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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.
| 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.
| 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.
| Pulsation of the δ Scuti star θ2 Tau: new multisite photometry and modelling of instability
The results of a multisite photometric campaign of θ2Tau are reported. This binary system consists of an evolved and amain-sequence A star, both situated inside the instability strip. The12th Delta Scuti Network campaign included 152 h of high-precisionphotometry obtained at four observatories. This leads to the derivationof 11 frequencies of pulsation in the 10.8 to 14.6 cycle d-1range. These frequencies confirm the results from previous Earth-based(1982-1986) as well as satellite (2000) photometry, although amplitudevariability on a time-scale of several years is present. We show that atleast two high frequencies (26.18 and 26.73 cycle d-1) arealso present in θ2 Tau. Arguments are given that thesehigh frequencies originate in the main-sequence companion and are notcombination frequencies, fi+fj, from the primary.Models for both the primary and the secondary components were checkedfor the instability against radial and non-radial oscillations. All hotmodels of the primary with Teff > 8000 K are stable in theobserved frequency range. The best fit between the theoretical andobserved frequency ranges is achieved for models with Teff~7800 K (or slightly higher), in agreement with photometric calibrations.The instability range spans two or three radial orders in the rangep4 to p6 for radial modes. Post-main-sequencemodels (with or without overshooting) are preferable for the primary,but main-sequence models with overshooting cannot be excluded. For theless-luminous secondary component the instability range is wider andspans 5 to 7 radial orders from p2 to p8. Theobserved frequencies lie around radial modes p5 top6. The main uncertainties of these results are caused by asimple treatment of the convective flux in the hydrogen ionization zone.
| 29 frequencies for the δ Scuti variable BI CMi: the 1997-2000 multisite campaigns
A multisite campaign of BI CMi was carried out with excellent frequencyresolution and high photometric accuracy from 1997 to 2000, includingtwo long observing seasons. 29 pulsation frequencies could be extractedfrom the 1024h (177 nights) of photometry used. The detected frequenciesinclude 20 pulsation modes in the main pulsation frequency range from4.8 to 13.0cycled-1 (55 to 150μHz), eight linearcombinations of these frequencies, and a very low frequency at1.66cycled-1. Since the value of the low frequency at1.66cycled-1 cannot be identified with a linear combinationof other frequencies, g-mode pulsation is suspected, but rotationalmodulation of abundance spots cannot be ruled out. BI CMi, which issituated near the cool edge of the classical instability strip, may beboth a δ Scuti and a γ Doradus star. Another outstandingproperty of BI CMi is the presence of a number of close frequency pairsin the power spectrum with separations as small as0.01cycled-1. A rotational velocity ofvsini=76+/-1kms-1 was determined from a high-dispersionspectrum. From phase differences, the dominant modes can be identifiedwith l values from 0 to 2. The spectral type and evolutionary status ofBI CMi are examined.
| Close frequency pairs in Delta Scuti stars
The majority of the well-studied delta Scuti stars shows frequency pairsin the power spectra with frequency separations less than 0.06cd-1 (0.7 mu Hz) as well as amplitude variability. We examinethe interpretation in terms of separate excited stellar pulsation modes,single modes with variable amplitudes, and observational problems. Thevariable-phase technique, which examines the phase jumps near the timesof minimum amplitude of an assumed single frequency, is applied to theextensive data of the star BI CMi, which shows some of the most extremebehavior. The following results are found for the 5 features in thepower spectrum which could be explained as single modes with variableamplitudes or as double modes: for three features it can be shown thatthese are indeed pairs of separate pulsation modes beating with eachother: at times of minimum amplitude the phase jumps are observed andboth the observed amplitude and phase variations can be predictedcorrectly by assuming two separate modes of nearly equal frequencies.Artifacts caused by observational error, insufficient frequencyresolution or variable amplitudes can be ruled out. A fourth pair has aprobable origin in two excited modes, while a 5th case is inconclusivedue to long time scales of variability and small amplitudes. Theexistence of close frequency needs to be taken into account in planningthe lengths of earth-based as well as space campaigns so that sufficientfrequency resolution is obtained. Possible reasons for the existence ofclose frequencies in delta Scuti stars are considered. They include thedense frequency spacing caused by the presence of mixed modes,rotational splitting as well as near-coincidence of the frequencies ofmodes with different l values (the so-called Small Spacing).
| 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
| 30+ frequencies for the delta Scuti variable 4 Canum Venaticorum: results of the 1996 multisite campaign
The evolved delta Scuti variable 4 CVn was observed photometrically for53 nights on three continents. We found a total of 34 significant and 1probable simultaneously excited frequencies. Of these, 16 can beidentified as linear combinations of other frequencies. All significantfrequencies outside the 4.5 to 10 cd(-1) (52 to 116 mu Hz) range can beidentified with frequency combinations, f_i +/- f_j, of other modes withgenerally high amplitudes. There exists a number of closely spacedfrequencies with separations of ~ 0.06 cd(-1) . This cannot be explainedin terms of amplitude variability. The results show that even for starson and above the main sequence other than the Sun, a very large numberof simultaneously excited nonradial oscillations can be detected byconventional means. Since all pulsation modes with photometricamplitudes of 1 mmag or larger have now been detected for this star, apresently unknown mode selection mechanism must exist to select betweenthe 1000+ of low-degree modes predicted to be excited for this (and manyother) stars. Phase differences and amplitude ratios between the y and vcolors are determined for the ten main modes. The phase differencesindicate p_1 to p_4 modes of l = 1 for four of these modes. The formulaeto determine the uncertainties in the amplitudes and phases ofsinusoidal fits to observational data are derived in the Appendix.
| YY Canis Minoris: Contact or near contact system?
New V photoelectric observations of the eclipsing system YY CMi,obtained at La Silla, Chile, and Merate Observatory, Italy, arepresented. New times of minima and ephemeris based on our observationsare also given. The V light curve was analysed by using the WD code toderive the geometrical and physical parameters of the system. Since nospectroscopic mass ratio is available, the q-search method was appliedto yield the preliminary range of the mass ratio in order to search forthe final solution. First the unspotted solution was carried out byusing the unperturbed parts of the light curve and applying the DCprogram of the WD code. The solution was performed by assuming contact(mode 3) and semi-detached (mode 4) configuration, since noclassification of the system is possible from the shape of the lightcurve. The solution in mode 4 does not lead to an acceptable model,since the secondary was found to be slightly overcontact. Therefore thecontact solution was finally adopted. Moreover the light curvepeculiarities (Max II fainter than Max I and excess of light around thephase 0.32) were explained by assuming a cool and a hot spot on thesurface of the secondary (cooler) component. The degree of contact isvery small (f~ 3%) and the thermal contact is poor (T_1-T_2)~ 650 K.These results together with the high photometric mass ratio q~ 0.89indicate that YY CMi is very probably a system at the beginning or theend of the contact phase. Based on observations partly made at theEuropean Southern Observatory (ESO). Table 1 is only available inelectronic form at the CDS via anonymous ftp to cdsarc.u-strasbg.fr(130.79.128.5) or via http://cdsweb.u-strasbg.fr/Abstract.html
| CCD photometry of a delta Scuti variable in an open cluster. III. V 465 Persei in the alpha Persei cluster
We present the results of real-time CCD differential photometry for thedelta Scuti variable V 465 Per. The observations were performed forthirteen nights between November, 1994 and January, 1995. Total 3345points of differential V magnitudes were collected during theobservation period of 76.4 hours. From the Fourier analysis, we havedetected four frequencies as follows; f_1=14.040 c/d, f_2=17.208 c/d,f_3=33.259 c/d and f_4=13.721 c/d. Two frequencies of 12.50 c/d and33.49 c/d detected previously by Slovak (1978, ApJ 223, 192) maycorrespond to our f_1 and f_3, respectively. For each frequency,pulsation constants of Q_1=0.0520+/-0.008, Q_2=0.0425+/-0.006,Q_3=0.0220+/-0.003 and Q_4=0.0533+/-0.008 were derived from severalobservational properties of V 465 Per. Only the value of Q_3 is found tobe within the range of theoretical p-mode oscillations and the otherones show large differences relative to the theoretical values. The highQ-values might be interpreted as the occurrence of g-mode oscillationsin V 465 Per, even though it can not rule out the possibility ofsystematic errors (Breger 1990; Delta Scuti Star Newsletter, 2, 13)related to rotational velocity.
| γ Doradus and δ Scuti stars: cousins or twins?
γ Doradus stars are a group of slowly pulsating early F dwarfswith typical low frequencies near 1c/d. The pulsation modes are probablyg modes. These stars are slightly cooler than the typical δ Scutivariables, which pulsate with higher frequencies of typically 10c/d(mostly nonradial p modes). This paper examines the relationship betweenthe two groups of variables. Additional low-frequency variability hasbeen reported for fewer than 10% of the 300 δ Scuti starsexamined. In at least one case (1 Mon), the observational data areconsistent with an alternate interpretation in terms of a modeinteraction, f_1_-f_2_, between two p modes of higher frequency, ratherthan by the excitation of g modes. In several other stars (e.g. 4 CVn),the reported low-frequency variability may originate in the comparisonstar used. Arguments are given that for a number of stars the observedlow-frequency variations are caused by observational errors (such asinstrumental drift and transparency variations). A few δ Scutistars remain for which intrinsic γ Doradus-type variability mayalready have been discovered, although no case is well-studied. One ofthe best candidates is the star BI CMi, which is situated in the smallregion of overlap of the two groups of pulsators in theHertzsprung-Russell diagram. The star deserves further study.
| Main Sequence Variables
The pulsators along and near the main sequence are well-suited forasteroseismology and provide a probe of the stellar interior and itschanges with evolution. With the exception of rapidly oscillating Apstars (roAp), the pulsation periods range from 0.5 h to days. Thisrequires multisite campaigns lasting several weeks. The delta Scuti,roAp and beta Cephei variables offer the greatest potential, while thelonger-period g-mode pulsators (SPB -- slowly pulsating B stars -- andgamma Doradus variables) are very difficult to study. A summary of themultiperiod structure of delta Scuti stars is given. The twobest-studied stars, FG Vir and CD--24(deg) 7599, both have been WETtargets. A preliminary analysis of the 1995 campaign of FG Vir hasalready detected 19 frequencies. The standard photometric WET techniquehas a high duty cycle since the variable star is observed continuouslywith one channel. The study of main sequence variables requiresphotometric stability at low frequencies. The extension of the WETtechnique to low frequencies and its modification are discussed.
| 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.
| Insight into the Pulsational Behaviour of δ Scuti Stars
Not Available
| 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.
| The delta Scuti star BI Canis Minoris (identically equals HD 66853): Pulsational behavior and a critical discussion of physical parameter determination
A two site photometric campaign on the delta Scuti star BI CMi (2302 Vobservations over 16 nights) has allowed us to detect unambiguously fourpulsation frequencies nul = 8.246, nu2 = 8.865,nu3 = 7.433 and nu4 = 8.515 c/d) with amplitudesbetween 22 and 5 mmag. The data also show the presence of the nonlinearcoupling term nu1 + nu2, the 2 nu1 termand the possible presence of two other frequencies with amplitudes of2-3 mmag. Other components with further smaller amplitudes are probablypresent, but the data do not allow reliable identifications. We discussthe identification of the pulsation modes in term of nonradical p modes,and we also point out the uncertainties on these identificationassociated to the physical parameter estimates. The possiblemicrovariability of HD 67028, one of the two comparison stars, is alsodiscussed.
| Doing research with small telescopes : frequency analysis of multiperiodic delta Scuti stars.
Not Available
| The 70th Name-List of Variable Stars
Not Available
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Observation and Astrometry data
| Constellation: | Canis Minor |
| Right ascension: | 08h05m31.71s |
| Declination: | +02°09'31.7" |
| Apparent magnitude: | 9.195 |
| Proper motion RA: | -14.8 |
| Proper motion Dec: | -3.5 |
| B-T magnitude: | 9.693 |
| V-T magnitude: | 9.237 |
Catalogs and designations:
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