Close Frequency Pairs in Delta Scuti Stars

AbstractThe power spectra of several δ Scuti stars show close peaks with similar frequencies and amplitudes. Apart from possible observational problems, this can be interpreted in terms of two separate pulsation modes with similar, close frequencies or an artifact of amplitude variability of a single pulsation mode. If sufficient data are available, it is possible to distinguish between the two hypotheses on the basis of expected systematic phase changes associated with the amplitude variations of an assumed single frequency. This phase-shift test has been applied to modes found for BI CMi. In this paper we present the evidence for one of the close frequency pairs found in this star.

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Mode and Period Changes in Pulsating Stars near the main Sequence: δ Scuti Stars

Highlights of Astronomy ◽

10.1017/s1539299600021006 ◽

1998 ◽

Vol 11 (1) ◽

pp. 349-349

Author(s):

M. Breger

Keyword(s):

Main Sequence ◽

Power Spectra ◽

Time Variable ◽

Evolutionary Models ◽

Equal Distribution ◽

Pulsating Stars ◽

Amplitude Variability ◽

Delta Scuti ◽

Scuti Stars ◽

Δ Scuti Stars

Reported mode changes in δ Scuti stars cna usually be explained by insufficient data to obtain multiperiodic solutions and by the effect of time-variable amplitudes. The extensive data on 4 CVn obtained by the Delta Scuti network are used to illustrate that the large changes in the appearance of the power spectra in the years from 1966 to 1996 can be ascribed to amplitude variability. The period changes of δ Scuti stars have been collected or redetermined from the available observations and are compared with values computed from evolutionary models. For the radial pulsators of Pop.I, the observations indicate (l/P)dP/dt values around 10−7 year−1 with equal distribution between period increases and decreases. The evolutionary models, on the other hand, predict that the vast majority should show increasing periods a factor of about 10 smaller than observed. Arguments are given why the rate of evolution for these relatively unevolved stars cannot yet be deduced from the observed period changes.

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Amplitude Variability of Delta Scuti Stars: 4 CVn

International Astronomical Union Colloquium ◽

10.1017/s025292110005822x ◽

2000 ◽

Vol 176 ◽

pp. 421-425 ◽

Cited By ~ 1

Author(s):

Michel Breger

Keyword(s):

Time Scales ◽

Rapid Decrease ◽

Photometric Data ◽

Amplitude Variability ◽

Scuti Star ◽

Delta Scuti ◽

Almost All ◽

Scuti Stars

AbstractThe amplitude variability of δ Scuti stars is demonstrated by the behavior of the evolved δ Scuti star 4 CVn. The data on 4 CVn covering over 30 yr shows the amplitudes of almost all modes to be extremely variable with a time scales of ten years or longer. The most rapid decrease of amplitude in V is shown by the 7.38 d−1 mode of 4 CVn, which collapsed from 15 mmag in 1974 to 4 mmag in 1976, and 1 mmag in 1977. Between 1974–6 and 1977–8 phase jumps of almost half a cycle occurred. While a simple beating model of two close frequencies can be ruled out from the photometric data, the change is compatible with the growth of a new mode between 1976 and 1977.

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Asteroseismology of δ Scuti Stars: Observations

Symposium - International Astronomical Union ◽

10.1017/s0074180900238898 ◽

1998 ◽

Vol 185 ◽

pp. 323-330

Author(s):

Michel Breger

Keyword(s):

Phase Shift ◽

Recent Progress ◽

Theoretical Models ◽

Shift Method ◽

Mode Identification ◽

Delta Scuti ◽

Scuti Stars ◽

Phase Shift Method ◽

Δ Scuti Stars

We review recent observational developments which provide important asteroseismological tools. Extensive multisite campaigns of individual δ Scuti stars show that 24 or more pulsation modes with ℓ = 0 to 2 can be detected photometrically. Spectroscopically, also about 30 modes have been detected, and these can be identified with modes of ℓ values up to 20. Since each technique favors the detection of specific types of modes, hundreds or thousands of modes must be excited in δ Scuti stars.We examine the quantities which can be matched between observations and theoretical models specifically computed for each star. Recent progress in tbe mode identification of multiple pulsation modes is illustrated by presenting an application of the phase shift method for the two stars, FG Vir and 4 CVn, recently measured by the Delta Scuti Network.

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Close frequency pairs in Delta Scuti stars

Astronomy and Astrophysics ◽

10.1051/0004-6361:20020124 ◽

2002 ◽

Vol 385 (2) ◽

pp. 537-545 ◽

Cited By ~ 31

Author(s):

M. Breger ◽

K. M. Bischof

Keyword(s):

Delta Scuti ◽

Close Frequency ◽

Scuti Stars

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Radial and Nonradial Oscillations in Delta Scuti Stars

International Astronomical Union Colloquium ◽

10.1017/s0252921100081793 ◽

1980 ◽

Vol 58 ◽

pp. 377-380

Author(s):

D. W. Kurtz

Keyword(s):

Phase Shift ◽

Main Sequence ◽

Selection Effect ◽

Light Curves ◽

Frequency Separation ◽

Giant Stars ◽

Theoretical Predictions ◽

Resonance Coupling ◽

Delta Scuti ◽

Scuti Stars

Mode identifications from the phase shift between the B-V color curves and the V light curves of Delta Scuti stars are discussed. For five Delta Scuti stars the frequency of highest amplitude is due to pulsation in a radial mode with one or more frequencies due to nonradial modes lying nearby. Thus there may be a resonance between the frequencies of radial and nonradial modes. This behavior has only been found in subgiant and giant stars so far, but this could easily be a selection effect. Theoretical predictions of frequencies for different 1-modes of the same overtone for main sequence, subgiant, and giant stars are needed to compare with these observations. Theoretical predictions of the strength of resonance coupling between radial and nonradial modes as a function of frequency separation are also needed.

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