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Equidistant frequency triplets in pulsating stars: the combination mode hypothesis
Context: .Multiplet structures are a common feature in pulsating stars,and can be the consequence of rotational splitting, mode interaction orsinusoidal amplitude variations. Aims: .In this paper we examinethe phenomenon of (nearly) equidistant triplets, which are unlikely tobe caused by rotational splitting, in different types of pulsatingstars: a δ Scuti variable (1 Mon), an RR Lyrae variable (RR Lyr)and a short-period Cepheid (V473 Lyr). We examine the hypothesis thatone of the modes forming the triplet results from a combination of theother two modes. Methods: .The analyses were carried out onrecent data sets by using multiple-frequency analyses and statisticswith the package PERIOD04. In particular, the small departures fromequidistance were calculated for the three selected stars.Results: .For the δ Scuti variable 1 Mon, the departure fromequidistance is only 0.000079 ± 0.000001 cd-1 (or 0.91± 0.01 nHz). For 1 Mon the Combination Mode Hypothesis with amode excited by resonance is the most probable explanation. For the starRR Lyr, the hypothesis of resonance through a combination of modesshould be considered. The results for the best-studied cepheid with aBlazhko period (V473 Lyr) are inconclusive because of an unfavorableperiod of 1.49d and insufficient data.
| Pulsation of the Lambda Bootis star HD 210111
Context.The λ Bootis stars are a small spectroscopic subgroup ofPopulation I A-type stars and show significant underabundances ofmetals. Many are δ Scuti pulsators.Aims.HD 210111 wasselected for a detailed multisite pulsation study to determine whetherits pulsation properties differ from those of normal A stars.Methods.262 h of high-precision photometry were obtained at the SAAOand SSO observatories.Results.13 statistically significantpulsation frequencies were detected with very small photometricamplitudes from 1 to 7 millimag in the visual. A comparison with earlier1994 measurements indicates a small increase in amplitude. As abyproduct, one of the comparison stars, HD 210571, was discovered to bea millimag variable with a frequency of 1.235 cd-1 and isprobably a new γ Doradus variable. The observed wide range ofexcited frequencies from 12 to 30 cd-1 in HD 210111 can beexplained with both the single- and double-star hypothesis. HD 210111 isin a similar evolutionary status to FG Vir, which also shows a widerange of excited frequencies with a similar frequency spacing near 4cd-1. This is interpreted as successive radial orders of theexcited nonradial modes. In the double-star hypothesis previously evokedfor HD 210111, the low and the high frequencies originate in differentstars: here HD 210111 would resemble θ2 Tau.Conclusions.The pulsation of the λ Bootis star HD 210111 doesnot differ from that of normal δ Scuti stars.
| A new method for the spectroscopic identification of stellar non-radial pulsation modes. II. Mode identification of the δ Scuti star FG Virginis
Aims.We present a mode identification based on new high-resolutiontime-series spectra of the non-radially pulsating δ Scuti star FGVir (HD 106384, V = 6.57, A5V). From 2002 February to June a globalDelta Scuti Network (DSN) campaign, utilizing high-resolutionspectroscopy and simultaneous photometry has been conducted for FG Virin order to provide a theoretical pulsation model. In this campaign wehave acquired 969 Echelle spectra covering 147 h at sixobservatories. Methods: .The mode identification was carried outby analyzing line profile variations by means of the Fourier parameterfit method, where the observational Fourier parameters across the lineare fitted with theoretical values. This method is especially wellsuited for determining the azimuthal order m of non-radial pulsationmodes and thus complementary with the method of Daszynska-Daszkiewicz(2002) which does best at identifying the degree ℓ. Results:.15 frequencies between 9.2 and 33.5 d-1 were detectedspectroscopically. We determined the azimuthal order m of 12 modes andconstrained their harmonic degree ℓ. Only modes of low degree (ℓ≤ 4) were detected, most of them having axisymmetric charactermainly due to the relatively low projected rotational velocity of FGVir. The detected non-axisymmetric modes have azimuthal orders between-2 and 1. We derived an inclination of 19°, which implies anequatorial rotational rate of 66 km s-1.
| A new method for the spectroscopic identification of stellar non-radial pulsation modes. I. The method and numerical tests
Aims.We present the Fourier parameter fit method, a new method forspectroscopically identifying stellar radial and non-radial pulsationmodes based on the high-resolution time-series spectroscopy ofabsorption-line profiles. In contrast to previous methods this onepermits a quantification of the statistical significance of the computedsolutions. The application of genetic algorithms in seeking solutionsmakes it possible to search through a large parameter space.Methods: .The mode identification is carried out by minimizing χ^2,using the observed amplitude and phase across the line profile and theirmodeled counterparts. Computations of the theoretical line profiles arebased on a stellar displacement field, which is described assuperposition of spherical harmonics and that includes the first ordereffects of the Coriolis force. Results: .We made numerical testsof the method on a grid of different mono- and multi-mode models for 0≤ ℓ ≤ 4 in order to explore its capabilities andlimitations. Our results show that whereas the azimuthal order m can beunambiguously identified for low-order modes, the error of ℓ is inthe range of ± 1. The value of m can be determined with higherprecision than with other spectroscopic mode identification methods.Improved values for the inclination can be obtained from the analysis ofnon-axisymmetric pulsation modes. The new method is ideally suited tointermediatley rotating δ Scuti and β Cephei stars.
| Amplitude variability or close frequencies in pulsating stars - the δ Scuti star FG Vir
The nature of the observed amplitude variability of several modes in theδ Scuti star FG Vir is examined. This is made possible by theextensive photometry obtained during 2002-04, as well as the longphotometric time-base starting in 1992. In this star, three frequenciesshow strong amplitude and phase variations. In the power spectrum, thesefrequencies also show up as frequency doublets. However, since trueamplitude variability of a single frequency can also lead to (false)frequency doublets in the power spectrum, a specific test examining indetail the observed amplitude and the phase variations of an assumedsingle frequency is applied. For the frequencies at 12.15 and 23.40cycle d-1, it is shown that the amplitude variability of asingle mode can be ruled out. In particular, an important property ofbeating between two modes is fulfilled: the amplitude and the phase varysynchronously with a phase shift close to 90°. The origin of theamplitude variability of a third mode, namely, near 19.86 cycled-1, is not clear due to the long beat period of 20+ yr, forwhich the amplitude-phase test suffers from gaps in the coverage.However, even for this frequency, the amplitude variations can beexpressed well by a mathematical two-mode model.If we examine these three close frequency pairs together with other(usually more widely separated) close frequencies in FG Vir, 18 pairs offrequencies with separations closer than 0.10 cycle d-1 havebeen detected. It is shown that the majority of the pairs occur near thetheoretically expected frequencies of radial modes. Mode identificationsare available for only a few modes: the only detected radial mode at12.15 cycle d-1 is part of a close pair.It is shown that accidental agreements between the frequencies ofexcited modes can be ruled out because of the large number of detectedclose frequency doublets.
| Evolutionary stages and dominant modes in delta Scuti stars .
An examination has been done on the contribution of dominant modes tothe star's light variation. A sample of delta Scuti stars (altogether30 stars) with well-determined frequency solution (based mostly onmultisite international campaigns) are overviewed. Correlation of thedominant (highest amplitude) modes and evolutionary stages have beeninvestigated. Attention is called to the importance of dominant modes inthe theoretical investigations.
| Progress in understanding and exploiting stellar oscillation spectra .
Rich oscillation spectra of dwarf-like pulsators contain a wealth ofinformation about the object interiors and, in particular, aboutmacroscopic transport processes, which is the most difficult aspect ofstellar physics. Examples of extracting such information from data onsolar-like and opacity driven pulsators are given. Problems inunderstanding new oscillation spectra are discussed. Importance ofemploying various data on excited mode is emphasized.
| Close frequencies in pulsating stars: common and mysterious! .
Amplitude and phase variability are commonly found in many differenttypes of pulsating stars. This suggests a common, presently unknownphysical origin. We have examined the phenomenon in several delta Scutistars with extensive data and find the beating of close frequencies tobe responsible. This is demonstrated for the star FG Vir by testing therelationship between the observed amplitude and phase variations. Mostclose frequency pairs are situated near the observed or theoreticallypredicted frequencies of radial modes. The large number of detectedclose frequencies excludes the possibility of accidental frequencyagreements.
| On the nature of small amplitude peaks in delta Scuti oscillation spectra
The standard assumption in interpretation of stellar oscillation spectrafrom photometry is that the excited mode have low angular degrees,typically ℓ< 3. Considering the case of FG Vir, the delta Scutistar with the richest known oscillation spectrum, we show that thisassumption is not justified for low amplitude peaks. The ℓ<3identifications have been found for 12 dominant peaks from pulsationamplitudes and phases. However, we show that for the rest of the peaks(55), whose amplitudes are typically below 1 mmag, much higher ℓ'sare most likely. We argue that improving amplitude resolution to themicromagnitude level, as expected from space observations, is not likelyto be rewarded with a credible mode identifications because the spectrawill be dominated by high-ℓ modes of unknown azimuthal order, m.
| Amplitude ratios as mode characterizors in delta Scuti stars .
Seismology of delta Scuti star s holds great potential for testingtheories of stellar structure and evolution. The ratio of modeamplitudes in light and in equivalent width of spectral lines can beused for mode identification. However, the amplitude ratios (AR)predicted from theory are usually inconsistent with observations. Wehere present the first results from a campaign aimed at calibratingobservationally the absolute values of the AR.
| Inferences from pulsational amplitudes and phases for multimode δ Sct star FG Vir
We combine photometric and spectroscopic data on twelve modes excited inFG Vir to determine their spherical harmonic degrees ℓ, and toobtain constraints on the star model. The effective temperatureconsistent with the mean colours and the pulsation data is about 7200 K.In six cases, the ℓ identification is unique with above 80%probability. Two modes are identified as radial. Simultaneously withℓ, we determine a complex parameter f which probes subphotosphericstellar layers. Comparing its values with those derived from modelsassuming different treatment of convection, we find evidence thatconvective transport in the envelope of this star is inefficient.
| A Dozen δ Scuti Stars in the Open Cluster NGC 1817
We obtained high-precision time-series observations of stars in the opencluster NGC 1817 in order to find δ Scuti stars among the clustermembers. The detection of 12 δ Scuti stars, of which our datasuggest that 11 are cluster members, makes NGC 1817 a key target forasteroseismology of 1.5-2.5 Msolar stars. One of the clustermember δ Scuti stars is also an eclipsing binary, potentiallyoffering very strong constraints for theoretical modeling. In addition,we find one δ Scuti star candidate, a γ Dor candidate, twovariables of currently unknown type, and two eclipsing binary systems.We also describe a method for combining the oscillation frequencies ofseveral δ Scuti stars in a single cluster to obtain informationabout the order n of the excited modes. This method will eventually beused to constrain the theoretical models to be compared with preciseoscillation frequencies determined from a future multisite campaign(asteroseismology).
| Asteroseismology of δ Scuti Stars: Problems and Prospects
We briefly outline the state-of-the-art seismology of δ Scutistars from a theoretical point of view: why is it so difficult a task?The recent theoretical advances in the field that these difficultieshave influenced are also discussed.
| Asteroseismology of Delta Scuti and Gamma Doradus Stars
We give an overview of past and present efforts to make seismology ofδ Scuti and γ Doradus stars possible. Previous work has notled to the observational detection and identification of a sufficientnumber of pulsation modes for these pulsators for the construction ofunique seis-mic models. However, recent efforts including largeground-based obser-vational campaigns, work on pre-main sequencepulsators, asteroseismic satellite missions, theoretical advances onmode identification methods, and the discovery of a star showingsimultaneous self-excited δ Scuti and γ Doradus oscillationssuggest that we may be able to explore the interiors of these pulsatorsin the very near future.
| Detection of 75+ pulsation frequencies in the δ Scuti star FG Virginis
Extensive photometric multisite campaigns of the δ Scuti variableFG Vir are presented. For the years 2003 and 2004, 926 h of photometryat the millimag precision level were obtained. The combinations withearlier campaigns lead to excellent frequency resolution and highsignal/noise. A multifrequency analysis yields 79 frequencies. Thisrepresents a new record for this type of star. The modes discoveredearlier were confirmed. Pulsation occurs over a wide frequency band from5.7 to 44.3 c/d with amplitudes of 0.2 mmag or larger. Within this wideband the frequencies are not distributed at random, but tend to clusterin groups. A similar feature is seen in the power spectrum of theresiduals after 79 frequencies are prewhitened. This indicates that manyadditional modes are excited. The interpretation is supported by ahistogram of the photometric amplitudes, which shows an increase ofmodes with small amplitudes. The old question of the "missing modes" maybe answered now: the large number of detected frequencies as well as thelarge number of additional frequencies suggested by the power spectrumof the residuals confirms the theoretical prediction of a large numberof excited modes. FG Vir shows a number of frequency combinations of thedominant mode at 12.7162 c/d (m = 0) with other modes of relatively highphotometric amplitudes. The amplitudes of the frequency sums are higherthan those of the differences. A second mode (20.2878 c/d) also showscombinations. This mode of azimuthal order m = -1 is coupled with twoother modes of m = +1.
| The chemical composition of δ Scuti*
We present chemical abundances in the photosphere of δ Scuti(δ Sct) - a prototype of the class of pulsating variables -determined from the analysis of a spectrum obtained by using the 2-mtelescope at the Peak Terskol Observatory and a high-resolutionspectrometer with R= 52000, a signal-to-noise ratio 250 and fromInternational Ultraviolet Explorer spectra. The abundance pattern ofδ Sct consists of 49 chemical elements. The abundances of 19elements have not been investigated previously. The abundances of Pr andNd obtained from the lines of the second and third spectra are equal.The abundances of heavy elements indicate the overabundances withrespect to the solar system values up to 1 dex. The abundance pattern ofδ Sct is similar to the abundance patterns of Am-Fm or δ Deltype stars.A splitting of the cores of all clean lines is observed for the spectraof δ Sct and HD 57749. This can signify evidence of non-radialpulsations in these stars.
| Astrophysics in 2004
In this 14th edition of ApXX,1 we bring you the Sun (§ 2) and Stars(§ 4), the Moon and Planets (§ 3), a truly binary pulsar(§ 5), a kinematic apology (§ 6), the whole universe(§§ 7 and 8), reconsideration of old settled (§ 9) andunsettled (§ 10) issues, and some things that happen only on Earth,some indeed only in these reviews (§§ 10 and 11).
| CHARM2: An updated Catalog of High Angular Resolution Measurements
We present an update of the Catalog of High Angular ResolutionMeasurements (CHARM, Richichi & Percheron \cite{CHARM}, A&A,386, 492), which includes results available until July 2004. CHARM2 is acompilation of direct measurements by high angular resolution methods,as well as indirect estimates of stellar diameters. Its main goal is toprovide a reference list of sources which can be used for calibrationand verification observations with long-baseline optical and near-IRinterferometers. Single and binary stars are included, as are complexobjects from circumstellar shells to extragalactic sources. The presentupdate provides an increase of almost a factor of two over the previousedition. Additionally, it includes several corrections and improvements,as well as a cross-check with the valuable public release observationsof the ESO Very Large Telescope Interferometer (VLTI). A total of 8231entries for 3238 unique sources are now present in CHARM2. Thisrepresents an increase of a factor of 3.4 and 2.0, respectively, overthe contents of the previous version of CHARM.The catalog is only available in electronic form at the CDS viaanonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/431/773
| 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.
| Asteroseismology with robotic telescopes
Asteroseismology explores the interior of pulsating stars by analysingtheir normal mode spectrum. The detection of a sufficient number ofpulsation modes for seismic modelling of main sequence variablesrequires large quantities of high-precision time resolved photometry.Robotic telescopes have become an asset for asteroseismology because oftheir stable instrumentation, cost- and time-efficient operation and thepotentially large amounts of observing time available. We illustratethese points by presenting selected results on several types ofpulsating variables, such as δ Scuti stars (main sequence andpre-main sequence), γ Doradus stars, rapidly oscillating Ap starsand β Cephei stars, thereby briefly reviewing recent successstories of asteroseismic studies of main sequence stars.
| The δ Scuti star FG Vir. V. The 2002 photometric multisite campaign
A high-accuracy multisite campaign was carried out from 2002 January toMay with a photometric coverage of 398 h at five observatories. Theconcentration on a few selected sites gives better consistency andaccuracy than collecting smaller amounts from a larger number of sites.23 frequencies were detected with a high statistical significance. 6 ofthese are new. The 17 frequencies found in common with the 1992-1995data are the modes with highest amplitudes. This indicates that thepulsation spectrum of FG Vir is relatively stable over the ten-yearperiod. Two frequencies have variable amplitudes and phases from year toyear as well as during 2002. These were both found to be double modeswith close frequencies. For the mode at 12.15 c/d this leads to anapparent modulation with a time scale of 129 d. The closefrequencies at 12.15 c/d are composed of a radial and a nonradial mode,suggesting a similarity with the Blazhko Effect seen in RR Lyrae stars.
| Instabilities in the excitation of non-radial pulsation modes in the δ Scuti star BV Circini
High resolution spectroscopic observations obtained in 1995 of theδ Scuti star BV Circini are analyzed and the results compared withthose obtained by Mantegazza et al. (\cite{Mantegazza02}) fromspectroscopic observations in 1996 and 1998. Non-radial pulsation modesboth of low and high degree have been observed. Most of them are thesame detected in the other two campaigns, however the strongesthigh-degree one (14.62 cd-1) is different from that observedin 1996 (13.85 cd-1), which in turn is different from thatobserved in 1998 (17.28 cd-1). The 13.85 cd-1smode is the only one of these independently detected in the threeseasons, in which it kept about the same amplitude. One high-degreeretrograde mode at 1.48 cd-1s has been independently detectedin the three campaigns. The mode amplitude variations are discussed andit is shown that large variations can occur from one year to the next.The mode identifications performed on the three datasets by means of thefit of line profile variations supply results in good agreement amongthemselves. The high degree prograde modes have azimuthal orders between12 and 14, while the retrograde one is about 7. Finally the stellarpulsation spectrum as derived from all the available spectroscopic andphotometric data, and which consists of about 20 terms, is discussed.Based on observations collected at ESO-La Silla.
| Non-adiabatic theoretical observables in δ Scuti stars
Phase differences and amplitude ratios at different colour photometricbands are currently being used to discriminate pulsation modes tofacilitate mode identification of κ-driven non-radial pulsatingstars. In addition to physical inputs (e.g., mass, T_eff, etc.), thesequantities depend on the non-adiabatic treatment of the atmosphere. Thispaper presents theoretical results concerning δ Scuti pulsatingstars. The envelope of each of these stellar structures possesses aconvection zone whose development is determined by various factors. Aninteracting pulsation-atmosphere physical treatment is introduced whichsupplies two basic non-adiabatic physical quantities: the relativeeffective temperature variation and the phase lag φT,defined as the angle between effective temperature variation and radialdisplacement. These quantities can be used to derive the phasedifferences and amplitude ratios. Numerivalues for these quantitiesdepend critically on the α MLT parameter used to calculate theconvection in the envelope. The dependence on α was analyzed andit was found that the use of colour observations may be of considerableimportance in testing the MLT. Finally, examples are given of howα introduces uncertainties in the theoretical predictionsregarding phases and amplitudes of photometric variations in δScuti pulsating stars.
| The rapidly rotating delta Scuti star AV Cetei
We present results from an international spectroscopic and photometriccampaign on the delta Scuti star AV Cet. The starhas a rich and complex pulsation spectrum, and we find 7 individualfrequencies, with evidence for many more present below our detectionlimit. We investigate the prospects for mode identification in fastrotators, using several different techniques. We compare the methods andconclude that although no single technique can give unambiguous modeidentification, the collective evidence does allow some conclusions tobe drawn, suggesting the presence of one radial mode at 14.598d-1. During the campaign we found the star HD9139 to be a variable. From our photometry we find evidencefor a variability time scale around 1 day, but we cannot find anunambiguous interpretation for its light variations.Based partly on observations made with the Danish 1.5 m telescope atESO, La Silla, Chile.
| 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
| Atmospheric properties and abundances of the delta Scuti star FG Virginis
Spectroscopic methods were used to investigate atmospheric parameters ofFG Virginis to pinpoint the position of this delta Scuti variable inthe HR diagram and to derive abundances. It was claimed in theliterature that this delta Scuti star is slightly metal overabundantcompared to the sun, but this could not be confirmed by us. The chemicalcomposition of FG Vir turned out to be solar. Temperature and log gvalues are in good agreement with the models which fit the observedpulsation frequencies best.
| Asteroseismological studies of three β Cephei stars: IL Vel, V433 Car and KZ Mus
We have acquired between 127 and 150 h of time-resolved multicolourphotometry for each of the three β Cephei stars IL Vel, V433 Carand KZ Mus over a time-span of 4 months from two observatories. Allthree objects are multiperiodic with at least three modes of pulsation.Mode identification from the relative colour amplitudes is performed. Weobtain unambiguous results for the two highest-amplitude modes of IL Vel(both are l= 1) and the three strongest modes of KZ Mus (l= 2, 0 and 1),but none for V433 Car. Spectroscopy shows the latter star to be a fastrotator (v sin i= 240 km s-1), whereas the other two havemoderate v sin i (65 and 47 km s-1, respectively).We performed model calculations using the Warsaw-New Jersey stellarevolution and pulsation code. We find that IL Vel is an object of about12 Msolar in the second half of its main-sequenceevolutionary track. Its two dipole modes are most probably rotationallysplit components of the mode originating as p1 on thezero-age main sequence; one of these modes is m= 0. V433 Car issuggested to be an unevolved 13-Msolar star just entering theβ Cephei instability strip. KZ Mus seems less massive (~12.7Msolar) and somewhat more evolved, and its radial mode isprobably the fundamental one. In this case its quadrupole mode would bethe one originating as g1, and its dipole mode would bep1.Two of our photometric comparison stars also turned out to be variable.HD 90434 is probably a new slowly pulsating B-type star, the dominantmode of which is a dipole, whereas the variability of HD 89768 seems tobe a result of binarity.It is suggested that mode identification of slowly rotating βCephei stars based on photometric colour amplitudes is reliable; weestimate that a relative accuracy of 3 per cent in the amplitudes issufficient for unambiguous identifications. Owing to the good agreementof our theoretical and observational results we conclude that theprospects for asteroseismology of multiperiodic slowly rotating βCephei stars are good.
| Variable stars in the globular cluster NGC 3201 - I. Multimode SX Phe type variables
We report on the discovery of 11 multimode SX Phoenicis type bluestragglers in the field of the southern globular cluster NGC 3201. Inthese variables both radial and non-radial modes are excited. For threevariables the derived period ratio is close to that observed in SXPhoenicis itself, suggesting that these stars are pulsating in thefundamental and the first-overtone radial modes. Using the McNamaraperiod-luminosity relation we have estimated the apparent distancemodulus to NGC 3201 to be 14.08 +/- 0.06 +/- 0.1 mag.
| Time-series spectroscopy of pulsating sdB stars - III. Line indices of PG 1605+072
We present the detection and analysis of line index variations in thepulsating sdB star PG 1605+072. We have found a strong dependence ofline index amplitude on Balmer line order, with high-order Balmer lineamplitudes up to 10 times larger than Hβ. Using a simple model, wehave found that the line index may not only be dependent on temperature,as is usually assumed for oscillating stars, but also on surfacegravity. This information will provide another set of observables thatcan be used for mode identification of sdBs.
| Near Continuous Photometry with the Whole Earth Telescope (WET)
The Whole Earth Telescope (WET) saw first light in 1988. It was inventedby scientists from the Astronomy Department, University of Texas atAustin. The idea was to generate a world-wide network of cooperatingastronomical observatories to obtain uninterrupted time-seriesmeasurements of some variable stars. The technological goal was toresolve the multi-periodic oscillations in these objects into theirindividual components; the scientific goal was to construct accuratetheoretical models of the target objects, constrained by their observedbehavior, from which fundamental astrophysical parameters could bederived. This approach has been extremely successful, and has placedstellar seismology at the forefront of stellar astrophysics. The networkis run as a single astronomical instrument with many operators, and thecollaboration includes scientists from all continents on our planet,taking part in the observations, data reduction, analysis andtheoretical interpretation. The expertise of Lithuanian astronomers inphotometry, and their access to the observing station Mt. Maidanak inUzbekistan, has been important for the success of the network.
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Observation and Astrometry data
| Constellation: | Virgo |
| Right ascension: | 12h14m15.46s |
| Declination: | -05°42'59.7" |
| Apparent magnitude: | 6.565 |
| Distance: | 83.056 parsecs |
| Proper motion RA: | -85.1 |
| Proper motion Dec: | 114.4 |
| B-T magnitude: | 6.863 |
| V-T magnitude: | 6.59 |
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