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Photoelectric Minima of Selected Eclipsing Binaries and Maxima of Pulsating Stars
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| Asteroseismology of the new multiperiodic γ Dor variable HD 239276
The variability of HD 239276 was suspected photometrically nearly twentyyears ago, but was confirmed with new observations obtained in 2001during a two-site photometric campaign carried out from Spain, inuvbyβ Strömgren-Crawford photometry, and China, using theJohnson V filter. Two low-dispersion spectra were also collected. Theresults establish this star as a new multiperiodic γ Dor-typepulsator with deficiency in metallicity. Its possible λ Boonature is discussed. The frequency analysis shows three pulsationalfrequencies as significant, but some more are probably present among theresiduals. The method based on phase shifts and amplitude ratios inmulticolour photometry is used to identify the excited modes withnon-adiabatic time-dependent convection models. A very good agreementbetween the theoretical and observed amplitude ratios is obtained andthe two main modes are identified as l=1 modes. Nevertheless, ourresults do not allow us to discriminate between a solar abundance and ametal deficient nature for this star. The frequency ratio method isfurther used for the identification of the modes. The results suggestlow metallicity for this star, but a λ Boo nature may be notruled out.
| A comprehensive study of the SX Phoenicis star BL Camelopardalis
Context.BL Cam is an extreme field multiperiodic short-periodlow-metallicity high-amplitude SX Phe-type variable where its probablycomplex pulsational content is subject of controversies. Aims.Acomprehensive study has been carried out to investigate the nature andpulsational properties of this object. Methods.The analysis isbased on new photometric data collected during the last few years atdifferent sites, as well as on all available previously published data.Frequency analyses have been performed on a number of reliable data setsto analyse the pulsational content. In addition, the classical O-Cmethod was used to study the behaviour of the main period. Results.Our frequency analysis confirms some aspects on themultiperiodicity of BL Cam, previously found by other authors, showing anumber of secondary modes close to the main frequency f_0=25.5769cd-1. The secondary modes present eventual amplitudevariations. However, the main frequency exhibits no significant changesin its amplitude and seems to correspond to the fundamental mode ofradial pulsation. Abrupt changes sometimes observed in the light curvescould be due to spurious activity on or close to the star's photosphere.We confirm the existence of a secondary frequency at 31.6 or 32.6cd-1, with variable amplitude, and with the possibility ofboth frequencies being intrinsic to the star. More than one hundred ofnew times of light maxima have been determined in the present work.These together with those available in the literature allow us a morediscriminating analysis of the O-C diagram. This shows that the observedvariations of the main period can be described by two terms: (i) asecular increase of the main period at a rate ofdP/Pdt=117(±3)×10-9 yr-1; and (ii) aperturbation from a companion star in a rather eccentric orbit with aperiod of 10.5(±0.2) yr causing a light time semi-amplitude of148(±12) s.
| 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.
| 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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| Four New High Amplitude delta Scuti Stars
Four new high amplitude delta Scuti variables were found in ASAS3 surveydata.
| A photometric monitoring of bright high-amplitude delta Scuti stars. II. Period updates for seven stars
We present new photometric data for seven high-amplitude delta Scutistars. The observations were acquired between 1996 and 2002, mostly inthe Johnson photometric system. For one star (GW UMa), our observationsare the first since the discovery of its pulsational nature from theHipparcos data. The primary goal of this project was to update ourknowledge on the period variations of the target stars. For this, wehave collected all available photometric observations from theliterature and constructed decades-long O-C diagrams of the stars. Thistraditional method is useful because of the single-periodic nature ofthe light variations. Text-book examples of slow period evolution (XXCyg, DY Her, DY Peg) and cyclic period changes due to light-time effect(LITE) in a binary system (SZ Lyn) are updated with the newobservations. For YZ Boo, we find a period decrease instead of increase.The previously suggested LITE-solution of BE Lyn (Kiss &Szatmáry \cite{Kiss95}) is not supported with the new O-Cdiagram. Instead of that, we suspect the presence of transient lightcurve shape variations mimicking small period changes.
| Period Changes in SX Phoenicis Stars. II. XX Cygni
We have conducted photometric monitoring of the SX Phoenicis star XX Cygin order to study the changes in pulsation period of this object. Wehave combined 20 new times of maximum light for XX Cyg with those fromthe literature to prepare an O-C diagram for XX Cyg. The results suggestthat contrary to earlier work, XX Cyg exhibits a continuous periodincrease, rather than sudden jumps in the period. We measure the changein period of XX Cyg to be (1/P)(dP/dt)=1.13(2)×10-8yr-1. This is in reasonably good agreement with thetheoretical predictions of Rodríguez et al. of(1/P)(dP/dt)=6.2×10-8 yr-1 change expectedfrom theoretical considerations. We marginally detect a bump in thedescending portion of the light curve of XX Cyg, as reported by previousauthors.
| 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.
| 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.
| Amplitude and Period Changes in the SX Phoenicis Star XX Cygni
The new time-resolved CCD photometry of XX Cyg was presented. Weinvestigate the time-dependent behaviour of the light variations byreanalyzing the data in the literature. XX Cyg was demonstrated beyondany doubt again to be a monoperiodic pulsator. Its light curves can bewell reproduced by the sinusoids with the fundamental frequencyf0 = 7.41481 +/- 0.00001 cycle d-1 (P0= 0d. 1348652 +/- 0.0000001) and its first nineharmonics. Fourier, wavelet and O-C analyses based on all the availabledata reveals the amplitude and period variations during the years 1974to 2000. The general trend of the amplitude changes is decreasing at arate of one percent milli-magnitudes per year. The parabolic analysis onthe updated 101 times of maximum light suggests a slowly continuousincreasing at a rate of 1.3 × 10-3 days per millionyears in the period.
| 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
| 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.
| delta Scuti and related stars: Analysis of the R00 Catalogue
We present a comprehensive analysis of the properties of the pulsatingdelta Scuti and related variables based mainly on the content of therecently published catalogue by Rodríguez et al.(\cite{retal00a}, hereafter R00). In particular, the primaryobservational properties such as visual amplitude, period and visualmagnitude and the contributions from the Hipparcos, OGLE and MACHOlong-term monitoring projects are examined. The membership of thesevariables in open clusters and multiple systems is also analyzed, withspecial attention given to the delta Scuti pulsators situated ineclipsing binary systems. The location of the delta Scuti variables inthe H-R diagram is discussed on the basis of HIPPARCOS parallaxes anduvbybeta photometry. New borders of the classical instability arepresented. In particular, the properties of the delta Scuti pulsatorswith nonsolar surface abundances (SX Phe, lambda Boo, rho Pup, delta Deland classical Am stars subgroups) are examined. The Hipparcos parallaxesshow that the available photometric uvbybeta absolute magnitudecalibrations by Crawford can be applied correctly to delta Scutivariables rotating faster than v sin i ~ 100 km s{-1} withnormal spectra. It is shown that systematic deviations exist for thephotometrically determined absolute magnitudes, which correlate with vsin i and delta m1. The photometric calibrations are found tofit the lambda Boo stars, but should not be used for the group ofevolved metallic-line A stars. The related gamma Dor variables and thepre-main-sequence delta Scuti variables are also discussed. Finally, thevariables catalogued with periods longer than 0fd 25 are examined on astar-by-star basis in order to assign them to the proper delta Scuti, RRLyrae or gamma Dor class. A search for massive, long-period delta Scutistars similar to the triple-mode variable AC And is also carried out.
| 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.
| Period Variation of XX Cygni Revisited
New CCD observations are presented and the period variation of XX Cygniis discussed. Five new times of maxima were determined and the mostrecent O-C diagram was created by collecting all available epochs ofmaximum. We did not find evidence of possible period change since thatjump in 1942 described in details by Szeidl & Mahdy (1981). A newaccurate ephemeris is given.
| The Milton Bureau Revisited
Under the direction of Cecilia Payne-Gaposchkin and Sergei Gaposchkin, aprogram was subsidized by the Milton Fund of Harvard Observatory in 1937for the study of all variable stars then known to be brighter than tenthphotographic magnitude at maximum. This included some 1512 stars forwhich a grand total of 1,263,562 estimates of magnitude were made,ranging from a low of 16 (except for a few novae) to 4084 observationsper star. The sky had been divided into 54 fields, and the results ofthe measurements presented field by field in two volumes of the Annalsof Harvard Observatory. Then, in another volume, the results werediscussed in four sections, each dealing with a particular class ofvariable: 1, those of RV Tauri type; 2, the eclipsing variables; 3,Cepheids and RR Lyrae variables, and 4, the red variables, especiallyMira-type and semiregular variables.For the present paper, many of these results have been compared withmodern determinations in the 1985-87 version of the "General Catalogueof Variable Stars (GCVS)". In particular, there are numerous instancesof disagreement as to whether a star should be classified RV or SR.Although there are many instances where the Milton Bureau determinationsof types of variability differ from the types given in moderncatalogues, the reasons for the differences are generallyunderstandable.For 17 RV Tauri type stars in this survey multiple periods have now beendetermined. Many of these still deserve continued observations in orderto ascertain the constance of the periods and improve the accuracy oftheir longest reported periods.
| Photoelectric Minima of Selected Eclipsing Binaries and Maxima of Pulsating 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
| The delta Scuti Star GSC 2985-01044
GSC 2985-01044 is a delta Scuti star with a period of 0.0933584 days anda V-magnitude range of 11.85-12.05 its light curve is slightly variable.The location, space motion, and other properties of this star indicatethat it is a higher amplitude delta Scuti star (or ``dwarf Cepheid'')that is a member of the old disk population. The problem of determiningthe local space densities of the various populations of the higheramplitude delta Scuti stars is discussed.
| Period changes of delta Scuti stars and stellar evolution
Period changes of delta Scuti stars have been collected or redeterminedfrom the available observations and are compared with values computedfrom evolutionary models with and without convective core overshooting.For the radial pulsators of Pop. I, the observations indicate (1/P)dP/dt values around 10(-7) year(-1) with equal distribution betweenperiod increases and decreases. The evolutionary models, on the otherhand, predict that the vast majority should show increasing periods.This increase should be a factor of about ten times smaller thanobserved. For nonradial delta Scuti pulsators of Pop. I, thediscrepancies are even larger. The behavior suggests that for theserelatively unevolved stars the rate of evolution cannot be deduced fromthe period changes. The period changes of most Pop. II delta Scuti (SXPhe) stars are characterized by sudden jumps of the order of Delta P/P ~10(-6) . However, at least one star, BL Cam, shows a large, continuousperiod increase. The variety of observed behavior also seems to excludean evolutionary origin of the changes. Model calculations show that theevolutionary period changes of pre-MS delta Scuti stars are a factor of10 to 100 larger than those of MS stars. Detailed studies of selectedpre-MS delta Scuti stars are suggested.
| HIPPARCOS parallaxes and period-luminosity relations of high-amplitude delta Scuti stars
Hipparcos parallaxes of high-amplitude delta Scuti stars are used toderive a period-luminosity relation with a scatter of about +/-0.1 mag,which is independent from photometric calibrations to absoluteluminosities. Comparisons with several P-L relations from the literatureshow satisfactory agreement, and all deviations from the Hipparcos meanrelation can be explained by uncertainties in the data available beforeHipparcos. Hipparcos data for a few stars of relatively small anduncertain parallaxes indicate that they may have systematically very lowluminosity. However, briefly discussing Lutz-Kelker corrections andconsidering the full sample of high-amplitude delta Scuti stars, it isconcluded that this sample is homogeneous and has similar basic physicalproperties as the ``normal'' low-amplitude delta Scuti stars. It isemphasized that the Hipparcos P-L relation defines a new distance scalewhich is independent from those of the classical Cepheids and RR Lyraestars. Therefore, observations of high-amplitude delta Scuti stars canbe used to check fundamental distance determinations to e.g. globularclusters, the Galactic bulge and the Magellanic Clouds.
| 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)
| 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)
| Structural Properties of Pulsating Star Light Curves Through Fuzzy Divisive Hierarchical Clustering
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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.
| SX Phoenicis stars : light curves to go.
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| Vitesses radiales. Catalogue WEB: Wilson Evans Batten. Subtittle: Radial velocities: The Wilson-Evans-Batten catalogue.
We give a common version of the two catalogues of Mean Radial Velocitiesby Wilson (1963) and Evans (1978) to which we have added the catalogueof spectroscopic binary systems (Batten et al. 1989). For each star,when possible, we give: 1) an acronym to enter SIMBAD (Set ofIdentifications Measurements and Bibliography for Astronomical Data) ofthe CDS (Centre de Donnees Astronomiques de Strasbourg). 2) the numberHIC of the HIPPARCOS catalogue (Turon 1992). 3) the CCDM number(Catalogue des Composantes des etoiles Doubles et Multiples) byDommanget & Nys (1994). For the cluster stars, a precise study hasbeen done, on the identificator numbers. Numerous remarks point out theproblems we have had to deal with.
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