Contents
Images
Upload your image
DSS Images Other Images
Related articles
Lithium abundances for early F stars: new observational constraints for the Li dilution
Aims.To investigate any correlation between Li abundances and rotationalvelocities among F-G evolved stars, we study a large sample of early Fstars from the Bright Star Catalogue (BSC), most of them classified inthe literature as giant stars.Methods.Physical parameters and Liabundances are estimated for each star, often for the first time, bycomparing observed and synthetic spectra. We analyse the position of thestars in the H-R Diagram based on Hipparcos data using stellarevolutionary tracks and we discuss their Li abundances and projectedrotational velocities.Results.Observed stars are mostly on theturnoff, with masses between 1.5 and 2.0 Mȯ. The starswith measured A(Li) abundance show high Li content, most of them withabundance near the cosmic value. The A(Li) versus V sin i diagram showsthe same trend as reported in previous studies: fast rotators (V sinigse 30 km s-1) are also stars with high Li content, whereasslow rotators present a wide range of values of A(Li), ranging from nodetected Li to the cosmic value.
| Spectroscopic observations of the rapid rotating post-AGB star IRAS 05381+1012
We report on the high-resolution stellar parameters and abundanceanalysis of the rapidly rotating post-AGB star IRAS 05381+1012. Analysisof high-resolution spectra shows that IRAS 05381+1012 has an effectivetemperature of T_eff=5200± 100 K and a surface gravity of logg=1.0± 0.5 corresponding to a spectral type G(2-3)I. Theseparameters result in an estimated luminosity of 970 Lȯand a distance of 2700 pc. We also show that IRAS 05381+1012 has aprojected rotational velocity vsin i=40± 10 km s-1.The abundance analysis based on a few available lines reveals that thisstar is an iron-deficient object with [Fe/H]=-0.8. We also analyze theabundance pattern and compare it to other classes of stars with similarstellar parameters.
| 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.
| The evolutionary status of the bright high-latitude supergiant HD 190390
Despite its mean apparent magnitude of mV = 6.39, theevolutionary status of HD 190390 (HR7671), a luminous F-type supergiant at high galactic latitude,is still not very clear, but in most papers a post-AGB classification isassumed. New observational material has been obtained with fourdifferent instruments and is presented here. An extensive abundanceanalysis based on high resolution, high signal-to-noise NTT+EMMI spectraconfirms the metal deficiency of this object ([Fe/H] = -1.6), togetherwith a high lithium content (log ɛ(Li) = 1.9). A variabilityanalysis based on Geneva photometry over seven years reveals beatingwith a period of ~3000 days. It is, however, not clear whether thisbeating is caused by a stable triplet, or it is the consequence of smallchanges in the main frequency. More recent data obtained with theHIPPARCOS satellite and the Mercator telescope not only confirm the mainperiod, but also support the presence of a second periodicity of 11days, which was also found in the Geneva photometry. A conclusiveevolutionary status of this object is not given, but alternative to theUU Her (i.e. post-AGB) status, a W Vir classification is discussed.Based on observations collected at the European Southern Observatory, LaSilla, Chile (programme 61.E-0426), and at the Observatorio del Roque delos Muchachos, La Palma, Spain.
| The Indo-US Library of Coudé Feed Stellar Spectra
We have obtained spectra for 1273 stars using the 0.9 m coudéfeed telescope at Kitt Peak National Observatory. This telescope feedsthe coudé spectrograph of the 2.1 m telescope. The spectra havebeen obtained with the no. 5 camera of the coudé spectrograph anda Loral 3K×1K CCD. Two gratings have been used to provide spectralcoverage from 3460 to 9464 Å, at a resolution of ~1 Å FWHMand at an original dispersion of 0.44 Å pixel-1. For885 stars we have complete spectra over the entire 3460 to 9464 Åwavelength region (neglecting small gaps of less than 50 Å), andpartial spectral coverage for the remaining stars. The 1273 stars havebeen selected to provide broad coverage of the atmospheric parametersTeff, logg, and [Fe/H], as well as spectral type. The goal ofthe project is to provide a comprehensive library of stellar spectra foruse in the automated classification of stellar and galaxy spectra and ingalaxy population synthesis. In this paper we discuss thecharacteristics of the spectral library, viz., details of theobservations, data reduction procedures, and selection of stars. We alsopresent a few illustrations of the quality and information available inthe spectra. The first version of the complete spectral library is nowpublicly available from the National Optical Astronomy Observatory(NOAO) via ftp and http.
| Optical and infrared spectroscopic analysis of the post-AGB star candidate IRAS 19386+0155
This work reports high-resolution spectroscopic stellar parameters andabundance analysis of the post-AGB star IRAS 19386+0155. The analysis ofthe high resolution spectrum shows that it has an effective temperatureof Teff=6800±100 K and a surface gravity of log g =1.4±0.2. The abundance analysis reveals IRAS 19386+0155 to be ametal-poor object having [Fe/H]=-1.1. Carbon, oxygen and nitrogen arefound to be slight underabundant than solar, and so are theα-elements (Mg, Si and Ca). The analysis of ISO spectra revealedan oxygen-rich envelope and showed crystalline silicate features. Thedust envelope of this object was modelled using a Monte Carlo typenumerical method and amorphous and crystalline silicate grains wereconsidered. The photospheric temperature obtained through the opticalspectroscopy was used to constrain these models. The Spectral EnergyDistribuition (SED) of this object is broad and extensive suggesting thepresence of a dust disk around IRAS 19386+0155.Based on observations made with the 1.52 m telescope at the EuropeanSouthern Observatory (La Silla, Chile) under the agreement with theCNPq-Observatório Nacional (Brazil) Based on observations withISO, an ESA project with instruments funded by ESA Member States(especially the PI countries: France, Germany, the Netherlands and theUK) and with the participation of ISAS and NASA.
| The nature of Hen 3-1312: A post-AGB star in a binary system
This work reports the low- and high-resolution spectroscopic diagnosticdiagrams, radial velocity, stellar parameters and abundance analysis ofthe planetary nebula Hen 3-1312. The low- and high-resolution spectrareveal that Hen 3-1312 is in fact a very-low-excitation object, in abinary system with a supergiant as a cool central star. The analysis ofthe high-resolution spectrum shows the cool stellar component to have aneffective temperature of Teff=6500±100 K and a surfacegravity of log g=0.8±0.2 corresponding to a spectral type ofF(6-7)I. These parameters result in an estimated primary luminosity of4100 Lȯ, implying a distance of 4400 pc which is inagreement with previous determinations. The abundance analysis revealsHen 3-1312 to be a metal-poor object having [Fe/H]=-1.1. The meanabundances of carbon, nitrogen and oxygen are found to be solar, howeverthe α-elements (Mg, Si and Ca) are underabundant relative to theSun. The abundance profile of Hen 3-1312 is analyzed and compared withother classes of stars with similar atmospheric parameters.Based on observations made with the 1.52 m telescope at the EuropeanSouthern Observatory (La Silla, Chile) under the agreement with theCNPq-Observatório Nacional (Brazil).Table \ref{tab4} is only available in electronic form athttp://www.edpsciences.org
| 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.
| 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).
| A Li-rich post-AGB star HD 172481
Our abundance analysis of this post-AGB candidate star confirms that theHD 172481 is indeed a post-AGB star. It belongs to an important, butrelatively rare class of post-AGB stars showing Li I features in theirspectra. The strength of OI triplet at 7774 Å confirms its highluminosity (log, (L/L?) ~ 4). It is moderately metal-poor with [Fe/H] of- 0.6 but shows significant enrichment of s-process elements indicatingthat the star has gone through the third dredge-up. We find C/O of ~ 0.4for this star. Hot Bottom Burning scenario can explain the production ofLi as well as the destruction of carbon via CN cycle that could preventC/O ratio from exceeding one.
| Stellar populations in Seyfert 2 galaxies. I. Atlas of near-UV spectra
We have carried out a uniform spectroscopic survey of Seyfert 2 galaxiesto study the stellar populations of the host galaxies. New spectra havebeen obtained for 79 Southern galaxies classified as Seyfert 2 galaxies,7 normal galaxies, and 73 stars at a resolution of 2.2 Å over thewavelength region 3500-5300 Å. Cross-correlation between thestellar spectra is performed to group the individual observations into44 synthesis standard spectra. The standard groups include a solarabundance sequence of spectral types from O5 to M3 for dwarfs, giants,and supergiants. Metal-rich and metal-weak F-K giants and dwarfs arealso included. A comparison of the stellar data with previouslypublished spectra is performed both with the individual spectra and thestandard groups. For each galaxy, two distinct spatial regions areconsidered: the nucleus and the external bulge. Spectroscopic variationsfrom one galaxy to another and from the central to the external regionare briefly discussed. It is found that the central region of a Seyfert2 galaxy, after subtracting the bulge stellar population, always shows anear-UV spectrum similar to one of three representative categories: a)many strong emission lines and only two visible absorption lines (Ca IiK and G band) (Sey2e); b) few emission lines, many absorption lines, anda redder continuum than the previous category (Sey2a); c) an almost flatcontinuum and high-order Balmer lines seen in absorption (Sey2b). Theproportion of Seyfert 2 galaxies belonging to each class is found to be22%, 28%, and 50% respectively. We find no significative differencesbetween morphology distributions of Seyfert 2 galaxies with Balmer linesdetected in absorption and the rest of the sample. This quick lookthrough the atlas indicates that half of Seyfert 2 galaxies harbour ayoung stellar population (about or less than 100 Myr) in their centralregion, clearly unveiled by the high order Balmer series seen inabsorption. Based on observations collected at the European SouthernObservatory, Chile (ESO 65.P-0014(A)). Tables 1-3 and 8 and Fig. A.1(Appendix A) are only available in electronic form athttp://www.edpsciences.org
| 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
| On the Variability of F1-F9 Luminosity Class III-V Stars
Hipparcos Satellite photometry of F1-F9 luminosity class III-V starsindicates that most are not particularly variable. A few stars for whichfurther study is desirable are identified.
| An Abundance Analysis of Two Carbon-rich Proto-Planetary Nebulae: IRAS Z02229+6208 and IRAS 07430+1115
In this paper, we present an LTE abundance analysis of two newproto-planetary nebulae, IRAS Z02229+6208 and IRAS 07430+1115, based onhigh-resolution (R~55,000) optical echelle spectra. Results show thatboth stars are metal-poor ([Fe/H]=-0.5) and overabundant in C, N, ands-process elements. The average elemental abundances are [C/Fe]=+0.8,[N/Fe]=+1.2, and[s-process/Fe]=+1.4 for IRAS Z02229+6208, and[C/Fe]=+0.6, [N/Fe]=+0.4, and [s-process/Fe]=+1.6 for IRAS 07430+1115.These abundances suggest that the stars have experienced nucleosynthesison the asymptotic giant branch (AGB), and the resultant products of CNO,3α, and s-process reactions were brought to the photosphere duringshell flashes and deep mixing episodes during the AGB phase of theirevolution. Of major significance is the measurement of a high Liabundance in both stars, log ɛ(Li)~2.3 and 2.4 for IRASZ02229+6208 and IRAS 07430+1115, respectively. This may be the result ofhot bottom burning, below the deep convective zone. We also present ananalysis of the circumstellar molecular (C_2 and CN) and atomic (Na Iand K I) absorption spectra of both stars. We derive rotationaltemperatures, column densities, and envelope expansion velocities usingmolecular C_2 Phillips and CN Red system bands. The values derived forexpansion velocities, 8-14 km s^-1, are typical of the values found forpost-AGB stars. IRAS 07430+1115 is unusual in that it shows PCygni-shaped C_2 emission profiles in the spectra of the circumstellarenvelope. A minimum distance for IRAS Z02229+6208, determined frominterstellar Na I lines, suggests that it is evolved from anintermediate-mass star. Including these two stars, the number ofpost-AGB stars for which clear C, N, and s-process elementaloverabundances are found rises to eight. IRAS Z02229+6208 is known topossess the 21 μm emission feature in its mid-infrared spectrum;these results support the idea that all 21 μm emission stars arecarbon-rich post-AGB stars.
| Spectroscopic studies of selected F-G supergiants
Not Available
| 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.
| Lithium and r-Process Abundances in the Population II Cepheid M5 V42
We report the results of an abundance analysis of the 25.7 dayPopulation II Cepheid V42 in the globular cluster M5. V42 is probably apost-asymptotic giant branch (AGB) star, in its final crossing of theH-R diagram. We find [Fe/H] = -1.22, in excellent agreement with asimilar analysis of this star by Gonzalez & Lambert, and of redgiants in M5 by Sneden et al. The analysis is based on six spectraobtained during three different phases of the star's pulsational cycle.Oxygen is depleted, and sodium is enhanced, while the ``alpha'' elementsMg, Si, Ca, and Ti are enhanced by about 0.3 dex. Most interesting,lithium is detected, with log ɛ(Li) ~ +1.8, suggesting theproduction of lithium and its rapid transport to the surface. Zinc andsilicon abundances are normal with respect to iron and calcium,suggesting that depletion onto dust grains during the AGB stage has notaffected the star's abundances. The neutron-capture elements show ratiosconsistent with a nearly pure r-process origin. This r-process dominanceis probably unrelated to the production of lithium, since the cluster'sred giant branch stars show a similar pattern. Nonetheless, it appearsthat some low-mass, metal-poor stars do not solely destroy lithium inthe course of their normal evolution.
| Elemental Abundances and Atmospheric Parameters of Seven F-G Supergiants
Spectroscopic abundance determinations for a sample of seven F-G starshave been carried out. The majority of them have large galacticlatitudes. One objective in deriving spectroscopic abundances is todifferentiate evolved objects seen at high galactic latitudes from theyoung population I supergiant stars that happened to have large galacticlatitudes but actually belong to the galactic disk. Secondly, it isimportant to get good calibrators for photometric metallicity indices.It has been suggested in the past that many high galactic latitude F-Gstars that are classified as supergiants are in reality subgiants ordwarfs. Our spectroscopically derived gravities show that two of thestars studied in this paper, HR 5165 and HD 114520, are not supergiantsas classified in Bright Star Catalogue but are subgiants belonging tothe solar neighbourhood. In our sample, HR 3229 and HR 8470 displaysolar abundances and the derived gravities support the bright giantluminosity class ascribed to them. HR 4114, HR 4912 and HR 7671 haveabundances significantly different from those of young supergiants ofgalactic disk. The evolutionary status of these objects is discussed.(SECTION: Stars)
| The Angular Momentum of Main Sequence Stars and Its Relation to Stellar Activity
Rotational velocities are reported for intermediate-mass main sequencestars it the field. The measurements are based on new, high S/N CCDspectra from the Coudé Feed Telescope of the Kitt Peak NationalObservatory. We analyze these rotation rates for a dependence on bothmass and age. We compare the average rotation speeds of the field starswith mean velocities for young stars in Orion, the Alpha Persei cluster,the Pleiades, and the Hyades. The average rotation speeds of stars moremassive than $\sim1.6$ \msun\experience little or no change during theevolutionary lifetimes of these stars on the zero age main sequence orwithin the main sequence band. Less massive stars in the range betwee n1.6\msun\ and 1.3\msun\ also show little decline in mean rotation ratewhile they are on the main sequence, and at most a factor of 2 decreasein velocity as they evolve off the main sequence. The {\it e}-foldingtime for the loss of angular momentum b y the latter group of stars isat least 1--2 billion years. This inferred characteristic time scale forspindown is far longer than the established rotational braking time forsolar-type stars with masses below $\sim1.3$ \msun. We conclude from acomparison of the trends in rotation with trends in chromospheric andcoronal activity that the overall decline in mean rotation speed alongthe main sequence, from $\sim2$ \msun\ down to $\sim1.3$ \msun, isimposed during the pre-main sequence phase of evolution, and that thispattern changes little thereafter while the star resides on the mainsequence. The magnetic activity implicated in the rotational spindown ofthe Sun and of similar stars during their main sequence lifetimes mus ttherefore play only a minor role in determining the rotation rates ofthe intermediate mass stars, either because a solar-like dynamo is weakor absent, or else the geometry of the magnetic field is appreciablyless effective in removing angular momentu m from these stars. (SECTION:Stars)
| 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
| A multiwavelength study of LS II+34 26: a hot post-AGB star in the process of becoming a planetary nebula.
We present the results from a multiwavelength analysis of LS II+34 26,recently identified as a low mass post-AGB star and not a massivepopulation I B-type star, as previously thought. We confirm that thecentral star is a carbon-poor post-AGB star surrounded by a very lowexcitation and compact nebula. Spectroscopic monitoring carried outsince 1991 reveals variations which suggest that this star has had amass loss episode in the period 1993-1995. The asymmetric profiles in afew absorption lines in high resolution optical spectra indicate thepresence of complex motions in the outer layers of the atmosphere. Theradial velocity variations (several tens of km/s) observed in spectrataken in a single epoch can be attributed to stellar pulsation. For afew lines stronger variations over the years (up to 70km/s) can beexplained if these lines are formed in the outflow. The anomalousextinction observed in the UV suggests that part of the reddening is ofcircumstellar origin and that the standard interstellar extinction lawis not applicable. On the other hand, the absence of a significant nearinfrared excess in LS II+34 26 suggests that the mass loss enhancementcorresponds to a short-lived episode of modest intensity. Althoughnon-LTE effects prevent the accurate determination of the atmosphericparameters and abundances of LS II+34 26, a comparative analysis with LSIV-12 111 indicates that both stars are very similar. Both areidentified as low mass carbon-poor hot post-AGB stars belonging to thehalo population of our Galaxy.
| Chemical composition of optically bright post-AGB stars.
We present a detailed LTE chemical analysis of 10 optically brightF-type post-AGB objects on the basis of the analysis of high-resolutionoptical spectra and compare the results with similar objects discussedin the literature. The iron content is low on average, and so confirmsthe old and hence low-mass nature of the supergiants, with a noticableexception of HD 95767. We emphasize the fact that the chemical patternsobserved are very diverse : several different classes can bedistinguished. Only a minor fraction of the objects are conform tostandard post third dredge-up theory. Only in HD 187885 (Van Winckel etal., 1996A&A...306L..37V), HD 56126 (Klochkova, 1995MNRAS.272..710K)and HD 158616 (this paper) is there conclusive chemical evidence thatthey occur in a post-AGB evolutionary phase : a high total CNOabundance, for HD 187885 a supersolar He content and-above all-a largeoverabundance of s-process elements. The other objects, together withother well studied high galactic latitude F-supergiants, display nos-process enhancement but even depletion in some cases. The high Nabondance and the mildly enhanced total CNO abundance indicate that theatmospheres of these objects contain a mixture of CNO-cycled materialand He-burning products. For some sources, however, this enhancement ofthe total CNO abundance is barely significant. HD 107369, the onlyobject in our sample with neither Hα emission nor observed IRexcess, displays also unique chemical patterns among our sample stars (aC deficiency coupled with a moderate Fe depletion of [Fe/H]=-1.1). Thisstar is the only object in our sample showing similar chemical patternsto the metal poor B stars at high galactic latitude (Conlon et al.,1993, in ASP Conf. Ser., Vol. 45, p. 146). Our chemical analysis doestherefore not point to an evolutionary connection between the dustyhigh-latitude supergiants and the metal-poor B stars, but rathersuggests that the latter evolve from stars such as HD 107369.
| 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.
| A uvbyβ photometric calibration of iron abundances in supergiant stars.
A photometric reddening-free calibration for [Fe/H] valid for giant andsupergiant stars of intermediate temperature, has been obtained usingthe Stroemgren uvbyβ system. Galactic supergiants, supergiants inthe Magellanic Clouds and Galactic metal deficient red giants withspectroscopic determinations of [Fe/H] were used as calibrators. Thecalibration can be used to predict [Fe/H] with an accuracy of 0.33 dex,valid for stars with 0.14<[m_1_]<0.70 in the iron abundance range-2.5<[Fe/H]<+0.3. This shows the potential of supergiant stars astracers of iron abundances in other galaxies. Evidence that Galacticluminous F-G stars are intrinsically bluer than their counterparts inthe Magellanic Clouds is offered.
| Spectroscopy of F supergiants with infrared excess
Atmospheric parameters, abundances of 26 chemical elements and radialvelocities, all based on CCD echelle spectra, are presented for twopeculiar F supergiants with a large infrared excess: IRAS 07134+1005 andIRAS 18095+2704. A moderate underabundance of metallicity is revealedfor both stars, [Fe/H]_=-1.0 and -0.78 dex, respectively. Thesignificant overabundance of CNO elements is confirmed for IRAS07134+0115: [C/Fe]=1.08 dex, [N/Fe]=1.03 dex and [O/Fe]=0.6 dex. ForIRAS 18095+2704 these overabundances are less marked: [X/Fe]~=0.5dex,but they are real. Large excesses of lanthanides are derived forboth stars. Significant unexplained non-LTE effects occur, revealed bydifferences for many metals in the abundances obtained from neutral andionized atomic lines. All of the characteristics of the IRAS sourcesstudied are consistent with the hypothesis that they are at a post-AGBevolutionary stage.
| 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.
| Radio continuum emission from stars: a catalogue update.
An updated version of my catalogue of radio stars is presented. Somestatistics and availability are discussed.
| Near-infrared spectroscopy of post-AGB stars.
The results of a medium resolution near-infrared spectral survey of 18post-AGB candidate stars are presented. Most of the stars havenear-infrared hydrogen lines in absorption, which is normal for theirspectral types. Three stars, HD 101584, HD 179821 and HD 170756 have theCO first overtone bands in emission; in two of these the emission isvariable. It is suggested that the CO emission is the result of post-AGBmass loss. HD 52961 shows the rarely occurring 3.5μm emission featureand is only the fourth object in which this feature has been detected.
| 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.
| 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.
|
Submit a new article
Related links
Submit a new link
Member of following groups:
|
Observation and Astrometry data
| Constellation: | Aigle |
| Right ascension: | 20h05m05.40s |
| Declination: | -11°35'58.0" |
| Apparent magnitude: | 6.34 |
| Distance: | 390.625 parsecs |
| Proper motion RA: | -2.2 |
| Proper motion Dec: | -15.5 |
| B-T magnitude: | 6.966 |
| V-T magnitude: | 6.433 |
Catalogs and designations:
|
INHABITED SKY
