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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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| 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.
| δ Scuti-type nature of the high-amplitude variable star GSC4619-450
We present the results of spectroscopy and B, V CCD photometry carriedout from 2003 to 2005 of GSC4619-450, a high-amplitude pulsatingvariable discovered by Zhang et al., [Zhang, X.B., Deng, L., Zhou, X.,Xin, Y., 2004. MNRAS, 355, 1369]. From this study, the star isclassified as a high-amplitude δ Scuti star. A Fourier analysisbased on the B and V photometric data indicates that GSC 4619-450 is amono-periodic radial pulsator, with a period of 0.13341195 days. From ashort time line we find that the pulsating period of this star isincreasing rapidly with a rate of 9.1 × 10‑2s/yr, and is thus suggested to be highly evolved and undergoing rapidevolving at the present time. A spectral type of F0 is assigned to thevariable considering the results from both the spectroscopy andphotometry.
| Times of Maxima for Selected Delta Scuti Stars
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| New galactic open cluster candidates from DSS and 2MASS imagery
An inspection of the DSS and 2MASS images of selected Milky Way regionshas led to the discovery of 66 stellar groupings whose morphologies,color-magnitude diagrams, and stellar density distributions suggest thatthese objects are possible open clusters that do not yet appear to belisted in any catalogue. For 24 of these groupings, which we consider tobe the most likely to be candidates, we provide extensive descriptionson the basis of 2MASS photometry and their visual impression on DSS and2MASS. Of these cluster candidates, 9 have fundamental parametersdetermined by fitting the color-magnitude diagrams with solarmetallicity Padova isochrones. An additional 10 cluster candidates havedistance moduli and reddenings derived from K magnitudes and (J-K) colorindices of helium-burning red clump stars. As an addendum, we alsoprovide a list of a number of apparently unknown galactic andextragalactic objects that were also discovered during the survey.
| Pulsational behaviour of the SX Phe variable BL Cam.
The pulsational behaviour of the field high-amplitude SX Phe variable BLCam is investigated here on the basis of new photometric data collectedduring the last few years at different sites together with a revision ofall the available photometric data sets in the literature. Our resultsconfirm the existence of multiperiodicity in this star previously foundby other authors. In addition to the main frequency f_0=25.5769 c/d andits harmonics 2f_0 and 3f_0, with stable amplitude, a secondaryfrequency f_1 exists in the region 31-32 c/d with variable amplitude.Microvariability takes also place in this star, in the region close tof_0, with some additional secondary peaks shown as significant togetherwith some frequency combinations of these modes with f_0.Concerning f_1,it is shown that there is a possibility of the existence of twoindependent peaks (around 31.6 c/d and 32.6 c/d), nonradial and withvariable amplitudes.
| uvby-beta photometry of the RR Lyrae star AC And .
In the present paper we determine the true nature of AC And an RR Lyraeor delta Scuti star and its physical parameters from multi-colorphotometry.
| uvby-β Photometry of the RR Lyrae Star AC And
Strömgren uvby-β and differential V photoelectric photometryof the variable star AC And is presented. Analysis of this data, as wellas data from the literature, corroborates the periods proposed by Fitch& Szeidl (1976). Strömgren photometry has been used for thedetermination of the reddening and the physical parameters log g and logTe, as well as the metallicity [Fe/H]. The determination ofMv is also discussed and, in view of the results, we proposethat AC And is an RR Lyrae star with possible anomalous chemicalcomposition.
| Photoelectric Minima of Selected Eclipsing Binaries and Maxima of Pulsating Stars
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| Beobachtungssergebnisse Bundesdeutsche Arbeitsgemeinschaft fuer Veraenderliche Sterne e.V.
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| Period Changes in the SX Phoenicis Star DY Pegasi
We report 69 new times of maximum light for the SX Phoenicis star DYPegasi. Combining these new times with previous published maxima, wefound the data to be well modeled with a triple linear fit. However, wealso determined a refined constant period change of-6.00×10-12 days day-1. From bothspectroscopic and photometric measurements, we determined-0.8<[Fe/H]<-0.6. Using phase-averaged indices, we found=7660 and =3.89. From evolutionarymodels, a mass of M=1.5 Msolar and an age of 1.7 Gyr weredetermined.
| Photoelectric Maxima of Selected Pulsating Stars
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| Asteroseismology of HADS stars: V974 Oph, a radial pulsator flavoured by nonradial components
The analysis of a dense time-series on V974 Oph disclosed the richpulsational content (at least five independent terms) of thishigh-amplitude (0.60 mag in B-light) delta Scts star. A mode with afrequency very close to the main one (probably the fundamental radialmode) has been detected: such a doublet is not a common feature in starsof the same class. Also another term can be considered a radial one, butthe high ratio (0.786) raises some problems that can be solved only byadmitting very low metallicity. It is quite evident that someundetectable terms are again hidden in the noise, as the least-squaresfit leaves a rms residual much higher than the observational noise. Allthat considered, nonradial modes seem to play a key rôle in thelight variability of V974 Oph. Revealing an unsuspected asteroseismicinterest, V974 Oph provides a link between low- and high-amplitude deltaScts stars.Based on observations collected at Europan Southern Observatory, LaSilla, Chile
| 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.
| 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.
| 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.
| 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.
| 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.
| Photoelectric Minima of Selected Eclipsing Binaries and Maxima of Pulsating Stars
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| 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.
| Structural Parameters of DY Pegasi Light Curves between 1949-1986
Structural change of DY Pegasi light curve shape are being studied usingboth traditional and Fourier-type structural parameters. In order toperform this investigation we applied the Fourier decompositiontechnique to each considered data set. The values of the above mentionedstructural parameters were then calculated.
| 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 Changes in the SX Phoenicis Stars. part I. BL Camelopardalis and DY Pegasi
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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
| Times of Extrema of Selected Eclipsing Binaries and two SX Phe Stars
On the basis of new CCD observations we present heliocentric times ofminima for 6 eclipsing binaries and heliocentric times of extrema forthe Delta Scuti stars DY Peg and BL Cam.
| 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.
| Stability in the Light Curves of High-Amplitude delta Scuti Stars: Selected Monoperiodic Stars
We have analyzed all the reliable photometric data sets available in thebibliography for a selected sample of monoperiodic high-amplitude deltaScuti stars in order to study the stability of their light curves. Atotal of 169 data sets and more than 22,000 points have been consideredfor seven stars: ZZ Mic, EH Lib, BE Lyn, YZ Boo, SZ Lyn, AD CMi, and DYHer. The results do not reveal significant long-term changes ofamplitude of the light curves for any of these stars.
| Photoelectric Minima of Selected Eclipsing Binaries and Maxima of Pulsating Stars
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| Takýmyýldýz: | Kanatli At |
| Sað Açýklýk: | 23h08m51.18s |
| Yükselim: | +17°12'55.9" |
| Görünürdeki Parlaklýk: | 10.353 |
| özdevim Sað Açýklýk: | 46 |
| özdevim Yükselim: | -23.6 |
| B-T magnitude: | 10.614 |
| V-T magnitude: | 10.375 |
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