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Публикации по объекту
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.
| VZ Velorum: 116 years of a Mira star
Using the Harvard College Observatory photographic plate collection andrecent CCD observations by the ASAS project we have reconstructed thelight variations of the southern pulsating red giant star VZ Velorumbetween 1890 and early 2006. Contrary to an early report on itslow-amplitude semiregular nature, we found a relatively stable Mira-likelight curve with a mean period of 318 days and amplitude up to 7magnitudes. The latest observations show evidence for a slightly shorterperiod (312 days). However, the difference does not exceed the intrinsicperiod jitter often seen in Mira type variables.
| Pulkovo compilation of radial velocities for 35495 stars in a common system.
Not Available
| Variability of long-period pulsating stars. II. Additional parameters for classifying stars
Results are presented from an analysis of observations in a sample of 53long-period pulsating stars (44 of which are Mira-type and 9 aresemiregular variables). A catalog of the characteristics of theindividual pulsation cycles of the light curves is obtained for thesestars. A correlation analysis of the characteristics of the individualpulsation cycles is carried out for each star. A number if diagramsrelating the variability of the characteristics of the individual cyclesto the average parameters of the variability of the stars and to theirspectral classes. New criteria for classifying long-period variables areproposed on the basis of these diagrams.
| The Skies Over Canada: Observing Committee News
Not Available
| Ubernahme der AFOEV Daten in die Einzelbeobachtungsdatenbank der BAV.
Not Available
| Automated Classification of 2000 Bright IRAS Sources
An artificial neural network (ANN) scheme has been employed that uses asupervised back-propagation algorithm to classify 2000 bright sourcesfrom the Calgary database of Infrared Astronomical Satellite (IRAS)spectra in the region 8-23 μm. The database has been classified into17 predefined classes based on the spectral morphology. We have beenable to classify over 80% of the sources correctly in the firstinstance. The speed and robustness of the scheme will allow us toclassify the whole of the Low Resolution Spectrometer database,containing more than 50,000 sources, in the near future.
| Long periodic variable stars
The information on Mira-type stars and stars adjacent to them at theHertzsprung -- Russel diagram is presented. A detailed description oftheir observational characteristics is given. We give a survey ofimportant observational works concerning: multicolor photometry withspecial attention to the IR emission, maser emission, shock waves, massloss, binarity, the problem of the pulsational mode, direct measurementsof angular and linear dimensions, statistic investigations, study ofkinematic characteristics etc. The most interesting problems regardinglong periodic variable stars are specified. Some attention is given tothe classification and evolutionary stage of these objects.
| 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.
| 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 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
| High Angular Resolution Observations of Late-Type Stars
This paper presents speckle observations of Mira (o Cet) and late-typestars with the PISCO speckle camera of Pic du Midi during the period1995-1998. A survey for binarity among a sample of late-type stars wasperformed, which led to seven positive detections out of 36 objects.Photometric and color variations of the companion of Mira were searchedfor, but no significant brightness variations could be found over atimescale of ~5-10 minutes. The position and photometry measurements,the restored images with high angular resolution of the binary systemMira A-B (ADS 1778) are in full agreement with Hubble Space Telescopedata obtained at the same epoch. A new orbit has been derived for MiraA-B.
| Beobachtungsergebnisse Bundesdeutsche Arbeitsgemeinschaft fur Veraenderliche Sterne e.V.
Not Available
| 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.
| 4 μm spectra of AGB stars I. Observations
We present times series of high resolution spectra of AGB variables at 4mu m. Line profiles from the major contributors to the spectra ofoxygen-rich stars at 4 mu m, OH, H_2O, HCl and SiO, are examined. Thevelocity as well as shape variations of these profiles with time arediscussed. The line profiles investigated frequently have emission andmultiple absorption components. The changes with time of the 4 mu mregion lines do not always follow the cyclic variability seen in NIRspectra and in the photometric light curve. We interpret and discuss theresults qualitatively considering comparing the spectral variabilitywith that of the well behaved 1.6 mu m region and of dynamical modelatmospheres. Miras and semiregular variables are compared. The originsof non-periodic behavior are discussed, including the role of spatialinhomogeneities in the stellar atmosphere.
| 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).
| The Amplitude Decrease of V Bootis
We Explain the amplitude decrease in V Bootis by interference betweentwo close peiods. We also discuss V Bootis in comparison withtheoretical predictions and with other stars that have undergoneamplitude decrease.
| R Centauri: An Unusual Mira Variable in a He-Shell Flash
We present an analysis of AAVSO visual observations of the Mira variableR Cen from 1918 to 2000. The period of the dominant mode has beensteadily decreasing from 550 days at JD 2,434,000 (1951) to its presentvalue of 505-510 days. In the same interval, the pulsational amplitudehas decreased by 3 mag, from 5.5-11.8 V to 6.3-9.1 V. We suggest thatboth are caused by a He-shell flash, as the period decrease is similarto that of other He-shell flash stars such as R Hya, R Aql, and T UMi.The period change is consistent with the luminosity drop expectedimmediately after the flash, as predicted by He-shell flash models forstars of 2-3 Msolar or less. The light curve shows thefamiliar pattern of alternating deep and shallow minima, giving theappearance of double maxima. While the amplitude of the main mode hasdecreased 3 mag in the last 50 years, the amplitude of the secondarymode near 274 days has remained almost constant, so that the doublemaxima have nearly vanished from the light curve in recent years. Thepower spectrum between 1930 and 1966 shows harmonics up to 8 times themain frequency at 1/548 cycle day-1. The most likelyexplanation for the double-peaked light curve is a resonance between twomodes.
| Aufsuchkarten fur intrinsic Variable Stars in Brno.
Not Available
| 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.
| 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.
| 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).
| H2 in the 2 micron infrared spectra of long period variables. I. Observations
Up to seven lines in the S branch of molecular hydrogen have beendetected in the 2 μm infrared absorption line spectra of long periodvariables. The H2 lines show very strong phase dependentchanges in velocity, equivalent width, and line profile, with thestrongest lines near minimum light. The strength of the H2lines also depends on variable type with Mira variables having deeplines (at minimum light), SRa variables generally having detectablelines, and the SRb and non-variables having weak to non-detectablelines. In addition H2 line strengths depend on period and onC/O abundance, with long period (i.e. cool), pure S-type Miras havingH2 lines with central depths of up to 80%. The appearance ofH2 lines in the spectra of cool giants is linked withgeometrical extension of the atmosphere. The greatly increased strengthof the H2 lines in Mira variables is observational evidenceof the role of stellar pulsation in greatly extending these stellaratmospheres. Weak emission is seen in H2 near maximum lightin Miras. We suggest this is resonant scattering in the sphericallyextended stellar atmosphere. The significant role of H2opacity in the blue is noted.
| The Maximum Age of Trapezium Systems
We sought to determine the maximum age of Trapezium systems by studyingpossible trapezium systems that were selected independently of theiroccurrence in H II regions. We started with the unpublished catalog byAllen, Tapia, & Parrao of all the known visual systems having threeor more stars in which the maximum separation is less than 3.0 times theminimum separation. Their catalog has 968 such systems whose mostfrequent primary type is F, which does not describe young systems. Witha CCD on the Kitt Peak 0.9 m telescope we obtained UBV frames for 265systems accessible with our equipment on Kitt Peak. The frames were usedto obtain UBV photometry for about 1500 stars with an accuracy of+/-0.04 mag between V=7 and 14 mag. Also these frames were used toobtain astrometry with an accuracy of +/-0.015d in position angle and+/-0.01" in separation. For the brightest star in each system weobtained a spectral type to determine the distance and reddening to thesystem. The measures were used to determine physical membership fromstars that (1) fit a single color-magnitude diagram, (2) fit a commoncolor-color diagram, and (3) show no astrometric motion compared tovisual measures made (mostly) a century ago. Combining the results withspectroscopic data for 20 additional Allen et al. systems by Abt, wefound that 126 systems had only optical companions to the primaries, 116systems contained only a single physical pair, 13 were hierarchicalsystems with 3-6 members and having separation ratios of more than afactor of 10, two were small clusters, and only 28 fitted the criteriaof Trapezium systems. However, as shown by Ambartsumian, about 9% of thehierarchical systems should appear to be Trapezium systems inprojection. Those, like other hierarchical systems, have a broaddistribution of primary spectral types. We isolated 14 systems that seemto be true Trapezium systems. They have primary types of B3 or earlier,indicating a maximum age of about 5×107 yr. This upperlimit is consistent with the estimate made by Allen & Poveda for anage of several million years for these dynamically unstable systems.These Trapezia are also large with a median radius of 0.2 pc and amaximum radius of 2.6 pc. We asked why the sample of 285 possibleTrapezium systems yielded only 14 true ones, despite the attempt made byAllen et al. to eliminate optical companions with a ``1% filter,'' i.e.,demanding that each companion have less than a 1% chance of being afield star of that magnitude within a circle of its radius from theprimary. The explanation seems to be that the double star catalogs arebased mostly on BD magnitudes that, fainter than V=12 mag, aresystematically too faint by 1 mag.
| 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.
| A comparison of light and velocity variations in semiregular variables
NIR velocity variations are compared with simultaneous visual lightcurves for a sample of late-type semiregular variables (SRV). Preciseradial velocity measurements are also presented for the SRV V450 Aql.Our aim is to investigate the nature of the irregular light changesfound in these variables. Light and velocity variations are correlatedin all stars of our sample. Based on these results we discuss severalpossibilities to explain the observed behavior. We find that pulsationis responsible for large amplitude variations. In a recent paperLebzelter (\cite{Lebzelter99}) invoked large convective cells tounderstand observed velocity variations. This possibility is discussedwith respect to the observed correlation between light and velocitychanges. In the light of these results we investigate the origin of thesemiregular variations.
| Multiperiodicity in semiregular variables. II. Systematic amplitude variations
We present a detailed lightcurve analysis for a sample of brightsemiregular variables based on long-term (70-90 years) visual magnitudeestimates carried out by amateur astronomers. Fundamental changes of thephysical state (amplitude and/or frequency modulations, mode change andswitching) are studied with the conventional Fourier and waveletanalysis. The light curve of the carbon Mira Y Per showing a gradualamplitude decrease has been re-analysed after collecting and addingcurrent data to earlier ones. The time scales of the sudden change andconvection are compared and their similar order of magnitude isinterpreted to be a possible hint for strong coupling between pulsationand convection. The periods of the biperiodic low-amplitude light curveand their ratios suggest a pulsation in the first and third overtonemodes. An alternative explanation of the observed behaviour could be aperiod halving due to the presence of weak chaos. Beside two examples ofrepetitive mode changes (AF Cyg and W Cyg) we report three stars withsignificant amplitude modulations (RY Leo, RX UMa and RY UMa). A simplegeometric model of a rotationally induced amplitude modulation in RY UMais outlined assuming low-order nonradial oscillation, while the observedbehaviour of RX UMa and RY Leo is explained as a beating of two closelyseparated modes of pulsation. This phenomenon is detected unambiguouslyin V CVn, too. The period ratios found in these stars (1.03-1.10)suggest either high-order overtone or radial+non-radial oscillation.
| Processing of Amateur Observations of Mira-Type Stars from Large Databases: Problems and Results
The problems of finding light curve characteristics of long-periodvariables and methods of light curve fit are discussed. A new``asymptotic parabolae" method is proposed for this task. The catalogueof individual cycle characteristics of LPVs is compiled. The resultsconcerning long-term variability of these stars and their classificationare listed.
| 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
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Наблюдательные данные и астрометрия
| Созвездие: | Лебедь |
| Прямое восхождение: | 21h40m39.10s |
| Склонение: | +54°19'28.9" |
| Видимая звёздная величина: | 8.646 |
| Расстояние: | 246.914 парсек |
| Собственное движение RA: | -6.6 |
| Собственное движение Dec: | -10.7 |
| B-T magnitude: | 10.527 |
| V-T magnitude: | 8.802 |
Каталоги и обозначения:
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