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Unresolved Hα Enhancements at High Galactic Latitude in the WHAM Sky Survey Maps
We have identified 85 regions of enhanced Hα emission at|b|>10deg subtending approximately 1° or less on theWisconsin Hα Mapper (WHAM) sky survey. These high-latitude ``WHAMpoint sources'' have Hα fluxes of 10-11-10-9ergs cm-2 s-1, radial velocities within about 70km s-1 of the LSR, and line widths that range from less than20 to about 80 km s-1 (FWHM). Twenty-nine of theseenhancements are not identified with either cataloged nebulae or hotstars and appear to have kinematic properties that differ from thoseobserved for planetary nebulae. Another 14 enhancements are near hotevolved low-mass stars that had no previously reported detections ofassociated nebulosity. The remainder of the enhancements are catalogedplanetary nebulae and small, high-latitude H II regions surroundingmassive O and early B stars.
| B Star Rotational Velocities in h and χ Persei: A Probe of Initial Conditions during the Star Formation Epoch?
Projected rotational velocities (vsini) have been measured for 216 B0-B9stars in the rich, dense h and χ Persei double cluster and comparedwith the distribution of rotational velocities for a sample of fieldstars having comparable ages (t~12-15 Myr) and masses (M~4-15Msolar). For stars that are relatively little evolved fromtheir initial locations on the zero-age main sequence (ZAMS) (those withmasses M~4-5 Msolar), the mean vsini measured for the h andχ Per sample is slightly more than 2 times larger than the meandetermined for field stars of comparable mass, and the cluster and fieldvsini distributions differ with a high degree of significance. Forsomewhat more evolved stars with masses in the range 5-9Msolar, the mean vsini in h and χ Per is 1.5 times thatof the field; the vsini distributions differ as well, but with a lowerdegree of statistical significance. For stars that have evolvedsignificantly from the ZAMS and are approaching the hydrogen exhaustionphase (those with masses in the range 9-15 Msolar), thecluster and field star means and distributions are only slightlydifferent. We argue that both the higher rotation rates and the patternof rotation speeds as a function of mass that differentiatemain-sequence B stars in h and χ Per from their field analogs werelikely imprinted during the star formation process rather than a resultof angular momentum evolution over the 12-15 Myr cluster lifetime. Wespeculate that these differences may reflect the effects of the higheraccretion rates that theory suggests are characteristic of regions thatgive birth to dense clusters, namely, (1) higher initial rotationspeeds; (2) higher initial radii along the stellar birth line, resultingin greater spin-up between the birth line and the ZAMS; and (3) a morepronounced maximum in the birth line radius-mass relationship thatresults in differentially greater spin-up for stars that become mid- tolate-B stars on the ZAMS.
| 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.
| Toward an adequate method to isolate spectroscopic families of diffuse interstellar bands
We divide some of the observed diffuse interstellar bands (DIBs) intofamilies that appear to have the spectral structure of single species.Three different methods are applied to separate such families, exploringthe best approach for future investigations of this type. Starting witha statistical treatment of the data, we found that statistical methodsby themselves give insufficient results. Two other methods of dataanalysis (`averaging equivalent widths' and `investigating the figureswith arranged spectrograms') were found to be more useful as tools forfinding the spectroscopic families of DIBs. On the basis of thesemethods, we suggest some candidates as `relatives' of 5780- and5797-Å bands.
| The total-to-selective extinction ratio determined from near IR photometry of OB stars
The paper presents an extensive list of the total to selectiveextinction ratios R calculated from the infrared magnitudes of 597 O andB stars using the extrapolation method. The IR magnitudes of these starswere taken from the literature. The IR colour excesses are determinedwith the aid of "artificial standards" - Wegner (1994). The individualand mean values of total to selective extinction ratios R differ in mostcases from the average value R=3.10 +/-0.05 - Wegner (1993) in differentOB associations. The relation between total to selective extinctionratios R determined in this paper and those calculated using the "methodof variable extinction" and the Cardelli et al. (1989) formulae isdiscussed. The R values presented in this paper can be used to determineindividual absolute magnitudes of reddened OB stars with knowntrigonometric parallaxes.
| 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.
| Stellar and circumstellar activity of the Be star omega CMa. I. Line and continuum emission in 1996-2002
Echelle spectroscopy and mostly unaided-eye photometry of the southernBe star omega CMa were obtained in the period1996-2003. The monitoring is bracketed by two brightenings by 0.4m-0.5m.The results of a literature search suggest that such phases occur aboutonce a decade and have various commonalities. Along with thesephotometric events goes enhanced line emission. This is due to anincreased total mass of the disk as well as to a change in its densityprofile. The models by Poeckert & Marlborough(\cite{1978ApJS...38..229P}, \cite{1979ApJ...233..259P}) imply that theenhanced continuum flux originates from the inner disk. Higher-orderBalmer line emission is correlated with brightness. The increase inHα is retarded by some months, possibly indicating a time delayin filling up and ionizing the outer disk. In the (U-B) vs. (B-V) colourdiagram and the D54 vs. D34 Balmer decrementdiagram the path from the ground to the bright state is distinct fromthe return path. This could result from the bulk of the disk matterbeing in the outer (inner) disk during the photometric ground (high)state, while the two transitions between the two states are both due tochanges progressing radially outward. Some mu Cen-like outbursts(Rivinius et al. \cite{1998A&A...333..125R}) seem to occur in allphases. It is conceivable that the build-up of the inner disk is causedby more frequent or more effective outbursts. During the photometricbright state various other phenomena gain in prominence and suggest thisto be a phase of increased activity. Of particular interest, butpossibly only apparently related to this phase, are absorptioncomponents at redshifts well beyond the range covered by the combinationof rotation and nonradial pulsation.Based on observations collected at the European Southern Observatory atLa Silla, Chile, ESO (proposal nos. 55.D-0502, 56.D-0381, 58.D-0697,62.H-0319, 64.H-0548).
| The ups and downs of a stellar surface: nonradial pulsation modelling of rapid rotators
The main result of the modelling project is the confirmation thatearly-type Be stars pulsate nonradially in g-modes. Based on thedetailed modelling of ω CMa, it could be shown that this star isproto-typical, and that the periodic lpv of early type Be stars ingeneral is due to nonradial pulsation.
| 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
| The proper motions of fundamental stars. I. 1535 stars from the Basic FK5
A direct combination of the positions given in the HIPPARCOS cataloguewith astrometric ground-based catalogues having epochs later than 1939allows us to obtain new proper motions for the 1535 stars of the BasicFK5. The results are presented as the catalogue Proper Motions ofFundamental Stars (PMFS), Part I. The median precision of the propermotions is 0.5 mas/year for mu alpha cos delta and 0.7mas/year for mu delta . The non-linear motions of thephotocentres of a few hundred astrometric binaries are separated intotheir linear and elliptic motions. Since the PMFS proper motions do notinclude the information given by the proper motions from othercatalogues (HIPPARCOS, FK5, FK6, etc.) this catalogue can be used as anindependent source of the proper motions of the fundamental stars.Catalogue (Table 3) is only available at the CDS via anonymous ftp tocdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strastg.fr/cgi-bin/qcat?J/A+A/365/222
| 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
| Sixth Catalogue of Fundamental Stars (FK6). Part I. Basic fundamental stars with direct solutions
The FK6 is a suitable combination of the results of the HIPPARCOSastrometry satellite with ground-based data, measured over more than twocenturies and summarized in the FK5. Part I of the FK6 (abbreviatedFK6(I)) contains 878 basic fundamental stars with direct solutions. Suchdirect solutions are appropriate for single stars or for objects whichcan be treated like single stars. From the 878 stars in Part I, we haveselected 340 objects as "astrometrically excellent stars", since theirinstantaneous proper motions and mean (time-averaged) ones do not differsignificantly. Hence most of the astrometrically excellent stars arewell-behaving "single-star candidates" with good astrometric data. Thesestars are most suited for high-precision astrometry. On the other hand,199 of the stars in Part I are Δμ binaries in the sense ofWielen et al. (1999). Many of them are newly discovered probablebinaries with no other hitherto known indication of binarity. The FK6gives, besides the classical "single-star mode" solutions (SI mode),other solutions which take into account the fact that hidden astrometricbinaries among "apparently single-stars" introduce sizable "cosmicerrors" into the quasi-instantaneously measured HIPPARCOS proper motionsand positions. The FK6 gives in addition to the SI mode the "long-termprediction (LTP) mode" and the "short-term prediction (STP) mode". TheseLTP and STP modes are on average the most precise solutions forapparently single stars, depending on the epoch difference with respectto the HIPPARCOS epoch of about 1991. The typical mean error of anFK6(I) proper motion in the single-star mode is 0.35 mas/year. This isabout a factor of two better than the typical HIPPARCOS errors for thesestars of 0.67 mas/year. In the long-term prediction mode, in whichcosmic errors are taken into account, the FK6(I) proper motions have atypical mean error of 0.50 mas/year, which is by a factor of more than 4better than the corresponding error for the HIPPARCOS values of 2.21mas/year (cosmic errors included).
| On correlations between diffuse interstellar bands
One way to better apprehend the problem of diffuse interstellar bands(DIBs) is to search for correlations between the bands in a large sampleof spectra towards various lines of sight: a strict correlation mayimply that a common carrier is at the origin of the bands, whereas anon-correlation means that different species are involved. We proposethis observational test for 10 DIBs collected in up to 62 Galactic linesof sight. Strong DIBs do not strictly correlate, and sometimes thecorrelation is very poor. Only one example of a strict correlation hasbeen found in our sample between the DIBs at 6614 and 6196 Ä, thatcould signify a single carrier for those two bands. The general absenceof strict correlations is discussed in the context of molecular carriersfor the DIBs.
| The Tokyo PMC catalog 90-93: Catalog of positions of 6649 stars observed in 1990 through 1993 with Tokyo photoelectric meridian circle
The sixth annual catalog of the Tokyo Photoelectric Meridian Circle(PMC) is presented for 6649 stars which were observed at least two timesin January 1990 through March 1993. The mean positions of the starsobserved are given in the catalog at the corresponding mean epochs ofobservations of individual stars. The coordinates of the catalog arebased on the FK5 system, and referred to the equinox and equator ofJ2000.0. The mean local deviations of the observed positions from theFK5 catalog positions are constructed for the basic FK5 stars to comparewith those of the Tokyo PMC Catalog 89 and preliminary Hipparcos resultsof H30.
| Infrared and H-alpha emission from Be stars
Not Available
| 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 ROSAT all-sky survey catalogue of optically bright OB-type stars.
For the detailed statistical analysis of the X-ray emission of hot starswe selected all stars of spectral type O and B listed in the Yale BrightStar Catalogue and searched for them in the ROSAT All-Sky Survey. Inthis paper we describe the selection and preparation of the data andpresent a compilation of the derived X-ray data for a complete sample ofbright OB stars.
| Atlas of high-resolution emission and shell lines in Be stars. Line profiles and short-term variability.
We present an atlas of high-S/N, high-resolution ({DELTA}v=6km/s) dataof Be star emission and shell profiles. We have collected profiles ofHα and of Fe II, mostly of the λ5317 transition. Theselines have been selected to provide measures for the overall emissionstrength and for the velocity field in these disks. We have collecteddata for 77 southern and equatorial programme stars, covering the period1982-1993. This is the most comprehensive overview of profile shapes inBe disks. We propose a three-dimensional scheme in which most observedprofiles can be classified. The parameters are i) inclination, ii)optical depth, and iii) the pattern of the velocity field. A search forshort-term variability (timescales between five days and a few minutes)in six stars ended with negative result. Shortest observed timescale forvariability is a few days for well-developed disks in binary systems (HR1910, HR 2142).
| High-resolution spectroscopy of 31 Pegasi. The Hγ and He I 4471 line variations.
We present high-resolution He I 4471, Mg II 4481 and Hγ lineprofiles of the Be star 31 Peg obtained simultaneously at four observingdates. In this paper we focus on the He I 4471 line and on theabsorption wings of the Hγ line which showed important variations.Models of static stellar atmospheres were calculated to determine thephotospheric parameters of the underlying star. However, non-static andout of radiative equilibrium models are needed to better understand thestructure of the atmosphere of 31 Peg and the characteristics of theobserved He I 4471 and Hγ lines. The implication of deepatmospheric layers in the mass-loss phenomena of Be stars is suggested.
| 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.
| 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.
| SANTIAGO 91, a right ascension catalogue of 3387 stars (equinox J2000).
The positions in right ascension of 3387 stars belonging to the Santiago67 Catalogue, observed with the Repsold Meridian Circle at Cerro Calan,National Astronomical Observatory, during the period 1989 to 1994, aregiven. The average mean square error of a position, for the wholeCatalogue, is +/-0.009 s. The mean epoch of the catalogue is 1991.84.
| Near Infrared Variability of Be-Stars
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1994MNRAS.269.1123D&db_key=AST
| 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.
| An IUE survey of interstellar H I LY alpha absorption. 1: Column densities
We measure Galactic interstellar neutral hydrogen column densities byanalyzing archival interstellar Ly alpha absorption line data toward 554B2 and hotter stars observed at high resolution with the IUE satellite.This study more than doubles the number of lines of sight with measuresof N(H I) based on Ly alpha. We have included the scattered lightbackground correction algorithm of Bianchi and Bohlin in our datareduction. We use the correlation between the Balmer discontinuity(c1) index and the stellar Ly alpha absorption in order toassess the effects of stellar Ly alpha contamination. Approximately 40%of the B stars with measured (c1) index, exhibit seriousstellar Ly alpha contamination. One table contains the derived values ofthe interstellar N(H I) for 393 stars with at most small amounts ofstellar contamination. Another lists the observed values of total N(H I)for 161 stars with suspected stellar Ly alpha contamination and/oruncertain stellar parameters.
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הכנס מאמר חדש
לינקים קשורים
הכנס לינק חדש
משמש של הקבוצה הבאה
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תצפית ומידע אסטרומטרי
| קבוצת-כוכבים: | פגסוס |
| התרוממות ימנית: | 22h21m31.10s |
| סירוב: | +12°12'19.0" |
| גודל גלוי: | 5.01 |
| מרחק: | 297.619 פארסק |
| תנועה נכונה: | 5.7 |
| תנועה נכונה: | 5.4 |
| B-T magnitude: | 4.668 |
| V-T magnitude: | 4.789 |
קטלוגים וכינוים:
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INHABITED SKY
