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Photoelectric Minima of Selected Eclipsing Binaries and Maxima of Pulsating Stars
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| 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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| 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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| Photoelectric Minima of Selected Eclipsing Binaries and Maxima of Pulsating Stars
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| Reclassification of ROTSE-I δ Scuti Stars with Multiband Photometry and Fourier Decomposition
We present new multiband photometric results for 29 ROTSE-I δScuti stars and a Fourier decomposition light-curve analysis in order toreclassify their variability types. For the classification betweeneclipsing and pulsating stars, we use the criterion that pulsating starshave larger amplitude differences between passbands than eclipsingbinaries, because the brightness changes in pulsating stars are mainlydue to variations in temperature. From this investigation, we find that24 of our 29 observation targets are W Ursae Majoris type eclipsingbinaries. Fourier analysis of the data for all 91 ROTSE-I δ Scutistars shows that the phase parameters φ21 of thehigh-amplitude δ Scuti variables identified in this study areconcentrated around 4.0. This high-probability area characterized byφ21 is in good agreement with the finding from OGLEdata. Our results suggest that most of the ROTSE-I δ Scuti starslocated outside the high-probability area are in fact W UMa typeeclipsing binaries.
| The Detached Solar-Type Binary CV Boo
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| Photoelectric Maxima of Selected Pulsating Stars
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| 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.
| A search for period changes in delta Scuti stars with the super-LOTIS sky patrol system
We have observed a sample of delta Scuti stars discovered by the ROTSEcollaboration in 1999 with Super-LOTIS in order to characterize changesin their pulsation periods over a time baseline of roughly three years.Achieving these goals required the creation of an automated astrometricand photometric data reduction pipeline for the Super-LOTIS camera.Applying this pipeline to data from a June 2002 observing campaign, wedetect pulsations in 18 objects, and find that in two cases the periodshave changed significantly over the three years between the ROTSE andSuper-LOTIS observations. Since theory predicts that evolutionary periodchanges should be quite small, sources of non-evolutionary periodchanges due to the interactions of pulsations modes are discussed.
| 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.
| 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
| 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.
| Photoelectric Minima of Selected Eclipsing Binaries and Maxima of Pulsating Stars
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| Coordinates and Identifications for Sonneberg Variables on MVS 308-316
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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
| 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.
| 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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| Mode and period changes in pulsating stars near the main sequence : delta Scuti stars.
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| 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.
| HIPPARCOS Parallaxes and Distances of High-Amplitude δ Scuti Stars
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