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2MASS observations of Be stars
A catalogue of almost all known Galactic Be stars in the 2MASS database(1185 in total) and in the MSX database (225 in total) is presented inthis paper. From the color color diagrams and spectral indexes, it isfound that the IR excesses for many samples are due to free free andfree bound emission from the ionized material around a Be star assuggested previously and that the mean spectral index derived for thesamples is 1.50 ± 0.34 between J to K bands and 1.14 ±0.42 between K to A bands, respectively. However, it is also found thatthere are eight Be stars that have large near infrared excess emissionwith spectral index values outside the range expected for free free andfree bound emission. This is likely attributed to circumstellar dustemission.
| Chandra Observations of Coronal Emission from the Early G Supergiants α and β Aquarii
We report Chandra detections of coronal X-rays from the early Gsupergiants α Aquarii (HD 209750: G2 Ib) and β Aquarii (HD204867: G0 Ib). Previous ROSAT observations of these archetypical``hybrid chromosphere'' stars were inconclusive, in the case of αAqr owing to a 38' mispointing, and for β Aqr because of a smallpositional discrepancy of the apparent source. The Chandra HighResolution Camera (HRC-I), with its superior spatial resolution andsensitivity, has obtained a positive detection of α Aqr andrecovered faint emission at the location of β Aqr, now wellseparated from the stronger source to the southeast that dominated theearlier ROSAT image. The coronal LX/LC IV luminosity ratiosof both supergiants are extremely depressed relative to early Gmain-sequence stars, continuing the ``X-ray deficiency syndrome''originally identified in late F/early G luminosity class III giants ofthe Hertzsprung gap.
| On the evolutionary status of Be stars. I. Field Be stars near the Sun
A sample of 97 galactic field Be stars were studied by taking intoaccount the effects induced by the fast rotation on their fundamentalparameters. All program stars were observed in the BCDspectrophotometric system in order to minimize the perturbationsproduced by the circumstellar environment on the spectral photosphericsignatures. This is one of the first attempts at determining stellarmasses and ages by simultaneously using model atmospheres andevolutionary tracks, both calculated for rotating objects. The stellarages (τ) normalized to the respective inferred time that eachrotating star can spend in the main sequence phase (τ_MS) reveal amass-dependent trend. This trend shows that: a) there are Be starsspread over the whole interval 0 τ/τ_MS 1 of themain sequence evolutionary phase; b) the distribution of points in the(τ/τMS,M/Mȯ) diagram indicates thatin massive stars (M 12~Mȯ) the Be phenomenon ispresent at smaller τ/τ_MS age ratios than for less massive stars(M 12~Mȯ). This distribution can be due to: i)higher mass-loss rates in massive objets, which can act to reduce thesurface fast rotation; ii) circulation time scales to transport angularmomentum from the core to the surface, which are longer the lower thestellar mass.
| A new approach to IRAS observations of Be stars
The IRAS associations for 193 Be stars are identified in this paper.From the infrared colors, the IRAS low-resolution spectra (LRS) and thespectral types, some physical properties and environment of the samplesare discussed. It can be concluded that not only free-free emission orfree-bound emission from the circumstellar ionized gas can beresponsible for the large IR excesses of Be stars as suggestedpreviously, but also, for some Be stars, thermal radiation from thecircumstellar dust and/or nebula around the star can produce large IRexcess as well. It is also found that the far IR excess of Be starsincreases with wavelengths.
| Autocorrelation Analysis of Hipparcos Photometry of Short-Period Be Stars
We have used Hipparcos epoch photometry and a form of autocorrelationanalysis to investigate the amplitude and timescale of the short-periodvariability of 82 Be stars, including 46 Be stars that were analyzed byHubert & Floquet using Fourier and CLEAN analysis and 36 other Bestars that were suspected of short-period variability. Our method hasgiven useful information for about 84% of these stars; for the rest, thetime distribution of the Hipparcos epoch photometry limits thecapability of our technique.
| Koordinierte Zusammenarbeit zwischen den VdS-FG 'BAV' und 'Spektroskopie' ?
Not Available
| 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
| 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
| Hα observations of Be stars
We present here the Hα spectra of 44 Be stars taken at aresolution of 0.5 Å. From the spectra, different emission lineparameters have been deduced. A study of the correlations betweendifferent pairs of these parameters has been made with a view tounderstanding the mechanisms of line formation and shaping in Be stars.
| 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.
| Long-term visual spectrophotometric behaviour of Be stars. II. Correlations with fundamental stellar parameters and interpretation
The long-term visual spectrophotometric (SPh) behaviour of Be stars as afunction of fundamental stellar parameters is studied. Some previous SPhresults obtained by other authors are confirmed. Moreover, a tendencyfor temperature and aspect angle dependency of SPh variations is found.From the characteristics of visual SPh behaviour in Be stars we deriveconstraints for models of regions in circumstellar envelopes where thevisual continuum spectrum is formed: (i) The SPh emission and absorptionphases should not imply preferential aspect angles, as they can bothappear whatever the stellar inclination. This phenomenon cannot bealways accounted for by strongly flattened circumstellar envelopes; (ii)Radii of the visible continuum forming regions cannot be larger than afew R_*; (iii) Electron densities of these regions should not exceed N_e~ 10(13) cm(-3) ; (iv) Electron temperature of circumstellar layersproducing the SPh emission phases compare with the stellar Balmercontinuum radiation temperature and it is much lower in those producingthe SPh absorption phases. Three scenarios were studied to produce theobserved characteristics of emissions in the V magnitude and in thesecond component of Balmer discontinuity (Delta D) during the SPhemission phases: (a) expansion of a massive circumstellar shell thatpreserves circumstellar envelope flattening; (b) expansion of acircumstellar shell which increases the global flattening, so that adisc-like structure is formed; (c) continuous mass ejection thatincreases the storage of mass in a constant volume with a givenflattening. Mechanisms (a) and (b) produce a double valued (DeltaV,Delta D) SPh relation, while (c) produces a single valued relation.Only mechanisms (a) and (c) can easily produce the observed amounts ofemission Delta V and Delta D without violating the modeling constraintsfrom (i) to (iv) imposed by observations. The model SPh slopes of (DeltaV,Delta D) show the global sin i and T_eff observed dependencies. Thescenarios used to describe the double valued (Delta V,Delta D) suggestanother possible way how to build up circumstellar envelopes around Bestars.
| 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
| 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
| 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
| 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.
| The Distribution of Dust Clouds in the Interstellar Medium
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1996ApJ...457..764D&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.
| 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.
| Multi-Band Polarimetry of Be Stars. I. X Persei
We analyzed the multi-band polarimetric data of X Per during 1988--1994around an extended low state in brightness. The variation in theintrinsic polarization correlated well with those of the Hα emissionstrength and the brightness variation. We give a rough estimate of thedisk development, adopting a cylindrically symmetric sector. The diskbecomes optically thick in its developed stage. It is a subtle problemwhether a large photometric variation with Delta V=0.8 mag can beexplained within the framework of the disk development, and is left as achallenging problem.
| 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.
| Radio continuum emission from stars: a catalogue update.
An updated version of my catalogue of radio stars is presented. Somestatistics and availability are discussed.
| Non-axisymmetric Be star circumstellar disks.
A new high resolution and high signal-to-noise ratio spectroscopic studyof Hα, FeII λ5317 and HeI λ5876 emission lines ofnorthern and equatorial Be stars is presented. The line profiles areanalyzed in order to test predictions of the recently proposed model ofglobal disk oscillations. The FeII and HeI line profiles are used toderive the kinematics and the radial extension of the circumstellardisk-like plasma. Based on line profile derivatives, we present a newmethod, the separation of the inflection points (SIP), to resolve theconvolved peaks of Hα winebottle-type profiles. The newly derivedpeak positions are used to determine Hα emission disk radii andmean optical line depths along the line of sight. We find that theseimproved Hα disk radii are smaller and closer to FeII disk radiithan those Hα disk radii derived from pure peak separations. Wefind evidence that class 2 profiles originate from quasi-Keplerian diskswith a non-axisymmetric density distribution.
| Near-infrared photometric observations of Be stars.
Not Available
| 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.
| 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'.
| 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.
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Наблюдательные данные и астрометрия
| Созвездие: | Жираф |
| Прямое восхождение: | 05h06m08.50s |
| Склонение: | +58°58'21.0" |
| Видимая звёздная величина: | 5.08 |
| Расстояние: | 205.761 парсек |
| Собственное движение RA: | 0 |
| Собственное движение Dec: | 0 |
| B-T magnitude: | 5.08 |
| V-T magnitude: | 5.197 |
Каталоги и обозначения:
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