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.
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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.
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BAV-Results of Observations - Photoelectric minima of selected eclipsing binaries and maxima of pulsating stars.
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Recent Maxima of 64 Short Period Pulsating Stars
This paper contains times of maxima for 64 short period pulsating stars(primarily RR Lyrae and d Scuti stars). This represents a portion of theCCD observations received by the AAVSO Short Period Pulsator (SPP)section through December 2009.
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BAV-Results of Observations - Photoelectric Minima of Selected Eclipsing Binaries and Maxima of Pulsating Stars
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Das BAV-programm der Delta-Scuti-Veraenderlichen - teil 1.
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BAV-Results of observations - Photoelectric Minima of Selected Eclipsing Binaries and Maxima of Pulsating Stars
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The beat-curve approach applied to AE UMa
An approach sometimes used to determine the dominant period of adoublemode pulsating star with strong beats in its light curve is tofind (O-C) for an observing season by averaging the individual valuesobtained from observed times of maximum light. The long-term graph of(O-C) versus time can then be used to determine the period and its rateof change. Methods of determining the secondary period usually involveFourier analysis of relatively complete sets of photometric data. Weshow that the beat-curve method, e.g., Elst (1973), Coates et al. (1979,1982) is an alternative approach also worth considering. The offset ofthe beat curve usually yields a more precise value of (O-C) for a seasonthan a simple average does, the phase of the beat curve leads to anestimate of the secondary period without the need for intensivephotometry, and the amplitude of the beat curve provides informationabout the relative amplitudes of the modes of oscillation of the star.
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Photoelectric Minima of Selected Eclipsing Binaries and Maxima of Pulsating Stars
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Photoelectric Minima of Selected Eclipsing Binaries and Maxima of Pulsating Stars
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Photoelectric Minima of Selected Eclipsing Binaries and Maxima of Pulsating Stars
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Times of Maxima for Selected Delta Scuti Stars
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New Times of Minima of Eclipsing Binary Systems and of Maximum of SXPHE Type Stars
We present 64 photoelectric minima observations of 31 eclipsingbinaries. We also report three new times of maxima of three SXPHE typepulsating stars.
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Photoelectric Minima of Selected Eclipsing Binaries and Maxima of Pulsating Stars
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The double-mode nature of the HADS star GSC 00144-03031 and the Petersen diagram of the class
The double-mode pulsation of GSC 00144-03031 has been detected whensearching for COROT targets. A very large dataset composed of 4722photometric measurements was collected at six observatories in Europeand America. There is no hint of the excitation of additional modes(down to 0.6 mmag) and therefore GSC 00144-03031 seems to be a puredouble-mode pulsator, with a very short fundamental radial mode (P = 84min). From uvbyβ photometry and evolutionary tracks it appears tobe a Pop. I star with M = 1.75 Mȯ, located in the middleof the instability strip, close to the Zero-Age Main Sequence. We alsodiscovered other new double-mode pulsators in the databases oflarge-scale projects: OGLE BW2_V142, OGLE BW1_V207, ASAS3 094303-1707.3,ASAS3 000116-6037.0, NSVS 3234596 and NSVS 3324715. An observationalPetersen diagram is presented and explained by means of new models. Acommon sequence connecting Pop. I stars from the shortest to the longestperiods is proposed and the spreads in the period ratios are ascribed todifferent metallicities (at the shortest periods) and to differentmasses (at the longest ones).
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Photoelectric Minima of Selected Eclipsing Binaries and Maxima of Pulsating Stars
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Photoelectric Maxima of Selected Pulsating Stars
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Long term behaviour of the double-mode high-amplitude delta Scuti star RV Arietis
Stability of both the fundamental and first overtone oscillations of RVAri was investigated by different methods which led to concordantresults. The fundamental period of RV Ari has been decreasing veryslowly with a rate of (1/P0)(dP0/dt)=-0.6x10-8 y-1 while the first overtone period has beenincreasing a little faster with a rate of(1/P1)(dP1/dt) =+0.9x 10-8y-1, if we assume linear period changes over the past 65years. Although the very slow change in the periods is consistent withthe evolutionary theories, the fact that the signs of the period changesfor the two modes are opposite indicates that the dominating part of theperiod variation may be the result of non-evolutionary effects. Theamplitudes of the fundamental and overtone oscillations have undergonesmall changes (several mmag) on a time scale of years, and a slightincrease in the amplitude of the first overtone pulsation is suspected.An additional frequency at f2=13.6116 cd-1 isfound. Table 2 is only available in electronic form at\http://www.edpsciences.org
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δ Scuti stars and their related objects
δ Scuti stars are a group of stars located on or a little abovethe main sequence of H-R diagram with spectral type from A3 to F5. Theyare low amplitude single or multi period pulsators with period shorterthan 0.3 d. Within the same area there are several groups of variablesor special stars correlated with them, e.g., Dwarf Cepheids, γ Dorvariables, Blue Stragglers, Am stars, Ap stars, ROAp variables, λBoo variables and δ Del variables. In this paper a general reviewin this field, including the number of new variables discovered after1995, is presented. The most reliable period variation rates for all thehigh amplitude variables and several low amplitude variables are listed.Statistic shows the higher the rotation rate v sin i is, the lower thelight variation amplitude is. Thus within young open clusters highamplitude variables cannot be found. The amplitudes-periods distributionhave 3 peaks with the highest of 1.0 mag in V at 0.17 d in period. Forδ Scuti variables in stellar systems the shorter the averageperiod is, the lower the metallicity and the older the age of thestellar system are.
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Photometry of δ Sct-type and Related Stars: Results of AD Ari, IP Vir and YZ Boo
Photometric results of three δ Scuti stars, AD Ari, IP Vir and YZBoo from new observations obtained at the Xinglong Station of theBeijing Astronomical Observatory (BAO) during 2000 and 2001 arereported. We present here the preliminary analyses. Detailed studies ofthese stars based on additional data will be published separately.
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Veroffentlichungen der Konkoly-Sternwarte an die BAV.
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The small period change of the Delta Scuti star AE UMa
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Period and amplitude variations in the high-amplitude delta Scuti star AE Ursae Majoris
We present a comprehensive investigation of the variations of period andamplitude in the high-amplitude delta Scuti star AE UMa based on our newJohnson V time-series measurements and the existing data. No additionalfrequencies were detected even though all the available data sets from1974 to 2001 were analysed. The light variations of AE UMa can bewell-reproduced with the fundamental and first-overtone radial modes andtheir coupled terms. New observations and analyses support the mostrecent results of Pócs & Szeidl (\cite{pocs}). Thefundamental period was essentially constant over the past 27 years withits standard value of 0fd 086017066 (f_0= 11.625600 cd-1),while the first overtone period decreased at a rate of(1)/(P_1)(dP_1)/(dt) = -4.3x 10-8 yr-1. Theamplitude variations in the two modes of AE UMa are detected at themilli-magnitude level on a time-scale of years. It seems that theamplitudes vary in opposite phases, implying an energy conservation orsome kind of intrinsic variability cause. We deny theover-interpretation of the period change given by Hintz et al.(\cite{hintz97}) and explore its reason. Figure~\ref{Fig:lightcurve} isonly available in electronic form at http://www.edpsciences.org
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Linear Nonadiabatic Properties of SX Phoenicis Variables
We present a detailed linear, nonadiabatic pulsational scenario foroscillating blue stragglers (BSs)/SX Phe variables in Galactic globularclusters (GGCs) and in Local Group (LG) dwarf galaxies. The sequences ofmodels were constructed by adopting a wide range of input parameters andproperly cover the region of the H-R diagram in which these objects areexpected to be pulsationally unstable. Current calculations togetherwith more metal-rich models already presented by Gilliland et al.suggest that the pulsation properties of SX Phe variables are partiallyaffected by metal content. In fact, the pulsation periods for the firstthree modes are marginally affected when moving from Z=0.0001 to 0.006,whereas the hot edges of the instability region move toward coolereffective temperatures by approximately 300-500 K. The inclusion of ametallicity term in the period-luminosity-color (P-L-C) relations causesa substantial decrease in the intrinsic scatter and in the individualerror of the coefficients. This supports the result recently brought outby Petersen & Christensen-Dalsgaard for δ Scuti stars.Moreover, we find that the discrepancy between our relation and similartheoretical and empirical relations available in the literature istypically smaller than 5%. The comparison between theory andobservations in the MV-logP plane as well as in theluminosity amplitude-logP plane does not help to disentangle thelong-standing problem of mode identification among SX Phe stars.However, our calculations suggest that the secular period change seemsto be a good observable to identify the pulsation mode of cooler SX Phevariables. Together with the previous models we also constructed newsequences of models by adopting selected effective temperatures andluminosities along two evolutionary tracks characterized by the samemass value and metal content (M/Msolar=1.2, Z=0.001) butdifferent He contents in the envelope, namely, Y=0.23 and 0.30. The Hecontent in the latter track was artificially enhanced soon after thecentral H exhaustion to mimic, with a crude approximation, thecollisional merging between two stars. Interestingly enough, we findthat the He-enhanced models present an increase in the pulsation periodand a decrease in the total kinetic energy of the order of 20% whencompared with the canonical ones. At the same time, the blue edge of thefundamental mode for the He-enhanced models is approximately 1000 Kcooler than for canonical ones. Moreover, we find that the secularperiod change for He-enhanced models is approximately a factor of 2larger than for canonical ones. According to this evidence, we suggestthat the pulsation properties of SX Phe variables can be soundly adoptedto constrain the evolutionary history of BSs and in turn to single outthe physical mechanisms that trigger their formation.
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Times of Maximum Light for AE Ursae Maioris
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Stability of pulsation of the double-mode high-amplitude delta Scuti star AE Ursae Majoris
Stability of both the fundamental and first overtone oscillations of AEUMa was investigated by different methods which led to concordantresults. The fundamental period of AE UMa has been essentially constantin the past 60 years consistent with the theoretical expectation (Breger& Pamyatnykh \cite{BP98}). The reported fast period decrease (Hintzet al. \cite{HHJ97}) is shown to be incorrect. The constancy of thefundamental period suggests that the star is in the post-main sequenceevolutionary state as suggested by the evolutionary theories. The firstovertone period is decreasing with a rate of (1/P_1) (dP_1/dt)=-7.310-8 y-1. The fact that the rate of period changefor two modes is quite different indicates that non-evolutionary effectsmay also generate period changes. The changes in amplitude of thefundamental and first overtone were examined by comparing theleast-squares amplitude solution for different segments of observations.Small long-term variations in the amplitudes have occurred in the past25 years.
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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.
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A revised catalogue of delta Sct stars
An extensive and up-dated list of delta Sct stars is presented here.More than 500 papers, published during the last few years, have beenrevised and 341 new variables have been added to our last list, sixyears ago. This catalogue is intended to be a comprehensive review onthe observational characteristics of all the delta Sct stars known untilnow, including stars contained in earlier catalogues together with othernew discovered variables, covering information published until January2000. In summary, 636 variables, 1149 references and 182 individualnotes are presented in this new list. Tables 1 and 2 will be accessibleonly in electronic form at the CDS via anonymous ftp tocdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/Abstract.html
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UBVRI photometry of AE Ursae Maioris at Konkoly Observatory (1974-1998).
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Photoelectric Minima of Selected Eclipsing Binaries and Maxima of Pulsating Stars
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INHABITED SKY
