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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).
| The Henize sample of S stars. II. Data
This paper presents data collected on the Henize sample of 205 S stars:(i) CORAVEL radial-velocity data; (ii) photometric data in the UBV bandsof the Geneva photometric system; (iii) photometric data in the JHKLbands of the SAAO photometric system; (iv) IRAS fluxes; (v)low-resolution spectra of 158 S stars. Close visual companions have beenfound for Hen 47, 94, 105 and 155. Spectroscopic orbital elements areprovided for Hen 2, 108, 121, 137 and 147. The analysis of these data ispresented in a companion paper. Based on observations carried out at theEuropean Southern Observatory (ESO, La Silla, Chile), at the 70~cm Swisstelescope at ESO and at the South African Astronomical Observatory.
| 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
| 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.
| A General Catalogue of Galactic S-Stars - ED.2
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| A general catalogue of S stars.
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