Contenidos
Imágenes
Subir su imagen
DSS Images Other Images
Artículos relacionados
The origin and chemical evolution of carbon in the Galactic thin and thick discs*
In order to trace the origin and evolution of carbon in the Galacticdisc, we have determined carbon abundances in 51 nearby F and G dwarfstars. The sample is divided into two kinematically distinct subsampleswith 35 and 16 stars that are representative of the Galactic thin andthick discs, respectively. The analysis is based on spectral synthesisof the forbidden [CI] line at 872.7nm using spectra of very highresolution (R~ 220000) and high signal-to-noise ratio (S/N >~ 300)that were obtained with the Coudé Echelle Spectrograph (CES)spectrograph by the European Southern Observatory (ESO) 3.6-m telescopeat La Silla in Chile. We find that [C/Fe] versus [Fe/H] trends for thethin and thick discs are totally merged and flat for subsolarmetallicities. The thin disc that extends to higher metallicities thanthe thick disc shows a shallow decline in [C/Fe] from [Fe/H]~ 0 and upto [Fe/H]~+0.4. The [C/O] versus [O/H] trends are well separated betweenthe two discs (due to differences in the oxygen abundances) and bear agreat resemblance to the [Fe/O] versus [O/H] trends. Our interpretationof our abundance trends is that the sources that are responsible for thecarbon enrichment in the Galactic thin and thick discs have operated ona time-scale very similar to those that are responsible for the Fe and Yenrichment [i.e. SNIa and asymptotic giant branch (AGB) stars,respectively]. We further note that there exist other observational datain the literature that favour massive stars as the main sources forcarbon. In order to match our carbon trends, we believe that the carbonyields from massive stars then must be very dependent on metallicity forthe C, Fe and Y trends to be so finely tuned in the two discpopulations. Such metallicity-dependent yields are no longer supportedby the new stellar models in the recent literature. For the Galaxy, wehence conclude that the carbon enrichment at metallicities typical ofthe disc is mainly due to low- and intermediate-mass stars, whilemassive stars are still the main carbon contributor at low metallicities(halo and metal-poor thick disc).
| Abundance trends in kinematical groups of the Milky Way's disk
We have compiled a large catalogue of metallicities and abundance ratiosfrom the literature in order to investigate abundance trends of severalalpha and iron peak elements in the thin disk and the thick disk of theGalaxy. The catalogue includes 743 stars with abundances of Fe, O, Mg,Ca, Ti, Si, Na, Ni and Al in the metallicity range -1.30 < [Fe/H]< +0.50. We have checked that systematic differences betweenabundances measured in the different studies were lower than randomerrors before combining them. Accurate distances and proper motions fromHipparcos and radial velocities from several sources have been retreivedfor 639 stars and their velocities (U, V, W) and galactic orbits havebeen computed. Ages of 322 stars have been estimated with a Bayesianmethod of isochrone fitting. Two samples kinematically representative ofthe thin and thick disks have been selected, taking into account theHercules stream which is intermediate in kinematics, but with a probabledynamical origin. Our results show that the two disks are chemicallywell separated, they overlap greatly in metallicity and both showparallel decreasing alpha elements with increasing metallicity, in theinterval -0.80 < [Fe/H] < -0.30. The Mg enhancement with respectto Fe of the thick disk is measured to be 0.14 dex. An even largerenhancement is observed for Al. The thick disk is clearly older than thethin disk with tentative evidence of an AMR over 2-3 Gyr and a hiatus instar formation before the formation of the thin disk. We do not observea vertical gradient in the metallicity of the thick disk. The Herculesstream has properties similar to that of the thin disk, with a widerrange of metallicity. Metal-rich stars assigned to the thick disk andsuper-metal-rich stars assigned to the thin disk appear as outliers inall their properties.
| α-, r-, and s-process element trends in the Galactic thin and thick disks
From a detailed elemental abundance analysis of 102 F and G dwarf starswe present abundance trends in the Galactic thin and thick disks for 14elements (O, Na, Mg, Al, Si, Ca, Ti, Cr, Fe, Ni, Zn, Y, Ba, and Eu).Stellar parameters and elemental abundances (except for Y, Ba and Eu)for 66 of the 102 stars were presented in our previous studies (Bensbyet al. [CITE], A&A, 410, 527, [CITE], A&A, 415, 155). The 36stars that are new in this study extend and confirm our previous resultsand allow us to draw further conclusions regarding abundance trends. Thes-process elements Y and Ba, and the r-element Eu have also beenconsidered here for the whole sample for the first time. With this newlarger sample we now have the following results: 1) smooth and distinctabundance trends that for the thin and thick disks are clearlyseparated; 2) the α-element trends for the thick disk show typicalsignatures from the enrichment of SN Ia; 3) the thick disk stellarsample is in the mean older than the thin disk stellar sample; 4) thethick disk abundance trends are invariant with galactocentric radii(R_m); 5) the thick disk abundance trends appear to be invariant withvertical distance (Z_max) from the Galactic plane. Adding furtherevidence from the literaure we argue that a merger/interacting scenariowith a companion galaxy to produce a kinematical heating of the stars(that make up today's thick disk) in a pre-existing old thin disk is themost likely formation scenario for the Galactic thick disk. The 102stars have -1 ≲ [Fe/H] ≲ +0.4 and are all in the solarneighbourhood. Based on their kinematics they have been divided into athin disk sample and a thick disk sample consisting of 60 and 38 stars,respectively. The remaining 4 stars have kinematics that make themkinematically intermediate to the two disks. Their chemical abundancesalso place them in between the two disks. Which of the two diskpopulations these 4 stars belong to, or if they form a distinctpopulation of their own, can at the moment not be settled. The 66 starsfrom our previous studies were observed with the FEROS spectrograph onthe ESO 1.5-m telescope and the CES spectrograph on the ESO 3.6-mtelescope. Of the 36 new stars presented here 30 were observed with theSOFIN spectrograph on the Nordic Optical Telescope on La Palma, 3 withthe UVES spectrograph on VLT/UT2, and 3 with the FEROS spectrograph onthe ESO 1.5-m telescope. All spectra have high signal-to-noise ratios(typically S/N≳ 250) and high resolution (R 80 000, 45 000,and 110 000 for the SOFIN, FEROS, and UVES spectra, respectively).Based on observations collected at the Nordic Optical Telescope on LaPalma, Spain, and at the European Southern Observatories on La Silla andParanal, Chile, Proposals # 65.L-0019(B), 67.B-0108(B), 69.B-0277. FullTables [see full text], [see full text] and [see full text] are 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/433/185
| Stellar Chemical Signatures and Hierarchical Galaxy Formation
To compare the chemistries of stars in the Milky Way dwarf spheroidal(dSph) satellite galaxies with stars in the Galaxy, we have compiled alarge sample of Galactic stellar abundances from the literature. Whenkinematic information is available, we have assigned the stars tostandard Galactic components through Bayesian classification based onGaussian velocity ellipsoids. As found in previous studies, the[α/Fe] ratios of most stars in the dSph galaxies are generallylower than similar metallicity Galactic stars in this extended sample.Our kinematically selected stars confirm this for the Galactic halo,thin-disk, and thick-disk components. There is marginal overlap in thelow [α/Fe] ratios between dSph stars and Galactic halo stars onextreme retrograde orbits (V<-420 km s-1), but this is notsupported by other element ratios. Other element ratios compared in thispaper include r- and s-process abundances, where we find a significantoffset in the [Y/Fe] ratios, which results in a large overabundance in[Ba/Y] in most dSph stars compared with Galactic stars. Thus, thechemical signatures of most of the dSph stars are distinct from thestars in each of the kinematic components of the Galaxy. This resultrules out continuous merging of low-mass galaxies similar to these dSphsatellites during the formation of the Galaxy. However, we do not ruleout very early merging of low-mass dwarf galaxies, since up to one-halfof the most metal-poor stars ([Fe/H]<=-1.8) have chemistries that arein fair agreement with Galactic halo stars. We also do not rule outmerging with higher mass galaxies, although we note that the LMC and theremnants of the Sgr dwarf galaxy are also chemically distinct from themajority of the Galactic halo stars. Formation of the Galaxy's thickdisk by heating of an old thin disk during a merger is also not ruledout; however, the Galaxy's thick disk itself cannot be comprised of theremnants from a low-mass (dSph) dwarf galaxy, nor of a high-mass dwarfgalaxy like the LMC or Sgr, because of differences in chemistry.The new and independent environments offered by the dSph galaxies alsoallow us to examine fundamental assumptions related to thenucleosynthesis of the elements. The metal-poor stars ([Fe/H]<=-1.8)in the dSph galaxies appear to have lower [Ca/Fe] and [Ti/Fe] than[Mg/Fe] ratios, unlike similar metallicity stars in the Galaxy.Predictions from the α-process (α-rich freeze-out) would beconsistent with this result if there have been a lack of hypernovae indSph galaxies. The α-process could also be responsible for thevery low Y abundances in the metal-poor stars in dSph's; since [La/Eu](and possibly [Ba/Eu]) are consistent with pure r-process results, thelow [Y/Eu] suggests a separate r-process site for this light(first-peak) r-process element. We also discuss SNe II rates and yieldsas other alternatives, however. In stars with higher metallicities([Fe/H]>=-1.8), contributions from the s-process are expected; [(Y,La, and Ba)/Eu] all rise as expected, and yet [Ba/Y] is still muchhigher in the dSph stars than similar metallicity Galactic stars. Thisresult is consistent with s-process contributions from lower metallicityAGB stars in dSph galaxies, and is in good agreement with the slowerchemical evolution expected in the low-mass dSph galaxies relative tothe Galaxy, such that the build-up of metals occurs over much longertimescales. Future investigations of nucleosynthetic constraints (aswell as galaxy formation and evolution) will require an examination ofmany stars within individual dwarf galaxies.Finally, the Na-Ni trend reported in 1997 by Nissen & Schuster isconfirmed in Galactic halo stars, but we discuss this in terms of thegeneral nucleosynthesis of neutron-rich elements. We do not confirm thatthe Na-Ni trend is related to the accretion of dSph galaxies in theGalactic halo.
| The photospheric abundances of active binaries. III. Abundance peculiarities at high activity levels
We report the determination from high-resolution spectra of theatmospheric parameters and abundances of 13 chemical species (amongwhich lithium) in 8 single-lined active binaries. These data arecombined with our previous results for 6 other RS CVn systems to examinea possible relationship between the photospheric abundance patterns andthe stellar activity level. The stars analyzed are generally found toexhibit peculiar abundance ratios compared to inactive, Galactic diskstars of similar metallicities. We argue that this behaviour is unlikelyto be an artefact of errors in the determination of the atmosphericparameters or non-standard mixing processes along the red giant branch,but diagnoses instead the combined action of various physical processesrelated to activity. The most promising candidates are cool spot groupscovering a very substantial fraction of the stellar photosphere or NLTEeffects arising from nonthermal excitation. However, we cannot excludethe possibility that more general shortcomings in our understanding ofK-type stars (e.g. inadequacies in the atmospheric models) also play asignificant role. Lastly, we call attention to the unreliability of the(V-R) and (V-I) colour indices as temperature indicators inchromospherically active stars.Based on observations collected at the European Southern Observatory,Chile (Proposals 64.L-0249 and 071.D-0260).Table A.1 is only available in electronic form at the CDS via anonymousftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/426/1007
| On the determination of oxygen abundances in chromospherically active stars
We discuss oxygen abundances derived from [O I] λ6300s and the OI triplet in stars spanning a wide range in chromospheric activitylevel, and show that these two indicators yield increasingly discrepantresults with higher chromospheric/coronal activity measures. While theforbidden and permitted lines give fairly consistent results forsolar-type disk dwarfs, spuriously high O I triplet abundances areobserved in young Hyades and Pleiades stars, as well as in individualcomponents of RS CVn binaries (up to 1.8 dex). The distinct behaviour ofthe [O I]-based abundances which consistently remain near-solar suggeststhat this phenomenon mostly results from large departures from LTEaffecting the O I triplet at high activity level that are currentlyunaccounted for, but also possibly from a failure to adequately modelthe atmospheres of K-type stars. These results suggest that some cautionshould be exercised when interpreting oxygen abundances in activebinaries or young open cluster stars.Based on observations collected at the European Southern Observatory,Chile (Proposals 64.L-0249 and 071.D-0260).Table \ref{tab_data} is only available in electronic form athttp://www.edpsciences.org
| Oxygen trends in the Galactic thin and thick disks
We present oxygen abundances for 72 F and G dwarf stars in the solarneighbourhood. Using the kinematics of the stars we divide them into twosub-samples with space velocities that are typical for the thick andthin disks, respectively. The metallicities of the stars range from[Fe/H] ≈ -0.9 to +0.4 and we use the derived oxygen abundances of thestars to: (1) perform a differential study of the oxygen trends in thethin and the thick disk; (2) to follow the trend of oxygen in the thindisk to the highest metallicities. We analyze the forbidden oxygen linesat 6300 Å and 6363 Å as well as the (NLTE afflicted) tripletlines around 7774 Å. For the forbidden line at 6300 Å wehave spectra of very high S/N (>400) and resolution (R ≳ 215000). This has enabled a very accurate modeling of the oxygen line andthe blending Ni lines. The high internal accuracy in our determinationof the oxygen abundances from this line is reflected in the very tighttrends we find for oxygen relative to iron. From these abundances we areable to draw the following major conclusions: (i) That the [O/Fe] trendat super-solar [Fe/H] continues downward which is in concordance withmodels of Galactic chemical evolution. This is not seen in previousstudies as it has not been possible to take the blending Ni lines in theforbidden oxygen line at 6300 Å properly into account; (ii) Thatthe oxygen trends in the thin and the thick disks are distinctlydifferent. This confirms and extends previous studies of the otherα-elements; (iii) That oxygen does not follow Mg at super-solarmetallicities; (iv) We also provide an empirical NLTE correction for theinfrared O I triplet that could be used for dwarf star spectra with aS/N such that only the triplet lines can be analyzed well, e.g. stars atlarge distances; (v) Finally, we find that Gratton et al. (1999)overestimate the NLTE corrections for the permitted oxygen triplet linesat 7774 Å for the parameter space that our stars span.Based on observations collected at the European Southern Observatory, LaSilla and Paranal, Chile, Proposals #65.L-0019, 67.B-0108, and69.B-0277.The full Table 4 is only available in electronic form at the CDS viaanonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?/A+A/415/155
| Elemental abundance trends in the Galactic thin and thick disks as traced by nearby F and G dwarf stars
Based on spectra from F and G dwarf stars, we present elementalabundance trends in the Galactic thin and thick disks in the metallicityregime -0.8< [Fe/H] < +0.4. Our findings can besummarized as follows. 1) Both the thin and the thick disks show smoothand distinct abundance trends that, at sub-solar metallicities, areclearly separated. 2) For the alpha -elements the thick disk showssignatures of chemical enrichment from SNe type Ia. 3) The age of thethick disk sample is in the mean older than the thin disk sample. 4)Kinematically, there exist thick disk stars with super-solarmetallicities. Based on these findings, together with other constraintsfrom the literature, we discuss different formation scenarios for thethick disk. We suggest that the currently most likely formation scenariois a violent merger event or a close encounter with a companion galaxy.Based on kinematics the stellar sample was selected to contain starswith high probabilities of belonging either to the thin or to the thickGalactic disk. The total number of stars are 66 of which 21 belong tothe thick disk and 45 to the thin disk. The analysis is based onhigh-resolution spectra with high signal-to-noise (R ~ 48 000 and S/Ngtrsim 150, respectively) recorded with the FEROS spectrograph on LaSilla, Chile. Abundances have been determined for four alpha -elements(Mg, Si, Ca, and Ti), for four even-nuclei iron peak elements (Cr, Fe,Ni, and Zn), and for the light elements Na and Al, from equivalent widthmeasurements of ~ 30 000 spectral lines. An extensive investigation ofthe atomic parameters, log gf-values in particular, have been performedin order to achieve abundances that are trustworthy. Noteworthy is thatwe find for Ti good agreement between the abundances from Ti I and TiIi. Our solar Ti abundances are in concordance with the standardmeteoritic Ti abundanceBased on observations collected at the European Southern Observatory, LaSilla, Chile, Proposals #65.L-0019(B) and 67.B-0108(B).Full Tables \ref{tab:linelist} and \ref{tab:abundances} are 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/410/527
| 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.
| Catalogue of Apparent Diameters and Absolute Radii of Stars (CADARS) - Third edition - Comments and statistics
The Catalogue, available at the Centre de Données Stellaires deStrasbourg, consists of 13 573 records concerning the results obtainedfrom different methods for 7778 stars, reported in the literature. Thefollowing data are listed for each star: identifications, apparentmagnitude, spectral type, apparent diameter in arcsec, absolute radiusin solar units, method of determination, reference, remarks. Commentsand statistics obtained from CADARS are given. The Catalogue isavailable 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/qcar?J/A+A/367/521
| Sixth Catalogue of Fundamental Stars (FK6). Part III. Additional fundamental stars with direct solutions
The FK6 is a suitable combination of the results of the HIPPARCOSastrometry satellite with ground-based data, measured over a longinterval of time and summarized mainly in the FK5. Part III of the FK6(abbreviated FK6(III)) contains additional fundamental stars with directsolutions. Such direct solutions are appropriate for single stars or forobjects which can be treated like single stars. Part III of the FK6contains in total 3272 stars. Their ground-based data stem from thebright extension of the FK5 (735 stars), from the catalogue of remainingSup stars (RSup, 732 stars), and from the faint extension of the FK5(1805 stars). From the 3272 stars in Part III, we have selected 1928objects as "astrometrically excellent stars", since their instantaneousproper motions and their mean (time-averaged) ones do not differsignificantly. Hence most of the astrometrically excellent stars arewell-behaving "single-star candidates" with good astrometric data. Thesestars are most suited for high-precision astrometry. On the other hand,354 of the stars in Part III are Δμ binaries in the sense ofWielen et al. (1999). Many of them are newly discovered probablebinaries with no other hitherto known indication of binarity. The FK6gives, besides the classical "single-star mode" solutions (SI mode),other solutions which take into account the fact that hidden astrometricbinaries among "apparently single-stars" introduce sizable "cosmicerrors" into the quasi-instantaneously measured HIPPARCOS proper motionsand positions. The FK6 gives, in addition to the SI mode, the "long-termprediction (LTP) mode" and the "short-term prediction (STP) mode". TheseLTP and STP modes are on average the most precise solutions forapparently single stars, depending on the epoch difference with respectto the HIPPARCOS epoch of about 1991. The typical mean error of anFK6(III) proper motion in the single-star mode is 0.59 mas/year. This isa factor of 1.34 better than the typical HIPPARCOS errors for thesestars of 0.79 mas/year. In the long-term prediction mode, in whichcosmic errors are taken into account, the FK6(III) proper motions have atypical mean error of 0.93 mas/year, which is by a factor of about 2better than the corresponding error for the HIPPARCOS values of 1.83mas/year (cosmic errors included).
| A New Association of Post-T Tauri Stars near the Sun
Observing ROSAT sources in an area 20°×25° centered at thehigh-latitude (b=-59°) active star ER Eri, we found evidences for anearby association, that we call the Horologium association (HorA),formed by at least 10 very young stars, some of them being bona fidepost-T Tauri stars. We suggest other six stars as possible members ofthis proposed association. We examine several requirements thatcharacterize a young stellar association. Although no one of them,isolated, gives an undisputed prove of the existence of the HorA, alltogether practically create a strong evidence for it. In fact, the Liline intensities are between those of the older classical T Tauri starsand the ones of the Local Association stars. The space velocitycomponents of the HorA relative to the Sun (U=-9.5+/-1.0, V=-20.9+/-1.1,W=-2.1+/-1.9) are not far from those of the Local Association, so thatit could be one of its last episodes of star formation. In this regionof the sky there are some hotter and non-X-ray active stars, withsimilar space velocities, that could be the massive members of the HorA,among them, the nearby Be star Achernar. The maximum of the massdistribution function of its probable members is around 0.7-0.9Msolar. We estimate its distance as ~60 pc and its size as~50 pc. If spherical, this size would be larger than the surveyed area,and many other members could have been missed. ER Eri itself was foundto be not a member, but a background RS CVn-like system. We alsoobserved three control regions, two at northern and southern Galacticlatitudes and a third one in the known TW Hya association (TWA), and theproperties and distribution of their young stars strengthen the realityof the HorA. Contrary to the TWA, the only known binaries in the HorAare two very wide systems. The HorA is much more isolated from cloudsand older (~30 Myr) than the TWA and could give some clues about thelifetime of the disks around T Tauri stars. Actually, none of theproposed members is an IRAS source indicating an advanced stage of theevolution of their primitive accreting disks. Based on observations madeunder the Observatório Nacional-ESO agreement for the jointoperation of the 1.52 m ESO telescope and at the Observatório doPico dos Dias, operated by MCT/Laboratório Nacional deAstrofísica, Brazil
| 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
| The rotation speed of the companion star in Aquila X-1.
We have obtained medium resolution spectra of the neutron star X-raytransient Aql X-1 during quiescence. We determine the spectral type ofthe companion star to be K1 and also estimate its rotation speed to be62^+30^_-20_km/s. By measuring the width of the Hα emission lineprofile of the accretion disc, we estimate the binary inclination to~50° and also estimate the semi-amplitude of the companion star'sradial velocity curve to be ~170km/s.
| 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.
| Evolved GK stars near the sun. I - The old disk population
A sample of nearly two thousand GK giants with intermediate band, (R,I),DDO and Geneva photometry has been assembled. Astrometric data is alsoavailable for most of the stars. The some 800 members of the old diskpopulation in the sample yield accurate luminosities (from two sources),reddening values and chemical abundances from calibrations of thephotometric parameters. Less than one percent of the objects arepeculiar in the sense that the flux distribution is abnormal. Thepeculiarity is signaled by strong CH (and Ba II) and weak CH. The CH+stars are all spectroscopic binaries, probably with white dwarfcompanions, whereas the CH- stars are not. A broad absorption band,centered near 3500 A, is found in the CH+ stars whereas the CH- objectshave a broad emission feature in the same region. The intensity of theseabsorptions and emissions are independent of the intensity of abnormalspectral features. Ten percent of the old disk sample have a heavyelement abundance from one and a half to three times the solar value.The distribution of the heavy element abundances is nearly a normal onewith a peak near solar abundance and ranges three times to one sixthsolar. The distribution of the (U, V) velocities is independent of theheavy element abundance and does not appear to be random. Ten percent ofthe old disk stars show a CN anomaly, equally divided between CN strongand CN weak. Several stars of individual astrometric or astrophysicalimportance are isolated.
| Fifth fundamental catalogue. Part 2: The FK5 extension - new fundamental stars
The mean positions and proper motions for 3117 new fundamental starsessentially in the magnitude range about 4.5 to 9.5 are given in thisFK5 extension. Mean apparent visual magnitude is 7.2 and is on average2.5 magnitudes fainter then the basic FK5 which has a mean magnitude of4.7. (The basic FK5 gives the mean positions and proper motions for theclassical 1535 fundamental stars). The following are discussed: theobservational material, reduction of observations, star selection, andthe system for the FK5 extension. An explanation and description of thecatalog are given. The catalog of 3117 fundamental stars for the equinoxand epoch J2000.0 and B1950.0 is presented. The parallaxes and radialvelocities for 22 extension stars with large forecasting effects aregiven. Catalogs used in the compilation of the FK5 fundamental catalogare listed.
| Large and kinematically unbiased samples of G- and K-type stars. IV - Evolved stars of the old disk population
Modified Stromgren and (R,I) photometry, along with DDO and Genevaphotometry, are presented for a complete sample of evolved old-disk Gand K giants in the Bright Star Catalogue. Stars with ages of between1.5 x 10 to the 9th and 10 to the 10th yr are found to have anear-normal distribution of heavy element abundances, centered on anFe/H abundance ratio of -0.1 dex. The old disk clusters NGC 3680 and IC4651 contain red-straggler young-disk giants that are probablycontemporaries of the blue stragglers in the clusters.
| Large and kinematically unbiased samples of G- and K-type stars. II - Observations of evolved stars in the Bright Star sample. III - Evolved young disk stars in the Bright Star sample
Four color and RI observations were obtained for a large sample ofG-type and K-type stars in the Bright Star Catalogue. Data are firstpresented for 110 evolved stars. Photometry of evolved young diskpopulation stars have then been calibrated for luminosity, reddening,and metallicity on the basis of results for members of the Hyades andSirius superclusters. New DDO results are given for 120 stars.
| UVBY BET photometry of equatorial and southern bright stars.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1977A&AS...27...47H&db_key=AST
|
Enviar un nuevo artículo
Enlaces relacionados
- - No se han encontrado enlaces -
En viar un nuevo enlace
Miembro de los siguientes grupos:
|
Datos observacionales y astrométricos
| Constelación: | Erídano |
| Ascensión Recta: | 02h42m08.50s |
| Declinación: | -46°31'28.0" |
| Magnitud Aparente: | 6.1 |
| Distancia: | 40.866 parsecs |
| Movimiento Propio en Ascensión Recta: | 9.6 |
| Movimiento Propio en Declinación: | -95.3 |
| B-T magnitude: | 7.209 |
| V-T magnitude: | 6.193 |
Catálogos y designaciones:
|
