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|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.
|Spectroscopic binary orbits from photoelectric radial velocities. Paper 175: BD+48 1048, HR 1736, HR 3416, and HD 199378/9|
|Reprocessing the Hipparcos Intermediate Astrometric Data of spectroscopic binaries. II. Systems with a giant component|
By reanalyzing the Hipparcos Intermediate Astrometric Data of a largesample of spectroscopic binaries containing a giant, we obtain a sampleof 29 systems fulfilling a carefully derived set of constraints andhence for which we can derive an accurate orbital solution. Of these,one is a double-lined spectroscopic binary and six were not listed inthe DMSA/O section of the catalogue. Using our solutions, we derive themasses of the components in these systems and statistically analyzethem. We also briefly discuss each system individually.Based on observations from the Hipparcos astrometric satellite operatedby the European Space Agency (ESA 1997) and on data collected with theSimbad database.
|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.
|Convective core mixing: A metallicity dependence?|
The main purpose of this paper is to investigate the possible existenceof a metallicity dependence of the overshooting from main sequence starturbulent cores. We focus on objects with masses in the range ~ 2.5Msun- ~ 25 Msun. Evolutionary time scale ratiosare compared with star number ratios on the main sequence. Starpopulations are synthesized using grids of evolutionary tracks computedwith various overshooting amounts. Observational material is provided bythe large and homogeneous photometric database of the OGLE 2 project forthe Magellanic clouds. Attention is paid to the study of uncertainties:distance modulus, intergalactic and interstellar reddening, IMF slopeand average binarity rate. Rotation and the chemical compositiongradient are also considered. The result for the overshooting distanceis loverSMC = 0.40+0.12-0.06Hp (Z0=0.004) and loverLMC =0.10+0.17-0.10 Hp (Z0=0.008)suggesting a possible dependence of the extent of the mixed centralregions with metallicity within the considered mass range. Unfortunatelyit is not yet possible to fully disentangle the effects of mass andchemical composition.
|The tidal effects on the lithium abundance of binary systems with giant component|
We analyse the behavior of lithium abundance as a function of effectivetemperature, projected rotational velocity, orbital period andeccentricity for a sample of 68 binary systems with giant component andorbital period ranging from about 10 to 6400 days. For these binarysystems the Li abundances show a gradual decrease with temperature,paralleling the well established result for single giants. We have alsoobserved a dependence of lithium content on rotation. Binary systemswith moderate to high rotation present also moderate to high Li content.This study shows also that synchronized binary systems with giantcomponent seem to retain more of their original lithium than theunsynchronized systems. For orbital periods lower than 100 to 250 days,typically the period of synchronization for this kind of binary systems,lithium depleted stars seems to be unusual. The suggestion is made thatthere is an ``inhibited zone" in which synchronized binary systems withgiant component having lithium abundance lower than a threshold levelshould be unusual. Based on observations collected at ESO, La Silla.
|The warm circumstellar envelope and wind of the G9 IIb star HR 6902|
IUE observations of the eclipsing binary system HR 6902 obtained atvarious epochs spread over four years indicate the presence of warmcircumstellar material enveloping the G9 IIb primary. The spectra showSi Iv and C Iv absorption up to a distance of 3.3 giant radii(Rg). Line ratio diagnostics yields an electron temperatureof ~ 78 000 K which appears to be constant over the observed heightrange. Applying a least square fit absorption line analysis we derivecolumn densities as a function of height. We find that the innerenvelope (< 3;Rg) of the bright giant is consistent with ahydrostatic density distribution. The derived line broadening velocityof ~ 70 km s-1 is sufficient to provide turbulent pressuresupport for the required scale height. However, an improved agreementwith observations over the whole height regime including the emissionline region is obtained with an outflow model. We demonstrate that thecommon β power-law as well as a P ∝ ρ wind yieldappropriate fit models. Adopting a continuous mass outflow we obtain amass-loss rate of Mȯ=0.8 - 3.4 × 10-11Msolar yr-1 depending on the particular windmodel. The emission lines observed during total eclipse are attributedmostly to resonance scattering of B star photons in the extendedenvelope of the giant. By means of a multi-dimensional line formationstudy we show that the global envelope properties are consistent withthe wind models derived from the absorption line analysis. We argue thatfuture high resolution UV spectroscopy will resolve the large-scalevelocity structure of the circumstellar shell. As an illustration wepresent theoretical Si Iv and C Iv emission profiles showingmodel-dependent line shifts and asymmetries.
|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 (18.104.22.168) or viahttp://cdsweb.u-strastg.fr/cgi-bin/qcat?J/A+A/365/222
|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.
|Empirical Luminosities and Radii of Early-Type Stars after Hipparcos|
Using Hipparcos parallaxes we derive empirical luminosities and radii ofthe early-type stars for which the effective temperatures are known fromdirectly measured angular diameters and total absolute fluxes. Theempirical luminosities allow a direct comparison of the position ofthese stars in the fundamental HR diagram with evolutionary tracks. Thecomparison shows an overall agreement with the Y=0.30 and Z=0.02 trackscomputed with OPAL opacities and moderate amount of overshooting fromthe convective core. In addition, we present evidence that systematicerrors of the masses read off the evolutionary tracks are below 10%.Consequently, the surface gravities obtained from these "evolutionary"masses and the empirical radii are very nearly model-independent.Spectrographic and photometric observations of these stars can thereforebe used for verifying model atmospheres and calibrating photometric logg indices.
|A Comparison of Stellar Evolution with Binary Systems|
We have compared stellar evolution models with the threeintermediate-mass binary systems V2291 Oph, alpha Aur, and eta And,whose masses are determined accurately within 7%. These systems wererecently regarded by Schröder and coworkers as systems that favorevolution with moderate overshoot mixing from the convective cores.While they assumed a standard Population I metallicity for thesebinaries, we have taken into account the available heavy-elementabundance data in the literature. We have taken two approaches for eachsystem. First, assuming no core overshooting, we have adjusted heliumabundance for each binary to obtain the best fit. Second, adopting ahelium abundance from a standard metallicity-helium relation, we haveestimated a required extent of core overshooting l_ov. Our resultsindicate that the required extent of core overshooting is less than~0.15H_p, which is smaller than the extent estimated by Schröderand his collaborators. The main reason for the difference is attributedto the fact that we have taken into account published estimates ofmetallicity for each system. We have found that to obtain a good fitwith red components we have to modify the ratio of mixing length topressure scale height for each system. The required ratio is found to besmaller for a metal-poor system and vice versa.
|Circularization of binary orbits.|
|Spectral classifications in the near infrared of stars with composite spectra. III. Study of a sample of 137 objects with the Aurelie spectrograph|
We provide spectral classifications for a sample of 137 stars mentionedas having composite spectra. The classifications were carried out on 33Angstroms /mm spectra in the region 8370 - 8870 Angstroms. Of these 137objects, 115 correspond in the infrared to cool stars (G, K or M) ofluminosity classes III, II and I; for 22 stars, we find only hot spectraof types B, A, F or Am, so that they do not fulfil our definition ofcomposite spectra. We detect four new Am stars, and one Am star (HD70826) turns out to be a composite spectrum object. As in Paper II, thecool components of composite spectra show a strong concentration in thevicinity of G8III. Based upon observations carried out at Observatoirede Haute-Provence (OHP).
|Late-type giants with infrared excess. I. Lithium abundances|
de la Reza et al. (1997) suggested that all K giants become Li-rich fora short time. During this period the giants are associated with anexpanding thin circumstellar shell supposedly triggered by an abruptinternal mixing mechanism resulting in the surface Li enrichment. Inorder to test this hypothesis twenty nine late-type giants withfar-infrared excess from the list of Zuckerman et al. (1995) wereobserved in the Li-region to study the connection between thecircumstellar shells and Li abundance. Eight giants have been found tohave log epsilon (Li) > 1.0. In the remaining giants the Li abundanceis found to be much lower. HD 219025 is found to be a rapidly rotating(projected rotational velocity of 23 +/-3 km s(-1) ), dusty and Li-rich(log epsilon (Li) = 3.0+/-0.2) K giant. Absolute magnitude derived fromthe Hipparcos parallax reveals that it is a giant and not apre-main-sequence star. The evolutionary status of HD 219025 seems to besimilar to that of HDE 233517 which is also a rapidly rotating, dustyand Li-rich K giant. The Hipparcos parallaxes of all the well studiedLi-rich K giants show that most of them are brighter than the ``clump"giants. Their position in the H-R diagram indicates that they have gonethrough mixing and the initial abundance of Li is not preserved. Thereseems to be no correlations between Li abundances, rotational velocitiesand carbon isotope ratios. The only satisfactory explanation for theoverabundance of lithium in these giants is the creation of Li by theextra deep mixing and the associated ``cool bottom processing". Based onobservations obtained at the European Southern Observatory, La Silla,Chile, and at the Observatoire de Haute Provence, France.
|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.
|A Search for Lithium-Rich Giants among Stars with Infrared Excesses|
The unusual nature of the single, rapidly rotating, lithium-rich K giantHDE 233517, which is currently undergoing significant mass loss,prompted a search for giants with similar properties. High-dispersionspectroscopic observations were obtained of HD 219025, a knownlithium-rich infrared-excess giant, plus 39 stars from a list of G and Kgiants with excess far-infrared emission. The projected rotationalvelocities of the vast majority of infrared-excess giants appear to besimilar to those of normal G and K giants. Six giants have lithiumabundances at or above theoretical upper envelope values. The percentageof such stars in the sample of 39 infrared-excess giants is similar tothat of normal giants. The three giants with the largest lithiumabundances have previously been discovered. None of the sample of 39giants have an Hα line similar to the broadened and veryasymmetric line of HDE 233517. The star with optical properties mostsimilar to HDE 233517 is HD 219025.
|UV observations of zeta Aurigae type binaries.|
|Li-rich giants: A survey based on IRAS colours|
In a previous work we studied the IRAS colours of known Li-rich redgiants and showed that they have flux ratiosF12/F25 and F25/F60 in welldefined ranges. By using this result as a selection criterion, weprepared a list of 280 IRAS Point Source candidates to be Li-rich giantstars. Up to the present we have obtained spectra for 57% of our targetlist. We identified five stars showing a strong LiI 670.079 nm line andsix ones with a Li line of medium strength. Most of the candidates showfeatures typical of normal giants having circumstellar dust, asindicated by their IRAS colours. Observations collected at theLaboratorio Nacional de Astrofisica - LNA, Brazil; Observatoire de HauteProvence - OHP, France; European Southern Observatory - ESO, Chile.
|Photospheric and chromospheric activity in the late-type giant component of the evolved binary system HD 185510|
UBV photometry and moderate resolution Hα spectrophotometry of theevolved binary system HD 185510 (sdB + K0 III), performed at CataniaAstrophysical Observatory, is presented and discussed. Thespectrophotometric data were collected in 1991, 1993, and 1994, whilethe photometric light curves were obtained in 1993, 1994 and 1995.>From the B and V photometry we determine a new photometricrotational period of 26(d) .23, confirming the asynchronous rotation ofthe cool giant component. The spectroscopic data confirm the vsin ivalue of 15 Km s(-1) measured by Fekel et al. (1993) and clearly reveala filled-in Hα line with appreciable variations. The excessemission of the line, observed at any orbital phase, is found to beanticorrelated with the V light curve and is primarily ascribed to thechromospheric activity on the cool star. The primary total eclipse isclearly visible in the U band, but undetectable in the V band. >Fromthe U observations we determined a total duration of the primary eclipse(from 1(st) to 4(rd) contact) of 1(d) .3883, with the ingress lastingonly 27 minutes. This new accurate monitoring and timing of the eclipseallowed us to improve the system solution which leads to R_C=8.8Rsun, T_C=4800K, R_H=0.11 Rsun, T_H=30000K for thecool and hot star respectively. The evolution of HD185510B is discussedalso in relation to the evolutionary status of HD 185510A and thesynchronization time scale. HD 185510B is probably a sdB near the zeroage extended horizontal branch, resulting from an enhanced mass loss inlate case B or case A mass exchange with a possible common envelopephase. A small amount (15-20%) of mass loss from the system which canaccount for the strong IR excess is suggested. The complete U B Vphotometric data set is available in electronic form at the CDS viaanonymous ftp to cdsarc.u-strasbg.fr or viahttp://cdsweb.u-strasbg.fr/Abstract.html
|Timing the eclipse of HD185510|
HD185510 (=V1379 Aql) is an eclipsing double-lined RS CVn binarycontaining a K0 III/IV giant and a hot subluminous companion. AnInternational Ultraviolet Explorer (IUE) ultraviolet light curve hasbeen obtained through the eclipse of the companion with an average timeresolution of one measurement every 19min. This was sufficient toresolve all four times of contact and, with data from previous work onthis system, to derive a solution for the absolute dimensions of thesystem. The atmospheric parameters of both components have beeninvestigated. From its out-of-eclipse flux distribution, the K0 star hasT_eff=4500+/-300K and appears to be metal-deficient. However, thesemeasurements are sensitive to the fractional spot coverage at the timephotometry was obtained. The IUE flux distribution, low-resolutionLyalpha profile and a noisy high-resolution UV spectrum of the hotcompanion have been analysed to obtain T_eff=31500+/-1500K,logg=7.2+/-0.3 and E(B-V)= 0.13+/-0.03. C and Si are deficient by ~1dex; it is not possible to deduce other metal abundances from theexisting data. The spectroscopic gravity is higher than indicated by theeclipse geometry, indicating a weakness in the Lyalpha analysis.Neglecting Lyalpha, an alternative solution of T_eff=31000+/-1500K,logg=605+/-0.2 and E(B-V)= 0.1+/-0.03 is obtained from the orbitalsolution below. The relative radii of the subdwarf and K giant arerelated by the secondary-to-primary ratio r_s/r_p=0. 0058+/-0.0010.These data were used with the eclipse geometry in an attempt to obtainthe orbital inclination. In order to avoid severe contradictions withother diagnostics it was necessary to introduce a non-negligible eclipsedue to the cool star atmosphere. Whilst available data favour i=90+/-5,uncertainties introduced by the atmospheric eclipse meant that i~80 degis also possible. With i=90 deg, the masses of the cool and hot starsare 2.27+/-0.17 and 0.304+/-0.015M_solar respectively. Whilst thehigh-gravity (Lyalpha) solution indicates the identification of the hotstar as a helium white dwarf, the orbital solution favours anidentification with sdOB stars such as SB707. A final resolution of thenature of the hot star is limited partly by data quality but also, to alarge extent, by the intrinsic properties of the system itself.
|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.
|Classification of Population II Stars in the Vilnius Photometric System. II. Results|
The results of photometric classification of 848 true and suspectedPopulation II stars, some of which were found to belong to Population I,are presented. The stars were classified using a new calibrationdescribed in Paper I (Bartkevicius & Lazauskaite 1996). We combinethese results with our results from Paper I and discuss in greaterdetail the following groups of stars: UU Herculis-type stars and otherhigh-galactic-latitude supergiants, field red horizontal-branch stars,metal-deficient visual binaries, metal-deficient subgiants, stars fromthe Catalogue of Metal-deficient F--M Stars Classified Photometrically(MDPH; Bartkevicius 1993) and stars from one of the HIPPARCOS programs(Bartkevicius 1994a). It is confirmed that high galactic latitudesupergiants from the Bartaya (1979) catalog are giants or even dwarfs.Some stars, identified by Rose (1985) and Tautvaisiene (1996a) as fieldRHB stars, appear to be ordinary giants according to our classification.Some of the visual binaries studied can be considered as physical pairs.Quite a large fraction of stars from the MDPH catalog are found to havesolar metallicity. A number of new possible UU Herculis-type stars, RHBstars and metal-deficient subgiants are identified.
|The UV O I triplet and H Lyman beta pumping in the zeta Aurigae star HR 6902.|
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1996MNRAS.283...77M&db_key=AST
|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|
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