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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
| 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
| Two-colour photometry for 9473 components of close Hipparcos double and multiple stars
Using observations obtained with the Tycho instrument of the ESAHipparcos satellite, a two-colour photometry is produced for componentsof more than 7 000 Hipparcos double and multiple stars with angularseparations 0.1 to 2.5 arcsec. We publish 9473 components of 5173systems with separations above 0.3 arcsec. The majority of them did nothave Tycho photometry in the Hipparcos catalogue. The magnitudes arederived in the Tycho B_T and V_T passbands, similar to the Johnsonpassbands. Photometrically resolved components of the binaries withstatistically significant trigonometric parallaxes can be put on an HRdiagram, the majority of them for the first time. Based on observationsmade with the ESA Hipparcos satellite.
| The 74th Special Name-list of Variable Stars
We present the Name-list introducing GCVS names for 3153 variable starsdiscovered by the Hipparcos mission.
| Speckle Interferometry of New and Problem HIPPARCOS Binaries
The ESA Hipparcos satellite made measurements of over 12,000 doublestars and discovered 3406 new systems. In addition to these, 4706entries in the Hipparcos Catalogue correspond to double star solutionsthat did not provide the classical parameters of separation and positionangle (rho,theta) but were the so-called problem stars, flagged ``G,''``O,'' ``V,'' or ``X'' (field H59 of the main catalog). An additionalsubset of 6981 entries were treated as single objects but classified byHipparcos as ``suspected nonsingle'' (flag ``S'' in field H61), thusyielding a total of 11,687 ``problem stars.'' Of the many ground-basedtechniques for the study of double stars, probably the one with thegreatest potential for exploration of these new and problem Hipparcosbinaries is speckle interferometry. Results are presented from aninspection of 848 new and problem Hipparcos binaries, using botharchival and new speckle observations obtained with the USNO and CHARAspeckle cameras.
| 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.
| ICCD Speckle Observations of Binary Stars.XVIII.An Investigation of Be =
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1997AJ....114.2112M&db_key=AST
| A Radial Velocity Database for Stephenson-Sanduleak Southern Luminous Stars
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1997AJ....113..823R&db_key=AST
| On the confinement of one-armed oscillations in discs of Be stars.
We discuss the effects due to the rotational deformation and theoptically-thin line force on the confinement of one-armed oscillationsin the inner part of Be-star discs. The period of these oscillations isidentified with the observed V/R variations in Balmer emission lines. Wetake into account the effect of rotation by including the quadrupolecontribution to the potential around the rotationally-distorted centralstar. For the radiative force due to an ensemble of optically thinlines, we adopt the parametric form proposed by Chen & Marlborough(1994ApJ...427.1005C). The disc is assumed to be isothermal. Based onthese assumptions, we examine the linear, one-armed eigenmodes confinedto the inner part of the disc. Our study strongly suggests that themechanism that causes the confinement of one-armed oscillations inearly-type Be stars is different from that in late-type Be stars. Inlate-type Be stars, the confinement occurs because of the deviation fromthe point-mass potential around the rotationally deformed star. On thispoint, we confirm the conclusions obtained by Papaloizou et al.(1992A&A...265L..45P). In early-type Be stars, however, it is theweak-line force that mainly contributes to the confinement. Therotational effect plays a much smaller role for these stars. The periodof the eigenmode confined to the disc depends sensitively on the effectby rotation or radiation. This sensitiveness, together with the range ofthe period of observed V/R variations, places rather narrow constraintson the parameters characterizing these effects. We compare our resultswith observed V/R properties, for which a list of 53 stars has beencompiled.
| ICCD Speckle Observations of Binary Stars. XIII. Measurements During 1989- 1994 From the Cerro Tololo 4 M Telescope
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1996AJ....111..936H&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.
| Atlas of high-resolution emission and shell lines in Be stars. Line profiles and short-term variability.
We present an atlas of high-S/N, high-resolution ({DELTA}v=6km/s) dataof Be star emission and shell profiles. We have collected profiles ofHα and of Fe II, mostly of the λ5317 transition. Theselines have been selected to provide measures for the overall emissionstrength and for the velocity field in these disks. We have collecteddata for 77 southern and equatorial programme stars, covering the period1982-1993. This is the most comprehensive overview of profile shapes inBe disks. We propose a three-dimensional scheme in which most observedprofiles can be classified. The parameters are i) inclination, ii)optical depth, and iii) the pattern of the velocity field. A search forshort-term variability (timescales between five days and a few minutes)in six stars ended with negative result. Shortest observed timescale forvariability is a few days for well-developed disks in binary systems (HR1910, HR 2142).
| 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.
| A spectroscopic database for Stephenson-Sanduleak Southern Luminous Stars
A database of published spectral classifications for objects in theStepenson-Sanduleak Luminous Stars in the Southern Milky Way catalog hasbeen compiled from the literature. A total of 6182 classifications for2562 stars from 139 sources are incorporated.
| 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.
| High-resolution spectroscopy of southern and equatorial Be stars: flux excess at λ4471 A.
We present a catalogue of high-resolution He I 4471, Mg II 4481 andHγ line profiles observed simultaneously for 37 southern andequatorial Be stars. In this paper we focus on the He I 4471 line, whichis studied using non-LTE model line profiles. A systematic difference isfound between the observed and the theoretical He I 4471 line equivalentwidths. This difference strongly correlates with the Hγ emissionand we interpret it as being due mainly to the veiling effect producedby the continuum emission excess originating in the circumstellarenvelope. To determine the continuum flux excess we use two methods. Onemethod enables us to obtain simultaneously the V sin i parameter. Theflux excess we determined is overestimated by about 9% on average,because in the line profile analysis we neglected the gravity darkeningeffect due to stellar rotation. We find that 14 program stars presenttwo possible solutions for V sin i. The second solution is, on average,14% smaller and produces a small residual or emission-like differencebetween the observed He I 4471 line profile and the model profile.
| Near Infrared Variability of Be-Stars
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1994MNRAS.269.1123D&db_key=AST
| On the rotation properties of Be stars and their envelopes.
We present the results of low resolution spectroscopy (4A) obtained atCTIO for a sample of 42 Be, 4 B and 3 O stars covering theλ3700-7000A spectral range. Equivalent widths of the Balmer lineswere measured up to H_10_. We also give the V/R state of the Hαemission line. In addition, the peak separation and the width at thebase of the Hβ and Hγ emission lines are tabulated for atotal of 243 medium resolution (1A) spectra of 51 southern Be starstaken at the Manuel Foster Observatory, Chile. We analyzed our Hαequivalent widths (Wα) together with published data for a total of122 Be and 2 Oe stars. An upper limit of Wα increasing with theprojected rotational velocity vsini is shown by the data. The Wαvalues depend strongly on spectral type, being lower for later-type Bestars. This could indicate that the maximum strength of emission dependsmainly on the spectral type and rotation velocity. The relation betweenWα(max) and vsini, together with the observed excess in number oflow vsini Be stars and the reported anti-correlation between photometricperiod and vsini give evidence for a considerable range of the truerotation velocities of Be stars: definitely there are intrinsically slowrotators among them. However, our results could also be interpreted interms of anisotropic Hα emission coming from the disk. Theanalysis of the net equivalent widths and peak separations of Hαdouble emission line profiles strongly favor a disk type emittingenvelope with a r^-j^ rotation law with j=1.4+/-0.2 which do not dependon the spectral subtype. This result is interpreted as evidence ofradial motions in the envelopes of Be stars. The mean radial extensionsof the regions which emit Balmer lines were determined to range between30% (H_10_) and 60% (Hβ) of the Hα emitting envelope in thecase j=1. The mean electron density within the envelope has been foundto vary only by a factor of 4. We compare our results with earlierinvestigations.
| Near-IR excess of Be stars.
The near-IR excess emission of 144 Be stars is derived from visual andnear-IR observations. The quasi-simultaneous nature of the observationsprovide colour excesses that are independent of temporal variations.Colour-colour diagrams are used to identify stars with excess coloursmarkedly different from the bulk of the sample stars. The near-IRemission of four stars that have markedly different colours isattributed to the presence of a binary companion or thermal dustemission. The percentage of stars with a significant excess increaseswith wavelength. The excess emission increases with wavelength and thelargest excesses occur in stars of earlier spectral type. The near-IRexcess colours are examined and compared to theoretical excess colourscalculated from a simple bremsstrahlung emitting disc model with aradial density distribution of the form ρ{prop.to}r^-β^. Theeffect of model parameters on the excess colours is discussed. Theobserved excesses for the bulk of the stars are well fit bycircumstellar discs with radii greater than ~10R_*_ and with a densityindex β, in the range 2.0-5.0. This is very similar to the range ofvalues previously determined by Waters et al. from IRAS far-IRobservations. A small number of stars cannot be reconciled with discswith a constant density index out to 10R_*_. It is argued that thecircumstellar plasma around these stars has a change in structure at~2-10R_*_. The possibilities of disc truncation or a change in thedensity index as the cause of the structure change are discussed.
| 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.
| A homogeneous catalog of new UBV and H-beta photometry of B- and A-type stars in and around the Scorpius-Centaurus OB association
B- and A-type stars in and near the Sco-Cen OB association areinvestigated with UBV and H-beta photometry to acquire data relevant tothe luminosity function of Sco-Cen. The measurements generally consistof two 10-s integrations of U, B, V, (W, N) filters, and theobservations are corrected iteratively for atmospheric extinction andinstrumental response. The data presented give the mean V magnitude,mean B-V, mean U-B, and the estimated uncertainties for these values.The catalog provides a homogeneous catalog of data for a large fieldwith stellar objects delineating membership to the association Sco-Cenand that affect the luminosity function of the aggregate.
| 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.
| A study of high-resolution emission-line profiles for Be stars
New high resolution high signal-to-noise emission line profiles wereobtained for 37 bright southern and equatorial Be stars at H-alpha,H-beta, Fe II 5317 A, and He I 5876 A. The program combines measurementsfor stars already included in previous high-resolution studies withfirst-time high-resolution observations for faint stars newly added tothe observing program. Characteristics of the profiles, includingequivalent width, FWHM intensity, and peak radial velocity are noted,and profiles are classified according to their typical shapes. SeveralBe stars having v sin i less than 200 km/s were found to exhibit shellcharacteristics at H-alpha and are suspected to rotate at equatorialrotational velocities distinctly below their critical velocities.
| Determination of Be-Star Parameters from Uvby-Beta Photometry and Hα Equivalent Widths
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1990MNRAS.247..407F&db_key=AST
| A study of Balmer decrements in Be star emission-line spectra
Balmer decrements are determined for 26 bright equatorial and southernearly-Be type stars and are compared with theoretical Balmer decrementscalculated for high-density hydrogen nebulae resembling typicalconditions expected for circumstellar envelopes around Be stars. Thederived Balmer decrement values comprise rather narrow ranges, at mostD(34) between 1.2 and 3.2 and D(54) between 0.4 and 1.0. Weakemission-line Be stars are often characterized by relatively flat Balmerdecrements. Among Be stars, very steep Balmer decrements are onlyobserved for Be shell stars. The main parameter governing the value ofBalmer decrements appears to be the mean electron density in thecircumstellar envelope.
| Be star variations associated with electron scattering in circumstellar envelopes of variable density
It is shown that the observed variations of visual brightness of the Bestars HR 2825 and HR 4930 are clearly correlated to variations of thewidths of their H-alpha emission-line wings. Both effects can beattributed to the influence of Thomson scattering in the circumstellarenvelopes of these stars. Observed photometric variations arequantitatively analyzed in terms of variations of emission measures ofthe envelopes and are found to be connected with important changes ofenvelope geometry and electron density. Plausible order-of-magnitudeestimates for electron column densities and resulting values of electrondensities and of envelope masses are presented and discussed.
| Ultraviolet observations of stellar winds in Be and 'normal' B non-supergiant stars
Model profile fits to high-resolution IUE C IV, Si IV, and Si IIIspectra are used to produce a homogeneous set of wind-velocity andcolumn-density measurements for 40 early-type Be stars and 40nonemission, nonsupergiant B stars. The mass-loss characteristics in theBe and normal B stars are compared. Results on stellar wind morphology,velocities, column densities, mass-loss, and ionization balance arepresented. The UV properties are compared to H-alpha, IR, andpolarization observations of Be stars. The results are used to discussthe roles of radiation pressure and rotation in driving the winds of Bestars.
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