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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.
| Polarization Measurements of Post-Asymptotic Giant Branch Candidates and Related Stars
We have obtained UBVRI polarization measurements of 26 post-asymptoticgiant branch (post-AGB) candidates and related stars. The extremelymetal-poor post-AGB star HR 4049 has been observed several times. Inmost cases we find the objects to be intrinsically polarized. Thepolarization measurements presented in this paper indicate asymmetriccircumstellar dust shells and disks around these stars. For some objectsthe steep percent polarization λ-dependence and large degree ofpolarization suggest that scattering by circumstellar dust grains may beresponsible for the observed polarizations in the blue.
| 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.
| A Revised Calibration of the MV-W(O I 7774) Relationship using Hipparcos Data: Its Application to Cepheids and Evolved Stars
A new calibration of the MV-W(O I 7774) relationship hasbeen calculated using better reddening and distance estimates for asample of 27 calibrator stars of spectral types A to G, based onaccurate parallaxes and proper motions from the Hipparcos and Tychocatalogues. The present calibration predicts absolute magnitude withaccuracies of +/-0.38mag for a sample covering a large range ofMV, from -9.5 to +0.35 mag. The color term included in aprevious paper has been dropped since its inclusion does not lead to anysignificant improvement in the calibration. The variation of the O I7774 feature in the classical cepheid SS Sct has been studied. Wecalculated a phase-dependent correction to random phase OI featurestrengths in Cepheids, such that it predicts mean absolute magnitudesusing the above calibration. After applying such a correction, we couldincrease the list of calibrators to 58 by adding MV and O Itriplet strength data for 31 classical Cepheids. The standard error ofthe calibration using the composite sample was comparable to thatobtained from the primary 27 calibrators, showing that it is possible tocalculate mean Cepheid luminosities from random phase observations ofthe O I 7774 feature. We use our derived calibrations to estimateMV for a set of evolved objects to be able to locate theirpositions in the HR diagram.
| 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 A6 to F9 Supergiants
Hipparcos Satellite photometry of A6 to F9 supergiants reveals theiractivity. A few are especially quiescient. A0-A5II stars are examinedto help connect this study with that of earlier supergiants.
| The peculiar post-AGB supergiant IRAS 04296+3429: optical spectroscopy and its spectral energy distribution
The optical spectrum of the infrared source IRAS 04296+3429 (opticalcounterpart - G0 Ia star, V = 14.2) was obtained with the echellespectrometer PFES at the prime focus of the 6 m telescope. We discoveremission bands (0,0) and (0,1) of the Swan system of the C_2 molecule inthe optical spectrum of IRAS 04296+3429. Comparison with the spectrum ofthe Hale-Bopp comet leads us to propose that in both cases the samemechanism (resonance fluorescence) is responsible for the emission inthe C_2 molecular bands. Several strong absorption features whosepositions coincide with known diffuse interstellar bands (DIBs) arerevealed in the spectrum of IRAS 04296+3429. The infrared spectrum ofIRAS 04296+3429 shows the famous 21 μm feature (Kwok et al. 1989),but this object has not been observed by KAO (Omont et al. 1995).However, like IRAS 05113+1347, IRAS 05341+0852 and IRAS 22223+4327 (Kwoket al. 1995, Szczerba et al. 1996), our detailed modelling of itsspectral energy distribution suggested that this source also should showthe 30 μm band. In fact, ISO discovered a broad, relatively strongfeature around 30 μm for IRAS 04296+3429 (Szczerba et al. 1999). Thesurface chemical composition of the source IRAS 04296+3429 ismetal-deficient (the averaged value of the abundances of the iron groupelements Ti, V, Cr and Fe relative to the solar values is [M/H]_{sun =-0.9}) and has been considerably altered during the evolution: carbon,nitrogen and s-process elements are overabundant relative to themetallicity. The totality of physical and chemical parameters derivedfor IRAS 04296+3429 confirms a relation between presence of the featureat 21 μm in the spectrum of a carbon rich star and an excess of thes-process elements.
| Spectroscopic studies of selected F-G supergiants
Not Available
| Photospheric composition of the carbon-rich 21 micron post-AGB stars IRAS 22223+4327 and IRAS 04296+3429
We present a detailed chemical analysis on the basis of high-resolution,high signal-to-noise optical spectra of two post-AGB objects IRAS22223+4327 and IRAS 04296+3429. Both display the unidentified 21 mu mfeature in their IR-spectra. The analysis is performed using HR 1865(F0Ib) and HR 1017 (F5Iab) as reference stars. The spectroscopicindicators provide accurate atmospheric parameters of T_eff=6500 K, logg=1.0 and xi_t =5.5 {kms(-1}) for IRAS 22223+4327 and T_eff=7000 K, logg=1.0 and xi_t =4.0 {kms(-1}) for IRAS 04296+3429. Our high-resolutiondata are inconsistent with the significantly lower temperatures deducedfrom spectral-type determinations in the literature based on lowresolution spectra and highlight the need of high-resolutionspectroscopy for the determination of accurate fundamental parameters ofchemically peculiar supergiants. Both photospheres are found to bemetal-deficient with [Fe/H]=-0.4 and -0.7 respectively. C and N arefound to be overabundant. Useful O-lines were only detected in thebrighter IRAS 22223+4327 and the O abundance is found to follow the Fedeficiency: the C/O photospheric abundance is about 1.3, but due to thelack of oxygen lines it is difficult to determine accurately. Thiscorroborates the fact that the carriers of the 21 mu m feature areformed in a carbon rich circumstellar chemistry. Moreover, theseIRAS-stars have large overabundances of s-process-elements. The meanabundance of all the measured s-process-elements is [s/Fe]=+1.0 for IRAS22223+4327 and +1.4 for IRAS 04296+3429. The distribution of thes-process elements can best be described as due to a distribution ofneutron exposures with a low mean neutron exposure of tau_ {0} = 0.2\{mbarn(-1}) . The 21 mu m stars form an interesting sub-group in thetotal post-AGB sample of stars, not only for their IR characteristics,but also in a broader context of stellar (chemical) evolution theory.They show, in contrast to other post-AGB stars, that the 3rd dredge-uphas been efficient during their AGB evolution. The mean neutron exposureis lower than expected for their metallicity. The spectroscopicparameters found for the massive spectral analogues (T_eff=7500 K, logg=2.0 and xi_t =3.0 {kms(-1}) for HR 1865 and T_eff=6500 K, log g=2.0and xi_t =3.5 {kms(-1}) for HR 1017) agree well with the values found inthe literature. Both stars display an enrichment in Na, which iscommonly observed in massive supergiants but theoretically not wellunderstood. Based on observations with the Utrecht Echelle Spectrograph,fed by the 4.2m William Herschel Telescope at La Palma
| 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)
| New and misclassified Planetary Nebulae
Altogether 86 objects discovered in the period 1991-1994 have beenaccepted by the author as new PN (Table 1). In Appendices A and B tothis table the lists of possible pre-PN as well as of possible post-PN,respectively, are given. Table 2 presents 6 misclassified objects whichwe suggest removing from CGPN.
| 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.
| Light and colour curves of the variable UU Herculis.
Not Available
| 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.
| Colour excesses of F-G supergiants and Cepheids from Geneva photometry.
A reddening scale for F-G supergiants and Cepheids is presented.Supergiants with low reddenings or in clusters form the basis of thecalibration. In this sense, it is entirely empirical. The data have beenobtained in the Geneva photometric system. Comparisons with otherreddening scales show no disagreement. The only problem is with Fernie'sscale for Cepheids (1990), where a systematic trend exists. Its originis not clear. It is suggested to extend the number of supergiants withindependently obtained colour excesses in order to test the existence ofa possible luminosity dependence of the calibration. A period-colourrelation for Cepheids is deduced, on the basis of the present reddeningcorrections. It gives strong support for V473 Lyr being a secondovertone pulsator.
| 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.
| An atlas of ultraviolet P Cygni profiles
We have selected spectra of 232 stars from the International UltravioletExplorer (IUE) archives for inclusion in an atlas intended for varioususes but tailored especially for the study of stellar winds. The atlascovers the range in spectral types from O3 to F8. The full atlas coversthe reduced and normalized high resolution spectra from the IUE long-and short-wavelength spectrographs. Here we discuss the selection of thestars and the data reduction, and we present in velocity units theprofiles of lines formed in the stellar winds. The selected lines covera wide range of ionizations, allowing a comparison of the profiles fromdifferent ions in the wind of each star and a comparison of thedifferent wind lines as a function spectral type and luminosity. We alsopresent the basic data on the program stars to facilitate study of thedependence of wind features on stellar parameters such as luminosity,temperature, escape velocity, and v sin i. We provide an overview of thecharacteristic behavior of the wind lines in the H-R diagram. Thecomplete spectra are available in digital form through the NASAAstrophysics Data System (ADS). We offer a description of the electronicdatabase that is available through the ADS and guidelines for obtainingaccess to that database.
| 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.
| 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.
| Calibrations of Mv, (Fe/H), and log G for yellow supergiant stars from O I 7774 and uvby-beta data
New calibrations of the absolute magnitude Mv from O I 7774data are derived from narrow-band photometry and low dispersionspectroscopy for AO-G2 low and high luminosity stars. The nonlineardependence of Mv from the equivalent width W(OI) and therelevance of the stellar temperature in the calibration are confirmed inagreement with previous calibrations obtained from high resolutionspectroscopy. Also functional formulas to estimate (Fe/H) and log g fromuvby-beta data for FO-G3 supergiants are offered. These calibrationspredict iron abundances and gravities for yellow supergiants withuncertainties not much higher than good spectroscopic determinations.
| 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.
| The mass loss history of high latitude supergiants
A sample of 25 high latitude supergiants with spectral types B-G weresurveyed in the (C-12)O J = 1-0 and J = 2-1 lines using the Swedish ESOSubmillimeter Telescope (SEST). Twenty percent of the sources weredetected. For the analysis an additional six sources were added forwhich CO observations are reported in the literature. The majority ofthe detected sources have post-AGB mass loss rates and expansionvelocities that confirm earlier suggestions that these stars, despitetheir supergiant-like spectra, are in fact low mass post-AGB stars(Trams et al. 1989). The nondetections and their systematic lower 60micron fluxes can be explained assuming that they are low mass post-AGBstars, whose remnant AGB shells are significantly diluted and which areevolving rather slowly to higher temperatures.
| Catalogue of Population II A-F supergiants - UU Herculis and related stars
The catalogue of Population II A-F supergiants collects the availableinformation on 18 UU Herculis type and related stars. For each entry,the following information is presented: star name, equatorial andgalactic coordinates, spectral type, mean magnitude V, color index B-V,color excess E(B-V), metallicity Fe/H, absolute magnitude MV, effectivetemperature Te, and gravity log g. A list of six suspected UUHerculis-type stars is also presented.
| SAO stars with infrared excess in the IRAS Point Source Catalog
We have undertaken a search for SAO stars with infrared excess in theIRAS Point Source Catalog. In contrast to previous searches, the entireIRAS (12)-(25)-(60) color-color diagram was used. This selection yieldeda sample of 462 stars, of which a significant number are stars withcircumstellar material. The stars selected can be identified aspre-main-sequence stars, Be stars, protoplanetary systems, post-AGBstars, etc. A number of objects are (visual) binary stars.Characteristic temperatures and IR excesses are calculated and theirrelations to spectral type are investigated.
| A library of near-IR stellar spectra from 1.328 to 2.5 microns
We present a library of 56 stellar spectra from 1.428 to 2.5 microns,sampling the Hertzsprung-Russell diagram in luminosity class andeffective temperature. Relative fluxes defining the stellar energydistributions throughout the H and K atmospheric windows, an infraredcolor temperature used to set a continuum for equivalent widthmeasurements, and relations between various spectral signatures, colortemperatures and gravity are determined. H2O is the dominant absorber inthe latest M giant stars. Its absorption is measured in both wings ofthe signature around 1.9 micron and a combined effect of H2O and H(-)opacity is measured shortward of 1.6 micron. The CO equivalent widthlongward of 2.29 microns increases with decreasing gravity andtemperature. CO and the OH radical are responsible for numerousabsorption bands below 1.8 micron.
| A new discussion on the M(v) - W(O I 7774 A) relationship for F-G stars in the light of high-resolution data
High-resolution CCD data and a large group of F-G stars of fundamentallydetermined distances are used here to investigate the intrinsic natureof the M(v) - W(O I) relation and the effect of other atmosphericparameters on this relation. The M(v) - W(O I) relation is not linear inthe absolute magnitude range -10 to +21. Introduction of the (b - y)0color index to represent stellar temperature leads to a calibration ofthe M(v) - W(O I) - (b-y)0 relationship in the above M(v) range, whichcan serve as a valuable tool to determine M(v) for F-G field stars. Nosystematic effect of the turbulent velocity on the calibration is found.
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Pozíciós és asztrometriai adatok
| Csillagkép: | Északi Vízikígyó |
| Rektaszcenzió: | 12h56m30.10s |
| Deklináció: | -26°27'37.0" |
| Vizuális fényesség: | 6.62 |
| Távolság: | 10000000 parszek |
| RA sajátmozgás: | 13.2 |
| Dec sajátmozgás: | -21.8 |
| B-T magnitude: | 7.552 |
| V-T magnitude: | 6.823 |
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