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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.
| 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.
| 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.
| Amateur observations - Successes and opportunities.
Not Available
| 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
| 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.
| 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.
| 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
| 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
| 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.
| SiO maser emission and the intrinsic properties of Mira variables
Observations of SiO maser emission from 161 Mira variables distributedover a wide range of intrinsic parameters like spectral type, bolometricmagnitude, and amplitude of pulsation are reported. The observationswere made at 86.243 GHz, using the 10.4 m millimeter-wave telescope ofthe Raman Research Institute at Bangalore, India. The maser emission isfound to be restricted to Miras having mean spectral types between M6and M10. The IR period-luminosity relation for Mira variables isemployed to calculate their distances and hence estimate their maserluminosities from the observed fluxes. The maser luminosity is found tobe correlated with the bolometric magnitude of the Mira variable. On anH-R diagram, the masing Mira variables are shown to lie in a regiondistinct from that for the nonmasing ones.
| Maxima and minima of long period variables, 1949-1975
Not Available
| IRAS low resolution spectrograph spectral class and M and S Miras
A large sample of 177 M and S Miras, as revealed by their IRAS LRSspectral class, have been examined to determine the dependence ofsilicate emission on the visual light curve asymmetry factor, f. It isconfirmed that 9.7-micron silicate emission feature not only in M but inS Miras also occurs only when f is not greater than 0.45. However, notall stars with f of not greater than 0.45 show the silicate emission;this nondetection reveals dependence on other parameters like the meanvisual light amplitude. Though strong emission feature in M Miras mayoccur for any value of f, very weak features are absent for small valuesof f, and the strongest features tend to appear for larger values of f.Infrared excess tends to increase with the strength of the silicateemission as well as with decrease in the value of f. The probability ofdetection of silicate emission is very high for the visual light curveclasses (Ludendorff, 1928) alpha 1, alpha 2, and alpha 3, decreases foralpha 4 and gamma 1, and is negligible for the beta class.
| Criteria for OH maser emission from circumstellar envelopes of oxygen-rich Mira-type red giants
A large and representative sample of oxygen-rich Mira stars was selectedand observed in the 18 cm OH lines at their optical maximum. A total of14 new OH sources were detected. The OH maser emission is found in theintrinsically bright far-IR objects with late M spectral type. Othercharacteristics of the Miras are high (H-K) and (K-L) colors. Theirperiods are on average longer and their (25-12) colors on average redderthan those of non-OH Miras. The (J-H) and (60-25) colors are the samefor OH and non-OH stars. In most cases, OH and H2O masers existsimultaneously. The observed stars form a sequence along which theperiod and the stellar luminosity increase, the stellar radiusincreases, the dust shell radius increases by a smaller factor, thephotospheric temperature decreases but the dust shell temperature isroughly constant, and the mass loss rate and thus the thickness and thebrighntess of the envelope increase considerably.
| Classification of Mira variables based on visual light curve shape
The paper presents classifications of 368 Mira variables of M, S and Cspectral classes based on the shape of their visual light curve. Theclassification is esentially based on Ludendorff's (1928) scheme and thelight curves used are mainly from the compilation of Campbell (1955).The distribution of light curves over period, mean amplitude, lightcurve asymmetry factor, period variability, and spectral class atmaximum is discussed.
| The visible spectra of Southern Hemisphere Mira variable stars
The 483 blue classification spectrograms of 72 Southern Hemisphere Miravariables presently added to the Keenan et al. (1974) catalog indicatethat the irregular behavior of absorption features in Mira variables canbe accounted for by a second shock front that lies higher in theatmosphere than the one producing Balmer emission. Since shock velocityprobably varies from cycle to cycle, the affected lines are not expectedto maintain the same equivalent width at the same phase in differentcycles.
| IRAS catalogues and atlases - Atlas of low-resolution spectra
Plots of all 5425 spectra in the IRAS catalogue of low-resolutionspectra are presented. The catalogue contains the average spectra ofmost IRAS poiont sources with 12 micron flux densities above 10 Jy.
| UBVRI photometry of red stars
A total of 50 Mira- and SR-type red variable stars were observed bymeans of the photoelectric photometry UBVRI Kron-Cousins system. Inaddition, 15 nearby red dwarf stars having spectral subtypes similar tothose of Mira stars at maximum were observed in order to show that theconversion of the natural system into the Landolt (1983) standard systemcan be made for stars as red as the Mira variables, in spite of theshortage of standard late M-type stars. The relationship function andspectral type-color index scale on the Johnson system was converted intothe present system. By means of VRI photometry, the spectral subtype canimmediately be determined in different phases of the light curve. SRvariables have the same color indices and spectral subclasses as Miravariables.
| A classification of miras from their visual and near-infrared light curves - an attempt to correlate them with their evolution
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1985A&A...144..463M&db_key=AST
| Spectral classification of southern-hemisphere Mira variables
The catalog of Keenan, Garrison and Deutsch (1974) has been extended bythe addition of 483 blue spectrograms of 72 southern-hemisphere Miravariables. About 190 direct and image-tube plates at a dispersion of 120A/mm were obtained in Chile between 1977 and 1982. Along with thespectral types, emission ratios H-delta 4101/H-gamma 4340/H-beta 4861and eye-estimated intensities of the Ca I 4226, Cr I 4254 and Sr II 4077absorption lines have been tabulated. Data for the 15 best-studied Mirasin the southern-hemisphere program are presented. In addition, spectralmontages for six stars have been prepared to illustrate changes in thevisual spectra of Mira variables through their respective cycles.
| The distance of large Amplitude Red Variables
It is pointed out that the determination of the distance for LargeAmplitude Red Variables (LARV) has presented difficulties in connectionwith problems regarding the derivation of the visual absolute magnitude(Mv) of the variables. The considered investigation provides estimatesof the distance of 43 LARV on the basis of a procedure which employs anew period-spectrum-luminosity relation to obtain Mv. The accuracy ofthe estimated values is discussed. For the relatively near stars, theaccuracy is improved more than 50 percent. The error in the reportedestimates is approximately 20 percent. For stars which do not show avery pronounced intrinsic variation from cycle to cycle, there may be anerror of 15 percent regarding the estimated distance, if the Mvdispersion is plus or minus 0.3.
| Intrinsic amplitude and molecular absorption of Mira stars
Interpretation of the luminous variation of the Mira stars results in anempirical relationship demonstrating that the visual amplitude isdetermined by the maximum magnitude variation and by the variation ofthe atmospheric molecular condensation of TiO in the time intervalrequired by a star to change from minimum to maximum magnitude. Theempirical relationship accounts for intrinsic characteristics of theMira stars, such as the period-luminosity relation noted by Clayton andFeast (1969). In addition, the amplitude relationship may be applied tothe SRa stars and probably to long-period variables in general.
| Light and colour variation of the Mira stars
A total of 3743 V, B-V and U-B photoelectric measurements of 60Mira-type variable stars, mainly in the southern hemisphere, were madeat the Cerro Tololo Inter-American Observatory during 14 observationperiods, from December 1972 to March 1974. Light curves are given foreach star based on a probable graphic interpolation as a function oftime. Elements of each light and color curve are derived. The principalcharacteristics observed in the V curves are that the form of variationremains the same in each star and that there are groups of stars whoselight curves are similar, even though the elements are not constant. Thevariation of the color indices is also analyzed, showing the mostimportant properties.
| A study of Mira variables - Implications of OH stars and galactic evolution
A maximum likelihood method has been used to study the properties oftype I OH Mira variables and the kinematical evolution of the Galaxy.The method takes into account dispersion in magnitude and employs propermotions and radial velocities. The V-I excess of type I OH stars withrespect to non OH stars is confirmed, and interpreted in terms of a hot,circumstellar disk around the OH Mira variables. The results support thenotion of a gradual flattening of the Galaxy as proposed by theories ofcollisional collapse.
| A Photometric Approach to the Absolute Magnitudes of Mira Variables
Not Available
| Near-Infrared Photometry of Mira Variables
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1972ApJS...24..375L&db_key=AST
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