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Correlations between Lithium and Technetium Absorption Lines in the Spectra of Galactic S Stars
Correlations between the presence of the 6707 Å line of lithiumand the resonance lines of technetium (4238 and 4262 Å) in a largesample of Galactic S stars are analyzed. Half of the sample stars areintrinsic S stars (those exhibiting technetium in their spectra), and1/3 of these stars also have strong lithium lines in their spectra.Stars having both lithium and technetium in their spectra areinterpreted as intermediate-mass thermally pulsating asymptotic giantbranch (TP-AGB) stars in which lithium is produced by the Cameron-Fowlermechanism. The production of lithium is predicted to occur inhigh-luminosity (Mbol<=-6) TP-AGB stars by the hot-bottomburning (HBB) mechanism. Data on the carbon isotope ratios of stars inour sample agree with the predictions of HBB; however, oxygen isotoperatios in these stars do not agree with the predictions of HBB.Furthermore, the available luminosities for our sample stars are belowthe minimum value necessary for HBB to occur in available models.Cool-bottom processing (CBP) is one possible explanation for thepresence of lithium in the spectra of these stars. Intrinsic S starshaving technetium but no lithium in their spectra are interpreted aslower mass (1.5-3 Msolar) thermally pulsating AGB stars thathave not undergone CBP. Extrinsic S stars constitute the remaining halfof the sample. Carbon and oxygen isotope ratios, as well as the lack oftechnetium and lithium in the spectra of these stars, are consistentwith these being low-mass red giant branch stars (1-2Msolar), with mass transfer from a now extinct thermallypulsating AGB star being responsible for the enhanced abundance ofs-process elements.
| Pulkovo compilation of radial velocities for 35495 stars in a common system.
Not Available
| Galactic model parameters for field giants separated from field dwarfs by their 2MASS and V apparent magnitudes
We present a method which separates field dwarfs and field giants bytheir 2MASS and V apparent magnitudes. This method is based onspectroscopically selected standards and is hence reliable. We appliedit to stars in two fields, SA 54 and SA 82, and we estimated a full setof Galactic model parameters for giants including their total localspace density. Our results are in agreement with the ones given in therecent literature.
| Really Cool Stars and the Star Formation History at the Galactic Center
We present λ/Δλ=550-1200 near-infrared H and Kspectra for a magnitude-limited sample of 79 asymptotic giant branch andcool supergiant stars in the central ~5 pc (diameter) of the Galaxy. Weuse a set of similar spectra obtained for solar neighborhood stars withknown Teff and Mbol that is in the same range asthe Galactic center (GC) sample to derive Teff andMbol for the GC sample. We then construct the H-R diagram forthe GC sample. Using an automated maximum likelihood routine, we derivea coarse star formation history of the GC. We find that (1) roughly 75%of the stars formed in the central few parsecs are older than 5 Gyr; (2)the star formation rate (SFR) is variable over time, with a roughly 4times higher SFR in the last 100 Myr compared to the average SFR; (3)our model can match dynamical limits on the total mass of stars formedonly by limiting the initial mass function to masses above 0.7Msolar (this could be a signature of mass segregation or ofthe bias toward massive star formation from the unique star formationconditions in the GC); (4) blue supergiants account for 12% of the totalsample observed, and the ratio of red to blue supergiants is roughly1.5; and (5) models with isochrones with [Fe/H]=0.0 over all ages fitthe stars in our H-R diagram better than models with lower [Fe/H] in theoldest age bins, consistent with the finding of Ramírez et al.that stars with ages between 10 Myr and 1 Gyr have solar [Fe/H].
| 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.
| 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
| 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.
| 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
| Fluorine in red giant stars - Evidence for nucleosynthesis
Flourine abundances were determined in several K giants and asymptoticgiant branch (AGB) stars, using the infrared vibration-rotation lines ofHF. The data presented constitute the only available information on thefluorine abundance outside the solar system and provide invaluable cluesto the question of the nucleosynthetic origin of F. The observationsconfirm that F production occurs at a He-burning site and constrain thecurrent models of AGB stars.
| S stars without technetium - The binary star connection
An exploratory survey of non-Mira MS and S star radial velocities andthe He I 10830 A triplet are used to test the assertion that S starswithout Tc are spectroscopic binaries, probably with white-dwarfcompanions. It is found that the He I 10830 A triplet is a prominentfeature of the spectra of S stars without Tc, but the He I line isundetectable in the spectra of most S stars without Tc. Also, whenradial-velocity variations attributable to orbital motion are detectedfor S stars without Tc, the variations have a higher frequency that thatof S stars with Tc. The results suggest that the S stars without Tc arespectroscopic binaries and are probably related to the G and K giantBarium stars.
| The chemical composition of red giants. III - Further CNO isotopic and s-process abundances in thermally pulsing asymptotic giant branch stars
Near-IR and IR spectra are analyzed to obtain elemental and isotopic C,N, and O abundance, iron peak abundances, and heavy element s-processabundances for a sample of M, MS, and S giants. The compositions of theM giants are similar to those of G and K giants and consistent withpredictions for giants that have deep convective envelopes and so haveexperienced the first dredge-up. The MS and S giants have compositionsthat show the signatures of the third dredge-up that occurs in thermallypulsing AGB stars. The sample shows that C-12, a principal product ofthe He-burning shell, has been added to the envelopes of MS and S stars.The C-12 enrichment is correlated with a more marked enrichment of thes-process elements that are predicted to be synthesized when a neutronsource is ignited in the He-burning shell. The MS and S giants show ahigher N abundance than the M giants, attributed to the expected deepmixing that occurs with the onset of the episodic third dredge-up.
| The Perkins catalog of revised MK types for the cooler stars
A catalog is presented listing the spectral types of the G, K, M, and Sstars that have been classified at the Perkins Observatory in therevised MK system. Extensive comparisons have been made to ensureconsistency between the MK spectral types of stars in the Northern andSouthern Hemispheres. Different classification spectrograms have beengradually improved in spite of some inherent limitations. In thecatalog, the full subclasses used are the following: G0, G5, G8, K0, K1,K2, K3, K4, K5, M0, M1, M2, M3, M4, M5, M6, M7, and M8. Theirregularities are the price paid for keeping the general scheme of theoriginal Henry Draper classification.
| A General Catalogue of Galactic S-Stars - ED.2
Not Available
| A revised spectral classification system in the red for S stars
Low-dispersion observations of S stars in the region 5450-7000 A havebeen used to establish a revised temperature classification scheme forthese objects. Bands of TiO and ZrO and the Na D lines are found to beuseful in placing all S type stars on a common temperature scale.Temperature subtypes for those objects exhibiting both ZrO and TiO bandsare assigned by a modified version of the Keenan 1954 system. For thepure S stars, a new system is introduced utilizing the ZrO bands and theD lines. Comparisons between the revised types and photometric colorsdemonstrate an improvement over Kennan's system, especially for the pureS stars. Further, a new abundance index is proposed based on therelative strength of the bands of YO as compared to ZrO and TiO. Itappears that this index is fundamentally related to the C/O ratio,though it may also be affected somewhat by the general enhancement ofs-process elements.
| A general catalogue of S stars.
Not Available
| Classification of the S-Type Stars.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1954ApJ...120..484K&db_key=AST
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| Yükselim: | +06°09'05.0" |
| Görünürdeki Parlaklýk: | 8.98 |
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