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Properties and nature of Be stars. 24. Better data and model for the Be+F binary V360 Lacertae
Aims.We include existing photometric and spectroscopic material with newobservations in a detailed study of the Be+F binary V360Lac. Methods: .We used the programs FOTEL and KOREL toderive an improved linear ephemeris and to disentangle the line profilesof both binary components and telluric lines. The BINSYN software suite(described in the paper) is used to calculate synthetic light curves andspectra to fit the {UBV} photometry, an {IUE} spectrum, blue and redground-based spectra, and observed radial-velocity curves.Results: .The observations provide evidence of circumstellar matter inthe system. The system model shows that the Be primary star iscritically rotating, and that the synchronously rotating secondary starfills its Roche lobe. The primary star has a mass of7.45ȯ. Radial-velocity observations establish a massratio of 0.163. Light curve synthesis demonstrates that the observedlight curves are controlled largely by tidal distortion and irradiationof the massive primary by the less massive secondary. Synthetic spectrafit both blue and red observed spectra with the exception of spectrallines affected by circumstellar matter in the system. The syntheticspectra allow for gravity darkening and are consistent with criticalrotation of the primary. Synthetic spectrum fits to a dereddened {IUE}spectrum produce a calculated system distance of 512 pc. This distanceis 2σ beyond the Hipparcos distance.
| 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.
| 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.
| Properties and nature of Be stars Dra. XXIII. Long-term variations and physical properties of κ Dra.
We present an analysis of new spectroscopic observations of the brightBe star κ Dra obtained at the Ondřejovobservatory during 1992-2003 and U BV photometric observations securedat several observatories. General characteristics and a lineidentification of the spectrum of κ Dra areobtained in the regions 3730-5650 Å and 5850-7800 Å by acomparison with the theoretical spectrum. The fundamental stellarparameters have been obtained from a comparison with a grid of NLTEmodel atmospheres. The best fit was found for Teff=14 000 K,log g = 3.5, and v sin i = 170 km s-1. These values togetherwith a Hipparcos parallax lead to a stellar mass M=4.8±0.8Mȯ and radius R=6.4±0.5 Rȯ. It isencouraging to see that these values agree well with the expectedevolutionary mass and radius for the effective temperature we derived.Long-term variations of κ Dra were analysedusing measurements of equivalent widths, central intensities, peakintensities of emission lines and emission peak velocity differences forHα, Hβ, Hγ, Hδ, and some helium, silicon, andiron lines. The previously reported period of 23 years in the variationof the emission strength is probably a cyclic, not a strictly periodicphenomenon. An attempt to find out a period from all available recordsof the Hβ emission strength led to a value of (8044 ± 167)days (22.0 years) but the phase plots show that each cycle has adifferent shape and length. The maximum strength of the emission lagsbehind the brightness maximum. This is a behaviour usually observed forlong-term changes of Be stars with a positive correlation between thebrightness and emission strength. Since there are obviously no publishedspeckle observations of the star, we suggest these should be carriedout. They could help to deny or confirm the possibility that theemission episodes are triggered by a periastron passage of a putativebinary companion moving in an eccentric orbit with a 8044-d period, asit seems to be the case for some Be binaries. For the moment, the natureand origin of the disk around κ Dra remainsunknown. From the comparison of the electronic spectra obtained atdifferent phases of the long-term cycle and synthetic spectra it appearsthat there are no detectable changes in the photospheric part of theBalmer lines related to variations in the Balmer emission strength whichcould be attributed to an extended photosphere corresponding to innerparts of the disk, optically thick in continuum.Tables 2 to 4 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/419/607
| Properties and nature of Be stars. XXII. Long-term light and spectral variations of the new bright Be star HD 6226
Photometric and spectroscopic monitoring of the B star HD 6226 resultedin the finding that this object is a new bright Be star with a clearpositive correlation between the brightness and emission-line strength.The emission-line episodes are relatively short and seem to repeatfrequently which makes this star an ideal target for studying the causesof the Be phenomenon. The general character of the light variations, thelow v sin i = 70 km s-1 and the very pronounced lineasymmetries of the He I 6678 line, seen both outside and duringemission-line episodes, are all attributes which make HD 6226phenomenologically very similar to the well-known Be star ω CMa.Radial velocities of the deepest parts of the metallic and He I 6678absorption lines vary with a strict period of 2.61507 d over the wholetime interval covered by the observations, the velocities of the broadouter wings of the same lines varying in anti-phase and with a loweramplitude. This periodicity could not be found in the radial-velocityvariations of the sharp core of Hα. There is some indication ofvariability on a time scale of 24-29 days but our data are insufficientto prove that conclusively. A comparison of the line spectrum obtainedoutside emission episodes with synthetic spectra, standard dereddeningof U BV magnitudes and Hipparcos parallax all agree with the conclusionthat HD 6226 is a star with the following basic properties:Teff ,= 17 000 K, log g = 3.0 [cgs], mass of 5m.s and radiusof 11 Rȯ. The strong emission-line episodes may appearregularly, in a cycle of 630 days but with different durations ofindividual cycles. HD 6226 is probably one of the first B stars forwhich the Be nature was predicted on the basis of the character of itslight and colour changes.Based on spectral and photometric observations from the followingobservatories: Castanet-Tolosan, Dominion Astrophysical Observatory,Heidelberg, Hvar, Ondřejov, Skalnaté Pleso andStará Lesná and also on photoelectric photometry by AAVSOmembers.Tables 2 and 4 are available only 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/416/669
| 3D mapping of the dense interstellar gas around the Local Bubble
We present intermediate results from a long-term program of mapping theneutral absorption characteristics of the local interstellar medium,motivated by the availability of accurate and consistent parallaxes fromthe Hipparcos satellite. Equivalent widths of the interstellar NaID-line doublet at 5890 Å are presented for the lines-of-sighttowards some 311 new target stars lying within ~ 350 pc of the Sun.Using these data, together with NaI absorption measurements towards afurther ~ 240 nearby targets published in the literature (for many ofthem, in the directions of molecular clouds), and the ~ 450lines-of-sight already presented by (Sfeir et al. \cite{sfeir99}), weshow 3D absorption maps of the local distribution of neutral gas towards1005 sight-lines with Hipparcos distances as viewed from a variety ofdifferent galactic projections.The data are synthesized by means of two complementary methods, (i) bymapping of iso-equivalent width contours, and (ii) by densitydistribution calculation from the inversion of column-densities, amethod devised by Vergely et al. (\cite{vergely01}). Our present dataconfirms the view that the local cavity is deficient in cold and neutralinterstellar gas. The closest dense and cold gas ``wall'', in the firstquadrant, is at ~ 55-60 pc. There are a few isolated clouds at closerdistance, if the detected absorption is not produced by circumstellarmaterial.The maps reveal narrow or wide ``interstellar tunnels'' which connectthe Local Bubble to surrounding cavities, as predicted by the model ofCox & Smith (1974). In particular, one of these tunnels, defined bystars at 300 to 600 pc from the Sun showing negligible sodiumabsorption, connects the well known CMa void (Gry et al. \cite{gry85}),which is part of the Local Bubble, with the supershell GSH 238+00+09(Heiles \cite{heiles98}). High latitude lines-of-sight with the smallestabsorption are found in two ``chimneys'', whose directions areperpendicular to the Gould belt plane. The maps show that the LocalBubble is ``squeezed'' by surrounding shells in a complicated patternand suggest that its pressure is smaller than in those expandingregions.We discuss the locations of several HI and molecular clouds. Usingcomparisons between NaI and HI or CO velocities, in some cases we areable to improve the constraints on their distances. According to thevelocity criteria, MBM 33-37, MBM 16-18, UT 3-7, and MBM 54-55 arecloser than ~ 100 pc, and MBM 40 is closer than 80 pc. Dense HI cloudsare seen at less than 90 pc and 85 pc in the directions of the MBM 12and MBM 41-43 clouds respectively, but the molecular clouds themselvesmay be far beyond. The above closest molecular clouds are located at theneutral boundary of the Bubble. Only one translucent cloud, G192-67, isclearly embedded within the LB and well isolated.These maps of the distribution of local neutral interstellar NaI gas arealso briefly compared with the distribution of both interstellar dustand neutral HI gas within 300 pc.Tables 1 and 2 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/411/447
| 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.
| On the role of duplicity in the Be phenomenon. I. General considerations and the first attempt at a 3-D gas-dynamical modelling of gas outflow from hot and rapidly rotating OB stars in binaries
This paper begins a new series of studies devoted to a criticalre-examination of the role of duplicity for the Be phenomenon and forthe variability patterns observed for many Be stars. Based on bothdynamical and energy considerations and a numerical gas-dynamicalmodelling, a new hypothesis of the formation of Be envelopes inbinaries, via an outflow from a rapidly rotating B star in a detachedbinary, is outlined. It is shown that such an outflow is facilitated bythe presence of a companion to the B star and leads to the formation ofan envelope but not to any significant mass exchange between the binarycomponents.
| Properties and nature of Be stars. XXI. The long-term and the orbital variations of V832 Cyg = 59 Cyg
An analysis of numerous homogenized UBV photoelectric observations andred spectra of the Be star V832 Cyg from several observatories led tothe following principal findings: 1. Pronounced long-term light andcolour variations of V832 Cyg result from a combination of two effects:from the gradual formation of a new Be envelope, and from an asymmetryand a slow revolution of the envelope (or its one-armed oscillation).The colour variations associated with the envelope formation arecharacterized by a positive correlation between brightness and emissionstrength, typical for stars which are not seen roughly equator-on. 2.The V magnitude observations prewhitened for the long-term changesfollow a sinusoidal orbital light curve with a small amplitude and aperiod of 28.1971d which is derived from observations spanning 43 years.This independently confirms a 12-year old suggestion that the star is aspectroscopic binary with a 29-d period. V832 Cyg thus becomes the fifthknown Be star with cyclic long-term V/R variations, the duplicity ofwhich has been proven, the four other cases being ζ Tau, V923 Aql,γ Cas and X Per. Therefore, the hypothesis that the long-term V/Rvariations may arise due to the attractive force of the binary companionat certain phases of the envelope formation is still worth consideringas a viable alternative to the model of one-armed oscillation. 3. Wehave shown that the RV and V/R variations of the Hα and He I 6678emission lines are all roughly in phase. In particular, the He I 6678emission also moves with the Be primary which differs from what wasfound for another Be binary, \varphi Per. 4. We derived the orbitalelements and found that in spite of the remaining uncertainties, thebasic physical properties of the 28.2d binary are well constrained. 5.The light minimum of the orbital light curve occurs at elongation whenthe Be star is approaching us and the object becomes bluest in (B-V) andreddest in (U-B) at the same time. This may indicate that a part of theoptically thick regions of the envelope is eclipsed at these orbitalphases. Guest investigator, Dominion Astrophysical Observatory, HerzbergInstitute of Astrophysics, National Research Council of Canada. Alsobased on observations from Castanet-Tolosan, Hvar, Ondřejov,Pic-du-Midi, Rozen, San Pedro Mártir, Toronto and Xing-LongObservatories and on photoelectric photometry by AAVSO members. Tables3, 5-7 are only available in electronic form at the CDS via anonymousftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/387/580}
| Search for duplicity in periodic variable Be stars
Four Be stars, HR 1960, HR 2968,HR 3237 and HR 3642, selectedaccording to their periodic variations in HIPPARCOS and GENEVAphotometries, were monitored from 1998 until 2001 with the CORALIEspectrograph. Among these stars, two are new spectroscopic binaries andone is a new lambda Eri short period variable. HR 1960 is a lowamplitude (K = 3.4 km s-1) SB1 with a period of 395.48 d inagreement with the photometric prediction. HR 3237 is a short period SB1(P = 5.1526 d). HR 3642 presents some interesting variations inphotometry and spectroscopy: indeed, a mid- and a short-term variationis present with periods of 137.99 d (Hp magnitude) and 1.13028 d (radialvelocity) respectively. The short-term variation, characteristic of thelambda Eri stars, probably implies non-radial pulsations orinhomogeneities in the corotating disc. The last star, HR 2968, is anexcellent photometric binary candidate, but no spectroscopic obviousnessof a companion has been found. Based on observations collected at theSwiss 40 cm, 70 cm and 120 cm telescopes at the European SouthernObservatory (La Silla, Chile) and on data from the ESA HIPPARCOSsatellite. The photometric and radial velocity data are only availablein electronic form at the CDS via anonymous ftp to cdsarc.u-strasbg.fr(130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/385/488 Table 3 is onlyavailable in electronic form at http://www.edpsciences.org
| Photometric Monitoring of Bright Be Stars. IV. 1996-1999
We report long-term UBV observations of 15 bright, active Be stars,namely: X Persei, EW Canis Majoris, θ Coronae Borealis, 4 (V839)Herculis, 88 (V744) Herculis, 66 (V2048) Ophiuchi, NW Serpentis, CXDraconis, 12 (V395) Vulpeculae, 28 (V1624) Cygni, QR Vulpeculae, 59(V832) Cygni, EW Lacertae, ο Andromedae, and KX Andromedae. Theobservations were made in 1996-1999 through the Automatic PhotometricTelescope Service in Arizona and through the American Association ofVariable Star Observers (AAVSO) photoelectric photometry program andhave been added to a database extending back 20 years. We describe thestars' recent behavior and also comment on the long-term behavior ofsome of them. They vary photometrically on timescales ranging from abouta day to many years.
| 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
| Properties and nature of Be stars. XIX. Spectral and light variability of 60 Cygni
An analysis of electronic spectra secured between 1992 and 1999 at theHaute Provence, Ondřejov and Dominion Astrophysical Observatoriesand of differential UBV measurements of 60 Cyg obtained between 1984 and1999 at Hvar, San Pedro Mártir, Toronto and XinglongObservatories, the all-sky Hipparcos satellite H_p photometrytransformed to Johnson V and B magnitudes, and all-sky UBV observationspublished by several authors and dating back to fifties, led to thefollowing findings: 1. 60 Cyg exhibits pronounced long-term spectralvariations characterized by the B -> Be -> B phase transitions.These long-term spectral changes of 60 Cyg are also accompanied bycorresponding, though rather mild, secular light and colour variations.The character of these variations is indicative of a positivecorrelation between the brightness and emission-line strength. 2. NLTEmodel atmosphere analysis of spectra secured during the quiescence state(B phase) of 60 Cyg shows that the star has overabundance of helium.Best results were obtained for N_He/N_H= 0.2. 3. The presence ofperiodic medium-term changes, with a period of 146.6 d +/- 0.6 d wasfound in the radial-velocity of the Hα He I 4471 Å lines. Ifconfirmed by future observations, these variations could indicate that60 Cyg is a spectroscopic binary. 4. There are clear rapid periodicline-profile changes of (a) overall line asymmetry, and (b) weaksub-features passing across the line profiles every about 0.1 d. Theradial velocity and asymmetry of He I lines vary with a period of 1.0647d and a double-wave curve. There is no evidence of this period inphotometry, however. 5. The rapid light variations of 60 Cyg aredominated by rapid changes with a full amplitude of almost 0.1 m. Aperiod analysis of V magnitude data prewhitened for the long-termchanges indicates a period of 0.2997029 d, reported earlier. The mostinteresting finding is that also all recorded series of movingsub-features in the line profiles can be reconciled with this period:the sub-features reappear at the same phase intervals of the 0.2997 dperiod in the line profiles over an interval of several years.Considering the acceleration of these sub-features, 1900 km s^{-1}d^{-1}, it is conceivable that the true physical (super) period of thesechanges is either 0.8991 d or 1.1988 d. 6. The findings mentioned inpoints 4 and 5 represent a challenge for the NRP scenario since thelight changes would be dominated by a high-order mode instead of alow-order one.
| A-shell stars in the Geneva system
Among the various kinds of A stars having a peculiar spectrum, we findthe A-shell stars. Many questions are still open concerning these stars,including their evolutionary status. In the present study we have useddata from the Hipparcos catalogue to examine this point. We have foundthat the majority of A-shell stars are well above the main sequence. Nodifferences could be established between A-shell stars in luminosityclasses III and I and those in luminosity class V as regardsvariability, duplicity, or the importance of the shell feature.
| 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.
| Long-term changes of the Be star OT Geminorum
We investigate the character of light variability of the bright Be starOT Gem . Two phases of the long-term light changes were distinguished: -a quiet phase which is characterized by mild light changes; and - anactive phase in which the sudden increases of brightness up to 0. (v (r)m m) 4 in V occur. During the active phases, a cyclic oscillation ofbrightness of a period between 70 and 80 days is present, with the mostprobable value being 71. (v (r) m d) 89. A positive correlation wasfound between the light and colour variations and the emission strengthin both phases.
| Central quasi-emission peaks in shell spectra and the rotation of disks of Be stars
New high-resolution echelle spectra are presented for all 6 B-type starscurrently known to exhibit so-called central quasi-emission peaks(CQE's). Empirical requirements are derived on the circumstances whichfavour the appearance of such features. The presence of a circumstellardisk seen edge-on is the most important. Furthermore, the disk should beoptically thin in the continuum, have a small spatial extent, and showlittle line broadening. Both this set of conditions and the observedline profiles are compared to a model by Hanuschik (\cite{hanuschik95})for the formation of shell lines in circumstellar disks with Keplerianrotation. This model predicts not only the existence of CQE's, but alsothe same actual circumstances of their occurrence. They result from thelocal minimum at zero radial velocity in the fraction of the stellardisk that is occulted by circumstellar gas in Keplerian orbital motion,i.e. by gas moving perpendicular to the line of sight. In particular,CQE's are in spite of their name not related to any emission process butare a pure absorption phenomenon. All currently available observationsof CQE's are consistent with this model, which appears to haveconsiderable diagnostic potential for the understanding of the structureand dynamics of Be star disks. Only one of the 6 stars (nu Pup) was notpreviously known to ever have displayed shell or only emission lines.But the new Hα and Hβ profiles clearly show the presence ofvariable amounts of circumstellar matter. Previously suggestedphotospheric explanations for CQE's are nevertheless briefly examined.In a given star, CQE's seem to appear with the highest probability attimes when the innermost regions of the disk are being re-supplied withmatter. With the success of Hanuschik's model, CQE's furthermore becomeone of the most important indicators of rotational support of disks ofBe stars. Together with other evidence for rotation compiled from theliterature, this leads to the conclusion that models for the formationof disks need to include a mechanism for sufficient angular momentumtransfer. In the context of Hanuschik's model for CQE's, theconsiderable acceleration inherent to wind-compressed disks (WCD's)presents an additional difficulty for the WCD model in its basic form.Based on observations collected at the European Southern Observatory atLa Silla, Chile, ESO prop.~Nos.~55.D-0502, 56.D-0381, 58.D-0697, and theGerman-Spanish Astronomical Centre, Calar Alto, operated by theMax-Planck-Institute for Astronomy, Heidelberg, jointly with the SpanishNational Commission for Astronomy, Visiting Astronomer TR
| Photometric Monitoring of Bright Be Stars. III. 1988-89 and 1992-95
We report long-term photometric (BV) observations of 23 bright, activeBe stars made in 1988 and 1989 and 1992 and 1995 with the 0.4m telescopeat the University of Toronto. Cumulative light curves, includingobservations made earlier at the University of Toronto, and with theAutomatic Photometric Telescope Service in Arizona, are presented forseveral of the stars. Many of the stars show cyclic variations of up to0.2 in V and B on time scales of a few years, as well as variations ontime scales of about a day. (SECTION: Stars)
| 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
| Properties and nature of Be stars. XVIII. Spectral, light and colour variations of 4 Herculis
An analysis of a rich series of spectroscopic and photometricobservations of the Be star 4 Her led to the following conclusions:4 Her is another example of a long-term Be variable with a type ofcorrelation between the brightness and emission strength, similar to 88Her (V744 Her) and BU Tau (Pleione). It is argued that the formation ofa new Be envelope of 4 Her starts with the creation of a slightly coolerpseudophotosphere at the equatorial regions of the star (seen under someintermediate inclination angle) which only gradually grows into anoptically thin extended envelope. Radial-velocity measurements of thecentre of the Hα emission and of the photospheric lines confirmthe binary nature of the star. The first reliable orbital elements arepresented. The 46-d orbit is nearly circular and has a semiamplitude of5-8 . () kms() -1. An LTE model atmosphere analysis of the photosphericspectrum of the primary leads to Teff=12500K, log g = 4.0,and v\sin i=300kms^-1. No direct evidence of the low-mass secondary wasfound and the possibility that the secondary fills its Roche lobe can besafely excluded. The central quasi-emission bumps (CQEB) visible as"doubling" of some shell lines appear during the phase of the formationof a new shell. They are strongest during the light minimum and becomefainter as the Hα emission strengthens. An unusual blue-shiftedabsorption component of the Hα line, never reported before,re-appears strictly periodically in the V peak of the Hα emissionat a limited range of velocities and orbital phases. It is argued thatthe observational facts about 4 Her are probably best reconciled by amodel which assumes that the secondary is a hot and rotationallyunstable object which looses mass towards the primary via a gas stream.However, some important findings remain unexplained. This research isbased on spectra from the \Ond\ and Haute Provence Observatories and onphotometry from Hvar, \Ond, Mt. Kobau, Toronto, APT Phoenix-10, andAAVSO observers.
| 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.
| Speckle observations of visual and spectroscopic binaries. VI.
Not Available
| 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.
| 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.
| The behavior of the O I line 7772 in Be and related stars
We describe the spectra of more than sixty stars in the 7570-7980region. We find that O I 7772 is always in emission in Be stars: in theearliest types it is seen in clear emission whereas in the later typesit fills in the observed absorption line. We find a good correlation ofthe line intensity of O I 8446 with O I 7772, the former being aboutfour times stronger than the latter. We confirm the correlation with FeII 7712. We also derive the outer radii of the line emission formingregions and find that O I 7772 is formed very close to the starssurface, whereas Fe II is formed farther away. We also provide criteriato distinguish, at this wavelength range, the classical Be, Herbig Ae-Beand B(e) stars.
| Coming Shell Phase of the Be-Star 4-HERCULIS
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1993A&A...277..521K&db_key=AST
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הכנס מאמר חדש
לינקים קשורים
הכנס לינק חדש
משמש של הקבוצה הבאה
|
תצפית ומידע אסטרומטרי
| קבוצת-כוכבים: | הרקולס |
| התרוממות ימנית: | 15h55m30.60s |
| סירוב: | +42°33'58.0" |
| גודל גלוי: | 5.75 |
| מרחק: | 147.71 פארסק |
| תנועה נכונה: | -25.2 |
| תנועה נכונה: | 16.5 |
| B-T magnitude: | 5.631 |
| V-T magnitude: | 5.729 |
קטלוגים וכינוים:
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INHABITED SKY
