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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.
| A catalogue of young runaway Hipparcos stars within 3 kpc from the Sun
Traditionally, runaway stars are O- and B-type stars with large peculiarvelocities. We would like to extend this definition to young stars (upto ?50 Myr) of any spectral type and to identify those present in theHipparcos catalogue by applying different selection criteria, such aspeculiar space velocities or peculiar one-dimensional velocities.Runaway stars are important for studying the evolution of multiple starsystems or star clusters, as well as for identifying the origins ofneutron stars. We compile the distances, proper motions, spectral types,luminosity classes, V magnitudes and B-V colours, and we utilizeevolutionary models from different authors to obtain star ages. We studya sample of 7663 young Hipparcos stars within 3 kpc from the Sun. Theradial velocities are obtained from the literature. We investigate thedistributions of the peculiar spatial velocity and the peculiar radialvelocity as well as the peculiar tangential velocity and itsone-dimensional components and we obtain runaway star probabilities foreach star in the sample. In addition, we look for stars that aresituated outside any OB association or OB cluster and the Galactic planeas well as stars for which the velocity vector points away from themedian velocity vector of neighbouring stars or the surrounding local OBassociation/cluster (although the absolute velocity might be small). Wefind a total of 2547 runaway star candidates (with a contamination ofnormal Population I stars of 20 per cent at most). Thus, aftersubtracting these 20 per cent, the runaway frequency among young starsis about 27 per cent. We compile a catalogue of runaway stars, which isavailable via VizieR.
| BAV-Results of Observations - Photoelectric minima of selected eclipsing binaries and maxima of pulsating stars.
Not Available
| BAV-Results of Observations - Photoelectric Minima of Selected Eclipsing Binaries and Maxima of Pulsating Stars
Not Available
| Automated Variable Star Classification Using the Northern Sky Variability Survey
We have identified 4659 variable objects in the Northern Sky VariabilitySurvey. We have classified each of these objects into one of the fivevariable star classes: (1) Algol/β Lyr systems includingsemidetached, and detached eclipsing binaries, (2) W Ursae Majorisovercontact and ellipsoidal variables, (3) long-period variables such asCepheid and Mira-type objects, (4) RR Lyr pulsating variables, and (5)short-period variables including δ Scuti stars. All the candidateshave outside of eclipse magnitudes of ~10-13. The primary classificationtool is the use of Fourier coefficients combined with period informationand light-curve properties to make the initial classification. Briefmanual inspection was done on all light curves to remove nonperiodicvariables that happened to slip through the process and to quantify anyerrors in the classification pipeline. We list the coordinates, period,Two Micron All Sky Survey colors, total amplitude variation, and anyprevious classification of the object. 548 objects previously identifiedas Algols in our previous paper are not included here.
| The luminosities and distance scales of type II Cepheid and RR Lyrae variables
Infrared and optical absolute magnitudes are derived for the type IICepheids κ Pav and VY Pyx using revised Hipparcos parallaxes andfor κ Pav, V553 Cen and SW Tau from pulsational parallaxes.Revised Hipparcos and HST parallaxes for RR Lyrae agree satisfactorilyand are combined in deriving absolute magnitudes. Phase-corrected J, Hand Ks mags are given for 142 Hipparcos RR Lyraes based onTwo-Micron All-Sky Survey observations. Pulsation and trigonometricalparallaxes for classical Cepheids are compared to establish the bestvalue for the projection factor (p) used in pulsational analyses.The MV of RR Lyrae itself is 0.16 +/- 0.12 mag brighter thanpredicted from an MV-[Fe/H] relation based on RR Lyrae starsin the Large Magellanic Cloud (LMC) at a modulus of 18.39 +/- 0.05 asfound from classical Cepheids. This is consistent with the prediction ofCatelan & Cortés that it is overluminous for its metallicity.The results for the metal- and carbon-rich Galactic disc stars, V553 Cenand SW Tau, each with small internal errors (+/-0.08 mag) have a meandeviation of only 0.02 mag from the period-luminosity (PL) relationestablished by Matsunaga et al. for type II Cepheids in globularclusters and with a zero-point based on the same LMC-scale. Comparingdirectly the luminosities of these two stars with published data on typeII Cepheids in the LMC and in the Galactic bulge leads to an LMC modulusof 18.37 +/- 0.09 and a distance to the Galactic Centre of R0= 7.64 +/- 0.21kpc. The data for VY Pyx agree with these results withinthe uncertainties set by its parallax. Evidence is presented thatκ Pav may have a close companion and possible implications of thisare discussed. If the pulsational parallax of this star is incorporatedin the analyses, the distance scales just discussed will be increased by~0.15 +/- 0.15 mag. V553 Cen and SW Tau show that at optical wavelengthsPL relations are wider for field stars than for those in globularclusters. This is probably due to a narrower range of masses in thelatter case.
| Modeling of RR Lyrae light curves: the case of M3
Context: A promising technique to derive the physical parameters and thedistance of pulsating stars is the fit of the observed light curves bynonlinear pulsation models. Aims: We apply this technique to asubsample of the RR Lyrae belonging to the Galactic globular cluster M3.The application of the method to cluster pulsators has the advantage ofdealing with a homogeneous sample at the same distance and with the samechemical composition allowing to be checked the internal consistency ofpulsational calculations. Methods: We selected seven pulsators(three RRc and four RRab) which cover a significant period range andshow detailed light curves in the B, V and in some cases I bands. Forfour of them, with different periods, pulsation modes and light curveproperties, we analyze the dependence of the theoretical light curvevariations on the model input parameters. Results: For allselected objects, except the reddest one, we are able to theoreticallyreproduce the observed light curve morphology for self-consistent rangesof intrinsic stellar parameters, in agreement with the evolutionarypredictions for the corresponding metal abundance. It is worth notingthat, even if the theoretical reproduction of individual light curvesgives for each variable only a range of stellar parameters anddistances, the analysis of several variables belonging to the samecluster provides a mean distance modulus, namely ?_V=15.10 ±0.1 mag, and also checks the self-consistency of the adopted theoreticalscenario. Taking also into account the evolutionary constraints, therange of the accepted distance modulus is significantly reduced giving aweighted mean value of 15.05 ± 0.02. Our estimates are inagreement with available results in the literature obtained fromindependent methods.Figures 1-23 are only available in electronic form athttp://www.aanda.org
| Photoelectric Minima of Selected Eclipsing Binaries and Maxima of Pulsating Stars
Not Available
| Kinematic structure in the Galactic halo at the North Galactic Pole: RR Lyrae and blue horizontal branch stars show different kinematics
Radial velocities and proper motions (derived from the GSC-II data base)are given for 38 RR Lyrae (RRL) stars and 79 blue horizontal branch(BHB) stars in a ~200 deg2 area around the North GalacticPole (NGP). Both heliocentric (UVW) and galactocentric (VR,V?, Vz) space motions are derived for thesestars using a homogeneous distance scale consistent with (m -M)0 = 18.52 for the Large Magellanic Cloud (LMC).An analysis of the 26 RRL and 52 BHB stars whose height (Z) above theplane is less than 8 kpc shows that this halo sample is not homogeneous.Our BHB sample (like that of Sirko et al.) has a zero galactic rotation(V?) and roughly isotropic velocity dispersions. The RRLsample shows a definite retrograde rotation (V? = -95+/- 29 kms-1) and non-isotropic velocity dispersions. Thecombined BHB and RRL sample has a retrograde galactic rotation (V) thatis similar to that found by Majewski for his sample of subdwarfs inSelected Area (SA) 57. The velocity dispersion of the RRL stars thathave a positive W motion is significantly smaller than the dispersion ofthose `streaming down' with a negative W. Also, the ratio of RRL to BHBstars is smaller for the sample that has positive W.Our halo sample occupies 10.4 kpc3 at a mean height of 5 kpcabove the Galactic plane. In this volume, one component (rich in RRLstars) shows retrograde rotation and the streaming motion that weassociate with the accretion process. The other component (traced by theBHB stars) shows essentially no rotation and less evidence of streaming.These two components have horizontal branch (HB) morphologies thatsuggest that they may be the field star equivalents of the young and oldhalo globular clusters, respectively. Clearly, it is quite desirable touse more than one tracer in any kinematic analysis of the halo.
| Pulkovo compilation of radial velocities for 35495 stars in a common system.
Not Available
| A catalogue of RR Lyrae stars from the Northern Sky Variability Survey
A search for RR Lyrae stars has been conducted in the publicly availabledata of the Northern Sky Variability Survey. Candidates have beenselected by the statistical properties of their variation; the standarddeviation, skewness and kurtosis with appropriate limits determined froma sample 314 known RRab and RRc stars listed in the General Catalogue ofVariable Stars. From the period analysis and light-curve shape of over3000 candidates 785 RR Lyrae have been identified of which 188 arepreviously unknown. The light curves were examined for the Blazhkoeffect and several new stars showing this were found. Six double-mode RRLyrae stars were also found of which two are new discoveries. Somepreviously known variables have been reclassified as RR Lyrae stars andsimilarly some RR Lyrae stars have been found to be other types ofvariable, or not variable at all.
| Photoelectric Minima of Selected Eclipsing Binaries and Maxima of Pulsating Stars
Not Available
| Proper identification of RR Lyrae stars brighter than 12.5 mag
RR Lyrae stars are of great importance for investigations of Galacticstructure. However, a complete compendium of all RR-Lyraes in the solarneighbourhood with accurate classifications and coordinates does notexist to this day. Here we present a catalogue of 561 local RR-Lyraestars (V_max ≤ 12.5 mag) according to the magnitudes given in theCombined General Catalogue of Variable Stars (GCVS) and 16 fainter ones.The Tycho2 catalogue contains ≃100 RR Lyr stars. However, manyobjects have inaccurate coordinates in the GCVS, the primary source ofvariable star information, so that a reliable cross-identification isdifficult. We identified RR Lyrae from both catalogues based on anintensive literature search. In dubious cases we carried out photometryof fields to identify the variable. Mennessier & Colome (2002,A&A, 390, 173) have published a paper with Tyc2-GCVSidentifications, but we found that many of their identifications arewrong.
| RR Lyrae stars: kinematics, orbits and z-distribution
RR Lyrae stars in the Milky Way are good tracers to study the kinematicbehaviour and spatial distribution of older stellar populations. Arecently established well documented sample of 217 RR Lyr stars withV<12.5 mag, for which accurate distances and radial velocities aswell as proper motions from the Hipparcos and Tycho-2 catalogues areavailable, has been used to reinvestigate these structural parameters.The kinematic parameters allowed to calculate the orbits of the stars.Nearly 1/3 of the stars of our sample have orbits staying near the MilkyWay plane. Of the 217 stars, 163 have halo-like orbits fulfilling one ofthe following criteria: Θ < 100 km s-1, orbiteccentricity >0.4, and normalized maximum orbital z-distance>0.45. Of these stars roughly half have retrograde orbits. Thez-distance probability distribution of this sample shows scale heightsof 1.3±0.1 kpc for the disk component and 4.6±0.3 kpc forthe halo component. With our orbit statistics method we found a(vertical) spatial distribution which, out to z=20 kpc, is similar tothat found with other methods. This distribution is also compatible withthe ones found for blue (HBA and sdB) halo stars. The circular velocityΘ, the orbit eccentricity, orbit z-extent and [Fe/H] are employedto look for possible correlations. If any, it is that the metal poorstars with [Fe/H] <1.0 have a wide symmetric distribution aboutΘ=0, thus for this subsample on average a motion independent ofdisk rotation. We conclude that the Milky Way possesses a halo componentof old and metal poor stars with a scale height of 4-5 kpc having randomorbits. The presence in our sample of a few metal poor stars (thus partof the halo population) with thin disk-like orbits is statistically notsurprising. The midplane density ratio of halo to disk stars is found tobe 0.16, a value very dependent on proper sample statistics.
| Photoelectric Minima of Selected Eclipsing Binaries and Maxima of Pulsating Stars
Not Available
| Pulsation models of RR Lyrae stars: dependence on the mixing-length parameter alpha
In order to provide a detailed analysis of the pulsational behavior ofRR Lyrae and in particular to investigate on the dependence of themodels on the free mixing-lenght parameter alpha , we have implementedthe existing set of models computed with alpha =1.5 with new sequencescomputed adopting alpha =2.0. The latter value is also adopted in recentevolutionary computations . We show the effects of this alpha increaseon both the width of the instability strip and the morphology of lightcurves. In order to attempt to calibrate the alpha parameter we alsoshow the comparison between model predictions and empirical data. Theresults of this comparison seem to suggest that the alpha parameter isnot the same at varying the effective temperature and the pulsationmode. Further tests are needed in order to confirm this conclusion.
| Photoelectric Maxima of Selected Pulsating Stars
Not Available
| Theoretical Models for Bump Cepheids
We present the results of a theoretical investigation aimed at testingwhether full-amplitude, nonlinear convective models account for theI-band light curves of bump Cepheids in the Large Magellanic Cloud(LMC). We selected two objects from the OGLE sample that show awell-defined bump along the decreasing (short-period) and the rising(long-period) branch respectively. We find that current models doreproduce the luminosity variation over the entire pulsation cycle ifthe adopted stellar mass is roughly 15% smaller than predicted byevolutionary models that neglect both mass loss and convective coreovershooting. Moreover, we find that the fit to the light curve of thelong-period Cepheid located close to the cool edge of the instabilitystrip requires an increase in the mixing length from 1.5Hp to1.8Hp. This suggests an increase in the efficiency of theconvective transport when moving toward cooler effective temperatures.Current pulsation calculations supply an LMC distance modulus rangingfrom 18.48 to 18.58 mag.
| On the second-overtone stability among Small Magellanic Cloud Cepheids
We present a new set of Cepheid, full amplitude, non-linear, convectivemodels which are pulsationally unstable in the second overtone (SO).Hydrodynamical models were constructed by adopting a chemicalcomposition typical of Cepheids in the Small Magellanic Cloud (SMC) andfor stellar masses ranging from 3.25 to 4Msolar. Predicted?21 Fourier parameters agree, within currentuncertainties, with empirical data for pure first- and second-overtonevariables as well as for first-/second-overtone (FO/SO) double-modeCepheids collected by Udalski et al. in the SMC. On the other hand,predicted I-band amplitudes are systematically larger than the observedones in the short-period range, but attain values that are closer to theempirical ones for logPSO>=-0.12 andlogPFO>=0.1. We also find, in agreement with empiricalevidence, that the region within which both second and first overtonesattain a stable limit cycle widens when moving towards lowerluminosities. Moreover, predicted PSO/PFO andPFO/PF period ratios agree quite well withempirical period ratios for FO/SO and fundamental/FO double-mode SMCCepheids. Interestingly enough, current models support the evidence thatpure SO Cepheids and SO components in FO/SO Cepheids are good distanceindicators. In fact, we find that the fit of the predictedperiod-luminosity-colour (V, V-I) relation to empirical SMC datasupplies a distance modulus (DM) of 19.11+/-0.08mag. The same outcomeapplies to pure FO Cepheids and FO components in FO/SO Cepheids, andindeed we find DM=19.16+/-0.19mag. Current distance estimates do notaccount for, within current uncertainties on photometry and reddening,the so-called short distance scale.
| Identification of Known and SuspectedVariables from the ROTSE1 Survey
Not Available
| U Com: a new route for comparing theory and observations
The high precision multiband photometric data of the first overtone RRLyrae U Com are used to investigate the predictive capability of fullamplitude, nonlinear, convective hydrodynamical models. The main outcomeof this investigation is that theoretical predictions properly accountfor the luminosity variations along a full pulsation cycle. Thisapproach, due to the strong dependence of the pulsation period onstellar parameters, supplies tight constraints on stellar mass,effective temperature, and distance modulus. Predicted pulsationalestimates of these parameters appear in good agreement with empiricalones. Moreover, the occurrence of a well-defined bump just before theluminosity maximum gives the unique opportunity to calibrate theturbulent convection model adopted for handling the coupling betweenpulsation and convection. Finally, the extention of this approach toclassical Cepheids is briefly discussed.
| 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.
| Kinematics of Metal-poor Stars in the Galaxy. II. Proper Motions for a Large Nonkinematically Selected Sample
We present a revised catalog of 2106 Galactic stars, selected withoutkinematic bias and with available radial velocities, distance estimates,and metal abundances in the range -4.0<=[Fe/H]<=0.0. This updateof the 1995 Beers & Sommer-Larsen catalog includes newly derivedhomogeneous photometric distance estimates, revised radial velocitiesfor a number of stars with recently obtained high-resolution spectra,and refined metallicities for stars originally identified in the HKobjective-prism survey (which account for nearly half of the catalog)based on a recent recalibration. A subset of 1258 stars in this cataloghave available proper motions based on measurements obtained with theHipparcos astrometry satellite or taken from the updated AstrographicCatalogue (second epoch positions from either the Hubble Space TelescopeGuide Star Catalog or the Tycho Catalogue), the Yale/San Juan SouthernProper Motion Catalog 2.0, and the Lick Northern Proper Motion Catalog.Our present catalog includes 388 RR Lyrae variables (182 of which arenewly added), 38 variables of other types, and 1680 nonvariables, withdistances in the range 0.1 to 40 kpc.
| The RR Lyrae Star U Comae as a Test for Nonlinear Pulsation Models
We use high-precision multiband photometric data of the first-overtoneRR Lyrae star U Comae to investigate the predictive capability offull-amplitude, nonlinear, convective hydrodynamical models. The mainoutcome of this investigation is that theoretical predictions properlyaccount for the luminosity variations along a full pulsation cycle.Moreover, we find that this approach, because of the strong dependenceof this observable and of the pulsation period on stellar parameters,supplies tight constraints on stellar mass, effective temperature, anddistance modulus. Pulsational estimates of these parameters appear ingood agreement with empirical ones. Finally, a well-defined bump justbefore the luminosity maximum gave the unique opportunity to calibratethe turbulent convection model adopted for handling the coupling betweenpulsation and convection.
| ROTSE All-Sky Surveys for Variable Stars. I. Test Fields
The Robotic Optical Transient Search Experiment I (ROTSE-I) experimenthas generated CCD photometry for the entire northern sky in two epochsnightly since 1998 March. These sky patrol data are a powerful resourcefor studies of astrophysical transients. As a demonstration project, wepresent first results of a search for periodic variable stars derivedfrom ROTSE-I observations. Variable identification, perioddetermination, and type classification are conducted via automaticalgorithms. In a set of nine ROTSE-I sky patrol fields covering roughly2000 deg2, we identify 1781 periodic variable stars with meanmagnitudes between mv=10.0 and mv=15.5. About 90%of these objects are newly identified as variable. Examples of manyfamiliar types are presented. All classifications for this study havebeen manually confirmed. The selection criteria for this analysis havebeen conservatively defined and are known to be biased against somevariable classes. This preliminary study includes only 5.6% of the totalROTSE-I sky coverage, suggesting that the full ROTSE-I variable catalogwill include more than 32,000 periodic variable stars.
| Photoelectric Minima of Selected Eclipsing Binaries and Maxima of Pulsating Stars
Not Available
| The absolute magnitudes of RR Lyraes from HIPPARCOS parallaxes and proper motions
We have used HIPPARCOS proper motions and the method of StatisticalParallax to estimate the absolute magnitude of RR Lyrae stars. Inaddition we used the HIPPARCOS parallax of RR Lyrae itself to determineit's absolute magnitude. These two results are in excellent agreementwith each other and give a zero-point for the RR Lyrae M_v,[Fe/H]relation of 0.77+/-0.15 at [Fe/H]=-1.53. This zero-point is in goodagreement with that obtained recently by several groups usingBaade-Wesselink methods which, averaged over the results from thedifferent groups, gives M_v = 0.73+/-0.14 at [Fe/H]=-1.53. Taking theHIPPARCOS based zero-point and a value of 0.18+/-0.03 for the slope ofthe M_v,[Fe/H] relation from the literature we find firstly, thedistance modulus of the LMC is 18.26+/-0.15 and secondly, the mean ageof the Globular Clusters is 17.4+/-3.0 GYrs. These values are comparedwith recent estimates based on other "standard candles" that have alsobeen calibrated with HIPPARCOS data. It is clear that, in addition toastrophysical problems, there are also problems in the application ofHIPPARCOS data that are not yet fully understood. Table 1, whichcontains the basic data for the RR Lyraes, is available only at CDS. Itmay be retrieved via anonymous FTP at cdsarc.u-strasbg.fr (130.79.128.5)or via the Web at http://cdsweb.u-strasbg.fr/Abstract.html
| Early evolution of the Galactic halo revealed from Hipparcos observations of metal-poor stars
The kinematics of 122 red giant and 124 RR Lyrae stars in the solarneighborhood are studied using accurate measurements of their propermotions obtained by the Hipparcos astrometry satellite, combined withtheir published photometric distances, metal abundances, and radialvelocities. A majority of these sample stars have metal abundances of(Fe/H) = -1 or less and thus represent the old stellar populations inthe Galaxy. The halo component, with (Fe/H) = -1.6 or less, ischaracterized by a lack of systemic rotation and a radially elongatedvelocity ellipsoid. About 16 percent of such metal-poor stars have loworbital eccentricities, and we see no evidence of a correlation between(Fe/H) and e. Based on the model for the e-distribution of orbits, weshow that this fraction of low-e stars for (Fe/H) = -1.6 or less isexplained by the halo component alone, without introducing the extradisk component claimed by recent workers. This is also supported by theabsence of a significant change in the e-distribution with height fromthe Galactic plane. In the intermediate-metallicity range, we find thatstars with disklike kinematics have only modest effects on thedistributions of rotational velocities and e for the sample at absolutevalue of z less than 1 kpc. This disk component appears to constituteonly 10 percent for (Fe/H) between -1.6 and -1 and 20 percent for (Fe/H)between -1.4 and -1.
| Radial velocities and iron abundances of field RR Lyraes. I.
We present systemic velocities and iron abundances for 56 RR Lyraes, themajority of which have been observed by the HIPPARCOS satellite.Comparison between our systemic velocities and previous valuesidentifies several binary candidates only one of which, TU UMa, waspreviously suspected of being a binary. However, spectra of the unusualRR Lyrae BB Vir show no evidence of line doubling and hence do notsupport the recent claims that this star may have a Blue HorizontalBranch companion. Comparison between our abundances and previousdeterminations shows reasonable agreement except with the recent work of\cite[Layden (1994)]{Lay94} where we find systematic differences.Several of the stars included on the HIPPARCOS observing list as RRLyraes are shown to be mis-classified. Of particular interest are thestars V363 Cas and AT And which, by analogy with XZ Cet, may beanomalous Cepheids. The Appendix is available in electronic form at theCDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/Abstract.html
| Photometry of the RR Lyrae Variable U Comae
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1996AJ....112.2142H&db_key=AST
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