Chemical composition of a sample of candidate post-asymptotic giant branch stars
We have derived elemental abundances for a sample of nine IRAS sourceswith colours similar to those of post-asymptotic giant branch (post-AGB)stars. For IRAS 01259+6823, IRAS 05208-2035, IRAS 04535+3747 and IRAS08187-1905, this is the first detailed abundance analysis based uponhigh-resolution spectra. Mild indication of s-processing for IRAS01259+6823, IRAS 05208-2035 and IRAS 08187-1905 has been found and amore comprehensive study of s-process-enhanced objects IRAS 17279-1119and IRAS 22223+4327 has been carried out.We have also made a contemporary abundance analysis of the high Galacticlatitude supergiants BD+39°4926 and HD 107369. The former is heavilydepleted in refractories and estimated [Zn/H] of -0.7 dex most likelygives initial metallicity of the star. For HD 107369 the abundances of? and Fe-peak elements are similar to those of halo objects andmoderate deficiency of s-process elements is seen. IRAS 07140-2321,despite being a short-period binary with a circumstellar shell, does notexhibit selective depletion of refractory elements.We have compiled the stellar parameters and abundances for post-AGBstars with s-process enhancement, those showing significant depletion ofcondensable elements and those showing neither. The compilation showsthat the s-process-enhanced group contains a very small number ofbinaries, and observed [?/Fe] are generally similar to thick-discvalues. It is likely that they represent AGB evolution of single stars.The compilation of the depleted group contains a larger fraction ofbinaries and generally supports the hypothesis of dusty discssurrounding binary post-AGB stars inferred via the shape of theirspectral energy distribution and mid-infrared interferometry. IRAS07140-2321 and BD+39°4926 are difficult to explain with thisscenario and indicate the existence of an additional parameter/conditionneeded to explain the depletion phenomenon. However, the conditions fordiscernible depletion, minimum temperature of 5000 K and initialmetallicity larger than -1.0 dex found from our earlier work still serveas useful criteria.
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Random forest automated supervised classification of Hipparcos periodic variable stars
We present an evaluation of the performance of an automatedclassification of the Hipparcos periodic variable stars into 26 types.The sub-sample with the most reliable variability types available in theliterature is used to train supervised algorithms to characterize thetype dependencies on a number of attributes. The most useful attributesevaluated with the random forest methodology include, in decreasingorder of importance, the period, the amplitude, the V-I colour index,the absolute magnitude, the residual around the folded light-curvemodel, the magnitude distribution skewness and the amplitude of thesecond harmonic of the Fourier series model relative to that of thefundamental frequency. Random forests and a multi-stage scheme involvingBayesian network and Gaussian mixture methods lead to statisticallyequivalent results. In standard 10-fold cross-validation (CV)experiments, the rate of correct classification is between 90 and 100per cent, depending on the variability type. The main mis-classificationcases, up to a rate of about 10 per cent, arise due to confusion betweenSPB and ACV blue variables and between eclipsing binaries, ellipsoidalvariables and other variability types. Our training set and thepredicted types for the other Hipparcos periodic stars are availableonline.
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BAV-results of observations.
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The PASTEL catalogue of stellar parameters
Aims: The PASTEL catalogue is an update of the [Fe/H] catalogue,published in 1997 and 2001. It is a bibliographical compilation ofstellar atmospheric parameters providing (T_eff, log g, [Fe/H])determinations obtained from the analysis of high resolution, highsignal-to-noise spectra, carried out with model atmospheres. PASTEL alsoprovides determinations of the one parameter T_eff based on variousmethods. It is aimed in the future to provide also homogenizedatmospheric parameters and elemental abundances, radial and rotationalvelocities. A web interface has been created to query the catalogue onelaborated criteria. PASTEL is also distributed through the CDS databaseand VizieR. Methods: To make it as complete as possible, the mainjournals have been surveyed, as well as the CDS database, to findrelevant publications. The catalogue is regularly updated with newdeterminations found in the literature. Results: As of Febuary2010, PASTEL includes 30151 determinations of either T_eff or (T_eff,log g, [Fe/H]) for 16 649 different stars corresponding to 865bibliographical references. Nearly 6000 stars have a determination ofthe three parameters (T_eff, log g, [Fe/H]) with a high qualityspectroscopic metallicity.The catalogue can be queried through a dedicated web interface at http://pastel.obs.u-bordeaux1.fr/.It is also available in electronic form at the Centre de DonnéesStellaires in Strasbourg (http://vizier.u-strasbg.fr/viz-bin/VizieR?-source=B/pastel),at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) orvia http://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/515/A111
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BAV-Results of observations
This 62nd compilation contains the results of visual observations ofBAV-members from the years 2007 and 2008. Here we publish altogether 337minima and maxima of 201 eclipsing binaries, pulsating and eruptivestars. The data were acquired by 14 observers. The compilation containsalso one photographic- and two ccd-results.
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(B-R)-Werte der Cepheiden in den BAV-Mitteilungen nr. 202.
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BAV-Results observations.
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On the Connection Between CWA and RVA Stars
Phase plots of ASAS-3 data of a large number of CWA and RVA variablestars reveal that there is no clear distinction in period or light curveshape between these two types of stars.
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Photoelectric observations of Cepheids in UBV(RI)c (Berdnikov, 2008)
This catalog gathers the observation of 894 Cepheids made between 1986to 2004.Observations are listed in alphabetical order of the constellations. Thestandard deviation for every magnitude and color is 0.01mag.This version supersedes the 1997 edition (Cat. )(3 data files).
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Aktuelle (B-R)-Werte f?r einige teleskopische Cepheiden.
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The Chemical Compositions of the Type II Cepheids-The BL Herculis and W Virginis Variables
Abundance analyses from high-resolution optical spectra are presentedfor 19 type II Cepheids in the Galactic field. The sample includes bothshort-period (BL Her) and long-period (W Vir) stars. This is the firstextensive abundance analysis of these variables. The C, N, and Oabundances with similar spreads for the BL Her and W Vir show evidencefor an atmosphere contaminated with 3α process and CN-cyclingproducts. A notable anomaly of the BL Her stars is an overabundance ofNa by a factor of about 5 relative to their presumed initial abundances.This overabundance is not seen in the W Vir stars. The abundanceanomalies running from mild to extreme in W Vir stars but not seen inthe BL Her stars are attributed to dust-gas separation that provides anatmosphere deficient in elements of high condensation temperature,notably, Al, Ca, Sc, Ti, and s-process elements. Such anomalies havepreviously been seen among RV Tau stars which represent a long-periodextension of the variability enjoyed by the type II Cepheids. Commentsare offered on how the contrasting abundance anomalies of BL Her and WVir stars may be explained in terms of the stars' evolution from theblue horizontal branch.
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The Peculiar Cepheid TW Capricorni
55 maxima since 1917 of the peculiar cepheid TW Cap is reported. Thestar is undergoing drastic period changes and has variable shape of thelightcurve.
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Beobachtungssergebnisse Bundesdeutsche Arbeitsgemeinschaft fuer Veraenderliche Sterne e.V.
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The Spectra of Type II Cepheids. III. The Hα Line and Helium Emission in Long-Period Stars
We have obtained Hα profiles from 175 spectra of 37 Cepheids withperiods longer than 8 days. About two-thirds of the stars are likelytype II Cepheids. In contrast to the situation among short-period stars,the velocity of Hα relative to the metal-line spectrum is not auseful parameter for distinguishing type I and type II Cepheids. On theother hand, at periods longer than 11 days and shorter than 34 daysstrong emission is observed in many stars and appears to be a gooddiscriminator of type. On this basis we identify one probable type ICepheid at a large distance from the Galactic plane. We have found Heλ5876 emission in seven Cepheids among the long-period starsdiscussed here and in one star with a short period, bringing to nine thenumber of type II Cepheids known to exhibit He emission.Based in part on observations obtained with the Apache Point Observatory3.5 m telescope, which is owned and operated by the AstrophysicalResearch Consortium.
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Photometry of Type II Cepheids. I. The Long-Period Stars
We present 1256 new photometric observations of 36 Cepheids with periodslonger than 8 days. The majority are likely type II Cepheids, but wehave included about a dozen classical Cepheids for comparison purposes,a few stars of uncertain type, and one putative RV Tauri star. Wediscuss the appearance of the light curves, the Fourier parameters, andthe light-curve stability in terms of differentiation between type I andtype II Cepheids. Although we encounter the same difficulties asprevious investigators in using these parameters for this purpose, weare able to identify some stars of particular interest, includingseveral likely type I Cepheids at large distances from the Galacticplane. Six stars with especially large period changes are identified anddiscussed.
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Cepheidenbeobachtung in der BAV: Ruckblick und Ausblick.
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Beobachtungsergebnisse Bundesdeutsche Arbeitsgemeinschaft fur Veranderlichen Serne e.V.
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Beobachtungsegebnisse Bundesdeutsche Arbeitsgemainschaft fur Veranderliche Sterne e.V.
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The Cepheids of Population II and Related Stars
The Type II Cepheids include most intrinsic variables with periodsbetween 1 and about 50 days, except for the classical Cepheids and theshortest semiregular variables of type M. The Type II Cepheids may bedivided in groups by period, such that the stars with periods beween 1and 5 days (BL Her class), 10-20 days (W Vir class), and greater than 20days (RV Tau class) have differing evolutionary histories. The chemicalcomposition of Type II Cepheids reflects the material they were madefrom as modified by their internal nuclear evolution and mixing.Finally, RV Tau stars are affected by mass loss by dust and speciesattached to the dust. The populations to which the various classes ofType II Cepheids are assigned constitute important clues to the originand evolution of the halo of our Galaxy and the dwarf spheroidal systemsfrom which at least part of the halo seems to have been accreted.
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Cepheiden: was wird beobachtet - was nicht ?
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Stars with the Largest Hipparcos Photometric Amplitudes
A list of the 2027 stars that have the largest photometric amplitudes inHipparcos Photometry shows that most variable stars are all Miras. Thepercentage of variable types change as a function of amplitude. Thiscompilation should also be of value to photometrists looking forrelatively unstudied, but large amplitude stars.
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Kinematics of Metal-poor Stars in the Galaxy. II. Proper Motions for a Large Nonkinematically Selected Sample
We present a revised catalog of 2106 Galactic stars, selected withoutkinematic bias and with available radial velocities, distance estimates,and metal abundances in the range -4.0<=[Fe/H]<=0.0. This updateof the 1995 Beers & Sommer-Larsen catalog includes newly derivedhomogeneous photometric distance estimates, revised radial velocitiesfor a number of stars with recently obtained high-resolution spectra,and refined metallicities for stars originally identified in the HKobjective-prism survey (which account for nearly half of the catalog)based on a recent recalibration. A subset of 1258 stars in this cataloghave available proper motions based on measurements obtained with theHipparcos astrometry satellite or taken from the updated AstrographicCatalogue (second epoch positions from either the Hubble Space TelescopeGuide Star Catalog or the Tycho Catalogue), the Yale/San Juan SouthernProper Motion Catalog 2.0, and the Lick Northern Proper Motion Catalog.Our present catalog includes 388 RR Lyrae variables (182 of which arenewly added), 38 variables of other types, and 1680 nonvariables, withdistances in the range 0.1 to 40 kpc.
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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
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Baade-Wesselink Radius Determination of Type II Cepheids
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1997AJ....113.1833B&db_key=AST
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Search for resonance effects in long period Cepheids.
Light curves of classical Cepheids with period longer than 8 days havebeen Fourier decomposed with the purpose of studying the characteristicsof high order Fourier parameters, and to detect possible effects ofresonances between pulsation modes other than the well known resonanceat P~10d. The possible effects of two expected resonances have beententatively identified: P_0_/P_1_=3/2 at P_0_~24 d and P_0_/P_3_=3 atP_0_~27d. The identification is not completely certain owing to the poornumber of Cepheids. The limitation could be overcome by observingaccurately other relatively faint Cepheids in our Galaxy, and severalCepheids in nearby galaxies.
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Kinematics of metal-poor stars in the galaxy
We discuss the kinematic properties of a sample of 1936 Galactic stars,selected without kinematic bias, and with abundances (Fe/H) is less thanor equal to -0.6. The stars selected for this study all have measuredradial velocities, and the majority have abundances determined fromspectroscopic or narrow-/intermediate-band photometric techniques. Incontrast to previous examinations of the kinematics of the metal-poorstars in the Galaxy, our sample contains large numbers of stars that arelocated at distances in excess of 1 kpc from the Galactic plane. Thus, amuch clearer picture of the nature of the metal-deficient populations inthe Galaxy can now be drawn.
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A catalogue of Fe/H determinations - 1991 edition
A revised version of the catalog of Fe/H determinations published by G.Cayrel et al. (1985) is presented. The catalog contains 3252 Fe/Hdeterminations for 1676 stars. The literature is complete up to December1990. The catalog includes only Fe/H determinations obtained from highresolution spectroscopic observations based on detailed spectroscopicanalyses, most of them carried out with model atmospheres. The catalogcontains a good number of Fe/H determinations for stars from open andglobular clusters and for some supergiants in the Magellanic Clouds.
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Color Excesses on a Uniform Scale for 328 Cepheids
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1990ApJS...72..153F&db_key=AST
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The Binary Type II Cepheids IX CAS and TX Del
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1989AJ.....98..981H&db_key=AST
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S-process deficiencies in low-mass supergiant variables
Abundance analyses of four low-mass supergiant variable stars and twoPopulation I Cepheids have been carried out. The Population I Cepheidsshow normal, solar element ratios, and the low-mass variables showmetallicities ranging from solar down to (Fe/H) values typical ofthick-disk and, in a few cases, of halo stars. Most low-mass variablesshow a systematic underabundance of the heavy s- and r-process elements.The heavy-element underabundances correlate with second ionizationpotential in a manner suggesting that they are a non-LTE phenomenonarising from overionization by Lyman-continuum photons. Several low-massvariables, including RU Cen and V553 Cen, show carbon enhancements andsolar s-process abundances. Relative to the majority of the type IIvariables, these stars are s-process enhanced, and it is argued thatthey are related to the Ba II and CH stars.
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INHABITED SKY
