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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.
| 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
| Simultaneous intensive photometry and high resolution spectroscopy of delta Scuti stars. IV. An improved picture of the pulsational behaviour of X Caeli
The delta Scuti star X Caeli has been the target of a simultaneousphotometric (14 consecutive nights) and spectroscopic campaign (8consecutive nights). From the analysis of light curves we were able topick up 17 frequency components, most of which were already detected intwo previous campaigns. The comparison with the results of the previouscampaigns shows that while some terms are rather stable (in particularthe dominant mode at 7.39 cd-1 ) others have conspicuousamplitude variations. 14 photometric terms have been also detected inthe radial velocity curve or in the analysis of the line profilevariations. There are no spectroscopic terms without photometriccounterparts, and this means that there are no high-degree modes asobserved in other delta Scuti stars. The simultaneous fit of light andline profile variations has allowed the estimation of the inclination ofrotational axis (about 70o) and the l,m identification formany modes. In particular there is clear evidence that the two shortestperiod modes are retrograde. Rather reliable results were found for thedominant mode which has l=1, m=-1. The resulting physical parameters ofits pulsation are in good agreement with the prediction of theoreticalmodels and suggest for this star a mixing length parameter of about 0.5.Finally the fundamental stellar physical parameters and their refinementare discussed in the light of the identification of the 7.47cd-1 term as a radial mode. Based on observations collectedat European Southern Observatory(Proposal 58.E-0278)
| Excitation and visibility of high-degree modes in stars
Observational evidence for excitation of non-radial modes in stars isconfronted with the results of linear stability surveys for stellarmodels. We consider various types of pulsators on the upper mainsequence as well as stars in the Cepheid strip. Our stability surveycovers the whole range of spherical harmonic degrees, l, whereinstability is found. There is fair agreement between the theoreticalinstability strip and the location of ζ Oph stars, but the observedand calculated periods do not agree in some stars. We suggest thateither pulsation is not responsible for the ζ Oph phenomenon orelse there are serious errors in mode identification in these cases. Wedo not find instability at long periods for early B-type stars,supporting the idea that pulsation is not responsible for the periodicvariations in Be stars. The agreement between the observed andcalculated periods of high-degree modes in δ Sct stars is not verysatisfactory. This is attributed to problems in mode identification. Wediscuss unstable modes of high degree in Cepheid models as a possiblemechanism for the low-amplitude radial velocities seen in some starswithin the instability strip. We find, however, that the observedperiods are at least a factor of 2 longer than the calculated periods.Finally, we discuss the possibility of observing modes of high degreephotometrically. We suggest that a large number of high-degree modes maybecome detectable by future space-borne photometric missions. Theconfusion arising from these modes may greatly reduce the value of suchobservations for asteroseismology. However, they will be very importantin studying the mechanism of mode selection.
| XCOV13 and Asteroseismology of Delta Scuti Stars
The Whole Earth Telescope XCOV13 campaign, which was carried out from atemporary command center in Vienna, included two main-sequencepulsators: the delta Scuti star 4 CVn and the new gamma Dor variable, HD108100. The astronomical results for these stars are summarized. Thepaper also discusses the progress as well as further potential of deltaScuti stars for asteroseismology. Extensive multi-site campaigns ofindividual delta Scuti stars show that 24 or more pulsation modes with lvalues of 0, 1 and 2 can be detected photometrically. Spectroscopically,also about 30 modes have been detected, and these can be identified withmodes of l values up to 20. Since each technique favors the detection ofspecific types of modes, hundreds or thousands of modes must be excitedin delta Scuti stars. We examine the quantities which can be matchedbetween observations and theoretical models specifically computed foreach star. Recent progress in the mode identification of multiplepulsation modes is illustrated by presenting an application of the phaseshift method for the two stars, FG Vir and 4 CVn, recently measured byDSN (Delta Scuti Network) and WET. The XCOV13 results on 4 CVn can beused to illustrate why less extensive studies of delta Scuti could leadto erroneous conclusions of unstable pulsation modes.
| High azimuthal number pulsation modes in fast rotating δ Scuti stars: the case of HD 101158 = V837 Cen.
The frequency analysis of the line profile variations of the fastrotating (vsini=132km/s) δ Scuti star HD 101158, observed forthree consecutive nights, shows the presence of two high azimuthalnumber non radial pulsation modes. The star is probably seen almostequator-on and both modes (ν_i_=12.9c/d and ν_2_=18.5 c/d) areprograde with m=-10 and m=-14 or -15 respectively; their frequencies aredifferent with respect to the three frequencies identified inphotometric data (Poretti 1991), which probably owe due to low l modes.Indications of the presence of these photometric modes have been foundfrom the frequency analysis of the first two line moments. The lineprofile variations also show the possible presence of further modes withfrequencies of 16.2, 20.3 and 21.1c/d and small amplitudes.
| 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.
| 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.
| Insight into the Pulsational Behaviour of δ Scuti Stars
Not Available
| Simultaneous UVBY Photometry of 28-ANDROMEDAE
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1993A&A...273..473R&db_key=AST
| Doing research with small telescopes : frequency analysis of multiperiodic delta Scuti stars.
Not Available
| Pulsational behaviour of the Delta Scuti star X Caeli
1013 V observations of the Delta Sct star X Caeli obtained at La SillaObservatory on 10 consecutive nights have been analyzed in the frequencydomain. Five independent pulsational modes have been detected, and froma comparison with theoretical models we suggest that two of them arenonradial modes and one of them is the first overtone radial mode. Thetwo strongest modes are nonlinearly coupled and their light curves areslightly nonsinusoidal. Finally, the highest frequency mode could be ahigh-order nonradial mode excited by resonance with a low-order one. Acomparison with the former data set of Smyth et al. (1975) shows noevidence of variations of the mode amplitudes.
| Frequency analysis and pulsation mode identification of the Delta Scuti star HD101158
The results of 13 quasi-consecutive nights of observation of the DeltaScuti star HD101158 are presented. The observations are carried out on a50-cm reflector and are subjected to 1234B measurements, a frequencyanalysis, and a Stromgen analysis. Three terms and their correspondingsemiamplitudes are identified: f1 = 12.16222c/d, f2 = 10.83219c/d, andf3 = 9.27215c/d, corresponding to semiamplitudes of 0.0155 mag, 0.007mag, and 0.006 mag, respectively. The ratios of these terms, consideredin conjunction with the pulsational constants Qi, offer the possibilitythat the star is pulsating in both the first overtone and thefundamental radial mode with the excitation of a nonradial mode.Comparisons with earlier observations show that the star has been stablefor a time interval of four years. The measurements show that the staris well inside the instability strip, and it is very close to the hotborderline of the fundamental radial mode.
| Study of Delta Scuti stars in the Geneva photometric system. I - New photometric data and period analysis for nine stars
Results are presented of the period analyses for nine Delta Scuti stars,of which six are new short-period variable stars. For some of thesestars, extensive data sets covering time bases of the order of two yearsor more were obtained. The results from year to year are consistent withthe multiperiodic solution derived from the combined data for thosestars with the largest data sets. In some cases of less frequentlyobserved stars, the results are not always compatible with one another.It is suggested that, generally, this is due to insufficient datasampling or too narrow time bases. The fact that many unevolved orslightly evolved Delta Scuti stars are multiperiodic with very smallamplitudes of a couple of hundredths of a magnitude is confirmed.
| 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.
| The 68th Name-List of Variable Stars
Not Available
| On the Variability of HD 66194 and of HD 101158
Not Available
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