Contents
Images
Upload your image
DSS Images Other Images
Related articles
Lithium abundances and rotational behavior for bright giant stars
Aims.We study the links possibly existing between the lithium content ofbright giant stars and their rotational velocity. Methods: .Weperformed a spectral analysis of 145 bright giant stars (luminosityclass II) spanning the spectral range from F3 to K5. All these starshave homogeneous rotational velocity measurements available in theliterature. Results: .For all the stars of the sample, we provideconsistent lithium abundances (A_Li), effective temperatures (T_eff),projected rotational velocity (v sin i), mean metallicity ([Fe/H]),stellar mass, and an indication of the stellar multiplicity. The gradualdecrease in lithium abundance with T_eff is confirmed for bright giantstars, and it points to a dilution factor that is at least assignificant as in giant stars. From the F to K spectral types, the A_Lispans at least three orders of magnitude, reflecting the effects ofstellar mass and evolution on dilution. Conclusions: .We find thatthe behavior of A_Li as a function of v sin i in bright giant starspresents the same trend as is observed in giants and subgiants: starswith high A_Li are moderate or fast rotators, while stars with low A_Lishow a wide range of v sin i values.
| Spectroscopic binary orbits from photoelectric radial velocities. Paper 180: zeta Aurigae
Not Available
| What a local sample of spectroscopic binaries can tell us about the field binary population
We study a sample of spectroscopic binaries (SBs) in the local solarneighbourhood (d<= 100 pc and MV<= 4) in an attempt tofind the distributions of the period, P, the primary mass,m1, and the mass ratio q(=m2/m1), aswell as the initial mass function (IMF) of the local population of fieldbinaries. The sample was collated using available SB data and theHipparcos catalogue, the latter being used for distances and to refernumbers of objects to fractions of the local stellar population as awhole. We use the better determined double-lined SBs (SB2s) to calibratea Monte Carlo approach to modelling the q distribution of thesingle-lined SBs (SB1s) from their mass functions, f(m), and primarymasses, m1. The totalq distribution is then found by addingthe observed SB2 distribution to the Monte Carlo SB1 distribution. Whilea complete sample is not possible, given the data available, we are ableto address important questions of incompleteness and parameter-specificbiases by comparing subsamples of SBs with different ranges in parameterspace. Our results show a clear peak in the q distribution of fieldbinaries near unity. This is dominated by the SB2s, but the flatdistribution of the SB1s is inconsistent with their components beingchosen independently at random from a steep IMF.
| Contribution to the study of composite spectra - X. HD 3210/1, 27395, 39847, 70826 and 218257/8: five new spectroscopic binaries in multiple systems
We present the results of a radial velocity (RV) study of five new SB1spectroscopic binaries with composite spectra: HD 3210/1, 27395, 39847,70826 and 218257/8. We analyse the composition of those objects whichare found to be triple systems (at least): all of them include a coolevolved star, a hot star of type B or A and a third component.From the RV measurements of the cool components, we derive the orbitalelements of the corresponding spectroscopic binaries for the first time.Their analysis leads us to propose a model which describes the nature ofthe individual components of those five systems, with some predictionson their angular separations and magnitudes. In some cases, thespectroscopic companion of the cool component is not the hot starcontributing to the composite spectrum.
| A New Version of Reimers' Law of Mass Loss Based on a Physical Approach
We present a new semiempirical relation for the mass loss of coolstellar winds, which so far has frequently been described by ``Reimers'law.'' Originally, this relation was based solely on dimensional scalingarguments without any physical interpretation. In our approach, the windis assumed to result from the spillover of the extended chromosphere,possibly associated with the action of waves, especially Alfvénwaves, which are used as guidance in the derivation of the new formula.We obtain a relation akin to the original Reimers law, but whichincludes two new factors. They reflect how the chromospheric heightdepends on gravity and how the mechanical energy flux depends, mainly,on the effective temperature. The new relation is tested and sensitivelycalibrated by modeling the blue end of the horizontal branch of globularclusters. The most significant difference from mass-loss rates predictedby the Reimers relation is an increase by up to a factor of 3 forluminous late-type (super)giants, in good agreement with observations.
| VLA Observations of ζ Aurigae: Confirmation of the Slow Acceleration Wind Density Structure
Studies of the winds from single K and early M evolved stars indicatethat these flows typically reach a significant fraction of theirterminal velocity within the first couple of stellar radii. The mostdetailed spatially resolved information of the extended atmospheres ofthese spectral types comes from the ζ Aur eclipsing binaries.However, the wind acceleration inferred for the evolved primaries inthese systems appears significantly slower than for stars of similarspectral type. Since there are no successful theories for mass loss fromK and early M evolved stars, it is important to place strong empiricalconstraints on potential models and determine whether this difference inacceleration is real or an artifact of the analyses. We have undertakena radio continuum monitoring study of ζ Aurigae (K4 Ib + B5 V)using the Very Large Array to test the wind density model of Baade etal. that is based on Hubble Space Telescope (HST) Goddard HighResolution Spectrograph ultraviolet spectra. ζ Aur was monitored atcentimeter wavelengths over a complete orbital cycle, and fluxvariations during the orbit are found to be of similar magnitude tovariations at similar orbital phases in the adjacent orbit. Duringeclipse, the flux does not decrease, showing that the radio emissionoriginates from a volume substantially larger thanR3K~(150Rsolar)3 surroundingthe B star. Using the one-dimensional density model of the K4 Ibprimary's wind derived from HST spectral line profile modeling andelectron temperature estimates from previous optical and new HSTstudies, we find that the predicted radio fluxes are consistent withthose observed. Three-dimensional hydrodynamic simulations indicate thatthe accretion flow perturbations near the B star do not contributesignificantly to the total radio flux from the system, consistent withthe radio eclipse observations. Our radio observations confirm the slowwind acceleration for the evolved K4 Ib component. ζ Aur's velocitystructure does not appear to be typical of single stars with similarspectral types. This highlights the need for more comprehensivemultiwavelength studies for both single stars, which have been sadlyneglected, and other ζ Aur systems to determine if its windproperties are typical.
| Astrometric orbits of SB^9 stars
Hipparcos Intermediate Astrometric Data (IAD) have been used to deriveastrometric orbital elements for spectroscopic binaries from the newlyreleased Ninth Catalogue of Spectroscopic Binary Orbits(SB^9). This endeavour is justified by the fact that (i) theastrometric orbital motion is often difficult to detect without theprior knowledge of the spectroscopic orbital elements, and (ii) suchknowledge was not available at the time of the construction of theHipparcos Catalogue for the spectroscopic binaries which were recentlyadded to the SB^9 catalogue. Among the 1374 binaries fromSB^9 which have an HIP entry (excluding binaries with visualcompanions, or DMSA/C in the Double and Multiple Stars Annex), 282 havedetectable orbital astrometric motion (at the 5% significance level).Among those, only 70 have astrometric orbital elements that are reliablydetermined (according to specific statistical tests), and for the firsttime for 20 systems. This represents a 8.5% increase of the number ofastrometric systems with known orbital elements (The Double and MultipleSystems Annex contains 235 of those DMSA/O systems). The detection ofthe astrometric orbital motion when the Hipparcos IAD are supplementedby the spectroscopic orbital elements is close to 100% for binaries withonly one visible component, provided that the period is in the 50-1000 drange and the parallax is >5 mas. This result is an interestingtestbed to guide the choice of algorithms and statistical tests to beused in the search for astrometric binaries during the forthcoming ESAGaia mission. Finally, orbital inclinations provided by the presentanalysis have been used to derive several astrophysical quantities. Forinstance, 29 among the 70 systems with reliable astrometric orbitalelements involve main sequence stars for which the companion mass couldbe derived. Some interesting conclusions may be drawn from this new setof stellar masses, like the enigmatic nature of the companion to theHyades F dwarf HIP 20935. This system has a mass ratio of 0.98 but thecompanion remains elusive.
| 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
| Local kinematics of K and M giants from CORAVEL/Hipparcos/Tycho-2 data. Revisiting the concept of superclusters
The availability of the Hipparcos Catalogue has triggered many kinematicand dynamical studies of the solar neighbourhood. Nevertheless, thosestudies generally lacked the third component of the space velocities,i.e., the radial velocities. This work presents the kinematic analysisof 5952 K and 739 M giants in the solar neighbourhood which includes forthe first time radial velocity data from a large survey performed withthe CORAVEL spectrovelocimeter. It also uses proper motions from theTycho-2 catalogue, which are expected to be more accurate than theHipparcos ones. An important by-product of this study is the observedfraction of only 5.7% of spectroscopic binaries among M giants ascompared to 13.7% for K giants. After excluding the binaries for whichno center-of-mass velocity could be estimated, 5311 K and 719 M giantsremain in the final sample. The UV-plane constructed from these datafor the stars with precise parallaxes (σπ/π≤20%) reveals a rich small-scale structure, with several clumpscorresponding to the Hercules stream, the Sirius moving group, and theHyades and Pleiades superclusters. A maximum-likelihood method, based ona Bayesian approach, has been applied to the data, in order to make fulluse of all the available stars (not only those with precise parallaxes)and to derive the kinematic properties of these subgroups. Isochrones inthe Hertzsprung-Russell diagram reveal a very wide range of ages forstars belonging to these groups. These groups are most probably relatedto the dynamical perturbation by transient spiral waves (as recentlymodelled by De Simone et al. \cite{Simone2004}) rather than to clusterremnants. A possible explanation for the presence of younggroup/clusters in the same area of the UV-plane is that they have beenput there by the spiral wave associated with their formation, while thekinematics of the older stars of our sample has also been disturbed bythe same wave. The emerging picture is thus one of dynamical streamspervading the solar neighbourhood and travelling in the Galaxy withsimilar space velocities. The term dynamical stream is more appropriatethan the traditional term supercluster since it involves stars ofdifferent ages, not born at the same place nor at the same time. Theposition of those streams in the UV-plane is responsible for the vertexdeviation of 16.2o ± 5.6o for the wholesample. Our study suggests that the vertex deviation for youngerpopulations could have the same dynamical origin. The underlyingvelocity ellipsoid, extracted by the maximum-likelihood method afterremoval of the streams, is not centered on the value commonly acceptedfor the radial antisolar motion: it is centered on < U > =-2.78±1.07 km s-1. However, the full data set(including the various streams) does yield the usual value for theradial solar motion, when properly accounting for the biases inherent tothis kind of analysis (namely, < U > = -10.25±0.15 kms-1). This discrepancy clearly raises the essential questionof how to derive the solar motion in the presence of dynamicalperturbations altering the kinematics of the solar neighbourhood: doesthere exist in the solar neighbourhood a subset of stars having no netradial motion which can be used as a reference against which to measurethe solar motion?Based on observations performed at the Swiss 1m-telescope at OHP,France, and on data from the ESA Hipparcos astrometry satellite.Full Table \ref{taba1} is only available in electronic form at the CDSvia anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/430/165}
| Spectroscopic binary orbits from photoelectric radial velocities. Paper 175: BD+48 1048, HR 1736, HR 3416, and HD 199378/9
Not Available
| Synthetic Lick Indices and Detection of α-enhanced Stars. II. F, G, and K Stars in the -1.0 < [Fe/H] < +0.50 Range
We present an analysis of 402 F, G, and K solar neighborhood stars, withaccurate estimates of [Fe/H] in the range -1.0 to +0.5 dex, aimed at thedetection of α-enhanced stars and at the investigation of theirkinematical properties. The analysis is based on the comparison of 571sets of spectral indices in the Lick/IDS system, coming from fourdifferent observational data sets, with synthetic indices computed withsolar-scaled abundances and with α-element enhancement. We useselected combinations of indices to single out α-enhanced starswithout requiring previous knowledge of their main atmosphericparameters. By applying this approach to the total data set, we obtain alist of 60 bona fide α-enhanced stars and of 146 stars withsolar-scaled abundances. The properties of the detected α-enhancedand solar-scaled abundance stars with respect to their [Fe/H] values andkinematics are presented. A clear kinematic distinction betweensolar-scaled and α-enhanced stars was found, although a one-to-onecorrespondence to ``thin disk'' and ``thick disk'' components cannot besupported with the present data.
| Wind accretion in binary stars. I. Mass accretion ratio
Three-dimensional hydrodynamic calculations are performed in order toinvestigate mass transfer in a close binary system, in which onecomponent undergoes mass loss through a wind. The mass ratio is assumedto be unity. The radius of the mass-losing star is taken to be about aquarter of the separation between the two stars. Calculations areperformed for gases with a ratio of specific heats γ=1.01 and 5/3.Mass loss is assumed to be thermally driven so that the other parameteris the sound speed of the gas on the mass-losing star.Here, we focus our attention on two features: flow patterns and massaccretion ratio, which we define as the ratio of the mass accretion rateonto the companion, \dot{M}acc, to the mass loss rate fromthe mass-losing primary star, \dot{M}loss. We characterizethe flow by the mean normal velocity of the wind on the critical Rochesurface of the mass-losing star, VR. WhenVR<0.4 AΩ, where A and Ω are the separationbetween the two stars and the angular orbital frequency of the binary,respectively, we obtain Roche-lobe over-flow (RLOF), while forVR>0.7 AΩ we observe wind accretion. We find verycomplex flow patterns in between these two extreme cases. We derive anempirical formula of the mass accretion ratio as 0.18 ×10-0.75VR/AΩ in the low velocity regime and0.05 (VR/AΩ)-4 in the high velocity regime.
| NLTE Radiative Transfer in the Extended Atmospheres and Winds of Cool Stars
Not Available
| Post-Main-Sequence Changes in Rotational Velocities
For 1377 dwarfs and 381 giants of types B and A, we present meanobserved projected rotational velocities for normal plus abnormalspectral types combined. For the dwarfs, Vsini is statistically constantat 127+/-15 km s-1 from B0 V to A5 V. Using the interiormodels of Bertelli et al., we predict the rotational velocities of thegiants. We assume an age of 30×106 yr for the observeddwarfs. The predicted giant rotational velocities agree well with theobserved values if angular momentum is conserved in rigid-body rotation;the observed minus the computed is -7+/-4 km s-1. Significantloss of angular momentum by mass loss (stellar winds) cannot occurbecause the observed rotational velocities of the giants are already atthe maximum level allowed by either conservation mechanism. Comparisonwith three other studies indicates that angular momentum is conserved byrigid-body rotation if the expansion is less than a factor of 4, butconserved in shells if the expansion is more.
| Koordinierte Zusammenarbeit zwischen den VdS-FG 'BAV' und 'Spektroskopie' ?
Not Available
| Spectral Classification of the Hot Components of a Large Sample of Stars with Composite Spectra, and Implication for the Absolute Magnitudes of the Cool Supergiant Components.
A sample of 135 stars with composite spectra has been observed in thenear-UV spectral region with the Aurélie spectrograph at theObservatoire de Haute-Provence. Using the spectral classifications ofthe cool components previously determined with near infrared spectra, weobtained reliable spectral types of the hot components of the samplesystems. The hot components were isolated by the subtraction methodusing MK standards as surrogates of the cool components. We also derivedthe visual magnitude differences between the components usingWillstrop's normalized stellar flux ratios. We propose a photometricmodel for each of these systems on the basis of our spectroscopic dataand the Hipparcos data. We bring to light a discrepancy for the Gsupergiant primaries between the visual absolute magnitudes deduced fromHipparcos parallaxes and those tabulated by Schmidt-Kaler for the GIbstars: we propose a scale of Mv-values for these stars incomposite systems. By way of statistics, about 75% of the hot componentsare dwarf or subgiant stars, and 25% should be giants. The distributionin spectral types is as follows: 41% of B-type components, 57% of typeA, and 2% of type F; 68% of the hot components have a spectral type inthe range B7 to A2. The distribution of the ΔMv-valuesshows a maximum near 0.75 mag.
| 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.
| Lick Spectral Indices for Super-Metal-rich Stars
We present Lick spectral indices for a complete sample of 139 candidatesuper-metal-rich stars of different luminosity classes (MK type from Ito V). For 91 of these stars we were able to identify, in anaccompanying paper, the fundamental atmosphere parameters. This confirmsthat at least 2/3 of the sample consists of stars with [Fe/H] in excessof +0.1 dex. Optical indices for both observations and fiducialsynthetic spectra have been calibrated to the Lick system according toWorthey et al. and include the Fe I indices of Fe5015, Fe5270, andFe5335 and the Mg I and MgH indices of Mg2 and Mg b at 5180Å. The internal accuracy of the observations is found to beσ(Fe5015)=+/-0.32 Å, σ(Fe5270)=+/-0.19 Å,σ(Fe5335)=+/-0.22 Å, σ(Mg2)=+/-0.004 mag,and σ(Mg b)=+/-0.19 Å. This is about a factor of 2 betterthan the corresponding theoretical indices from the synthetic spectra,the latter being a consequence of the intrinsic limitations in the inputphysics, as discussed by Chavez et al. By comparing models andobservations, we find no evidence for nonstandard Mg versus Fe relativeabundance, so [Mg/Fe]=0, on the average, for our sample. Both theWorthey et al. and Buzzoni et al. fitting functions are found tosuitably match the data and can therefore confidently be extended forpopulation synthesis application also to supersolar metallicity regimes.A somewhat different behavior of the two fitting sets appears, however,beyond the temperature constraints of our stellar sample. Its impact onthe theoretical output is discussed, as far as the integratedMg2 index is derived from synthesis models of stellaraggregates. A two-index plot, such as Mg2 versus Fe5270, isfound to provide a simple and powerful tool for probing distinctiveproperties of single stars and stellar aggregates as a whole. The majoradvantage, over a classical CM diagram, is that it is both reddeningfree and distance independent. Based on observations collected at theInstituto Nacional de Astrofísica, Optica y Electrónica(INAOE) ``G. Haro'' Observatory, Cananea (Mexico).
| A Large Spectral Class Dependence of the Wilson-Bappu Effect among Luminous Stars
The striking correlation between Ca II K-line emission width andabsolute visual magnitude has not previously been well calibrated forstars more luminous than giants. From a sample of binary systems fit toisochrones, we find deviations of more than 2 mag, correlated withspectral class, between these binarity Mv values and theWilson-Bappu relation. Additional Mv values derived fromHipparcos parallaxes are used to explore the systematics. The spectralclass dependence vanishes for K-line parameterlogW0<=1.80. Linear spectral class corrections are derivedfor the more luminous stars, with logW0>=2.00, while atable is provided for the transition region. The dispersion from theserelations is about +/-0.6 mag. This recalibration extends thedemonstrated applicability of the Wilson-Bappu technique toMv~=-5 or distance ~20 kpc.
| Exploring the nature of the symbiotic stars with high resolution spectroscopy.
There are some fundamental aspects of the "symbiotic phenomenon" whichare poorly understood. Modern technology now allows to observe faintstars with efficient very high resolution spectrographs, such as theSARG mounted at TNG, which will be crucial for our understanding of thenature and evolutionary stage of symbiotic stars and related sytems. Ofgreat importance will be the determination of luminosity, rotation, massloss, chemical composition of the cool stellar components which is basicfor settling the mass transfer in the system and tracing back its pasthistory. High resolution observations are also needed to derive thevelocity, temperature and abundance gradients in the nebula, and tounveil peculiar excitation processes.
| Infrared Photometry of Five Long-Period Binaries
We present and discuss JHKLM photometry for five long-period binaries(VV Cep, ZZ CMi, WY Gem, epsilon Aur, and zeta Aur). The IR radiationfrom WY Gem may contain a component with a period of ~430 days,attributable to temperature pulsations of an M supergiant. The 3.5- and5-micrometer radiation from the eclipsing binary epsilon Aur outside theeclipse exhibits excess (relative to the light from an F supergiant)fluxes which correspond to the emission from a cool source with atemperature of ~1000 K. For the eclipsing binary epsilon Aur, we presentthe hitherto unpublished results of our optical and IR photometry during1982-1985, when a primary eclipse was observed in the system.
| Optical Interferometry
The field of optical and infrared (IR) interferometry has seen rapidtechnical and scientific progress over the past few years. A number ofinstruments capable of precise visibility measurements have been built,and closure-phase imaging with multitelescope arrays has beendemonstrated. Astronomical results from these instruments includemeasurements of stellar diameters and their wavelength dependence, limbdarkening, stellar surface structure, and distances of Cepheids and ofNova Cygni 1992. Precise stellar masses have been obtained frominterferometric observations of spectroscopic binaries, andcircumstellar disks and shells have been resolved. Searches forsubstellar companions and extrasolar planets with interferometricastrometry will begin soon. Nulling interferometry will enable studiesof exozodiacal disks from the ground and the detection andcharacterization of terrestrial extrasolar planets from space. Thesedevelopments are reviewed, as well as progress in some key technologicalareas.
| The Asymmetric Nebula Surrounding the Extreme Red Supergiant Vy Canis Majoris
We present HST/WFPC2 images plus ground-based infrared images andphotometry of the very luminous OH/IR star VY Canis Majoris. Our WFPC2data show a complex distribution of knots and filamentary arcs in theasymmetric reflection nebula around the obscured central star. Thereflection arcs may result from multiple, asymmetric ejection episodesdue to localized events on VY CMa's surface. Such events probablyinvolve magnetic fields and convection, by analogy with solar activity.Surface photometry indicates that the star may have experienced enhancedmass loss over the past 1000 yr. We also demonstrate that the apparentasymmetry of the nebula results from a combination of high extinctionand backscattering by dust grains. Thermal-infrared images reveal a moresymmetric distribution, elongated along a nearly east-west direction. VYCMa probably has a flattened disklike distribution of dust with anortheast-southwest polar axis and may be experiencing activityanalogous to solar prominences. The presence of an axis of symmetryraises interesting questions for a star the size of Saturn's orbit.Magnetic fields and surface activity may play an important role in VYCMa's mass-loss history. Based on observations made with the NASA/ESAHubble Space Telescope, obtained at the Space Telescope ScienceInstitute, which is operated by the Association of Universities forResearch in Astronomy, Inc., under NASA contract NAS 5-26555.
| What can HST-GHRS Fe II observations of α Orionis (M2 Iab) tell us about short-period heating?
Cuntz (\cite{Cuntz97}) suggested that apparent velocity shifts in Fe IIemission lines observed in Betelgeuse (alpha Orionis: M2 Iab) indicatethat non-magnetic wave modes are relevant for the heating and dynamicsof alpha Ori's chromosphere. This claim was based on the similarity ofcomputed stochastic velocities in 1-D short-period acoustic wave modelsand velocity shifts in profile fits to Fe II emission lines (Carpenter& Robinson \cite{Carpenter97}), which is now identified ascoincidental. While acoustic waves may indeed be important for theheating and dynamics of alpha Ori's chromosphere, the interpretation ofthe Fe II emission line profiles does not provide evidence for thispossibility. The line formation of optically thick scattering lines inan extended outflow makes Fe II emission lines poorly suited as adiagnostic for small-scale structure in hydrodynamical models. Betterdiagnostics include electron density sensitive, low opacity lines suchas C II]. In the view of these findings, we discuss directions of futureresearch. Based on observations made with the NASA/ESA Hubble SpaceTelescope, obtained at the Space Telescope Science Institute, which isoperated by the Association of Universities for Research in Astronomy,Inc., under NASA contract NAS 5-26555.
| On the Wilson-Bappu relationship in the Mg II k line
An investigation is carried out on the Wilson-Bappu effect in the Mg Iik line at 2796.34 Å. The work is based on a selection of 230 starsobserved by both the IUE and HIPPARCOS satellites, covering a wide rangeof spectral types (F to M) and absolute visual magnitudes (-5.4<=MV <=9.0). A semi-automatic procedure is used to measurethe line widths, which applies also in the presence of strong centralabsorption reversal. The Wilson-Bappu relationship here provided isconsidered to represent an improvement over previous recent results forthe considerably larger data sample used, as well as for a properconsideration of the measurement errors. No evidence has been found fora possible dependence of the WB effect on stellar metallicity andeffective temperature.
| 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
| Spectrum analysis of the binary systems with expanding shell due to stellar wind.
Not Available
| Observations and Atmospheric Parameters of Super-Metal-rich Candidates
The spectroscopic properties of a sample of 92 Population I bright stars(V<8) with literature values of [Fe/H]>=+0.1 are reviewed in orderto study the metallicity scale at supersolar regimes. For 73 of thesecandidate super-metal-rich (SMR) stars we identified the photosphericfiducial parameters (Teff, logg, [M/H]) from among publishedparameter sets via a comparison of new observations in the wavelengthrange 5034-5398 Å with synthetic spectra derived from the 1997database of Chavez et al. As a main issue in our analysis, we find thata ``genuine'' SMR stellar component in the Galactic disk exists withmore than one-fourth of the stars in our sample fulfilling the criterion[Fe/H]>=0.2 dex, and three of them as rich as [Fe/H]>+0.4 dex.Based on observations collected at the INAOE ``G. Haro'' Observatory,Cananea (Mexico).
| Composite spectraPaper 10: the equal-mass binary HR 2030 (K0IIb+B8IV)
We separate the spectra of the individual components of HR 2030, asixth-magnitude composite-spectrum binary system, and show that theyhave types close to K0IIb and B8IV, and masses that are equal to withinthe precision of the measurements (mass ratio=1.00+/-0.03). The orbitappears to have a very small eccentricity, although reasons are givenfor believing that such eccentricity is spurious; it has a period of 66dand an inclination estimated at 30° to the line of sight. Ourphotometric model of the system confirms the luminosity types derivedfrom the spectra and indicates an interstellar absorption of 0.4mag, inaccord with the observed strength of the interstellar K line. We derivethe physical parameters (Teff, Mbol, R, L) of thecomponents, and calculate that the mass of each star is close to4.0Msolar. We further show that the hot component(R=5.9+/-0.6Rsolar) has already evolved to a positionsignificantly above the zero-age main sequence (ZAMS), and we proposethat the primary (R=41+/-5Rsolar) is making its first ascentof the red-giant branch. From comparisons with evolutionary tracks, wededuce that the age of the binary (since its arrival at the ZAMS) is inthe range 1-2×108yr. While we suspect that thecomponents are sufficiently close for some tidal distortion to occur,the effects are not discernible in our data owing to the rather loworbital inclination. The system shows Sii in emission as a result ofirradiation of the primary by the hot secondary, but in the opticalspectrum we see little other clear evidence of interaction between thecomponents even though the object has a relatively short period and is astrong X-ray source. On the other hand, Hipparcos photometry suggeststhe existence of a major non-uniformity of the surface of the primarystar.
|
Submit a new article
Related links
Submit a new link
Member of following groups:
|
Observation and Astrometry data
| Constellation: | Ηνίοχος |
| Right ascension: | 05h02m28.70s |
| Declination: | +41°04'33.0" |
| Apparent magnitude: | 3.75 |
| Distance: | 241.546 parsecs |
| Proper motion RA: | 9.4 |
| Proper motion Dec: | -23.1 |
| B-T magnitude: | 5.236 |
| V-T magnitude: | 3.888 |
Catalogs and designations:
|
