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Polarimetry of Li-rich giants
Context: .Protoplanetary nebulae typically present non-sphericalenvelopes. The origin of such geometry is still controversial. There areindications that it may be carried over from an earlier phase of stellarevolution, such as the AGB phase. But how early in the star's evolutiondoes the non-spherical envelope appear? Aims.Li-rich giants show dustycircumstellar envelopes that can help answer that question. We study asample of fourteen Li-rich giants using optical polarimetry in order todetect non-spherical envelopes around them. Methods.We used the IAGPOLimaging polarimeter to obtain optical linear polarization measurementsin {V} band. Foreground polarization was estimated using the field starsin each CCD frame.Results.After foreground polarization was removed,seven objects presented low intrinsic polarization (0.19-0.34)% and two(V859 Aql and GCSS 557) showedhigh intrinsic polarization values (0.87-1.16)%. This intrinsicpolarization suggests that Li-rich giants present a non-sphericaldistribution of circumstellar dust. The intrinsic polarization level isprobably related to the viewing angle of the envelope, with higherlevels indicating objects viewed closer to edge-on. The correlation ofthe observed polarization with optical color excess gives additionalsupport to the circumstellar origin of the intrinsic polarization inLi-rich giants. The intrinsic polarization correlates even better withthe IRAS 25 μ m far infrared emission. Analysis of spectral energydistributions for the sample show dust temperatures for the envelopesthat tend to be between 190 and 260 K. We suggest that dust scatteringis indeed responsible for the optical intrinsic polarization in Li-richgiants.Conclusions.Our findings indicate that non-spherical envelopesmay appear as early as the red giant phase of stellar evolution.
| Classification of Spectra from the Infrared Space Observatory PHT-S Database
We have classified over 1500 infrared spectra obtained with the PHT-Sspectrometer aboard the Infrared Space Observatory according to thesystem developed for the Short Wavelength Spectrometer (SWS) spectra byKraemer et al. The majority of these spectra contribute to subclassesthat are either underrepresented in the SWS spectral database or containsources that are too faint, such as M dwarfs, to have been observed byeither the SWS or the Infrared Astronomical Satellite Low ResolutionSpectrometer. There is strong overall agreement about the chemistry ofobjects observed with both instruments. Discrepancies can usually betraced to the different wavelength ranges and sensitivities of theinstruments. Finally, a large subset of the observations (~=250 spectra)exhibit a featureless, red continuum that is consistent with emissionfrom zodiacal dust and suggest directions for further analysis of thisserendipitous measurement of the zodiacal background.Based on observations with the Infrared Space Observatory (ISO), aEuropean Space Agency (ESA) project with instruments funded by ESAMember States (especially the Principle Investigator countries: France,Germany, Netherlands, and United Kingdom) and with the participation ofthe Institute of Space and Astronautical Science (ISAS) and the NationalAeronautics and Space Administration (NASA).
| Rapidly Rotating Lithium-rich K Giants: The New Case of the Giant PDS 365
PDS 365 is a newly detected, rapidly rotating (vsini=20 kms-1), single, low-mass giant star that with HD 233517 and HD219025 forms a remarkable ensemble of single K giants with the uniqueproperties of rapid rotation, very strong Li lines, an asymmetricalHα profile, and a large far-infrared excess. Their vsini valuesare between 18 and 23 km s-1, and their LTE Li abundances,logɛ(Li), are between 2.9 and 3.9. Detailed analysis of PDS 365reveals it to be a ~1 Msolar giant with a value of12C/13C approximately equal to 12. A clearrelation between high rotational velocities and very high Li abundancesfor K giant stars is found only when asymmetrical Hα profiles andlarge far-infrared excesses are present. If we consider single K giants,we find that among rapid (vsini>=8 km s-1) rotators, avery large proportion (~50%) are Li-rich giants. This proportion is incontrast with a very low proportion (~2%) of Li-rich stars among themuch more common slowly rotating K giants. This striking difference isdiscussed in terms of proposed mechanisms for Li enrichment.
| Two K Giants with Supermeteoritic Lithium Abundances: HDE 233517 and HD 9746
Two unusual Li-rich K giants, HDE 233517 and HD 9746, have been studied.Optical spectroscopy and photometry have been obtained to determine thefundamental parameters of HDE 233517, a single K2 III with an extremelylarge infrared excess. The spectra yield Teff=4475 K,logg=2.25, [Fe/H]=-0.37, vsini=17.6 km s-1, and a non-LTElogɛ(7Li)=4.22. Photometric observations reveallow-amplitude light variability with a period of 47.9 days. Combinedwith other parameters, this results in a minimum radius of 16.7Rsolar and minimum distance of 617 pc. Comparison of spectraobtained in 1994 and 1996 show profile variations in Hα and the NaD lines indicative of changing mass loss. Optical spectra of HD 9746, achromospherically active giant, were analyzed. The Teff=4400K and revised Hipparcos-based gravity of logg=2.30 lead to a non-LTElogɛ(7Li)=3.75. The Li abundances in both stars aresupermeteoritic. By the inclusion and exclusion of 6Li in thesyntheses, we show that consistent 7Li abundances areobtained only when 6Li is absent in the synthetic fit. Thisprovides evidence for fresh 7Li production and excludes bothpreservation of primordial Li and planetary accretion as viablescenarios for the formation of Li-rich giants. Both stars lie in closeproximity to the red giant luminosity bump supporting the hypothesisthat 7Li production is caused by the same mixing mechanismthat later results in CN processing and lowers the12C/13C ratio to nonstandard values.
| The Nature of the lithium rich giants. Mixing episodes on the RGB and early-AGB
We present a critical analysis of the nature of the so-called Li-richRGB stars. For a majority of the stars, we have used Hipparcosparallaxes to determine masses and evolutionary states by comparingtheir position on the Hertzsprung-Russell diagram with theoreticalevolutionary tracks. Among the twenty Li-rich giants whose location onthe HR diagram we were able to determine precisely, five appear to beLi-rich because they have not completed the standard first dredge-updilution, and three have abundances compatible with the maximum allowedby standard dilution. Thus, these should be re-classified as Li-normal.For the remaining stars, the high Li abundance must be a result of freshsynthesis of this fragile element. We identify two distinct episodes ofLi production which occur in advanced evolutionary phases depending uponthe mass of the star. Low-mass RGB stars, which later undergo the heliumflash, produce Li at the phase referred to as the bump in the luminosityfunction. At this evolutionary phase, the outwardly-moving hydrogenshell burns through the mean molecular weight discontinuity created bythe first dredge-up. Any extra-mixing process can now easily connect the3He-rich envelope material to the outer regions of thehydrogen-burning shell, enabling Li production by the Cameron &Fowler (1971) process. While very high Li abundances are then reached,this Li-rich phase is extremely short lived because once the mixingextends deep enough to lower the carbon isotopic ratio below thestandard dilution value, the freshly synthesized Li is quicklydestroyed. In intermediate-mass stars, the mean molecular weightgradient due to the first dredge-up is not erased until after the starhas begun to burn helium in its core. The Li-rich phase in these starsoccurs when the convective envelope deepens at the base of the AGB,permitting extra-mixing to play an effective role. Li production ceaseswhen a strong mean molecular weight gradient is built up between thedeepening convective envelope and the shell of nuclear burning thatsurrounds the inert CO core. This episode is also very short lived.Low-mass stars may undergo additional mixing at this phase. The compileddata provide constraints on the time scales for extra mixing and someinsight on processes suggested in the literature. However, our resultsdo not suggest any specific trigger mechanism. Since the Li-rich phasesare extremely short, enrichment of the Li content of the ISM as a resultof these episodes is negligible.
| Speckle Interferometry of New and Problem HIPPARCOS Binaries
The ESA Hipparcos satellite made measurements of over 12,000 doublestars and discovered 3406 new systems. In addition to these, 4706entries in the Hipparcos Catalogue correspond to double star solutionsthat did not provide the classical parameters of separation and positionangle (rho,theta) but were the so-called problem stars, flagged ``G,''``O,'' ``V,'' or ``X'' (field H59 of the main catalog). An additionalsubset of 6981 entries were treated as single objects but classified byHipparcos as ``suspected nonsingle'' (flag ``S'' in field H61), thusyielding a total of 11,687 ``problem stars.'' Of the many ground-basedtechniques for the study of double stars, probably the one with thegreatest potential for exploration of these new and problem Hipparcosbinaries is speckle interferometry. Results are presented from aninspection of 848 new and problem Hipparcos binaries, using botharchival and new speckle observations obtained with the USNO and CHARAspeckle cameras.
| 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.
| 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.
| The ROSAT all-sky survey catalogue of optically bright late-type giants and supergiants
We present X-ray data for all late-type (A, F, G, K, M) giants andsupergiants (luminosity classes I to III-IV) listed in the Bright StarCatalogue that have been detected in the ROSAT all-sky survey.Altogether, our catalogue contains 450 entries of X-ray emitting evolvedlate-type stars, which corresponds to an average detection rate of about11.7 percent. The selection of the sample stars, the data analysis, thecriteria for an accepted match between star and X-ray source, and thedetermination of X-ray fluxes are described. Catalogue only available atCDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/Abstract.html
| 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.
| 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
| Giants with infrared excess.
We have correlated optical and infrared catalogs in order to extract alarge sample of luminosity class III stars with known infrared fluxdensities. For a non-negligible fraction of G and K giants, afar-infrared excess emission was found, starting beyond 25μm. Anexplanation in terms of present-day mass loss thus becomes unlikely,since the dust should then be warmer and the excess emission less far inthe infrared. We believe that the far-infrared excesses of theseobjects, most likely first-ascent giants, are related to the Vegaphenomenon. The dusty disks around these stars, gradually cooled downduring their main-sequence phase, could be reheated once the star leavesthe main sequence and enters the luminous post-main-sequence phase. Thefairly large sample we constructed enables us to derive an estimationfor the occurrence of excesses. This fraction of G or K giants withfar-infrared excess appears to be distinctly smaller than amongmain-sequence stars. Since the higher radiation field of giants couldlead to a larger evaporation rate of the circumstellar debris, this factdoes not conflict with our hypothesis.
| Lithium Enrichment--Mass-Loss Connection in K Giant Stars
Based on observed far-infrared properties of K giant stars, we propose ascenario linking the high Li abundances of some of these stars to theevolution of circumstellar shells. In this model, every K giant withmasses between 1.0 and 2.5 Mȯ become Li rich during the red giantbranch stage, and the internal mechanism responsible for the Lienrichment will initiate a prompt mass-loss event. The evolutionarypaths of the detached shells are compatible with observations for lowexpansion velocities of the order of 2 km s-1 and mass loss of (2--5) x10-8 Mȯ yr-1. This modest mass loss is, however, 2 orders ofmagnitude larger than those of normal, Li-poor K giants. A "Li time" ofthe order of 80,000 yr or somewhat larger is possible. This Li phase is,nevertheless, not related to the 12C/13C ratio which appears to evolve,for these low-mass stars, over a much longer time. This model requires arapid internal process of Li enrichment and depletion. New argumentsappearing in the literature concerning this internal process arediscussed. Reference is also made to the importance of these stars tothe Galactic Li evolution.
| The Li K giant stars
Not Available
| A search for Li-rich giants
Not Available
| Luminosity Class III Stars with Excess Far-Infrared Emission
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1995ApJ...446L..79Z&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.
| Analysis of the moderately Li-rich giant HD 146850.
We report the identification of 3 Li-rich giants discovered in anongoing survey based on IRAS colours. A detailed analysis of one ofthese, HD 146850, is presented here. High-resolution spectra wereobtained for this star, using CASPEC at the 3.6m telescope of ESO. Wederived the stellar parameters (T_eff_, log g, [M/H])=4000, 1.5, -0.3. Alithium abundance of ɛ(Li)=1.6 is found, whereas [C/Fe]~0.0 and[N/Fe]~-0.1 indicating that no convective mixing has occurred. Theabundances of oxygen [O/Fe]=~+0.1 and α-elements[Mg/Fe]=[Ti/Fe]=[Ca/Fe]=~0.0 suggest that we are dealing with a diskstar, for which the radial velocity v_r_=42km/s is also moderate.
| Walraven photometry of nearby southern OB associations
Homogeneous Walraven (VBLUW) photometry is presented for 5260 stars inthe regions of five nearby southern OB associations: Scorpio Centaurus(Sco OB2), Orion OB1, Canis Major OB1, Monoceros OB1, and Scutum OB2.Derived V and (B - V) in the Johnson system are included.
| Differential population synthesis of early-type galaxies. I - Spectrophotometric atlas of synthesis standard spectra
Continuous spectrophotometry has been obtained for 200 objects at aresolution of 10-17 A over the wavelength region 3600-10,000 A.Kron-Cousins BVRI colors are computed from the spectra and compared withpublished photoelectric photometry. The (V - R)C color index is used togroup the individual observations to form synthesis standard spectra for48 common spectral types. The standard groups include a solar abundancesequence of most spectral types and luminosity classes, metal-rich andmetal weak G - K giant-branch sequences, and horizontal-branch giants.The variations with color, luminosity, and metallicity of severalprominent line strengths are discussed. The spectral atlas is availableas a FITS magnetic tape.
| Carbon monoxide band intensities in M giants
The strength of CO (2.3 micron) bands was measured using the photometercomponent of the Kitt Peak 1.3-m telescope in an attempt to identifyextremely carbon-poor M giants. Magnitudes for about 200 bright M starswere obtained through a J filter, and narrow filters were centered on2.17 and 2.40 microns, respectively. No M giants were found with COindices indicative of extremely low carbon abundances. The correlationof CO index to effective temperature did not extend to the extremelylate and variable M giants. The dependence of CO index upon carbonabundance, 12-C/13-C ratio, surface gravity, effective temperature, andmicroturbulent velocity indices were also investigated. It is found thatthe predicted and observed CO indices are in good agreement for starswith spectroscopically determined carbon abundance.
| Strong-Cyanogen Stars: Photometry and Kinematics
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1971ApJ...165..561J&db_key=AST
| A study of the positions and proper motions of 83 stars in the regionof SCO X-1.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1969AJ.....74...20S&db_key=AST
| The corrected magnitudes and colours of 278 stars near S.A. 1-139 in the UBV system
Not Available
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Osservazione e dati astrometrici
| Costellazione: | Scorpione |
| Ascensione retta: | 16h19m00.40s |
| Declinazione: | -14°52'21.0" |
| Magnitudine apparente: | 5.94 |
| Distanza: | 265.252 parsec |
| Moto proprio RA: | -22.2 |
| Moto proprio Dec: | 1.8 |
| B-T magnitude: | 7.947 |
| V-T magnitude: | 6.177 |
Cataloghi e designazioni:
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