Contents
Images
Upload your image
DSS Images Other Images
Related articles
Distances and Metallicities of High- and Intermediate-Velocity Clouds
A table is presented that summarizes published absorption linemeasurements for the high- and intermediate-velocity clouds (HVCs andIVCs). New values are derived for N(H I) in the direction of observedprobes, in order to arrive at reliable abundances and abundance limits(the H I data are described in Paper II). Distances to stellar probesare revisited and calculated consistently, in order to derive distancebrackets or limits for many of the clouds, taking care to properlyinterpret nondetections. The main conclusions are the following. (1)Absolute abundances have been measured using lines of S II, N I, and OI, with the following resulting values: ~0.1 solar for one HVC (complexC), ~0.3 solar for the Magellanic Stream, ~0.5 solar for a southern IVC,and ~solar for two northern IVCs (the IV Arch and LLIV Arch). Finally,approximate values in the range 0.5-2 solar are found for three moreIVCs. (2) Depletion patterns in IVCs are like those in warm disk or halogas. (3) Most distance limits are based on strong UV lines of C II, SiII, and Mg II, a few on Ca II. Distance limits for major HVCs aregreater than 5 kpc, while distance brackets for several IVCs are in therange 0.5-2 kpc. (4) Mass limits for major IVCs are0.5-8×105 Msolar, but for major HVCs theyare more than 106 Msolar. (5) The Ca II/H I ratiovaries by up to a factor 2-5 within a single cloud, somewhat morebetween clouds. (6) The Na I/H I ratio varies by a factor of more than10 within a cloud, and even more between clouds. Thus, Ca II can beuseful for determining both lower and upper distance limits, but Na Ionly yields upper limits.
| A Search for High-Velocity Be Stars
We present an analysis of the kinematics of Be stars based uponHipparcos proper motions and published radial velocities. We findapproximately 23 of the 344 stars in our sample have peculiar spacemotions greater than 40 km s-1 and up to 102 kms-1. We argue that these high-velocity stars are the resultof either a supernova that disrupted a binary or ejection by closeencounters of binaries in young clusters. Be stars spun up by binarymass transfer will appear as high-velocity objects if there wassignificant mass loss during the supernova explosion of the initiallymore massive star, but the generally moderate peculiar velocities of BeX-ray binaries indicate that the progenitors lose most of their massprior to the supernova (in accordance with model predictions). Binaryformation models for Be stars predict that most systems bypass thesupernova stage (and do not receive runaway velocities) to createultimately Be+white dwarf binaries. The fraction of Be stars spun up bybinary mass transfer remains unknown, since the post-mass transfercompanions are difficult to detect.
| Statistical analysis of intrinsic polarization, IR excess and projected rotational velocity distributions of classical Be stars
We present the results of statistical analyses of a sample of 627 Bestars. The parameters of intrinsic polarization (p*),projected rotational velocity (v sin i), and near IR excesses have beeninvestigated. The values of p* have been estimated for a muchlarger and more representative sample of Be stars (~490 objects) thanpreviously. We have confirmed that most Be stars of early spectral typehave statistically larger values of polarization and IR excesses incomparison with the late spectral type stars. It is found that thedistributions of p* diverge considerably for the differentspectral subgroups. In contrast to late spectral types (B5-B9.5), thedistribution of p* for B0-B2 stars does not peak at the valuep*=0%. Statistically significant differences in the meanprojected rotational velocities (/line{vsin i}) are found for differentspectral subgroups of Be stars in the sense that late spectral typestars (V luminosity class) generally rotate faster than early types, inagreement with previously published results. This behaviour is, however,not obvious for the III-IV luminosity class stars. Nevertheless, thecalculated values of the ratio vt/vc of the truerotational velocity, vt, to the critical velocity forbreak-up, vc, is larger for late spectral type stars of allluminosity classes. Thus, late spectral type stars appear to rotatecloser to their break-up rotational velocity. The distribution of nearIR excesses for early spectral subgroups is bi-modal, the position ofthe second peak displaying a maximum value E(V-L)~ 1 . m 3for O-B1.5 stars, decreasing to E(V-L)~0. m8 for intermediatespectral types (B3-B5). It is shown that bi-modality disappears for latespectral types (B6-B9.5). No correlations were found betweenp* and near IR excesses and between E(V-L) and vsin i for thedifferent subgroups of Be stars. In contrast to near IR excesses, arelation between p* and far IR excesses at 12 mu m is clearlyseen. A clear relation between p* and vsin i (as well asbetween p* and /line{vsin i}/vc) is found by thefact that plots of these parameters are bounded by a ``triangular"distribution of p*: vsin i, with a decrease of p*towards very small and very large vsin i (and /line{vsini}/vc) values. The latter behaviour can be understood in thecontext of a larger oblateness of circumstellar disks for the stars witha rapid rotation. From the analysis of correlations between differentobservational parameters we conclude that circumstellar envelopes forthe majority of Be stars are optically thin disks with the range of thehalf-opening angle of 10degr
| On the Variability of O4-B5 Luminosity Class III-V Stars
We investigate the Hipparcos Satellite photometry of O4-B5 luminosityclass III-V stars. Some for which further study is desirable areidentified. These stars in general are more variable than cooler stars
| 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).
| A NA I Absorption Map of the Small-Scale Structure in the Interstellar Gas toward M15
Using the DensePak fiber-optic array on the KPNO WIYN telescope, we haveobtained high signal-to-noise ratio echelle spectra of the Na I Dwavelength region toward the central 27^''x43^'' of the globular clusterM15 at a spatial resolution of 4". The spectra exhibit significantinterstellar Na I absorption at LSR velocities of 3 km s^-1 (localinterstellar medium [LISM] component) and 68 km s^-1(intermediate-velocity cloud [IVC] component). Both components varyappreciably in strength on these scales. The derived Na I columndensities differ by a factor of 4 across the LISM absorption map and bya factor of 16 across the IVC map. Assuming distances of 500 and 1500 pcfor the LISM and IV clouds, respectively, these maps show evidence ofsignificant ISM structure down to the minimum scales of 2000 and 6000 AUprobed in these absorbers. The smallest scale N(Na I) variationsobserved in the M15 LISM and IVC maps are typically comparable to orhigher than the values found at similar scales in previous studies ofinterstellar Na I structure toward binary stars. The physicalimplications of the small and larger scale Na I features observed in theM15 maps are discussed in terms of variations in the H I column densityas well as in the Na ionization equilibrium.
| The 74th Special Name-list of Variable Stars
We present the Name-list introducing GCVS names for 3153 variable starsdiscovered by the Hipparcos mission.
| Radio HI and optical absorption-line spectra of an intermediate-velocity cloud in the general direction of the M15 globular cluster
Using HI spectra obtained with the Lovell telescope (FWHM ~ 12 arcmin)we present maps showing the HI distribution and velocity structure of anintermediate-velocity cloud (IVC; v_LSR~70 km s^-1) which is observed inthe general direction of the globular cluster M15. The gas is shown tobe clumpy in nature and we examine its position and velocity structure.The IVC is detected in absorption in the CaII K line towards fivecluster stars in intermediate resolution spectra obtained with ISIS/WHTand in high resolution UES/WHT NaI D line spectra of two cluster stars(II-75; IV-38). The clumpy nature of the gas is indicated by the NaI andKI spectra obtained in the II-75 and IV-38 sightlines, which haveangular separation ~ 3.5 arcmin. The IVC is detected in KI in the highercolumn density II-75 sightline; this appears to be the first detectionof IVC or HVC gas in KI. The IVC gas towards M15 has a similar velocityto that observed towards HD 203664, some 3.1 deg away from the cluster.Similarities in the IVC gas velocity suggest a gas structure thatextends across both sightlines, although gas column densities areconsiderably higher towards M15. For a common feature, this would placethe M15 IVC at a height above the Galactic plane (z-distance) of<~1.5 kpc based on the Little et al. estimate of the HD 203664distance. From the fine-scale structure and column density observations,estimates are made of the space density of the small-scaleconcentrations. However, these remain uncertain and the presentobservations emphasize the need for higher spatial and spectralresolution studies to provide firmer estimates of cloud properties. Wereport also on a radio HI and CaII line survey towards a sample of 24stars over a wider field. This was carried out in an attempt to detectany wider distribution of the IVC gas and to place better limits on itsdistance. Although these observations are of sufficient spectralquality, no new optical detections are reported.
| Near infrared low-resolution spectra of 7 Be stars and AG CAR
We present and discuss lambda 6470-8780 spectra of 7 poorly-studied Bestars and of one Luminous Blue Variable (AG Car), and give equivalentwidths and radial velocities of selected spectral lines. Based onobservations obtained at Las Campanas Observatory and at the EuropeanSouthern Observatory in Chile
| 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.
| Observations of High Velocity Gas in the Galactic Halo
High resolution optical and stellar interstellar observations towardsthe halo star HD 203664 and 6 surrounding early-type stars have beencombined with a 21 cm mapping of the region to investigate a 70 km/shigh velocity cloud (HVC). The distance of the HVC from the galacticplane (z) has been constrained to lie between 200 pc and 1500 pc, upperlimits to temperature and velocity dispersion of 4600 K and 2.2 km/shave been estimated, and a column density ratio of N(Na I)/n(Ca II) =0.32 has been deduced. These parameters are consistent with the materialbeing shocked gas, possibly arising from an old supernova remnant. TheN(Na I)/N(H I) and N(Ca II)/N(H I) ratios are anomalously large byfactors of approximately 20 and 110 respectively, with respect to normaldiffuse gas.
| Optical and H I observations of high-velocity gas toward HD 203664
High-resolution optical stellar and interstellar observations toward thehalo star HD 203664 and six surrounding early-type stars have beencombined with a 21 cm mapping of the region to investigate a 70 kms-1 between 200 and 1500 pc; upper limits to temperature andvelocity dispersion of 4600 K and 2.2 km s-1 have beenestimated; and a column density ratio N(Na II)/N (Ca II) approx. equalto 0.32 has been deduced. These parameters are consistent with thematerial being shocked gas, possibly arising from an old supernovaremnant. The N(Na I)/N(H I) and N(Ca II)/N(H I) ratios are anomalouslylarge by factors of approximately 20 and 100, respectively, with respectto normal diffuse gas; several scenarios are presented as possibleexplanations of this phenomenon.
| A study of Be stars in the wavelength region around Paschen 7
This paper presents a study of the wavelength region 9840 - 10200centered upon P 7 in 74 Be type stars (B0-A0). We find a correlation ofthe P 7 emission with spectral type, the emission being strongest inearly types and disappearing toward A0. All emission lines are doublepeaked. Besides P 7 also several Fe II lines appear in emission, thestrongest being λ 9997. A strong positive correlation existsbetween all emissions and we conclude that Fe II is in emission wheneverP 7 is in emission. P 7 and λ 9997 also show a strong similarityin the details of the line structure. By comparison to stellar radii,the radii of emission-line regions are small and are similar for P 7 andthe Fe II emission lines.
| A high-resolution optical and radio study of Milky Way halo gas
Optical interstellar absorption lines of Ti II and Ca II and the 21 cmemission line of H I were observed at high-resolution (6 and 1 km/s,respectively) and high detection sensitivity along 25 lines of sight inthe Galactic halo. The sample includes 16 distant halo stars matchedwith one or more nearly aligned foreground stars as well as local starsalong five extragalactic sight lines. The data show substantialinterstellar material, at both low and intermediate velocities, between250 and 1000 pc beyond the Galactic plane. As much as one-third of thetotal gas observed in Ca II absorption may be beyond 1 kpc, and thegaseous Ti II may lie in an even thicker layer. The directly determinedgaseous Ti abundance above the Galactic plane exceeds that in the disk,on the average, by a factor of 4 to 6 and, for individual cloudcomponents, is further enhanced at higher LSR velocity. Thirty threediscrete high-latitude clouds are detected in Ca II absorption, and 17discrete clouds, including three high-velocity clouds, are identified inH I emission. The kinematics of the high-latitude gas observed in Ti IIand Ca II absorption is characterized by significant peculiar velocitieswith respect to a model corotating halo.
| Improved Mean Positions and Proper Motions for the 995 FK4 Sup Stars not Included in the FK5 Extension
Not Available
| A southern Be star survey - Spectra and envelope radii
We describe the hydrogen line spectra of 63 southern Be stars, obtainedat ESO, Chile, in one observational run in August 1978. The spectra wererecorded on photographic plates. We also provide the outer radii of theline emission forming region for a number of stars, based upon theemission peak separation of the H4 and H5 lines. Average values soobtained are in good agreement with other determinations based upon asmaller number of objects.
| An astrometric catalogue of stars in the region of M15
We present positions and proper motions with respect to the PPMcatalogue of 863 stars in a field of 8 deg x 6 deg centered on theglobular cluster M15. The catalogue is based on measurements of 136plates from the Carte du Ciel telescope of Bordeaux, the CERGA Schmidttelescope, and the double refractor of Bonn. The modal accuracy of theproper motions is +/- 0 arcsec 15/100 a.
| Large and kinematically unbiased samples of G- and K-type stars. V - Evolved stars in the selected areas at + 15-deg declination
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1990PASP..102..242E&db_key=AST
| Rotational velocity of Be stars correlated with emission characteristics
A sample of shell and nonshell B0e-B5e stars with weak and strongemission, and shell and nonshell B6e-B9e stars with weak emission, arestudied to seek a correlation between the rotational velocity of Bestars and the emissive strength. These results and the distributions ofV sin i indicate that the hottest Be stars, B0e-B5e, with rotationalvelocities of about 345 km/s can develop the characteristics of strongemission. For stars which are slightly less hot, or stars with slightlysmaller rotational velocities, only characteristics of weak emission canbe developed, and the shell characteristics only develop when the staris viewed at a greater-than-33-deg inclination to the pole. It is alsonoted that stars with large rotational velocities, the strong-emissionB0e-B5e and weak-emission B6e-B9e stars, can show metallic shellcharacteristics when seen near the equatorial plane.
| Catalog of O-B stars observed with Tokyo Meridian Circle
A catalog of the O-B stars, selected from 'Blaauw-Parenago' list andRubin's catalog, has been compiled on the FK4 system by the observationsmade with Gautier 8-inch Meridian Circle at the Tokyo AstronomicalObservatory during the period, 1971 to 1979. It contains 1059 stars andwas compiled for the future establishment of high precision propermotions of O-B stars.
| The galactic reddening law - The evidence from uvby-beta photometry of B stars
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1985A&A...142..189T&db_key=AST
| Be-Stars and Shell Stars Observed with the 13-COLOR Photometric System - Part Two
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1984RMxAA...9..141S&db_key=AST
| A second catalog of the profile of the H-alpha line in 55 Be stars
A second catalog of the H-alpha line profile of 55 Be stars ispresented, thereby raising the total H-alpha line profiles for Be starsto 127 stars. The measurements were made with the echelle spectrographon the 152 cm telescope at the Haute Provence Observatory. Photosphericabsorption was dominant in 12 percent of the stars, and not visible atall in 64 percent of the objects, where H-alpha and H-beta radiationwere combined. A central absorption for the H-alpha emission wasdetected in 73 percent of the cases, and FWHM emission intensities werecorrelated with the rotational velocities of the stars. The group I Bestars displayed emission lines which were not detectable of stars ofother groupings.
| A classification of Be stars
Based upon a sample of 140 stars observed over 20 years for which about5,000 spectrograms are available, a classification scheme of Be stars ispresented. This is the first attempt to subdivide the Be star group intophysically significant subgroups, from which typical objects can beselected for further study. The four groups proposed are based upon adiscussion of spectrum characteristics, multicolor photometry,polarization, rotational velocities, UV spectral types and timevariability. Starting with the group membership of a Be star,predictions can be made of the future behavior of it.
| Absolute ultraviolet spectrophotometry with the TD-1 satellite. XI - Spectrophotometric study of Be and shell stars with the S 2/68 experiment
Low resolution S 2/68 observations are used to show that Be stars ofspectral type B0-B5 have a deficiency of ultraviolet radiation (at 2100A) as compared to the visible with respect to normal stars of the samespectral type. The deficiency is statistically correlated with thestrength of visual emission lines, with the existence of an infraredexcess and with the presence of a shell. Comparison criteria for Be andB stars are discussed along with the relation between the interstellarcolor excess and the depth of the 2200 A absorption feature for normal Bstars. In addition, the origin of the flux deficiency is considered, andit is shown that the stars with a shell of hydrogen and metals (a strongshell) have a source of absorption different from that of the Be starswith strong emission.
| Etude photometrique a bande etroite de l'emission dans les etoiles Be
Not Available
| Some Spectroscopic Characteristics of the OB Stars: an Investigation of the Space Distribution of Certain OB Stars and the Reference Frame of the Classification
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1971ApJS...23..257W&db_key=AST
| Observations of the 21-CM Hydrogen Line Toward High-Latitude Stars
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1969ApJ...157.1101G&db_key=AST
| Be stars and galactic rotation.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1968AJ.....73..338C&db_key=AST
| Spectral Classifications of 239 Early-Type Stars
Not Available
|
Submit a new article
Related links
Submit a new link
Member of following groups:
|
Observation and Astrometry data
| Constellation: | Πήγασος |
| Right ascension: | 21h23m35.39s |
| Declination: | +14°03'00.6" |
| Apparent magnitude: | 6.742 |
| Distance: | 10000000 parsecs |
| Proper motion RA: | 7.9 |
| Proper motion Dec: | -7.8 |
| B-T magnitude: | 6.651 |
| V-T magnitude: | 6.735 |
Catalogs and designations:
|
