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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Bayesian inference of stellar parameters and interstellar extinction using parallaxes and multiband photometry
Astrometric surveys provide the opportunity to measure the absolutemagnitudes of large numbers of stars, but only if the individualline-of-sight extinctions are known. Unfortunately, extinction is highlydegenerate with stellar effective temperature when estimated frombroad-band optical/infrared photometry. To address this problem, Iintroduce a Bayesian method for estimating the intrinsic parameters of astar and its line-of-sight extinction. It uses both photometry andparallaxes in a self-consistent manner in order to provide anon-parametric posterior probability distribution over the parameters.The method makes explicit use of domain knowledge by employing theHertzsprung-Russell Diagram (HRD) to constrain solutions and to ensurethat they respect stellar physics. I first demonstrate this method byusing it to estimate effective temperature and extinction from BVJHKdata for a set of artificially reddened Hipparcos stars, for whichaccurate effective temperatures have been estimated from high-resolutionspectroscopy. Using just the four colours, we see the expected strongdegeneracy (positive correlation) between the temperature andextinction. Introducing the parallax, apparent magnitude and the HRDreduces this degeneracy and improves both the precision (reduces theerror bars) and the accuracy of the parameter estimates, the latter byabout 35 per cent. The resulting accuracy is about 200 K in temperatureand 0.2 mag in extinction. I then apply the method to estimate theseparameters and absolute magnitudes for some 47 000 F, G, K Hipparcosstars which have been cross-matched with Two-Micron All-Sky Survey(2MASS). The method can easily be extended to incorporate the estimationof other parameters, in particular metallicity and surface gravity,making it particularly suitable for the analysis of the 109stars from Gaia.
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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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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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Pulkovo compilation of radial velocities for 35495 stars in a common system.
Not Available
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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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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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Using BV Photometry to Distinguish between Type I and Type II Cepheids
We use Johnson BV photometry of Galactic type I and type II Cepheids ina variety of diagrams to see whether the two populations can beadequately separated. The diagrams include the Fourier parametersphi_21, phi_31, phi_41, R_21, R_31, R_41, the loop width in the V-(B-V)plane, the relative phasing of V and B-V extrema, and the amplituderatios of B-V to V, all versus period. We found the R_i1 diagramsuseless in this regard, while a plot of the phasing parameter versusamplitude ratio was best, closely followed by the phi_i1 diagrams. Amajor difficulty was arriving at a sample of Cepheids that could bereliably taken to be definitely type II. We found it necessary to useonly stars that would have been more than 2 kpc from the Galactic planehad they been type I for this sample, and even then it is uncertainwhether such overlap between types as we find in our diagrams is due toinadequacy of the tests or is due to type I stars' having contaminatedour type II sample. We point out evidence strongly suggesting that typeI stars can be found at least up to 2 kpc from the plane. Selectioneffects in our sample of type II Cepheids resulted in only one BLHerculis star (short-period type II) being included, so our conclusionsbasically apply only to W Virginis stars.
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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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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.
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Photoelectric observations of Cepheids in 1992
During August-September 1992, 1635 UBVR photometric observations for 74Cepheids were obtained with the 60-cm reflector of the Mt. MaidanakObservatory of the Tashkent Astronomical Institute. Tables ofobservations and plots of light curves are given. These observationstogether with previously published ones will be used to study the periodvariability of Cepheids and to determine their radii and light excesses.
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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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A catalogue of field Type II Cepheids
A catalogue of field Type II Cepheids is presented. The primary listconsists of 152 Cepheids sufficiently far from the galactic plane to bevery probably Type II stars. A second list contains 56 additional starsthat are likely, but less certain, Type II Cepheids, including bothstars estimated to be at large distances from the galactic plane butwith uncertain distances and stars close to the galactic plane believedto be Type II for independent reasons.
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Kinematics of field Type II Cepheid variables
The spectra of 49 field Type II Cepheids have been assembled andcombined with 14 additional stars with previously published radialvelocities in order to investigate the kinematics and spectralcharacteristics of these stars. Many of the stars have low peculiarvelocities consistent with circular rotation around the galaxy, whilesome are high-velocity stars. Outside the nuclear bulge, the velocitiesare correlated with photometric metallicities in the sense thatmetal-rich stars show a nearly normal, disklike rotation velocity and alow velocity dispersion. This correlation shows that the low-velocity,metal-rich stars have an old-disk origin. Fewer Cepheids are found inthe field than expected relative to clusters, suggesting a differencebetween the populations of the halo field and clusters. The kinematicproperties of Cepheids in the nuclear bulge appear to be different inthat both metal-poor and metal-rich Cepheids have a high velocitydispersion and show little systematic galactic rotation.
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On the alternation of the 21-day light curves in even and odd cycles and the period change of MZ Cygni.
Not Available
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Photometric abundances of Type II Cepheid variables
Washington-system colors and V magnitudes of 63 Type II Cepheids areused to investigate the distribution of metal abundances in these starsand correlations of their abundances with position in the Galaxy. Only asmall fraction of Cepheids in the field represent a true halopopulation; most have characteristics of a transition population betweenthe halo and the disk. The origin of the metal-rich stars and theirrelation to the metal-rich RR Lyraes is discussed. The abundancedistribution of all Type II Cepheids shows no strong dependence ondistance from the galactic center.
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The structure of the Cepheid instability strip
The properties of Cepheids in the Galaxy, LMC, and SMC are analyzed tocompare them with theoretical models. The PLC relationships of the LMCand SMC agree with theoretically derived PLC relationships when fittingof data is done by the maximum likelihood method. Differences in the tworelationships can be ascribed to abundance differences. Empirical blueedges in the period-color plane agree with models for log P not greaterthan 1.1, but have significantly steeper slopes at longer periods; theredoes not seem to be any satisfactory explanation of this.
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W Virginis Stars with Properties of RV Tauri Stars
Not Available
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The light curve parameters of photoelectrically observed galactic Cepheids
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1971A&AS....4..265S&db_key=AST
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A catalogue of fundamental data for classical cepheids in the galaxies.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1968AJ.....73..492F&db_key=AST
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Metal-to-H ratios in the Galaxy as indicated by narrow-band photometry of Cepheids.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1966AJ.....71..615W&db_key=AST
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A search for cepheids - New possible members of open clusters: preliminary results.
Not Available
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Le type de population des céphéides galactiques; critères de distinction des types et catalogue
Not Available
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Radial Velocities and Spectral Characteristics of the Population II Cepheids m5 No. 42, m5 No. 84, and TW Capricorni.
Abstract image available at:http://adsabs.harvard.edu/abs/1958ApJ...127..583W
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Studies on Galactic Cepheids System. I. Absorption of Cepheids with known radial velocities and a nomogram for the computation of the galactocentric distance
Not Available
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A search for Cepheids in galactic clusters.
Abstract image available at:http://adsabs.harvard.edu/abs/1957ApJ...126..323V
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On the differential galactic rotation of the system of cepheid variable stars
Abstract image available at:http://adsabs.harvard.edu/abs/1956MNRAS.116..453S
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316 neue Veränderlilche
Not Available
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INHABITED SKY
