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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.
| CHARM2: An updated Catalog of High Angular Resolution Measurements
We present an update of the Catalog of High Angular ResolutionMeasurements (CHARM, Richichi & Percheron \cite{CHARM}, A&A,386, 492), which includes results available until July 2004. CHARM2 is acompilation of direct measurements by high angular resolution methods,as well as indirect estimates of stellar diameters. Its main goal is toprovide a reference list of sources which can be used for calibrationand verification observations with long-baseline optical and near-IRinterferometers. Single and binary stars are included, as are complexobjects from circumstellar shells to extragalactic sources. The presentupdate provides an increase of almost a factor of two over the previousedition. Additionally, it includes several corrections and improvements,as well as a cross-check with the valuable public release observationsof the ESO Very Large Telescope Interferometer (VLTI). A total of 8231entries for 3238 unique sources are now present in CHARM2. Thisrepresents an increase of a factor of 3.4 and 2.0, respectively, overthe contents of the previous version of CHARM.The catalog is only available in electronic form at the 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/431/773
| Far-infrared loops in the 2nd Galactic Quadrant
We present the results of an investigation of the large-scale structureof the diffuse interstellar medium in the 2nd Galactic Quadrant(90°≤l≤180°). 145 loops were identified on IRAS-basedfar-infrared maps. Our catalogue lists their basic physical properties.The distribution clearly suggests that there is an efficient processthat can generate loop-like features at high Galactic latitudes.Distances are provided for 30 loops. We also give an observationalestimate of the volume filling factor of the hot gas in the Local Arm,4.6%≤f2nd<6.4%.Appendices A-C 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/418/131
| Interstellar Matter near the Pleiades. VI. Evidence for an Interstellar Three-Body Encounter
This paper seeks a comprehensive interpretation of new data on Na Iabsorption toward stars in and near the Pleiades, together with existingvisible and infrared data on the distribution of dust and with radiodata on H I and CO in the cluster vicinity. The use of dust and gasmorphology to constrain tangential motions in connection with themeasured radial velocities yields estimates for the space motion of gasnear the Pleiades. Much of the kinematic complexity in the interstellarabsorption toward the Pleiades, including the presence of stronglyblueshifted components that arise in shocked gas, finds explanation inthe interaction between the cluster and foreground gas withVr(LSR)~7 km s-1 associated with the Taurus dustclouds. Taurus gas, however, cannot readily account for an absorptioncomponent having Vr(LSR)~10 km s-1 with a wide,but not continuous distribution and 21 cm emission from gas in thecluster having Vr(LSR)~0 km s-1 associated witheast-west dust filaments. Successive hypotheses for the origin of theseadditional features include Taurus gas at a higher velocity than thepervasive foreground component, additional gas at a radial velocityintermediate between that of the Taurus component and the cluster, and acloud having Vr(LSR)~10 km s-1 approaching thePleiades from the west. A satisfactory account of the full complexity ofthe interstellar medium near the Pleiades requires the last feature andthe Taurus gas, both interacting with the Pleiades and also with eachother.
| Kinematical Structure of the Local Interstellar Medium: The Galactic Anticenter Hemisphere
A survey of interstellar Na I D1 and D2 absorption features in thespectra of 104 early-type stars in the second and third Galacticquadrants reveals the large-scale kinematics of the interstellar gaswithin the Galactic anticenter hemisphere at distances from the Sunbetween ~70 and ~250 pc. Employing a technique that uses both the radialvelocities and column densities of the Na I absorptions produced by theintervening gas we have identified the velocity vectors and determinedthe spatial distribution of eight interstellar clouds in the volumeexplored. The average internal H I+H2 densities of the cloudsrange between 0.03 and 1.7 cm-3, and their masses between 80and 104 Msolar, although uncertainties in thesizes of the clouds, their possible extension beyond the regionexplored, and the presence of denser gas embedded in the larger cloudsimply that these will tend to be lower limits. We have clearlyidentified clumps of denser gas immersed in the low-density gas in oneof the clouds; these clumps show internal H I+H2 densities oforder 50 cm-3. Although we are not able to detect anyinterstellar Na I within 70 pc, the sizes of some of the clouds implythat their near edges are within that range of distances from the Sun.With respect to the local standard of rest the clouds move withvelocities between 19 and 54 km s-1. Their velocity vectorsdo not support the view of a local interstellar medium uniquelydominated by expansion from centers in the Scorpio-Centaurus OBassociation; our results suggest that this expansion is present in theGalactic center hemisphere but in the Galactic anticenter hemisphere isrestricted to the immediate neighborhood of the Sun.
| The Pleiades Reflection Nebula. II. Simple Model Constraints on Dust Properties and Scattering Geometry
We have used wide-field ultraviolet, optical, and far-infraredphotometric images of Pleiades reflection nebulosity to analyze dustproperties and the three-dimensional nebular geometry. Scattered lightdata were taken from 1650 and 2200 Å Wide-Field Imaging SurveyPolarimeter images and a large 4400 Å mosaic of Burrell SchmidtCCD frames. Dust thermal emission maps were extracted from IRAS data.The scattering geometry analysis is complicated by the blending of lightfrom many stars and the likely presence of more than one scatteringlayer. Despite these complications, we conclude that most of thescattered light comes from dust in front of the stars in at least twoscattering layers, one far in front and extensive, the other nearer thestars and confined to areas of heavy nebulosity. The first layer can beapproximated as an optically thin, foreground slab whose line-of-sightseparation from the stars averages ~0.7 pc. The second layer is alsooptically thin in most locations and may lie at less than half theseparation of the first layer, perhaps with some material among orbehind the stars. The association of nebulosities peripheral to the maincondensation around the brightest stars is not clear. Models withstandard grain properties cannot account for the faintness of thescattered UV light relative to the optical. Some combination ofsignificant changes in grain model albedo and phase function asymmetryvalues is required. Our best-performing model has a UV albedo of0.22+/-0.07 and a scattering asymmetry of 0.74+/-0.06. Hypotheticaloptically thick dust clumps missed by interstellar sight linemeasurements have little effect on the nebular colors but might shiftthe interpretation of our derived scattering properties from individualgrains to the bulk medium.
| The Pleiades Reflection Nebula. I. Ultraviolet, Optical, and Far-Infrared Imaging Photometry
We present new wide-field optical and ultraviolet images of the Pleiadesreflection nebula that allow a more thorough evaluation of the dustscattering than any prior data set. Vacuum-UV images were taken at 1650and 2200 Å during the first flight of the Wide-Field ImagingSurvey Polarimeter (WISP), a sounding rocket-borne telescope. WISPcaptured the brighter parts of the nebula at both wavelengths, with 3σ sensitivities of 22.5 and 23.4 UV mag arcsec-2,respectively. The 5.0d×1.7d WISP field was also mapped at 4400Å with a mosaic of 40 Burrell Schmidt CCD frames using a broadbandBJ filter. The Schmidt mosaic shows extensive and intricatenebulosity down to a 5 σ sensitivity limit of 27.6 B magarcsec-2, including features undetected by photographicsurveys. We explore the intensity and color behavior of the nebula inour UV and optical images and far-infrared IRAS data. We find that thephotometric structure near bright stars is more complex than previousstudies have implied, but general trends are still apparent. The colorgradients around the stars are caused by phase function effects ratherthan internal reddening. The greater concentration of scattered lightversus thermal emission indicates that most of the observed scatteringis from foreground dust. A somewhat greater concentration of UV versusoptical light suggests grain scattering is more forward-directed atshorter wavelengths. The UV nebula is much fainter than expected fromthe stellar photometry and interstellar reddening. Explaining this UVfaintness requires either more reddening than is measured or significantalterations to current dust property estimates.
| Observations of Star-Forming Regions with the Midcourse Space Experiment
We have imaged seven nearby star-forming regions, the Rosette Nebula,the Orion Nebula, W3, the Pleiades, G300.2-16.8, S263, and G159.6-18.5,with the Spatial Infrared Imaging Telescope on the Midcourse SpaceExperiment (MSX) satellite at 18" resolution at 8.3, 12.1, 14.7, and21.3 μm. The large angular scale of the regions imaged (~7.2-50deg2) makes these data unique in terms of the combination ofsize and resolution. In addition to the star-forming regions, twocirrus-free fields (MSXBG 160 and MSXBG 161) and a field near the southGalactic pole (MSXBG 239) were also imaged. Point sources have beenextracted from each region, resulting in the identification over 500 newsources (i.e., no identified counterparts at other wavelengths), as wellas over 1300 with prior identifications. The extended emission from thestar-forming regions is described, and prominent structures areidentified, particularly in W3 and Orion. The Rosette Nebula isdiscussed in detail. The bulk of the mid-infrared emission is consistentwith that of photon-dominated regions, including the elephant trunkcomplex. The central clump, however, and a line of site toward thenorthern edge of the cavity show significantly redder colors than therest of the Rosette complex.
| X-ray variability of Pleiades late-type stars as observed with the ROSAT-PSPC
We present a comprehensive analysis of X-ray variability of thelate-type (dF7-dM) Pleiades stars, detected in all ROSAT-PSPCobservations; X-ray variations on short (hours) and medium (months) timescales have been explored. We have grouped the stars in two samples: 89observations of 42 distinct dF7-dK2 stars and 108 observations of 61dK3-dM stars. The Kolmogorov-Smirnov test applied on all X-ray photontime series show that the percentage of cases of significant variabilityis quite similar on both samples, suggesting that the presence ofvariability does not depend on mass for the time scales and mass rangeexplored. The comparison between the Time X-ray Amplitude Distributionfunctions (XAD) of the set of dF7-dK2 and of the dK3-dM show that, onshort time scales, dK3-dM stars show larger variations than dF7-dK2. Asubsample of eleven dF7-dK2 and eleven dK3-dM Pleiades stars allowsthe study of variability on longer time scales: we found thatvariability on medium - long time scales is relatively more commonamong dF7-dK2 stars than among dK3-dM ones. For both dF7-dK2 Pleiadesstars and dF7-dK2 field stars, the variability on short time scalesdepends on Lx while this dependence has not been observedamong dK3-dM stars. It may be that the variability among dK3-dM stars isdominated by flares that have a similar luminosity distribution forstars of different Lx, while flaring distribution in dF7-dK2stars may depend on X-ray luminosity. The lowest mass stars showsignificant rapid variability (flares?) and no evidence of rotationmodulation or cycles. On the contrary, dF7-dK2 Pleiades stars showboth rapid variability and variations on longer time scales, likelyassociated with rotational modulation or cycles.
| Merged catalogue of reflection nebulae
Several catalogues of reflection nebulae are merged to create a uniformcatalogue of 913 objects. It contains revised coordinates,cross-identifications of nebulae and stars, as well as identificationswith IRAS point sources.The catalogue is 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/399/141
| Quantitative Stellar Spectral Classification. II. Early Type Stars
The method developed by Stock & Stock (1999) for stars of spectraltypes A to K to derive absolute magnitudes and intrinsic colors from theequivalent widths of absorption lines in stellar spectra is extended toB-type stars. Spectra of this type of stars for which the Hipparcoscatalogue gives parallaxes with an error of less than 20% were observedwith the CIDA one-meter reflector equipped with a Richardsonspectrograph with a Thompson 576×384 CCD detector. The dispersionis 1.753 Å/pixel using a 600 lines/mm grating in the first order.In order to cover the spectral range 3850 Å to 5750 Å thegrating had to be used in two different positions, with an overlap inthe region from 4800 Å to 4900 Å . A total of 116 stars wasobserved, but not all with both grating positions. A total of 12measurable absorption lines were identified in the spectra and theirequivalent widths were measured. These were related to the absolutemagnitudes derived from the Hipparcos catalogue and to the intrinsiccolors (deduced from the MK spectral types) using linear and secondorder polynomials and two or three lines as independent variables. Thebest solutions were obtained with polynomials of three lines,reproducing the absolute magnitudes with an average residual of about0.40 magnitudes and the intrinsic colors with an average residual of0.016 magnitudes.
| 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.
| Computing the Parallax of the Pleiades from the Hipparcos Intermediate Astrometry Data: An Alternative Approach
The inconsistency between the mean parallax of the Pleidaes open clusterfrom the Hipparcos catalog and that obtained from the stellar evolutiontheory and photometric measurements is probed by recomputing theHipparcos data in a different way that reduces the propagation of thealong-scan attitude errors. This is achieved by coupling observations ofstars made nearly simultaneously in the two separate fields of view ofthe telescope. A direct calculation of astrometric quantities of 54Pleiades members by the new method, based on the Intermediate AstrometryData, provides a correction of -0.71+/-0.14 mas to the weighted meanparallax of the cluster. The mean corrected parallax of the Pleiades is7.75+/-0.20 mas.
| CHARM: A Catalog of High Angular Resolution Measurements
The Catalog of High Angular Resolution Measurements (CHARM) includesmost of the measurements obtained by the techniques of lunaroccultations and long-baseline interferometry at visual and infraredwavelengths, which have appeared in the literature or have otherwisebeen made public until mid-2001. A total of 2432 measurements of 1625sources are included, along with extensive auxiliary information. Inparticular, visual and infrared photometry is included for almost allthe sources. This has been partly extracted from currently availablecatalogs, and partly obtained specifically for CHARM. The main aim is toprovide a compilation of sources which could be used as calibrators orfor science verification purposes by the new generation of largeground-based facilities such as the ESO Very Large Interferometer andthe Keck Interferometer. The Catalog is available in electronic form atthe 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/386/492, and from theauthors on CD-Rom.
| Astrometric radial velocities. III. Hipparcos measurements of nearby star clusters and associations
Radial motions of stars in nearby moving clusters are determined fromaccurate proper motions and trigonometric parallaxes, without any use ofspectroscopy. Assuming that cluster members share the same velocityvector (apart from a random dispersion), we apply a maximum-likelihoodmethod on astrometric data from Hipparcos to compute radial and spacevelocities (and their dispersions) in the Ursa Major, Hyades, ComaBerenices, Pleiades, and Praesepe clusters, and for theScorpius-Centaurus, alpha Persei, and ``HIP 98321'' associations. Theradial motion of the Hyades cluster is determined to within 0.4 kms-1 (standard error), and that of its individual stars towithin 0.6 km s-1. For other clusters, Hipparcos data yieldastrometric radial velocities with typical accuracies of a few kms-1. A comparison of these astrometric values withspectroscopic radial velocities in the literature shows a good generalagreement and, in the case of the best-determined Hyades cluster, alsopermits searches for subtle astrophysical differences, such as evidencefor enhanced convective blueshifts of F-dwarf spectra, and decreasedgravitational redshifts in giants. Similar comparisons for the ScorpiusOB2 complex indicate some expansion of its associations, albeit slowerthan expected from their ages. As a by-product from the radial-velocitysolutions, kinematically improved parallaxes for individual stars areobtained, enabling Hertzsprung-Russell diagrams with unprecedentedaccuracy in luminosity. For the Hyades (parallax accuracy 0.3 mas), itsmain sequence resembles a thin line, possibly with wiggles in it.Although this main sequence has underpopulated regions at certaincolours (previously suggested to be ``Böhm-Vitense gaps''), suchare not visible for other clusters, and are probably spurious. Futurespace astrometry missions carry a great potential for absoluteradial-velocity determinations, insensitive to the complexities ofstellar spectra. Based on observations by the ESA Hipparcos satellite.Extended versions of Tables \ref{tab1} and \ref{tab2} are available inelectronic form at the CDS via anonymous ftp to cdsarc.u-strasbg.fr(130.79.125.8) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/381/446
| Interstellar Matter Near the Pleiades. V. Observations of NA I toward 36 Stars
This paper reports high-resolution, moderate to high signal-to-noiseratio observations of 23 certain Pleiades members, four possiblemembers, and nine nonmembers in the Na I D lines, as well asobservations of 12 of the stars in the Na I ultraviolet doublet. Inspite of the relative proximity of the stars to the sun (even most ofthe nonmembers lie within 200 pc), the line profiles exhibit remarkablecomplexity, with up to five absorption components and equally remarkablestar-to-star variation. The velocity range, 2-20 km s-1,conforms well to the range expected for gas deflected by the passage ofthe cluster. The paper includes a careful discussion of uncertainties inthe data, the most important conclusions of which are that the velocityscatter is consistent with that expected from random errors in thewavelength calibration and that systematic errors probably are <~0.1km s-1. Appendices detail the choice of stellar data and theprocedure adopted for removing telluric absorption lines. Analysisfollows in a separate paper.
| 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.
| Microstructure of the Local Interstellar Cloud and the Identification of the Hyades Cloud
We analyze high-resolution UV spectra of the Mg II h and k lines for 18members of the Hyades to study inhomogeneity along these proximate linesof sight. The observations were taken by the Space Telescope ImagingSpectrograph (STIS) instrument on board the Hubble Space Telescope(HST). Three distinct velocity components are observed. All 18 lines ofsight show absorption by the Local Interstellar Cloud (LIC); 10 starsshow absorption by an additional cloud, which we name the Hyades Cloud;and one star exhibits a third absorption component. The LIC absorptionis observed at a lower radial velocity than predicted by the LICvelocity vector derived by Lallement & Bertin in 1992 and Lallementet al. in 1995[vpredicted(LIC)-vobserved(LIC)=2.9+/-0.7 kms-1], which may indicate a compression or deceleration at theleading edge of the LIC. We propose an extension of the Hyades Cloudboundary based on previous HST observations of other stars in thegeneral vicinity of the Hyades, as well as ground-based Ca IIobservations. We present our fits of the interstellar parameters foreach absorption component. The availability of 18 similar lines of sightprovides an excellent opportunity to study the inhomogeneity of thewarm, partially ionized local interstellar medium (LISM). We find thatthese structures are roughly homogeneous. The measured Mg II columndensities do not vary by more than a factor of 2 for angular separationsof <~8°, which at the outer edge of the LIC correspond tophysical separations of <~0.6 pc.
| Barnard's Merope Nebula Revisited: New Observational Results
IC 349 is a small, fan-shaped reflection nebula located only 30" from 23Tau; its nucleus is, by a factor 15, the brightest area of the Pleiadesnebulosity. We propose that IC 349 is a fragment of the Taurus-Aurigamolecular cloud that has been encountered by the Pleiades in thatcluster's southward motion and is being illuminated and shaped by theradiation field of 23 Tau. New Hubble Space Telescope multicolor imageryand the structure, colors, and surface brightness of IC 349 arediscussed in terms of that hypothesis. What is known of the propermotion of the nebula, what can be inferred of the properties of thenebula from its color, and what is expected from radiation pressuretheory appear to be compatible with this cloudlet-encounter hypothesis.
| 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
| The IMF of open star clusters with Tycho-2
We studied the fields of nine nearby open star clusters based on theTycho-2 catalogue. We determined membership probabilities for the starsin the cluster fields from the stellar proper motions and used theTycho-2 photometry to compute the initial mass function (IMF) of theclusters from the main sequence turn-off point down to approx. 1 M_sun.We found IMF slopes ranging from Gamma =-0.69 down to Gamma =-2.27 (whenthe Salpeter \cite{salpeter} value would be Gamma =-1.35). We alsostudied the membership of individual stars of special astrophysicalinterest. In some cases previous results had to be revised. As aby-product, we investigated some general properties of the Tycho-2catalogue; we confirmed that the Tycho-2 proper motions show onlymarginal deviations from the Hipparcos catalogue. On the other hand, insome regions the completeness of the catalogue seems to decrease atmagnitudes brighter than claimed by Høg et al. (\cite{tycho2}).Based on observations of the ESA Hipparcos satellite.
| 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
| Another Search for Maia Variable Stars
We have used the Hipparcos epoch photometry database, andautocorrelation analysis, to search for the elusive Maiavariables-short-period B7-A3 near-main-sequence pulsating variablestars. Of several hundred stars considered, and several dozen starsstudied in detail, only a handful are possible variables: three arepossible shallow eclipsing variables; three have possible periods in therange 0.25-0.5 day, but their amplitudes are so low that they areprobably nonvariable. The most promising are HD 29573, with a period of1.6 days (but possibly a rotating variable), and γ CrB, with aperiod of 0.9 day-a period also found spectroscopically by Lehmann andcoworkers. Sirius shows variations which are probably instrumental. Twopreviously suspected Maia stars-Maia and γ UMi-are photometricallyconstant. The Maia variables-if they exist-are very rare and veryelusive.
| The UV spectrum of nebulae
This paper presents an analysis of the UV spectrum of some nebulae withclearly identified illuminating stars, all observed by the IUEsatellite.The data show remarkable properties of the UV spectrum of thenebulae. Each spectrum is the product of the star spectrum and a linearfunction of 1/lambda. There is no peculiar behaviour in the spectrums at2200 A: no bump created in the spectrum of a nebula and no excess ofscattering. When moving away from the star, the surface brightness of anebula decreases as the inverse of the square of the angular distance tothe star.These results can logically be interpreted in terms ofscattering of starlight. They imply constant properties of theinterstellar grains in the UV and in the directions of space sampled bythe nebulae, and probably a strong forward scattering phase function.There is no evidence for any particular type of grain which wouldspecifically extinguish starlight at 2200 A. Concerning the UV spectrumof a star, this may imply a revisal of the traditional interpretation ofthe 2200 A bump.
| Search for X-ray flares in the Pleiades using SoHO LASCO C3 images.
Not Available
| The Normal Energy Distributions in Stellar Spectra: Giants and Supergiants
We have derived the normal spectral energy distributions for thoseearly-type subgiants, giants, and supergiants that were not investigatedin our earlier studies, which were in most cases also not included inthe studies of Sviderskiene. Color indices computed using our normalenergy distributions are in good agreement with normal colors derivedfrom observations in the Vilnius photometric system. The reliability ofour distribution curves is also demonstrated by comparisons of observedand computed (W-B)-(B-V) two-color diagrams in the WBVR system. Normalcolor indices for the photometric WBVR system are derived.
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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: | שור |
| התרוממות ימנית: | 03h44m52.50s |
| סירוב: | +24°06'48.0" |
| גודל גלוי: | 3.7 |
| מרחק: | 113.636 פארסק |
| תנועה נכונה: | 0 |
| תנועה נכונה: | 0 |
| B-T magnitude: | 3.558 |
| V-T magnitude: | 3.674 |
קטלוגים וכינוים:
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