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Two Micron All Sky Survey, Infrared Astronomical Satellite, and Midcourse Space Experiment Color Properties of Intrinsic and Extrinsic S Stars
We attempt to select new candidate intrinsic and extrinsic S stars inthe General Catalogue of Galactic S Stars (GCGSS) by combining data fromthe Two Micron All Sky Survey, the Infrared Astronomical Satellite, andthe Midcourse Space Experiment. Catalog entries are cross-identified,yielding 528 objects, out of which 29 are known extrinsic S stars and 31are known intrinsic S stars. Their color-color diagrams,(H-[12])-(K-[12]) and (K-[12])-(J-[25]), are drawn and used to identifya new sample of 147 extrinsic and 256 intrinsic S star candidates, whilethe nature of 65 stars remains identified. We infer that about 38%+/-10%of the GCGSS objects are of extrinsic type. Moreover, we think thatcolors such as J-[25] can be used to split off the two categories of Sstars, while single colors are not appropriate. The color-colordiagrams, such as (H-[12])-(K-[12]) and (K-[12])-(J-[25]), are proven tobe powerful tools for distinguishing the two kinds of S stars.
| 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
| 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.
| New periodic variables from the Hipparcos epoch photometry
Two selection statistics are used to extract new candidate periodicvariables from the epoch photometry of the Hipparcos catalogue. Theprimary selection criterion is a signal-to-noise ratio. The dependenceof this statistic on the number of observations is calibrated usingabout 30000 randomly permuted Hipparcos data sets. A significance levelof 0.1 per cent is used to extract a first batch of candidate variables.The second criterion requires that the optimal frequency be unaffectedif the data are de-trended by low-order polynomials. We find 2675 newcandidate periodic variables, of which the majority (2082) are from theHipparcos`unsolved' variables. Potential problems with theinterpretation of the data (e.g. aliasing) are discussed.
| 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 74th Special Name-list of Variable Stars
We present the Name-list introducing GCVS names for 3153 variable starsdiscovered by the Hipparcos mission.
| CO observations and mass loss of MS- and S-stars
We present (12) CO J = 1-0 and 2-1 observations of 14 S-stars, andreport 6 new detections. Two stars were observed in the (13) CO J = 1-0and 2-1 lines, and one tentative 2-1 detection is reported. Acompilation is presented of all CO observations of S-stars. The stars inthis sample are separated into ``intrinsic'' and ``extrinsic'' S-stars,based on direct observation of the Technetium line, or infraredproperties. The dust mass loss rate per unit distance is derived fromIRAS 60 mu m data taking into the fact that for small mass loss ratesthe observed flux is an overestimate of the excess emission due to dust.The gas mass loss rate per unit distance is derived from CO data.Distances and luminosities are estimated, partly from hipparcos parallaxdata. The largest mass loss rate derived is that for W Aql with(0.8-2.0) x 10(-5) {Msun} yr(-1) , and the lowest is that foro Ori with <1.2 x 10(-9) {Msun} yr(-1) . The S-starswithout Tc have smaller mass loss rates, than those with Tc. Diagramsshowing mass loss rate, dust-to-gas ratio and expansion velocity versuspulsation period are presented, and compared to similar data for carbon-and oxygen-rich Miras. The S-Miras stand not out in any way from the C-or O-Miras in these diagrams. In the diagram with expansion velocityversus pulsation period, the S-SRs span the same range in velocity asthe S-Miras, but they have periods which are about a factor of 2.5shorter. This was previously noted for O-rich SRs. As in that case, themost straightforward explanantion is that the SRs among the S-starspulsate in a higher order pulsation mode. Based on data from the ESAhipparcos astrometry satellite.
| 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
| 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.
| 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.
| Circumstellar CO emission in S stars. I. Mass-loss with little or no dust.
47 S stars have been searched for circumstellar CO (J=1-0 and/or 2-1)emission, and 29 have been detected, including 4 which show no evidenceof dust in their IRAS LRS spectra, and one with possibly no Tc (andtherefore not an AGB star). Six stars show anomalous features in theirprofiles, showing the presence of more than one kinematic component inthe expanding outflow. Two stars may have detached-shell envelopes. Theexpansion velocity distribution for S stars envelopes is different thanthat for C-rich stars, with the former having a slightly lower meanexpansion velocity, and a significantly higher fraction of objects withvery low expansion velocities (<~5.5km/s). In most S stars, themass-loss rates are >2x10^-7^Msun_/yr and the gas-to-dustratios are >1000. Our detection of CO in S stars with little or nodetectable dust implies substantial mass-loss in these objects. Theexpansion velocities and mass-loss rates of the relatively dust-freestars show a much steeper dependence on the the far-infrared excess({DELTA}IR_e_), as compared to the more dusty stars. This suggests thatwhen the amount of dust becomes small, mass-loss may be partially drivenby a different mechanism than radiation pressure on grains, whichprobably dominates in the dusty envelopes.
| 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
| S stars: infrared colors, technetium, and binarity
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1993A&A...271..463J&db_key=AST
| A survey for infrared excesses among high galactic latitude SAO stars
This project involves extending the previous analysis of infraredexcesses among a volume-limited sample of 134 nearby A-K main-sequencestars to a magnitude-limited sample of stars, culled from the SAOCatalog, with excesses determined from the IRAS Point Source Catalogflux density ratios. This new sample includes 5706 B-M type stars, 379of which have infrared excesses. The objective involved use of astatistically complete survey of objects in a standard catalog in orderto assess the frequency with which different physical processes canaffect the infrared output of stars. These processes include, but arenot limited to, orbiting cold particle clouds and the onset of rapidmass loss. It is concluded that cold disks are consistent with theinfrared excesses found among A-G dwarfs and G-K giants in the sample.
| Emission features in IRAS low-resolution spectra of MS, S and SC stars
A progression of emission features due to dust grains in the 8-22-micronregion of IRAS low-resolution spectra has been detected which parallelstheir increasing C:O ratio and s-process enhancement. Strong S starstypically have a 9-14-micron emission feature which peaks around 10.8microns, while mild S or MS stars reveal a variety of features such as athree-component feature and a 10-micron silicate emission. The infraredexcesses in the 8-22-micron region are found to correlate with theperiod of Mira S, MS, and SC variables and to increase sharply for Miravariables with periods of between 380 and 400 days.
| IRAS catalogues and atlases - Atlas of low-resolution spectra
Plots of all 5425 spectra in the IRAS catalogue of low-resolutionspectra are presented. The catalogue contains the average spectra ofmost IRAS poiont sources with 12 micron flux densities above 10 Jy.
| A General Catalogue of Galactic S-Stars - ED.2
Not Available
| Catalogue of stars with CaII H and K emissions
Not Available
| A composite Hertzsprung-Russell diagram for the peculiar red giants
A composite H-R diagram for the peculiar red giants of the diskpopulation is constructed using the available data for stars of types R,N, S, SC, MS, and Ba, along with theoretical evolutionary tracks. The N,S, SC, and MS stars approximately coincide with the sequence of normal Mgiants in the H-R diagram and can be identified with thehelium-shell-flash phase of evolution. The early R stars and most Bastars occupy the same region of the H-R diagram as normal K giants; thepositions of these stars cannot be reconciled with currentstellar-evolution calculations.
| A general catalogue of S stars.
Not Available
| Spectral classfication of some southern late-type peculiar stars
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1963MNRAS.126...61W&db_key=AST
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Observation and Astrometry data
| Constellation: | Pavo |
| Right ascension: | 20h14m25.80s |
| Declination: | -62°16'45.1" |
| Apparent magnitude: | 6.785 |
| Distance: | 847.458 parsecs |
| Proper motion RA: | -3.9 |
| Proper motion Dec: | -6.2 |
| B-T magnitude: | 8.998 |
| V-T magnitude: | 6.968 |
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