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Random forest automated supervised classification of Hipparcos periodic variable stars
We present an evaluation of the performance of an automatedclassification of the Hipparcos periodic variable stars into 26 types.The sub-sample with the most reliable variability types available in theliterature is used to train supervised algorithms to characterize thetype dependencies on a number of attributes. The most useful attributesevaluated with the random forest methodology include, in decreasingorder of importance, the period, the amplitude, the V-I colour index,the absolute magnitude, the residual around the folded light-curvemodel, the magnitude distribution skewness and the amplitude of thesecond harmonic of the Fourier series model relative to that of thefundamental frequency. Random forests and a multi-stage scheme involvingBayesian network and Gaussian mixture methods lead to statisticallyequivalent results. In standard 10-fold cross-validation (CV)experiments, the rate of correct classification is between 90 and 100per cent, depending on the variability type. The main mis-classificationcases, up to a rate of about 10 per cent, arise due to confusion betweenSPB and ACV blue variables and between eclipsing binaries, ellipsoidalvariables and other variability types. Our training set and thepredicted types for the other Hipparcos periodic stars are availableonline.
| 3.6 Years of DIRBE Near-infrared Stellar Light Curves
The weekly averaged near-infrared fluxes for 2652 stars were extractedfrom the cold and warm era all-sky maps of the Diffuse InfraredBackground Experiment (DIRBE). Since the DIRBE program only archived theindividual Calibrated Infrared Observations for the 10 month cold eramission, the weekly averaged fluxes were all that were available for thewarm era. The steps required to extract stellar fluxes are described asare the adjustments that were necessary to correct the results forseveral systematic effects. The observations are at a cadence of once aweek for 3.6 years (~1300 days), providing continuous sampling onvariable stars that span the entire period for the longest fundamentalpulsators. The stars are divided into three categories: those with largeamplitude of variability, smaller amplitude variables, and sources whosenear-infrared brightness do not vary according to our classificationcriteria. We show examples of the results and the value of the addedbaseline in determining the phase lag between the visible and infrared.
| Polarization observations of circumstellar OH masers
Results of observations of circumstellar OH masers in lines withwavelengths near 18 cm are reported. The observations were carried outon the radio telescope of the Nan cay Radio Astronomy Observatory(France). In 2007–2009, 70 late-type stars were observed(including Mira and semi-regular variables). For 53 of these, emissionwas detected in at least one of three OH lines (1612, 1665, or 1667MHz). Circular and linear polarization of the maser emission wasmeasured, yielding all four Stokes parameters. Polarized emissionfeatures were detected in the OH line spectra of 41 stars. A summary ofall the observations is given. The results obtained for T Lep, R LMi,and R Crt are discussed. Emission in the 1665 and 1667 MHz OH lines wasdetected in T Lep for the first time. Features probably due to Zeemansplitting were detected in the OH line profiles of all three stars.Estimates of the magnetic-field strengths in the maser sources wereobtained (0.46–2.32 mG). Variability of the polarizationcharacteristics of the maser emission of the stars on time intervals ofseveral months was found.
| Simultaneous Observations of SiO and H2O Masers Toward Known Stellar SiO and H2O Maser Sources. I.
We present the results of simultaneous observations of both SiO andH2O masers toward 166 known SiO and H2O masersources using the Korean VLBI Network Yonsei 21 m radio telescope during2009 June. Both SiO and H2O maser emission were detected from112 sources giving a detection rate of 67% at one epoch observation.SiO-only maser emission was detected from 42 sources, whileH2O-only maser emission was detected from four sources. Mostof the SiO masers appear around the stellar velocity, whileH2O masers show different characteristics compared with SiOmasers. There are more than 20 sources that show a one-way peak ordouble peaks with respect to the stellar velocity and SiO maser peakvelocity. The H2O maser peak and integrated intensity ratioswith respect to those of SiO (v = 1) show increasingly larger valuesfrom Mira variables, to OH/IR stars, to semi-regular variables. Inaddition, the IRAS two-color diagram of SiO and H2O maserobservational results is discussed.
| Correlation between technetium and lithium in a sample of oxygen-rich AGB variables
Context. The elements technetium and lithium are two importantindicators of internal nucleosynthesis and mixing in late-type stars.Studying their occurrence and abundance can give deep insight into thestructure and evolution in the late phases of the stellar life cycle. Aims: The aims of this paper are: 1) to revisit the Tc content ofa sample of oxygen-rich (M-type) asymptotic giant branch (AGB) variablesand 2) to increase the number of such stars for which the Li abundancehas been measured to provide constraints on the theoretical models ofextra-mixing processes. Methods: To this end, we analysedhigh-resolution spectra of 18 sample stars for the presence ofabsorption lines of Tc and Li. The abundance of the latter wasdetermined by comparing the observed spectra to hydrostatic MARCS modelspectra. Bolometric magnitudes were established from near-IR photometryand pulsation periods. Results: We correct the classificationwith respect to the presence of Tc for a number of stars. We reclassifythe star V441 Cyg as Tc-rich, and the unusual Mira star R Hya, as wellas W Eri, as Tc-poor. The abundance of Li, or an upper limit to it, wasdetermined for all of the sample stars. In all stars with Tc we alsodetected Li. Most of them have a Li content slightly below the solarphotospheric value, except for V441 Cyg, which is super-Li rich with1000 times the solar abundance. We also found that, similar to Tc, alower luminosity limit seems to exist for the presence of Li. Conclusions: We conclude that the higher Li abundance found in thecooler and higher luminosity objects could stem from a Li productionmechanism operating on the thermally pulsing AGB. The stellar mass mighthave a crucial influence on this (extra mixing) production mechanism.Our findings for R Hya and V441 Cyg have some important consequences forthese intriguing objects. It was speculated that the declining pulsationperiod of R Hya is caused by a recent thermal pulse (TP). While notdetecting Tc does not rule out a TP, it indicates that the TPs are notstrong enough to drive 3DUP in R Hya. The pieces of evidence concerningthe mass of V441 Cyg are not entirely conclusive. It could either be alow-mass, intrinsic S-star that produced its large amount of Li byextra-mixing processes, or an intermediate-mass star (M? 4{M}&sun;) undergoing Li production via hot bottom burning.Based on observations at the Very Large Telescope of the EuropeanSouthern Observatory, Cerro Paranal/Chile under Programme 65.L-0317(A),and at the Calar Alto Observatory Centro Astronómico HispanoAlemán, Calar Alto, Spain.
| Statistical Properties of Stellar H2O Masers --- Results of Three-Year Single-Dish Observations with the VERA Iriki Telescope
We report on the results of monitoring observations of 242 stellarH2O masers, which have been made with the Iriki 20m telescopeof the VLBI Exploration of Radio Astrometry (VERA) from 2003 July to2006 November. The present paper mainly focuses on 85 stellarH2O masers that have been tightly observed with a timespacing of typically 1--2 months. In particular, 46 masers out of themhave been recognized concerning their periodic flux variation and havelight-curve data of stellar visual light. Thus, the present paper showssome statistical views of the observed time variability properties ofstellar H2O masers. We found a good correlation between atime delay of the variation in the H2O masers flux withrespect to that in the stellar visual light and the stellar pulsationperiod. The corresponding phase lags are mildly scattered, but aremainly concentrated in the range, 0.7 ≤ Δφ ≤ 1.5. Wealso measured line-of-sight velocity drifts of the individual spectralpeaks of H2O maser emission, which indicate radialacceleration of mass-loss outflows from the evolved stars. We discusspossible pulsation-driven shock waves that are enhanced near the stellarsurface, and are propagating outwards in the circumstellar envelope.
| AGB variables and the Mira period-luminosity relation
Published data for large-amplitude asymptotic giant branch variables inthe Large Magellanic Cloud (LMC) are re-analysed to establish theconstants for an infrared (K) period-luminosity relation of the formMK = ρ[logP - 2.38] + δ. A slope of ρ = -3.51+/- 0.20 and a zero-point of δ = -7.15 +/- 0.06 are found foroxygen-rich Miras (if a distance modulus of 18.39 +/- 0.05 is used forthe LMC). Assuming this slope is applicable to Galactic Miras we discussthe zero-point for these stars using the revised Hipparcos parallaxestogether with published very long baseline interferometry (VLBI)parallaxes for OH masers and Miras in globular clusters. These result ina mean zero-point of δ = -7.25 +/- 0.07 for O-rich Galactic Miras.The zero-point for Miras in the Galactic bulge is not significantlydifferent from this value.Carbon-rich stars are also discussed and provide results that areconsistent with the above numbers, but with higher uncertainties. Withinthe uncertainties there is no evidence for a significant differencebetween the period-luminosity relation zero-points for systems withdifferent metallicity.
| Pulkovo compilation of radial velocities for 35495 stars in a common system.
Not Available
| 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.
| Sektion "Mirasterne": Beobachtungsplanung 2004.
Not Available
| Technetium and the third dredge up in AGB stars. I. Field stars
We searched for Tc in a sample of long period variables selected bystellar luminosity derived from Hipparcos parallaxes. Tc, as an unstables-process element, is a good indicator for the evolutionary status ofstars on the asymptotic giant branch (AGB). In this paper we study theoccurrence of Tc as a function of luminosity to provide constraints onthe minimum luminosity for the third dredge up as estimated from recentstellar evolution models.A large number of AGB stars above the estimated theoretical limit forthe third dredge up are found not to show Tc. We confirm previousfindings that only a small fraction of the semiregular variables show Tclines in their spectra. Contrary to earlier results by Little et al.(\cite{llmb87}) we find also a significant number of Miras without Tc.The presence and absence of Tc is discussed in relation to the massdistribution of AGB stars. We find that a large fraction of the stars ofour sample must have current masses of less than 1.5 Msun .Combining our findings with stellar evolution scenarios we conclude thatthe fraction of time a star is observed as a SRV or a Mira is dependenton its mass.Partly based on observations collected at the European SouthernObservatory, Paranal, Chile (ESO-Programme 65.L-0317(A)).
| 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
| Stellar and circumstellar evolution of long period variable stars
In a first paper, HIPPARCOS astrometric and kinematic data were used tocalibrate both infrared K and IRAS luminosities at the same time askinematic parameters of Long Period Variable stars (LPVs). Individualestimated absolute magnitudes and a probabilistic assignation togalactic populations were deduced from these calibrations for each LPVof our sample. Here we propose a scenario of simultaneous stellar andcircumstellar evolution according to the galactic populations. Thetransitory states of S and Tc stars allow us to confirm the location ofthe first dredge-up at Mbol=-3.5. There is also evidencesuggesting that a previous enrichment in s-elements from a more evolvedcompanion may accelerate the evolution along the AGB. The possibleevolution to OH LPVs is included in this scenario, and any of thesestars may have a mass at the limit of the capability for a C enrichmentup to C/O > 1. A list of bright massive LPVs with peculiar envelopeand luminosity properties is proposed as Hot Bottom Burning candidates.The He-shell flash star, R Cen, is found to be exceptionally bright andcould become, before leaving the AGB, a C-rich LPV brighter than theusual luminosity limit of carbon stars.
| 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).
| 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.
| 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.
| Dust features in the 10-mu m infrared spectra of oxygen-rich evolved stars
We have analyzed the 8-13.5 mu m UKIRT CGS3 spectra of 142 M-type starsincluding 80 oxygen-rich AGB stars and 62 red supergiants, with a viewto understanding the differences and similarities between the dustfeatures of these stars. We have classified the spectra into groupsaccording to the observed appearance of the infrared features. In eachcase the normalized continuum-subtracted spectrum has been compared tothose of the other stars to find similarities and form groups. The dustfeatures of the AGB stars are classified into six groups: broad AGB,where the feature extends from 8 mu m to about 12.5 mu m with littlestructure; broad+sil AGB, which consists of a broad feature with anemerging 9.7 mu m silicate bump; and four silicate AGB groups in which a``classic'' 9.7 mu m silicate feature gets progressively narrower.Likewise, the supergiant spectra have also been classified into groups,however these do not all coincide with the AGB star groups. In thesupergiant case we again have six groups: featureless, where there islittle or no emission above the continuum; broad Super, where thefeature extends from about 9 mu m to about 13 mu m; and four silicateSuper groups, which again show a progression towards the narrowest``classic'' 9.7 mu m silicate feature. We compare the mean spectrum foreach group, which yields two main results. Firstly, while the``classic'' silicate feature is essentially identical for both AGB starsand red supergiants, the broad features observed for these two stellartypes are quite different. We suggest that the dust in these twoenvironments follows different evolutionary paths, with the dust aroundMira stars, whose broad feature spectra can be fit by a combination ofalumina (Al2O3) and magnesium silicate,progressing from this composition to dust dominated by magnesiumsilicate only, while the dust around supergiants, whose broad featurecan be fit by a combination of Ca-Al-rich silicate andAl2O3, progresses from this initial composition toone eventually also dominated by magnesium silicate. The reason for thedifference in the respective broad features is not clear as yet, butcould be influenced by lower C/O ratios and chromospheric UV radiationfields in supergiant outflow environments. The second result concernsthe 12.5 - 13.0 mu m feature discovered in IRAS LRS spectra and widelyattributed to Al2O3. This feature is seenpredominantly in the spectra of semiregular variables, sometime in Mirasand only once (so far) in supergiant spectra. We argue that it isunlikely that this feature is due to Al2O3 or, ashas more recently been suggested, spinel(MgAl2O4), but could be associated with silicondioxide or highly polymerized silicates (not pyroxenes or olivines).
| 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.
| Modelling of oxygen-rich envelopes using corundum and silicate grains
A set of 31 oxygen-rich stars has been modelled using corundum andsilicate grains. These stars were selected according to theirdust-envelope class, as suggested by Little-Marenin and Little in 1990.Then 16 stars classified as Sil were modelled using silicate grains; 10Broad class stars using corundum (Al2O3) grains;and 5 `Intermediate' class stars using two kinds of grainsimultaneously: corundum and silicate. The temperature of the centralstars and some characteristics of their circumstellar envelopes such astheir extinction opacities and extensions were determined by fitting theflux curves. The corundum/silicate ratios as well as the energydistributions and temperature laws have been obtained. Based on theauthors' results they suggest the existence of chemical and structuralevolution of the modelled circumstellar dust shells. The temperature ofthe central stars and the temperature of the hottest grains decreasefrom Broad to Intermediate to Sil classes, while the inner radii andoptical depths increase in this sequence.
| Millimeter and some near infra-red observations of short-period Miras and other AGB stars
Millimeter observations of 48 oxygen- and 20 carbon-rich AGB Miras withperiods shorter than 400 days are presented. In addition, observationsof 14 O-rich and 15 C-stars with longer, or no known, periods have alsobeen obtained. The detection statistics is as follows: in12CO J=1-0 and 2-1 we observed 97 stars, and detected 66 inat least one line. We find 24 new detections in the 1-0 line, 38 newdetections in the 2-1 line, and 29 stars have been detected for thefirst time in one or both lines. In 12CO J=3-2 we observed 14stars and detected 11, with 4 new detections. In 13CO J=2-1,3-2 we observed 2 stars and had one new detection. In HCN(1-0) weobserved 5 carbon stars and detected 3, one new. In SO(6_5-5_4) weobserved the same 5 stars and detected none. In CS(3-2) we observed 8carbon stars and detected 3, all new. In SiO(3-2, v=0) we observed 34O-rich stars and detected 25, all new except one. Near-infrared JHKphotometry is presented for seven stars. For four stars it is the firstNIR data published. The luminosity and dust mass loss rate are obtainedfor seven very red stars with unknown pulsation period from modellingthe spectral energy distribution (SED) and IRAS LRS spectra. Thereby, anew IR supergiant is confirmed (AFGL 2968). For the rest of the sample,luminosity and distance are obtained in a variety of ways: usinghipparcos parallaxes, period-luminosity and period-M_K-relationscombined with apparent K magnitudes, and kinematic distances. The dustmass loss rate is obtained from model fitting of the SED (either fromthe literature, or presented in the present paper), or from the observedIRAS 60 mu m flux, corrected for the photospheric contribution. The gasmass loss rate is derived from the observed CO line intensities, aspresented here, combined with existing literature data, if any. Thisallows the derivation of the dust-to-gas ratio. Our and literature CO J= 3-2 data has been used to calibrate the relation between mass lossrate and peak intensity of the CO(3-2) line. Diagrams showing mass lossrate, dust-to-gas ratio and expansion velocity versus pulsation periodare presented. Our observations confirm the existence of an upper limitfor the expansion velocity of C- and O-rich stars, and that this maximumis larger for C-stars, as predicted by the theory of radiation pressureon dust particles. The James Clerk Maxwell Telescope is operated by theObservatories on behalf of the Science and Engineering Council of theUK, the Netherlands Organization for Scientific Research, and theNational Research Council of Canada. Based on observations made with theCarlos Sanchez telescope operated on the island of Tenerife in theSpanish Observatorio del Teide of the Instituto de Astrof\'\i sica deCanarias. Based on observations collected at the European SouthernObservatory, La Silla, Chile within programs ESO 57.E-0105, 59.E-0198and 61.E-0254. Based on data from the ESA Hipparcos astrometrysatellite.
| 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
| The Infrared Spectral Classification of Oxygen-rich Dust Shells
This paper presents infrared spectral classifications for a flux-limitedsample of 635 optically identified oxygen-rich variables includingsupergiants and sources on the asymptotic giant branch (AGB). Severalclasses of spectra from oxygen-rich dust exist, and these can bearranged in a smoothly varying sequence of spectral shapes known as thesilicate dust sequence. Classification based on this sequence revealsseveral dependencies of the dust emission on the properties of thecentral star. Nearly all S stars show broad emission features fromalumina dust, while most of the supergiants exhibit classic featuresfrom amorphous silicate dust. Mira variables with symmetric light curvesgenerally show broad alumina emission, while those with more asymmetriclight curves show classic silicate emission. These differences may arisefrom differences in the photospheric C/O ratio.
| 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
| Semiregular variables of types SRa and SRb. Silicate dust emission features.
We have analysed the IRAS-LRS spectra of representative samples ofO-rich Semiregular (SR) variables of types SRa and SRb and of Miravariables. The silicate features were extracted by fitting the energydistribution with two blackbodies, approximating the continuous emissionfrom the photosphere and the circumstellar dust. The shape and strengthof the silicate features in the LRS range were then studied by computingthe residual fluxes in 5 selected wavelength regions covering the whole10μm and 18μm features and parts of the 10μm feature assignedto emission from olivine and possibly corundum. We compare our approachwith previous investigations and argue that a quantitative study ofdetails in the feature shape requires subtraction of the stellar and thedust continuum and the use of flux ratios rather than a discreteclassification system. The Miras form an extension of the SRb's towardslower stellar temperatures and higher dust shell opacities and they haveslightly higher average dust temperatures. The SRa's seem to be moresimilar to the Miras in their dust shell properties. The average 10μmfeature shapes of the three groups of variables agree, but taking intoaccount the photospheric and dust shell parameters, systematicdifferences show up. For stars hotter than about 2900K, the 10μmfeature width shows a wide range of values but no clear trend with thestellar temperature or the optical depth of the dust shell. These starsare generally SRb variables and have the thinnest dust envelopes. Atcooler stellar temperatures, where mostly Miras are found, the opticaldepth of the dust shell determines the feature width in the sense thatthicker shells have narrower features. It appears that the 13μmfeature is obvious only in a narrow range of effective temperature andoptical depth of the dust shell. We discuss our results in terms ofradiative transfer effects, differences in the average grain size,annealing and hydration of amorphous silicates and contributions fromother dust components. Of these possibilities the last one seems to bemost plausible with regard to the behavior of the 10μm feature width.The observations can be interpreted in terms of changing contributionsfrom olivine and corundum possibly caused by an increasing amount ofdust processing (Miras) and the influence of the atmospheric structureon the formation of these dust components (SRb's).
| AGB stars: densities and formation rates obtained from OH/IR stars.
We determine densities and star formation rates of AGB stars from ananalysis of OH/IR stars in the solar neighbourhood. The stars aredivided into three distinct mass ranges corresponding to the precursorsof type I, II and III planetary nebulae, according to the Peimbertclassification scheme. The adopted distance scale is based on theperiod-luminosity relationship by Feast et al. (1989). The formation (ordeath) rates are calculated using stellar evolution models for AGBstars, and are compared with the corresponding rates for planetarynebulae and white dwarfs. The results indicate that both surface andvolume densities of AGB stars are in good agreement with previousdeterminations in the literature. The formation rates are found to bevery sensitive to the evolution time at the AGB, and depend also on theadopted model.
| 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.
| A search for observational evidence of OH molecule photoproduction
Observational evidence for OH molecule photoproduction by theinterstellar UV radiation in the circumstellar envelopes of Miravariables has been searched for. A sample of Me-type Miras was observedin the main OH maser lines with the Nancay radio telescope. Two newlines were detected. The intensity of the 156.5-nm wavelengthinterstellar radiation is estimated by integration of the observed UVlight of OB stars in common star catalogues. A statistically significanttrend is found that OH Miras are illuminated by stronger UV fields thannon-OH objects.
| Spectral evolution of the H2O maser in late-type stars
We have carried out almost simultaneous observations of H2O and SiO (J =1-0, v = 1) masers for 171 known late-type maser stars with the 34 mradio telescope at Kashima. We found a systematic change in the H2Omaser spectra related to the evolution of the stars. Typically, H2Omaser spectral profiles are singly peaked in Mira variables, but doublypeaked in IRC/AFGL objects and OH/IR stars. The expansion velocity ofH2O masers increases with decreasing IRAS color temperature. This isexplained by the shock excitation model proposed by Cooke and Elitzur(1985). The blue shifted peak in the profiles is more prominent than thered shifted peak in most of the IRC/AFGL objects and OH/IR stars. Ablocking model of the redshifted peak is introduced.
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Группы:
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Наблюдательные данные и астрометрия
| Созвездие: | Эридан |
| Прямое восхождение: | 04h11m31.03s |
| Склонение: | -25°08'02.3" |
| Видимая звёздная величина: | 9.985 |
| Собственное движение RA: | -9.1 |
| Собственное движение Dec: | -11.8 |
| B-T magnitude: | 10.77 |
| V-T magnitude: | 10.05 |
Каталоги и обозначения:
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