Садржај
Слике
Уплоадјуј своје слике
DSS Images Other Images
Везани чланци
The heterogeneous class of lambda Bootis stars
We demonstrate that it is arduous to define the lambda Boo stars as aclass of objects exhibiting uniform abundance peculiarities which wouldbe generated by a mechanism altering the structure of their atmosphericlayers. We collected the stars classified as lambda Boo up to now anddiscuss their properties, in particular the important percentage ofconfirmed binaries producing composite spectra (including our adaptiveoptics observations) and of misclassified objects. The unexplained RVvariables (and thus suspected binaries), the known SB for which we lackinformation on the companion, the stars with an UV flux inconsistentwith their classification, and the fast rotating stars for which noaccurate abundance analysis can be performed, are also reviewed.Partly based on observations collected at the CFH Telescope (Hawaii) andat TBL of the Pic du Midi Observatory (France).Table \ref{tab5} is only available in electronic form athttp://www.edpsciences.org
| The status of Galactic field λ Bootis stars in the post-Hipparcos era
The λ Bootis stars are Population I, late B- to early F-typestars, with moderate to extreme (up to a factor 100) surfaceunderabundances of most Fe-peak elements and solar abundances of lighterelements (C, N, O and S). To put constraints on the various existingtheories that try to explain these peculiar stars, we investigate theobservational properties of λ Bootis stars compared with areference sample of normal stars. Using various photometric systems andHipparcos data, we analyse the validity of standard photometriccalibrations, elemental abundances, and Galactic space motions. Therecrystallizes a clear picture of a homogeneous group of Population Iobjects found at all stages of their main-sequence evolution, with apeak at about 1 Gyr. No correlation of astrophysical parameters such asthe projected rotational velocities or elemental abundances with age isfound, suggesting that the a priori unknown mechanism, which createsλ Bootis stars, works continuously for late B- to early F-typestars in all stages of main-sequence evolution. Surprisingly, the sodiumabundances seem to indicate an interaction between the stars and theirlocal environment.
| On the Period-Luminosity-Colour-Metallicity relation and the pulsational characteristics of lambda Bootis type stars
Generally, chemical peculiarity found for stars on the upper mainsequence excludes delta Scuti type pulsation (e.g. Ap and Am stars), butfor the group of lambda Bootis stars it is just the opposite. This makesthem very interesting for asteroseismological investigations. The groupof lambda Bootis type stars comprises late B- to early F-type,Population I objects which are basically metal weak, in particular theFe group elements, but with the clear exception of C, N, O and S. Thepresent work is a continuation of the studies by Paunzen et al.(\cite{Pau97}, \cite{Pau98}), who presented first results on thepulsational characteristics of the lambda Bootis stars. Since then, wehave observed 22 additional objects; we found eight new pulsators andconfirmed another one. Furthermore, new spectroscopic data (Paunzen\cite{Pau01}) allowed us to sort out misidentified candidates and to addtrue members to the group. From 67 members of this group, only two arenot photometrically investigated yet which makes our analysis highlyrepresentative. We have compared our results on the pulsationalbehaviour of the lambda Bootis stars with those of a sample of deltaScuti type objects. We find that at least 70% of all lambda Bootis typestars inside the classical instability strip pulsate, and they do sowith high overtone modes (Q < 0.020 d). Only a few stars, if any,pulsate in the fundamental mode. Our photometric results are inexcellent agreement with the spectroscopic work on high-degree nonradialpulsations by Bohlender et al. (\cite{Boh99}). Compared to the deltaScuti stars, the cool and hot borders of the instability strip of thelambda Bootis stars are shifted by about 25 mmag, towards smaller(b-y)_0. Using published abundances and the metallicity sensitiveindices of the Geneva 7-colour and Strömgren uvbybeta systems, wehave derived [Z] values which describe the surface abundance of theheavier elements for the group members. We find that thePeriod-Luminosity-Colour relation for the group of lambda Bootis starsis within the errors identical with that of the normal delta Scutistars. No clear evidence for a statistically significant metallicityterm was detected. Based on observations from the Austrian AutomaticPhotoelectric Telescope (Fairborn Observatory), SAAO and Siding SpringObservatory.
| The accretion/diffusion theory for lambda Bootis stars in the light of spectroscopic data
Most of the current theories suggest the lambda Bootis phenomenon tooriginate from an interaction between the stellar surface and its localenvironment. In this paper, we compare the abundance pattern of thelambda Bootis stars to that of the interstellar medium and find largerdeficiencies for Mg, Si, Mn and Zn than in the interstellar medium. Acomparison with metal poor post-AGB stars showing evidence forcircumstellar material indicates a similar physical process possiblybeing at work for some of the lambda Bootis stars, but not for all ofthem. Despite the fact that the number of spectroscopically analysedlambda Bootis stars has considerably increased in the past, a test ofpredicted effects with observations shows current abundance andtemperature data to be still controversial.
| The abundance pattern of lambda Bootis stars
Within a project to investigate the properties of lambda Bootis stars,we report on their abundance pattern. High resolution spectra have beenobtained for a total of twelve candidate lambda Bootis stars, four ofthem being contained in spectroscopic binary systems, and detailedabundance analyses have been performed. All program stars show acharacteristic lambda Bootis abundance pattern (deficient heavy elementsand solar abundant light elements) and an enhanced abundance of Na. Thiswork raises the fraction of lambda Bootis stars with known abundances to50%. The resulting abundances complemented by literature data are usedto construct a ``mean lambda Bootis abundance pattern'', which exhibits,apart from general underabundances of heavy elements (~-1 dex) and solarabundances of C, N, O, Na and S, a star-to-star scatter which is up totwice as large as for a comparable sample of normal stars. Based onobservations obtained at the Osservatorio Astronomico di Padua-Asiago,OPD/LNA, KPNO and DSO.
| Light element non-LTE abundances of lambda Bootis stars. II. Nitrogen and sulphur
One of the main characteristics proclaimed for the group of the lambdaBootis stars is the apparent solar abundance of the light elements C, N,O and S. The typical abundance pattern is completed by the strongunderabundances of the Fe-peak elements. In the first paper of thisseries, we have shown that carbon is less abundant than oxygen but bothelements are still significantly more abundant than Fe-peak elements.The mean abundances, based on a detailed non-LTE investigation, werefound -0.37 dex and -0.07 dex, respectively. As a further step, we nowpresent non-LTE abundances of nitrogen and sulphur for thirteen membersof the lambda Bootis group based on several spectral lines between 8590Å, and 8750 Å. Furthermore, LTE abundances for calcium inthe same spectral range were derived and compared with values from theliterature. Similar to the mean abundances of carbon and oxygen, nearlysolar values were found (-0.30 dex for nitrogen and -0.11 dex forsulphur) for our sample of program stars. Among our sample, onepreviously undetected binary system (HD 64491) was identified. From astatistical point of view, the abundances of the light elements rangefrom slightly overabundant to moderately underabundant compared to theSun. However, the individual objects always exhibit a similiar pattern,with the Fe-peak elements being significantly more underabundant thanthe light elements. No correlation of the derived abundances withastrophysical parameters such as the effective temperature, surfacegravity or projected rotational velocity was found. Furthermore, theabundances of the light elements do not allow us to discriminate betweenany proposed theory. Based on observations obtained at BNAO Rozhen andComplejo Astronómico el Leoncito (CASLEO), operated under theagreement between the Consejo Nacional de InvestigacionesCientíficas y Técnicas de la República Argentinaand the National Universities of La Plata, Córdoba y San Juan.
| Physical parameters of lambda Bootis stars
This is the first of two papers whose main goal is to update and improvethe information available on the physical properties of the lambdaBootis stars. The determination of the stellar parameters is offundamental importance to shed light into the different theoriesproposed to explain the lambda Bootis phenomenon. With this aim,projected rotational velocities, effective temperatures, surfacegravities and chemical abundances of a sample of suspected lambda Bootisstars have been calculated. Five objects showing composite spectratypical of binary systems were found in our analysis. The abundancedistribution of the program stars does not resemble the chemicalcomposition of the class prototype, lambda Boo, which poses someconcerns regarding the idea of a well-defined, chemically homogeneousgroup of stars. A possible relation between rotational velocities andthe lambda Bootis phenomenon has been found. This result would be inagreement with the accretion scenario proposed by Turcotte &Charbonneau (\cite{Turcotte93}). Figure 3 is only available inelectronic form at http://www.edpsciences.org
| A spectroscopic survey for lambda Bootis stars. III. Final results
In the third paper of a series dedicated to the spectroscopic survey fornew lambda Bootis stars, we present all new and confirmed members of thegroup as well as a detailed analysis of the observed sample. The natureof this small group of chemically peculiar stars of the upper mainsequence still challenges our understanding of processes like diffusion,mass-loss and accretion. The typical abundances pattern (nearly solarvalues for C, N, O and S whereas the Fe-peak elements are moderate tostrong underabundant) can still not be explained by any proposed theory.Hence, the significant increase of new members gives the opportunity toinvestigate the group properties in more detail. We report the discoveryof 26 new members of the group and the confirmation of 18 candidatesfrom the literature. This almost triples the number of known lambdaBootis stars. The existence of one member in the young open cluster NGC2264 and four members in the Orion OB1 association proves that thelambda Bootis phenomenon already works at very early stages of stellarevolution. Recent results from the Hipparcos mission have shown that thewell established lambda Bootis stars of the Galactic field comprise thewhole area from the Zero Age Main Sequence to the Terminal Age MainSequence (~ 109 yr for an A-type star). There is a continuoustransition between very young and rather evolved evolutionary stages. Wefind that the overall percentage of lambda Bootis type among all normaltype stars in the spectral range from B8 to F4 is 2% in the Galacticfield as well as in open clusters. Furthermore, 44 metal-weak objectsare listed which might be connected with the lambda Bootis phenomenon.Our biased sample (chosen by photometric boxes) is not distinguishedfrom all A-type stars in the corresponding spectral region by therotational velocity distribution. Only for the luminosity classes IV andIII (especially for the cooler program stars) the determined mean v sini values are very high compared to those of the literature. Based onobservations from the Observatoire de Haute-Provence, OsservatorioAstronomico di Padova-Asiago, Observatório do Pico dosDias-LNA/CNPq/MCT, Chews Ridge Observatory (MIRA) and University ofToronto Southern Observatory (Las Campanas).
| A spectroscopic survey for lambda Bootis stars. II. The observational data
lambda Bootis stars comprise only a small number of all A-type stars andare characterized as nonmagnetic, Population i, late B to early F-typedwarfs which show significant underabundances of metals whereas thelight elements (C, N, O and S) are almost normal abundant compared tothe Sun. In the second paper on a spectroscopic survey for lambda Bootisstars, we present the spectral classifications of all program starsobserved. These stars were selected on the basis of their Strömgrenuvbybeta colors as lambda Bootis candidates. In total, 708 objects insix open clusters, the Orion OB1 association and the Galactic field wereclassified. In addition, 9 serendipity non-candidates in the vicinity ofour program stars as well as 15 Guide Star Catalogue stars were observedresulting in a total of 732 classified stars. The 15 objects from theGuide Star Catalogue are part of a program for the classification ofapparent variable stars from the Fine Guidance Sensors of the HubbleSpace Telescope. A grid of 105 MK standard as well as ``pathological''stars guarantees a precise classification. A comparison of our spectralclassification with the extensive work of Abt & Morrell(\cite{Abt95}) shows no significant differences. The derived types are0.23 +/- 0.09 (rms error per measurement) subclasses later and 0.30 +/-0.08 luminosity classes more luminous than those of Abt & Morrell(\cite{Abt95}) based on a sample of 160 objects in common. The estimatederrors of the means are +/- 0.1 subclasses. The characteristics of oursample are discussed in respect to the distribution on the sky, apparentvisual magnitudes and Strömgren uvbybeta colors. Based onobservations from the Observatoire de Haute-Provence, OsservatorioAstronomico di Padova-Asiago, Observatório do Pico dosDias-LNA/CNPq/MCT, Chews Ridge Observatory (MIRA) and University ofToronto Southern Observatory (Las Campanas).
| 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
| delta Scuti and related stars: Analysis of the R00 Catalogue
We present a comprehensive analysis of the properties of the pulsatingdelta Scuti and related variables based mainly on the content of therecently published catalogue by Rodríguez et al.(\cite{retal00a}, hereafter R00). In particular, the primaryobservational properties such as visual amplitude, period and visualmagnitude and the contributions from the Hipparcos, OGLE and MACHOlong-term monitoring projects are examined. The membership of thesevariables in open clusters and multiple systems is also analyzed, withspecial attention given to the delta Scuti pulsators situated ineclipsing binary systems. The location of the delta Scuti variables inthe H-R diagram is discussed on the basis of HIPPARCOS parallaxes anduvbybeta photometry. New borders of the classical instability arepresented. In particular, the properties of the delta Scuti pulsatorswith nonsolar surface abundances (SX Phe, lambda Boo, rho Pup, delta Deland classical Am stars subgroups) are examined. The Hipparcos parallaxesshow that the available photometric uvbybeta absolute magnitudecalibrations by Crawford can be applied correctly to delta Scutivariables rotating faster than v sin i ~ 100 km s{-1} withnormal spectra. It is shown that systematic deviations exist for thephotometrically determined absolute magnitudes, which correlate with vsin i and delta m1. The photometric calibrations are found tofit the lambda Boo stars, but should not be used for the group ofevolved metallic-line A stars. The related gamma Dor variables and thepre-main-sequence delta Scuti variables are also discussed. Finally, thevariables catalogued with periods longer than 0fd 25 are examined on astar-by-star basis in order to assign them to the proper delta Scuti, RRLyrae or gamma Dor class. A search for massive, long-period delta Scutistars similar to the triple-mode variable AC And is also carried out.
| On the Variability of A3-F0 Luminosity Class III-V Stars
I investigate the Hipparcos Satellite photometry of A3-F0 stars ofluminosity classes III-V to learn about their variability and identify afew stars for which further study is desirable.
| A revised catalogue of delta Sct stars
An extensive and up-dated list of delta Sct stars is presented here.More than 500 papers, published during the last few years, have beenrevised and 341 new variables have been added to our last list, sixyears ago. This catalogue is intended to be a comprehensive review onthe observational characteristics of all the delta Sct stars known untilnow, including stars contained in earlier catalogues together with othernew discovered variables, covering information published until January2000. In summary, 636 variables, 1149 references and 182 individualnotes are presented in this new list. Tables 1 and 2 will be accessibleonly in electronic form at the CDS via anonymous ftp tocdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/Abstract.html
| How many lambda Bootis stars are binaries?
In the attempt to shed new light on the lambda Boo phenomenon weanalyzed the astrometric, photometric and spectroscopic characteristicsof stars out of a list of recently selected lambda Boo candidates. Weshow that the class is still ill-defined and discuss the possibilitythat some, if not most stars presently classified as lambda Boo, are infact binary pairs and that peculiar abundances may not correspond toactual values if the average values of the atmospheric parameters{Teff} and log g are assumed and the effect of veiling is nottaken into account. Partly based on data from the ESA Hipparcosastrometry satellite.
| Light element non-LTE abundances of lambda Bootis stars. I. Carbon and oxygen
Abundances for the light elements of {lambda Bootis} stars are a mainkey to understand the astrophysical processes behind the so-called{lambda Bootis} phenomenon. These stars are characterized by a typicalabundance pattern (strong underabundances of the Fe-peak elementswhereas the light elements have apparently solar abundances) which isstill based mainly on LTE-calculations. Therefore we started aninvestigation to derive accurate abundances of the light elements (C, N,O and S). For this purpose a new oxygen model atom was implemented inthe Kiel non-LTE code. High resolution and high signal-to-noise spectrawere used. For each element only a single wavelength region with linesof the specific element was selected and observed in order to avoidcontamination from other elements. In the first paper we presentabundances for carbon and oxygen of a statistically significant numberof well established {lambda Bootis} stars. The second paper will dealwith nitrogen and sulphur. The most important result is that on averagecarbon is less abundant than oxygen but still both elements aresignificant more abundant than the Fe-peak elements. Furthermore theanticorrelation of carbon and oxygen with the silicon abundance isproven, which strongly supports the accretion/diffusion theory. Based onobservations obtained at ESO-La\,Silla and BNAO Rozhen
| The Age Range of Hyades Stars
On the basis of canonical models, the age of Hyades supercluster stars,whether in the Hyades and Praesepe clusters or the noncluster field,ranges from (5-6) x 10^8 to 10^9 yr. The difference between the parallaxderived from the supercluster motion and that obtained from Hipparcosobservations has a dispersion only twice that of the mean dispersion ofthe individual Hipparcos values. The supercluster appears not to containred giants on the first ascent of the red giant branch, but onlyasymptotic giant branch (``clump'') stars. The masses obtained forindividual components of binary stars in the supercluster show adispersion of less than 10% when compared with model predictions.
| Pulsation in lambda Bootis stars
In this paper we present a further step in applying asteroseismictechniques to the group of lambda Bootis stars which can becharacterized as nonmagnetic A to F-type Population I dwarfs withsignificant (surface) underabundances of Fe-peak elements. Since noconclusive theory explaining the origin of the observed abundanceanomalies exists, an extensive photometric survey for pulsation in thisgroup has been initiated. Knowledge about the pulsational properties(most members are located within the classical instability strip) couldhelp to establish constrains about the overall abundance of these starsas well as on the evolutionary status. New photometric observations werecarried out for eleven stars. Variability was detected in four stars(e.g. lambda Bootis itself) whereas the remaining seven objects areprobably constant. In total, 52 members of this group have beenphotometrically investigated so far. With 22 pulsating and 30``constant'' stars, we derive a ratio of at least 50 % for variable tononvariable members inside the classical instability strip. This resultis based on high quality Hipparcos and new photometric data. Theobserved log /lineρ//lineρ_ȯ and log P values for thepulsating members are compatible with standard (solar abundant) deltaScuti models supporting the hypothesis that the found abundanceanomalies are restricted to the surface only. Otherwise the pulsationalproperties of this group are not outstanding compared to ``normal''delta Scuti stars, indicating that the mechanism driving the pulsationsis very similar. Based on observations obtained at ESO-La\,Silla, CTIO,SAAO, McDonald Observatory, Instituto Astrofisica Andalucia Observatoryand with the Hipparcos satellite
| The 73rd Name-List of Variable 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 consolidated catalogue of lambda Bootis stars
lambda Bootis stars challenge our understanding of diffusion andaccretion processes related to stars and their circumstellarenvironment, and they are interesting components of the classicalinstability strip. Attempts to derive group properties with statisticalmethods are severely limited by the small number of unambiguouslyidentified lambda Bootis stars. In general, the subject appears to beobscured by incorrect memberships and it is therefore essential toprovide a sufficiently large catalogue of definitive group membersbefore modeling the lambda Bootis phenomenon. This paper describes thefirst steps towards this goal, based on our current knowledge of wellinvestigated members, leading to a concise definition of lambda Bootisstars: {Pop I hydrogen burning metal poor (except of C,N,O and S) A-typestars.} The definition does not depend on phenomenological features,like flux depressions, colour excesses, v sin i values, etc. Based on anew homogeneous catalogue with 45 lambda Bootis stars, we discussclassification criteria which can be used for a spectroscopic andphotometric all-sky survey for lambda Bootis stars in the field and inclusters of different ages. Based on observations obtained atESO-La,Silla, CTIO, Observatoire de Haute-Provence, OsservatorioAstronomico di Padua-Asiago, Univ. Toronto Southern Observatory,Observatorio do Pico dos Dias-LNA/CNPq/MCT (Brazil). Table 1 is alsoavailable in electronic form at the CDS via anonymous ftp tocdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/Abstract.html.
| On the evolutionary status of λ Bootis stars using HIPPARCOS data.
We have used the Hipparcos data to derive absolute magnitudes and thusthe evolutionary status for the group of λ Bootis stars. Theorigin for this small group of nonmagnetic, chemically peculiar stars,still remains a matter of debate. Using new evolutionary tracks, we areable to provide an age determination to distinguish between the twoproposed theories - the diffusion/mass-loss and the accretion theory.Our results establish the member of this group as objects which are veryclose to the Main Sequence. This is also supported by Pre-Main Sequenceevolutionary tracks as well as by observational results. We thereforecontradict prior conclusions that most of these stars are in the middleof their Main Sequence lifetime. The new results strongly support thepredictions of the accretion theory.
| HD 168740: a New Variable lambda Bootis Star
Not Available
| Blue Stragglers in the Solar Vicinity: Newborn or Reborn
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1995AJ....110..823E&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.
| Accretion from Circumstellar Discs and the Lambda-Bootis Phenomenon
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1994MNRAS.269..209K&db_key=AST
| The nature of the F STR λ4077 stars. V. Spectroscopic data
We report first high-resolution spectroscopic observations of 17 starsclassified F str λ4077 by Bidelman. They are compared todifferent types of stars, which have been observed at the same time,including 3 CH subgiants, 3 barium stars, 5 λ Bootis stars, Ap/Amstars, and normal main-sequence stars. The detailed equivalent widthsand abundances are given for all measured spectral lines, as well as themean abundance per species for each object. These data and theirsignificance are described in detail and discussed in an articlepublished in the Main Journal.
| The nature of the F STR lambda 4077 stars. 3: Spectroscopy of the barium dwarfs and other CP stars
The abundances of C, O, Al, Ca, iron-peak and s-process elements havebeen derived from high-resolution spectra for a sample of starsclassified as F str lambda 4077 by Bidelman. Among the 20 starsmentioned by Bidelman, we have discovered 8 barium dwarfs (or CHsubgiants, according to Bond's terminology), while a 9th star, HD182274, was already known as a CH subgiant. In addition, we haveanalyzed three barium stars taken from the list of Lu et al. (1983)which are probably dwarfs rather than giants, and three CH subgiants.The other 11 F str lambda 4077 stars resemble either the delta Delphinistars, since their iron abundance is enhanced while Ca is normal, or areprobably spectrum composites. A few Am, Ap, lambda Bootis and normalstars have been analyzed for comparison. In particular, we have includedthree lambda Boo candidates, selected from their photometric properties,and their iron deficiency is confirmed. The spectroscopic, photometricand statistical evidences concerning the Ba dwarfs, support the ideathat these stars may be the main sequence counterparts, and possibly theprogenitors of the Ba giants. The C/O ratio varies in these stars fromnormal values to a maximum of 1.5, but mostly within 0.6 and 1.2. Someof these objects may therefore be considered, in this sense, as carbonstars. On the other hand, the abundances of carbon and s-processelements relative to iron are inversely correlated with metallicity, andmay even exceed significantly those of typical, solar-metallicity carbonstars. Metal-deficient C stars must therefore have (C/Fe) greater thanor approximately equal to 1 and (s/Fe) greater than or approximatelyequal to 1.5 as soon as (Fe/H) less than or approximately equal to -1.The neutron exposure is shown to increase when the metallicitydecreases, which is compatible with the C-13 (alpha, n) O-16 neutronsource, but not with the Ne-22 (alpha, n) Mg-25 one. The evolutionarystate (within the main sequence) of the Ba dwarfs, is rediscussed inrelation with their photometric and spectroscopic surface gravity, butit remains unclear.
| The 71st Name-List of Variable Stars
Not Available
| Longterm Photometry of Variables at ESO - Part Two - the Second Data Catalogue 1986-1990
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1993A&AS..102...79S&db_key=AST
| Long-term photometry of variables at ESO. I - The first data catalogue (1982-1986)
This paper presents the catalog of photometric data in the Stromgrensystem obtained during the first four years (October 1982 - September1986) of the Long-Term Photometry of Variables (LTPV) program at ESO.The data are available in computer-readable form.
|
Додај нови чланак
Линкови у сродству са темом
Додај нови линк
Чланови следећих група \:
|
Посматрања и Астрометриски подаци
| Сазвежђа: | Паун |
| Ректацензија: | 18h25m31.50s |
| Deклинација: | -63°01'17.0" |
| Apparent магнитуда: | 6.14 |
| Даљина: | 71.276 parsecs |
| Proper motion RA: | 1 |
| Proper motion Dec: | -102.7 |
| B-T magnitude: | 6.36 |
| V-T magnitude: | 6.147 |
Каталог и designations:
|
INHABITED SKY
