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Chemical Composition and Differential Time-Series CCD Photometry of V2314 Ophiuchi: A New λ Bootis-Type Star
We investigated V2314 Oph using high-resolution (R=45,000) spectralobservations. The atmospheric parameters were determined using iron-lineabundance analysis. We derived a mean effective temperature ofTeff=7510 K, mean surface gravity of logg=3.30, metallicityof [Fe/H]=-0.59, and rotation velocity of vsini=38 km s-1.The abundances of 19 chemical elements were determined. The abundancepattern of V2314 Oph was found to be similar to that of λBootis-type stars. V2314 Oph is also a variable star, as are a majorityof λ Bootis stars. A frequency analysis of 10 selected nights ofprecise differential photometry has preliminarily revealed fourpulsational modes. The multiperiodic solution of the light curve isprobably more similar to a low-amplitude Population I δ Scutivariable pattern, as is apparent for many λ Bootis stars. Forasteroseismic investigations of the star it is necessary to obtain moreprolonged, continuous time-series observations. These features, as wellas the small proper motion and relatively large rotational velocity ofV2314 Oph, specify the star as not likely to be a field SX PhoenicisPopulation II variable, as was suggested previously.
| 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.
| Binarity and multiperiodicity in high-amplitude delta Scuti stars .
We present our first results for a sample of southern high-amplitudedelta Scuti stars (HADS), based on a spectrophotometric survey startedin 2003. For CY Aqr and AD CMi, we found very stable light and radialvelocity (RV) curves; we confirmed the double-mode nature of ZZ Mic, BQInd and RY Lep. Finally, we detected gamma -velocity changes in RS Gruand RY Lep.
| 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
| Beobachtungssergebnisse Bundesdeutsche Arbeitsgemeinschaft fuer Veraenderliche Sterne e.V.
Not Available
| Auffallige Vergleichssterne bei CY Aqr und AL Ari.
Not Available
| Photoelectric Maxima of Selected Pulsating Stars
Not Available
| Long-term variability of the SX Phoenicis star CY Aquarii
We present 23 new times of maximum light of the SX Phoenicis star CYAquarii. The O-C diagram reveals a new value of the periodP=0fd061038394 +/- 0fd000000006 since 1996. CY Aqr is the first SX Phestar where the major component of the long-term period change can berepresented without invoking large-amplitude period jumps. A linearperiod change combined with the light-time effect in a highly-eccentricorbit yields a reasonably precise solution. The binary explanation,however, does not account for the full magnitude of the period changes,and small residuals in the time interval 1930-1950 seem to remain.Based in part on observations obtained at ESO La Silla, application269.D-5038.
| Fast CCD Photometry in the Taiwan-America Occultation Survey
We describe the efforts of the Taiwan-America Occultation Survey (TAOS)project to develop a data acquisition and analysis scheme for fast CCDimaging photometry. The TAOS project aims to conduct a census of theKuiper-belt objects (KBOs) by detecting chance stellar occultationevents by these small bodies in the outer reach of the solar system. Anarray of telescopes, each with fast optics (f/2) of 0.5 m aperture andequipped with a 2K CCD camera (3 square degrees FOV), have been set upin central Taiwan to monitor a couple thousand stars simultaneously. Byreading out the CCD chip sequentially a few rows of pixels at a time(pause-and-shift), it is possible to achieve stellar photometry with asampling rate up to several hertz. Here we report how such a setup hasbeen used to observe the SX Phoenicis type variable CY Aqr to illustratethe potential usefulness of the TAOS database in stellar variabilitystudies.
| 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.
| The TASS Mark IV Photometric Survey
The Amateur Sky Survey (TASS) had developed its next generationwidefield CCD camera system. This paper describes and discusses thepotential contributions the Mark IV can have for the AAVSO.
| 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.
| 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
| Photoelectric Minima of Selected Eclipsing Binaries and Maxima of Pulsating Stars
Not Available
| 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.
| 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.
| 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
| Period and amplitude changes in the delta Scuti star V 1162 Orionis
We present yb time-series CCD photometry of the high-amplitude deltaScuti star V 1162 Ori. A period break and a significant decrease inamplitude (50 percent) has been reported for this star by {Hintz et al.(1998)}. New observations carried out over two observing seasons suggestthat the period found by {Hintz et al. (1998)} was no longer valid inearly 1998, and that the period again changed during March or April1998. The latter period change was accompanied by an increase inamplitude of the order of 10 percent. The existing data can be explainedby a frequently changing period or by a possible cyclic variation in theO-C diagram indicating sudden changes, a binary system or the presenceof two very closely-spaced pulsation frequencies. Based on observationsobtained at the European Southern Observatory at La Silla, Chile(applications ESO 62H-0110, 64H-0065 and 64L-0182)
| The light curves of SX Phe stars in NGC 6752
The light curves of the SX Phe stars found in the globular cluster NGC6752 were processed and the properties of their Fourier parameters werediscussed
| 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.
| The light curves of the short-period variable stars in omega Centauri
The Fourier decomposition was applied to the light curves of the shortperiod variable stars discovered by the OGLE team (Kaluzny et al. 1996,1997) in omega Cen. The progression of the {f_2} u parameter as afunction of the period is extended toward very short periods as the newvalues connected directly to those of stars located in the Galaxy.However, two groups of stars deviate: the first is located around 0.038d and it shows rather high {f_2} u values; the second is the origin of asmall change in the slope around 0.050 d. The reality of the twofeatures is discussed. The peculiarity of the light curve of OGLEGC 26is also emphasized.
| Photoelectric Minima of Selected Eclipsing Binaries and Maxima of Pulsating Stars
Not Available
| The light curves of the short-period variable stars in the Carina dwarf Spheroidal galaxy
The light curves of the high-amplitude, short-period variable starsdiscovered by Mateo et al. (1998) in the Carina dwarf Spheroidal Galaxywere re-analyzed to refine their properties and compare them with thoseof galactic stars. In spite of a different pulsation mode established bymeans of different PLM relationships, the Fourier parameters did notreveal a separation between the two groups; however, they are slightlydifferent from those of galactic stars. The possibility that some ofthese stars are double-mode pulsators is suggested.
| A review of the O-C method and period change.
The classical O--C curves are discussed in different cases in whichvarious period changes involved. Among them, the analytic O--C curveswith frequency, amplitude modulations and with double modes are closelyinspected, respectively. As a special, the light-time effect isillustrated. The features of period change noise and period change tometallicity are added at the end.
| Photometric Abundance Calibration of delta Scuti Stars Using HK Photometry
The hk index has been used as a metallicity indicator for RR Lyraevariable stars. It is now being applied to the shorter period deltaScuti variables. Employing spectroscopic abundances of stars withpublished hk values and photometric indices calculated from stellaratmosphere models, a three-dimensional interpolation is used todetermine [Fe/H] from intrinsic b-y, c_1, and hk values. The resulting[Fe/H], log g, and T_eff values for 10 delta Scuti stars are presented.
| 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.
| 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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| Takýmyýldýz: | Kova |
| Sað Açýklýk: | 22h37m47.86s |
| Yükselim: | +01°32'03.8" |
| Görünürdeki Parlaklýk: | 11 |
| özdevim Sað Açýklýk: | 39.6 |
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| B-T magnitude: | 10.971 |
| V-T magnitude: | 10.998 |
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