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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.
| Photoelectric Minima of Selected Eclipsing Binaries and Maxima of Pulsating Stars
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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 Maxima of Selected Pulsating Stars
Not Available
| Light Time Effects in Pulsating Variables and Brown Dwarfs
Dwarf cepheids DY Her, AD CMi, and BE Lyn show light time effects, whichmay be caused by orbital motion due to a low mass unseen companion.Their mass is probably between 0.015 to 0.07 Mȯ, so theymay be brown dwarfs.
| 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
| 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.
| 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.
| Spectroscopic survey of field stars : A search for metal-poor stars
We have undertaken a spectroscopic survey of field stars to finemetal-poor objects among them. Though the main objective of the surveyis to find new metal-poor stars, stellar parameterization is carried outfor all the sample stars so that the other categories of interestingobjects like composite stars, weak or strong CN, CH stars etc. can alsobe identified. Observations are carried out using OMR spectrographattached to VBT, Kavalur. The sample of candidate stars are chosen fromprismatic survey of Beers and his collaborators covering a large part ofthe Galaxy. At the first phase of this project, the analysis ofcompleted for a set of 19 relatively hot stars (Teff in 6000 to 8000Krage). The metallicities of the program stars are derived bysynthesizing the spectrum in the wavelength range 4900 to 5400 Åfor different metallicities and matching them with the observed spectra.This spectral region contains strong feature of Fe I at 5269 Å andone moderately strong Fe I blend at 5228 Å. These features weregenerally relied upon for Fe/H determination. More than half of thecandidate stars were found to show (Fe/H) in -0.7 to -1.2 range. Twomost metal-poor stars have (Fe/H) values of -1.3 and -1.8. It appearsthat metal-poor candidates suggested by Beers et al. from theirprismatic survey has a very significant fraction of metal-poor stars.The significantly metal-poor stars found so far would be studied indetail using high resolution spectra to understand nucleosynthesisprocesses that might have occurred in early Galaxy.
| Photoelectric Minima of Selected Eclipsing Binaries and Maxima of Pulsating Stars
Not Available
| Simultaneous uvby photometry of the delta Sct star HD 129231
We present the results of a three-year Strömgren uvby photometricstudy of the recently discovered multiperiodic low amplitude deltaSct-type pulsator HD 129231. Some additional Hbeta -Crawfordmeasurements were also collected. Multiperiodicity is needed to describethe pulsational behaviour of this variable during each of the observingruns. A set of five significant frequencies has been found as the bestfitting for the 1997 dataset, but only the two main ones result assignificant during the 1995 and 1996 observing runs. Amplitudevariations from season to season are also found for the main frequencyf_1. Nonradial pulsation is suggested for some of the modes. Using thederived uvbybeta indices, the most relevant physical parameters of HD129231 are also determined placing this object as a hot Population Idelta Sct star evolving on its main sequence stage.
| 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.
| Photoelectric Minima of Selected Eclipsing Binaries and Maxima of Pulsating Stars
Not Available
| Preliminary Baade-Wesselink Radii Solutions for Several Dwarf Cepheids
It has been shown (Laney 1995) that VJHK photometry when combined withradial velocities leads to improved Baade-Wesselink radii solutions forCepheids. Preliminary results indicate the same method can be applied todwarf Cepheids (also known as High-Amplitude Delta Scuti stars). Ourobservations obtained at the South African Astrophysical Observatoryinclude echelle spectroscopy with simultaneous visual and infraredphotometry. This procedure helps remove phase discrepancies andstrengthen the radius solution. Initial results for BS Aqr, AD CMi, RYLep, and EH Lib are presented. Special thanks to SAAO for the observingtime, support from the American Astronomical Society through a smallresearch grant, and continued funding from the Department of Physics andAstronomy at Brigham Young University.
| 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)
| 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.
| Mode and period changes in pulsating stars near the main sequence : delta Scuti 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.
| Red supergiants in the LMC - III: luminous F and G stars
New BVRI observations for 40 and spectrophotometric measurements for 23F to G LMC supergiant candidates (and 3 galactic F to G supergiants) arepresented. The errors of the BVRI data are 0.01 to 0.03 mag in mostcases. The wavelength range of the spectra is 3400 to 6400 Angstroms,their resolution 10 Angstroms. The mean error of the fluxes is 0.03 mag.Spectral indices measuring the strengths of the Hβ , Hγ ,Hdelta , NaD and CaII H+K lines, the CHα_ {0} and CNbeta_ {0}bands, of the Balmer jump and the slope of the continuum redwards arediscussed as measures of effective temperature and luminosity on thebasis of galactic stars with accurate MK types and parallaxes. TheHγ line and the continuum gradient are very good temperaturecriteria, the CHα_ {0} band and especially the Balmer jump forluminosity. The luminosity classification given for F to G supergiantcandidates in the LMC in the literature is often doubtful. 5 of the 23stars observed spectrophotometrically turn out to be probably galacticforeground dwarfs on the basis both of the Balmer jump and thecomparison of their flux distributions with synthetic ones based on theKurucz model atmospheres. Surface gravities derived purely on the basisof flux distributions and such ones given by models of stellar evolutionagree with each other for dwarfs and giants only. For supergiants theformer are about 1.0 dex higher than the latter. As a consequenceeffective temperatures and metallicities given by these two methodsdeviate from each other for such stars, too. The intrinsic colours andtemperatures of galactic and LMC supergiants do not differ. Withabsolute magnitudes up to -9.6 mag the upper luminosity limit in the LMCdoes not exceed that in the Galaxy, where Ia-0 supergiants haveMV of up to -9.5 mag. The metallicities of the supergiantsshow a rather large scatter. Nevertheless the mean metallicities of 0.02+/- 0.09 dex for the Galaxy and -0.26 +/- 0.10 dex for the LMC agreewell with other observations.
| 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.
| HIPPARCOS Parallaxes and Distances of High-Amplitude δ Scuti Stars
Not Available
| Photoelectric Minima of Selected Eclipsing Binaries and Maxima of Pulsating Stars
Not Available
| 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.
| The HIPPARCOS Mission
Not Available
| 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)
| Time-Series Ensemble Photometry of SX Phoenicis Stars. II. AE Ursae Majoris
We have examined the short period, double-mode variable star AE UrsaeMajoris. Using time series ensemble photometry we have determined sixnew times of maximum light. We also applied a Fourier decomposition tothe data to determine the component frequencies of the light curve.Using our data, along with archival data, we find that the period of AEUMa is continually decreasing at a rate of -1.14x 10(-10) d d(-1) .However, from the Fourier decomposition we find that the period ratioP1/P0 has remained constant at 0.773. We also findthat AE UMa is incorrectly classified as a SX Phoenicis star. (SECTION:Stars)
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