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Hipparcos red stars in the HpV_T2 and V I_C systems
For Hipparcos M, S, and C spectral type stars, we provide calibratedinstantaneous (epoch) Cousins V - I color indices using newly derivedHpV_T2 photometry. Three new sets of ground-based Cousins V I data havebeen obtained for more than 170 carbon and red M giants. These datasetsin combination with the published sources of V I photometry served toobtain the calibration curves linking Hipparcos/Tycho Hp-V_T2 with theCousins V - I index. In total, 321 carbon stars and 4464 M- and S-typestars have new V - I indices. The standard error of the mean V - I isabout 0.1 mag or better down to Hp~9 although it deteriorates rapidly atfainter magnitudes. These V - I indices can be used to verify thepublished Hipparcos V - I color indices. Thus, we have identified ahandful of new cases where, instead of the real target, a random fieldstar has been observed. A considerable fraction of the DMSA/C and DMSA/Vsolutions for red stars appear not to be warranted. Most likely suchspurious solutions may originate from usage of a heavily biased color inthe astrometric processing.Based on observations from the Hipparcos astrometric satellite operatedby the European Space Agency (ESA 1997).}\fnmsep\thanks{Table 7 is onlyavailable 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/qcat?J/A+A/397/997
| Zirconium to Titanium Ratios in a Large Sample of Galactic S Stars
The [Zr/Ti] ratio for a large sample of Galactic S stars has beendetermined using high-quality, high-resolution spectra. The pattern ofZr enhancements in intrinsic and extrinsic S stars is found to differ,and the [Zr/Ti] ratio in the extrinsic S stars clearly links them to thestrong barium stars. In addition, the pattern of [Zr/Ti] ratios seems toindicate that the progression of spectral type M to MS to S to SC is duelargely to an increase in the abundance of s-process elements and notsolely to a changing C/O ratio as claimed by some investigators (such asScalo and Ross).
| The Henize sample of S stars. IV. New symbiotic stars
The properties of the few symbiotic stars detected among the 66 binary Sstars from the Henize sample are discussed. Two stars (Hen 18 and Hen121) exhibit both a strong blue-violet continuum and strongHalpha emission (FWHM of 70 km s-1), whereas Hen134 and 137 exhibit weak Halpha emission. TheHalpha profiles are typical of non-dusty symbiotic starsbelonging to class S-3 as defined by Van Winckel et al. (1993, A&AS102, 401). In that class as in the Henize symbiotic S stars, He I, [NII] or [S II] emission lines are absent, suggesting that the nebulardensity is high but the excitation rather low. The radial velocity ofthe centre of the Halpha emission is identical to that of thecompanion star (at least for Hen 121 where this can be checked from theavailable orbital elements), thus suggesting that the Halphaemission originates in gas moving with the companion star. For Hen 121,this is further confirmed by the disappearance of the ultraviolet Balmercontinuum when the companion is eclipsed by the S star. Hen 121 is thusthe second eclipsing binary star discovered among extrinsic S stars (thefirst one is HD 35155). A comparison of the available data on orbitalperiods and Halpha emission leads to the conclusion thatHalpha emission in s stars seems to be restricted to binarysystems with periods in the range 600-1000 d, in agreement with thesituation prevailing for red symbiotic stars (excluding symbioticnovae). Symbiotic S stars are found among the most evolved extrinsic Sstars. Based on observations carried out at the European SouthernObservatory (ESO, La Silla, Chile; program 60.E-0805) and at the Swiss70 cm telescope (La Silla, Chile).
| Near-infrared observations of candidate extrinsic S stars
Photometric observations in the near infrared for 161 S stars, including18 Tc-rich (intrinsic) stars, 19 Tc-deficient (extrinsic) ones and 124candidates for Tc-deficient S stars, are presented in this paper. Basedon some further investigations into the infrared properties of bothTc-rich and Tc-deficient S stars, 104 candidates are identified as verylikely Tc-deficient S stars. The large number of infrared-selectedTc-deficient S stars provides a convenient way to study the physicalproperties and the evolutionary status of this species of S stars.
| The Coudé Echelle Spectrograph for the Xinglong 2.16 Telescope
A brief description of the NAO coudé echelle spectrograph mountedon the 2.16 m telescope at Xinglong station is given. This echellespectrograph is located at the coudé focus with a prism crossdisperser. The echelle image covers the spectral region from 330 to 1100nm displayed in 80 spectral orders in one exposure through two lightbeams. With a slit height of 2 mm, spectral orders are separated by 15to 23 pixels in blue region and by 7 to 19 pixels in red region.Alternatively, two additional resolution modes corresponding todifferent focal length cameras with resolving power R =16 000, 170 000in the blue beam and R = 13 000, 170 000 in the red beam could beprovided by this spectrograph. The bias, dark, wavelength calibration,flat field and science exposure are described in details. The limitingmagnitude for 1 hour exposure with an S/N ratio of 100 scales to V = 9.5in the red path and to V = 7.2 in the blue path.
| Nucleosynthesis and Mixing on the Asymptotic Giant Branch. III. Predicted and Observed s-Process Abundances
We present the results of s-process nucleosynthesis calculations forasymptotic giant branch (AGB) stars of different metallicities anddifferent initial stellar masses (1.5 and 3 Msolar), and wepresent comparisons of them with observational constraints fromhigh-resolution spectroscopy of evolved stars over a wide metallicityrange. The computations were based on previously published stellarevolutionary models that account for the third dredge-up phenomenonoccurring late on the AGB. Neutron production is driven by the13C(α,n)16O reaction during the interpulseperiods in a tiny layer in radiative equilibrium at the top of the He-and C-rich shell. The neutron source 13C is manufacturedlocally by proton captures on the abundant 12C; a few protonsare assumed to penetrate from the convective envelope into the radiativelayer at any third dredge-up episode, when a chemical discontinuity isestablished between the convective envelope and the He- and C-richzones. A weaker neutron release is also guaranteed by the marginalactivation of the reaction 22Ne(α,n)25Mgduring the convective thermal pulses. Owing to the lack of a consistentmodel for 13C formation, the abundance of 13Cburnt per cycle is allowed to vary as a free parameter over a wideinterval (a factor of 50). The s-enriched material is subsequently mixedwith the envelope by the third dredge-up, and the envelope compositionis computed after each thermal pulse. We follow the changes in thephotospheric abundance of the Ba-peak elements (heavy s [hs]) and thatof the Zr-peak ones (light s [ls]), whose logarithmic ratio [hs/ls] hasoften been adopted as an indicator of the s-process efficiency (e.g., ofthe neutron exposure). Our model predictions for this parameter show acomplex trend versus metallicity. Especially noteworthy is theprediction that the flow along the s-path at low metallicities drainsthe Zr and Ba peaks and builds an excess at the doubly magic208Pb, which is at the termination of the s-path. We thendiscuss the effects on the models of variations in the crucialparameters of the 13C pocket, finding that they are notcritical for interpreting the results. The theoretical predictions arecompared with published abundances of s-elements for AGB giants ofclasses MS, S, SC, post-AGB supergiants, and for various classes ofbinary stars, which supposedly derive their composition by mass transferfrom an AGB companion. This is done for objects belonging both to theGalactic disk and to the halo. The observations in general confirm thecomplex dependence of neutron captures on metallicity. They suggest thata moderate spread exists in the abundance of 13C that isburnt in different stars. Although additional observations are needed,it seems that a good understanding has been achieved of s-processoperation in AGB stars. Finally, the detailed abundance distributionincluding the light elements (CNO) of a few s-enriched stars atdifferent metallicities are examined and satisfactorily reproduced bymodel envelope compositions.
| Rapidly oscillating M giant stars?
The Hipparcos mission discovered a few dozen M giant stars with periodsP shorter than 10d. Similar stars may be found in other large data basesof new variables (e.g., OGLE). The three possible sources of themagnitude variations - pulsation, starspots and ellipsoidal deformation- are discussed in general terms. The parallaxes and V-I colour indicesare used to calculate radii and temperatures for all M giant variableswith P<100d. Masses are estimated from the positions of the stars ina Hertzsprung-Russell (HR) diagram, using evolutionary tracks. Usingthese data, it is shown that starspots can be ruled out as a variabilitymechanism in almost all cases, and ellipsoidal variations in about halfof the stars. Pulsation in very high-overtone modes appears to be theonly viable explanation for the stars with P<10d. Many of the starsmay be multiperiodic. IRAS data are used to deduce information aboutreddening and circumstellar dust. The apparently low level of mass-loss,as well as the kinematics and the spatial distribution of the stars,indicates that they are from a relatively young (i.e., thin disc) giantstar population.
| The 75th Name-List of Variable Stars
We present the next regular Name-List of variable stars containinginformation on 916 variable stars recently designated in the system ofthe General Catalogue of Variable Stars.
| Re-processing the Hipparcos Transit Data and Intermediate Astrometric Data of spectroscopic binaries. I. Ba, CH and Tc-poor S stars
Only 235 entries were processed as astrometric binaries with orbits inthe Hipparcos and Tycho Catalogue (\cite{Hipparcos}). However, theIntermediate Astrometric Data (IAD) and Transit Data (TD) made availableby ESA make it possible to re-process the stars that turned out to bespectroscopic binaries after the completion of the Catalogue. This paperillustrates how TD and IAD may be used in conjunction with the orbitalparameters of spectroscopic binaries to derive astrometric parameters.The five astrometric and four orbital parameters (not already known fromthe spectroscopic orbit) are derived by minimizing an objective function(chi 2) with an algorithm of global optimization. This codehas been applied to 81 systems for which spectroscopic orbits becameavailable recently and that belong to various families ofchemically-peculiar red giants (namely, dwarf barium stars, strong andmild barium stars, CH stars, and Tc-poor S stars). Among these 81systems, 23 yield reliable astrometric orbits. These 23 systems make itpossible to evaluate on real data the so-called ``cosmic error''described by Wielen et al. (1997), namely the fact that an unrecognizedorbital motion introduces a systematic error on the proper motion.Comparison of the proper motion from the Hipparcos catalogue with thatre-derived in the present work indicates that the former are indeed faroff the present value for binaries with periods in the range 3 to ~ 8years. Hipparcos parallaxes of unrecognized spectroscopic binaries turnout to be reliable, except for systems with periods close to 1 year, asexpected. Finally, we show that, even when a complete orbital revolutionwas observed by Hipparcos, the inclination is unfortunately seldomprecise. Based on observations from the Hipparcos astrometric satelliteoperated by the European Space Agency (ESA 1997).
| On the Variability of S Stars as Observed by the Hipparcos
The Hipparcos photometry of S type stars shows that they are allvariable. The intrinsic S stars show a larger range of amplitudes thando the extrinsic S stars.
| A CORAVEL radial-velocity monitoring of S stars: Symbiotic activity vs. orbital separation. III.
Orbital elements are presented for the Tc-poor S stars HR 363 (= HD7351) and HD 191226. With an orbital period of 4592 d (=12.6 y), HR 363has the longest period known among S stars, and yet it is a strong X-raysource. Its X-ray flux is similar to that of HD 35155, an S star withone of the shortest orbital periods (640 d). This surprising result isput in perspective with other diagnostics of binary interaction observedin binary S stars. They reveal that there is no correlation between thelevel of binary interaction and the orbital period. All these activitydiagnostics moreover exhibit a strong time-variability. In thewell-documented case of HR 1105, this time-variability appears to be acombination of orbital modulation and secular variation. A stream of gasfrom the red-giant wind, which is heated when funneled through the innerLagrangian point, has been proposed as the source of the hard photons\cite[(Shcherbakov & Tuominen 1992).]{S} Different viewing angles ofthe stream during the orbital cycle account for the orbital modulation,whereas long-term fluctuations of the mass-loss rate account for thesecular variations. Little dependence to the orbital separation isexpected for this kind of activity. If such streams are causing theactivity observed in the other binary S stars as well, it would providea natural explanation for the absence of correlation between orbitalperiods and activity levels, since the red-giant mass loss rate would bethe dominant factor. The existence of such funneled streams is moreoverpredicted by smooth particle hydrodynamics simulations of mass transferin detached binary systems. Based on observations performed with theSwiss telescope at the Haute-Provence Observatory, France.
| A CORAVEL radial-velocity monitoring of giant BA and S stars: Spectroscopic orbits and intrinsic variations. I.
With the aim of deriving the binary frequency among Ba and S stars, 56new spectroscopic orbits (46 and 10, respectively) have been derived forthese chemically-peculiar red giants monitored with the \coravel\spectrometers. These orbits are presented in this paper (38 orbits) andin a companion paper \cite[(Udry et al. 1998,]{Udry} Paper II; 18orbits). The results for 12 additional long-period binary stars (6 and6, respectively), for which only minimum periods (generally exceeding 10y) can be derived, are also presented here (10) and in Paper II (2). Theglobal analysis of this material, with a few supplementary orbits fromthe literature, is presented in \cite[Jorissen et al.(1998).]{Jorissen98} For the subsample of Mira S, SC and (Tc-poor) Cstars showing intrinsic radial-velocity variations due to atmosphericphenomena, orbital solutions (when available) have been retained if thevelocity and photometric periods are different (3 stars). However, it isemphasized that these orbit determinations are still tentative. Threestars have been found with radial-velocity variations synchronous withthe light variations. Pseudo-orbital solutions have been derived forthose stars. In the case of RZ Peg, a line-doubling phenomenon isobserved near maximum light, and probably reflects the shock wavepropagating through the photosphere. Based on observations obtained atthe Haute-Provence Observatory (France) and at the European SouthernObservatory (ESO, La Silla, Chile).
| Infrared study of the two categories of S stars
Photometric observations of 20 Tc-deficient and 24 Tc-rich S stars inthe near infrared are presented in this paper. With the IRAS data,infrared two color diagrams, IRAS low-resolution spectra and energydistributions are discussed to summarize the way to segregate Tc-richstars from Tc-deficient ones.
| Insights into the formation of barium and Tc-poor S stars from an extended sample of orbital elements
The set of orbital elements available for chemically-peculiar red giant(PRG) stars has been considerably enlarged thanks to a decade-longCORAVEL radial-velocity monitoring of about 70 barium stars and 50 Sstars. When account is made for the detection biases, the observedbinary frequency among strong barium stars, mild barium stars andTc-poor S stars (respectively 35/37, 34/40 and 24/28) is compatible withthe hypothesis that they are all members of binary systems. Thesimilarity between the orbital-period, eccentricity and mass-functiondistributions of Tc-poor S stars and barium stars confirms that Tc-poorS stars are the cooler analogs of barium stars. A comparative analysisof the orbital elements of the various families of PRG stars, and of asample of chemically-normal, binary giants in open clusters, revealsseveral interesting features. The eccentricity - period diagram of PRGstars clearly bears the signature of dissipative processes associatedwith mass transfer, since the maximum eccentricity observed at a givenorbital period is much smaller than in the comparison sample of normalgiants. be held The mass function distribution is compatible with theunseen companion being a white dwarf (WD). This lends support to thescenario of formation of the PRG star by accretion of heavy-element-richmatter transferred from the former asymptotic giant branch progenitor ofthe current WD. Assuming that the WD companion has a mass in the range0.60+/-0.04 Msb ȯ, the masses of mild and strong barium starsamount to 1.9+/-0.2 and 1.5+/-0.2 Msb ȯ, respectively. Mild bariumstars are not restricted to long-period systems, contrarily to what isexpected if the smaller accretion efficiency in wider systems were thedominant factor controlling the pollution level of the PRG star. Theseresults suggest that the difference between mild and strong barium starsis mainly one of galactic population rather than of orbital separation,in agreement with their respective kinematical properties. There areindications that metallicity may be the parameter blurring the period -Ba-anomaly correlation: at a given orbital period, increasing levels ofheavy-element overabundances are found in mild barium stars, strongbarium stars, and Pop.II CH stars, corresponding to a sequence ofincreasingly older, i.e., more metal-deficient, populations. PRG starsthus seem to be produced more efficiently in low-metallicitypopulations. Conversely, normal giants in barium-like binary systems mayexist in more metal-rich populations. HD 160538 (DR Dra) may be such anexample, and its very existence indicates at least that binarity is nota sufficient condition to produce a PRG star. This paper is dedicated tothe memory of Antoine Duquennoy, who contributed many among theobservations used in this study
| The HIPPARCOS Hertzsprung-Russell diagram of S stars: probing nucleosynthesis and dredge-up
HIPPARCOS trigonometrical parallaxes make it possible to compare thelocation of Tc-rich and Tc-poor S stars in the Hertzsprung-Russell (HR)diagram: Tc-rich S stars are found to be cooler and intrinsicallybrighter than Tc-poor S stars. The comparison with the Genevaevolutionary tracks reveals that the line marking the onset of thermalpulses on the asymptotic giant branch (AGB) matches well the observedlimit between Tc-poor and Tc-rich S stars. Tc-rich S stars are, asexpected, identified with thermally-pulsing AGB stars of low andintermediate masses, whereas Tc-poor S stars comprise mostly low-massstars (with the exception of 57 Peg) located either on the red giantbranch or on the early AGB. Like barium stars, Tc-poor S stars are knownto belong exclusively to binary systems, and their location in the HRdiagram is consistent with the average mass of 1.6+/-0.2 Msb ȯderived from their orbital mass-function distribution (Jorissen et al.1997, A&A, submitted). A comparison with the S stars identified inthe Magellanic Clouds and in the Fornax dwarf elliptical galaxy revealsthat they have luminosities similar to the galactic Tc-rich S stars.However, most of the surveys of S stars in the external systems did notreach the lower luminosities at which galactic Tc-poor S stars arefound. The deep Westerlund survey of carbon stars in the SMC uncovered afamily of faint carbon stars that may be the analogues of thelow-luminosity, galactic Tc-poor S stars. Based on data from theHIPPARCOS astrometry satellite
| The nucleosynthesis of heavy elements in low-mass AGB stars
We take 13C(α,n)16O as neutron source, allowfor variation of the mass of the nucleus with thermal pulse number andadopt the unbranched s process path from 56Fe to210Bi in an attempt to explain the overabundance of heavyelements in MS and S stars. We found stars with larger masses havelarger dilution factors because of a stronger convection and that thesestars fall in four different regions in the abundance diagram, thusenabling a rough estimate of the mass to be made. We show that, for a2.5 Msolar star, the third dredge-up stops after a certain number ofpulses because of the formation of a hollow shell structure, so the starwill show no Tc and this can account for the existence of binary systemsconsisting of a ``Tc-no'' AGB star with a main-sequence star companion.
| 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.
| Classification and Identification of IRAS Sources with Low-Resolution Spectra
IRAS low-resolution spectra were extracted for 11,224 IRAS sources.These spectra were classified into astrophysical classes, based on thepresence of emission and absorption features and on the shape of thecontinuum. Counterparts of these IRAS sources in existing optical andinfrared catalogs are identified, and their optical spectral types arelisted if they are known. The correlations between thephotospheric/optical and circumstellar/infrared classification arediscussed.
| Proper motions, absolute magnitudes and spatial distribution of zirconium stars.
Not Available
| A catalogue of [Fe/H] determinations: 1996 edition
A fifth Edition of the Catalogue of [Fe/H] determinations is presentedherewith. It contains 5946 determinations for 3247 stars, including 751stars in 84 associations, clusters or galaxies. The literature iscomplete up to December 1995. The 700 bibliographical referencescorrespond to [Fe/H] determinations obtained from high resolutionspectroscopic observations and detailed analyses, most of them carriedout with the help of model-atmospheres. The Catalogue is made up ofthree formatted files: File 1: field stars, File 2: stars in galacticassociations and clusters, and stars in SMC, LMC, M33, File 3: numberedlist of bibliographical references The three files are only available inelectronic form at the Centre de Donnees Stellaires in Strasbourg, viaanonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5), or viahttp://cdsweb.u-strasbg.fr/Abstract.html
| BD-21 3873: another yellow-symbiotic barium star.
An abundance analysis of the yellow symbiotic system BD-21 3873 revealsit to be a metal-poor K-giant ([Fe/H]=-1.3) which is enriched in theheavy s-process elements. In that respect, this star appears to be atwin of AG Dra, another yellow symbiotic system analyzed in a previouspaper (Smith et al., 1996A&A...315..179S). The heavy-elementabundance distributions of AG Dra and BD-21 3873 are almost identical,and are best reproduced by a s-process with a neutron exposure parameterof 1.2-1.3mb^-1^ and a neutron density logN_n_=8.3 (as derived from theRb/Zr ratio). These two systems thus link the symbiotic stars to thebinary barium and CH stars which are also s-process enriched. Thesebinary systems, which exhibit overabundances of the heavy elements, owetheir abundance peculiarities to mass transfer from thermally-pulsingasymptotic giant branch stars, which have since evolved to becomewhite-dwarf companions of the cool stars we now view as thechemically-peculiar primaries. The spectroscopic orbits of BD-21 3873(derived from CORAVEL measurements) and AG Dra are similar to those ofbarium and CH stars. With an orbital period of 281.6d, BD-21 3873 is oneof the closest systems in these families, and its light curve indeedsuggests that variations due to reflection and ellipticity effects arepresent. The amplitude of the ellipsoidal variations indicates that thegiant must be close to filling its Roche lobe. However, no acceptablesolution simultaneously satisfies the constraints from the light curve,the orbital elements and the evolutionary tracks in the framework of thestandard Roche lobe geometry. We suggest that this discrepancy may beresolved by taking into account the deformation of the Roche lobe causedby the force driving the large mass loss of the giant.
| The heavy elements nucleosynthesis in the low mass AGB stars.
Not Available
| Abundances in the symbiotic star AG Draconis: the barium-symbiotic connection.
An abundance analysis of the yellow symbiotic system AG Draconis revealsit to be a metal-poor K-giant ([Fe/H]=-1.3) which is enriched in theheavy s-process elements. This star thus provides a link between thesymbiotic stars and the binary barium and CH stars which are alsos-process enriched. These binary systems, which exhibit overabundancesof the heavy elements, owe their abundance peculiarities to masstransfer from thermally-pulsing asymptotic giant branch stars, whichhave since evolved to become white-dwarf companions of the cool stars wenow view as the chemically peculiar primaries. A comparison of theheavy-element abundance distribution in AG Dra with theoreticalnucleosynthesis calculations shows that the s-process is defined by arelatively large neutron exposure (τ=1.3mb^-1^), while an analysisof the rubidium abundance suggests that the s-process occurred at aneutron density of about 2x10^8^cm^-3^. The derived spectroscopic orbitof AG Dra is similar to the orbits of barium and CH stars. Because theluminosity function of low-metallicity K giants is skewed towards higherluminosities by about 2 magnitudes relative to solar-metallicity giants,it is argued that the lower metallicity K giants have larger mass-lossrates. It is this larger mass-loss rate that drives the symbioticphenomena in AG Dra and we suggest that the other yellow symbiotic starsare probably low-metallicity objects as well.
| New X-ray sources detected among mild barium and S stars.
We report on the detection by ROSAT of X-rays from the mild barium starHD 165141 (K0III/IIBa1) and from the S stars HD 35155 (S4,1) and HR 363(S3/2). For the S stars, the X-ray flux is attributed to the accretionof the red-giant wind by the white dwarf companion. The strongvariability observed in the X- and UV fluxes on time scales of bothhours and months may be due to irregularities in the accretion rate, orto variable obscuration by cool gas present in the system. In the caseof HD 35155, the absence of ROSAT detection at the phase where eclipsesare observed in the UV and optical domains suggests that part of theX-ray variability may be associated with eclipses of the compactcompanion. HD 165141 is more puzzling since this star seems to share theproperties of RS CVn and barium systems. The properties of the X-raysemitted by this system are typical of RS CVn systems, as is thephotometric period of 35d and the rapid rotation. However, the rapidrotation does not seem to be due to synchronism with the orbital period,as is usually the case for RS CVn systems. The companion appears to be ahot white dwarf rather than a main sequence star, with a long orbitalperiod (~5200d), more typical of barium than of RS CVn systems. Theseconflicting properties could be explained if this particular barium starformed on the giant branch, accreting not only mass but also spinangular momentum. The two giants HR 5692 (G8IIIBa0.3) and HR 6468(G8IIIBa0.6) appear to be coronal X-ray sources. The barium nature ofthese stars is questioned, given their small Ba indices and their normalDDO photometric indices. Moreover, since HR 6468 is a radial-velocitystandard star, it is likely not a binary star as required for bariumstars.
| The Chemical Composition of Red Giants. IV. The Neutron Density at the s-Process Site
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1995ApJ...450..302L&db_key=AST
| 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.
| A catalogue of associations between IRAS sources and S stars.
Cross identifications between the General Catalogue of Galactic S Stars(GCGSS), the IRAS Point Source Catalogue (PSC), and the Guide StarCatalogue (GSC) are presented. The purpose of the present catalogue isi) to provide a clean sample of S stars with far-IR data, and ii) toprovide accurate GSC positions for S stars, superseding those listed inthe GCGSS. The IRAS colour-colour diagram and the galactic distributionof S stars associated with an IRAS source are presented. Several S starshaving extended images in at least one IRAS band have also beenidentified.
| Radio continuum emission from stars: a catalogue update.
An updated version of my catalogue of radio stars is presented. Somestatistics and availability are discussed.
| Circumstellar Properties of S Stars. I. Dust Features
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1993ApJ...416..769C&db_key=AST
| Companions to bright S and MS stars - Technetium deficiency and binarity
To test the popular hypothesis that technetium-deficient stars ofspectral types S and MS are mass-transfer binaries, we have searched forultraviolet light from the putative hot secondaries in spectra takenwith the SWP spectrograph of IUE. Although most S and MS stars areapparently thermally pulsing AGB (asymptotic giant branch) stars whosesurfaces have been enriched with s-process elements and carbon dredgedup from the interior, those stars whose spectra show enhanced s-processelements but no Tc are widely believed to be cooler analogs of the Ba IIstars, which apparently owe their unusual abundances to prior masstransfer, the Tc from which has decayed away. We report IUE observationsof 15 S and MS stars with the SWP, including the identification of sixhot companions. Assembling all the IUE observations made to date, wefind clear support for the mass-transfer hypothesis, confirming evidencefrom other lines of research. We further discuss the ages of thecompanions and the implications of these discoveries for stellarevolution.
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