Contingut
Imatges
Carregar la teva Imatge
DSS Images Other Images
Articles Relacionats
Observations of Hα, iron, and oxygen lines in B, Be, and shell stars
We carried out a spectroscopic survey of several B, Be, and shell starsin optical and near-infrared regions. Line profiles of the Hα lineand of selected Fe II and O I lines are presented.
| Far-infrared loops in the 2nd Galactic Quadrant
We present the results of an investigation of the large-scale structureof the diffuse interstellar medium in the 2nd Galactic Quadrant(90°≤l≤180°). 145 loops were identified on IRAS-basedfar-infrared maps. Our catalogue lists their basic physical properties.The distribution clearly suggests that there is an efficient processthat can generate loop-like features at high Galactic latitudes.Distances are provided for 30 loops. We also give an observationalestimate of the volume filling factor of the hot gas in the Local Arm,4.6%≤f2nd<6.4%.Appendices A-C are only available in electronic form at the CDS viaanonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/418/131
| Merged catalogue of reflection nebulae
Several catalogues of reflection nebulae are merged to create a uniformcatalogue of 913 objects. It contains revised coordinates,cross-identifications of nebulae and stars, as well as identificationswith IRAS point sources.The catalogue is only available in electronic form at the CDS viaanonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/399/141
| 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.
| 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.
| High and intermediate-resolution spectroscopy of Be stars 4481 lines
We present an atlas of Hγ , He i lambda 4471 and Mg ii lambda 4481line profiles obtained in a 10 year observation period of 116 Be stars,which enabled many of them to be observed at quite different emissionepochs. From the best fit of the observed He i lambda 4471 line profileswith non-LTE, uniform (Teff,log g) and full limb-darkenedmodel line profiles, we determined the V sin i of the program stars. Toaccount, to some degree, for the line formation peculiarities related tothe rapid rotation-induced non-uniform distributions of temperature andgravity on the stellar surface, the fit was achieved by considering(Teff,log g) as free parameters. This method produced V sin iestimations that correlate with the rotational velocities determined bySlettebak (1982) within a dispersion sigma <= 30 km s-1and without any systematic deviation. They can be considered as given inthe new Slettebak's et al. (1975) system. Only 13 program stars havediscrepant V sin i values. In some objects, this discrepancy could beattributed to binary effects. Using the newly determined V sin iparameters, we found that the ratio of true rotational velocitiesV/Vc of the program Be stars has a very low dispersion aroundthe mean value. Assuming then that all the stars are rigid rotators withthe same ratio V(/lineω)/Vc, we looked for the value of/line ω that better represents the distribution of V sini/Vc for randomly oriented rotational axes. We obtained/lineω = 0.795. This value enabled us to determine the probableinclination angle of the stellar rotation axis of the program stars. Inthe observed line profiles of Hγ , He i lambda 4471, Mg ii lambda4481 and Fe ii lambda 4351 we measured several parameters related to theabsorption and/or emission components, such as: equivalent width,residual emission and/or absorption intensity, FWHM, emission peakseparations, etc. The parameters related to the Hγ line emissionprofiles were used to investigate the structure of the nearbyenvironment of the central star. From the characteristics of thecorrelations between these quantities and the inferred inclinationangle, we concluded that in most of cases the Hγ line emissionforming regions may not be strongly flattened. Using a simplerepresentation of the radiation flux emitted by the star+envelopesystem, we derived first order estimates of physical parameterscharacterizing the Hγ line emission formation region. Thus, weobtained that the total extent of the Hγ region is Rf=~ 2.5 +/- 1.0 R* and that the density distribution in theselayers can be mimicked with a power law rho ~ R-alpha , wherealpha =2.5+2.2-0.6. The same approach enabled usto estimate the optical depth of the Hγ line emission formationregion. From its dependence with the aspect angle, we concluded thatthese regions are caracterized by a modest flattening and that the rho(equator)/rho (pole) density contrast of the circumstellar envelope nearthe star should be two orders of magnitude lower than predicted bymodels based on a priori disc-shaped circumstellar envelopes. We foundthat the separation between the emission peaks, Deltap, andthe full width at half maximum, Delta 1/2, of the Hγline emission are not only sensitive to kinematic effects, but to lineoptical depth as well. This finding agrees with previous theoreticalpredictions and confirms that Huang's (1972) relation overestimates theextent of the Hγ line emission formation region. Data obtained atCASLEO operated under agreement between the CONICET and the NationalUniversities of La Plata, Córdoba and San Juan, Argentina, at ESOLa Silla, Chile and at OHP, France.}\fnmsep\thanks{Tables 2 to 7 andFigs. 1 and 2 are only available in full in electronic form at CDS viaanonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via\http://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/378/861}} \subtitle{Anatlas of Hγ , He {\fontsize {10pt}{12pt}\selectfont I} 4471 and Mg{\fontsize {10pt}{12pt}\selectfont II
| 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
| 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
| 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).
| 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
| Morphology and kinematics of the Cepheus Bubble
We investigate the spatial and velocity distribution of atomic hydrogenassociated with the Cepheus Bubble, a giant (~10deg inangular diameter) dust ring around the Cep OB2 association. HI 21 cmdata, taken from the Leiden/Dwingeloo survey, reveal HI structures inthe [-14,+2] kms-1 velocity range which can be associatedwith prominent parts of the dust ring. In the same area the HI maps alsoshow an expanding shell with a well-defined approaching side atVLSR=-37 kms-1 and a less well-defined recedingside at VLSR~-4 kms-1. The kinematics and size ofthis shell are best modelled by a supernova explosion, occurring in CepOB2a at about 1.7 Myrs ago. Since the ages of several parts of theCepheus Bubble are considerably higher than the age of the expandingshell, the supernova probably exploded in a pre-existing cavity, and itsshock front might have interacted with the already existing star formingregions Sh2-140, IC 1396, and NGC 7129, leading to a new wave of starformation there.
| Six intermediate-mass stars with far-infrared excess: a search for evolutionary connections
We present the results of high-resolution spectroscopic, low-resolutionspectrophotometric and spectropolarimetric and broad-band multicolourobservations of four B-type stars (HD 4881, 5839, 224648 and 179218) andtwo A-type stars (HD 32509 and 184761) with strong far-infrared (IR)excesses. The excess in HD 184761, which is located at a distance of 65pc from the Sun, was recognized for the first time. Double-peakedHα emission line profiles are found in HD 4881 and HD 5839, whileHD 184761, HD 224648 and HD 32509 display no emission in Hα. Theremarkable variations observed in the Hα profile of HD 179218 arealso observed in some classical Be and Herbig Ae/Be stars. An intrinsiccomponent of polarization is clearly present in HD 179218, only aninterstellar component is detected in HD 4881 and HD 224648, and HD184761 was found to be unpolarized. Improved effective temperatures forall six objects were derived. Parallaxes measured by the Hipparcossatellite were used to determine positions of the stars in the HRdiagram. HD 4881 and HD 5839 are an order of magnitude more luminousthan main-sequence stars of similar temperatures and are most likelynewly discovered classical Be stars. Study of the high-resolution IRASmaps and modelling of the spectral energy distributions of HD 4881, HD5839 and HD 224648 suggest that the observed large IR excesses arecaused by radiation from circumstellar dust rather than free--freeradiation or infrared cirrus, so they may be higher mass counterparts ofbeta Pictoris stars. HD 32509, HD 224648 and HD 184761, which have verysmall near-IR excesses, are probably young main-sequence stars. HD179218, which exhibits the largest near- and far-IR excess in thesample, is an isolated pre-main-sequence Herbig Be star.
| A Second Catalog of Orbiting Astronomical Observatory 2 Filter Photometry: Ultraviolet Photometry of 614 Stars
Ultraviolet photometry from the Wisconsin Experiment Package on theOrbiting Astronomical Observatory 2 (OAO 2) is presented for 614 stars.Previously unpublished magnitudes from 12 filter bandpasses withwavelengths ranging from 1330 to 4250 Å have been placed on thewhite dwarf model atmosphere absolute flux scale. The fluxes wereconverted to magnitudes using V=0 for F(V)=3.46x10^-9 ergs cm^-2 s^-1Å^-1, or m_lambda=-2.5logF_lambda-21.15. This second catalogeffectively doubles the amount of OAO 2 photometry available in theliterature and includes many objects too bright to be observed withmodern space observatories.
| Investigation of the variability of bright Be stars using HIPPARCOS photometry
The high accuracy and the homogeneity of Hipparcos data for bright starshave allowed us to quantify the degree of variability of Be stars. Thisdegree has been found to be highly dependent on the temperature of thestar. Rapid variability is the main feature of the 86% of early Be andless than 20% of late Be stars taking into account the limit ofdetection considered. In addition to Be stars reported in the Hipparcoscatalogue (ESA 1997) as short-period variables, we have been able toenlarge the number of detections as well as to confirm periodspreviously determined. Be stars that show larger amplitude rapidvariations are proposed as candidates for a search of multiperiodicityi.e. as non-radial pulsators. We have also searched for the presence ofoutbursts and fading events in the Hipparcos data. Outbursts have beenfrequently and preferentially detected in early Be stars with rather lowto moderate v sini while fading events seem to be more conspicuous instars with higher v sini. Mid-term and long-term variations have alsobeen investigated. Several stars have shown some evidence of temporaryquasi-periodic oscillations ranging between 10 and 200 days. Finallyinformation concerning long-term variations is reported. Cycles shorterthan or equal to the Hipparcos mission have mainly been detected instars earlier than B6. Long-term time scales of late Be stars areconfirmed to be longer by far. Tables 1 and 2 are only available inelectronic form at CDS via ftp to cdsarc.u-strasbg.fr (130.79.128.5) orvia http://cdsweb.u-strasbg.fr/Abstract.html
| Bow Shocks Around Runaway Stars.III.The High Resolution Maps
In a recent survey for bow shock structures around OB runaway starsusing the ISSA/IRAS archival data and excess maps at 60 \mum, 58candidates were found. These objects are surrounded by extended infraredemission at 60 \mum, characteristic of warm dust heated by ultravioletphotons, a signature of wind bow shocks. High resolution IRAS (HiRes)images have been produced for these 58 objects and some of thosespatially resolved are presented in this study. The images were used todistinguish between multiple confused IR sources, possible artifacts andunambiguous bow shocks, as the sources of the extended 60 \mum emission.Six new bow shocks have been identified using this method, and threehave been rejected. Twenty two of the targets, however, remain spatiallyunresolved even at the nominal HiRes resolution of ~ 1arcmin . For thelarger and better defined bow shocks some internal substructure isdiscernible. The length of these features suggest that they arise as theresult of a subtle dynamical instability. It can not be ruled out,however, that some of the bow shock morphology could be imprinted by thesurrounding medium.
| UBV photometry of Be stars at Hvar: 1972--1990
A summary of results of the systematic UBV photoelectric monitoring ofbright northern Be stars carried out at the Hvar Observatory between1972 and 1990 is presented. Altogether, 76 Be stars of all luminosityclasses were observed and 13,848 UBV measurements secured.Simultaneously, 9,648 UBV measurements of 48 check stars (most of themof early spectral types) were obtained. A careful transformation of allobservations into the standard Johnson system allowed detection andmonitoring of even very mild long-term light and colour variations ofthese objects. Almost all early-type Be stars in the sample turned outto be variable. For several stars phase-locked light variations relatedto their binary nature were established. Sudden brightenings, on a timescale of a few days, were detected for o Cas and QR Vul. Tables 2 and 3are only available in electronic form at CDS via ftp tocdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsweb.u-strasbg.fr/Abstract.html
| 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.
| On the structure of Be star disks.
We investigate the geometrical structure of the emitting part ofcircumstellar envelopes around Be stars from an empirical point of view.We use new high-resolution, high-S/N spectroscopic data of the FeIIλ5317 and some other faint FeII emission lines in 27 Be starsshowing symmetrical emission lines (class 1). We find a clearcorrelation between its total width (measuring the maximum velocities ofcircumstellar matter) and the stellar rotational velocity. Thiscorrelation means that a typical Be envelope (or, more precisely, thatpart of it which is visible in optical emission lines) is anaxisymmetric, rotationally supported disk. For empirical investigationof the vertical structure, we use the occurrence of shell lines. Wedefine, as shell criterion based on FeII lines, a Be shell star as onewith FeII central intensity F_cd_/F_*_(FeII)<1. Using this forcalibrating an appropriate parameter for the much more frequentlyobserved Hα line, we find that shell stars are those withF_p_/F_cd_(Hα)>=1.5 where F_p_ is the mean peak intensity atHα. In a sample of 114 programme stars, we find a shell starfraction of 22.8%. This number is readily transformed into a halfopening angle of Be star disks, φ=13deg. We furthermore show thatBe disks must be thin at the inner edge, and may become fairly thick atthe outer rim. This, together with the small value of φ, isevidence for a conical or concave shape, the latter typical of ahydrostatically balanced disk. Finally we provide evidence that thefamous "shell-Be" phase transitions can naturally occur in such disks asa geometrical effect if they are seen under inclination i=~70deg and iftheir outer radius is variable with time.
| IRAS-selected Galactic star-forming regions - II. Water maser detections in the extended sample
The results of the analysis of the occurrence of 22.2-GHz H_2O maseremission in a sample of 1409 IRAS sources north of declination -30 degassociated with star-forming regions are presented. Our sample containsall the IRAS sources that satisfy Emerson criteria for selectingmolecular cores associated with the earliest evolutionary stages of thestar-forming process. In a previous paper, we have reported the resultsof the observations of about one third of the sample. In the presentpaper the observations of the remaining IRAS sources are presented: 18of them are newly detected maser sources. The results show that 20 percent of all IRAS sources that satisfy the Wood & Churchwell criteriahave H_2O water masers. This is in agreement with the assumption thatthese criteria select objects that are connected with the early phasesof the evolution of high-mass star-forming regions. Moreover, about onethird of the whole sample selected according to Emerson criteriacontains IRAS sources that are not associated with massive star-formingprocesses, but probably with molecular cores in low-mass star-formingregions.
| The 72nd Name-List of Variable Stars
Not Available
| 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.
| Ultraviolet spectral classification and stellar winds in a sample of Be and standard stars
Equivalent widths of 16 lines of C I, C II, C III, C IV, Si II, Si III,Si IV, Al II, Al III, Fe II, and Fe III, plus centriod and edgevelocities of the Si IV and C IV lines, were measured in InternationalUltraviolet Explorer spectra of 39 Ble-B8e and 18 B1-B8 standardnon-emission-line stars. These suggest the following: (1) Certain lineratios of Si II/III, C II/III, Al II/III, and Fe II/III are verysensitive to spectral type and represent excellent UV criteria forspectral classification. (2) UV line strengths and line ratios show thatthere are no significant differences between the photospheric linespectra of Be and normal, non-emission-line stars of corresponding type.(3) The Si IV and C IV wind lines in the Be stars are correlated withboth spectral type and luminosity class in the sense that the hotteststars have the strongest lines with the largest centroid and edgevelocities, and the giants and subgiants have stronger lines than themain-sequence stars. (4) The Si IV wind lines persist to spectral typeB8 in both the Be stars and the standard stars but are stronger in theBe stars than in the standards for the earlier types. (5) The C IV windlines persist to spectral type B8 in the Be stars, but only to B3 in thestandard stars, and are stronger in the Be stars than in the standardsat all spectral types. (6) The equivalent widths of the Si IV and C IVwind lines are only very weakly correlated with v sin i, if at all, buta threshold in v sin i near 150 kn/sec exists, below which no largeequivalent widths of Si IV or C IV may be seen. Assuming that the Bestars are all rapid rotators, such a correlation is essentially acorrelation with i and suggests that the winds from Be stars arisepreferentially from the equatorial regions. (7) Shell stars have weakerC IV absorption and smaller centroid and edge velocities than other Bestars, suggesting that they have weaker winds. Since there isconsiderable evidence that these are stars with cool, low-velocity diskswhich are being viewed edge-on or nearly edge-on, the winds may beinhibited and modified by the denser material in the equatorial regions.(8) Mg II emission is detected in about half of the program Be starswith long-wavelength IUE spectra, and seems not to be correlated withspectral type, v sin i, or strength of the Si IV wind lines. Since theMg II emission presumably originates in the cool, low-velocity envelope,and since Mg II emission also correlates with hydrogen Balmer emissionin the Be stars, this sugests that there is no strong physicalrelationship between the stellar winds and the cool disk. (9) The Beshell stars have stronger resonance lines of Si II, C I, C II, Al II, FeII, presumably formed in the cool shells, than the other Be stars andthe normal, non-emission-line stars of the same spectral types,consistent with the strong lines arising from metastable levels in theoptical spectra of these stars.
| 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.
| Improved Mean Positions and Proper Motions for the 995 FK4 Sup Stars not Included in the FK5 Extension
Not Available
| The distribution of interstellar dust in the solar neighborhood
We surveyed the IRAS data base at the positions of the 1808 O6-B9.5stars in The Bright Star Catalog for extended objects with excessemission at 60 microns, indicating the presence of interstellar dust atthe location of the star. Within 400 pc the filling factor of theinterstellar medium, for dust clouds with a density greater than 0.5/cucm is 14.6 + or - 2.4%. Above a density of 1.0/cu cm, the densitydistribution function appears to follow a power law index - 1.25. Whenthe dust clouds are mapped onto the galactic plane, the sun appears tobe located in a low-density region of the interstellar medium of widthabout 60 pc extending at least 500 pc in the direction of longitudes 80deg - 260 deg, a feature we call the 'local trough'.
| 6 Cephei
IAUC 5813 available at Central Bureau for Astronomical Telegrams.
| A catalogue of radii of Be star line emitting regions
A bibliographic catalog of the radii of the line-emitting regions aroundBe stars is presented. The table also provides the separation of theemission peaks, the wavelength of the line used, observing date, and theV sin i value given by the author.
| Infrared environment of 6 Cephei
This paper deals with the study of various features in the interstellarenvironment of the Be star 6 Cephei analyzing IRAS maps and opticaldata. We suggest that the conspicuous nearly circular arc on the IRASmaps is a stellar wind bubble (SWB). It has been shown that the faint HII region S 133 is probably a part of a chain of ionized arcssurrounding the older group of the Cepheus OB2 association. Therelationship of 6 Cephei to a giant infrared ring (Cepheus Bubble)indicates a distance of about 800 pc and an unusually high absolutebrightness of -5 mag for the star. 21 H alpha emission stars have beenfound in the 6 Cep area. We constructed a model for the infrared pointsource associated with 6 Cephei in terms of the infrared emission of thesurrounding reflection nebula, and modeled the extended infraredemission of the reflection nebula adopting the dust model of Desert etal. (1990). The model resulted in a significant underabundance of verysmall grains and a normal abundance of PAH's with respect to the biggrains. The model gives 0.23 solar mass for the dust mass of thereflection nebula which is not sufficient to account for the measuredreddening of the star.
| Physical properties of Be star envelopes from Balmer and Fe II emission lines
The study obtains H-alpha, B-beta, H-gamma, and Fe II 6516 line profileswith resolution 0.45 A for 41 bright Be stars with a CCD detonatorduring two observing periods in 1989. Analysis of the structure of theemission profiles indicates that the Be star emitting envelope is mostlikely axially symmetric, consistent with a rotating, equatorial disk. Anumber of Be stars show either a 'wine bottle' structure or inflectionpoints on one side of their H-alpha emission profiles, suggesting atwo-component structure for the emitting envelope: an inner disk,possibly turbulent, and an outer extended disk. Differentially rotatingdisks producing weak H-alpha emission are closer to the central starwhere rotation broadens the line more strongly, relative to stars withextended envelopes which emit strongly but rotate more slowly. From theBalmer emission decrements it is found that Be star envelopes with Tenear 10,000 K have electron densities in the range 10 exp 11 to 10 exp13/cu cm. Be stars with weak Balmer emission have, on average, somewhatflatter Balmer decrements than stars with strong emission, suggestingenvelopes with higher electron densities.
| SAO stars with infrared excess in the IRAS Point Source Catalog
We have undertaken a search for SAO stars with infrared excess in theIRAS Point Source Catalog. In contrast to previous searches, the entireIRAS (12)-(25)-(60) color-color diagram was used. This selection yieldeda sample of 462 stars, of which a significant number are stars withcircumstellar material. The stars selected can be identified aspre-main-sequence stars, Be stars, protoplanetary systems, post-AGBstars, etc. A number of objects are (visual) binary stars.Characteristic temperatures and IR excesses are calculated and theirrelations to spectral type are investigated.
|
Enviar un nou article
Enllaços Relacionats
- - No s'ha trobat enllaços -
Enviar un nou enllaç
Membre dels grups següents:
|
Dades d'Observació i Astrometria
| Constel·lació: | Cepheus |
| Ascensió Recta: | 21h19m22.20s |
| Declinació: | +64°52'19.0" |
| Magnitud Aparent: | 5.18 |
| Distancia: | 331.126 parsecs |
| Moviment propi RA: | 2.4 |
| Moviment propi Dec: | 5 |
| B-T magnitude: | 5.11 |
| V-T magnitude: | 5.169 |
Catàlegs i designacions:
|
INHABITED SKY
