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First detection of photospheric depletion in the Large Magellanic Cloud
Context: .Recent photospheric abundance studies of galactic field RVTauri stars show that depletion of refractory elements is rather commonin these evolved objects. Aims: .The process that creates thischemical anomaly is not understood well, but it probably requires thepresence of gravitationally bound dust in a binary system. We test forthe presence of depletion in extra-galactic objects. Methods: .Adetailed photospheric abundance study on the basis of high-quality UVESspectra was performed on the RV Tauri star in the LMC: MACHO 82.8405.15.Abundances were derived using a critically compiled line list withaccurate log(gf) values and the latest Kurucz model atmospheres.Results: .With [Fe/H] = -2.6 in combination with [Zn/Fe] = +2.3 and[S/Ti] = +2.5, MACHO 82.8405.15 displays a strong depletion abundancepattern. The effect of the depletion is comparable to the strongestdepletions seen in field Galactic RV Tauri stars. Conclusions:.The chemical analysis of MACHO 82.8405.15 proves that the depletionprocess also occurs in the extragalactic members of the RV Tauripulsation class. Our program star is a member of a larger sample of LMCRV Tauri objects. This sample is unique, since the distances of themembers are well-constrained. Further studies of this sample aretherefore expected to gain deeper insight into the poorly understooddepletion phenomenon and of the evolutionary status of RV Tauri stars ingeneral.Basedon observations collected at the European Southern Observatory, Chile(programme 074.D-0619(A)).
| MACHO 82.8405.15: the First Extragalactic Depleted RV Tauri Star
RV Tauri stars are a heterogeneous subclass of the Population IICepheids, probably in the post-AGB stage of evolution. Many RV Tauristars show some degree of depletion in their photospheres, which iscaused by a gas-dust separation in the circumstellar environment and asubsequent gas accretion, making the photosphere devoid of refractoryelements. The most favorable circumstance for this process to occur iswhen the circumstellar dust is trapped in a disk. The presence of a diskin evolved objects is likely related to binarity. In this contribution,we present the results of our abundance study of the first depleted RVTauri star in the Large Magellanic Cloud, MACHO 82.8405.15, based onhigh-resolution VLT-UVES spectra. While our analysis of other LMC RVTauri stars is still in progress, it is clear that, also in the LMC,depletion seems to be quite common amongst RV Tauri objects.
| Mixed Chemistry Phenomenon during Late Stages of Stellar Evolution
We discuss phenomenon of simultaneous presence of O- and C-basedmaterial in the surroundings of evolutionary advanced stars. Weconcentrate on silicate carbon stars and present observations thatdirectly confirm for them the binary model scenario. We discuss also theclass of C-stars with OH emission detected, to which some [WR] planetarynebulae do belong.
| On the CO Near-Infrared Band and the Line-splitting Phenomenon in the Yellow Hypergiant ρ Cassiopeiae
We report on multiepoch optical and near-infrared spectroscopy aroundthe first-overtone rovibrational band of CO in the pulsating yellowhypergiant ρ Cas, one of the most massive stars in the Galaxy and acandidate SN II progenitor. We argue that the double cores of the COabsorption lines, which have previously been attributed to separatecircumstellar shells expelled during its recurrent outbursts, result infact from a superposition of a wide absorption line and a narrow centralemission line. The CO line doubling returns over subsequent pulsationcycles, where the superposed line emission assumes its largest intensitynear phases of maximum light. We find that the morphology and behaviorof the CO band closely resemble the remarkable ``line-splittingphenomenon'' also observed in optical low-excitation atomic lines. Basedon radiative transport calculations, we present a simplified model ofthe near-infrared CO emission emerging from cooler atmospheric layers inthe immediate vicinity of the photosphere. We speculate that the kinetictemperature minimum in our model results from a periodicpulsation-driven shock wave. We further discuss a number of alternativeexplanations for the origin of the ubiquitous emission-line spectrum,possibly due to a quasi-chromosphere or a steady shock wave at theinterface of a fast expanding wind and the interstellar medium. Wepresent a number of interesting spectroscopic similarities between ρCas and other types of cool variable supergiants, such as the RV Tau andR CrB stars. We further propose a possibly common mechanism for theenigmatic outburst behavior of these luminous pulsating cool stars.
| 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.
| Extended envelopes around Galactic Cepheids. I. ℓ Carinae from near and mid-infrared interferometry with the VLTI
We present the results of long-baseline interferometric observations ofthe bright southern Cepheid ℓ Carinae in the infrared N (8-13 μm)and K (2.0-2.4 μm) bands, using the MIDI and VINCI instruments of theVLT Interferometer. We resolve in the N band a large circumstellarenvelope (CSE) that we model with a Gaussian of 3 Rstar(≈500 Rȯ ≈ 2-3 AU) half width at half maximum. Thesignature of this envelope is also detected in our K band data as adeviation from a single limb darkened disk visibility function. Thesuperimposition of a Gaussian CSE on the limb darkened disk model of theCepheid star results in a significantly better fit of our VINCI data.The extracted CSE parameters in the K band are a half width at halfmaximum of 2 Rstar, comparable to the N band model, and atotal brightness of 4% of the stellar photosphere. A possibility is thatthis CSE is linked to the relatively large mass loss rate of ℓ Car.Though its physical nature cannot be determined from our data, wediscuss an analogy with the molecular envelopes of RV Tauri, redsupergiants and Miras.
| Binary post-AGB stars and their Keplerian discs .
In this contribution we give a progress report on our systematic studyof a large sample of post-AGB stars. The sample stars were selected onthe basis of their infrared colours and the selection criteria weretuned to discover objects with hot dust in the system. We started a veryextensive, multi-wavelength programme which includes the analysis of ourradial velocity monitoring; our optical high-resolution spectra; ourgroundbased N-band spectral data as well as the Spitzer full spectralscans; the broad-band SED and the high spatial-resolutioninterferometric experiments with the VLTI. In this contribution wehighlight the main results obtained so far and argue that all systems inour sample are indeed binaries, which are surrounded by dusty Kepleriancircumbinary discs. The discs play a lead role in the evolution of thesystems.
| The long-term phenomenon in U Mon.
The nature and origin of the long-term variability in U Mon has beeninvestigated using multicolour photometry and high-resolution echellespectroscopy. The photometry shows long-term dimming, damping andreddening of the system, as well as the extremely variable nature ofthis modulation. The new spectroscopic observations show enhanced Halphaemission during long-term light minimum. Our radial velocities werecombined with those from the literature to determine orbital parametersfor the U Mon system (P2600 d, e=0.43). Obscuration by dust atcertain orbital phases explains the light decrease and reddening, whilethe enhanced H-alpha emission and damping of the light and colour curvesmay indicate that mass loss or interaction is occurring at (or close to)periastron passage in the U Mon system.
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| 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.
| Strong dust processing in circumstellar discs around 6 RV Tauri stars. Are dusty RV Tauri stars all binaries?
We present extended Spectral Energy Distributions (SEDs) of sevenclassical RV Tauri stars, using newly obtained submillimetre continuummeasurements and Geneva optical photometry supplemented with literaturedata. The broad-band SEDs show a large IR excess with a black-body slopeat long wavelengths in six of the seven stars, R Sct being thenoticeable exception. This long wavelength slope is best explainedassuming the presence of a dust component of large grains in thecircumstellar material. We show that the most likely distribution of thecircumstellar dust around the six systems is that the dust resides in adisc. Moreover, very small outflow velocities are needed to explain thepresence of dust near the sublimation temperature and we speculate thatthe discs are Keplerian. The structure and evolution of these compactdiscs are as yet not understood but a likely prerequisite for theirformation is that the dusty RV Tauri stars are binaries.
| High-Resolution Mid-Infrared Imaging of the Asymptotic Giant Branch Star RV Bootis with the Steward Observatory Adaptive Optics System
We present high-resolution (~0.1"), very high Strehl ratio (0.97+/-0.03)mid-IR adaptive optics (AO) images of the asymptotic giant branch (AGB)star RV Boo utilizing the MMT adaptive secondary AO system. RV Boo wasobserved at a number of wavelengths over two epochs (9.8 μm in 2003May and 8.8, 9.8, and 11.7 μm in 2004 February) and appeared slightlyextended at all wavelengths. While the extension is very slight at 8.8and 11.7 μm, the extension is somewhat more pronounced at 9.8 μm.With such high Strehl ratios, we can achieve superresolutions of 0.1" bydeconvolving RV Boo with a point-spread function (PSF) derived from anunresolved star. We tentatively resolve RV Boo into a 0.16" FWHMextension at a position angle of 120°. At a distance of390+250-100 pc, this corresponds to a FWHM of60+40-15 AU. We measure a total flux at 9.8 μmof 145+/-24 Jy for the disk and star. Based on a dust thermal emissionmodel for the observed IR spectral energy distribution and the 9.8 μmAO image, we derive a disk dust mass of 1.6×10-6Msolar and an inclination of 30°-45° from edge-on. Wediscuss whether the dust disk observed around RV Boo is an example ofthe early stages in the formation of asymmetric structure in planetarynebulae.
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| Self-Correlation Studies of RV Tauri Variables and Related Objects
RV Tauri (RVT) variables are old, low-mass, yellow supergiant pulsatingvariable stars whose light curves show alternating deep and shallowminima. They are related to Population II Cepheid (CW) variables and toyellow semiregular (SRD) variables. We describe the results ofself-correlation analysis of a large body of visual photometry of 9bright RVT and SRd variables, namely AG Aur, AV Cyg, SU Gem, AC Her, SXHer, TT Oph, UZ Oph, TX Per, and V Vul. Self-correlation analysis, whichprobes the cycle-to-cycle behavior of a variable, averaged over adataset, has proven to be a useful tool for investigating these stars,because their classification is actually based on their cycle-to-cyclebehavior. Our results are consistent with those of our analysis of RVTand CW variables in the Large Magellanic Cloud (Percy, Hosic, and Leigh2003), and support the view that the RV Tauri phenomenon has twodimensions: (i) the relative depths of the primary and secondary minima,and (ii) the number of cycles over which the alternating minimacorrelate. If the RVT phenomenon is due to the presence of two pulsationmodes, then these dimensions are equivalent to: (i) the relativeamplitudes of the two modes, and (ii) the closeness of the ratio of thepulsation periods to 2:1. There is therefore a "spectrum" of behaviorfrom CW to RVT to SRd, depending on the values of these two parameters.
| Classification of Spectra from the Infrared Space Observatory PHT-S Database
We have classified over 1500 infrared spectra obtained with the PHT-Sspectrometer aboard the Infrared Space Observatory according to thesystem developed for the Short Wavelength Spectrometer (SWS) spectra byKraemer et al. The majority of these spectra contribute to subclassesthat are either underrepresented in the SWS spectral database or containsources that are too faint, such as M dwarfs, to have been observed byeither the SWS or the Infrared Astronomical Satellite Low ResolutionSpectrometer. There is strong overall agreement about the chemistry ofobjects observed with both instruments. Discrepancies can usually betraced to the different wavelength ranges and sensitivities of theinstruments. Finally, a large subset of the observations (~=250 spectra)exhibit a featureless, red continuum that is consistent with emissionfrom zodiacal dust and suggest directions for further analysis of thisserendipitous measurement of the zodiacal background.Based on observations with the Infrared Space Observatory (ISO), aEuropean Space Agency (ESA) project with instruments funded by ESAMember States (especially the Principle Investigator countries: France,Germany, Netherlands, and United Kingdom) and with the participation ofthe Institute of Space and Astronautical Science (ISAS) and the NationalAeronautics and Space Administration (NASA).
| Binary post-AGB stars
An overview is given on the observational characteristics of someindividual post-AGB stars in binary systems, which inspired us to starta systematic search for binarity in a sample of post-AGB stars. In thiscontribution a preliminary report is presented of this search. One ofthe fundamental ingredients in the evolution of the systems discussedhere is the creation of a circumbinary dusty disc, probably during theAGB evolutionary phase. There is observational evidence that the discsare Keplerian and that they have important impact on the systems'(chemical) evolution. We discuss briefly the relation to other evolvedbinary classes, in which one of the components went through the AGBevolution.
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| Polarimetry of evolved stars. III. RV Tau and R CrB stars
We present broadband optical polarimetry, and broadband optical andinfrared photometry, of eight RV Tau-type and five R CrB-type stars;much of the photometry and polarimetry was obtained simultaneously. Fornine of the objects polarimetric data is reported for the first time. Wehave estimated and subtracted the interstellar component ofpolarization, allowing us to determine the level of intrinsicpolarization. In some cases this is =~ 1%-2% even when the star is in abright photometric state. We consider this to be evidence for thepresence of permanent clumpy non-spherical dust shells around the RV Tauand R CrB-type stars we observed. Our polarimetric and photometric datalead us to conclude that, for most of our programme stars, neutralextinction must be significant in their circumstellar envelopes. Apartfrom the brightness variations due to pulsations and changes in theeffective temperature of stars, there is clear evidence ofwavelength-independent flux variations - with amplitude from 0fm 5 to1fm 0 - implying the presence of large (a>~ 0.15 mu m) dustparticles. Rapid ( ~ 2 hours) evolution of the infrared fluxdistribution at the level of ~ 0fm 6 in the JHKL bands was detected inthe RV Tau star R Sct.Table 2 is only available in electronic form at the CDS via anomymousftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/412/405Tables 3-6 are only available in electronic form athttp://www.edpsciences.org
| Mid-Infrared Imaging of the Post-Asymptotic Giant Branch Star AC Herculis with the Multiple Mirror Telescope Adaptive Optics System
We utilized the unique 6.5 m Multiplie Mirror Telescope deformablesecondary adaptive optics (AO) system to produce high-resolution(FWHM=0.3"), very high Strehl mid-infrared (9.8, 11.7, and 18 μm)images of the post-asymptotic giant branch star AC Her. The very high(98%+/-2%) Strehls achieved with mid-IR AO led naturally to anultrastable point-spread function (PSF) independent of air mass, seeing,or location on the sky. We find no significant difference between ACHer's morphology and our unresolved PSF calibration stars (μ UMa andα Her) at 9.8, 11.7, and 18 μm. Our current observations do notconfirm any extended mid-IR structure around AC Her. These observationsare in conflict with previously reported Keck (seeing-limited) 11.7 and18 μm images that suggested the presence of a resolved ~0.6" edge-oncircumbinary disk. We conclude that AC Her has no extended mid-IRstructure on scales greater than 0.2" (R<75 AU). These first resultsof mid-IR AO science are very encouraging for future high-accuracymid-IR imaging with this technique.The results presented here made use of the of Multiple Mirror Telescope(MMT) Observatory, a facility jointly operated by the University ofArizona and the Smithsonian Institution.
| IRAS 08544-4431: A new post-AGB star in a binary system surrounded by a dusty disc
We present an analysis of our extensive data-set on IRAS 08544-4431. Itis the first object we discuss of our newly defined sample of stars,selected for their position in the ``RV Tauri'' box in the IRAS[12]-[25], [25]-[60] two-color diagram. Moreover, our selection criteriaincluded an observed excess in the L-band, indicative of a dusty disc.The SED of IRAS 08544-4431 shows a broad IR excess starting already atH. Our optical photometric data reveal some evidence for deep andshallow minima in the light curve and a pulsation time-scale of around100 days with a small amplitude (Delta V peak-to-peak = 0.17 mag). OurCORALIE radial velocity measurements show that IRAS 08544-4431 is abinary system with a period of 499 +/- 3 days and a mass function of0.02 Msun. Moreover, IRAS 08544-4431 is detected in both theCO (2-1) and (1-0) mm-wave emission lines. The triangular shape of theweak CO profile confirms that part of the circumstellar material is notfreely expanding but resides probably in a dusty circumbinary disc. Ourchemical abundance analysis of a high resolution spectrum of high S/Nreveals that a depletion process has modified the photosphericabundances to a moderate extent ([Zn/Fe]=+0.4). All these findingsconfirm that the F-type IRAS 08544-4431 is another good example of abinary Post-AGB star surrounded by a dusty disc. The Hα , P-Cygniprofile shows ongoing mass-loss with a very high outflow velocity, theorigin of which is not understood. The strength and velocity of theHα -absorption are modulated with the orbital motion; the maximaof both quantities ( ~ 400 \kms, 5 Å, respectively) occur atsuperior conjunction.Based on observations collected at the European Southern Observatory inChile (62.L-0508) and at SAAO. The radial velocity data was obtainedwith the Swiss 1.2 m Euler telescope at La Silla, Chile.
| A weakly non-adiabatic one-zone model of stellar pulsations: application to Mira stars
There is growing observational evidence that the irregular changes inthe light curves of certain variable stars might be due to deterministicchaos. Supporting these conclusions, several simple models of non-linearoscillators have been shown to be capable of reproducing the observedcomplex behaviour. In this paper, we introduce a non-linear,non-adiabatic one-zone model intended to reveal the factors leading toirregular luminosity variations in some pulsating stars. We have studiedand characterized the dynamical behaviour of the oscillator as the inputparameters are varied. The parametric study implied values correspondingto stellar models in the family of long period variables and inparticular of Mira-type stars. We draw attention to certain solutionsthat reproduce with reasonable accuracy the observed behaviour of somepeculiar Mira variables.
| Self-Correlation Analysis of RV Tauri Stars and Related Objects
We have used self-correlation-a simple form of variogram analysis-tostudy 33 RV Tauri and related stars in the LMC, using MACHO data. Weconfirm the periods and classifications of Alcock et al. and discuss afew stars of special interest. We find that self-correlation is a usefuladjunct to Fourier analysis, especially for stars whose classificationis based on their cycle-to-cycle behavior. In particular, it canidentify stars whose behavior is more complicated than the standard``alternating deep and shallow minima'' and begin to investigate thequestion of whether the Population II Cepheids, the RV Tauri variables,and the SRd variables form a continuous sequence from periodicity toirregularity. Our results also emphasize that the RV Tauri phenomenonhas two dimensions: the relative depths of adjacent minima and thenumber of cycles over which the alternating minima persist.
| Studies of the RV Tauri phenomenon.
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| 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).
| Polarimetry of evolved stars. II. The carbon star R Scl
We present broadband optical polarimetry of the carbon star R Scl,primarily in the VRCIC bands. Polarimetricvariability was detected on time-scales from hours to years. Thepolarization of R Scl showed a ~ lambda -4wavelength-dependence, which we attribute to scattering by smallamorphous carbon dust grains. We deduce the properties of thecircumstellar condensations in which the scattering takes place, andfind consistency with infrared data if the condensations move ineccentric orbits. We also conclude that the condensations are tidallydispersed on a time-scale ~ 1 day. On longer time-scales, polarimetricvariations may possibly be linked with photometric variations.
| The ISO-SWS post-helium atlas of near-infrared stellar spectra
We present an atlas of near-infrared spectra (2.36 mu m-4.1 mu m) of ~300 stars at moderate resolution (lambda /delta lambda ~ 1500-2000). Thespectra were recorded using the Short-Wavelength Spectrometer aboard theInfrared Space Observatory (ISO-SWS). The bulk of the observations wereperformed during a dedicated observation campaign after the liquidhelium depletion of the ISO satellite, the so-called post-heliumprogramme. This programme was aimed at extending the MK-classificationto the near-infrared. Therefore the programme covers a large range ofspectral types and luminosity classes. The 2.36 mu m-4.05 mu m region isa valuable spectral probe for both hot and cool stars. H I lines(Bracket, Pfund and Humphreys series), He I and He II lines, atomiclines and molecular lines (CO, H2O, NH, OH, SiO, HCN,C2H2, ...) are sensitive to temperature, gravityand/or the nature of the outer layers of the stellar atmosphere(outflows, hot circumstellar discs, etc.). Another objective of theprogramme was to construct a homogeneous dataset of near-infraredstellar spectra that can be used for population synthesis studies ofgalaxies. At near-infrared wavelengths these objects emit the integratedlight of all stars in the system. In this paper we present the datasetof post-helium spectra completed with observations obtained during thenominal operations of the ISO-SWS. We discuss the calibration of the SWSdata obtained after the liquid helium boil-off and the data reduction.We also give a first qualitative overview of how the spectral featuresin this wavelength range change with spectral type. The dataset isscrutinised in two papers on the quantitative classification ofnear-infrared spectra of early-type stars ({Lenorzer} et al.\cite{lenorzer:2002a}) and late-type stars (Vandenbussche et al., inprep). Based on observations with ISO, an ESA project with instrumentsfunded by ESA Members States (especially the PI countries France,Germany, the Netherlands and the United Kingdom) and with theparticipation of ISAS and NASA. The full atlas is available inelectronic form at www.edpsciences.org Table 1 is only available inelectronic form at the CDS via anonymous ftp to cdsarc.u-strasbg.fr(130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?/A+A/390/1033
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לינקים קשורים
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משמש של הקבוצה הבאה
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תצפית ומידע אסטרומטרי
| קבוצת-כוכבים: | הרקולס |
| התרוממות ימנית: | 18h30m16.24s |
| סירוב: | +21°52'00.6" |
| גודל גלוי: | 7.65 |
| מרחק: | 1428.571 פארסק |
| תנועה נכונה: | -3.8 |
| תנועה נכונה: | -1.6 |
| B-T magnitude: | 8.48 |
| V-T magnitude: | 7.719 |
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