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IRAS 11472-0800: an extremely depleted pulsating binary post-AGB star
Aims: We focus here on one particular and poorly studied object,IRAS 11472-0800. It is a highly evolved post-asymptotic giant branch(post-AGB) star of spectral type F, with a large infrared excessproduced by thermal emission of circumstellar dust. Methods: Wedeployed a multi-wavelength study that includes the analyses of opticaland IR spectra as well as a variability study based on photometric andspectroscopic time-series. Results: The spectral energydistribution (SED) properties as well as the highly processed silicateN-band emission show that the dust in IRAS 11472-0800 is likely trappedin a stable disc. The energetics of the SED and the colour variabilityshow that our viewing angle is close to edge-on and that the opticalflux is dominated by scattered light. With photospheric abundances of[Fe/H] = -2.7 and [Sc/H] = -4.2, we discovered that IRAS 11472-0800 isone of the most chemically-depleted objects known to date. Moreover,IRAS 11472-0800 is a pulsating star with a period of 31.16 days and apeak-to-peak amplitude of 0.6 mag in V. The radial velocity variabilityis strongly influenced by the pulsations, but the significantcycle-to-cycle variability is systematic on a longer time scale, whichwe interpret as evidence for binary motion. Conclusions: Weconclude that IRAS 11472-0800 is a pulsating binary star surrounded by acircumbinary disc. The line-of-sight towards the object lies close tothe orbital plane, therefore the optical light is dominated by scatteredlight. IRAS 11472-0800 is one of the most chemically-depleted objectsknown so far and links the dusty RV Tauri stars to the non-pulsatingclass of strongly depleted objects.Based on observations collected at the European Southern Observatory,Chile. Programme ID: 65.L-0615(A), on observations made with theMercator Telescope, operated on the island of La Palma by the FlemishCommunity, at the Spanish Observatorio del Roque de los Muchachos and onobservations obtained with the HERMES spectrograph, which is supportedby the Fund for Scientific Research of Flanders (FWO), Belgium, theResearch Council of K.U. Leuven, Belgium, the Fonds National RecherchesScientific (FNRS), Belgium, the Royal Observatory of Belgium, theObservatoire de Genève, Switzerland and the ThüringerLandessternwarte Tautenburg, Germany.Tables 3 and 6 are only availableat the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) orvia http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/542/A53
| An approach to effective temperature and surface gravity in post-AGB and RV Tauri stars in the near-IR region
A number of empirical correlations that allow us to calculate theeffective temperature and surface gravity for a set of evolved post-AGBand RV Tauri stars are determined using as calibrators the intrinsiccolors of 2MASS (Two Micron All Sky Survey) photometry. We have analyzeda total sample of 36 stars of which 25 are post-AGB stars and 11 are RVTauri stars, respectively. A group of 11 stars with parallax measureswere used as calibrators of the absolute magnitude. The result for T_effand log g from intrinsic colors (J - H)_0 and (H-K_s)_0 at thenear-infrared pass bands reach a dispersion of 220 K and 0.2,respectively. We can estimate the absolute magnitude using the intrinsiccolor in the near-infrared band with an uncertainty of 0.28 mag. Thisindicates that (J - H)_0 and (H - K_s)_0 show sensitivity to theabsolute magnitude.
| 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.
| uvby? photometry of early type open cluster and field stars
Context. The ? Cephei stars and slowly pulsating B (SPB) stars aremassive main sequence variables. The strength of their pulsationaldriving strongly depends on the opacity of iron-group elements. As manyof those stars naturally occur in young open clusters, whosemetallicities can be determined in several fundamental ways, it islogical to study the incidence of pulsation in several young openclusters. Aims: To provide the foundation for such aninvestigation, Strömgren-Crawford uvby? photometry of opencluster target stars was carried out to determine effectivetemperatures, luminosities, and therefore cluster memberships. Methods: In the course of three observing runs, uvby? photometryfor 168 target stars was acquired and transformed into the standardsystem by measurements of 117 standard stars. The list of target starsalso included some known cluster and field ? Cephei stars, as wellas ? Cephei and SPB candidates that are targets of theasteroseismic part of the Kepler satellite mission. Results: Theuvby? photometric results are presented. The data are shown to beon the standard system, and the properties of the target stars arediscussed: 140 of these are indeed OB stars, a total of 101 targets liewithin the ? Cephei and/or SPB star instability strips, and eachinvestigated cluster contains such potential pulsators. Conclusions: These measurements will be taken advantage of in a numberof subsequent publications.Based on measurements obtained at McDonald Observatory of the Universityof Texas at Austin.Tables 3-6 are only available in electronic form atthe CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/528/A148
| Chemical composition of A-F type post-AGB candidates
An abundance analysis has been conducted for a sample of ninepost-asymptotic giant branch (AGB) candidate stars; eight of them havenot been explored before. We find four very promising objects likeHD105262, HD53300 and CpD-62° 5428 among them. We find strongevidence of dust-gas separation through selective depletion ofrefractive elements in HD105262. The same effect is also observed inHD53300, CpD-62° 5428 and HD114855 although abundance peculiaritiesare relatively smaller for the last two stars. We find strong enrichmentof nitrogen for HD725, HD842, HD1457, HD9233 and HD61227 but no furtherevidence to support their post-AGB nature. We have compared the observed[N/C] ratios of these stars with the predictions of evolutionary modelswhich include the rotation-induced mixing.
| The PASTEL catalogue of stellar parameters
Aims: The PASTEL catalogue is an update of the [Fe/H] catalogue,published in 1997 and 2001. It is a bibliographical compilation ofstellar atmospheric parameters providing (T_eff, log g, [Fe/H])determinations obtained from the analysis of high resolution, highsignal-to-noise spectra, carried out with model atmospheres. PASTEL alsoprovides determinations of the one parameter T_eff based on variousmethods. It is aimed in the future to provide also homogenizedatmospheric parameters and elemental abundances, radial and rotationalvelocities. A web interface has been created to query the catalogue onelaborated criteria. PASTEL is also distributed through the CDS databaseand VizieR. Methods: To make it as complete as possible, the mainjournals have been surveyed, as well as the CDS database, to findrelevant publications. The catalogue is regularly updated with newdeterminations found in the literature. Results: As of Febuary2010, PASTEL includes 30151 determinations of either T_eff or (T_eff,log g, [Fe/H]) for 16 649 different stars corresponding to 865bibliographical references. Nearly 6000 stars have a determination ofthe three parameters (T_eff, log g, [Fe/H]) with a high qualityspectroscopic metallicity.The catalogue can be queried through a dedicated web interface at http://pastel.obs.u-bordeaux1.fr/.It is also available in electronic form at the Centre de DonnéesStellaires in Strasbourg (http://vizier.u-strasbg.fr/viz-bin/VizieR?-source=B/pastel),at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) orvia http://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/515/A111
| Could the Ultra-Metal-poor Stars be Chemically Peculiar and Not Related to the First Stars?
Chemically peculiar stars define a class of stars that show unusualelemental abundances due to stellar photospheric effects and not due tonatal variations. In this paper, we compare the elemental abundancepatterns of the ultra-metal-poor stars with metallicities [Fe/H]~-5 tothose of a subclass of chemically peculiar stars. These include post-AGBstars, RV Tauri variable stars, and the Lambda Bootis stars, which rangein mass, age, binarity, and evolutionary status, yet can have ironabundance determinations as low as [Fe/H]~-5. These chemicalpeculiarities are interpreted as due to the separation of gas and dustbeyond the stellar surface, followed by the accretion of dust-depletedgas. Contrary to this, the elemental abundances in the ultra-metal-poorstars are thought to represent yields of the most metal-poor supernovaeand, therefore, observationally constrain the earliest stages ofchemical evolution in the universe. Detailed chemical abundances are nowavailable for HE 1327-2326 and HE 0107-5240, the two extremeultra-metal-poor stars in our Galaxy, and for HE 0557-4840, anotherultra-metal-poor star found by the Hamburg/ESO survey. There areinteresting similarities in their abundance ratios to those of thechemically peculiar stars; e.g., the abundances of the elements in theirphotospheres are related to the condensation temperature of thatelement. If these three stars are chemically peculiar, then their CNOabundances suggest true metallicities of [X/H]~-2 to -4. It is importantto establish the nature of these stars, since they are used as tests ofthe early chemical evolution of the Galaxy.
| Variability and evolution in various classes of post-AGB stars
We aim to compare properties of early-type post-asymptotic giant-branch(post-AGB) stars, including normal first-time B-type post-AGB stars, andextreme helium stars (EHes). Hipparcos photometry for 12 post-AGB starsand 7 EHe stars has been analyzed; 5 post-AGB stars are clearlyvariable. The Hipparcos data are not sufficiently sensitive to detectvariability in any of the EHes.
| 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
| Progenitors of type Ia supernovae: Binary stars with white dwarf companions
Type Ia SNe (SNe Ia) are thought to come from carbon oxygen white dwarfsthat accrete mass from binary companions until they approach theChandrasekhar limit, ignite carbon, and undergo complete thermonucleardisruption. A survey of the observed types of binaries that containwhite dwarfs is presented. We propose that certain systems that seemmost promising as SN Ia progenitors should be more intensively observedand modeled, to determine whether the white dwarfs in these systems willbe able to reach the Chandrasekhar limit. In view of the number ofpromising single-degenerate systems and the dearth of promisingdouble-degenerate systems, we suspect that single-degenerates producemost or perhaps all SNe Ia, while double-degenerates produce some orperhaps none.
| Optical spectrum of the post-AGB Star HD56126 in the wavelength interval 4010-8790 Å Å
The optical spectrum of the post-AGB star HD56126 identified with theinfrared source IRAS07134+1005 is studied in detail using high spectralresolution observations (R = 25000 and 60000) performed with the echellespectrographs of the 6-m telescope. A total of about one and a halfthousand absorptions of neutral atoms and ions, absorption bands ofC2, CN, and CH molecules, and interstellar bands (DIBs) areidentified in the 4012 to 8790 Å Å wavelength interval, andthe depths and radial velocities of these spectral features aremeasured. Differences are revealed between the variations of the radialvelocities measured from spectral features of different excitation. Inaddition to the well-known variability of the H α profile, wefound variations in the profiles of a number of FeII, YII, and BaIIlines. We also produce an atlas of the spectrum of HD56126 and itscomparison star α Per. The full version of the Atlas is availablein electronic form from: http://www.sao.ru/hq/ssl/Atlas/Atlas.html.
| Medium-resolution Isaac Newton Telescope library of empirical spectra - II. The stellar atmospheric parameters
We present a homogeneous set of stellar atmospheric parameters(Teff, logg, [Fe/H]) for MILES, a new spectral stellarlibrary covering the range λλ 3525-7500Å at2.3Å (FWHM) spectral resolution. The library consists of 985 starsspanning a large range in atmospheric parameters, from super-metal-rich,cool stars to hot, metal-poor stars. The spectral resolution, spectraltype coverage and number of stars represent a substantial improvementover previous libraries used in population synthesis models. Theatmospheric parameters that we present here are the result of aprevious, extensive compilation from the literature. In order toconstruct a homogeneous data set of atmospheric parameters we have takenthe sample of stars of Soubiran, Katz & Cayrel, which has very welldetermined fundamental parameters, as the standard reference system forour field stars, and have calibrated and bootstrapped the data fromother papers against it. The atmospheric parameters for our clusterstars have also been revised and updated according to recent metallicityscales, colour-temperature relations and improved set of isochrones.
| Medium-resolution Isaac Newton Telescope library of empirical spectra
A new stellar library developed for stellar population synthesismodelling is presented. The library consists of 985 stars spanning alarge range in atmospheric parameters. The spectra were obtained at the2.5-m Isaac Newton Telescope and cover the range λλ3525-7500 Å at 2.3 Å (full width at half-maximum) spectralresolution. The spectral resolution, spectral-type coverage,flux-calibration accuracy and number of stars represent a substantialimprovement over previous libraries used in population-synthesis models.
| 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.
| Keplerian discs around post-AGB stars: a common phenomenon?
Aims.We aim at showing that the broad-band SED characteristics of oursample of post-AGB stars are best interpreted, assuming thecircumstellar dust is stored in Keplerian rotating passivediscs.Methods.We present a homogeneous and systematic study of theSpectral Energy Distributions (SEDs) of a sample of 51 post-AGB objects.The selection criteria to define the whole sample were tuned to coverthe broad-band characteristics of known binary post-AGB stars. The wholesample includes 20 dusty RV Tauri stars from the General Catalogue ofVariable Stars (GCVS). We supplemented our own Geneva optical photometrywith literature data to cover a broad range of fluxes from the UV to thefar-IR.Results.All the SEDs display very similar characteristics: alarge IR excess with a dust excess starting near the sublimationtemperature, irrespective of the effective temperature of the centralstar. Moreover, when available, the long wavelength fluxes show ablack-body slope indicative of the presence of a component of large mmsized grains.Conclusions.We argue that in all systems, gravitationallybound dusty discs are present. The discs must be puffed-up to cover alarge opening angle for the central star and we argue that the discshave some similarity with the passive discs detected around youngstellar objects. We interpret the presence of a disc to be a signaturefor binarity of the central object, but this will need confirmation bylong-term monitoring of the radial velocities. We argue that dusty RVTauri stars are those binaries which happen to be in the Population IIinstability strip.
| Chemical composition of evolved stars of high galactic latitude
We have carried out abundance analysis for a sample of high galacticlatitude supergiants in search of evolved stars.We find that HD 27381 has atmospheric parameters and an abundancepatternvery similar to that of the post-AGB star HD 107369.HD 10285 and HD 25291 are moderately metal-poor andshow the influence of mixing that has brought the productsof NeNa cycle to the surface.The high galactic latitude B supergiant HD 137569 shows selectivedepletion of refractory elements normally seen in post-AGB stars.We find that the high velocity B typestar HD 172324 shows moderate deficiency of Fe group elements butthe CNO abundances are verysimilar to that of disk B supergiants. The observed variations inthe radial velocities, transient appearance of emission componentsin hydrogen line profiles and doublingof O I lines at 7774 Å support the possibility of this star beinga pulsating variable or a binary star.
| Post-Agb Stars
In this contribution, a review is presented on the ample data obtainedon post-AGB stars, both on the central stars and their circumstellarmaterial. The fast evolutionary phase is characterized by a rapid changein the properties of the objects, but the variety is so large that thereis yet no clear consensus on how the detailed studies of individualobjects are linked together by evolutionary channels. The absence ofstrong molecular veiling in the photospheres of the central stars,together with a spread in intrinsic metallicity make post-AGB stars veryuseful in constraining AGB chemical evolutionary models. We discuss thesurprisingly wide variety of chemical signatures observed. The onset inthe creation process of the panoply of structures and shapes observed inplanetary nebulae occurs during the short post-AGB evolution, but thephysical nature of the processes involved is still badly understood. Inthe rapidly growing field of circumstellar mineralogy, post-AGB starshave their story to tell and also the molecular envelope changessignificantly due to dilution and hardening of the stellar radiation.The real-time evolution of some objects suffering a late thermal flashis reviewed and their possible link to other hydrogen-deficient objectsis discussed. Any review on stellar evolution has a section on binariesand this contribution is no exception because binaries make up asignificant fraction of the post-AGB stars known to date.
| RU Cen and SX Cen: Two strongly depleted RV Tauri stars in binary systems. The RV Tauri photometric b phenomenon and binarity
We present a chemical abundance analysis on the basis of highsignal-to-noise and high-resolution (lambda /Delta lambda ~ 48 000)optical spectra of two RV Tauri stars RU Cen and SX Cen. With an [Fe/H]= -1.9 and a [Zn/Fe] = +0.9 for RU Cen and a [Fe/H] = -1.1 and a [Zn/Fe]= +0.6 for SX Cen, both stars of spectroscopic class B display strongdepletion of refractory elements in their photospheres. Our CORALIEradial velocity measurements prove the stars to be members of binarysystems and a detailed construction of the spectral energy distributionindicate the presence of a large amount of hot circumstellar dust.Moreover, the orbital period of SX Cen of around 600 days is similar tothe published period of mean magnitude variation in the light curve (RVTauri phomometric class b phenomenon). All these observations indicatethe presence of a stable circumbinary disk in the objects and strengthenthe model that this is a necessary condition for the depletion processto take place. Based on observations collected at the European SouthernObservatory in Chile (64.L-0117(A), 67.D-0054(A)), on the 1.2 m SwissEuler telescope on La Silla and on the 70 cm Swiss photometric telescopealso on La Silla.
| BVRIJHK photometry of post-AGB candidates
BVRIJHK photometric observations are presented for 27 post-AGBcandidates. Almost all objects show a double peaked SED curve in theoptical to far-infrared wavelengths. Seventeen objects were classifiedas post-AGB stars on the basis of their spectral type, location in theIRAS color-color diagram and SED. The physical parameters of theobserved post-AGB stars, the inner radius of the detached shell, themass of the shell and the distance were derived using the simple dustshell model. We compared our observational sequence of post-AGB objectsto the theoretical evolutionary sequence (Schönberner\cite{schonberner1983}; Blöcker \cite{blocker}) in the stellartemperatures versus age diagram. We found that two post-AGB stars, IRAS05040+4820 and 08187-1905, have low stellar temperature with a largedynamical age of the dust shell. They appear to provide the firstobservational evidence that some low-mass stars bypass the planetarynebulae stage because of their slow increase in stellar temperature.Based on observations obtained at Kiso Observatory, Nagano, Japan.Table2 is also available in electronic form at the CDS via anonymous ftp tocdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/385/884
| Atmospheric abundances in post-AGB candidates of intermediate temperature
Detailed atmospheric abundances have been calculated for a sample of -Gsupergiant stars with IR fluxes and/or high galactic latitudes. HD172481 and HD 158616 show clear indications of being post-AGB stars thathave experienced third dredge-up. HD 158616 is carbon-rich while theabundance pattern of HD 172481 and its large Li enhancement givessupport to the hot bottom burning scenario that explains paucity ofcarbon-rich stars among AGB stars. HD 172324 is very likely a hotpost-AGB star that shows a strong carbon deficiency. HD 725, HD 218753and HD 331319 also appear to be evolved objects between the red giantand the AGB. HD 9167, HD 173638 with a few exceptions, reflect solarabundances and no signs of post red giant evolution. They are mostlikely young massive disk supergiants. Further analysis ofproto-Planetary Nebula HDE 341617 reveals that He lines show signs ofvelocity stratification. The emission lines have weakened considerablysince 1993. The envelope expands at 19 km s-1 relative to thestar. Atmospheric abundances, evolutionary tracks and isochrones areused to estimate masses and ages of all stars in the sample. Based onobservations obtained at the Haute-Provence Observatory, France. Tables11 and 12 are only available in electronic form athttp://www.edpsciences.org
| Binary "Post-AGB" Stars
Not Available
| Chemical Composition and Evolution of Post-AGB 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.
| The First 50 Years at Palomar, 1949-1999 Another View: Instruments, Spectroscopy and Spectrophotometry and the Infrared
We review the research on a wide variety of topics using data obtainedwith the 200-inch Hale telescope. Using state-of-the-art spectrographs,photometers, spectrometers and infrared detectors, the Palomarastronomers investigated the spectra of stars, interstellar matter, AGNsand quasars in great detail. Spectral resolutions ranged from 1000 A forbroad-band photometry to 0.04 A using interferometric techniques.
| The RV\ Tauri phenomenon and binarity
We present accurate radial velocity measurements on the pulsatingextremely iron-deficient post-AGB object HD 52961 and the RV Tauri starEN TrA (HD 131356) proving them to be binaries. Our long-termphotometric monitoring campaign shows that the RV Tauri photometricclass ``b'' phenomenon in HD 52961 is due to variable circumstellarextinction during orbital motion. By comparing carefully theobservational characteristics of RV Tauri stars and the class ofextremely iron-deficient post-AGB objects we conclude that binarity is awidespread phenomenon in the RV Tauri class of objects. The observedchemical depletion patterns, weak circumstellar CO emission, peculiarspectral energy distribution and the difference in photospheric class ofthe RV Tauri objects can all be naturally explained by assuming that thecircumstellar material is not freely expanding, but trapped in thebinary system. Based on observations collected at the European SouthernObservatory (proposals codes 51.7-0052; 51.7-0053; 52.7-0048; 58.E-0462;59.E-0432; 61.E-0426); with the Swiss telescopes at ESO and OHP and theAPT telescope at Mt. Hopkins
| A HIPPARCOS Census of the Nearby OB Associations
A comprehensive census of the stellar content of the OB associationswithin 1 kpc from the Sun is presented, based on Hipparcos positions,proper motions, and parallaxes. It is a key part of a long-term projectto study the formation, structure, and evolution of nearby young stellargroups and related star-forming regions. OB associations are unbound``moving groups,'' which can be detected kinematically because of theirsmall internal velocity dispersion. The nearby associations have a largeextent on the sky, which traditionally has limited astrometricmembership determination to bright stars (V<~6 mag), with spectraltypes earlier than ~B5. The Hipparcos measurements allow a majorimprovement in this situation. Moving groups are identified in theHipparcos Catalog by combining de Bruijne's refurbished convergent pointmethod with the ``Spaghetti method'' of Hoogerwerf & Aguilar.Astrometric members are listed for 12 young stellar groups, out to adistance of ~650 pc. These are the three subgroups Upper Scorpius, UpperCentaurus Lupus, and Lower Centaurus Crux of Sco OB2, as well as VelOB2, Tr 10, Col 121, Per OB2, alpha Persei (Per OB3), Cas-Tau, Lac OB1,Cep OB2, and a new group in Cepheus, designated as Cep OB6. Theselection procedure corrects the list of previously known astrometricand photometric B- and A-type members in these groups and identifiesmany new members, including a significant number of F stars, as well asevolved stars, e.g., the Wolf-Rayet stars gamma^2 Vel (WR 11) in Vel OB2and EZ CMa (WR 6) in Col 121, and the classical Cepheid delta Cep in CepOB6. Membership probabilities are given for all selected stars. MonteCarlo simulations are used to estimate the expected number of interloperfield stars. In the nearest associations, notably in Sco OB2, thelater-type members include T Tauri objects and other stars in the finalpre-main-sequence phase. This provides a firm link between the classicalhigh-mass stellar content and ongoing low-mass star formation. Detailedstudies of these 12 groups, and their relation to the surroundinginterstellar medium, will be presented elsewhere. Astrometric evidencefor moving groups in the fields of R CrA, CMa OB1, Mon OB1, Ori OB1, CamOB1, Cep OB3, Cep OB4, Cyg OB4, Cyg OB7, and Sct OB2, is inconclusive.OB associations do exist in many of these regions, but they are eitherat distances beyond ~500 pc where the Hipparcos parallaxes are oflimited use, or they have unfavorable kinematics, so that the groupproper motion does not distinguish it from the field stars in theGalactic disk. The mean distances of the well-established groups aresystematically smaller than the pre-Hipparcos photometric estimates.While part of this may be caused by the improved membership lists, arecalibration of the upper main sequence in the Hertzsprung-Russelldiagram may be called for. The mean motions display a systematicpattern, which is discussed in relation to the Gould Belt. Six of the 12detected moving groups do not appear in the classical list of nearby OBassociations. This is sometimes caused by the absence of O stars, but inother cases a previously known open cluster turns out to be (part of) anextended OB association. The number of unbound young stellar groups inthe solar neighborhood may be significantly larger than thoughtpreviously.
| Spectral variability of the binary HR 4049
The C I, Na I D, and H? lines of the post-AGB binary HR 4049 havebeen studied. Na I D variability results from a photospheric absorptioncomponent ([Na/H]=-1.6+/-0.2) which follows the velocity of the primaryand a stationary, non-photospheric component. An emission component isattributed to the circumbinary disc, and an absorption component tomass-loss from the system with a velocity of 5.3+/-0.5 km s(-1) . TheH? profile varies with the orbital period. The two strong shelltype emission peaks are identified as from one single broad emissionfeature with an absorption centered around -7.5 km s(-1) . The intensityvariations are largely attributed to a differential amount of reddeningtowards the H? emitting region and the stellar continuum. Theradial velocities suggest that the H? emission moves in phase withthe primary, but with a slightly lower velocity amplitude. From this weinfer that the H? emission comes from outside the orbit of theprimary, but still gravitationally bound to the primary. H? alsoshows a weak emission feature at -21.3+/-3.5 km s(-1) , which originatesfrom the circumbinary disc and a weak absorption feature at -7.5+/-1.6km s(-1) due to absorption by the circumbinary disc. We propose twocompeting models that could account for the observed velocity andintensity variations of the H? profile. Model I: light from theprimary reflects on a localized spot near the inner radius of thecircumbinary disc which is closest to the primary. Model II: H?emission originates in the outer layers of the extended atmosphere ofthe primary due to activity. These activities are locked to the positionof the primary in its orbit. We discuss the similarities of variabilityand shape of the H? emission of HR 4049 with those of early typeT-Tauri stars (e.g SU Aur). Based on observations obtained at theMcDonald, ESO, CTIO, and La Palma observatories.
| Spectroscopic studies of selected F-G supergiants
Not Available
| A catalogue of [Fe/H] determinations: 1996 edition
A fifth Edition of the Catalogue of [Fe/H] determinations is presentedherewith. It contains 5946 determinations for 3247 stars, including 751stars in 84 associations, clusters or galaxies. The literature iscomplete up to December 1995. The 700 bibliographical referencescorrespond to [Fe/H] determinations obtained from high resolutionspectroscopic observations and detailed analyses, most of them carriedout with the help of model-atmospheres. The Catalogue is made up ofthree formatted files: File 1: field stars, File 2: stars in galacticassociations and clusters, and stars in SMC, LMC, M33, File 3: numberedlist of bibliographical references The three files are only available inelectronic form at the Centre de Donnees Stellaires in Strasbourg, viaanonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5), or viahttp://cdsweb.u-strasbg.fr/Abstract.html
| Circumstellar Molecular Spectra Towards Evolved Stars
In this paper we discuss the relevance, and possible scientific gains,which can be acquired from studying circumstellar molecular spectratoward evolved stars. Where can we expect circumstellar molecularspectra, why would we want to study these spectra, which molecules mightbe present, and what can we learn from these studies? We present anoverview of reported detections, and discuss some of the results.
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הכנס מאמר חדש
לינקים קשורים
הכנס לינק חדש
משמש של הקבוצה הבאה
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תצפית ומידע אסטרומטרי
| קבוצת-כוכבים: | לטאה |
| התרוממות ימנית: | 22h46m11.23s |
| סירוב: | +40°06'26.3" |
| גודל גלוי: | 9.268 |
| תנועה נכונה: | -1.4 |
| תנועה נכונה: | -2.7 |
| B-T magnitude: | 9.483 |
| V-T magnitude: | 9.286 |
קטלוגים וכינוים:
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