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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Post-AGB stars as testbeds of nucleosynthesis in AGB stars
We construct a data base of 125 post-AGB objects (including R CrB andextreme helium stars) with published photospheric parameters (effectivetemperature and gravity) and chemical composition. We estimate themasses of the post-AGB stars by comparing their position in the (logT{eff}, log g) plane with theoretical evolutionary tracks ofdifferent masses. We construct various diagrams, with the aim of findingclues to AGB nucleosynthesis. This is the first time that a large sampleof post-AGB stars has been used in a systematic way for such a purposeand we argue that, in several respects, post-AGB stars should be morepowerful than planetary nebulae to test AGB nucleosynthesis. Our mainfindings are that: the vast majority of objects which do not showevidence of N production from primary C have a low stellar mass(Mstar < 0.56 Mȯ); there is no evidencethat objects which did not experience 3rd dredge-up have a differentstellar mass distribution than objects that did; there is clear evidencethat 3rd dredge-up is more efficient at low metallicity. The sample ofknown post-AGB stars is likely to increase significantly in the nearfuture thanks to the ASTRO-F and follow-up observations, making theseobjects even more promising as testbeds for AGB nucleosynthesis.
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FIP effect in RV Tauri stars.
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Abundance Analyses of Field RV Tauri Stars. VI. An Extended Sample
An abundance analysis is presented and discussed for a sample of 14 RVTauri stars. The present abundance data and those from our previouspapers and by other workers are combined in an attempt to furtherunderstanding of the dust-gas separation process that afflicts many RVTauri variables. We propose that a star's intrinsic (i.e., initial)metallicity is given by the photospheric zinc abundance. Variableswarmer than about 5000 K and with an initial metallicity [Fe/H]>=-1are affected by dust-gas separation. Variables of all metallicities andcooler than about Teff~=5000 K are unaffected by dust-gasseparation. The RV Tauri variables show a spread in their C abundances,with the lower boundary of the points in the C versus Zn plane fallingclose to the predicted trend for giants after the first dredge-up. Theupper boundary is inhabited by a few stars that are carbon-rich. The Oabundances in the mean follow the predicted trend from unevolved stars,in line with the expectation that photospheric O abundance is unaffectedby the first dredge-up. An evolutionary scenario involving mass loss bya first-ascent or early-AGB red giant, the primary star of a binary, issketched.
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Highlights from the Observatories
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High-resolution spectroscopy of the high galactic latitude RV Tauri star CE Virginis
Analysis of the surface composition of the suspected cool RV Tauri starCE Virginis shows no systematic trend in depletions of elements withrespect to condensation temperature. However, there is a significantdepletion of the elements with respect to the first ionization potentialof the element. The derived Li abundance of logɛ (Li) = 1.5 +/-0.2 indicates production of Li in the star. Near-infrared coloursindicate sporadic dust formation close to the photosphere.
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Beobachtungssergebnisse Bundesdeutsche Arbeitsgemeinschaft fuer Veraenderliche Sterne e.V.
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Beobachtungsegebnisse Bundesdeutsche Arbeitsgemainschaft fur Veranderliche Sterne e.V.
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Beobachtungsergebnisse Bundesdeutsche Arbeitsgemeinschaft fur Veraenderliche Sterne e.V.
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Aus der Sektion Halb-und Unregelmassige.
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Beobachtungsergebnisse Bundesdeutsche Arbeitsgemeinschaft fur Veraenderliche Sterne e.V.
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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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Studies of Yellow Semiregular(SRd) Variables
We have used the Hipparcos database of epoch photometry to study thevariability of several yellow semiregular(SRd) variables. For some ofthe stars (V847 Cas, RW Cep, BM Sco, CE Vir), the results wereinconclusive. For SX Lac and TY Vir, the periods found were consistentwith the General Catalogue of Variable Stars (190 and 50 daysrespectively). For UU Her, the known periods of about 45 and 72 dayswere recovered. For WY And, RU Cep, and SX Her, reliable periods werefound; we used archival data to construct (O-C) diagrams to study boththe random and systematic period changes in these three stars.
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The Milton Bureau Revisited
Under the direction of Cecilia Payne-Gaposchkin and Sergei Gaposchkin, aprogram was subsidized by the Milton Fund of Harvard Observatory in 1937for the study of all variable stars then known to be brighter than tenthphotographic magnitude at maximum. This included some 1512 stars forwhich a grand total of 1,263,562 estimates of magnitude were made,ranging from a low of 16 (except for a few novae) to 4084 observationsper star. The sky had been divided into 54 fields, and the results ofthe measurements presented field by field in two volumes of the Annalsof Harvard Observatory. Then, in another volume, the results werediscussed in four sections, each dealing with a particular class ofvariable: 1, those of RV Tauri type; 2, the eclipsing variables; 3,Cepheids and RR Lyrae variables, and 4, the red variables, especiallyMira-type and semiregular variables.For the present paper, many of these results have been compared withmodern determinations in the 1985-87 version of the "General Catalogueof Variable Stars (GCVS)". In particular, there are numerous instancesof disagreement as to whether a star should be classified RV or SR.Although there are many instances where the Milton Bureau determinationsof types of variability differ from the types given in moderncatalogues, the reasons for the differences are generallyunderstandable.For 17 RV Tauri type stars in this survey multiple periods have now beendetermined. Many of these still deserve continued observations in orderto ascertain the constance of the periods and improve the accuracy oftheir longest reported periods.
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Abundance Analyses of Field RV Tauri Stars. V. DS Aquarii, UY Arae, TW Camelopardalis, BT Librae, U Monocerotis, TT Ophiuchi, R Scuti, and RV Tauri
Abundance analyses are presented and discussed for eight RV Taurivariables. The RVB star UY Ara shows the abundance anomalies seen inother RVB stars, namely, elements that condense into grains at hightemperature are underabundant, but elements of low condensationtemperature are much less underabundant. This pattern is ascribed to aseparation of dust from gas with accretion of gas but not dust by theatmosphere. Abundances for two RVC stars with earlier results for otherRVC stars show that these intrinsically metal-poor stars do not showeffects of dust-gas separation. Analyses of five RVA stars show thatthese cooler stars are very largely unaffected by dust-gas separation.It is proposed that the deeper convective envelope of cooler starsdilutes anomalies resulting from dust-gas separation. Possible sites fordust formation and dust-gas separation-the dusty wind off the RV Taurivariable or a dusty circumbinary disk-are reviewed and observationaltests suggested.
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Abundance Analyses of Field RV Tauri Stars. IV. AD Aquilae, DS Aquarii, V360 Cygni, AC Herculis, and V453 Ophiuchi
Abundance analyses are presented and discussed for five RV Taurivariables. Three stars-DS Aqr, V360 Cyg, and V453 Oph-are RV C stars byspectroscopic classification, i.e., metal lines are weak. They are shownto be metal poor with [Fe/H] from -1.0 to -2.2 with normal relativeabundances of other elements. By contrast, AD Aql and AC Her are RV Bstars with an odd abundance pattern: elements that condense into grainsat a high temperatures are underabundant (i.e., [Fe/H] = -2.1 for ADAql) but elements with a low condensation temperatures are much lessunderabundant (i.e., [S/H] = 0.0 and [Zn/H] = -0.1 for AD Aql). Thisabundance pattern is ascribed to a separation of dust and gas in theupper atmosphere of the star. The present analyses with previouslypublished results are used to investigate the systematics of thedust-gas separation in RV Tauri variables. The process is apparentlyinoperative in stars with an initial metallicity of about [Fe/H] <~-1.0 RV C stars and similar variables in globular clusters are immune tothe dust-gas separation. The process achieves more severe effects in RVB than in RV A stars. The strength of the abundance anomalies attributedto dust-gas separation is not correlated with reported infraredexcesses. After correction for the effects of the dust-gas separation,there is no strong evidence from the abundances that evolution along theAGB and experience of the third dredge-up preceded the formation of themajority of the RV Tauri variables.
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Abundance Analyses of Field RV Tauri Variables. III. DY Aquilae, SS Geminorum, CT Orionis, and CE Virginis
Analyses of the photospheric compositions of the four field RV Tauristars, DY Aql, SS Gem, CT Ori, and CE Vir, indicate that to varyingdegrees they have experienced fractionation processes that havepreferentially depleted their atmospheres of elements with highcondensation temperatures. This corroborates our previous studies, whichshowed similar patterns in five other field RV Tauri stars. Two stars inour sample, DY Aql and CE Vir, were found to have strong Li I resonancelines, with corresponding lithium abundances near log epsilon (Li) =0.0; this is not significantly different from that found in less evolvedM giants. These are also the coolest stars displaying a correlation ofphotospheric abundances with condensation temperatures.
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Professional-amateur collaboration in variable star research: V. Observations of yellow semi-regular variables
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The radial velocities of 116 southern red stars
Using a photoelectric speedometer based on the radial velocityspectrometer of Griffin (1967), radial velocities of 116 southern redstars, many of them semi-regular variables, were measured. Theinstrument was placed at the Newtonian focus of the 130-inch (4.2-m)camera of the Coude spectrograph of the Mount Stromlo 74-inch (1.88-m)reflector. The stellar spectrum was focused on a mask 50 mm in length,designed to match the spectrum of the M-giant Beta Pegasi. The inversedispersion was 2.5 angstroms per millimeter in the second order. Thewavelength range used (5338-5449 angstroms) was chosen because it isbetween two TiO bands and so suffers less blanketing in M stars. Resultsare tabulated and compared with standard values.
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Factor analysis of the DDO colours of RV Tauri and SRd stars
The properties of RV Tauri and SRd stars in the DDO photometric systemhave been examined by means of the factor analysis. Within the limitsdue to the restricted sample, this analysis supports the spectroscopicclassification of these objects, and confirms the usefulness of the DDOphotometry to study them. Some objects with peculiar characteristics arediscussed.
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Photometry of Rv-Tauri and Yellow Semiregular Variables - Part One
Abstract image available at:http://adsabs.harvard.edu/abs/1982PASP...94..574D
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Objective-prism discoveries in the declination zone 0 deg to -20 deg
An inspection of 130 10-deg-prism plates taken for the University ofMichigan Southern Spectral Survey has yielded 154 new peculiar orotherwise interesting stars. The regions surveyed are mainly at fairlyhigh galactic latitudes; this fills a gap in previous work of this type.About three-quarters of the objects will eventually be reclassified byHouk in a systematic work on all of the Henry Draper Catalogue stars,but many of these are of sufficient interest to justify earlypublication.
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A photometric investigation of RV Tauri and yellow semiregular variables
Results are presented for DDO and UBV photoelectric photometry of 52 RVTau and semiregular variables and candidates. CN abundances, effectivetemperatures, surface gravities, absolute visual magnitudes, and massestimates are derived in the framework of the spectroscopic groupingsproposed by Preston et al. (1963). The photometry suggests a furtherdivision of Preston's group A, and a possible physical connection isindicated between this group and the semiregular variables. Thespectroscopic groups are shown to be well separated in the DDOcolor-color diagrams when mean colors are used for individual stars. Anupper limit of about 3 solar masses is determined for stars in eachgroup. A correlation between derived iron abundances and published IRexcesses obtained from flux measurements at 3.6 and 11.3 microns isfound which supports the contention that dust production incircumstellar shells increases with increasing metallicity.
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Absolute magnitudes of semi-regular variables in the solar vicinity from statistical parallaxes.
Abstract image available at:http://adsabs.harvard.edu/abs/1973MNRAS.165..337A
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Narrow-and broad-band photometry of red stars. VII. Luminosities and temperatures for halo-population red stars of high luminosity
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1972ApJ...172..639E&db_key=AST
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- and Broad-Band Photometry of Red Stars. Northern Giants
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1967ApJS...14..307E&db_key=AST
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162 neue Veräderliche
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INHABITED SKY
