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Публикации по объекту
s-Process in low metallicity Pb stars.
We consider a sample of very metal-poor, C-rich, s-rich and lead-richstars observed at high-resolution spectroscopy, and some recentspectroscopic data of C+s-rich stars obtained at moderate resolution.The spectroscopic data of these stars are interpreted with AGBtheoretical models of different 13C-pocket efficiencies,initial mass and initial r-enrichment. When lead is not measured we giveour theoretical prediction. The observed stars are not on the AGB phase,but are main sequence or giant stars. They acquired the C and senrichments by mass transfer in a close binary system from the moremassive companion while on the AGB (now a white dwarf). A considerablefraction of the stars show both high s and r enrichments. To explain thes+r enriched stars we assume a parental cloud already enriched inr-elements. The measurement of Nb is an indicator of an extrinsic AGB ina binary system. The intrinsic indicator [hs/ls] constrains the initialmass, while [Pb/hs] and [Pb/ls] are a measure of the s-processefficiency. The apparent discrepancies of C and N abundances may bereconciled by assuming a strong cool bottom process occurring during theAGB. An important primary production of light elements, from Ne to Si,increasing with the star mass, is predicted for AGB models at very lowmetallicity, induced by n capture on primary 22Ne and itsprogenies.
| 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.
| CH stars at high Galactic latitudes
Carbon-rich stars of Population II, such as CH stars, can provide directinformation on the role of low- to intermediate-mass stars of the haloin early Galactic evolution. Thus accurate knowledge of the CH stellarpopulation is a critical requirement for building up scenarios for earlyGalactic chemical evolution. In the present work, we report on severalCH stars identified in a sample of faint high-latitude carbon stars fromthe Hamburg survey and discuss their medium-resolution spectra coveringthe wavelength range 4000-6800 Å. Estimation of the depths of the(1,0)12C12C λ4737 and(1,0)12C13C λ4744 bands in these starsindicates an isotopic ratio 12C/13C ~ 3, apartfrom a few exceptions; these ratios are consistent with existingtheories of CH stellar evolution. The stars of the Hamburg survey, atotal of 403 objects, were reported to be carbon star candidates withstrong C2 and CN molecular bands. In the first phase ofobservation, we acquired spectra of 91 objects. Inspection of thespectra of those objects shows 51 objects with C2 molecularbands in their spectra, of which 13 stars have low flux below about 4300Å. There are 25 objects that show weak or moderate CH and CNbands, 12 objects that show weak but detectable CH bands, and threeobjects that do not show any molecular bands due to C2, CN orCH in their spectra. Objects with C2 molecular bands and withgood signals bluewards of 4300 Åthat show prominent CH bands intheir spectra are potential candidate CH stars. There were 35 suchcandidates found in the present sample of 91 objects observed so far.The set of CH stars identified could be the targets of subsequentobservation at high resolution for a detailed and comprehensive analysisto understand their role in early Galactic chemical evolution.
| Lead and mathbf s-process elements in stars of various metallicities: AGB predictions compared with observation
We present AGB predictions for all heavy elements within a large rangeof 13C-pocket efficiencies for stars of differentmetallicities, and compare them in detail with a number of spectroscopicobservations of s-rich and lead-rich in the Galaxy. The current conceptof the s-process efficiency, specified by the [hs/ls] index, is shown tobe inappropriate for the metal poor AGB stars and a second independentindex, [Pb/hs] or [Pb/ls], needs to be introduced. The state-of-the-artconcerning the interpretation of lead stars allows a very large spreadof [Pb/hs] in metal poor stars, as typically observed. We discussagreements and discrepancies for a large range of elements.
| 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).
| The Geneva-Copenhagen survey of the Solar neighbourhood. Ages, metallicities, and kinematic properties of 14 000 F and G dwarfs
We present and discuss new determinations of metallicity, rotation, age,kinematics, and Galactic orbits for a complete, magnitude-limited, andkinematically unbiased sample of 16 682 nearby F and G dwarf stars. Our63 000 new, accurate radial-velocity observations for nearly 13 500stars allow identification of most of the binary stars in the sampleand, together with published uvbyβ photometry, Hipparcosparallaxes, Tycho-2 proper motions, and a few earlier radial velocities,complete the kinematic information for 14 139 stars. These high-qualityvelocity data are supplemented by effective temperatures andmetallicities newly derived from recent and/or revised calibrations. Theremaining stars either lack Hipparcos data or have fast rotation. Amajor effort has been devoted to the determination of new isochrone agesfor all stars for which this is possible. Particular attention has beengiven to a realistic treatment of statistical biases and errorestimates, as standard techniques tend to underestimate these effectsand introduce spurious features in the age distributions. Our ages agreewell with those by Edvardsson et al. (\cite{edv93}), despite severalastrophysical and computational improvements since then. We demonstrate,however, how strong observational and theoretical biases cause thedistribution of the observed ages to be very different from that of thetrue age distribution of the sample. Among the many basic relations ofthe Galactic disk that can be reinvestigated from the data presentedhere, we revisit the metallicity distribution of the G dwarfs and theage-metallicity, age-velocity, and metallicity-velocity relations of theSolar neighbourhood. Our first results confirm the lack of metal-poor Gdwarfs relative to closed-box model predictions (the ``G dwarfproblem''), the existence of radial metallicity gradients in the disk,the small change in mean metallicity of the thin disk since itsformation and the substantial scatter in metallicity at all ages, andthe continuing kinematic heating of the thin disk with an efficiencyconsistent with that expected for a combination of spiral arms and giantmolecular clouds. Distinct features in the distribution of the Vcomponent of the space motion are extended in age and metallicity,corresponding to the effects of stochastic spiral waves rather thanclassical moving groups, and may complicate the identification ofthick-disk stars from kinematic criteria. More advanced analyses of thisrich material will require careful simulations of the selection criteriafor the sample and the distribution of observational errors.Based on observations made with the Danish 1.5-m telescope at ESO, LaSilla, Chile, and with the Swiss 1-m telescope at Observatoire deHaute-Provence, France.Complete Tables 1 and 2 are only available in electronic form at the CDSvia anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/418/989
| First stars IV. CS 29497-030: Evidence for operation of the s-process at very low metallicity
We present an abundance analysis of the very metal-poor, carbon-enhancedstar CS 29497-030. Our results indicate that this unusually hot turnoffstar (Teff = 6650 K, log g = 3.5) has a metallicity [Fe/H] =-2.8, and exhibits large overabundances of carbon ([C/Fe] = +2.38),nitrogen ([N/Fe] = +1.88), and oxygen ([O/Fe] = +1.67). This star alsoexhibits a large enhancement in its neutron-capture elements; thepattern follows that expected to arise from the s-process. Inparticular, the Pb abundance is found to be very high with respect toiron ([Pb/Fe] = +3.5), and also with respect to the second peaks-process elements (e.g., Ba, La, Ce, Nd), which fits into the newlyintroduced classification of lead (Pb) stars. The known spectroscopicbinary status of this star, along with the observed s-process abundancepattern, suggest that it has accreted matter from a companion, whichformerly was an Asymptotic Giant-Branch (AGB) star. In a preliminaryanalysis, we have also identified broad absorption lines of metallicspecies that suggest a large axial rotational velocity for this star,which may be the result of spin-up associated with the accretion ofmaterial from its previous AGB companion. In addition, this star isclearly depleted in the light element Li. When considered along with itsrather high inferred temperature, these observations are consistent withthe expected properties of a very low metallicity halo blue straggler.Based on observations made with the ESO Very Large Telescope at ParanalObservatory, Chile (program ID 165.N-0276(A)).Table \ref{tab6} is only available in electronic form athttp://www.edpsciences.org
| A search for diffuse absorption bands in carbon-rich stars - I. Barium and related stars
The results of a search for interstellar and circumstellar absorptionlines in high-resolution optical spectra of seven late-type stars arepresented. All these stars are single-lined spectroscopic binaries withunseen companions, presumably white dwarfs. Some residual materialindicative of recent mass transfer from an asymptotic giant branch (AGB)star might still be associated with the systems. Peculiar energydistribution and the sodium D1 and D2 lines givedirect evidence about the material in the line of sight in some cases.Absorption features of simple carbon-bearing molecules (C2,CN) have been detected in most of the examined stars, confirming acarbon-rich nature of the corresponding medium. The presence of fourwell-known prominent diffuse absorption bands at 5780, 5797, 5705, and5844 Å, belonging to different families, was examined. We have notfound clear evidence for these bands in the programme stars. Thepossible explanations are discussed in brief.
| Improved Astrometry and Photometry for the Luyten Catalog. II. Faint Stars and the Revised Catalog
We complete construction of a catalog containing improved astrometry andnew optical/infrared photometry for the vast majority of NLTT starslying in the overlap of regions covered by POSS I and by the secondincremental Two Micron All Sky Survey (2MASS) release, approximately 44%of the sky. The epoch 2000 positions are typically accurate to 130 mas,the proper motions to 5.5 mas yr-1, and the V-J colors to0.25 mag. Relative proper motions of binary components are measured to 3mas yr-1. The false-identification rate is ~1% for11<~V<~18 and substantially less at brighter magnitudes. Theseimprovements permit the construction of a reduced proper-motion diagramthat, for the first time, allows one to classify NLTT stars intomain-sequence (MS) stars, subdwarfs (SDs), and white dwarfs (WDs). We inturn use this diagram to analyze the properties of both our catalog andthe NLTT catalog on which it is based. In sharp contrast to popularbelief, we find that NLTT incompleteness in the plane is almostcompletely concentrated in MS stars, and that SDs and WDs are detectedalmost uniformly over the sky δ>-33deg. Our catalogwill therefore provide a powerful tool to probe these populationsstatistically, as well as to reliably identify individual SDs and WDs.
| More lead stars
The standard model for the operation of the s-process in asymptoticgiant branch (AGB) stars predicts that low-metallicity ([Fe/H] <~ -1)AGB stars should exhibit large overabundances of Pb and Bi as comparedto other s-elements. The discovery of the first three such ``leadstars'' (defined as stars enriched in s-elements with [Pb/hs] >~ 1,hs being any of Ba, La or Ce) among CH stars has been reported in aprevious paper (Van Eck et al. \cite{VanEck-01}). Five more CH stars(with [Fe/H] ranging from -1.5 to -2.5) are studied in the presentpaper, and two of them appear to be enriched in lead (with [Pb/Ce] =~0.7). The Pb I line at lambda4057 .812 Å is detected and clearlyresolved thanks to high-resolution spectra (R = lambda /Delta lambda =135ts000 ). The abundances for these two stars (HD 198269 and HD 201626)are consistent with the predictions for the s-process operating inlow-metallicity AGB stars as a consequence of the ``partial mixing'' ofprotons below the convective hydrogen envelope. Another two stars (HD189711 and V Ari) add to a growing number of low-metallicity stars (alsoincluding LP 625-44 and LP 706-7, as reported by Aoki et al.\cite{Aoki2001}) which do not conform to these predictions. Variationson the canonical proton-mixing scenario for the operation of thes-process in low-metallicity stars, that could account for thesediscrepant stars, are briefly discussed.Based on observations carried out at the European Southern Observatory(La Silla, Chile; Program 65.L-0354) and at the Observatoire de HauteProvence (operated by CNRS, France).
| 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
| Carbon-rich giants in the HR diagram and their luminosity function
The luminosity function (LF) of nearly 300 Galactic carbon giants isderived. Adding BaII giants and various related objects, about 370objects are located in the RGB and AGB portions of the theoretical HRdiagram. As intermediate steps, (1) bolometric corrections arecalibrated against selected intrinsic color indices; (2) the diagram ofphotometric coefficients 1/2 vs. astrometric trueparallaxes varpi are interpreted in terms of ranges of photosphericradii for every photometric group; (3) coefficients CR andCL for bias-free evaluation of mean photospheric radii andmean luminosities are computed. The LF of Galactic carbon giantsexhibits two maxima corresponding to the HC-stars of the thick disk andto the CV-stars of the old thin disk respectively. It is discussed andcompared to those of carbon stars in the Magellanic Clouds and Galacticbulge. The HC-part is similar to the LF of the Galactic bulge,reinforcing the idea that the Bulge and the thick disk are part of thesame dynamical component. The CV-part looks similar to the LF of theLarge Magellanic Cloud (LMC), but the former is wider due to thesubstantial errors on HIPPARCOS parallaxes. The obtained meanluminosities increase with increasing radii and decreasing effectivetemperatures, along the HC-CV sequence of photometric groups, except forHC0, the earliest one. This trend illustrates the RGB- and AGB-tracks oflow- and intermediate-mass stars for a range in metallicities. From acomparison with theoretical tracks in the HR diagram, the initial massesMi range from about 0.8 to 4.0 Msun for carbongiants, with possibly larger masses for a few extreme objects. A largerange of metallicities is likely, from metal-poor HC-stars classified asCH stars on the grounds of their spectra (a spheroidal component), tonear-solar compositions of many CV-stars. Technetium-rich carbon giantsare brighter than the lower limit Mbol =~ -3.6+/- 0.4 andcentered at =~-4.7+0.6-0.9 at about =~(2935+/-200) K or CV3-CV4 in our classification. Much like the resultsof Van Eck et al. (\cite{vaneck98}) for S stars, this confirms theTDU-model of those TP-AGB stars. This is not the case of the HC-stars inthe thick disk, with >~ 3400 K and>~ -3.4. The faint HC1 and HC2-stars( =~ -1.1+0.7-1.0) arefound slightly brighter than the BaII giants ( =~-0.3+/-1.3) on average. Most RCB variables and HdC stars range fromMbol =~ -1 to -4 against -0.2 to -2.4 for those of the threepopulation II Cepheids in the sample. The former stars show the largestluminosities ( <~ -4 at the highest effectivetemperatures (6500-7500 K), close to the Mbol =~ -5 value forthe hot LMC RCB-stars (W Men and HV 5637). A full discussion of theresults is postponed to a companion paper on pulsation modes andpulsation masses of carbon-rich long period variables (LPVs; Paper IV,present issue). This research has made use of the Simbad databaseoperated at CDS, Strasbourg, France. Partially based on data from theESA HIPPARCOS astrometry satellite. Table 2 is only available inelectronic form at the CDS via anonymous ftp to cdsarc.u-strasbg.fr(130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/390/967
| Nucleosynthesis and Mixing on the Asymptotic Giant Branch. III. Predicted and Observed s-Process Abundances
We present the results of s-process nucleosynthesis calculations forasymptotic giant branch (AGB) stars of different metallicities anddifferent initial stellar masses (1.5 and 3 Msolar), and wepresent comparisons of them with observational constraints fromhigh-resolution spectroscopy of evolved stars over a wide metallicityrange. The computations were based on previously published stellarevolutionary models that account for the third dredge-up phenomenonoccurring late on the AGB. Neutron production is driven by the13C(α,n)16O reaction during the interpulseperiods in a tiny layer in radiative equilibrium at the top of the He-and C-rich shell. The neutron source 13C is manufacturedlocally by proton captures on the abundant 12C; a few protonsare assumed to penetrate from the convective envelope into the radiativelayer at any third dredge-up episode, when a chemical discontinuity isestablished between the convective envelope and the He- and C-richzones. A weaker neutron release is also guaranteed by the marginalactivation of the reaction 22Ne(α,n)25Mgduring the convective thermal pulses. Owing to the lack of a consistentmodel for 13C formation, the abundance of 13Cburnt per cycle is allowed to vary as a free parameter over a wideinterval (a factor of 50). The s-enriched material is subsequently mixedwith the envelope by the third dredge-up, and the envelope compositionis computed after each thermal pulse. We follow the changes in thephotospheric abundance of the Ba-peak elements (heavy s [hs]) and thatof the Zr-peak ones (light s [ls]), whose logarithmic ratio [hs/ls] hasoften been adopted as an indicator of the s-process efficiency (e.g., ofthe neutron exposure). Our model predictions for this parameter show acomplex trend versus metallicity. Especially noteworthy is theprediction that the flow along the s-path at low metallicities drainsthe Zr and Ba peaks and builds an excess at the doubly magic208Pb, which is at the termination of the s-path. We thendiscuss the effects on the models of variations in the crucialparameters of the 13C pocket, finding that they are notcritical for interpreting the results. The theoretical predictions arecompared with published abundances of s-elements for AGB giants ofclasses MS, S, SC, post-AGB supergiants, and for various classes ofbinary stars, which supposedly derive their composition by mass transferfrom an AGB companion. This is done for objects belonging both to theGalactic disk and to the halo. The observations in general confirm thecomplex dependence of neutron captures on metallicity. They suggest thata moderate spread exists in the abundance of 13C that isburnt in different stars. Although additional observations are needed,it seems that a good understanding has been achieved of s-processoperation in AGB stars. Finally, the detailed abundance distributionincluding the light elements (CNO) of a few s-enriched stars atdifferent metallicities are examined and satisfactorily reproduced bymodel envelope compositions.
| The Abundance Pattern of Two Barium Stars in the Galactic Halo: HD 104340 and HD 206983
We present the abundance pattern of two barium stars in the Galactichalo, HD 104340 and HD 206983, based on high-resolution optical spectra.We also determined the spectroscopic stellar atmospheric parameters,temperature, and microturbulent velocity, as well as stellar surfacegravity from a solution of excitation and ionization equilibria of Fe Iand Fe II lines under the assumption of local thermodynamic equilibrium.The abundance analysis reveals HD 104340 to be a metal-poor K giant with[Fe/H]=-1.72 and HD 206983 also a metal-poor K giant with [Fe/H]=-1.43.From a set of Fe I lines, the radial velocity is found to be 263.3+/-0.6km s-1 and -319.2+/-4.4 km s-1 for HD 104340 andHD 206983, respectively. Their high velocity, low metallicity, and highgalactic latitude imply that both stars are members of a Galactic halopopulation. From our study and by using information from the literaturewe believe that HD 206983 is another member of a group known asmetal-deficient barium stars. We compare the abundance pattern with theabundances of a halo population. We found that the abundances of theiron group, α-elements, manganese, copper, and zinc, as well assodium and magnesium, of HD 104340 and HD 206983 follow the abundancepattern of a halo population. The heavy element abundance pattern ofboth stars shows enhancement by a factor of 4-8 with respect to themetal-poor stars with the same metallicity as that analyzed by us. Wealso discuss the abundances of the s-process elements and compare ourresults with other objects that display the same degree of enrichmentdue to neutron capture reactions, binary systems, and AGB stars, througha diagram of metallicity versus neutron exposure given by the [hs/ls]index. Based on the observations made with the 1.52 m telescope at theEuropean Southern Observatory (La Silla, Chile) under agreement withObservatório Nacional (Brazil).
| The effective temperatures of carbon-rich stars
We evaluate effective temperatures of 390 carbon-rich stars. Theinterstellar extinction on their lines of sights was determined andcircumstellar contributions derived. The intrinsic (dereddened) spectralenergy distributions (SEDs) are classified into 14 photometric groups(HCi, CVj and SCV with i=0,5 and j=1,7). The newscale of effective temperatures proposed here is calibrated on the 54angular diameters (measured on 52 stars) available at present from lunaroccultations and interferometry. The brightness distribution on stellardiscs and its influence on diameter evaluations are discussed. Theeffective temperatures directly deduced from those diameters correlatewith the classification into photometric groups, despite the large errorbars on diameters. The main parameter of our photometric classificationis thus effective temperature. Our photometric < k right >1/2 coefficients are shown to be angular diameters on arelative scale for a given photometric group, (more precisely for agiven effective temperature). The angular diameters are consistent withthe photometric data previously shown to be consistent with the trueparallaxes from HIPPARCOS observations (Knapik, et al. \cite{knapik98},Sect. 6). Provisional effective temperatures, as constrained by asuccessful comparison of dereddened SEDs from observations to modelatmosphere predictions, are in good agreement with the values directlycalculated from the observed angular diameters and with those deducedfrom five selected intrinsic color indices. These three approaches wereused to calibrate a reference angular diameter Phi 0 and theassociated coefficient CT_eff. The effective temperatureproposed for each star is the arithmetic mean of two estimates, one(``bolometric'') from a reference integrated flux F0, theother (``spectral'') from calibrated color indices which arerepresentative of SED shapes. Effective temperatures for about 390carbon stars are provided on this new homogeneous scale, together withvalues for some stars classified with oxygen-type SEDs with a total of438 SEDs (410 stars) studied. Apparent bolometric magnitudes are given.Objects with strong infrared excesses and optically thick circumstellardust shells are discussed separately. The new effective temperaturescale is shown to be compatible and (statistically) consistent with thesample of direct values from the observed angular diameters. Theeffective temperatures are confirmed to be higher than the mean colortemperatures (from 140 to 440 K). They are in good agreement with thepublished estimates from the infrared flux method forTeff>= 3170 K, while an increasing discrepancy is observedtoward lower temperatures. As an illustration of the efficiency of thephotometric classification and effective temperature scale, the C/Oratios and the Merrill-Sanford (M-S) band intensities are investigated.It is shown that the maximum value, mean value and dispersion of C/Oincrease along the photometric CV-sequence, i.e. with decreasingeffective temperature. The M-S bands of SiC2 are shown tohave a transition from ``none'' to ``strong'' at Teff =~(2800+/- 150right ) K. Simultaneously, with decreasing effectivetemperature, the mean C/O ratio increases from 1.04 to 1.36, thetransition in SiC2 strength occurring while 1.07<= C/O<= 1.18. This research has made use of the Simbad database operatedat CDS, Strasbourg, France. Table 10 is only available in electronicform at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5)}or via http://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/369/178
| The First 50 Years at Palomar, 1949-1999 Another View: Instruments, Spectroscopy and Spectrophotometry and the Infrared
We review the research on a wide variety of topics using data obtainedwith the 200-inch Hale telescope. Using state-of-the-art spectrographs,photometers, spectrometers and infrared detectors, the Palomarastronomers investigated the spectra of stars, interstellar matter, AGNsand quasars in great detail. Spectral resolutions ranged from 1000 A forbroad-band photometry to 0.04 A using interferometric techniques.
| Stellar Iron Abundances: Non-LTE Effects
We report new statistical equilibrium calculations for Fe I and Fe II inthe atmosphere of late-type stars. We used atomic models for Fe I and FeII having, respectively, 256 and 190 levels, as well as 2117 and 3443radiative transitions. Photoionization cross sections are from the IronProject. These atomic models were used to investigate non-LTE (NLTE)effects in iron abundances of late-type stars with different atmosphericparameters. We found that most Fe I lines in metal-poor stars are formedin conditions far from LTE. We derived metallicity corrections of about0.3 dex with respect to LTE values for the case of stars with[Fe/H]~-3.0. Fe II is found not to be affected by significant NLTEeffects. The main NLTE effect invoked in the case of Fe I isoverionization by ultraviolet radiation; thus classical ionizationequilibrium is far from being satisfied. An important consequence isthat surface gravities derived by LTE analysis are in error and shouldbe corrected before final abundance corrections. This apparently solvesthe observed discrepancy between spectroscopic surface gravities derivedby LTE analyses and those derived from Hipparcos parallaxes. A table ofNLTE [Fe/H] and log g values for a sample of metal-poor late-type starsis given.
| Catalogs of temperatures and [Fe/H] averages for evolved G and K stars
A catalog of mean values of [Fe/H] for evolved G and K stars isdescribed. The zero point for the catalog entries has been establishedby using differential analyses. Literature sources for those entries areincluded in the catalog. The mean values are given with rms errors andnumbers of degrees of freedom, and a simple example of the use of thesestatistical data is given. For a number of the stars with entries in thecatalog, temperatures have been determined. A separate catalogcontaining those data is briefly described. Catalog only available atthe CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/Abstract.html
| Dust extinction and intrinsic SEDs of carbon-rich stars. II. The hot carbon stars
The present work is an extension of a recent study by Knapik &Bergeat (\cite{knapik}, henceforth called Paper I) of the spectralenergy distributions (SEDs) of about 300 cool carbon-rich variables andof the interstellar extinction observed on their line of sights. Themethods were originally developed for Semi-Regular (SR) and Irregular(L)-variables. Shortly, this is a kind of a pair method making usesimultaneously of the whole SED from UV to IR. Our approach is appliedhere to the galactic carbon-rich giants with bluer SEDs, namely the hotcarbon (HC) stars, including many ``constant'' stars and a minority ofvariables: AC Her a RV Tau star, the R Coronae Borealis (RCB) stars andothers. Some HdC (i.e. carbon-rich hydrogen deficient stars) and Ba IIstars are also considered. The total number of studied HC stars amountsto about 140. With few exceptions, the colour excesses for interstellarextinction are found in good agreement with the field values from mapspublished in the literature, taking into account the approximatedistances to our stars from HIPPARCOS data (\cite{esa}, henceforthcalled ESA) or binarity. We propose a classification scheme with sixphotometric groups (or boxes: HC0 to HC5) from the bluest to the reddestSEDs. Oxygen-rich SEDs earlier than HC0, are attributed to the hotteststars (AC Her, most RCB-variables and a few others). Previous findingsare confirmed of a junction between oxygen-rich and carbon-rich SEDs atspectral type G. The latest (HC5) group is immediately close to theearliest one in Paper I, namely CV1. The sequence of groups then goesregularly from HC0 to CV6. Substantial infrared excesses with respect toour solutions are found in HD 100764 a HC1 carbon star, AC Her a G0g RVTau star, and the RCB stars classified in either HC or oxygen-groups.The colour excesses at maximum light can usually be attributed tointerstellar reddening, with neutral circumstellar (CS) reddening (largegrains) or no CS extinction at all on the line of sight (non sphericalgeometry) as possible explanations. The latter model (disc or patchydistribution through successive puffs) is favoured. Two RCB variablesfor which we exploit SEDs on a rising branch (V CrA) or minimum light(RS Tel), show CS laws, respectively a selective extinction compatiblewith small grains and an extinction partly neutral indicative of largegrains on the line of sight. This research has made use of the Simbaddatabase operated at CDS, Strasbourg, France.}\fnmsep\thanks{Partiallybased on data from the ESA HIPPARCOS astrometrysatellite}\fnmsep\thanks{Tables~3 and 4 are only available in electronicform at the CDS via anonymous ftp 130.79.128.5
| Towards a fundamental calibration of stellar parameters of A, F, G, K dwarfs and giants
I report on the implementation of the empirical surface brightnesstechnique using the near-infrared Johnson broadband { (V-K)} colour assuitable sampling observable aimed at providing accurate effectivetemperatures of 537 dwarfs and giants of A-F-G-K spectral-type selectedfor a flux calibration of the Infrared Space Observatory (ISO). Thesurface brightness-colour correlation is carefully calibrated using aset of high-precision angular diameters measured by moderninterferometry techniques. The stellar sizes predicted by thiscorrelation are then combined with the bolometric flux measurementsavailable for a subset of 327 ISO standard stars in order to determineone-dimensional { (T, V-K)} temperature scales of dwarfs and giants. Theresulting very tight relationships show an intrinsic scatter induced byobservational photometry and bolometric flux measurements well below thetarget accuracy of +/- 1 % required for temperature determinations ofthe ISO standards. Major improvements related to the actual directcalibration are the high-precision broadband { K} magnitudes obtainedfor this purpose and the use of Hipparcos parallaxes for dereddeningphotometric data. The temperature scale of F-G-K dwarfs shows thesmallest random errors closely consistent with those affecting theobservational photometry alone, indicating a negligible contributionfrom the component due to the bolometric flux measurements despite thewide range in metallicity for these stars. A more detailed analysisusing a subset of selected dwarfs with large metallicity gradientsstrongly supports the actual bolometric fluxes as being practicallyunaffected by the metallicity of field stars, in contrast with recentresults claiming somewhat significant effects. The temperature scale ofF-G-K giants is affected by random errors much larger than those ofdwarfs, indicating that most of the relevant component of the scattercomes from the bolometric flux measurements. Since the giants have smallmetallicities, only gravity effects become likely responsible for theincreased level of scatter. The empirical stellar temperatures withsmall model-dependent corrections are compared with the semiempiricaldata by the Infrared Flux Method (IRFM) using the large sample of 327comparison stars. One major achievement is that all empirical andsemiempirical temperature estimates of F-G-K giants and dwarfs are foundto be closely consistent between each other to within +/- 1 %. However,there is also evidence for somewhat significant differential effects.These include an average systematic shift of (2.33 +/- 0.13) % affectingthe A-type stars, the semiempirical estimates being too low by thisamount, and an additional component of scatter as significant as +/- 1 %affecting all the comparison stars. The systematic effect confirms theresults from other investigations and indicates that previousdiscrepancies in applying the IRFM to A-type stars are not yet removedby using new LTE line-blanketed model atmospheres along with the updatedabsolute flux calibration, whereas the additional random component isfound to disappear in a broadband version of the IRFM using an infraredreference flux derived from wide rather than narrow band photometricdata. Table 1 and 2 are only available in the electronic form of thispaper
| 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
| Barium stars, galactic populations and evolution.
In this paper HIPPARCOS astrometric and kinematical data together withradial velocities from other sources are used to calibrate bothluminosity and kinematics parameters of Ba stars and to classify them.We confirm the results of our previous paper (where we used data fromthe HIPPARCOS Input Catalogue), and show that Ba stars are aninhomogeneous group. Five distinct classes have been found i.e. somehalo stars and four groups belonging to disk population: roughlysuper-giants, two groups of giants (one on the giant branch, the otherat the clump location) and dwarfs, with a few subgiants mixed with them.The confirmed or suspected duplicity, the variability and the range ofknown orbital periods found in each group give coherent resultssupporting the scenario for Ba stars that are not too highly massivebinary stars in any evolutionary stages but that all were previouslyenriched with Ba from a more evolved companion. The presence in thesample of a certain number of ``false'' Ba stars is confirmed. Theestimates of age and mass are compatible with models for stars with astrong Ba anomaly. The mild Ba stars with an estimated mass higher than3Msun_ may be either stars Ba enriched by themselves or``true'' Ba stars, which imposes new constraints on models.
| Absolute magnitudes and kinematics of barium stars.
The absolute magnitude of barium stars has been obtained fromkinematical data using a new algorithm based on the maximum-likelihoodprinciple. The method allows to separate a sample into groupscharacterized by different mean absolute magnitudes, kinematics andz-scale heights. It also takes into account, simultaneously, thecensorship in the sample and the errors on the observables. The methodhas been applied to a sample of 318 barium stars. Four groups have beendetected. Three of them show a kinematical behaviour corresponding todisk population stars. The fourth group contains stars with halokinematics. The luminosities of the disk population groups spread alarge range. The intrinsically brightest one (M_v_=-1.5mag,σ_M_=0.5mag) seems to be an inhomogeneous group containing bariumbinaries as well as AGB single stars. The most numerous group (about 150stars) has a mean absolute magnitude corresponding to stars in the redgiant branch (M_v_=0.9mag, σ_M_=0.8mag). The third group containsbarium dwarfs, the obtained mean absolute magnitude is characteristic ofstars on the main sequence or on the subgiant branch (M_v_=3.3mag,σ_M_=0.5mag). The obtained mean luminosities as well as thekinematical results are compatible with an evolutionary link betweenbarium dwarfs and classical barium giants. The highly luminous group isnot linked with these last two groups. More high-resolutionspectroscopic data will be necessary in order to better discriminatebetween barium and non-barium stars.
| Carbon isotope ratio in carbon stars of the galactic halo.
We analysed CN red system (~8000Å) and C_2_ Swan system(~4700Å) to know carbon isotope ratios (^12^C/^13^C) for carbonstars in the Galactic halo, named CH stars. The isotope ratios areobtained for 6 CH stars by the curve-of-growth analysis of the isolated^12^CN and ^13^CN lines. In this analysis, we compared directly ^12^CNand ^13^CN lines of similar intensities (iso-intensity method), and theresulting ^12^C/^13^C ratios are almost independent of the modelatmosphere and its parameters. The ^13^CN lines appear to be too weak insome CH stars, for which we applied the spectral synthesis method to thestronger C_2_ Swan band, obtained ^12^C/^13^C ratios for two stars andestimated the lower limits of ^12^C/^13^C ratios for two stars. In thiscase, however, the results depend on model atmosphere and itsparameters. Results from our present and previous works show that mostof them (12 stars) distribute around ^12^C/^13^C~10 and two stars havevery high values (^12^C/^13^C>=500). The distribution of ^12^C/^13^Cratios in CH stars is different from that of the population I carbonstars as well as population II oxygen-rich giants (G~K types). The CHstars of very high ^12^C/^13^C ratios can be explained by dredge-up of^12^C due to 3α-process as in population I carbon stars (N-type).On the other hand the formation of the CH stars with low ^12^C/^13^Cratios requires the large supply of ^12^C followed by a process ofdecreasing ^12^C/^13^C ratio.
| A New Version of the Catalog of CH and Related Stars (CH95 Catalog)
A new version of the catalog of CH and related stars contains 244 fieldstars and 17 globular cluster stars. Here a list of these stars withtheir coordinates, their positions in the HR diagram and somestatistical diagrams is presented. The catalog will soon be available inthe printed and computerized versions.
| Classification of Population II Stars in the Vilnius Photometric System. I. Methods
The methods used for classification of Population II stars in theVilnius photometric system are described. An extensive set of standardswith known astrophysical parameters compiled from the literature sourcesis given. These standard stars are classified in the Vilnius photometricsystem using the methods described. The accuracy of classification isevaluated by a comparison of the astrophysical parameters derived fromthe Vilnius photometric system with those estimated from spectroscopicstudies as well as from photometric data in other systems. For dwarfsand subdwarfs, we find a satisfactory agreement between our reddeningsand those estimated in the uvbyscriptstyle beta system. The standarddeviation of [Fe/H] deter mined in the Vilnius system is about 0.2 dex.The absolute magnitude for dwarfs and subdwarfs is estimated with anaccuracy of scriptstyle <=0.5 mag.
| A Moderate-Resolution Spectral Atlas of Carbon Stars: R, J, N, CH, and Barium Stars
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1996ApJS..105..419B&db_key=AST
| Observations of Variable Stars with the R-Coronae Phenomenon and Other Unique Objects
Not Available
| Nine Seasons of Velocity Measurements in the Draco and Ursa Minor Dwarf Spheroidal Galaxies with the MMT Echelle
We have used the Multiple Mirror Telescope echelle spectrograph tomeasure 112 velocities of 42 stars in the Draco and Ursa Minor dwarfspheroidal galaxies and three velocities of three foreground starsbetween 1982 April and 1990 September. We used 11 A resolution spectraobtained with the MX multifiber spectrograph at the Steward 90" to findadditional giant candidates; 5 UMi and 13 Draco stars were then observedat the MMT and added to the original sample of velocity members. Inaddition, the MX spectra were used to eliminate 74 stars in thedirection of UMI and 59 stars in Draco as likely foreground dwarfs. Wedetected 7 velocity variables, defined as those stars whose probabilityof exceeding the measured X^2^ by chance is less than 1.5%. Three ofthese stars are Carbon (C) stars (UMi K and VA 335 and Draco C1); twohave emission lines (Draco CI and UMi M). We show that the C star DracoC4, with a proper motion membership probability of 7%, has a velocityconsistent with membership. It is not surprising that these C (mostlikely CH) stars are binaries because McClure has shown that mostGalactic CH stars are in binary systems. Of the remaining 35 stars, only4 are velocity variables, with measured velocity extrema of 29.1 kms^-1^ (UMi M), 7.2 km s^-1^ (Draco XI-2), 9.0 km s^-1^ (Draco 24), and8.3 km s^-1^ (Draco 473). The velocity dispersions are 10.1 +/- 1.7 kms^-1^ for UMi, and 9.9 +/- 1.4 km s^-1^ for Draco. These dispersionschange to 10.5 +/- 2.0 for UMi, and 8.2 +?- 1.3 for Draco if weeliminate the velocity variables. Our dispersion for UMi differs fromthat of Hargreaves et al. [MNRAS, 271,693 (1994b)] by 1.3σ of thecombined errors. These velocities are combined with the one-componentKing models of Pryor & Kormendy [AJ, 100,127 (1990)] to give M/L =73 for UMi, and 77 for Draco.
| Ca II H and K Filter Photometry on the UVBY System. II. The Catalog of Observations
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1995AJ....109.2828T&db_key=AST
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Группы:
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Наблюдательные данные и астрометрия
| Созвездие: | Рыбы |
| Прямое восхождение: | 00h05m22.21s |
| Склонение: | +08°47'16.1" |
| Видимая звёздная величина: | 8.232 |
| Расстояние: | 591.716 парсек |
| Собственное движение RA: | 260.9 |
| Собственное движение Dec: | -59.2 |
| B-T magnitude: | 9.563 |
| V-T magnitude: | 8.342 |
Каталоги и обозначения:
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