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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
| Search for Nanosecond Optical Pulses from Nearby Solar-Type Stars
With ``Earth 2000'' technology we could generate a directed laser pulsethat outshines the broadband visible light of the Sun by 4 orders ofmagnitude. This is a conservative lower bound for the technicalcapability of a communicating civilization; optical interstellarcommunication is thus technically plausible. We have built a pair ofsystems to detect nanosecond pulsed optical signals from a target listthat includes some 13,000 Sun-like stars, and we have made some 16,000observations totaling nearly 2400 hr during five years of operation. Abeam splitter-fed pair of hybrid avalanche photodetectors at the 1.5 mWyeth Telescope at the Harvard/Smithsonian Oak Ridge Observatory(Agassiz Station) triggers on a coincident pulse pair, initiatingmeasurement of pulse width and intensity at subnanosecond resolution. Anidentical system at the 0.9 m Cassegrain at Princeton's Fitz-RandolphObservatory performs synchronized observations with 0.1 μs eventtiming, permitting unambiguous identification of even a solitary pulse.Among the 11,600 artifact-free observations at Harvard, the distributionof 274 observed events shows no pattern of repetition, and is consistentwith a model with uniform event rate, independent of target. With onepossible exception (HIP 107395), no valid event has been seensimultaneously at the two observatories. We describe the search andcandidate events and set limits on the prevalence of civilizationstransmitting intense optical pulses.
| Long periodic variable stars
The information on Mira-type stars and stars adjacent to them at theHertzsprung -- Russel diagram is presented. A detailed description oftheir observational characteristics is given. We give a survey ofimportant observational works concerning: multicolor photometry withspecial attention to the IR emission, maser emission, shock waves, massloss, binarity, the problem of the pulsational mode, direct measurementsof angular and linear dimensions, statistic investigations, study ofkinematic characteristics etc. The most interesting problems regardinglong periodic variable stars are specified. Some attention is given tothe classification and evolutionary stage of these objects.
| New periodic variables from the Hipparcos epoch photometry
Two selection statistics are used to extract new candidate periodicvariables from the epoch photometry of the Hipparcos catalogue. Theprimary selection criterion is a signal-to-noise ratio. The dependenceof this statistic on the number of observations is calibrated usingabout 30000 randomly permuted Hipparcos data sets. A significance levelof 0.1 per cent is used to extract a first batch of candidate variables.The second criterion requires that the optimal frequency be unaffectedif the data are de-trended by low-order polynomials. We find 2675 newcandidate periodic variables, of which the majority (2082) are from theHipparcos`unsolved' variables. Potential problems with theinterpretation of the data (e.g. aliasing) are discussed.
| A Cepheid is No More: Hubble's Variable 19 in M33
We report on the remarkable evolution in the light curve of a variablestar discovered by Hubble in M33 and classified by him as a Cepheid.Early in the 20th century, the variable, designated as V19, exhibited a54.7 day period, an intensity-weighted mean B magnitude of 19.59+/-0.23mag, and a B amplitude of 1.1 mag. Its position in the period-luminosityplane was consistent with the relation derived by Hubble from a total of35 variables. Modern observations by the DIRECT project show a dramaticchange in the properties of V19: its mean B magnitude has risen to19.08+/-0.05 mag, and its B amplitude has decreased to less than 0.1mag. V19 does not appear to be a classical (Population I) Cepheidvariable at present, and its nature remains a mystery. It is not clearhow frequent such objects are or how often they could be mistaken forclassical Cepheids.
| 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.
| 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.
| 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.
| Chemical Composition and Evolution of Post-AGB Stars
Not Available
| The Chemical Compositions of the SRd Variable Stars. I. XY Aquarii, RX Cephei, AB Leonis, and SV Ursae Majoris
Chemical compositions are derived from high-resolution spectra for fourstars classed as SRd variables in the General Catalogue of VariableStars. Two stars-XY Aquarii and RX Cephei-are of solar metallicity andmost likely not variable stars. Their spectroscopic effectivetemperatures and surface gravities correspond to the spectral types G0 Vfor XY Aqr and G8 III for RX Cep. Two stars are undisputed variables andshown here to be metal-poor supergiants: AB Leonis with [Fe/H] ~=-1.6and SV Ursae Majoris with [Fe/H] ~=-1.4. The metallicities and highradial velocities show them to be halo stars.
| The Program to Link the HIPPARCOS Reference Frame to an Extragalactic Reference System Using the Fine Guidance Sensors of the Hubble Space Telescope
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1997AJ....114.2796H&db_key=AST
| The spectral evolution of post-asymptotic giant branch stars
A parameter study of the spectral evolution of a typical post-AGB star,with particular emphasis on the evolution of the IR colours, ispresented. The models are based on the latest evolutionary tracks forhydrogen-burning post-AGB stars. For such tracks the evolutionary rateis very dependent on the assumed mass-loss rate as a function of time.We investigate this effect by modifying the mass-loss prescription. Thenewly calculated evolutionary rates and density distributions are usedto model the spectral evolution of a post-AGB star with thephotoionization code cloudy, including dust in the radiative transfer.Different assumptions for the dust properties and dust formation areconsidered. It is shown that by varying these parameters in a reasonableway, entirely different paths are followed in the IRAS colour-colourdiagram. First of all, the effects of the evolution of the central staron the expanding dust shell cannot be neglected. Also the dustproperties and the definition of the end of the AGB phase have animportant effect. The model tracks show that objects occupying the samelocation in the IRAS colour-colour diagram can have a differentevolutionary past, and therefore the position in the IRAS colour-colourdiagram alone cannot a priori give a unique determination of theevolutionary status of an object. An alternative colour-colour diagram,the K-[12] versus [12]-[25] diagram, is presented. The tracks in thisdiagram seem less affected by particulars of the grain emission. Thisdiagram may be a valuable additional tool for studying post-AGBevolution.
| Is UU Herculis a post-AGB star?
In order to understand the evolutionary status of the anomaloussupergiant UUHer, the prototype of the class of variable supergiantslocated at high galactic latitudes, we obtained several high-resolutionspectra of this star, with the 6m telescope, over 5 years. This materialwas used for a search of possible temporal variations of the radialvelocity at different depths in the photosphere and for studying thechemical composition. The average radial velocity V_r_=~130km/s suggeststhat UUHer belongs to the old population of the Galaxy. No systematicdependence of the velocity on depth of the line formation layer or onionization and excitation potential is observed. The radial velocity ofthe Hα absorption differs strongly from the average photosphericvelocity. The iron abundance in the photosphere of UUHer issignificantly lower than that of the Sun: [Fe/H]=-1.32. The enhancementof nitrogen relatively to iron content [N/Fe]sun_=0.40 incombination with the carbon underabundance [C/Fe]sun_=-0.30suggests that only a first dredge-up episode occurred. The Na content isnormal relatively to iron, therefore there is no evidence fordredging-up of Ne-Na cycle products. The heavy s-process metals Y, Baare depleted relative to H and Fe, which again implies that the thirddredge-up did not occur. From the high luminosity (logg=~1), the largeradial velocity and the chemical abundance pattern, we conclude that UUHer is a low-mass halo star, but not a post-AGB star.
| Abundance Analyses of the Field RV Tauri Variables: EP Lyrae, DY Orionis, AR Puppis, and R Sagittae
Analyses of the photospheric compositions of the four field RV Tauristars, EP Lyr, DY Ori, AR Pup, and R Sge, indicate that to varyingdegrees they have experienced fractionation processes that havepreferentially depleted their atmospheres of elements with highcondensation temperatures. The depletion, as indicated by, for instance,[S/Fe], is greatest for DY Ori, [S/Fe] = 2.5, and least for R Sge,[S/Fe] = 0.9. The initial composition, presumably indicated by thesulfur abundance, was nearly solar for AR Pup, R Sge, and DY Ori, whileit was about 0.6 dex less than solar for EP Lyr. This implies that theRV Tauri stars as a group may not be as metal-poor as previouslythought---they are instead "metal-depleted." The field RV Tauri's arenot halo stars, but probably belong to the thick disk. This brings toseven the number of type II Cepheids that show such a trend; the otherthree are IW Car and V1 in omega Cen, RV Tauri stars, and ST Pup, a WVirginis star. The 12C/13C ratios for EP Lyr and DY Ori are 9 +/- 1 and6 +/- 3, respectively, indicating that CN-cycled material has been mixedwith their surface layers. This is consistent with the general consensusthat RV Tau stars are in a post-AGB evolutionary stage. There is alsoevidence that EP Lyr has a stellar mass companion, but additionalobservations are required to calculate an orbit; hence, EP Lyr could bea link to the group of metal-depleted, high-latitude A--F supergiants,all of which are binaries.
| Supergiants with large IR excesses.
Not Available
| 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
| Light and colour curves of the variable UU Herculis.
Not Available
| 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.
| Pulsations of luminous intermediate-mass stars with applications to UU Herculis
Pulsation models for the enigmatic F-type supergiant variable, UUHerculis are investigated. It is shown that irregular pulsations withsmall amplitude is realized, if UU Her is assumed to be anintermediate-mass-F-type supergiant star which has evolved with massloss and rotational mixing and thus highly luminous, compared with whatis obtained by conventional evolution.
| HD6474: an UU Her Spectrum Variable?
Not Available
| Radio continuum emission from stars: a catalogue update.
An updated version of my catalogue of radio stars is presented. Somestatistics and availability are discussed.
| Evidence for the early onset of aspherical structure in the planetary nebula formation process: Spectropolarimetry of post-AGB stars
We present optical spectropolarimetry of 31 post-asymptotic giant branch(post-AGB) stars, objects that are believed to represent the firstphases of the transition from the AGB to the planetary nebula stage. 24of these objects are found to be intrinsically polarized. We group theseobjects into four classes based on their observed polarizationproperties, rho (lambda) and theta (lambda), and discuss possibleexplainations for the observed behaviors. Type 1 objects display highlevels of polarization and large position angle rotations. Type 2objects lack large position angle rotations, but have polarizations toolarge to be attributed to foreground interstellar material. Type 3objects show position angle rotations and polarization changes acrossTiO absorption features; and finally, Type 4 are objects in which theobserved polarization can be entirely attributed to interstellareffects. The currently popular paradigm of planetary nebula morphologyof a dense torus plus bipolar lobes can explain the rho and thetabehavior of the Type 1 and Type 2 objects. However, a large number ofthe objects exhibit time-variable rho and theta. This implies that theirmorphologies may not be stable, but rather evolving or transientstructures. Regardless of any specific model for the morphology, ourmain result is that aspherical structure appears very early in thetransition from the AGB to the planetary nebula stage. We compare thepolarization properties of the post-AGB stars to the morphologicalcharacteristics of evolved planetary nebulae. Our results indicate thatthe nebular morphology may originate at an early evolutionary stage. Wedo not observe any correlation between chemistry (O-rich vs C-rich) andpolarization class in the AGB stars. We examine the formation ofaspherical planetary nebulae in the context of binary star evolution. Ifbipolar geometry is a consequence of binary star evolution, the numberof highly polarized post-AGB stars in our sample requires a high binarystar frequency.
| The pulsations of yellow semi-regular variables II. The F supergiant in the high-latitude binary BL Telescopii
Photoelectric observations of the F-type component of the high-latitudeeclipsing binary BL Telescopii outside eclipse were analysed. Twoperiods (92.5d and 64.8)d were found to be present in the light curve.They are identified as belonging to the fundamental mode and the firstovertone. It seems that BL Telescopii prefers overtone pulsation. Thepresence of the two periods and their ratio indicates that the high-massinterpretation of the variable could be valid. Together with UU Her andV487 Cas it belongs to the re-defined UU Herculis group of stars.
| A study of dust shells around high latitude supergiants
A sample of 22 stars with infrared excess emission and many of whichhave supergiant-like spectra was surveyed in the submillimeter continuumat 438, 761 and 1100μm using the James Clerk Maxwell Telescope (JCMT,Mauna Kea, Hawaii). Most of the sources are at high galactic latitudesbut stars with similar properties at lower galactic latitudes are alsoincluded. For 16 sources it is believed that they are post AsymptoticGiant Branch stars (post-AGB stars) and 6 of them are detected. The restof the sample consists of 2 binaries, 1 Herbig Ae star, 1 Luminous BlueVariable and 2 sources for which the post-AGB nature is uncertain. Theobservations are combined with optical, near infrared and IRAS data andare fitted with a spherically symmetric and optically thin dust shellmodel. It is found that a large fraction of the excess emissionoriginates from relatively hot dust near the star. Only 2 sources lacksuch a hot dust component. For all stars with a hot dust component itwas found that the emission longward of 60μm cannot be explained withonly one dust shell. Several possible explanations are discussed and itis concluded that the extra excess at far IR and submm wavelengths iscaused by a second colder and thus more distant dust component. For thepost-AGB stars this component is believed to be the remnant AGB shell.The relatively low stellar temperatures (<10,000 K) in combinationwith the relatively large ages of the remnant AGB shell (>10^3^ yr)confirm earlier suggestions that many of these stars are very slowlyevolving towards higher temperatures, as expected for low mass post-AGBstars. Evidence was found that stars may stop losing mass and evolve offthe AGB at temperatures below 5,000 K (as assumed for the Schoenbernertracks) causing a slower evolution towards higher temperatures.
| Line-profiles of F supergiant stars as candidates of proto-planetary nebulae
In this report the results of spectroscopic observations on selected Fsupergiant stars as the candidates of proto-planetary nebulae (PPNs) arepresented. Volk and Kwok (1989) selected nearly one hundred newcandidates of PPNs based upon the scenario on the evolution of them.They summarized four classes of stars which should be the PPNs and aredescribed in various papers. These are (1) High galactic latitudesupergiants, (2) Nonvariable OH/IR stars, (3) Low color temperatureinfrared objects, and (4) R CrB. In order to examine the extendedenvelope of the PPNs we have started our project to obtain the H alphaprofile which should give us some clue to the structure of the envelope.We are mainly concerned with F supergiant stars. Our sample objects aremostly classified as pulsating or semiregular variables.
| Supergiant variables: Recent observational results
Recent observations of several types of supergiant variable stars arereviewed: massive blue, yellow and red supergiants; classical andpopulation II Cepheids; RV Tauri stars; yellow semi-regular (SRd)variables, including UU Herculis stars; and R Coronae Borealis stars.The emphasis is on non-linear aspects such as: amplitude and shape ofthe light and velocity curves; multiperiodicity, irregularity and chaos;long-term changes in period and amplitude; episodic and continuous massloss.
| A photometric and spectroscopic search for luminous high latitude stars
Formulas, derived by Arellano Ferro and Mendoza in Paper I (1993), tocalculate Mv, log g, and (Fe/H) were applied to a group of 73A, F, and G stars of high galactic latitude previously classified assupergiant stars. The only star that showed, from data on hand, to beluminous, slightly iron deficient, and out of the galactic plane was BLTelescopii. The remainder of the sample either present controversialresults or are definitively giant or dwarf stars misclassified assupergiants. Thus, if luminous, young stars indeed exist out of thegalactic plane, they are extremely rare.
| V487 Cassiopeiae (HD 6474): a UU Herculis variable in the galactic plane?
New photoelectric photometry of V487 Cassiopeiae (HD 6474) made between1984 and 1992 is presented. The star has a rather complicated lightvariation: at least two periods (P1 = 160.3 days andP2 = 99.6 days) are present in the light curve, one of thempossibly with variable amplitude. The period ratio(P2/P1 = 0.62) and the nature of the lightvariation (i.e. the simultaneous presence of two modes, the amplitudechange) are both very similar to that of UU Herculis. This similarityindicates that V487 Cassiopeiae is a UU Her-type variable though it isin the galactic plane. A distinction between the UU Her-type and 89Her-type variables is suggested.
| Pulsational properties of post-AGB stars
Linear stability analysis and hydrodynamic calculations are performedfor post-asymptotic giant branch star models using the new OPALopacities of Iglesias et al. The linear pulsational calculations showthat for low mass stars with L/M greater than 104 solarluminosity/solar mass the low order radial modes are unstable across thewhole Hertzsprung-Russell diagram. Excited are radial fundamental modeand first overtone, and in the intermediate temperature range(log(Teff) approximately = 4.2) higher overtone modes becomeexcited. With the new opacities the instability region is not confinedto the extension of the Cepheid instability strip but extends muchfurther towards higher effective temperatures. The behavior on nonlinearpulsations in selected models is presented. These calculations show thatat higher temperatures the nonlinear models exhibit low amplitudeapproximately = 0.001 - 0.04 semiregular pulsations. The amplitudes arehigher close to the regions where the driving in the H/He ionization orZ-bump zones is most efficient. In the intermediate temperature rangethe amplitudes are much smaller.
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| Sað Açýklýk: | 16h35m57.29s |
| Yükselim: | +37°58'02.1" |
| Görünürdeki Parlaklýk: | 9.016 |
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| B-T magnitude: | 9.636 |
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