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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The high-amplitude delta Scuti star GP Andromedae
We publish 70 times of light maximum of GP And. Scrutinizing thephotometric observations we conclude that the observed discrepancies inthe light curve is a result of the defect of the photometry caused by aclose companion of the variable. The period changes of GP And arestudied also.
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Times of Maxima for Selected Delta Scuti Stars
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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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Beobachtungssergebnisse Bundesdeutsche Arbeitsgemeinschaft fuer Veraenderliche Sterne e.V.
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Photoelectric Maxima of Selected Pulsating Stars
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On the period variability of GP andromedae
The present paper deals with the pulsation period variability of thehigh-amplitude δ Scuti star GP Andromedae using a data setcovering a time base of 26.9 years. The possibility of a periodiccomponent (reflecting the light-time effect induced by a hypotheticbinarity) in the O-C curve is inferred. The presence of this periodicityin the period variation of GP And leads to a diminution of thediscrepancy between predicted and observed relative period change rates.The hypothesis of the existence of an unseen companion is discussed. Thestatistical analysis of the final O-C residuals distribution, indicatestheir normal or close to normal character.
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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.
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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.
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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.
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Photoelectric Minima of Selected Eclipsing Binaries and Maxima of Pulsating Stars
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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.
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CCD measurements of visual double stars made with the 50 cm refractor of the Nice Observatory (2nd series)
We present the measurements of 65 visual double stars made in 1998 withthe 50 cm refractor of the Nice Observatory (Table 1). A CCD camera wasattached to this refractor. 6 new binaries discovered by Hipparcos havebeen measured. The algorithm used for these measurements is based on theadjustment of a tridimensional mathematical surface. Table 1 is alsoavailable 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
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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
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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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Photoelectric Minima of Selected Eclipsing Binaries and Maxima of Pulsating Stars
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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.
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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.
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HIPPARCOS Parallaxes and Distances of High-Amplitude δ Scuti Stars
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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)
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Luminosity and related parameters of δ Scuti stars from HIPPARCOS parallaxes. General properties of luminosity.
The absolute magnitudes of δ Scuti stars derived from parallaxesmeasured by the Hipparcos astrometric satellite are discussed andcompared with the previous estimates based on photometric uvbyβindices. There are significant differences which are related tophotometric effects of metallicity and rotational velocity, but thepossible effect of a close companion on the measured apparent magnitudeshould be also taken into account. The possibility of differentgroupings of δ Scuti stars based on the absolute magnitudes isbriefly discussed. Some high amplitude δ Scuti stars withintermediate or normal metallicity and small and uncertain parallax haveapparently a very low luminosity; this could be a systematic effectrelated to the observational errors.
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Spectroscopic survey of delta Scuti stars. I. Rotation velocities and effective temperatures
Projected rotational velocities and effective temperatures for 68 deltaSct stars as well as 41 non-variable stars of similar spectral type andluminosity are presented here. The rotational velocities have beencalculated following the method developed in \cite[Gray (1992)]{ref38}and effective temperatures have been derived using the Balmer lineprofiles. The temperatures obtained from this method are shown to be inreasonable agreement with those calculated using the Infrared FluxMethod (IRFM) or spectrophotometric methods. This result has allowed usto use our temperatures to compare different uvby beta photometriccalibrations. We find that the calibration given by \cite[Moon \&Dworetsky (1985)]{ref72} is the most consistent. In the second part ofthis paper we have studied the relation between the pulsationalproperties (periods and amplitudes) and the physical parameters (v sin iand Teff). Where pulsation modes have been determined, thelow amplitude $\delta$ Scutis tend to be multimode (radial andnon-radial) pulsators, consistent with the theory that non-linearcoupling between modes acts to limit the amplitude in these stars. Wehave compared the distribution of v sin i for low amplitude $\delta$Scutis and non-variable stars. This shows the $\delta$ Scutis have abroader distribution in v sin i suggesting that a high rotation velocitymay favour pulsation. We find that the large amplitude delta Scuti starstend to have longer periods, cooler temperatures and lower rotationvelocities. Given that the large amplitude stars are also relativelyrare all the above are consistent with the hypothesis that these starsare more evolved (sub-giants) than the low amplitude delta Scutis (mainsequence or early post-main sequence).
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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.
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Period changes and evolution in the lower part of the Instability Strip.
Observed period changes in SX Phe and Population I high amplitude deltaSct stars have been collected and compared with those expected fromdifferent stellar evolutionary tracks inside the Lower Instability Stripincluding modern evolution models using the new opacities by Rogers& Iglesias (???) and Kurucz (???).
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The Behlen Observatory variable star survey. Paper 3.
Finding charts, accurate coordinates and light curves are presented for146 variable stars including three which are newly discovered.Parameters descriptive of the light curves are tabulated includingperiods for eight stars which lacked them in the General Catalogue ofVariable Stars (the GCVS). GCVS periods of twelve stars were found to beseriously in error. The classification of the stars is discussed.Revisions or refinements of the classifications from the GeneralCatalogue of Variable of Stars are suggested for thirty-one stars. Ofthe nineteen stars classified as Bailey type c RR Lyrae stars in theGeneral Catalogue of Variable Stars, five are found to be short periodeclipsing or ellipsoidal variables. Seventeen percent of the Bailey typeab RR Lyrae stars and 14% of the type c's show scatter in their lightcurves which is suggestive of the Blazhko effect.
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A catalogue of variable stars in the lower instability strip.
Identifications, positions, photometry, spectra, some pulsationalfeatures, other astrophysical parameters and literature for 302pulsating variable stars in the lower instability strip, near the ZAMS,are given. About 185 stars have near homogeneous photometric informationin the Stroemgren's uvby-β photometric system. Thiscatalogue/database covers information published until November 1993.
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INHABITED SKY
