Delta Scuti, SX Phoenicis, and RR Lyrae Stars in Galaxies and Globular Clusters
The distances to four galaxies and two globular clusters which arederived with the aid of period-luminosity and period-color relations of? Scuti and SX Phe stars are compared to the distances derived byother methods, in particular RR Lyrae stars. We examine the luminositiesof horizontal branch or RR Lyrae stars in Oosterhoff I and II globularclusters. Observational data from a variety of sources indicate adiscontinuous jump of ~0.2 mag in the luminosities of RR Lyrae variablesat [Fe/H] ? -1.5 as we transition from Oosterhoff I to Oosterhoff IIclusters. If Oosterhoff I clusters have RR Lyrae variables with averageM V values of M V = 0.53 mag at [Fe/H] = -1.5, itimplies that RR Lyrae stars in Oosterhoff II clusters average MV values are ~0.34 mag. Unlike the Oosterhoff I clusterswhich show an increase in the V luminosity of RR Lyrae stars as [Fe/H]becomes smaller, little or no change in the V luminosity of RR Lyraevariables is evident in Oosterhoff II clusters in the interval of [Fe/H]from -1.5 to -2.2. We find distance moduli found with RR Lyrae variablesagree to <=0.04 mag with those found with the ? Scuti and/or SXPhe variables if the M V values of RR Lyrae stars above areadopted. We find evidence of recent star formation (presence of nearsolar-metallicity ? Scuti stars with ages of 150 Myr to 1 Gyr) inthe Large Magellanic Cloud (LMC), Small Magellanic Cloud, and thecentral region of the Fornax (dSph) galaxies. We also find an olderpopulation of metal-poor ? Scuti variables (SX Phe stars) in theLMC and Fornax galaxies. The Carina dSph is unique in that only an oldpopulation of metal-poor ? Scuti variables is evident. No evidenceof recent ? Scuti star formation is found. The minimum periodsobserved for the SX Phe variables (blue stragglers) in the globularclusters M55 and ? Cen indicate that they could have been formedin a burst of metal-poor single star formation in the last 2.9-6 Gyr. Ifformed by the more acceptable scenario of stellar mergers, it is likelythat the merged remnant resembles a normal star in a relatively advancedstage of main-sequence evolution with an enriched He core and ordinaryHe envelope. We present equations to calculate intrinsic-color indicesfor ? Scuti, SX Phe, and RR Lyrae stars at mean light. Finally, weshow that the fundamental-radial-pulsating stars (? Sct and SX Phevariables) have larger average light amplitudes than the first-overtonepulsating variables. The fundamental metal-poor variables (SX Phe stars)have the largest average and individual amplitudes.
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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.
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BAV-Results of observations - Photoelectric minima of selected eclipsing binaries and maxima of pulsating stars.
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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.
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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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Photoelectric Minima of Selected Eclipsing Binaries and Maxima of Pulsating Stars
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Variable Stars in the Field of NGC 6882/6885: The Case of V381 Vulpeculae and V382 Vulpeculae
We present photometric and spectroscopic results for two reportedδ Scuti stars in the field of NGC 6882/6885. We find that V381 Vulhas a period of 0.1185 days and is a δ Scuti variable, aspreviously reported. The spectra of V382 Vul shows it to be a B3 starand therefore not a δ Scuti. All evidence points to V382 Vul beinga β Cephei star with a period of 0.1808 days. Additionally, wereport five new variables and eight suspected variable stars. Of thefive new variables, two are pulsators and three are eclipsing binarysystems. In our search for new variable stars, we use a ``robust medianstatistic'' that is proven to be better at finding low-amplitudevariables than the traditional error curve approach.
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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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The Monoperiodic δ Scuti Star UY Camelopardalis: An Analog to SX Phoenicis and RR Lyrae Variables
We present the results of a 4 year photometric study of thehigh-amplitude δ Scuti (HADS) star UY Camelopardalis. Analysis ofthe available data from 1985 to 2003 shows that UY Cam is monoperiodic.Fourier solutions for individual data sets do not reveal period changesin the star. Although forced parabolic fits to the O-C residualsindicate a measurable period change, the distribution of the data pointsin the O-C diagram and the deviations between fits and observationssuggest that the existence of the period change still has not beenestablished. We demonstrate the presence of amplitude variations fromcycle to cycle and on longer timescales. The pulsation amplitude seemedto change from 1985 to the 2000s, but it remained constant in 2000-2003.UY Cam is located in the upper portion of the δ Scuti instabilityregion. Its photometric properties and estimated physical parametersreveal that UY Cam is an interesting object in terms of its poormetallicity, long period, high luminosity, low surface gravity, andlarge radius among the HADS stars. UY Cam could be a younger (0.7+/-0.1Gyr) Population I HADS star with low metal abundance (Z=0.004) evolvingon its post-main-sequence shell hydrogen burning evolutionary phase. UYCam intervenes among the Population I/II HADS and type c RR Lyraevariables. These characteristics suggest the star to be an analog ofHADS, SX Phoenicis, and RRc variables.
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On the Red Edge of the δ Scuti Instability Strip
The δ Scuti star catalogue is used to derive the observationallocations of such stars on the HR diagram. The theoretical andobservational instability strips are compared to check the theoreticalred edge obtained by considering non-local time-dependent convectiontheory. The observational instability strip almost overlaps with thetheoretical one, but the observed blue and red envelopes are hotter thanthe theoretical edges. The distribution of δ Scuti stars in thepulsation strip is not uniform.
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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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Photoelectric Minima of Selected Eclipsing Binaries and Maxima of Pulsating Stars
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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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Determination of physical parameters of five large amplitude delta Scuti stars
uvby-beta photometry of the large amplitude delta Scuti stars BP Peg, DYPeg, DY Her, CY Aqr and YZ Boo is presented. Since the data wereobtained almost simultaneously in all filters, meaningful physicalparameters have been derived for each star along their pulsation cyclesusing the calibrations from \cite[Nissen (1988)]{nis88} for A and Fstars to determine the reddening and derive the unreddened photometricvalues. The utilization of the theoretical grids of \cite[Relyea &Kurucz (1978)]{rel78} has allowed temperature and gravity values to bedetermined. A comparison with previously reported values is presented.
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Photoelectric Minima of Selected Eclipsing Binaries and Maxima of Pulsating Stars
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Mode identification and asteroseismology of delta Scuti stars
The use of multicolour photometry for mode identification in pulsatingstars is discussed. We present a new, statistically based, algorithm forfinding the best estimate of the spherical harmonic degree, and aconfidence level from which the uniqueness can be ascertained. Themethod is applied to some well-observed delta Sct stars with multicolourphotometry. We also propose an algorithm to deduce the effectivetemperature, luminosity and equatorial velocity from the observedfrequencies. We find that fixing the modes of at least some frequenciesis essential for a unique solution. The method is applied to a subset ofthe delta Sct stars which have a suitable number of frequencies and modeidentifications.
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CCD Photometry of the High-Amplitude delta Scuti Stars V798 Cygni and V831 Tauri
New CCD measurements of the two high-amplitude delta Scuti stars V798Cyg and V831 Tau were carried out. The double-mode pulsation of V798 Cygis demonstrated beyond any doubt. The f_1/f_2 ratio of 0.800 isconfirmed to be related to the unusual shape of the f_1 light curve. Theproperties of the Fourier parameters were revisited also by consideringthe new light curve of V831 Tau. In particular, the classicaldouble-mode pulsators cannot fill the gap in the R_21 distribution. Twonew variable stars were discovered in the field of V798 Cyg.
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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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Luminosities of SX Phoenicis, Large-Amplitude Delta Scuti, and RR Lyrae Stars
Strömgren _uvbyβ photometry of SX Phoenicis andlarge-amplitude δ Scuti variables is analyzed to determine themean temperatures, metal abundances, and surface gravities of the stars.The mean temperatures and fundamental periods are used in conjunctionwith the pulsation equation and stellar models to derive masses, radii,surface gravities, and M_bol of the variables. The stars exhibit aperiod-luminosity relation. With the aid of Hipparcos trigonometricparallaxes the zero-point of the M_v, p is set. We find M_v = -3.725 logP - 1.933. This P-L relation is utilized to find the M-v values of RRLyrae stars or horizontal-branch stars in globular clusters and theCarina galaxy-objects that contain both SX Phe, and RR Lyrae variables,or horizontal-branch stars. The M_v values of the metal-poor RR Lyraestars are found to be consistent with M_v [Fe/H] calibrations derived bySandage (1993) and by McNamara (1997) from revised Baade- Wesselink M_vvalues. At [Fe/H] = -1.9 M_v is 0.42. Feast and Catchpole (1997)suggestion that M_v = 0.25 at [Fe/H] = -1.9 for RR Lyrae is discussed.This M_v value is too luminous because it makes the (T_eff) of RR Lyraestoo high-well off any (T_eff) = _f (color index) calibration. (SECTION:Stars)
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Fourier Decomposition of the Light Curves of Three Dwarf Cepheids: CY Aquarii, XX Cygni, and V798 Cygni
The three dwarf Cepheid variable stars CY Aquarii, XX Cygni, and V798Cygni were examined with CCD time series ensemble photometry. TheFourier decomposition of the light curves showed no evidence that any ofthe three stars was a double-mode variable. CY Aqr was fit with a nineterm harmonic series with a residual error of 10 mmag. XX Cyg was fitwith a ten term harmonic series with a residual error of 10 mmag. V798Cyg was fit with a four term harmonic series with a residual error of 7mmag. In addition, we examined a set of double-mode dwarf Cepheids withthe same Fourier decomposition techniques. We present evidence thatthese double-mode dwarf Cepheids fill the gap in the amplitude ratiodistribution reported by Antonello et al.(1986) and Poretti et al.(1990.(SECTION: Stars)
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Time-Series Ensemble Photometry of SX Phoenicis Stars. I. BL Camelopardalis
We present an analysis of the multiperiodic SX Phoenicis star BLCamelopardalis (GD 428). Along with 24 times of maximum light fromarchival data, six previously unpublished times of maximum light fromphotomultiplier observations and 39 new CCD observations of maximumlight are reported. The new CCD observations indicate that BL Cam is adouble-mode variable with a primary period of 0.0391 day, a secondaryperiod of 0.0306 day, and a $\pi1$/ $\pi0$ ratioof 0.783. The relation between metallicity and period ratio for largeamplitude $\delta$ Scuti variables is examined in detail. Finally,evidence is presented that the fundamental period $\pi0$ hasincreased by 0.009 seconds in the last 20 years. (SECTION: Stars)
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Photoelectric Minima and Maxima of Selected Eclipsing and Pulsating Variables
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Pulsation models of δ Scuti variables. I. The high-amplitude double-mode stars.
The relations between high-amplitude δ Scuti stars and the muchmore abundant low-amplitude δ Sct variables are not clear. Bothgroups have similar periods and seem to have almost the same basicphysical properties, although their light-curve characteristics are verydifferent. In the last few years much improved observational data havebeen published, and improved theoretical physics - in particular the newOPAL/OP opacities - now allows much more accurate calculations oftheoretical evolution models including the normal-mode pulsationfrequencies. We here use new series of stellar envelope models to givecalibrations of the first overtone-to-fundamental mode and thesecond-to-first overtone period ratios in terms of the primary modelparameters: metal content and mass-luminosity relation. Effects of thesecondary model parameters: hydrogen content, position within theinstability strip and assumed efficiency of convection are also studiedin detail, and shown to be small. These results combined with pulsationanalysis of new stellar evolution models are applied to discuss theavailable information for double-mode high-amplitude δ Sct stars.We conclude that observed period ratios and positions in the HR-diagramare in agreement with the assumption that these variables are normalstars following standard evolution. Observational data for SX Phoenicisand AI Velorum are compared with theoretical evolution sequences. It isshown that the photometry and the observed two periods of SX Pheconstrain the metal content to Z=0.001, the mass to 1.0 solar masses andthe bolometric magnitude to about 2.70mag. The inferred distance of SXPhe gives a parallax of 0.012+/-0.002arcsec compared with that of theHIPPARCOS Input Catalogue of 0.023+/-0.008arcsec. For AI Vel theavailable photometry and the two primary observed periods do not providea unique solution. Models based on OPAL opacities allow Z=0.01-0.02 withcorresponding masses 1.6-2.0 solar masses. This can be understood by thecompensating effects from Z and the mass-luminosity relation in thecalibration of the period ratio. It is suggested that the surprisinglynarrow interval in the first overtone-to-fundamental mode period ratioobserved in the double-mode δ Sct stars may be due to thesecompensating effects. Attempting to fit low-amplitude modes observed inAI Vel in addition to the primary oscillations, it is concluded that thepresent models cannot explain these oscillations in terms of radialmodes. The little understood relations between high- and low-amplitudeδ Sct stars are briefly discussed, and the problem of modeidentification is emphasized.
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Pulsation in high amplitude delta Scuti stars.
It has been pointed out by earlier authors that radial pulsation seemsto be the only type present in high amplitude δ Sct stars, atleast for monoperiodic stars. In order to confirm this or not, we havecollected all the multicolor data available for these stars in theStroemgren and Johnson photometric systems. Then, the type of pulsationhas been analysed on the basis of the phase shifts and amplitude ratiosbetween observed light and colour variations. The results indicate thatall the stars analysed, including both high amplitude δ Sct(Population I) and SX Phe (Population II) stars, are radial pulsators.This is also true for the monoperiodic medium amplitude δ Sctstars analysed.
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A catalogue of variable stars in the lower instability strip.
Identifications, positions, photometry, spectra, some pulsationalfeatures, other astrophysical parameters and literature for 302pulsating variable stars in the lower instability strip, near the ZAMS,are given. About 185 stars have near homogeneous photometric informationin the Stroemgren's uvby-β photometric system. Thiscatalogue/database covers information published until November 1993.
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