral range forclassification has obvious advantages over optical classification whenapplied to heavily reddened stars, such as in star-forming regions ordeeply embedded lines of sight within the plane of the Galaxy, such asthe Galactic center. Furthermore, the H band is less likely to becontaminated by infrared excess emission, which is frequently seenaround massive young stellar objects beyond 2 mum.
| Long-term visual spectrophotometric behaviour of Be stars
The long-term spectrophotometric variations of 49 Be stars are studiedusing the U and V magnitudes of the UBV system, the total Balmerdiscontinuity D and the visible gradient Phi _rb. BCD spectrophotometricand photometric data in five different photometric systems, obtained inmost cases since 1950 and reduced to the BCD system, were used. The(U,D), (V,D), (Phi _rb,D) and (Phi _rb,V) correlations obtained differfrom star to star and they can be single or double-valued. They differclearly for Be phases or Be-shell phases. Be stars with small Vsin ishowing the ``spectrophotometric shell behaviour'': D > D_*, werefound. This finding implies either that strongly flattened models ofcircumstellar envelopes are in doubt for these stars, or that not all Bestars are rapid rotators. Comparison of observed variations with thosepredicted for model Be stars with spherical circumstellar envelopes ofvariable densities and dimensions implies that spectrophotometricpatterns of Be phases are due to circumstellar envelopes in low opacityregimes, while those of spectrophotometric shell phases are due tocircumstellar envelopes in high opacity regimes. In a given star, theenvelope regions responsible for the observed variations of D and Phi_rbin spectrophotometric shell phases seem to be smaller and denser thanthose producing the observed variations of these parameters inspectrophotometric Be phases. The high positive RV found in strong shellphases might favor the formation of compact circumstellar layers nearthe star. Figure 6 is only available in electronic form at CDS viaanonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/Abstract.html
| Helium peculiar stars in the red spectral region
Based upon 33 A/mm dispersion spectroscopic material we examine ifequivalent widths of H and He lines can be used for the detection of newhelium-peculiar stars. The answer is affirmative and we present some newcandidates discovered this way. We have also investigated if the use ofdifferent helium lines than those of the (3) D series (4026, 4471)modifies the assignments of helium peculiar stars. This is not the case,since the use of lambda 6678 ((1) D) and lambda 7065 (3S) gives the sameresults. Based on observations obtained at the Haute ProvenceObservatory (CNRS)
| Hα variability of the B-type binary chi Aurigae
We report several new radial velocities of the early-type spectroscopicbinary chi Aur derived from photographic and RETICON spectrograms.Improved orbital elements are computed and a new orbital period P = 676days of this system is derived. The secondary component lines areinvisible in the spectrum of the system with the supergiant primary.Spectral type of the secondary component is discussed. The descriptionof the spectrum chi Aur in the wavelength range from 6300 to 6700Angstroms is presented. Hα emission and its variability wasdiscovered and Hα profile behaviour is described and analyzed.
| A note on infrared standard stars
During the preparation of the infrared spectral atlas for early typestars, a large number of MK standards was observed in the lambda lambda8400-8800{ Angstroms} region. A list of eighteen standards is givenwhich present some degree of inconsistency between the infrared and theMK type. It is suggested to modify the list of MK standards, excludingthe PI's, so that the list can also be used for the infrared spectralregion. This research was completed before the untimely death ofMercedes Jaschek, who should have figured as the principal author.
| The Tokyo PMC catalog 90-93: Catalog of positions of 6649 stars observed in 1990 through 1993 with Tokyo photoelectric meridian circle
The sixth annual catalog of the Tokyo Photoelectric Meridian Circle(PMC) is presented for 6649 stars which were observed at least two timesin January 1990 through March 1993. The mean positions of the starsobserved are given in the catalog at the corresponding mean epochs ofobservations of individual stars. The coordinates of the catalog arebased on the FK5 system, and referred to the equinox and equator ofJ2000.0. The mean local deviations of the observed positions from theFK5 catalog positions are constructed for the basic FK5 stars to comparewith those of the Tokyo PMC Catalog 89 and preliminary Hipparcos resultsof H30.
| Cross-correlation characteristics of OB stars from IUE spectroscopy
We present a catalogue of homogeneous measures of the linewidthparameter, v_esin i, for 373 O-type stars and early B supergiants(including the separate components of 25 binary and three triplesystems), produced by cross-correlating high-resolution,short-wavelength IUE spectra against a `template' spectrum of tauSco. Wealso tabulate terminal velocities. There are no O supergiants in oursample with v_esin i<65 km s^-1, and only one supergiant earlier thanB5 has v_esin i<50 km s^-1, confirming that an important linebroadening mechanism in addition to rotation must be present in theseobjects. A calibration of the area under the cross-correlation peakagainst spectral type is used to obtain estimates of continuum intensityratios of the components in 28 spectroscopically binary or multiplesystems. At least seven SB2 systems show evidence for the `Struve-Sahadeeffect', a systematic variation in relative line strength as a functionof orbital phase. The stellar wind profiles of the most rapid rotator inour sample, the O9III:n* star HD 191423 (v_esin i=436km s^-1), show itto have a `wind-compressed disc' similar to that of HD 93521; this starand other rapid rotators are good candidates for studies of non-radialpulsation.
| Accurate Two-dimensional Classification of Stellar Spectra with Artificial Neural Networks
We present a solution to the long-standing problem of automaticallyclassifying stellar spectra of all temperature and luminosity classeswith the accuracy shown by expert human classifiers. We use the 15Angstroms resolution near-infrared spectral classification systemdescribed by Torres-Dodgen & Weaver in 1993. Using the spectrum withno manual intervention except wavelength registration, artificial neuralnetworks (ANNs) can classify these spectra with Morgan-Keenan types withan accuracy comparable to that obtained by human experts using 2Angstroms resolution blue spectra, which is about 0.5 types (subclasses)in temperature and about 0.25 classes in luminosity. Accuratetemperature classification requires a hierarchy of ANNs, whileluminosity classification is most successful with a single ANN. Wepropose an architecture for a fully automatic classification system.
| A Spectral Atlas of Hot, Luminous Stars at 2 Microns
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1996ApJS..107..281H&db_key=AST
| A Medium-Resolution Search for Polarmetric Structure: Moderate Y Reddening Sightlines
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1996AJ....111..856W&db_key=AST
| 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.
| The photoelectric astrolabe catalogue of Yunnan Observatory (YPAC).
The positions of 53 FK5, 70 FK5 Extension and 486 GC stars are given forthe equator and equinox J2000.0 and for the mean observation epoch ofeach star. They are determined with the photoelectric astrolabe ofYunnan Observatory. The internal mean errors in right ascension anddeclination are +/- 0.046" and +/- 0.059", respectively. The meanobservation epoch is 1989.51.
| The Diffuse Interstellar Bands
The diffuse interstellar bands are absorption features observed in thespectra of stars seen through significant column densities ofinterstellar material. Of the 127 confirmed DIBs in the optical regionbetween 0.4 and about 1.3 $\mu$m, only 2 have (tentatively) beenidentified with a specific carrier. Because DIB strengths increaseroughly in proportion to color excess, they were originally suspected ofbeing produced on or in the interstellar grains, but current evidencefavors some species of free polyatomic molecules, either neutral orionized. DIBs are conspicuously broader than the atomic interstellarlines, having widths at half-depth ranging from 0.8 to about 30 \AA.These widths are presumably due to unresolved rotational structure,possibly compounded by lifetime broadening of the upper state. Recentproposals that C60, some members of the PAH family, or polycarbon chainsare responsible for the DIB spectrum are either not supported byobservation or await better data.
| Terminal Velocities and the Bistability of Stellar Winds
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1995ApJ...455..269L&db_key=AST
| 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.
| SANTIAGO 91, a right ascension catalogue of 3387 stars (equinox J2000).
The positions in right ascension of 3387 stars belonging to the Santiago67 Catalogue, observed with the Repsold Meridian Circle at Cerro Calan,National Astronomical Observatory, during the period 1989 to 1994, aregiven. The average mean square error of a position, for the wholeCatalogue, is +/-0.009 s. The mean epoch of the catalogue is 1991.84.
| Radio continuum emission from stars: a catalogue update.
An updated version of my catalogue of radio stars is presented. Somestatistics and availability are discussed.
|
Додај нови чланак
Линкови у сродству са темом
Додај нови линк
Чланови следећих група \:
|
Посматрања и Астрометриски подаци
| Сазвежђа: | Кочијаш |
| Ректацензија: | 05h32m43.70s |
| Deклинација: | +32°11'31.0" |
| Apparent магнитуда: | 4.76 |
| Даљина: | 1250 parsecs |
| Proper motion RA: | -2 |
| Proper motion Dec: | -2.4 |
| B-T magnitude: | 5.049 |
| V-T magnitude: | 4.763 |
Каталог и designations:
|
