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Secular Evolution in Mira Variable Pulsations
Stellar evolution theory predicts that asymptotic giant branch (AGB)stars undergo a series of short thermal pulses that significantly changetheir luminosity and mass on timescales of hundreds to thousands ofyears. These pulses are confirmed observationally by the existence ofthe short-lived radioisotope technetium in the spectra of some of thesestars, but other observational consequences of thermal pulses are subtleand may only be detected over many years of observations. Secularchanges in these stars resulting from thermal pulses can be detected asmeasurable changes in period if the star is undergoing Mira pulsations.It is known that a small fraction of Mira variables exhibit largesecular period changes, and the detection of these changes among alarger sample of stars could therefore be useful in evolutionary studiesof these stars. The American Association of Variable Star Observers(AAVSO) International Database currently contains visual data for over1500 Mira variables. Light curves for these stars span nearly a centuryin some cases, making it possible to study the secular evolution of thepulsation behavior on these timescales. In this paper we present theresults of our study of period change in 547 Mira variables using datafrom the AAVSO. We use wavelet analysis to measure the period changes inindividual Mira stars over the span of available data. By making linearfits to the period versus time measurements, we determine the averagerates of period change, dlnP/dt, for each of these stars. We findnonzero dlnP/dt at the 2 σ significance level in 57 of the 547stars, at the 3 σ level in 21 stars, and at the level of 6 σor greater in eight stars. The latter eight stars have been previouslynoted in the literature, and our derived rates of period change largelyagree with published values. The largest and most statisticallysignificant dlnP/dt are consistent with the rates of period changeexpected during thermal pulses on the AGB. A number of other starsexhibit nonmonotonic period change on decades-long timescales, the causeof which is not yet known. In the majority of stars, the periodvariations are smaller than our detection threshold, meaning theavailable data are not sufficient to unambiguously measure slowevolutionary changes in the pulsation period. It is unlikely that morestars with large period changes will be found among heretoforewell-observed Mira stars in the short term, but continued monitoring ofthese and other Mira stars may reveal new and serendipitous candidatesin the future.
| A study of bright Southern long period variables
In this paper we present radial velocity curves of AGB variables thatexhibit various kinds of anomalies: semiregular variables (SRVs) withtypical mira periods, SRVs exceeding the mira 2.5 mag amplitude limit,miras with secondary maxima in their light curves, and a SRV with a longsecondary period. The stars with reliable Hipparcos parallaxes from thisand from previous studies are plotted in a log P-MK-diagram.Our objects nicely follow the log P-MK-relations determinedfor the LMC. This allows the pulsation mode to be identified. While allmiras fall on the fundamental mode sequence, the SRVs fall on both thefirst overtone and fundamental mode sequences. The SRVs on thefundamental mode sequence occur at both high and low luminosities, someof them being more luminous than larger amplitude miras. Thisdemonstrates observationally that some parameter other than luminosityaffects the stability of long period variables, probably mass. Firstovertone pulsators all show velocity amplitudes around 4 kms-1. For the fundamental mode pulsators, the velocityamplitude shows a correlation with light amplitude. The two miras R Cenand R Nor, known for their double-peaked light curves, have velocitycurves that are quite different. The R Nor velocity curve shows noevidence of the double peaks, meaning that the true pulsation period isthe time between alternate minima or maxima. There is slight evidencefor a double bump in the R Cen velocity curve. It is suggested thatthese stars are relatively massive (3-5 Mȯ).
| Reprocessing the Hipparcos data of evolved stars. III. Revised Hipparcos period-luminosity relationship for galactic long-period variable stars
We analyze the K band luminosities of a sample of galactic long-periodvariables using parallaxes measured by the Hipparcos mission. Theparallaxes are in most cases re-computed from the Hipparcos IntermediateAstrometric Data using improved astrometric fits and chromaticitycorrections. The K band magnitudes are taken from the literature andfrom measurements by COBE, and are corrected for interstellar andcircumstellar extinction. The sample contains stars of several spectraltypes: M, S and C, and of several variability classes: Mira, semiregularSRa, and SRb. We find that the distribution of stars in theperiod-luminosity plane is independent of circumstellar chemistry, butthat the different variability types have different P-L distributions.Both the Mira variables and the SRb variables have reasonablywell-defined period-luminosity relationships, but with very differentslopes. The SRa variables are distributed between the two classes,suggesting that they are a mixture of Miras and SRb, rather than aseparate class of stars. New period-luminosity relationships are derivedbased on our revised Hipparcos parallaxes. The Miras show a similarperiod-luminosity relationship to that found for Large Magellanic CloudMiras by Feast et al. (\cite{Feast-1989:a}). The maximum absolute Kmagnitude of the sample is about -8.2 for both Miras and semi-regularstars, only slightly fainter than the expected AGB limit. We show thatthe stars with the longest periods (P>400 d) have high mass lossrates and are almost all Mira variables.Based on observations from the Hipparcos astrometric satellite operatedby the European Space Agency (ESA \cite{Hipparcos}).Table \ref{Tab:data1} is only available in electronic form at the CDSvia anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/403/993
| Hipparcos red stars in the HpV_T2 and V I_C systems
For Hipparcos M, S, and C spectral type stars, we provide calibratedinstantaneous (epoch) Cousins V - I color indices using newly derivedHpV_T2 photometry. Three new sets of ground-based Cousins V I data havebeen obtained for more than 170 carbon and red M giants. These datasetsin combination with the published sources of V I photometry served toobtain the calibration curves linking Hipparcos/Tycho Hp-V_T2 with theCousins V - I index. In total, 321 carbon stars and 4464 M- and S-typestars have new V - I indices. The standard error of the mean V - I isabout 0.1 mag or better down to Hp~9 although it deteriorates rapidly atfainter magnitudes. These V - I indices can be used to verify thepublished Hipparcos V - I color indices. Thus, we have identified ahandful of new cases where, instead of the real target, a random fieldstar has been observed. A considerable fraction of the DMSA/C and DMSA/Vsolutions for red stars appear not to be warranted. Most likely suchspurious solutions may originate from usage of a heavily biased color inthe astrometric processing.Based on observations from the Hipparcos astrometric satellite operatedby the European Space Agency (ESA 1997).}\fnmsep\thanks{Table 7 is onlyavailable in electronic form at the CDS via anonymous ftp tocdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/397/997
| The modelling of intermediate-age stellar populations. II. Average spectra for upper AGB stars, and their use
The upper Asymptotic Giant Branch (AGB) is populated with oxygen richand carbon rich Long Period Variables (LPVs). These stars are essentialcontributors to the near-IR light of intermediate age stellarpopulations. Individual observed spectra of LPVs are so diverse thatthey cannot be used directly in the synthesis of galaxy spectra. In thispaper, the library of individual spectra of Lançon & Wood(\cite{LM00_fluct}) is used to construct averages that can beincorporated conveniently in population synthesis work. The connectionbetween such spectra and stellar evolution tracks is discussed. In orderto select a sorting criterion and to define averaging bins for the LPVspectra, correlations between their spectrophotometric properties arereexamined. While optical properties and broad baseline colours such as(I-K) are well correlated, a large dispersion is observed when theseindices are plotted against near-IR ones. This is partly due to theintrinsic width of the upper AGB, which is illustrated by locating eachof the multiple observations of individual LPVs on the HR diagram. It isargued that broad baseline colour-temperatures are the most sensiblesorting criteria. The properties of the resulting sequence of averagespectra indeed vary regularly. We further address: (i) the bolometriccorrections and temperature scales needed to associate a spectrum with agiven point on a theoretical stellar evolution track (or isochrone),(ii) the simplifying assumptions that will be implicitely made whenusing the average spectra, (iii) potential biases in the sample ofLançon & Wood and their effects, (iv) the small contributionof LPVs to the interstellar hydrogen emission lines in galaxies. It isemphasized that an a posteriori calibration of the effective temperaturescale remains necessary, until consistent models for the evolution, thepulsation and the spectral appearance of LPVs become available. Wesuggest a recipe for the use of the average spectra at variousmetallicities.
| Mira kinematics in the post-Hipparcos era
The complete data set of Mira variables from the 4th edition of theGeneral Catalog of Variable Stars was analyzed and supplemented by theproper motions and radial velocities presently available for Miras. Theresulting sample of 724 Miras with periods between 78 and 612 dayscontains proper motions reduced to the Hipparcos system, radialvelocities and V magnitudes. For each of 10 subgroups of Miras dividedaccording to their periods and spectral types, statistical parallaxeswere determined by application of five different methods. The meanabsolute magnitudes, the spatial velocities and their dispersions aswell as the elements of the Galactic orbits were computed as functionsof the periods. The (Mbol-< ~ g P) relation obtained wasfound to be considerably steeper than the PLR usually assumed for LMCMiras. For Miras in the period range 145-200 days, no significant netmotion radially outwards in the Galaxy as suggested by Feast &Whitelock (2000) was found. The predicted frequency of Miras wascomputed as a function of the visual magnitude.
| Asymptotic giant branch variables in Baade's Windows
In this work, a sample of luminous M-type giants in the Baade's Windowstowards the inner Galactic bulge is investigated in the near-infrared.The ISOGAL survey at 7 and 15μm has given information concerning themass-loss rates of these stars and their variability characteristicshave been extracted from the MACHO data base. Most are known to besemi-regular variables (SRVs). Here we discuss how theirIJHKS-region colours depend on period and on the presence orabsence of mass loss, using results mainly taken from the DENIS and2MASS surveys. In order to compare their colours with solarneighbourhood stars, photometric colours on the DENIS, 2MASS and ESOphotometric systems have been synthesized for objects in thespectrophotometric atlas of Lançon & Wood. In addition, theyhave been used to predict the differences in colour indices when starswith strong molecular bands are observed using different photometricsystems. The SRVs are found to inhabit the upper end of theJ-KS, KS colour-magnitude diagram, lying justbelow the Miras. High mass-loss rates are associated with highluminosity. The near-infrared colours of the SRVs increase in a generalway with period and are the reddest for stars with significant massloss. The average colours of Mira variables, whose periods start ataround 200d in the bulge, are bluer than those of the semi-regulars atthis period, particularly in J-H, thanks to the association of deepwater vapour bands with large amplitude.
| Stars with the Largest Hipparcos Photometric Amplitudes
A list of the 2027 stars that have the largest photometric amplitudes inHipparcos Photometry shows that most variable stars are all Miras. Thepercentage of variable types change as a function of amplitude. Thiscompilation should also be of value to photometrists looking forrelatively unstudied, but large amplitude stars.
| Polarimetry of 167 Cool Variable Stars: Data
Multicolor photoelectric polarimetry is presented for 167 stars, most ofwhich are variable stars. The observations constitute a data set thatfor some stars covers a time span of 35 yr. Complex variations are foundover time and wavelength and in both the amount of polarization and itsposition angle, providing constraints for understanding the polarizingenvironments in and around these cool stars.
| Galactic mass-losing AGB stars probed with the IRTS. I.
AGB mass-losing sources are easy to identify and to characterize in thenear-infrared range (1-5 mu m). We make use of the near-infrared dataacquired by the Japanese space experiment IRTS to study a sample ofsources detected in the 2 celestial strips surveyed by the IRTS.Mass-loss rates and distances are estimated for 40 carbon-rich sourcesand 86 oxygen-rich sources of which 8 are probably of S-type. Althoughthe sample is small, one sees a dependence of the relative contributionof the two kinds of sources to the replenishment of the interstellarmedium (ISM) on the galactocentric distance. E.g. from 6 to 8 kpc,oxygen-rich sources in our sample contribute 10-12 times as much ascarbon rich sources, whereas from 10 to 12 kpc, the latters contribute3-4 times as much as the formers. Therefore, one would expect a gradientin the composition of the ISM between 6 and 12 kpc from the GalacticCentre, especially in its dust component. Most of the replenishment(>50%) by AGB stars is due to sources with mass-loss rate larger than10-6 Msun yr-1.
| Long period variable stars: galactic populations and infrared luminosity calibrations
In this paper HIPPARCOS astrometric and kinematic data are used tocalibrate both infrared luminosities and kinematical parameters of LongPeriod Variable stars (LPVs). Individual absolute K and IRAS 12 and 25luminosities of 800 LPVs are determined and made available in electronicform. The estimated mean kinematics is analyzed in terms of galacticpopulations. LPVs are found to belong to galactic populations rangingfrom the thin disk to the extended disk. An age range and a lower limitof the initial mass is given for stars of each population. A differenceof 1.3 mag in K for the upper limit of the Asymptotic Giant Branch isfound between the disk and old disk galactic populations, confirming itsdependence on the mass in the main sequence. LPVs with a thin envelopeare distinguished using the estimated mean IRAS luminosities. The levelof attraction (in the classification sense) of each group for the usualclassifying parameters of LPVs (variability and spectral types) isexamined. Table only available in electronic form at the CDS viaanonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/374/968 or via ASTRIDdatabase (http://astrid.graal.univ-montp2.fr).
| On the shock-induced variability of emission lines in M-type Mira variables. I. Observational data
We present time-resolved observations of metallic emission lines of MgI, Mn I, Si I, Fe I and Fe II, including forbidden emission lines of [FeII], for the six M-type Mira variables RR Sco, R Aql, R Car, R Leo, SScl and R Hya, which range in period from 281 to 389 days. Data is alsopresented for the Balmer emission lines Hγ , Hdelta , Hzeta andHeta . The observations were carried out in the optical wavelengthregion 3600-5700 Å. Narrow-slit observations with dispersion of1.53 km s-1 pixel-1 and a 3-pixel resolution of4.6 km s-1 were made in some cases while most observationswere done with a wide slit corresponding to a resolution of 15.3 kms-1. The variation of line shape, flux and velocity withphase is discussed. The data presented in this paper will be used insubsequent papers for comparison with detailed models of the emissionfrom shock waves in the upper atmospheric layers of Mira variables. Itis in these important upper layers that dust formation occurs and massloss is initiated.
| Catalogue of Apparent Diameters and Absolute Radii of Stars (CADARS) - Third edition - Comments and statistics
The Catalogue, available at the Centre de Données Stellaires deStrasbourg, consists of 13 573 records concerning the results obtainedfrom different methods for 7778 stars, reported in the literature. Thefollowing data are listed for each star: identifications, apparentmagnitude, spectral type, apparent diameter in arcsec, absolute radiusin solar units, method of determination, reference, remarks. Commentsand statistics obtained from CADARS are given. The Catalogue isavailable in electronic form at the CDS via anonymous ftp tocdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcar?J/A+A/367/521
| Hipparcos parallaxes for Mira-like long-period variables
This paper concerns the calibration of the K period-luminosity relationfor Mira variables using Hipparcos parallaxes. K magnitudes areavailable for 255 Mira-like variables which were observed by Hipparcos.Period-luminosity zero-points are evaluated for various subgroups ofdata. The best solution for oxygen-rich Miras, which uses 180 stars,omitting the short-period red group (which had different kinematics fromthe short-period blue stars) and the low-amplitude variables, provides azero-point of σ2σ2π +(0.4605)2π2PL(K)σ2K + σ2PL(K),0.84+/-0.14mag, which implies a distance modulus for the LargeMagellanic Cloud of σK = 0.3ΔK√N,18.64+/-0.14mag, or perhaps slightly greater if a metallicity correctionis required, in good agreement with the value derived from Cepheids. Thezero-point of the period-luminosity relation for carbon stars is brieflydiscussed. Linear diameters are derived for red variables with measuredangular diameters and parallaxes, and are used to examine thelong-standing question of the pulsation mode(s) of these stars. Evidenceis presented to suggest that most of them are pulsating in the same modeand, if published model atmospheres are correct, this is probably thefirst overtone. Some discussion is given of sequences in theperiod-luminosity and period-colour diagrams and their bearing on thepulsation mode problem.
| Infrared colours for Mira-like long-period variables found in the (Mȯ<~10-7 Msolar yr-1) Hipparcos Catalogue
Near-infrared, JHKL, photometry is presented for 193 Mira andsemi-regular variables that were observed by Hipparcos; periods,bolometric magnitudes and amplitudes are derived for 92 of them. Becauseof the way in which the Hipparcos targets were selected, this group ofstars provides a useful data base of Miras with low mass-loss rates(Mȯ<~10-7Msolaryr-1).Various period-colour relationships are discussed in detail. The colour,particularly BCK = 10.86 - 38.10 K (J - K)0 +64.16(J - K)20 - 50.72(J -K)30 + 19, K-L, at a given period is found todepend on the pulsation amplitude of the star. A comparison with modelssuggests that this is a consequence of atmospheric extension, in thesense that large-amplitude pulsators have very extended atmospheres andredder Mȯ<10-7Msolaryr-1, K-L and H-K but bluerJ-H than their lower amplitude counterparts. The stars with veryextended atmospheres also have higher values of K-[12] and hence highermass-loss rates. This finding provides further evidence for the causalconnection between pulsation and mass loss. Two sequences are identifiedin the Hp-K versus logP diagram (where Hp is the Hipparcos broad-bandmagnitude) at short periods (logP<2.35). At a given period these twogroups have, on average, the same pulsation amplitude, but differentJHKL colours and spectral types. The short-period stars in the bluersequence have similar near-infrared colours to the Miras found inglobular clusters. Long-term trends in the infrared light curves arediscussed for stars that have sufficient data.
| Mira kinematics from Hipparcos data: a Galactic bar to beyond the Solar circle
The space motions of Mira variables are derived from radial velocities,Hipparcos proper motions and a period-luminosity relation. Thepreviously known dependence of Mira kinematics on the period ofpulsation is confirmed and refined. In addition, it is found that Miraswith periods in the range 145-200d in the general Solar neighbourhoodhave a net radial outward motion from the Galactic Centre of75+/-18kms-1. This, together with a lag behind the circularvelocity of Galactic rotation of 98+/-19kms-1, is interpretedas evidence for an elongation of their orbits, with their major axesaligned at an angle of ~17° with the Sun-Galactic Centre line,towards positive Galactic longitudes. This concentration seems to be acontinuation to the Solar circle and beyond of the bar-like structure ofthe Galactic bulge, with the orbits of some local Miras probablypenetrating into the bulge. These conclusions are not sensitive to thedistance scale adopted. A further analysis is given of the short-period(SP) red group of Miras discussed in companion papers in this series. InAppendix A the mean radial velocities and other data for 842 oxygen-richMira-like variables are tabulated. These velocities were derived frompublished optical and radio observations.
| On the Variability of K5-M Stars
I investigate the Hipparcos Satellite photometry of K5-M stars to seethe pattern of activity of these stars. A few stars for which furtherstudy is desirable are identified.
| Studying the Pulsation of Mira Variables in the Ultraviolet
We present results from an empirical study of the Mg II h and k emissionlines of selected Mira variable stars, using spectra from theInternational Ultraviolet Explorer (IUE). The stars all exhibit similarMg II behavior during the course of their pulsation cycles. The Mg IIflux always peaks after optical maximum near pulsation phaseφ=0.2-0.5, although the Mg II flux can vary greatly from one cycleto the next. The lines are highly blueshifted, with the magnitude of theblueshift decreasing with phase. The widths of the Mg II lines are alsophase dependent, decreasing from about 70 km s-1 to 40 kms-1 between φ=0.2 and φ=0.6. We also study other UVemission lines apparent in the IUE spectra, most of them Fe II lines.These lines are much narrower and not nearly as blueshifted as the Mg IIlines. They exhibit the same phase-dependent flux behavior as Mg II, butthey do not show similar velocity or width variations.
| A library of 0.5 to 2.5 mu m spectra of luminous cool stars
We present a library of 0.5-2.5 mu m digital spectra of cool, mostlyvariable, giant and supergiant stars which should be useful for spectralsynthesis applications, as well as for comparison with theoretical modelatmosphere calculations. The library includes carbon stars, GalacticBulge and Magellanic Cloud stars, and OH/IR stars. The stars observedcover a range of metallicities and masses. Most variable objects wereobserved several times, at different phases of their pulsation cycle. Wediscuss the effects of various fundamental parameters and of variabilityon the spectra. Based on period-luminosity relations and stellarevolutionary tracks, we tentatively assign initial masses to eachobject.
| Optical and near-infrared spectrophotometric properties of Long Period Variables and other luminous red stars
Based on a new and large sample of optical and near-infrared spectraobtained at the Mount Stromlo and Siding Spring Observatories(Lançon & Wood 1998; Lançon & Wood, inpreparation), spectrophotometric properties of cool oxygen- andcarbon-rich Long Period Variables and supergiants are presented.Temperatures of oxygen-rich stars are assigned by comparison withsynthetic spectra computed from up-to-date oxygen-rich model atmospheregrids. The existence of reliable optical and near-infrared temperatureindicators is investigated. A narrow relation between the bolometriccorrection BC_I and the broad-band colour I-J is obtained foroxygen-rich cool stars. The ability of specific near-infrared indices toseparate luminosity classes, atmospheric chemistry or variabilitysubtypes is discussed. Some comments are also given on extinctioneffects, water band strengths in Long Period Variables and theevaluation of \element[][12]{CO}/\element[][13]{CO} ratio in red giants.
| Period-Luminosity-Colour distribution and classification of Galactic oxygen-rich LPVs. I. Luminosity calibrations
The absolute K magnitudes and kinematic parameters of about 350oxygen-rich Long-Period Variable stars are calibrated, by means of anup-to-date maximum-likelihood method, using Hipparcos parallaxes andproper motions together with radial velocities and, as additional data,periods and V-K colour indices. Four groups, differing by theirkinematics and mean magnitudes, are found. For each of them, we alsoobtain the distributions of magnitude, period and de-reddened colour ofthe base population, as well as de-biased period-luminosity-colourrelations and their two-dimensional projections. The SRa semiregulars donot seem to constitute a separate class of LPVs. The SRb appear tobelong to two populations of different ages. In a PL diagram, theyconstitute two evolutionary sequences towards the Mira stage. The Mirasof the disk appear to pulsate on a lower-order mode. The slopes of theirde-biased PL and PC relations are found to be very different from theones of the Oxygen Miras of the LMC. This suggests that a significantnumber of so-called Miras of the LMC are misclassified. This alsosuggests that the Miras of the LMC do not constitute a homogeneousgroup, but include a significant proportion of metal-deficient stars,suggesting a relatively smooth star formation history. As a consequence,one may not trivially transpose the LMC period-luminosity relation fromone galaxy to the other Based on data from the Hipparcos astrometrysatellite. Appendix B is only available in electronic form at the CDSvia anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/Abstract.html
| Are low-order resonances observed in Mira pulsation?
The possibility of a low-order, two-mode resonance in the pulsation ofLPVs is investigated by means of Fourier analysis of lightcurves,supplemented by spectral types and by kinematic population analysisbased on HIPPARCOS astrometric data. The question might be positivelyanswered. Based on data from the HIPPARCOS astrometry satellite.
| Pulsation modes of Mira stars and questioning of linear modelling: indications from HIPPARCOS and the LMC
Thorough discussion of the previous theoretical works on the pulsationof Long Period Variables leads us to the conclusion that the modeperiods predicted by linear models must significantly differ from thereality, and that, if one nevertheless relies upon such a modelling, itis at least necessary to change the mixing length. The hypothesis thatthe so-derived mode periods be reasonably reliable is supported byconfrontation between a model grid based on these grounds and theluminosities of LPVs in the Large Magellanic Cloud and in LMC clusters,as well as the luminosities and effective temperatures of Miras in thesolar neighbourhood. A wide majority of the Miras appear probablypulsating on the first overtone, and the sample Semi-Regulars on thesecond. However, a significant proportion of Miras seem to befundamental pulsators. Individual masses are derived. A few stars areprobably undergoing hot bottom burning, while two seem to have apeculiar dust envelope. Based on data from the HIPPARCOS astrometrysatellite
| First results from HIPPARCOS trigonometrical parallaxes of Mira-type variables
HIPPARCOS trigonometrical parallaxes are given for 16 pre-selected Miravariables. Linear diameters are derived for eight oxygen-rich Miras withknown angular diameters. Comparison with pulsation theory shows that twoof them (both with periods over 400d) are fundamental pulsators, whilethe others (all with periods of less than 400d) pulsate in an overtone.The Mira PL relations in M_K and M_bol are calibrated for oxygen-richovertone pulsators, adopting slopes for these relations from LMC data. Amean LMC distance modulus of 18.54 is derived; this is very close tothat of 18.57 derived from the Cepheids. The uncertainty in the valuederived from the Miras is estimated to be less than 0.2 mag. Theabsolute magnitude of the only carbon-rich Mira in the sample, R Lep(period of 427d), indicates that it is a fundamental pulsator. Otherstars discussed individually are: the symbiotic Mira, R Aqr; thedouble-period Mira, R Cen; and two Miras with decreasing periods, R Aqland R Hya.
| Line emission in stellar envelopes
We examine the problem of what could be called a `compact planetarynebula' in studying the radiative equilibrium of a spherical envelopewith inner radius comparable or equal to the radius of the illuminatingcore. The envelope is composed of hydrogen atoms in statisticalequilibrium and photoionized by a central radiation of relatively hightemperature T*>15 000K. We consistently solve the equations ofradiative transfer in spherical geometry for all lines and continua,including the Lyman transitions, together with the equations ofstatistical equilibrium. Yet we ignore the energy balance equation andconsider the electronic temperature as a given parameter. We show thatBalmer and other subordinate lines may appear in emission, even at lowtemperature, provided that (i) the density is low enough for theradiative terms to partly control the populations of the levels and (ii)the geometrical extension of the H II region is significant. Althoughthe present model is only intended to isolate and illustrate a specificphysical mechanism, we suggest that the emission features detected inthe spectrum of cool giant or supergiant stars could result from purelyradiative processes, at least in some cases.
| Classification and Identification of IRAS Sources with Low-Resolution Spectra
IRAS low-resolution spectra were extracted for 11,224 IRAS sources.These spectra were classified into astrophysical classes, based on thepresence of emission and absorption features and on the shape of thecontinuum. Counterparts of these IRAS sources in existing optical andinfrared catalogs are identified, and their optical spectral types arelisted if they are known. The correlations between thephotospheric/optical and circumstellar/infrared classification arediscussed.
| Mean light curves of long-period variables and discrimination between carbon- and oxygen-rich stars
Using 75 years of AAVSO data, mean light curve parameters of a sample of355 long period M, S, and C mira and semi-regular variable stars areinvestigated. We present a classification of the light curves of LPVsinto 6 distinct groups. Combining this classification with IRAS colorsmakes it possible to distinguish oxygen-rich from carbon-rich miras.Table 2 is only available in electronic form at the CDS via anonymousftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/Abstract.html
| Phase and cycle dependence of the photospheric structure and observable properties of Mira variables.
Nonlinear pulsation models designed to represent the prototype Miravariable o Ceti have been produced. Both fundamental mode andfirst-overtone models were examined. The fundamental mode models havelight and velocity amplitudes similar to those observed and they exhibitbumps on the rising parts of the light curve and aperiodic motion in theupper layers as found observationally in Mira variables. As first foundin previous studies, the first-overtone models were not able to producethe observed velocity amplitudes of Mira variables, largely because ofthe low gravity of the models. This problem suggests that Miras arefundamental mode pulsators. The effect of radiation pressure acting onH_2_O molecules in the outer stellar layers was examined as a source ofdriving mass loss. It was found that the radiation force on H_2_Omolecules had very little effect on the pulsation and did not lead toany mass loss. A series of photospheric models were made based on thedensity stratifications of the pulsation models at different phases.Synthetic spectra were computed and these were used to derivemonochromatic radii to compare with observations of Mira variables withdifferent periods. The computed radii for τlambda_=1 atdifferent phases in continuum windows was very close to the Rosselandradii. The general appearance of the synthetic spectra and theirvariation with phase resembled the observations of Mira variables quitewell. The behaviour of absorption line profiles from the movingatmospheres was followed through the different phases and cycles of thedifferent model series. A complex behaviour of some lines with phase ispredicted. Better agreement between theoretical and observed spectra,colors and radii of Mira variables can be expected to follow fromimprovements to the treatment of the molecular line opacity.
| Lumnosity attenuation and distances of red giant stars
The Mv of M red variable stars is increased by the molecularTiO bands which grow from M0 to M10 in an inherent spectral darkeningsequence. The Mv is the result of both the effective visualflux and the equivalent radius. The equivalent radius is apparentlysmaller than the empirical radius due to a molecular covering process instars later than M3. The full range of optical red giant stars forms asequence from the brightest M early spectral types (S Car, M0(max),Mv approx = -3.2 mag) to the faintest M-latest spectral types(IK Tau, M10.5 min), Mv approx. = 16.5 mag). The typicalMiras and SR stars of M-medium and M-late spectral types are betweenthese two extremes. The sequence has a range of 20 mag on the visual(HR) diagram which extends from the red giant branch (RGB) passingbeyond the Mv of red dwarf stars as far as the point where itintercepts with the prolongation of the zero-age main sequence (ZAMS) inthe latest spectral type. Typical M10-stars at 200 pc has a V approx. =20 mag. M-latest stars at larger distances are unobservable stars in thevisual band. The distances of 134 variable stars are also given. Thedistances to 86 stars were determined by using a pure photometricmethod, while preliminary distances (less than 200 pc) for the remaining48 M-latest stars were determined by the spectral-photometric method.Since the local stellar density of M stars up to 100 pc rises at least7.5 times, it is possible to discuss that the long-standing problem ofdark matter in spiral galaxies could be resolved by these very dimmassive giant stars and by the molecular covered stars at the extremeend of the attenuating sequence. Furthermore, post M-latest stars may bethe only nonvisual stellar objects that can explain the enormousquantity of faint and point infrared sources found by IRAS. These weakobjects suggest the existence of an infrared Milky Way which is moredense than the optical one.
| 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.
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