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|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.
|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.
|NLTE Radiative Transfer in the Extended Atmospheres and Winds of Cool Stars|
|Ultraviolet Eclipse Observations and Fundamental Parameters of the Binary HR 2554 (G6 II+A1 V)|
HR 2554 is an eclipsing binary system that contains a G6 II primary starand an A dwarf secondary. We have obtained ultraviolet spectra duringtwo eclipses of HR 2554 in 1994 March-April and 1995 May using the HSTGoddard High Resolution Spectrograph (GHRS) to study the atmosphericstructure of the primary and to better establish the properties of thebinary system. We have determined accurate orbital elements for bothcomponents, using new and existing optical spectra for the primary andthe GHRS spectra for the secondary, in conjunction with eclipsephotometry presented in 1992 by Schröder & Hünsch. Thederived orbital period is 195.258+/-0.003 days, the derived radii are31.3+/-0.9 Rsolar and 1.9+/-0.1 Rsolar, and thederived masses are 3.14+/-0.17 Msolar and 1.98+/-0.11Msolar, respectively. The resulting positions of HR 2554 inthe Hertzsprung-Russell (H-R) diagram are somewhat inconsistent with theindependent evolution of the component stars; in particular, the G starprimary is both overluminous and too blue for its mass. The difficultiesmight be overcome if the metallicity of the system were unusually low([Fe/H]~-1), but this possibility appears to be ruled out by the[Fe/H]=-0.04 determination of Eggen. We suspect HR 2554 has undergone amore complicated evolutionary history involving mass transfer than hasbeen considered previously. Based on observations 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, and fromthe European Southern Observatory.
|Speckle Interferometry of New and Problem HIPPARCOS Binaries|
The ESA Hipparcos satellite made measurements of over 12,000 doublestars and discovered 3406 new systems. In addition to these, 4706entries in the Hipparcos Catalogue correspond to double star solutionsthat did not provide the classical parameters of separation and positionangle (rho,theta) but were the so-called problem stars, flagged ``G,''``O,'' ``V,'' or ``X'' (field H59 of the main catalog). An additionalsubset of 6981 entries were treated as single objects but classified byHipparcos as ``suspected nonsingle'' (flag ``S'' in field H61), thusyielding a total of 11,687 ``problem stars.'' Of the many ground-basedtechniques for the study of double stars, probably the one with thegreatest potential for exploration of these new and problem Hipparcosbinaries is speckle interferometry. Results are presented from aninspection of 848 new and problem Hipparcos binaries, using botharchival and new speckle observations obtained with the USNO and CHARAspeckle cameras.
|Ultraviolet and Optical Studies of Binaries with Luminous Cool Primaries and Hot Companions. V. The Entire IUE Sample|
We have obtained or retrieved IUE spectra for over 100 middle- andlate-type giant and supergiant stars whose spectra indicate the presenceof a hot component earlier than type F2. The hot companions areclassified accurately by temperature class from their far-UV spectra.The interstellar extinction of each system and the relative luminositiesof the components are derived from analysis of the UV and opticalfluxes, using a grid of UV intrinsic colors for hot dwarfs. We find thatthere is fair agreement in general between current UV spectralclassification and ground-based hot component types, in spite of thedifficulties of assigning the latter. There are a few cases in which thecool component optical classifications disagree considerably with thetemperature classes inferred from our analysis of UV and opticalphotometry. The extinction parameter agrees moderately well with otherdeterminations of B-V color excess. Many systems are worthy of furtherstudy especially to establish their spectroscopic orbits. Further workis planned to estimate luminosities of the cool components from the dataherein; in many cases, these luminosities' accuracies should becomparable to or exceed those of the Hipparcos parallaxes.
|The ROSAT all-sky survey catalogue of optically bright late-type giants and supergiants|
We present X-ray data for all late-type (A, F, G, K, M) giants andsupergiants (luminosity classes I to III-IV) listed in the Bright StarCatalogue that have been detected in the ROSAT all-sky survey.Altogether, our catalogue contains 450 entries of X-ray emitting evolvedlate-type stars, which corresponds to an average detection rate of about11.7 percent. The selection of the sample stars, the data analysis, thecriteria for an accepted match between star and X-ray source, and thedetermination of X-ray fluxes are described. Catalogue only available atCDS via anonymous ftp to cdsarc.u-strasbg.fr (18.104.22.168) or viahttp://cdsweb.u-strasbg.fr/Abstract.html
|A critical test of stellar evolution and convective core `overshooting' by means of zeta Aurigae systems|
Quantitative tests of late stellar evolution are presented by computingmodels with our evolutionary code to match the exact properties ofcertain zeta Aurigae eclipsing binaries and related non-eclipsingsystems. Those binaries have a late- type giant or supergiant primaryand their orbital inclination is well determined from either eclipses orspeckle orbits. They provide the only direct measurements of masses forsuch evolved stars, together with other well-determined physicalparameters. In the computations all effects of enhanced mixing beyondthe convective cores during central hydrogen burning stages, e.g., coreovershooting and any rotationally induced meridional mixing, arerepresented by a simple overshooting prescription. Its single parametercan be constrained to within 25 per cent of its value and leads to anovershooting length l_ov of ~0.24 H_P (pressure scaleheights) for 2.5Msolar, slightly increasing to ~0.32 H_P for 6.5 Msolar. Those valuesare required by our code to reproduce the well-determined luminositiesof the giants in or at the end of their blue loop. This new methodprovides the currently most sensitive test of the overshooting issue.
|Non-LTE model chromospheres of zeta Aurigae stars|
Plane-parallel, one-component, non-local thermodynamic equilibrium(LTE), semi-empirical model chromospheres have been constructed for theprimary stars in the zeta Aurigae systems HR 6902 and 22 Vul. This hasbeen accomplished by means of radiative transfer calculations undertakenwith a non-LTE multilevel radiative transfer code, MULTI, and curves ofgrowth applied to chromospheric eclipse spectra. The former are thesubject of this paper, which is divided into two parts. The firstbriefly describes the observations and derivation of basic stellarparameters, while the second concerns the radiative transfercalculations and conclusions which follow from them. In particular, thecalculated model photospheres plus chromospheres are used to investigatethe relative contribution of primary and secondary stars to the overallradiation field. The radiation field of the hot secondary isapproximated by use of an appropriate Kurucz model atmosphere. Althoughthe hot companion is wholly responsible for the ionization of themetals, this is not the case as far as excitation is concerned. Use of a47-level Fe atomic model demonstrates the intimate convolution betweenatomic and atmospheric physics. The chromospheres calculated byradiative transfer methods are compared with those derived empiricallyby curves of growth and are found to be comparable in the line-formingregion of CaII H & K, MgII h & k and the many FeII lines.Finally, owing to the effects of radiative transitions from high-lyinglevels which are enhanced by the radiation field of the hot companion,it is found that lines resulting from transitions from the a^4F, a^4Dand a^4P levels of FeII may not be used to derive an inner windtemperature for 22 Vul. This is the first time that zeta Aurigaechromospheres have been the subject of such intensive radiative transfercalculations.
|A Catalogue of Correlations Between Eclipsing Binaries and Other Categories of Double Stars|
Among the 9110 stars in The Bright Star Catalogue, there are 225eclipsing or ellipsoidal variables. A search has been made for these incatalogues of spectroscopic binaries, visual double or multiple stars,speckle interferometry, occulation binaries, and galatic clusters. Themajority of the photometric binaries are also members of groups ofhigher multiplicity. The variables are in systems ranging from one to 91stars, five on the average. 199 are either spectroscopic binaries (SB)or stars with variable radial velocity, with orbital periods known for160. Photometric periods are lacking for 48 while SB periods areavailable for 23 of these. Observers with photoelectric equipment areencouraged to plan observations to test if the SB periods are consistentwith photometric data. Observers are likewise encouraged to examinethose stars for which the photometric and SB periods appear to beinconsistent. Parallaxes are available for 86 of the stars, 41 of themindicating distances nearer than 50 parsecs.
|The measurement of mass loss rates of binary systems enveloped in winds or expanding shells.|
|Optical spectra of ζ Aurigae systems. VIII. The chromosphere of HR6902.|
We analyze chromospheric spectra of the ζ Aur system HR6902observed during its 1987 and 1989 eclipses, deriving empirical columndensities, number densities and ionization characteristics for 5distinct heights within the giant primary's chromosphere. Columndensities for CaII are determined from K-line profiles and for otherions by a curve-of-growth technique, modelling iteratively the scaleheights of the line-forming regions according to the known geometry ofthe eclipses and dimensions of the system. We find evidence for theexistence of two plasma components in and beyond the chromosphere thatare physically different. The inner component has a low turbulence(v_tur_=15km/s); its ion column densities decrease steeply outwards andseem to outline the geometrically-thin chromosphere itself. There issome evidence that the geometrical extent of this component varies fromone eclipse to another. The outer component has a significantly higherturbulence (v_tur_=45km/s) and a scale height that is nearly an order ofmagnitude larger. Because its column density is much lower, we have onlybeen able to observe it by our technique in the strongest chromosphericlines (i.e. CaII); it extends much farther outwards than the innercomponent - probably into regions beyond the top of the chromosphere,for which IUE observations give evidence of plasma at transition-regiontemperatures (=~10^5^). We consider the evolutionary status of the twocomponents, and conclude that the primary star is an ordinary3.9Msun_ blue-loop giant that is 2.0x10^8^years old. Wecompare the chromosphere of HR6902 with those of other ζ Aur giantsand discuss the meaning of the `dividing lines' as tracers of the verydifferent conditions which are encountered in G and K (super)giantchromospheres.
|Hybrid stars and the reality of "dividing lines" among G to K bright giants and supergiants.|
We present results of pointed ROSAT PSPC observations of 15 hybridstars/candidates, which have been analyzed in a homogenous way. 7 ofthese stars were observed in X-rays for the first time. 12 out of 15hybrid stars have been detected as X-ray sources, some of them close tothe detection limit. We conclude that essentially all hybrid stars asdefined by the simultaneous presence of transition region line emissionand cool stellar winds are X-ray sources if exposed sufficiently deep.The X-ray luminosities of hybrid stars cover a range between 2x10^27^and ~10^30^erg/s. Their X-ray surface fluxes can be as low as =~20erg/cm^2^/s and thus considerably lower than those of normal luminosityclass (LC) III giants. X-ray spectra of hybrid stars tend to be harderthan that of normal LC III giants, moreover, the X-ray brightest starshave the hardest spectra. We find that for K II giants the normalizedX-ray flux versus C IV flux obeys a power law with an exponent a=2.9,steeper than among normal giants (1.5). Hybrid K II stars are X-rayunderluminous by a factor of 5 to 20 compared to LC III giants at thesame level of normalized CIV flux f_CIV_/f_bol_; hybrid G supergiantsare even more X-ray deficient. We reanalyze the CaII wind dividing lineand find it vertical at B-V=1.45 for LC III giants. It is nearlyhorizontal between B-V=1.45 and 1.0 (at M_bol_=~-2...-3), and not welldefined for supergiants with B-V<1.0. We therefore suggest thatpossibly all LC II and Ib G and K giants are hybrid stars and that the"dividing line" concept in its simplest form is not valid for G/K giantsbrighter than M_bol_=~-2. Hybrid stars are supposed to be evolvedintermediate mass stars and their coronal activity may in principle bedetermined by the individual history of each star.
|ROSAT X-ray observations of a complete, volume-limited sample of late-type giants.|
We have investigated a complete sample of the nearest 39 late typegiants (d<=25pc) for which we have probed the X-ray luminosityfunction with unprecedented sensitivity by deep (3...18ksec) ROSATPSPC-observations in the pointed mode, together with ROSAT All-Skysurvey (RASS) data. We confirm the X-ray dividing line for luminosityclass III giants as proposed by Haisch et al. (1991, 1992) and we findevidence, that essentially all luminosity class III giants withB-V<1.2 or spectral type
|Professional-amateur collaboration in variable star research: IV. One possibility for amateur/professional collaboration|
|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.
|The corona of the G-type giant HR 2554: Discovery of co-existing, very different temperature regimes|
We present direct observational evidence for two different co-existingcoronal temperature regimes in the sigma Aur-type binary HR 2554 (G7II +A1V). ROSAT observations reveal the presence of plasma at temperaturesaround 106.7 K, typical of coronal plasma found in giants,while IUE observations, taken during egress from eclipse, showcircumstellar (CS) C IV and Si IV absorption lines in the spectrum ofthe secondary, which reveal a significant amount of geometricallyextended (0 less than h less than 1R*) plasma in thetemperature regime of about 105 K, similar to that found inHR 6902.
|Circumstellar MGII Absorption in Ultraviolet Spectra of Hot Companions of Red Giants and the Meaning of the MGII Asymmetry Dividing Line|
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1993A&A...276..161H&db_key=AST
|Zeta-Aurigae Type Binaries|
|Optical spectra of Zeta Aurigae systems. IV - The January 1990 eclipse of HR 2554: Detection of chromospheric absorption and extended plasma at approximately 10 exp 5 K|
Eclipse observations of HR 2554 are presented. These observations wereobtained simultaneously during the January 1990 eclipse with ESOtelescopes and the IUE satellite. Chromospheric absorption and changesin the circumstellar matter were investigated. Improved systemparameters were derived from the light curve. For each of the compositespectra a surrogate primary was subtracted revealing the Ca and Fe lineabsorption superimposed on the extracted spectrum of the companion. Thedivision in the HR diagram between cool winds and extended coolchromospheres to the right and hotter circumstellar matter to the leftis discussed.
|A study of the ultraviolet spectra of Zeta Aurigae/VV Cephei systems. XII - The physical state of supergiant chromospheres at the transition from coronae to cool winds|
Results are reported from an analysis of 20 IUE spectra of the Zeta Aurbinaries HR 6902, HR 2554, and Tau Per during their near-eclipse phasesin 1987-1988. The data are presented in tables and graphs andcharacterized in detail, with comparison of similar results for 22 Vul.It is shown (1) that the Fe II column densities at low heights (about 10to the 6th km) vary by 3-4 orders of magnitude among the stars, and (2)that the changes are related to their positions on the HR diagram andthus to the onset of cool stellar winds. A new type of hot CS matter ispostulated, extended like a corona but at temperatures similar to thosein the solar transition region (100,000 K or less). The potential rolesof thermal instabilities and ionization in this phase are explored.
|Optical spectra of Zeta Aurigae binary systems. I - The 1987 eclipse of Zeta Aurigae|
High S/N, high-resolution observations of Zeta Aur which were made atoptical wavelengths during its 1987 ingress and total eclipse arepresented. The spectra have been analyzed by spectral subtraction,enabling the spectra of the B star and of the K supergiant chromosphereto be isolated for the first time in the wavelength region 3650-4650 A.Over 260 absorption features believed to originate in the supergiant'schromosphere have been identified. Determinations of the masses, sizesand relative velocity of the component stars are used to construct amodel of the geometry of the eclipse. If the lower chromosphere rotatesrigidly with the supergiant, its radial velocity measured at ingressindicates a rotation period that may be synchronous with the orbitalperiod of the system.
|Large and Kinematically Unbiased Samples of G- and K-Type Stars. III. Evolved Young Disk Stars in the Bright Star Sample|
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1989PASP..101...54E&db_key=AST
|Large and kinematically unbiased samples of G- and K-type stars. II - Observations of evolved stars in the Bright Star sample. III - Evolved young disk stars in the Bright Star sample|
Four color and RI observations were obtained for a large sample ofG-type and K-type stars in the Bright Star Catalogue. Data are firstpresented for 110 evolved stars. Photometry of evolved young diskpopulation stars have then been calibrated for luminosity, reddening,and metallicity on the basis of results for members of the Hyades andSirius superclusters. New DDO results are given for 120 stars.
|The 69th Name-List of Variable Stars|
|The November 1987 eclipse of the zeta-Aur system HR 2554|
It is confirmed that HR 2554 (G6 II + A0 V) is an atmospheric eclipsingsystem of the zeta-Aur type. The IUE observations of the Nov. 1987eclipse indicate that the eclipse of the A star lasts 4 days and is nottotal. Absorption lines due to the extended atmosphere of the primarycan be seen a day before and after the eclipse and are missing 2 daysfrom first and 4th contact. Thus the outer envelope of the primaryextends to less than 1 stellar radius beyond the photosphere. Comparedto 22 Vul (G3 Ib-II + B9 V), where the absorption can be traced to a fewstellar radii, HR 2554 is a more moderate case of mass outflow, whichimplies there is reduced interaction of the secondary within the windfrom the primary as is seen in the other zeta-Aur systems.
|Are tides responsible for enhanced MG II emission in late-type binaries?|
Mg II h and k fluxes are measured for a homogeneous sample of 30 G IIIand K III binaries. The spectra have been obtained from the IUE archiveand calibrated in absolute units (erg/sq cm sec). Contrary to thegenerally accepted view that the rate of rotation is responsible for theenhanced chromospheric activity, the Mg II h and k fluxes correlate muchbetter with parameters containing the separation of components in binarysystems. It is suggested that the enhanced chromospheric emission inlate-type giant binary systems is due to tides rather than to rotationalvelocities.
|HR 2554 - a Possible New zeta Aur System|
|On the rarity of FK COM stars|
Very high-dispersion spectra (2.5 A/mm) were obtained of 31 southernlate-type stars, predominantly early G giants, in an effort to find newrapidly rotating, active stars which would be FK Com-like. Measurementsof linewidths and the strength of chromospheric Ca II K-line emissionare presented, but no new star could be added to the class of 'rapidrotators'. Space densities and evolutionary lifetimes for FK Com starsare discussed.