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Photometric Properties of the Variable Star LZ Herculis
We present BV photometric results of the variable star LZ Her. Frolov& Irkaev classified it as a field SX Phe-type pulsating star, butour observations clearly show that LZ Her is not an SX Phe star, butrather a W UMa-type eclipsing binary, as reported by Garrido et al. Theorbital period is derived to be 0.33173646 days by combining our datawith that in the literature. The eclipsing light-curve solution from theWilson-Devinney code shows that LZ Her belongs to the W subgroup of WUMa stars; the primary component is less massive and hotter, with aspectral type of F9-G0, and the secondary is more massive and cooler,with a spectral type G5-G6. The spectral types were estimated from thephotometric light-curve solution. Asymmetric light curves could beexplained by assuming a cool spot on the secondary star. In theobserving field of LZ Her, we found a new eclipsing binary, 2MASS17500367+2928020, with an orbital period of 0.3056 days.
| Spectral Classification of Stars in A Supplement to the Bright Star Catalogue
MK spectral types are given for about 584 stars in A Supplement to theBright Star Catalogue. These are compared with Hipparcos parallaxes tocheck the reliability of those classifications. The estimated errors are+/-1.2 subtypes, and 10% of the luminosity classes may be wrong.
| Mt. Dushak-Erekdag Observatory: A Chance to Close the Asian Gaps in WET Coverage
The Mt. Dushak-Erekdag Observatory (Central Asia, Turkmenistan,58deg E longitude) is located just in the longitudes gap ofasteroseismological networks. It is the southernmost observatory of theformer Soviet Union, its latitude is +38deg . The sky seeingat the site is one of the best in Central Asia: a low light pollution,high and stable sky transparency, over 200 usable nights per year. Thealtitude is above 2000 m. Odessa Astronomical Observatory has its 0.8 mtelescope with a two-star high-speed photometer there, which frequentlyparticipates in international programs and multi-site campaigns. Anaccuracy of the photometry amounts to 1 mmag. Besides, a 1 m wide-angletelescope and a dual-tube telescope with 0.5 m mirrors are installed atthe observatory. The developed infrastructure at the site and thestable economy in Turkmenistan make the Mt. Dushak-Erekdag Observatoryvery interesting for the WET observations.
| The heterogeneous class of lambda Bootis stars
We demonstrate that it is arduous to define the lambda Boo stars as aclass of objects exhibiting uniform abundance peculiarities which wouldbe generated by a mechanism altering the structure of their atmosphericlayers. We collected the stars classified as lambda Boo up to now anddiscuss their properties, in particular the important percentage ofconfirmed binaries producing composite spectra (including our adaptiveoptics observations) and of misclassified objects. The unexplained RVvariables (and thus suspected binaries), the known SB for which we lackinformation on the companion, the stars with an UV flux inconsistentwith their classification, and the fast rotating stars for which noaccurate abundance analysis can be performed, are also reviewed.Partly based on observations collected at the CFH Telescope (Hawaii) andat TBL of the Pic du Midi Observatory (France).Table \ref{tab5} is only available in electronic form athttp://www.edpsciences.org
| 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 status of Galactic field λ Bootis stars in the post-Hipparcos era
The λ Bootis stars are Population I, late B- to early F-typestars, with moderate to extreme (up to a factor 100) surfaceunderabundances of most Fe-peak elements and solar abundances of lighterelements (C, N, O and S). To put constraints on the various existingtheories that try to explain these peculiar stars, we investigate theobservational properties of λ Bootis stars compared with areference sample of normal stars. Using various photometric systems andHipparcos data, we analyse the validity of standard photometriccalibrations, elemental abundances, and Galactic space motions. Therecrystallizes a clear picture of a homogeneous group of Population Iobjects found at all stages of their main-sequence evolution, with apeak at about 1 Gyr. No correlation of astrophysical parameters such asthe projected rotational velocities or elemental abundances with age isfound, suggesting that the a priori unknown mechanism, which createsλ Bootis stars, works continuously for late B- to early F-typestars in all stages of main-sequence evolution. Surprisingly, the sodiumabundances seem to indicate an interaction between the stars and theirlocal environment.
| Rotational velocities of A-type stars in the northern hemisphere. II. Measurement of v sin i
This work is the second part of the set of measurements of v sin i forA-type stars, begun by Royer et al. (\cite{Ror_02a}). Spectra of 249 B8to F2-type stars brighter than V=7 have been collected at Observatoirede Haute-Provence (OHP). Fourier transforms of several line profiles inthe range 4200-4600 Å are used to derive v sin i from thefrequency of the first zero. Statistical analysis of the sampleindicates that measurement error mainly depends on v sin i and thisrelative error of the rotational velocity is found to be about 5% onaverage. The systematic shift with respect to standard values fromSlettebak et al. (\cite{Slk_75}), previously found in the first paper,is here confirmed. Comparisons with data from the literature agree withour findings: v sin i values from Slettebak et al. are underestimatedand the relation between both scales follows a linear law ensuremath vsin inew = 1.03 v sin iold+7.7. Finally, thesedata are combined with those from the previous paper (Royer et al.\cite{Ror_02a}), together with the catalogue of Abt & Morrell(\cite{AbtMol95}). The resulting sample includes some 2150 stars withhomogenized rotational velocities. Based on observations made atObservatoire de Haute Provence (CNRS), France. Tables \ref{results} and\ref{merging} are only available in electronic form at the CDS viaanonymous ftp to cdsarc.u-strasbg.fr (130.79.125.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/393/897
| On the Period-Luminosity-Colour-Metallicity relation and the pulsational characteristics of lambda Bootis type stars
Generally, chemical peculiarity found for stars on the upper mainsequence excludes delta Scuti type pulsation (e.g. Ap and Am stars), butfor the group of lambda Bootis stars it is just the opposite. This makesthem very interesting for asteroseismological investigations. The groupof lambda Bootis type stars comprises late B- to early F-type,Population I objects which are basically metal weak, in particular theFe group elements, but with the clear exception of C, N, O and S. Thepresent work is a continuation of the studies by Paunzen et al.(\cite{Pau97}, \cite{Pau98}), who presented first results on thepulsational characteristics of the lambda Bootis stars. Since then, wehave observed 22 additional objects; we found eight new pulsators andconfirmed another one. Furthermore, new spectroscopic data (Paunzen\cite{Pau01}) allowed us to sort out misidentified candidates and to addtrue members to the group. From 67 members of this group, only two arenot photometrically investigated yet which makes our analysis highlyrepresentative. We have compared our results on the pulsationalbehaviour of the lambda Bootis stars with those of a sample of deltaScuti type objects. We find that at least 70% of all lambda Bootis typestars inside the classical instability strip pulsate, and they do sowith high overtone modes (Q < 0.020 d). Only a few stars, if any,pulsate in the fundamental mode. Our photometric results are inexcellent agreement with the spectroscopic work on high-degree nonradialpulsations by Bohlender et al. (\cite{Boh99}). Compared to the deltaScuti stars, the cool and hot borders of the instability strip of thelambda Bootis stars are shifted by about 25 mmag, towards smaller(b-y)_0. Using published abundances and the metallicity sensitiveindices of the Geneva 7-colour and Strömgren uvbybeta systems, wehave derived [Z] values which describe the surface abundance of theheavier elements for the group members. We find that thePeriod-Luminosity-Colour relation for the group of lambda Bootis starsis within the errors identical with that of the normal delta Scutistars. No clear evidence for a statistically significant metallicityterm was detected. Based on observations from the Austrian AutomaticPhotoelectric Telescope (Fairborn Observatory), SAAO and Siding SpringObservatory.
| The accretion/diffusion theory for lambda Bootis stars in the light of spectroscopic data
Most of the current theories suggest the lambda Bootis phenomenon tooriginate from an interaction between the stellar surface and its localenvironment. In this paper, we compare the abundance pattern of thelambda Bootis stars to that of the interstellar medium and find largerdeficiencies for Mg, Si, Mn and Zn than in the interstellar medium. Acomparison with metal poor post-AGB stars showing evidence forcircumstellar material indicates a similar physical process possiblybeing at work for some of the lambda Bootis stars, but not for all ofthem. Despite the fact that the number of spectroscopically analysedlambda Bootis stars has considerably increased in the past, a test ofpredicted effects with observations shows current abundance andtemperature data to be still controversial.
| The abundance pattern of lambda Bootis stars
Within a project to investigate the properties of lambda Bootis stars,we report on their abundance pattern. High resolution spectra have beenobtained for a total of twelve candidate lambda Bootis stars, four ofthem being contained in spectroscopic binary systems, and detailedabundance analyses have been performed. All program stars show acharacteristic lambda Bootis abundance pattern (deficient heavy elementsand solar abundant light elements) and an enhanced abundance of Na. Thiswork raises the fraction of lambda Bootis stars with known abundances to50%. The resulting abundances complemented by literature data are usedto construct a ``mean lambda Bootis abundance pattern'', which exhibits,apart from general underabundances of heavy elements (~-1 dex) and solarabundances of C, N, O, Na and S, a star-to-star scatter which is up totwice as large as for a comparable sample of normal stars. Based onobservations obtained at the Osservatorio Astronomico di Padua-Asiago,OPD/LNA, KPNO and DSO.
| Light element non-LTE abundances of lambda Bootis stars. II. Nitrogen and sulphur
One of the main characteristics proclaimed for the group of the lambdaBootis stars is the apparent solar abundance of the light elements C, N,O and S. The typical abundance pattern is completed by the strongunderabundances of the Fe-peak elements. In the first paper of thisseries, we have shown that carbon is less abundant than oxygen but bothelements are still significantly more abundant than Fe-peak elements.The mean abundances, based on a detailed non-LTE investigation, werefound -0.37 dex and -0.07 dex, respectively. As a further step, we nowpresent non-LTE abundances of nitrogen and sulphur for thirteen membersof the lambda Bootis group based on several spectral lines between 8590Å, and 8750 Å. Furthermore, LTE abundances for calcium inthe same spectral range were derived and compared with values from theliterature. Similar to the mean abundances of carbon and oxygen, nearlysolar values were found (-0.30 dex for nitrogen and -0.11 dex forsulphur) for our sample of program stars. Among our sample, onepreviously undetected binary system (HD 64491) was identified. From astatistical point of view, the abundances of the light elements rangefrom slightly overabundant to moderately underabundant compared to theSun. However, the individual objects always exhibit a similiar pattern,with the Fe-peak elements being significantly more underabundant thanthe light elements. No correlation of the derived abundances withastrophysical parameters such as the effective temperature, surfacegravity or projected rotational velocity was found. Furthermore, theabundances of the light elements do not allow us to discriminate betweenany proposed theory. Based on observations obtained at BNAO Rozhen andComplejo Astronómico el Leoncito (CASLEO), operated under theagreement between the Consejo Nacional de InvestigacionesCientíficas y Técnicas de la República Argentinaand the National Universities of La Plata, Córdoba y San Juan.
| A spectroscopic survey for lambda Bootis stars. III. Final results
In the third paper of a series dedicated to the spectroscopic survey fornew lambda Bootis stars, we present all new and confirmed members of thegroup as well as a detailed analysis of the observed sample. The natureof this small group of chemically peculiar stars of the upper mainsequence still challenges our understanding of processes like diffusion,mass-loss and accretion. The typical abundances pattern (nearly solarvalues for C, N, O and S whereas the Fe-peak elements are moderate tostrong underabundant) can still not be explained by any proposed theory.Hence, the significant increase of new members gives the opportunity toinvestigate the group properties in more detail. We report the discoveryof 26 new members of the group and the confirmation of 18 candidatesfrom the literature. This almost triples the number of known lambdaBootis stars. The existence of one member in the young open cluster NGC2264 and four members in the Orion OB1 association proves that thelambda Bootis phenomenon already works at very early stages of stellarevolution. Recent results from the Hipparcos mission have shown that thewell established lambda Bootis stars of the Galactic field comprise thewhole area from the Zero Age Main Sequence to the Terminal Age MainSequence (~ 109 yr for an A-type star). There is a continuoustransition between very young and rather evolved evolutionary stages. Wefind that the overall percentage of lambda Bootis type among all normaltype stars in the spectral range from B8 to F4 is 2% in the Galacticfield as well as in open clusters. Furthermore, 44 metal-weak objectsare listed which might be connected with the lambda Bootis phenomenon.Our biased sample (chosen by photometric boxes) is not distinguishedfrom all A-type stars in the corresponding spectral region by therotational velocity distribution. Only for the luminosity classes IV andIII (especially for the cooler program stars) the determined mean v sini values are very high compared to those of the literature. Based onobservations from the Observatoire de Haute-Provence, OsservatorioAstronomico di Padova-Asiago, Observatório do Pico dosDias-LNA/CNPq/MCT, Chews Ridge Observatory (MIRA) and University ofToronto Southern Observatory (Las Campanas).
| 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
| Unification of VW ARIETIS observations obtained in multisite campaign.
Not Available
| The unusual A-star VW Ari: chemical composition revisited
Seven high-resolution and high S/N CCD spectra were used to deriveelemental abundances in the atmosphere of VW Ari A (T(eff)=7200, logg=3.7) which is the primary component of a visual binary system. Thesynthetic spectrum technique applied in the analysis allowed to revealthe following feature: the atmosphere of this star is strongly deficientin some metals, while light elements have solar-like abundances. Takinginto account these results, one can suggest that VW Ari A is a lambdaBoo type star. Another argument supporting this supposition is thefollowing: on the diagrams "(b-y)-c(1)", "(b-y)-m(1)" and "(b-y)-beta"VW Ari A falls exactly in the region occupied by the lambda Boo stars.Note also, that a previous analysis has shown that the secondarycomponent of VW Ari has a normal metallicity. Differences in chemicalcompositions of the two components appear to be due to the specificevolution of the primary VW Ari A.
| Central Asian Network (CAN) - the history and present status
No abstract submitted
| 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.
| Pulsation, binarity and close frequency spacing in $delta Scuti ta$ Scuti stars: BQ and BW Cancri. Results of the STEPHI VI campaign in Praesepe Cluster
New pulsation modes in two delta Scuti stars of Praesepe cluster, BQ andBW Cnc, have been detected during the STEPHI VI campaign in 1995. Inparticular, 3 frequencies for BQ Cnc and 9 frequencies for BW Cnc havebeen found above a 99% confidence level. The possibility of the presenceof a g-mode present in BQ Cnc is discussed, considering its binarity.The effect of mutual interference between very close detectedfrequencies in BW Cnc during the observations, is also considered. Thislast effect reveals the necessity of long-period observing runs, inorder to avoid its influence in the final number of detected modes. Insuch situation, studies of secular amplitude changes can be stronglyaffected.
| A catalogue of [Fe/H] determinations: 1996 edition
A fifth Edition of the Catalogue of [Fe/H] determinations is presentedherewith. It contains 5946 determinations for 3247 stars, including 751stars in 84 associations, clusters or galaxies. The literature iscomplete up to December 1995. The 700 bibliographical referencescorrespond to [Fe/H] determinations obtained from high resolutionspectroscopic observations and detailed analyses, most of them carriedout with the help of model-atmospheres. The Catalogue is made up ofthree formatted files: File 1: field stars, File 2: stars in galacticassociations and clusters, and stars in SMC, LMC, M33, File 3: numberedlist of bibliographical references The three files are only available inelectronic form at the Centre de Donnees Stellaires in Strasbourg, viaanonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5), or viahttp://cdsweb.u-strasbg.fr/Abstract.html
| 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).
| 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.
| On the multiperiodicity of the δ Scuti star BDS 1269A (VW Arietis). The fifth campaign of STEPHI network in 1993.
This paper reports on the fifth STEPHI multi-site photometric campaignin 1993 devoted to the δ Scuti star BDS 1269A (VW Ari). Theobservation yielded a data set of 150.7 hours. Our analysis has resultedin 7 identified frequencies. These frequencies exhibit threecouple-frequency character, and also fit the previous investigationsquite well. An attempt to identify the pulsation modes is made, but noequidistant evidence can be detected, and a second-order effect forrotational splitting has to be considered to explain the complicatednature of BDS 1269A.
| The remarkable visual binary system VW Arietis: Chemical composition of its components
We present results of a spectroscopic investigation of the A and Bcomponents of the visual binary VW Ari. Results are as follows: (1) Theatmospheric parameters for the stars are Teff = 7100 K, log g= 3.7 (A component), Teff = 7300 K, log g = 4.3,Vt = 1.9 km/s (B component); (2) the masses and radii are:RA approximately equal to 3.5 solar radii, RBapproximately equal to 1.6 solar radii; MA approximatelyequal to 2.2 solar mass, MB approximately equal to 1.8 solarmass; (3) abundances of 16 elements have been determined for VW Ari B.This star shows solarlike chemical composition for most of the elements.(4) Because of the complicated spectrum of VW Ari A (only a few veryshallow lines are seen), we were able to estimate only Ca and Feabundances in its atmosphere: (Ca/H) = -0.73, (Fe/H) = -0.46. Theremarkable metallicity difference between the components stronglysupports the hypothesis of stellar capture as the most probable originof the VW Ari system.
| 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.
| Pulsational Activity on Ik-Pegasi
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1994MNRAS.267.1045W&db_key=AST
| δ Scuti stars: a new revised list
An extensive and up to date list of δ Sct stars is presented. Thiscatalogue is intended to be a comprehensive review of observationalcharacteristics of all the δ Sct stars known until now, includingstars contained in earlier catalogues together with other new discoveredvariables, covering information published until November 1993. Globalinformation in the form of histograms and diagrams are also shown.
| Multiple Frequencies Pulsation of the Delta-Scuti Variable BDS:1269A
Not Available
| CCD Observations of Short-Period Variables at Middlebury College
The Middlebury College Observatory is equipped with a 0.41-m reflectingtelescope and a CCD imaging camera. Among the observational programs wehave undertaken is the photometric study of short-period variable stars,especially delta Sct variables. There are many short-period (P < 6h)variables with amplitudes of several hundredths of a magnitude orgreater, which are ideal objects for study with CCDs on smalltelescopes, especially in educational settings.
| Empirical P-L-C relation for Delta Scuti stars - A catalogue
An extensive and up-to-date list of 192 Delta Scuti stars is presented.Empirical period - luminosity - color (P-L-C) relations are obtained forthe four lowest modes corresponding to radial pulsations. Agreement withpredicted values indicates that, in general, both Stroemgren photometriccalibration and pulsation theory work well for these stars.
| Quasi-160-minute oscillation period of Delta Scuti stars
The resonance power spectrum (or commensurability spectrum) computed for217 Delta Scuti stars indicates that the dominant (most commensurate)period for the total set of oscillation periods of these stars is 162.2+ or - 2.8 min. Within the error limits, this period coincidesapproximately with the 160-min period of global oscillations of the sun.
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Pozíciós és asztrometriai adatok
| Csillagkép: | Kos |
| Rektaszcenzió: | 02h26m45.65s |
| Deklináció: | +10°33'55.1" |
| Vizuális fényesség: | 6.694 |
| Távolság: | 117.509 parszek |
| RA sajátmozgás: | 35.1 |
| Dec sajátmozgás: | -13.1 |
| B-T magnitude: | 6.999 |
| V-T magnitude: | 6.72 |
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