Pulsation Constants Research Articles

HD 8801: A Unique Single Am Star with γ Doradus and δ Scuti Pulsations

We have discovered the first example of a star pulsating intrinsically with both γ Doradus and δ Scuti frequencies. The star, HD 8801, is an Am metallic-line star that appears to be single. Since the vast majority of Am stars are members of binary systems with periods less than 1000 days and also do not pulsate, HD 8801 possesses a very unusual, if not unique, combination of physical properties. Our photometry, acquired with an automatic telescope at Fairborn Observatory, resolves six independent pulsation periods between 0.048 and 0.404 days. The two longest periods lie within the range of γ Dor variables, while the four shorter periods are within the range of δ Sct stars. Eleven radial velocities, obtained over an 11 month period, have a mean of 0.8 ± 0.3 km s-1, providing no evidence for a spectroscopic companion. The star is on the main sequence and lies within both the γ Dor and δ Sct instability strips. Pulsation constants computed for the six periods agree with pulsation constants computed for other γ Dor and δ Sct variables. HD 8801 is also the first confirmed case of a metallic-line star pulsating with γ Dor frequencies. Its projected rotational velocity of 55 km s-1 is typical for Am stars, which, as a group, rotate more slowly than normal A stars. HD 8801's slow rotation compared to normal A stars does not appear to arise from either a binary companion or evolutionary expansion and thus remains a puzzle. The coexistence of metallicism and pulsation in several main-sequence stars near the red edge of the δ Sct strip contradicts recent models that predict pulsations only in more evolved stars.

Multiperiodicity in pulsating red giants

AbstractWe describe several aspects of the variability of bright pulsating red giant (PRG) stars, with emphasis on the determination of pulsation modes and pulsation masses by using observed multiperiodicity and pulsation constants (Q- values). Our studies of bright PRGs provide a model for the analysis and interpretation of the thousands of PRGs being discovered in surveys of Local Group galaxies.

Analysis of a δ Scuti spectroscopic binary: CQ Lyncis

CQ Lyn is a new double-lined spectroscopic binary, composed of an Am Scuti and a solar-like star, with an orbital period of 12.50736 d and a zero-eccentricity. Physical parameters of both stars are well constrained. The characteristics of the primary are the following: M = 1:714 M, Te = 6760 K, log L=L = 1:097 and logg = 3:85 dex. Power spectra of Hipparcos photometry and Coravel radial velocities show multi-period pulsation behaviour. Three frequencies are identified: f1 = 8:86725, f2 = 8:81150 and f3 = 8:91007 c/d and are assumed to be l = 2 f -modes split by rotation, considering their pulsation constants Q1= 0:0356, Q2= 0:0359 and Q3= 0:0355 d. Two combination oscillations are also present in the power spectrum at frequency f1+f2 and f2+f3.

On the relationship between the δ Scuti and γ Doradus pulsators

We searched for δ Scuti-type pulsations amongst known and candidate γ Doradus stars. The motivations for such a project come from the need to understand the relationship of these two classes of pulsator better, from the present poor knowledge of the hot border of the γ Doradus phenomenon, and from the exciting prospects for asteroseismology should stars be found which have both types of pulsation excited. We acquired 270 h of observations and monitored a total of 26 stars. One target, HD 209295, turned out to be a member of both classes of pulsating star, but this object is peculiar in the sense that it is a close binary. We classify six of our targets as new bona fide γ Doradus stars, whereas nine more are good γ Doradus candidates, and three turned out to be ellipsoidal variables. One of our programme stars was found to be a δ Scuti star, with no additional γ Doradus variations. Furthermore, one star was already known to be a bona fide γ Doradus star, and we could not find an unambiguous explanation for the variability of five more stars. The analysis of our data together with improved knowledge of stars from the literature enabled us to revise the blue border of the γ Doradus phenomenon towards cooler temperatures. This new blue edge is much better defined than the previous one and extends from a temperature of about 7550 K on the ZAMS to 7400 K one magnitude above it. Five bona fide γ Doradus stars we observed are located inside the δ Scuti instability strip, but none of them exhibited observable δ Scuti pulsations. We therefore suggest that γ Doradus stars are less likely to be δ Scuti pulsators compared with other normal stars in the same region of the lower instability strip. In addition, we show that there is a clear separation between the pulsation constants Q of δ Scuti and γ Doradus stars. The γ Doradus stars known to date all have Q>0.23 d.

A Photoelectric Study of the Am δ Scuti Variable 60 Tau

AbstractFive nights of photoelectric photometric observations through v and y filters confirm the pulsation of the Am δ Scuti variable 60 Tau. Power spectra of the light curves show multiple periods; two modes f1 = 13.0364 d−1 and f2 = 11.8521 d−1 are definitely identified. The phase differences, ϕv − ϕy, suggest that 60 Tau pulsates in low-degree modes; the pulsation constants, Q, suggest these are low overtone modes; and the frequency ratio implies that at least one mode is nonradial.

CCD photometry of a δ Scuti variable in an open cluster

We present the results of real-time CCD differential photometry for the δ Scuti variable V 465 Per. The observations were performed for thirteen nights between November, 1994 and January, 1995. Total 3345 points of differential V magnitudes were collected during the observation period of 76.4 hours. From the Fourier analysis, we have detected 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 and 33.49 c/d detected previously by Slovak (1978, ApJ 223, 192) may correspond to our f 1 and f 3 , respectively. For each frequency, pulsation constants of , , and were derived from several observational properties of V 465 Per. Only the value of Q 3 is found to be within the range of theoretical p-mode oscillations and the other ones show large differences relative to the theoretical values. The high Q -values might be interpreted as the occurrence of g-mode oscillations in V 465 Per, even though it can not rule out the possibility of systematic errors (Breger 1990; Delta Scuti Star Newsletter, 2, 13) related to rotational velocity.

The early-type variables

We review the observational status of several different kinds of intrinsic variables among the early-type stars and attempt to interpret the variations in terms of our current understanding of stellar pulsation. Four distinct types of intrinsic variable can be defined: theβ Cep, 53 Per,ζ Oph and λ Eri stars. A simple observational classification scheme, which is readily interpreted in terms of pulsation properties, is proposed. The limits of the instability strip and pulsation constants for theβ Cep and 53 Per stars is discussed. Problems with the interpretation of λ Eri stars in terms of pulsation are pointed out. The observations are consistent with rotational modulation. A problem with mode identification in λ Eri stars is discussed.

Observations of Pulsating OB Stars

Using examples from the literature, I try to show how astrophysical parameters of pulsating stars are derived and how certain (or, occasionally, uncertain) they are. The examples are arranged in the order of increasing input of a priori knowledge. Thus, I start with pulsation periods, because in most cases they can be obtained directly from observations. Then I consider the two stars for which pulsation constants have been determined without recourse to photometric calibrations. Next I show how multicolour photometry can help identify pulsation modes. Finally, I discuss the photometric Teff, log g, and pulsation constants. This leads to conclusions which contain some recommendations for the observers, including a list of promising targets for asteroseismology.

Baade-Wesselink radii for NGC 1866 Cepheids

Radial velocities and CCD photometry suitable for a Baade-Wesselink analysis are now available for six short-period Cepheids (HV12198, HV12199, HV12202, HV12203, HV12204, and V4) in the LMC cluster NGC 1866. As a prerequisite for such an analysis, O-C diagrams have been constructed and examined for seven of the NGC 1866 Cepheids (HV12197, HV12198, HV12199, HV12200, HV12202, HV12203, and HV12204), yielding improved periods and estimates of the rate of period change in these coeval variables. One star, HV12198, shows possible evidence for period change, but the phase mismatch due to that change is small enough to have negligible effect on its Baade-Wesselink radius. The computed radii are in good agreement with the Baade-Wesselink, theoretical and cluster/association period-radius relations of Fernie (1984) and the Galactic relation of Coulson and Caldwell (1989). The Flower (1977) color-effective temperature relation and the Becker et al. (1977) mass-luminosity relation lead to mean masses of 4.9 + or - 0.5 solar masses and 4.6 + or - 0.5 solar masses for the respective metallicities of (Y,Z) = (0.0273,0.0016) and (0.026,0.02). Pulsation constants are also computed for these stars.

Theoretical growth rates, periods, and pulsation constants for long-period variables

view Abstract Citations (195) References (42) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Theoretical growth rates, periods, and pulsation constants for long-period variables. Fox, M. W. ; Wood, P. R. Abstract An extensive set of linear, nonadiabatic pulsation models for red giant and supergiant stars is computed, in order that the dependence of pulsation periods (P), pulsation constants (Q), and growth rate on physical input parameters can be determined from the systematic behavior seen in the models. Also investigated is the extent of the dependence of P, Q, and growth rate on uncertain quantities such as atmospheric molecular opacity, surface boundary conditions, and effective temperature. The growth rate for the fundamental mode is found to increase with luminosity on the giant branch while the growth rate for the first overtone decreases. Dynamical instabilities found in previous adiabatic models of extreme red giants do not occur when nonadiabatic effects are included in the models. Publication: The Astrophysical Journal Pub Date: August 1982 DOI: 10.1086/160160 Bibcode: 1982ApJ...259..198F Keywords: Long Term Effects; Pulse Duration; Red Giant Stars; Stellar Oscillations; Supergiant Stars; Variable Stars; Linear Equations; Magellanic Clouds; Mass To Light Ratios; Propagation Modes; Stellar Models; Astrophysics full text sources ADS | data products SIMBAD (2)

L O,1,2, and 3 Pulsation Constants for Evolutionary Models of Delta-Scuti Stars

Evolutionary sequences at M/M/sub sun/ = 1.5, 2.0, and 2.5 were calculated with a version of the Eggleton stellar evolution code for an initial composition X = 0.70, Z = 0.02. From these sequences 14 models spanning the lower part of the Cepheid instability strip were selected for pulsation calculations. All the linear adiabatic m-degenerate eigenvalues with l< or =3 for pulsation constants Q( = P(/)/sup 1/2/) in the range 0/sup d/.0096< or =Q< or =0/sup d/.067 were obtained with a modified version of Dziembowski's second pulsation code, and our code uses a variant of the Cowling approximation for the nonradial modes. Four hundred and eighty-nine Q-values for 35 modes of types F--7H and g/sub 2/--p/sub 7/ are presented. Interpolation formulae are provided which predict the model masses, radii, and luminosities from the model periods and temperatures, with worst case errors of 4.4, 2.4, and 1.2% in M, L, and R, respectively, when using any of the radial mode or some of the nonradial f- and p-mode results. These formulae were applied to a selection of eight delta Scuti and three AI Velorum type variables to yield masses and luminosities in the ranges 1.68< or =M/M/sub sun/< or =2.56 andmore » 15.4< or =L/L/sub sun/< or =78.0, respectively. If our pulsation constants are relevant, then the primary uncertainties in these results follow from the uncertainties in the effective temperatures for these stars, which are here discussed.« less

THE DISTRIBUTION OF PULSATION CONSTANTS Q OF DEL SCT STARS.

ABSTRACT The distribution of pulsation constants Q of 127 δ Scuti stars indicates that these stars pulsate mainly in an overtone rather than in the fundamental mode.

The Pulsation Properties of Red Variables

AbstractRecently derived bolometric absolute magnitudes are used to investigate the pulsational properties of some classes of red variables. The Mira variables with periods over 200 days have pulsation constants appropriate to overtone pulsatore but the shorter period 135 day Miras seem to be hotter and less luminous and may be fundamental pulsators. The large amplitude Shapley-Nail variables in the SMC are probably fundamental pulsators with masses in the 5-10 solar range. Bright supergiant red variables in the LMC show evidence of the period-luminosity relation expected if they are in the early stages of core helium burning.

The effect of radial and non-radial stellar oscillations on the light, colour and velocity variations

The effect of radial and non-radial stellar oscillations on the observed light, colour and velocity variations is examined. A method of estimating the phase lag, radius and other pulsation constants is applied to classical cepheids. Amplitude and phase relations for non-radially oscillating stars are discussed with particular emphasis on the quadrupole mode. The radial pulsation and quadrupole oscillation models for β Cep stars are discussed. Some effects are predicted for multiperiodic stars and a method of determining the radius and pulsation modes is suggested.

GD 428 AND THE NATURE OF THE DWARF CEPHEIDS.

ABSTRACT Results are reported for a narrow- and intermediate-band uvby-beta photometric study of the dwarf Cepheid GD 428, which was performed to determine the star's temperature variation, color excess, reddening-free color indices, and surface gravity. A spectrum trailed synchronously through four cycles of the star was also obtained in an attempt to ascertain the spectral type and radial-velocity variations. An average radial velocity of -52 km/s is determined along with a total velocity amplitude of about 30 km/s, an average approximate (b-y) color excess of +0.238, an average log g of about 4.18, and an average effective temperature of 8050 K. It is found that GD 428 is extremely metal-poor and has an absolute magnitude of at least 2.6. The physical properties of 16 dwarf Cepheids are examined, a period-radius relation is obtained, and bolometric magnitudes, masses, pulsation constants, and ages are calculated for the 16 stars. It is concluded that dwarf Cepheids are post-main-sequence stars in the hydrogen shell-burning stage of evolution and that metal-poor stars must have formed in the Galaxy as recently as 2 billion years ago.

Evolutionary problems of Cepheids and other giants investigated with new radiative opacities

Comparison of evolutionary tracks, pulsation constants, and linearized pulsational-stability coefficients for stellar models applicable to the problems of classical Cepheids, whose structures were calculated using the Cox-Stewart (1965) opacities and a recently computed set of opacities. The latter are based on the hot 'Thomas-Fermi' statistical model of the atom for all elements heavier than hydrogen and helium; they contain larger helium and metals contributions, but a smaller hydrogen contribution than the former ones for the same chemical composition. The difference in metals contribution affects mainly the location and shape of the evolutionary tracks on the H-R diagram, while the difference in hydrogen and helium contributions has its greatest effect on the pulsational properties of the Cepheid models. From the comparison of evolutionary tracks it is concluded that: (1) the theoretical M/L relation for evolved giants is changed very little by using the second set of opacities; (2) Q-values for the fundamental mode of radial pulsation in Cepheid envelope models increase if the second set is used, but the classical mass discrepancy remains; and (3) the second set leads to pulsational-instability.

Applications of linear pulsation theory to the Cepheid mass problem and the double-mode Cepheids

view Abstract Citations (33) References (35) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Application of linear pulsation theory to the cepheid mass problem and the double-mode cepheids. King, D. S. ; Hansen, C. J. ; Ross, R. R. ; Cox, J. P. Abstract Linear pulsation constants and transition lines for Cepheids with hydrogen mass fractions of 0.7 and 0.8 and heavy-element mass fraction of 0.02 are presented. These results are applied to the problem of the Cepheid mass discrepancy where it is found that self-consistent masses may be obtained if a color-temperature scale is used which reduces Cepheid effective temperatures by 300-650 K below those usually assumed. This cooler scale closely resembles a recently proposed theoretical scale. Using the linear results, the masses and radii of eight double-mode Cepheids are also obtained. For one of these stars, U TrA, we find that in order to obtain a ratio of first-harmonic to fundamental periods close to the observed value and at the same time for it to be unstable in both modes it must be overluminous for its mass and lie near the red instability edge. Publication: The Astrophysical Journal Pub Date: January 1975 DOI: 10.1086/153344 Bibcode: 1975ApJ...195..467K Keywords: Astronomical Models; Cepheid Variables; Dynamic Stability; Mass Ratios; Stellar Mass; Stellar Temperature; Harmonic Oscillation; Line Spectra; Modal Response; Stellar Spectra; Ubv Spectra; Astrophysics full text sources ADS | data products SIMBAD (3)

Theoretical Pulsation Constants and Cepheid Masses

Theoretical Pulsation Constants and Cepheid Masses

The Long Period Variables

Table I lists determinations of radial velocity from 281 spectrograms for 114, mostly southern, long period variables. The wavelength and velocity systems are investigated for both absorption and emission lines. Relative velocity shifts between different emission lines are discussed. A new mean relation of absorption minus emission line velocities to period is derived (Fig. 1) using more than twice the previously available material. This relation is used to obtain absorption velocities for many variables for which only emission velocities have been measured. Table II gives a homogeneous set of velocities for 405 long period variables arranged in nine groups according to period and other characteristics. A detailed study of S Ind in the 1953 cycle shows relatively rapid velocity changes soon after maximum light. Other observed phenomena are related to these changes. The results on S Ind are compared with those for other stars (Section 6). Spectral types and luminosity classes are given for the Me variables (Sections 7 and 8 and Table I). A considerable spread in luminosity is indicated, especially at the shorter periods (Fig. 3). The mean results agree fairly well with the statistical parallaxes. Peculiarities in the ratio Cr I 4254/ Fe I 4250 are noted for some stars in agreement with previous findings for the variables in 47 Tuc. 353 Me variables are divided into seven groups (Table II) according to period, corrected for basic solar motion, and analysed for residual systematic motion (Table IV). There is no K -term or deviation of the antapex from the direction of galactic rotation. The results (Fig. 12 and Section 11) show that the Me variables cover almost the whole range of population types. The anomalous motion of the stars with periods less than 149 days suggests that these stars are variables pulsating in the first overtone. The ratio of the pulsation constants Q0 / Q1 is estimated as about 2.4 (Section 12), larger than for RR Lyrae stars and in agreement with the larger value of Q0 (0.056) also derived (Section 14). Comparison with the Woolley-Eggen classes of stars leads to ages and masses for the longer period stars similar to those of the Hyades giants. The shorter period stars have ages and masses similar to RR Lyrae stars of period about 0 d .45 and stars in metal-rich globular clusters. The bulk of the Me variables are associated with Disk and Intermediate Population II. is derived, considerably smaller than that appropriate to extreme Population I objects but in agreement with the prediction from the velocity ellipsoids and systematic motions for the Me variables of mean period near 250 days. Differential galactic rotation for the Se variables leads to M υ = −3.4, in agreement with the determination of Takayanagi but brighter than the results recently obtained from statistical parallaxes.

The Calculation of Pulsation Constants for the RR Lyrae Stars in M3.

view Abstract Citations (49) References (22) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS The Calculation of Pulsation Constants for the RR Lyrae Stars in M3. Preston, George Abstract A rigorous method of computing the pulsation constant, Q, from photometric observations of variable stars is applied to the data for forty-six RR Lyrae stars in M3, using relations between color index and effective temperature suggested for solar-type main-sequence stars and for unbianketed models. A simpler method that gives nearly identical results is also described. The values of Q and the ratio (Q / (Q depend on the effective temperature scale that is employed; an increase in Q-values for RR Lyrae stars in M3 with the longest periods is found to be insensitive to the choice of a temperature scale. The possibility that the RR Lyrae stars in M3 do not constitute a homologous family of variable stars is discussed briefly. Publication: The Astrophysical Journal Pub Date: January 1961 DOI: 10.1086/147000 Bibcode: 1961ApJ...133...29P full text sources ADS | data products SIMBAD (2) NED (1)