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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.
| An evolutionary catalogue of galactic post-AGB and related objects
Aims.With the ongoing AKARI infrared sky survey, of much greatersensitivity than IRAS, a wealth of post-AGB objects may be discovered.It is thus time to organize our present knowledge of known post-AGBstars in the galaxy with a view to using it to search for new post-AGBobjects among AKARI sources. Methods: We searched the literatureavailable on the NASA Astrophysics Data System up to 1 October 2006, anddefined criteria for classifying sources into three categories: verylikely, possible and disqualified post-AGB objects. The category of verylikely post-AGB objects is made up of several classes. Results: We havecreated an evolutionary, on-line catalogue of Galactic post-AGB objects,to be referred to as the Toruń catalogue of Galactic post-AGB andrelated objects. The present version of the catalogue contains 326 verylikely, 107 possible and 64 disqualified objects. For the very likelypost-AGB objects, the catalogue gives the available optical and infraredphotometry, infrared spectroscopy and spectral types, and links tofinding charts and bibliography.A stable version of the catalogue is available at the CDS via anonymousftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/469/799
| First detection of photospheric depletion in the Large Magellanic Cloud
Context: .Recent photospheric abundance studies of galactic field RVTauri stars show that depletion of refractory elements is rather commonin these evolved objects. Aims: .The process that creates thischemical anomaly is not understood well, but it probably requires thepresence of gravitationally bound dust in a binary system. We test forthe presence of depletion in extra-galactic objects. Methods: .Adetailed photospheric abundance study on the basis of high-quality UVESspectra was performed on the RV Tauri star in the LMC: MACHO 82.8405.15.Abundances were derived using a critically compiled line list withaccurate log(gf) values and the latest Kurucz model atmospheres.Results: .With [Fe/H] = -2.6 in combination with [Zn/Fe] = +2.3 and[S/Ti] = +2.5, MACHO 82.8405.15 displays a strong depletion abundancepattern. The effect of the depletion is comparable to the strongestdepletions seen in field Galactic RV Tauri stars. Conclusions:.The chemical analysis of MACHO 82.8405.15 proves that the depletionprocess also occurs in the extragalactic members of the RV Tauripulsation class. Our program star is a member of a larger sample of LMCRV Tauri objects. This sample is unique, since the distances of themembers are well-constrained. Further studies of this sample aretherefore expected to gain deeper insight into the poorly understooddepletion phenomenon and of the evolutionary status of RV Tauri stars ingeneral.Basedon observations collected at the European Southern Observatory, Chile(programme 074.D-0619(A)).
| AGB nucleosynthesis in the Large Magellanic Cloud. Detailed abundance analysis of the RV Tauri star MACHO?47.2496.8
Context: Abundance analysis of post-AGB objects as probes of AGBnucleosynthesis. Aims: A detailed photospheric abundance study isperformed on the carbon-rich post-AGB candidate MACHO 47.2496.8 in theLMC. Methods: High-resolution, high signal-to-noise ESO VLT-UVESspectra of MACHO 47.2496.8 are analysed by performing detailed spectrumsynthesis modelling using state-of-the-art carbon-rich MARCS atmospheremodels. Results: The spectrum of MACHO 47.2496.8 is not onlydominated by bands of carbon bearing molecules, but also by lines ofatomic transitions of s-process elements. The metallicity of [Fe/H] =-1.4 is surprisingly low for a field LMC star. The C/O ratio, howeverdifficult to quantify, is greater than 2, and the s-process enrichmentis large: the light s-process elements are enhanced by 1.2 dex comparedto iron ([ls/Fe] = +1.2), while for the heavy s-process elements an evenstronger enrichment is measured: [hs/Fe] = +2.1. The lead abundance iscomparable to the [hs/Fe]. With its low intrinsic metallicity and itsluminosity at the low end of the carbon star luminosity function, thestar represents likely the final stage of a low initial mass star. Conclusions: .The LMC RV Tauri star MACHO 47.2496.8 is highly carbonand s-process enriched, and is most probable a genuine post-C(N-type)AGB star. This is the first detailed abundance analysis of anextragalactic post-AGB star to date.
| CS 30322-023: an ultra metal-poor TP-AGB star?
Context: .The remarkable properties of CS 30322-023 became apparentduring the course of a high-resolution spectroscopic study of a sampleof 23 carbon-enhanced, metal-poor (CEMP) stars. Aims: .This sampleis studied in order to gain a better understanding of s- and r-processnucleosynthesis at low metallicity, and to investigate the role ofduplicity. Methods: .High-resolution UVES spectra have beenobtained, and abundances are derived using 1-D, plane-parallel OSMARCSmodels under the LTE hypothesis. The derived atmospheric parameters andobserved abundances are compared to evolutionary tracks andnucleosynthesis predictions to infer the evolutionary status of CS30322-023. Results: .CS 30322-023 is remarkable in having thelowest surface gravity (log g ? -0.3) among the metal-poor starsstudied to date. As a result of its rather low temperature (4100 K),abundances could be derived for 35 chemical elements; the abundancepattern of CS 30322-023 is one of the most well-specified of all knownextremely metal-poor stars. With [Fe/H] = -3.5, CS 30322-023 is the mostmetal-poor star to exhibit a clear s-process signature, and the mostmetal-poor "lead star" known. The available evidence indicates that CS30322-023 is presently a thermally-pulsing asymptotic giant branch(TP-AGB) star, with no strong indication of binarity thus far (althougha signal of period 192 d is clearly present in the radial-velocity data,this is likely due to pulsation of the stellar envelope). Low-massTP-AGB stars are not expected to be exceedingly rare in amagnitude-limited sample such as the HK survey, because their highluminosities make it possible to sample them over a very large volume.The strong N overabundance and the low 12C/13Cratio (4) in this star is typical of the operation of the CN cycle.Coupled with a Na overabundance and the absence of a strong Coverabundance, this pattern seems to imply that hot-bottom burningoperated in this star, which should then have a mass of at least 2M_?. However, the luminosity associated with this mass would putthe star at a distance of about 50 kpc, in the outskirts of the galactichalo, where no recent star formation is expected to have taken place. Weexplore alternative scenarios in which the observed abundance patternresults from some mixing mechanism yet to be identified occurring in asingle low-metallicity 0.8 M_? AGB star, or from pollution bymatter from an intermediate-mass AGB companion which has undergonehot-bottom burning. We stress, however, that our abundances may besubject to uncertainties due to NLTE or 3D granulation effects whichwere not taken into consideration.
| A non-LTE abundance analysis of the post-AGB star ROA5701
An analysis of high-resolution Anglo-Australian Telescope(AAT)/University College London Échelle Spectrograph(UCLÉS) optical spectra for the ultraviolet (UV)-bright starROA5701 in the globular cluster ω Cen (NGC5139) is performed,using non-local thermodynamic equilibrium (non-LTE) model atmospheres toestimate stellar atmospheric parameters and chemical composition.Abundances are derived for C, N, O, Mg, Si and S, and compared withthose found previously by Moehler et al. We find a general metalunderabundance relative to young B-type stars, consistent with theaverage metallicity of the cluster. Our results indicate that ROA5701has not undergone a gas-dust separation scenario as previouslysuggested. However, its abundance pattern does imply that ROA5701 hasevolved off the asymptotic giant branch (AGB) prior to the onset of thethird dredge-up.
| 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.
| A strongly s-process enriched RV Tauri star in the LMC.
A detailed abundance analysis is presented of an intriguing object inthe Large Magellanic Cloud that links the class of RV Tauri stars to thepost-AGB phase of evolution: MACHO 47.2496.8. The spectrum, taken withVLT-UVES, is dominated by molecular lines of carbon bearing molecules,together with strong transitions of s-process species. Detailed spectralsyntheses were made using a state-of-the-art carbon rich MARCS model. Asurprisingly low metallicity ([Fe/H] = -1.4), together with strongcarbon (C/O>2) and s-process overabundances were found, reachingvalues of [ls/Fe] = +1.2 for the light s-process elements, and even[hs/Fe] = +2.1 for the heavy ones. The strong s-process enhancements arein agreement with the theoretical expectations at that metallicity. Onlythe combination of a low lead content and a high [hs/ls] is not easilyexplained by the current nucleosynthetic models. It is not clear whetherthis star is intrisically or extrinsically enriched, but severalarguments favour an intrisic enrichment, implying the object to be agenuine post carbon (N-type) AGB star. With the low metallicity and aluminosity at the very low end of the carbon star luminosity function,MACHO 47.2496.8 represents the final evolutionary state of a star of lowinitial mass.Based on observations collected at ESO, Chile (programme 074.D-0619(A))
| New Estimates of the Solar-Neighborhood Massive Star Birthrate and the Galactic Supernova Rate
The birthrate of stars of masses >=10 Msolar is estimatedfrom a sample of just over 400 O3-B2 dwarfs within 1.5 kpc of the Sunand the result extrapolated to estimate the Galactic supernova ratecontributed by such stars. The solar-neighborhood Galactic-plane massivestar birthrate is estimated at ~176 stars kpc-3Myr-1. On the basis of a model in which the Galactic stellardensity distribution comprises a ``disk+central hole'' like that of thedust infrared emission (as proposed by Drimmel and Spergel), theGalactic supernova rate is estimated at probably not less than ~1 normore than ~2 per century and the number of O3-B2 dwarfs within the solarcircle at ~200,000.
| V453 Oph: a s-process enriched, but carbon-deficient RV Tauri star of low intrinsic metallicity
This paper reports the detection of a heavy element enriched RV Taurivariable with an abundance pattern that differs significantly from astandard s-process enriched object: V453 Oph. Basedon optical high-resolution spectra, we determined that this object oflow intrinsic metallicity ([Fe/H]=-2.2) has a mild, but significant,enrichment ([s/Fe]˜ + 0.5) of heavy elements for which thedistribution points to slow neutron capture nucleosynthesis. This resultis strengthened by a comparative analysis to the non-enriched RV Tauristar DS Aqr ([s/Fe]= 0.0). Although V453 Oph is thefirst RV Tauri star showing a strong s-process signature, it is notaccompanied by C enhancement, challenging our current nucleosyntheticmodels of post-AGB stars that predict a simultaneous enrichment in C ands-process elements. The low N abundance excludes CN cycling as beingresponsible for the low C abundance. We explore three differentscenarios to explain the heavy element distribution in this evolvedobject: an enrichment of the parental cloud, an accretion scenario inwhich the chemical patterns were acquired by mass transfer in a binarysystem and an intrinsic enrichment by dredge-up.
| s-process nucleosynthesis in very metal-deficient post-AGB stars
In this contribution, we present a detailed abundance study of a starthat challenges our current understanding of the s-process: V453 Oph.This RV Tauri star of low intrinsic metallicity displays simultaneouslymild s-process overabundances and a low C content. The remarkablepattern is confirmed and strengthened in an analysis relative toanother, very similar RV Tauri star without s-process enrichment: DSAqr. Two nucleosynthetic models have been explored to explain theabundances of V453 Oph. In a radiative model, s-process elements aregenerated in the radiative zone in the He-rich intershell during theinterpulse phase, while in the convective model, the s-process elementsare produced in convective conditions during the thermal pulse only.Both models succeed in explaining the mild s-process overabundances, butonly the convective model is able to produce s-process elements withoutenhancing the carbon content significantly.Based on observations collected at ESO, La Silla, Chile (programme67.D-0054)
| Catalog of Galactic OB Stars
An all-sky catalog of Galactic OB stars has been created by extendingthe Case-Hamburg Galactic plane luminous-stars surveys to include 5500additional objects drawn from the literature. This work brings the totalnumber of known or reasonably suspected OB stars to over 16,000.Companion databases of UBVβ photometry and MK classifications forthese objects include nearly 30,000 and 20,000 entries, respectively.
| 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.
| 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.
| 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.
| V529 Coronae Austrinae: An RV Tauri Variable of Type RVb
We present an analysis of the photometric data on V529 CrA. The datainclude published photographic data as well as our ownUBV(RI)C measurements. Two dominant modulations with periodsof 23.571 and 761.5 days are present in the light curve. The double ofthe 23.571 day period (47.142 days) shows the alternating deep/shallowminima behavior of the RV Tauri class of variables, while the presenceof a longer modulation indicates a classification in the photometricsubclass RVb. Medium-resolution optical spectroscopy is also presented.Based partially on observations made at Laboratório Nacional deAstrofísica/CNPq, Brazil, and Cerro Tololo Inter-AmericanObservatory (CTIO), Chile.
| 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.
| RV Tauri stars - II. A spectroscopic study
A long-term photometric and spectroscopic survey of eleven RV Tauristars has been undertaken with a view to obtaining a betterunderstanding of the nature of these pulsating variables. Pollard et al.presented the results from the long-term multicolour photometric survey.This paper presents the contemporaneous moderate- to high-resolutionspectroscopy of these stars. All the RV Tauri stars in our sampledisplay, or are consistent with, two shock waves propagating in theiratmospheres per `formal' period (the time between successive deepminima). This is consistent with the few previous high-resolutionspectroscopic studies of the three brightest RV Tauri stars: R Sct, UMon and AC Her. Specifically, the Hα profiles exhibit twoenhancements of emission per cycle following the passage of the primaryand secondary shock waves through the photosphere around phases 0.1 and0.6. Metallic lines showed `doubled' profiles characteristic of anatmospheric shock wave around these phases, with evidence of two radialvelocity cycles per formal period. In the RVb-type stars, an additionalcontribution to the Hα emission is seen and this appears to becorrelated with the long-term period. Two stars, AI Sco and IW Car,display extended blueward Hα absorption which may arise from massoutflow. Evidence of long-term radial velocity variations is also seenin a number of the RVb stars.
| RV Tauri stars - I. A long-term photometric survey.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1996MNRAS.279..949P&db_key=AST
| 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.
| The nature of RV Tauri variables. II- Properties of the peculiar F stars
Basic atmospheric parameters for six RV Tauri variables are considered.The Fe/H abundance ratios for the stars are found to be between -1 and -1.7, inclusively. Stars of the Preston (1962) type B and C subclasses donot appear segregated by metallicity. In comparison to the coolerPreston type A stars, types B and C are shown to be more metal poor by afactor of 10, on average. The results are consistent with the theorythat RV Tau type B and C variables are a direct evolutionary analog tothe cluster type II Cepheids.
| The nature of RV Tauri variables. I - Spectrophotometric atlas of selected field stars
Multiphase observations of a selected sample of field RV Tauri variablesare presented, consisting of 10-A resolution spectrophotometry in the3500-6200-A wavelength range. The data confirm the previous suggestionthat most of the RV Tau variables exhibit clear deviations from normalsupergiants which cannot be related simply to metallicity. Evidence isfound for strong molecular absorption (CN for AC Her and EP Lyr; TiO forR Sct and V Vul) at phases where the inferred stellar temperature isinconsistent with such absorption, possibly due to atmospheric shockswhich arise in at least two separate episodes (most notably, in the risefrom primary and secondary minimum).
| Merged log of IUE observations.
Not Available
| Optical and infrared observations of RV Tauri stars
Optical and IR photometry of RV Tauri stars, much of which was obtainednearly simultaneously over the wavelength range 0.36-10 microns, ispresented. From the dereddened optical-IR flux distributions, stellarand dust shell parameters are deduced. The deduced stellar colors are ingood agreement with those inferred from optical spectroscopy. The Planckmean optical depths of the dusty RV Tauri stars range from 0.07 to 0.63,the corresponding circumstellar contributions to E(B-V) ranging fromabout 0.02 to about 0.2. The observations show that the fluxdistributions of oxygen- and carbon-rich types are indistinguishablephotometrically, that some of these objects may have multiple dustshells, and hence that dust production in RV Tauri stars probably occurssporadically rather than continuously.
| Optical/infrared observations of RV Tauri stars.
Not Available
| Analysis of the light variations of the RV Tauri star V 453 Ophiuchi
The light variations of the RV Tauri star V453 Ophiuchi have beenanalysed on the basis of 1127 photographic measurements published byErleskova (1979) which cover about 30 years. It has resulted that: (1)most if not all of the power of the light variations is attributable tofew periodic terms; (2) three of these terms have periods which areexactly in integer ratios, but it is possible to see that they are notFourier harmonics of the same wave, i.e. they are resonant independentwaves; (3) some of the terms are split into two, which could indicatethe presence of non-radial pulsations.
| 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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