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Non-radially pulsating Be stars
Based on more than 3000 high-resolution echelle spectra of 27 early-typeBe stars, taken over six years, it is shown that the short-term periodicline profile variability of these objects is due to non-radialpulsation. The appearance of the line profile variability depends mostlyon the projected rotational velocity v sin i and thus, since all Bestars rotate rapidly, on the inclination i. The observed variability ofthe investigated stars is described, and for some of them line profilevariability periods are given for the first time. For two of theinvestigated stars the line profile variability was successfully modeledas non-radial pulsation with l=m=+2 already in previous works. Since Bestars with similarly low v sin i share the same variability properties,these are in general explainable under the same model assumptions. Theline profile variability of stars with higher v sin i is different fromthe one observed in low v sin i stars, but can be reproduced by thesame model, if only the model inclination is modified to more equatorialvalues. Only for a few stars with periodic line profile variability thel=m=2 non-radial pulsation mode is not able to provide a satisfyingexplanation. These objects might pulsate in different modes (e.g.tesseral ones, l != |m|). Almost all stars in the sample show traces ofoutburst-like variability, pointing to an ephemeral nature of themass-loss phenomenon responsible for the formation of the circumstellardisk of early-type Be stars, rather than a steady star-to-disk masstransfer. In addition to the variability due to non-radial pulsationpresent in most stars, several objects were found to show other periodsresiding in the immediate circumstellar environment. The presence ofthese secondary periods is enhanced in the outburst phases. Short-livedaperiodic phenomena were clearly seen in two stars. But, given theunfavourable sampling of our database to follow rapid variability oftransient nature, they might be more common. Only in two out of 27 starsshort-term spectroscopic variability was not detected at all.Based on observations collected at the European Southern Observatory atLa Silla, Chile, 55.D-0502, 56.D-0381, 58.D-0697, 62.H-0319, 63.H-0080,64.H-0548, and 267.D-5702, the German-Spanish Astronomical Centre, CalarAlto, operated by the Max-Planck-Institute for Astronomy, Heidelberg,jointly with the Spanish National Commission for Astronomy, and onobservations with the Wendelstein 80-cm and the Ondřejov 2-mtelescopes, both equipped with the HEROS spectrograph provided by theLandessternwarte Heidelberg.
| 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
| A Search for High-Velocity Be Stars
We present an analysis of the kinematics of Be stars based uponHipparcos proper motions and published radial velocities. We findapproximately 23 of the 344 stars in our sample have peculiar spacemotions greater than 40 km s-1 and up to 102 kms-1. We argue that these high-velocity stars are the resultof either a supernova that disrupted a binary or ejection by closeencounters of binaries in young clusters. Be stars spun up by binarymass transfer will appear as high-velocity objects if there wassignificant mass loss during the supernova explosion of the initiallymore massive star, but the generally moderate peculiar velocities of BeX-ray binaries indicate that the progenitors lose most of their massprior to the supernova (in accordance with model predictions). Binaryformation models for Be stars predict that most systems bypass thesupernova stage (and do not receive runaway velocities) to createultimately Be+white dwarf binaries. The fraction of Be stars spun up bybinary mass transfer remains unknown, since the post-mass transfercompanions are difficult to detect.
| Statistical analysis of intrinsic polarization, IR excess and projected rotational velocity distributions of classical Be stars
We present the results of statistical analyses of a sample of 627 Bestars. The parameters of intrinsic polarization (p*),projected rotational velocity (v sin i), and near IR excesses have beeninvestigated. The values of p* have been estimated for a muchlarger and more representative sample of Be stars (~490 objects) thanpreviously. We have confirmed that most Be stars of early spectral typehave statistically larger values of polarization and IR excesses incomparison with the late spectral type stars. It is found that thedistributions of p* diverge considerably for the differentspectral subgroups. In contrast to late spectral types (B5-B9.5), thedistribution of p* for B0-B2 stars does not peak at the valuep*=0%. Statistically significant differences in the meanprojected rotational velocities (/line{vsin i}) are found for differentspectral subgroups of Be stars in the sense that late spectral typestars (V luminosity class) generally rotate faster than early types, inagreement with previously published results. This behaviour is, however,not obvious for the III-IV luminosity class stars. Nevertheless, thecalculated values of the ratio vt/vc of the truerotational velocity, vt, to the critical velocity forbreak-up, vc, is larger for late spectral type stars of allluminosity classes. Thus, late spectral type stars appear to rotatecloser to their break-up rotational velocity. The distribution of nearIR excesses for early spectral subgroups is bi-modal, the position ofthe second peak displaying a maximum value E(V-L)~ 1 . m 3for O-B1.5 stars, decreasing to E(V-L)~0. m8 for intermediatespectral types (B3-B5). It is shown that bi-modality disappears for latespectral types (B6-B9.5). No correlations were found betweenp* and near IR excesses and between E(V-L) and vsin i for thedifferent subgroups of Be stars. In contrast to near IR excesses, arelation between p* and far IR excesses at 12 mu m is clearlyseen. A clear relation between p* and vsin i (as well asbetween p* and /line{vsin i}/vc) is found by thefact that plots of these parameters are bounded by a ``triangular"distribution of p*: vsin i, with a decrease of p*towards very small and very large vsin i (and /line{vsini}/vc) values. The latter behaviour can be understood in thecontext of a larger oblateness of circumstellar disks for the stars witha rapid rotation. From the analysis of correlations between differentobservational parameters we conclude that circumstellar envelopes forthe majority of Be stars are optically thin disks with the range of thehalf-opening angle of 10degr
| 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
| Geneva photometry of the open cluster NGC 2451 and its exceptional Be star HR 2968 satellite.}
During many years, several authors discussed whether NGC2451 was a real open star cluster or not. By using parallaxesand proper motions from Hipparcos satellite, and Geneva multicolourphotometric measurements of 64 stars, the existence of two clusters Aand B is confirmed. Distances and Geneva colour excesses E[B-V] arerespectively 197 pc, 0.01 and 358 pc, 0.12 for NGC2451 A and B. The two clusters have the same age (log t =7.7). A unique Be star, HR 2968, which belongs tocluster B, has been monitored from 1978 to 1998 in Geneva photometry andfrom November 1989 to March 1993 by the Hipparcos satellite. This starshows exceptional luminosity variations: i) The mean luminosity, whichhas been stable since 1978 (normal B-star phase), increased from 1990 to1995 (Be phase), and then decreased until 1998; ii) Also, in 1990started a periodic light variation with a period of 371 d. Five periodsof this mid-term light variation were observed. Hipparcos and Genevaphotometries are in perfect agreement. A model is proposed to explainthis periodic variability: the Be star is the main component of a binarysystem having an eccentric orbit of period 371 d; from 1990, the Be starwas surrounded by matter expelled in its equatorial plane and, at eachperiastron passage, the companion star interacts gravitationally and/orradiatively with the disk. The physical parameters of the Be star andits companion (most probably a main sequence star) are determined byusing their belonging to NGC 2451 B and bycalculating an approximate orbit from published radial velocities. Themean values of the photometric data are only available in electronicform at the CDS via anonymous ftp to cdsarc.u.strasbg.fr (130.79.128.5)or via http://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
| 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.
| Vitesses radiales. Catalogue WEB: Wilson Evans Batten. Subtittle: Radial velocities: The Wilson-Evans-Batten catalogue.
We give a common version of the two catalogues of Mean Radial Velocitiesby Wilson (1963) and Evans (1978) to which we have added the catalogueof spectroscopic binary systems (Batten et al. 1989). For each star,when possible, we give: 1) an acronym to enter SIMBAD (Set ofIdentifications Measurements and Bibliography for Astronomical Data) ofthe CDS (Centre de Donnees Astronomiques de Strasbourg). 2) the numberHIC of the HIPPARCOS catalogue (Turon 1992). 3) the CCDM number(Catalogue des Composantes des etoiles Doubles et Multiples) byDommanget & Nys (1994). For the cluster stars, a precise study hasbeen done, on the identificator numbers. Numerous remarks point out theproblems we have had to deal with.
| Ultraviolet spectral classification and stellar winds in a sample of Be and standard stars
Equivalent widths of 16 lines of C I, C II, C III, C IV, Si II, Si III,Si IV, Al II, Al III, Fe II, and Fe III, plus centriod and edgevelocities of the Si IV and C IV lines, were measured in InternationalUltraviolet Explorer spectra of 39 Ble-B8e and 18 B1-B8 standardnon-emission-line stars. These suggest the following: (1) Certain lineratios of Si II/III, C II/III, Al II/III, and Fe II/III are verysensitive to spectral type and represent excellent UV criteria forspectral classification. (2) UV line strengths and line ratios show thatthere are no significant differences between the photospheric linespectra of Be and normal, non-emission-line stars of corresponding type.(3) The Si IV and C IV wind lines in the Be stars are correlated withboth spectral type and luminosity class in the sense that the hotteststars have the strongest lines with the largest centroid and edgevelocities, and the giants and subgiants have stronger lines than themain-sequence stars. (4) The Si IV wind lines persist to spectral typeB8 in both the Be stars and the standard stars but are stronger in theBe stars than in the standards for the earlier types. (5) The C IV windlines persist to spectral type B8 in the Be stars, but only to B3 in thestandard stars, and are stronger in the Be stars than in the standardsat all spectral types. (6) The equivalent widths of the Si IV and C IVwind lines are only very weakly correlated with v sin i, if at all, buta threshold in v sin i near 150 kn/sec exists, below which no largeequivalent widths of Si IV or C IV may be seen. Assuming that the Bestars are all rapid rotators, such a correlation is essentially acorrelation with i and suggests that the winds from Be stars arisepreferentially from the equatorial regions. (7) Shell stars have weakerC IV absorption and smaller centroid and edge velocities than other Bestars, suggesting that they have weaker winds. Since there isconsiderable evidence that these are stars with cool, low-velocity diskswhich are being viewed edge-on or nearly edge-on, the winds may beinhibited and modified by the denser material in the equatorial regions.(8) Mg II emission is detected in about half of the program Be starswith long-wavelength IUE spectra, and seems not to be correlated withspectral type, v sin i, or strength of the Si IV wind lines. Since theMg II emission presumably originates in the cool, low-velocity envelope,and since Mg II emission also correlates with hydrogen Balmer emissionin the Be stars, this sugests that there is no strong physicalrelationship between the stellar winds and the cool disk. (9) The Beshell stars have stronger resonance lines of Si II, C I, C II, Al II, FeII, presumably formed in the cool shells, than the other Be stars andthe normal, non-emission-line stars of the same spectral types,consistent with the strong lines arising from metastable levels in theoptical spectra of these stars.
| 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'.
| Rotational velocity of Be stars correlated with extinction law
The paper presents the comparison of the extinction curves extractedfrom spectra of 35 Be stars. It is suggested that high rotationalvelocity relates to 'peculiar' shape of extinction curve i.e., the lackof the 2200 A bump. This phenomenon occurs only if the total reddeningis not very high. We assume that such extinction curves originate solelyin circumstellar disks surrounding the high rotational velocity stars.Other objects are probably also obscured by some additional interstellarclouds.
| Binary Be-Stars and Be-Binaries
Not Available
| Atlas of extinction curves derived from ultraviolet spectra of the TD-1 satellite
The collection of 166 extinction curves derived from the publishedlow-resolution spectra acquired with the aid of the spectrometer onboard the TD-1 satellite is presented. The observed variety ofextinction laws is apparently due to the varied physical parameters ofinterstellar clouds; for example, the bright stars, included in thesample of TD-1 material, are very likely to be obscured by single clouds(interstellar or circumstellar). The system of standards constructedwith the aid of a special procedure allowing the possible effects ofspectral mismatch to be avoided and making possible the derivation ofextinction curves even in cases of very small E(B-V)S, was applied. Thecurves are presented in the form of plots, normalized to E(B-V) = 1.
| V/R variations in H-beta emission profiles of Be stars
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1991A&A...241..159M&db_key=AST
| Be stars with peculiar infrared excess and their classification.
Not Available
| Catalogue of i and w/w crit values for rotating early type stars
Not Available
| Effects of stellar rotation on the Geneva photometric system
The effects of stellar rotation on colors and parameters of the Genevaphotometric system are considered, using homogeneous material. Attentionis focused on these parameters useful for deriving physical propertiesof B- and A-type stars. Two major photometric planes in this respect,the (X, Y) plane and the (d, Delta) plane, are not discernibly affectedby rotation. The temperature parameter, B(2) - V(1) is reddened byrotation to an extent that is in agreement with model calculations foruniformly rotating stars.
| Spectroscopy of southern Be stars 1984-1987
The 93-cm Manuel Foster Observatory telescope in Chile has been used toobtain 919 spectrograms of 85 southern Be III-V stars. Balmeremission-lines (mainly H-beta) were noted in 74 percent of the stars,and Fe-II emission in 48 percent of them. Variations noted include rapidV/R variations of HR 1956, a primary shell phase of HR 2142, a shellphase of HR 2356, a transitory emission state of HR 2745, and thedisappearance of the H-beta emission of HR 5193.
| Spectroscopic monitoring of southern Be stars.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1987RMxAA..14..323B&db_key=AST
| A photometric survey of the bright southern Be stars
Repeated UBV photometric measurements were made of the 86 bright Bestars south of declination -20 deg, and a network of comparison starswas set up. From a statistical study of the differential photometry itwas found that short- or intermediate-term variability seems to beoccurring in about half of the Be stars, and to be more evident in thestars of earlier spectral type. It was also possible to identify 11individual short- or intermediate-term variables. Four of these (all ofearly B spectral type) appear to exhibit significant variability on atime-scale of a day or less. More intensive observations of one of thesestars, 28 Omega CMA, indicate short-term variations consistent with thepublished spectroscopic period of 1.37 day.
| Highly ionized stellar winds in Be stars - The evidence for aspect dependence
The paper presents the results of an ultraviolet survey of stellar windsin 62 Be and 43 normal B stars covering spectral types B0.5-B5 andluminosity classes V-III. Excess wind absorption in Be stars over thatdetected in normal B stars is found in C IV and Si IV, confirmingresults of previous surveys. The stars showing excess wind absorptionalso show one or more shortward-shifted discrete absorption components,suggesting that much of the excess wind absorption is in the form ofdiscrete absorption components. Evidence is presented that thehigh-velocity and highly ionized stellar wind observed in some Be starsis a function of latitude.
| The evidence for aspect dependent winds in Be stars
A stellar wind survey in 62 Be and 43 B stars covering 80 III-V to B5III-V is presented. It is found that the wind absorption seen in C IV inBe stars is due to blended absorption from multiple shortward-shifteddiscrete components. Such components are not observed in normal B stars,but occur in 63% of the Be stars in the sample. Shortward-shifteddiscrete components in Be stars are observed only if v sin i is greaterthan 150 km/sec. Ten Be stars in the sample, including two low v sin istars, show strong unshifted absorption components, similar to featuresseen in Beta Cep stars.
| Far ultraviolet colors of B and Be stars
A far-UV color index, G, which is free of interstellar reddening effectsis applied to TD-1 satellite observations of B and Be stars listed inthe catalogs of Jamar et al. (1976) and Macau-Hercot et al. (1978). Theexpressions defining G(in terms of the wavelengths 146, 235, and 274 nm)and the S70 index of spectral type are set forth. Tables of mean andindividual-star G and S70 indices and plots of G versus S70, Delta-Gversus spectral type, Delta-G versus H-alpha and H-beta intensity, and Gversus V(sin i) are presented and discussed. The Be stars are classifiedas strong if they show strong Balmer emission, some Paschen and Fe IIemission, and IR excess; otherwise they are 'weak'. Weak Be stars arefound to have G similar to that of B stars, while G in strong Be starsis either much more negative or much less negative than in the B stars.No correlation is found between G and V(sin i) for either B or Be stars.
| Spectral types and rotational velocities of the brighter Be stars and A-F type shell stars
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1982ApJS...50...55S&db_key=AST
| The interstellar 2200 A band - A catalogue of equivalent widths
Not Available
| Near infrared excesses in Be stars
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1981PASP...93..110F&db_key=AST
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| Sað Açýklýk: | 09h05m38.30s |
| Yükselim: | -70°32'20.0" |
| Görünürdeki Parlaklýk: | 4.71 |
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