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Публикации по объекту
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.
| 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.
| Beobachtungssergebnisse Bundesdeutsche Arbeitsgemeinschaft fuer Veraenderliche Sterne e.V.
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| Beobachtungsergebnisse Bundesdeutsche Arbeitsgemeinschaft fur Veranderlichen Serne e.V.
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| Polarimetry of evolved stars. III. RV Tau and R CrB stars
We present broadband optical polarimetry, and broadband optical andinfrared photometry, of eight RV Tau-type and five R CrB-type stars;much of the photometry and polarimetry was obtained simultaneously. Fornine of the objects polarimetric data is reported for the first time. Wehave estimated and subtracted the interstellar component ofpolarization, allowing us to determine the level of intrinsicpolarization. In some cases this is =~ 1%-2% even when the star is in abright photometric state. We consider this to be evidence for thepresence of permanent clumpy non-spherical dust shells around the RV Tauand R CrB-type stars we observed. Our polarimetric and photometric datalead us to conclude that, for most of our programme stars, neutralextinction must be significant in their circumstellar envelopes. Apartfrom the brightness variations due to pulsations and changes in theeffective temperature of stars, there is clear evidence ofwavelength-independent flux variations - with amplitude from 0fm 5 to1fm 0 - implying the presence of large (a>~ 0.15 mu m) dustparticles. Rapid ( ~ 2 hours) evolution of the infrared fluxdistribution at the level of ~ 0fm 6 in the JHKL bands was detected inthe RV Tau star R Sct.Table 2 is only available in electronic form at the CDS via anomymousftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/412/405Tables 3-6 are only available in electronic form athttp://www.edpsciences.org
| Beobachtungsegebnisse Bundesdeutsche Arbeitsgemainschaft fur Veranderliche Sterne e.V.
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| Detection of Zinc in the Very Metal-Poor Post-AGB Star HR 4049
We report on the detection of two Zn I lines at4722.15Å and 4810.53Å in the high-quality spectrum of thevery metal-poor post-AGB star HR4049, which was obtained with the HighDispersion Spectrograph attached to the Subaru Telescope. The strengthsof these lines indicate an appreciable underabundance of Zn by ~ -1.3dex relative to the Sun. The fact that this volatile element, similarlyto others belonging to the same group (e.g., C, N, O, S), does notconform to the extreme depletion ( > 4 dex) of refractory metals(e.g., Fe), strongly suggests that grain formation has something to dowith the origin of the chemical peculiarity. This (not extremely butsignificantly) subsolar value of [Zn/H] is quantitatively discussed inconnection with those of other volatile species, especially with respectto S. We also detected a new Fe II line at5159.03Å along with the already known Fe II4923.93Å line; based on these two lines the Fe abundance of HR4049is determined to be ~ 2.8 ([Fe/H] ~ -4.7).
| Beobachtungsergebnisse Bundesdeutsche Arbeitsgemeinschaft fur Veraenderliche Sterne e.V.
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| Beobachtungsergebnisse Bundesdeutsche Arbeitsgemeinschaft fur Veraenderliche Sterne e.V.
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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.
| Spectral Characteristics of RV Tauri Stars
Not Available
| 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.
| 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.
| UBV beta Database for Case-Hamburg Northern and Southern Luminous Stars
A database of photoelectric UBV beta photometry for stars listed in theCase-Hamburg northern and southern Milky Way luminous stars surveys hasbeen compiled from the original research literature. Consisting of over16,000 observations of some 7300 stars from over 500 sources, thisdatabase constitutes the most complete compilation of such photometryavailable for intrinsically luminous stars around the Galactic plane.Over 5000 stars listed in the Case-Hamburg surveys still lackfundamental photometric data.
| 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.
| The Nature of the Period Changes in RV Tauri Stars
We have studied the period changes in 15 RV Tauri stars, using theEddington- Plakidis hypothesis, which assumes that the (O-C) diagramscan be interpreted as a superposition of random errors in the measuredtimes of minimum, and random cycle-to-cycle fluctuations in the period.Except for three stars for which the data are sparse, the hypothesisfits the (O-C) data very well, suggesting that the assumptions arecorrect. The magnitude of the random period fluctuations does not appearto correlate with any obvious physical property of stars. (SECTION:Stars)
| The nature of the period changes in RV Tauri stars.
Not Available
| 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.
| 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.
| Photometry of EP Lyrae and period changes in RV Tauri stars.
The RV Tauri variable EP Lyrae was observed between 1985 and 1992 in theUBV-system. The star, like AC Herculis, has a relatively regular lightcurve. Its period is rather stable during most of the observations, itscurrent value is 83.46d EP Lyrae is classified as an RVB variable, i.e.its mean brightness is supposed to vary. It is shown that thisclassification is not correct, the mean brightness of the star isconstant. The question of period changes in RV Tauri stars is discussedand a possible relation between colour and O-C amplitude is found. Thedifficulties with the usually assumed post-AGB evolutionary status ofthese variables are also highlighted.
| Period Changes in RV Tauri Stars: Observations and Simulations
We have determined the times and magnitudes of minimum brightness of twoRV Tauri stars (SS Gem and V Vul) using data from the AAVSO and from theliterature. We have used these to construct (O-C) diagrams. These aredominated by cyclic features with time scales ranging from several toseveral hundred pulsation periods. By constructing simulated (O-C)diagrams, we have shown that the observed (O-C) diagrams could beexplained by the accumulation of random, cycle-to-cycle fluctuations inperiod, as in the case of most Mira stars.
| The metallicity and luminosity of RV Tauri variables from medium-resolution spectra
Results are reported from spectroscopic observations of members of theRV Tauri class of pulsating variable stars at moderate resolution, andfrom photometric observations of these stars with the B and V filters ofthe Johnson UBV system and the first four filters of the Wingeight-color narrowband near-IR system. Of the 22 variables observed, TiOabsorption was detected in eight, and 10 variables displayedhydrogen-line emission at some phase. Spectral classifications wereassigned relative to the MK process. Color excesses were determined forthose variables for which spectroscopic and photometric data wereobtained within a few days of each other. The spectra obtained at aresolution of 2.5 A were fitted with synthetic spectra to determine thestellar atmospheric parameters. The range in metallicity among thevariables was found to be quite extensive, -0.3 to -0.7, and may reflecta mixture of stellar populations or masses.
| Classification of Population II supergiants and related stars in the Vilnius system
The results of photometric classification in the Vilnius system of 117Population II supergiants, suspected supergiants, and related stars aregiven. Their photometric spectral types, intrinsic color indices (Y-V)0,color excesses E(Y-V), metallicities Fe/H, and absolute magnitudes MVare determined. It is shown that the system allows us to detect the UUHerculis-type supergiants photometrically. The analyzed SRd star samplefalls into two groups of metallicity and luminosity. Our photometricclassification assigns luminosity classes from III to V to 37 F-K starswith /b/ greater than 16 deg classified by Bartaya (1979) from objectiveprism spectra as supergiants.
| Photometry of yellow semi-regular variables - TW Cam
This study presents new photoelectric photometry of TW Cam. Fourieranalysis of the light curve shows a group of peaks at 43 d. The firstreturn maps of the primary and secondary minima differ remarkably; thoseof the secondary minima show significantly larger scatter. It isinferred from this difference that the pulsation period of the star isthe formal period (i.e., the distance between two primary minima).
| Photometry of yellow semi-regular variables - SS GEM
New photoelectric photometry of SS Gem is presented. The period analysisand light curve fits show that the formal period is the pulsation periodand there is a strong harmonic. The period variation of SS Gem is foundto be similar to that of AC Her. It is argued that being a Population Iobject, SS Gem is not a low-mass star in the post-AGB phase but anintermediate-mass variable related to classical Cepheids.
| Near infrared spectra of RV Tauri stars
Medium resolution spectrograms of the near infrared spectral region in asample of RV Tauri stars with spectral types F and early G have beencompared with those of a sample of population I objects. It is shownthat the equivalent widths of Ca II infrared triplet and Paschen linesallow to separate RV Tauri stars from population I supergiants.Moreover, the possibility of using the O I triplet at 7774 A as a toolfor testing the period-luminosity relation for RV Tauri stars isdiscussed.
| The envelopes of RV Tauri stars. I - Linear polarimetric and spectroscopic observations
Simultaneous spectroscopic and polarimetric observations are presentedfor five RV Tauri stars and one RV Tauri-like semiregular variable.Time-dependent variations are found in the polarizations for four of theobjects, as are wavelength-dependent variations in two and possiblythree stars. In general, the largest polarizations and strongestwavelength dependences in the polarization occur immediately followingprimary light minima.
| Catalogue of CH and metal-deficient barium stars
Not Available
| Circumstellar material and the light variations of RV Tauri stars
Infrared photometry on the JHKL system is given for 35 stars of the RVTauri and related types. The RV Tauri stars show infrared excessesindicating the presence of circumstellar dust with a temperature ofabout 900 K. These dust shells can be equally prominent in oxygen-richor carbon-rich stars; the high carbon content of the latter appears tocounteract the inhibiting effect of their generally lower metalabundance in promoting dust formation. The wide range of energydistributions of RV Tauri stars is attributed in part to differences inthe radial distribution of dust. The RVb stars (whose mean light variescyclically) are redder than the RVa stars (which have constant meanlight), indicating that their dust shells are denser (especially in theinner regions, which radiate strongly in the 1-3 micron band).Far-infrared data reveal cooler dust around some of the stars of groupa. Three W Virginis stars, two of which were already known to showaffinities to the RV Tauri stars, have dust shells. The dust shells forwhich IRAS infrared spectra are available show the 10-micron silicateemission feature regardless of whether the optical spectra are carbon-or oxygen-rich. Some considerations regarding possible models are given.A comparison with the R Coronae Borealis variables has revealedsimilarities.
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Группы:
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Наблюдательные данные и астрометрия
| Созвездие: | Близнецы |
| Прямое восхождение: | 06h08m35.11s |
| Склонение: | +22°37'01.9" |
| Видимая звёздная величина: | 9.051 |
| Собственное движение RA: | 0.8 |
| Собственное движение Dec: | -2.3 |
| B-T magnitude: | 10.635 |
| V-T magnitude: | 9.182 |
Каталоги и обозначения:
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