Overtone Pulsators Research Articles

The Masses and Pulsation Modes of Classical Cepheids

AbstractRecent general observations pertaining to the masses and pulsation modes of classical Cepheids are reviewed. Certain special ones of these variables that display unusual behavior such as long term amplitude variations, overtone pulsations, and double-mode behavior, including one Cepheid in the first and second overtones as well as those in the fundamental and first overtone, are discussed in some detail. I suggest that the amplitude varying supergiant Cepheid HR 7308, which seems to be pulsating in the second radial overtone, is alternating between states where there is enough helium to barely give kappa and gamma effect driving, and where the helium has settled too deep for this driving. Reestablishment of the helium may be due to rapid levitation of the CNONe elements which cause convection and which then dredge-up the helium again to suppress the convection and also to drive pulsations. The use of Fourier fitting to the light and velocity curves have revealed some features that are interesting and are discussed, such as the pulsation mode discrimination and the derivation of accurate Wesselink radii. The seven methods of determining the masses of these stars are presented with a short critique of each. Evolution and pulsation masses depend on uncertain observed luminosities, and these have been revised recently. Evolution masses also depend on the blue looping yellow giant evolution tracks that may need revision because of convective core overshooting and possible opacity, Z, or Y abundance increases. The most discrepant masses, however, are those that depend on period ratios – the “bump” and “beat” masses. The possibility that the Cepheid internal structure can be modified enough by doubling the material opacity seems unlikely. It is suggested, though, that perhaps the period ratio mass anomaly solution can be found in CNONe element enhancement by radiation absorption levitation that would give higher opacities by abundance effects instead of any revisions in the opacity calculations. Some details for this mass anomaly “solution” are presented.

Fourier coefficients of the RR Lyrae variables in NGC 6171

view Abstract Citations (9) References (12) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Fourier Coefficients of the RR Lyrae Variables in NGC 6171 Stellingwerf, R. F. ; Dickens, R. J. Abstract The set of Fourier coefficients of the RR Lyrae stars in the globular cluster NGC 6171 is presented, based on the observations of Dickens (1970). The Fourier phases and amplitudes are shown to vary smoothly and correlate well with the skewness and the acuteness of the light curve. The fundamental and overtone pulsators follow a smooth relation as these quantities vary, but a change in the slope is apparent when the mode changes. The U, B, and V Fourier parameters show no systematic deviation from the average trend. Phase-phase diagrams can now be compared for NGC 6171, Omega Cen, field RR Lyrae stars, and simple models. Publication: The Astrophysical Journal Pub Date: November 1987 DOI: 10.1086/165710 Bibcode: 1987ApJ...322..133S Keywords: Fourier Analysis; Globular Clusters; Stellar Models; Stellar Oscillations; Variable Stars; Coefficients; Spectral Energy Distribution; Stellar Magnitude; Ubv Spectra; Astrophysics; CLUSTERS: GLOBULAR; STARS: PULSATION; STARS: RR LYRAE full text sources ADS | data products SIMBAD (2)

A CHECK ON EU TAURI.

ABSTRACT New uvby beta RI photometry has been obtained to check the suggestion of Gieren and Matthews (1987) that the two-day classical Cepheid EU Tau had changed its period slightly and also showed a secondary period half the primary period. The present photometry does not support this suggestion. The earlier period is confirmed and improved, and there is no evidence of a secondary period. An improved color excess is derived, and this, when compared to values from a period-color relation, supports the view that EU Tau is an overtone pulsator.

Overtone pulsation in stars

view Abstract Citations (37) References (12) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Overtone Pulsation in Stars Stellingwerf, R. F. ; Gautschy, A. ; Dickens, R. J. Abstract It is well known that type 'c' RR Lyrae stars pulsate in the first-overtone mode. These stars also show a distinctive light curve shape. It is shown, using a simple model, that this shape is indeed an expected feature of the overtone and is caused by the reversal of phase of the luminosity variation at the pulsation node, deep in the star. This result also applies to other types of radially pulsating stars and should aid in identifying overtone pulsation directly from the light-curve shape. The model is then used to predict the light variation of type 'e' (second-overtone) pulsators. Publication: The Astrophysical Journal Pub Date: February 1987 DOI: 10.1086/184834 Bibcode: 1987ApJ...313L..75S Keywords: Blue Stars; Stellar Models; Stellar Oscillations; Variable Stars; Giant Stars; Light Curve; Stellar Luminosity; Astrophysics; STARS: PULSATION; STARS: RR LYRAE full text sources ADS |

CLASSICAL CEPHEID LIGHT CURVES REVISITED.

ABSTRACT Fourier decompositions are made of the B, V, R, and I classical Cepheid observations of Moffett and Barnes. The Fourier diagrams for V agree very well with the corresponding plots of Simon and Lee. The B, R, and I diagrams resemble the plots for V, but with small, systematic shifts in the phases φ21 and φ31. The 2.5-day star, DT Cyg, is confirmed as a likely overtone pulsator by its anomalous position in the Fourier plots. Finally, the authors study the Fourier phase quantity φ41, and introduce phase-phase diagrams to look at the Hertzsprung progression. Discontinuities in these diagrams support the idea that the long-period and short-period Cepheids may reach their limit cycles in different ways.

Convection, the blue edge of the RR Lyrae gap, and a comparison of one-dimensional and two-dimensional hydrodynamic simulations

view Abstract Citations (13) References (19) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Convection, the blue edge of the RR Lyrae gap, and a comparison of one-dimensional and two-dimensional hydrodynamic simulations Deupree, R. G. Abstract Two-dimensional hydrodynamic simulations of the interaction of convection and pulsation at the blue edge of the RR Lyrae gap are performed. These calculations confirm the results found by Stellingwerf that convection makes the blue edge bluer and that the effect is more pronounced for overtone pulsation and for lower helium abundance. This reduces the sensitivity to helium abundance of the blue edge location and of the color width of the instability strip to the extent that neither quantity can be expected to be a reliable indicator of the helium abundance in the surface layers of RR Lyrae variables in globular clusters. Publication: The Astrophysical Journal Pub Date: September 1985 DOI: 10.1086/163430 Bibcode: 1985ApJ...296..160D Keywords: Cepheid Variables; Convection; Hydrodynamic Equations; Stellar Models; Stellar Oscillations; Eddy Viscosity; Helium; Stability; Stellar Cores; Astrophysics full text sources ADS |

BRIGHT LONG-PERIOD VARIABLES IN THE DIRECTION OF THE MAGELLANIC CLOUDS : FOREGROUND STARS OR SUPERGIANTS ?

ABSTRACT Radial velocities and infrared photometry have been obtained for seven bright long-period variables in the direction of the Magellanic Clouds. Five stars with periods shorter than 250 days were found to be Cloud members. They are probably core-helium burning supergiants of about 15 times the solar mass; there is also a possibility that they are overtone pulsators on the upper asymptotic branch with masses in the 7-9 solar mass range. It had previously been suggested that the bright short-period (100-250 days) LPVs might be foreground Mira variables of low mass in the Galactic halo. The supergiant long-period variables in the Magellanic Clouds exhibit a distinct period-luminosity relation which should be useful for the purpose of extra-Galactic distance determination.

Kinematic Evidence For Fundamental Mode Pulsation in the Short-Period Classical Cepheid SU Cassiopeiae

The short period and small amplitude of pulsation for the 1d.95 Cepheid SU Cas make it an excellent candidate for pulsation in a purely excited mode, and, as summarized by Gieren (1982), there is some evidence from recent radius determinations for this variable which suggests that it is indeed an overtone pulsator.

A Study of the Short-Period Cepheid EU Tauri

EU Tauri is a classical Cepheid with one of the shortest period known. A Fourier decomposition study of its V light curve by Simon S Lee (1981) revealed a peculiar position in phase-period diagrams, very similar to the star SU Cas which is probably an overtone pulsator (Gieren, 1982). This suggested the possibility that EU Tau might be another galactic overtone pulsator. In order to investigate this question, some 100 new photometric observations of this star on the UBVRI (Johnson) system were obtained with the #2 0.9m telescope of KPNO. Simultaneously, 43 CCD spectra of the star were secured on the Coudé feed telescope of KPNO which were measured for radial velocities using a correlation technique. These velocities have an internal accuracy of better than 0.5 km/s and define a complete velocity curve of EU Tau.

Phase lags and pulsation modes of classical Cepheids

The first-order phase lag between light and velocity is calculated from Fourier decompositions of the variations of 12 classical Cepheids. The phase lags have a narrow range, with maximum expansion velocity always retarded with respect to maximum light. The average value of the first-order phase lag is found to be approximately -0.3, close to the theoretical value obtained from the models of Simon and Davis. When the phase lag is plotted against period, two of the stars stand out. These stars are SU Cas and AZ Cen, both suspected overtone pulsators. We further investigate AZ Cen by combining the light curves of three observers and plotting the star on the cP21-period diagram of Simon and Lee. The tentative result is seen to strengthen both the identification of AZ Cen as an overtone pulsator and the possible role of the first-order phase lag as a discriminator of mode. We close with a discussion of our results and of the uncertainties which remain. Subject headings: stars: Cepheids stars: pulsation

OH/IR massers. IV - Evolution, pulsation, and nature of the sources

The evolution, pulsation, and nature of the type II OH/IR stars is analyzed using the extensive data base and trends described in the third paper in this series. Using evolutionary tracks and pulsation theory, the lowest luminosity (M/sub bol/>-5) masers on the asymptotic giant branch (AGB) are shown to be cool, fundamental mode pulsators which are possibly metal rich. Comparison of the positions in the period-luminosity plane of the masers width the long-period variables in the Magellanic Clouds and in the Galactic bulge suggests that in fact all of the redder (>5) and more efficient (>1) masers on the AGB are fundamental mode pulsator. The periods of several of the bluer (<3) and less efficient (<0) AGB masers are consistent with first overtone pulsation; these objects are similar to the classical IRC Miras except bolometrically brighter. As well as the AGB maser sources, there is a class of sources which are core helium burning supergiants, but whether they pulsate in the fundamental or first overtone models or not at all is not clear at present.

INCREASED EVIDENCE FOR OVERTONE PULSATION IN GALACTIC CEPHEIDS : SU CAS.

ABSTRACT The status and the pulsation mode of the classical cepheid SU Cas are discussed in light of a radius value which has been determined on the basis of a homogeneous and accurate data set and two independent methods. It is hypothesized that (1) the radius within its error limits is not compatible with currently accepted period-radius relations, assuming fundamental mode pulsations, (2) the anomalously large Wesselink radius mass can only be explained if first- or second-order pulsation is assumed, (3) the location of the star in the H-R diagram with respect to the fundamental mode blue edge indicates the likelihood of first overtone pulsation, (4) the relative radius variation and effective temperature show the star to belong to a very small group of cepheids which are probably overtone pulsators, and (5) the peculiar properties of the light curve Fourier components can probably be understood in terms of a nonfundamental mode pulsation.

New Observations of the Beat Cepheid Variable AX Velorum

Evidence exists for mode energy changes in beat Cepheid variable stars over the 20-30 year interval during which photoelectric observations of the objects have been obtained. For TU Cas, Hodson, Stellingwerf and Cox (1979) have found that the first overtone amplitude has been decreasing with time from 0.4 to 0.25 mag over a 67 year timebase; these authors also included some early visual estimates in their analysis. For U TrA, Faulkner &amp; Shobbrook (1979) have found that the first overtone pulsation has been increasing relative to the fundamental over a twenty year timebase.

Radii and luminosities of classical cepheids

The radiii of 17 classical Cepheids are determined. The linear surface brightness-colour relationS v=b(B−V)o+const is accepted. The present method permits the determination of the coefficientb for each star separately and the obtaining of the absolute magnitude of Cepheids. The coefficientb shows a slight dependence on the periodP of stars. The period-luminosity relation is approximately the same as the one obtained by van den Bergh (1976) for Cepheids in open clusters. The simultaneous radial velocity and photoelectric observation may show the phase shifts between motions of the continuum layer and of the level where the Fe I line is formed. The Cepheidl Car is outside the instability strip, and probably has a red companion as was suggested by Schmidt (1980a). Conclusions about the existence of overtone pulsators cannot probably be drawn only from the scattering in the period-radius relation.

RR Lyrae AND BL Herculis Variables

AbstractThe RR Lyrae variables are currently believed to have masses between about 0.5 and 0.8 M⊙, effective surface temperatures between 6350 and 7500K, radii from about 4.0 to 6.0 R⊙ and luminosities between log L/L⊙ of 1.5 and 2.0. Since they are found in population II locations, they generally have Y = 0.3 and Z = 10−3 , but there are exceptions for both higher Z like the sun and lower Z like 0.0002. In globular clusters the periods range from 0.25 - 0.45 day for the first overtone pulsators and 0.40 - 0.80 day for those in the fundamental mode, depending on their luminosity. At transition lines, to be discussed in detail below, the switch from fundamental to first overtone, or maybe vice versa, involves a period change factor of about 0.74 - 0.75.

HD 185332 A NEW DEL SCT STAR.

ABSTRACT Recent photometric observations show that HD 185332 is a new δ Scuti variable star. Spectrograms of this star fix its spectral type as A3 V. Indirect determination of MV and (b - y) plus the deduced period place this star in agreement with the PLCR and establish it as a first overtone pulsator.

A PHOTOELECTRIC STUDY OF THREE SOUTHERN DEL SCT STARS.

ABSTRACT Differential photoelectric observations of three Delta Scuti stars AI Scl, WZ Scl, and XX Scl were obtained on ten nights during October 1978. Al Scl did not exhibit strictly periodic behavior, but showed a tendency to pulsate at 134 minutes. WZ Scl and XX Scl were both found to be multiperiodic, with period ratios of 0.6853 and 0.9522, respectively. As the period for radial fundamental and first overtone pulsation is 0.76, the observed period ratios are interpreted as caused by nonradial pulsation. A slightly modified Jurkevich period search method, used to obtain these results, is described.

RR Lyrae and BL Herculis variables

The RR Lyrae variables are currently believed to have masses between about 0.5 and 0.8 M/sub solar mass/, effective surface temperatures between 6350 and 7500/sup 0/K, radii from about 4.0 to 6.0 R/sub solar mass/ and luminosities between log L/L/sub solar mass/ of 1.5 and 2.0. Since they are found in population II locations, they generally have Y = 0.3 and Z = 10/sup -3/, but there are exceptions for both higher Z like the sun and lower Z like 0.0002. In globular clusters the periods range from 0.25 to 0.45 day for the first overtone pulsators and 0.40 to 0.80 day for those in the fundamental mode, depending on their luminosity. At transition lines, discussed in detail, the switch from fundamental to first overtone, or maybe vice versa, involves a period change factor of about 0.74 to 0.75.

Variables in NGC 4590

A photoelectric sequence has been set up in the Oosterhoff Type II cluster NGC 4590 (M68) and UBV photographic photometry has been secured for all the uncrowded stars using the Radcliffe 1.9 m telescope. A series of 40 plates in each of UBV have enabled light and colour curves to be obtained for all the uncrowded RR Lyrae variables. For most of these, periods were found very similar to those found by Osterhoff. One star, however, showed variable amplitude from night to night and great difficulty was encountered in fitting a single period. Subsequent p.e. photometry with the 1.0 m SAAO reflector has indicated that this RR Lyrae variable is pulsating in at least two modes. The mean colour is that of the transition from fundamental to first overtone pulsators, as shown by the other ab and c type variables in the cluster. The two periods found are 0.526 and 0.392 days with amplitudes 0.39 and 0.47 mag indicating a ratio P1/Po ~ 0.745. Further observations are planned to give an accurate value for this ratio and to obtain simultaneous radial velocities to give mass and radius information.

Theoretical pulsation of metallic-line stars

The linear-theory radial-pulsation stability of low-helium delta Scuti variable models (1.0--2.5 Msun) has been investigated to see if metallicism and pulsation can occur simultaneously. Metallicism, which occurs in slowly rotating stars after the gravitational settling of He and the loss of the He II convection zone and its deep mixing for Y< or approx. =0.1, can then be established rapidly compared with the evolution time scale. Pulsation can still occur with driving due to the residual helium and the enhanced hydrogen. With the reduced helium giving no connection zone, the pulsation instability strip, whose blue and edges are estimated in this paoer, is about half as wide as with a normal helium abundance. Zero helium in the surface driving regions, however, produces blue edges so red that probably no instability strip exists at all. The red edge, predicted theoretically on the basis of the importance of convection in the outer zone, agrees well with the observational one. Cool, low-helium and metallic-line stars are then predicted to pulsate in a 200--500 K wide strip that is widest between the main-sequence luminosity of 5 Lsun and 15 Lsun. This strip reasonably includes the observed pulsating delta Del and mild Am stars, butmore » there may be conflicts. Since blue edges for varying ionization-zone helium content occur across the entire instability strip, bluer first and higher overtone pulsations are also predicted everywhere from less than 7000 K to over 8000 K, the redder ones probably showing metallicism.« less