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Binarity and multiperiodicity in high-amplitude ? Scuti stars
We have carried out a photometric and spectroscopic survey of brighthigh-amplitude ? Scuti (HADS) stars. The aim was to detectbinarity and multiperiodicity (or both) in order to explore thepossibility of combining binary star astrophysics with stellaroscillations. Here, we present the first results for 10, predominantlysouthern, HADS variables. We detected the orbital motion of RS Gru witha semi-amplitude of ~6.5 kms-1 and 11.5 d period. Thecompanion is inferred to be a low-mass dwarf star in a close orbitaround RS Gru. We found multiperiodicity in RY Lep from both photometricand radial velocity data and detected orbital motion in the radialvelocities with hints of a possible period of 500-700 d. The data alsorevealed that the amplitude of the secondary frequency is variable onthe time-scale of a few years, whereas the dominant mode is stable.Radial velocities of AD CMi revealed cycle-to-cycle variations, whichmight be due to non-radial pulsations. We confirmed the multiperiodicnature of BQ Ind, while we obtained the first radial velocity curves ofZZ Mic and BE Lyn. The radial velocity curve and the O-C diagram of CYAqr are consistent with the long-period binary hypothesis. We took newtime series photometry on XX Cyg, DY Her and DY Peg, with which weupdated their O-C diagrams.
| Photometric Observations of High-Amplitude Delta Scuti Stars
271 maxima of 19 High-Amplitude Delta Scuti Stars (HADS) obtained fromCCD observations are presented. The list also includes data on eightnewly discovered HADS.
| Incidence of High-Amplitude ? Scuti-Type Variable Stars
An order-of-magnitude estimate for the incidence of high-amplitude? Scuti-type variable stars (HADS) in the ? Scuti area ofthe H-R diagram was calculated. Using a model for the stellardistribution in the Milky Way, we calculated the number of stars thatare expected to fall in the ? Scuti area of the H-R diagram withinthe magnitude range and sky coverage of the ROTSE Survey for VariablesI(RSV1). The incidence of the HADS phenomenon was then obtained bycomparing the number of stars calculated by the model with the actual,observed number of HADS in the RSV1. We find that ˜0.24% of thestars that lie in the ? Scuti area of the H-R diagram within theRSV1 observational limits exhibit the HADS phenomenon. This number ismuch lower than the incidence of low-amplitude ? Scuti stars(LADS), ? 1/3, implying that the HADS phenomenon takes place in avery small fraction of stars and/or its duration is very short, comparedto the LADS.
| Pulkovo compilation of radial velocities for 35495 stars in a common system.
Not Available
| 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
Not Available
| 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
Not Available
| Photoelectric Minima of Selected Eclipsing Binaries and Maxima of Pulsating Stars
Not Available
| Multiband photometric re-classification of ROTSE-I delta Scuti type stars
We present multi-passband CCD photometry of 20 ROTSE-I delta Scuti typepulsating stars and 1 RR Lyrae star to re-classify their variable typesusing the comparison of amplitudes between V and I passbands. For there-classification, we used a criterion that pulsating stars have largeramplitude differences between passbands than eclipsing binaries becausebrightness changes of pulsating stars are mainly due to the temperaturevariations. As a result, only six stars were re-confirmed as delta Scutivariables and thirteen stars turned out to be W UMa type eclipsingbinaries. The other two stars were identified as one cataclysmicvariable and one non-variable, respectively. Our results suggest that anumber of ROTSE-I delta Scuti type stars, which do not show typicalpulsating light curves of high amplitude delta Scuti stars, are W UMatype eclipsing binaries.Table 3 is only available in electronic form at the CDS via anonymousftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/404/621
| 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.
| Not Available
Not Available
| A photometric monitoring of bright high-amplitude delta Scuti stars. I. The double-mode pulsation of V567 Ophiuchi
We present the first results of an observational project, whichaddresses the period changing behaviour of a sample of high-amplitudedelta Scuti stars. In this paper we discuss the double-mode nature ofV567 Ophiuchi. It was observed on 15 nights in two consecutive years inorder to resolve the long-standing ambiguity related to its secondaryperiod. A frequency analysis of almost 5000 individual single-filteredCCD V measurements resulted in two independent frequencies(f1=6.6879 d-1 and f2=11.8266d-1) with a ratio of f1/f2=0.565.Earlier data taken from the literature were used to refine the dominantperiod, and the re-analysis supports the existence of the secondaryperiod. Possible asteroseismological implications are briefly discussed.
| 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.
| Catalogue of Apparent Diameters and Absolute Radii of Stars (CADARS) - Third edition - Comments and statistics
The Catalogue, available at the Centre de Données Stellaires deStrasbourg, consists of 13 573 records concerning the results obtainedfrom different methods for 7778 stars, reported in the literature. Thefollowing data are listed for each star: identifications, apparentmagnitude, spectral type, apparent diameter in arcsec, absolute radiusin solar units, method of determination, reference, remarks. Commentsand statistics obtained from CADARS are given. The Catalogue isavailable in electronic form at the CDS via anonymous ftp tocdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcar?J/A+A/367/521
| 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.
| 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
| 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.
| DY Herculis: Member of a Binary System?
Not Available
| 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
Not Available
| 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.
| Mode and period changes in pulsating stars near the main sequence : delta Scuti stars.
Not Available
| 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.
| Photoelectric Minima of Selected Eclipsing Binaries and Maxima of Pulsating Stars
Not Available
| Studies of Large-Amplitude delta Scuti Variables. III. DY Pegasi
This is the third in a series of papers on large-amplitude delta Scutiand related stars intended to determine Baade-Wesselink radii andluminosities with precision. The first two papers discussed our methodof analysis and its application to the delta Scuti variables EH Libraeand DY Herculis; in the present paper we discuss the observations andanalysis of the SX Phoenicis variable DY Pegasi. Optical (BVI) andinfrared (JH) photometry and cross-correlated radial velocity data havebeen obtained and analyzed. Fourier representations for the BVIH lightcurves and for the radial velocity curve were used to derive a value forthe minimum radius for each of 22 combinations of flux and color index,from which we obtain a mean value for the minimum radius ofR_min=2.09+/-0.25 R_solar. When combined with effective temperaturesfrom Burki & Meylan, we find a mean bolometric luminosity of=11.34 L_solar and a mean absolute magnitude of=2.11. The radial excursion (R_max-R_min) is 0.073 R_solar.
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| Takýmyýldýz: | Herkul |
| Sað Açýklýk: | 16h31m17.96s |
| Yükselim: | +11°59'52.5" |
| Görünürdeki Parlaklýk: | 10.482 |
| özdevim Sað Açýklýk: | -5.4 |
| özdevim Yükselim: | 6.6 |
| B-T magnitude: | 10.877 |
| V-T magnitude: | 10.515 |
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