Seismology of δ Scuti Stars: Problems and Prospects

2002 ◽  
Vol 185 ◽  
pp. 306-318
Author(s):  
M.J. Goupil ◽  
S. Talon
Keyword(s):  
Main Sequence ◽  
Instability Strip ◽  
Pulsating Stars ◽  
Current State ◽  
Cno Cycle ◽  
The Mean ◽  
Scuti Stars ◽  
High Temperature Sensitivity ◽  
Δ Scuti Stars ◽  
Mean Molecular Weight

The current state of seismology of δ Scuti stars is reviewed with particular emphasis on seismic signatures of the extension of their mixed central region and of rotation. We refer also to Goupil et al. (2000) and more generally to Breger & Montgomery (2000) for more details.δ Scuti stars are population I pulsating stars with spectral type A-early F, located on or near the main sequence. They are found in the lower part of the classical instability strip in a HR diagram (Fig. 1). Masses range from ∼ 1.5M⊙ to ∼ 2.5M⊙ and δ Scuti stars are either in a stage of H-core or H-shell burning. On the main sequence, the high temperature sensitivity of the dominant CNO cycle causes a large convective core to develop, which later shrinks leaving behind a gradient ∇μ in the mean molecular weight.

scholarly journals Theoretical properties of regularities in the oscillation spectra of A-F main-sequence stars

2013 ◽  
Vol 9 (S301) ◽  
pp. 89-92 ◽  
Author(s):  
Juan Carlos Suárez ◽  
Antonio García Hernández ◽  
Andrés Moya ◽  
Carlos Rodrigo ◽  
Enrique Solano ◽  
...  
Keyword(s):  
Main Sequence ◽  
Low Frequency ◽  
Average Density ◽  
Stellar Structure ◽  
Main Sequence Stars ◽  
Mode Identification ◽  
Pulsating Stars ◽  
The Mean ◽  
Scuti Stars ◽  
Δ Scuti Stars

AbstractWe study the theoretical properties of the regular spacings found in the oscillation spectra of δ Scuti stars. A linear relation between the large separation and the mean density is predicted to be found in the low-frequency domain (i.e. radial orders spanning from 1 to 8, approximately) of the main-sequence δ Scuti stars' oscillation spectrum. This implies an independent direct measure of the average density of δ Scuti stars, analogous to that of the Sun, and places tight constraints on the mode identification and hence on the stellar internal structure and dynamics, and allows a determination the radii of planets orbiting around δ Scuti stars with unprecedented precision. This opens the way for studying the evolution of regular patterns in pulsating stars, and its relation to stellar structure and evolution.

scholarly journals Finding binaries from phase modulation of pulsating stars with Kepler – VI. Orbits for 10 new binaries with mischaracterized primaries

2020 ◽  
Vol 493 (4) ◽  
pp. 5382-5388
Author(s):  
Simon J Murphy ◽  
Nicholas H Barbara ◽  
Daniel Hey ◽  
Timothy R Bedding ◽  
Ben D Fulcher
Keyword(s):  
Phase Modulation ◽  
White Dwarfs ◽  
Binary Systems ◽  
Main Sequence ◽  
Classification Algorithm ◽  
Orbital Parameters ◽  
Pulsating Stars ◽  
Stellar Properties ◽  
Scuti Stars ◽  
Δ Scuti Stars

ABSTRACT Measuring phase modulation in pulsating stars has proven to be a highly successful way of finding binary systems. The class of pulsating main-sequence A and F variables, known as δ Scuti stars consists of particularly good targets for this, and the Kepler sample of these has been almost fully exploited. However, some Keplerδ Scuti stars have incorrect temperatures in stellar properties catalogues, and were missed in previous analyses. We used an automated pulsation classification algorithm to find 93 new δ Scuti pulsators among tens of thousands of F-type stars, which we then searched for phase modulation attributable to binarity. We discovered 10 new binary systems and calculated their orbital parameters, which we compared with those of binaries previously discovered in the same way. The results suggest that some of the new companions may be white dwarfs.

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

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.

scholarly journals Spectroscopical analysis of δ Scuti stars

1994 ◽  
Vol 162 ◽  
pp. 47-48
Author(s):  
E. Solano ◽  
J. Fernley
Keyword(s):  
Spectral Range ◽  
Main Sequence ◽  
Pulsating Stars ◽  
Characteristic Period ◽  
Rr Lyrae ◽  
Scuti Stars ◽  
Δ Scuti Stars

δ Scuti are pulsating stars with a characteristic period of several hours, lying in the A2-F5 spectral range and placed on or a little above the main sequence. Unlike the well-known “classical” RR Lyrae or Cepheids, which show a homogeneous pulsational behaviour (i.e. radial modes with large amplitudes), δ Scuti stars have peculiarities: their amplitudes vary from millimagnitudes to tenths of magnitude and their pulsation modes can be both radial and non-radial.

scholarly journals The Luminosities of δ Scuti Stars

2002 ◽  
Vol 185 ◽  
pp. 116-117
Author(s):  
D.H. McNamara
Keyword(s):  
Fundamental Mode ◽  
Globular Clusters ◽  
Main Sequence ◽  
Light Curves ◽  
Instability Strip ◽  
Period Range ◽  
Blue Straggler ◽  
Scuti Stars ◽  
Δ Scuti Stars ◽  
Nonradial Pulsation

The δ Scuti stars are variables found in the instability strip above the zero-age main sequence. Radial and nonradial pulsation modes have been detected in these stars. The large-amplitude variables with asymmetric light curves are radial pulsators. The pulsation periods are found to be in the period range of 0.03 – 0.25 days. Generally, the light amplitudes are small (total range < 0.3 mag), but some fundamental-mode variables reach 0.70 mag. The majority of the variables have light amplitudes <0.10 mag. Population II δ Scuti variables are frequently called SX Phe stars. Many of these variables have been found in globular clusters, where they populate the blue-straggler domain of the color-magnitude diagrams.

scholarly journals Non-Adiabatic Seismic Study of The Thin Convective Envelope of δ Scuti Stars

2004 ◽  
Vol 193 ◽  
pp. 470-473
Author(s):  
M.-A. Dupret ◽  
A. Grigahcène ◽  
R. Garrido ◽  
J. Montalban ◽  
M. Gabriel ◽  
...  
Keyword(s):  
Instability Strip ◽  
Full Spectrum ◽  
Convective Envelope ◽  
Theoretical Predictions ◽  
Mode Stability ◽  
Different Color ◽  
Mixing Length Theory ◽  
Scuti Stars ◽  
Δ Scuti Stars ◽  
Phase Differences

AbstractFor δ Sct stars, the theoretical predictions of a non-adiabatic pulsation code are very dependent on the characteristics of the thin convective envelope of the models (Balona & Evers 1999). The treatment of the non-adiabatic interaction between convection and pulsation also has a significant impact on the results, particularly near the red edge of the instability strip. The non-adiabatic theoretical predictions can be tested upon observations by comparing them to the amplitude ratios and phase differences as observed in different color passbands (Dupret et al. 2003). In the first part of this paper, we compare the results obtained by adopting different treatments of convection in the interior and atmosphere models: mixing-length theory (MLT) and full spectrum of turbulence (FST) (Canuto et al. 1996, CGM). In the second part, we examine the problem of the interaction between convection and pulsation and compare the mode stability obtained with and without including time-dependent convection in our non-adiabatic code.

scholarly journals Do the Pre-Main Sequence δ Scuti Stars Really Exist?

2002 ◽  
Vol 185 ◽  
pp. 346-347
Author(s):  
J.H. Peña ◽  
R. Peniche ◽  
J.C. Plascencia ◽  
M.A. Hobart ◽  
C. de la Cruz ◽  
...  
Keyword(s):  
Main Sequence ◽  
Variable Stars ◽  
Current Status ◽  
Excellent Review ◽  
Scuti Stars ◽  
Δ Scuti Stars

Recently, new views of the current status of δ Scuti stars have been developed by Rodríguez & Breger (2001) who carried out an excellent review, listing 8 pre-main-sequence (PMS) δ Scuti candidates and examined the possibility of the existence of PMS δ Scuti variable stars. Here we discuss the nature of 4 stars from their list: 2 said to be members of NGC 2264 and 2 of NGC 6823.

scholarly journals Pulsation among TESS A and B stars and the Maia variables

2020 ◽  
Vol 493 (4) ◽  
pp. 5871-5879
Author(s):  
L A Balona ◽  
D Ozuyar
Keyword(s):  
Main Sequence ◽  
Large Fraction ◽  
Single Mode ◽  
Distinct Region ◽  
Low Frequencies ◽  
B Stars ◽  
High Frequencies ◽  
Pulsating Stars ◽  
Scuti Stars

ABSTRACT Classification of over 50 000 TESS stars in sectors 1–18 has resulted in the detection of 766 pulsating main-sequence B stars as well as over 5000 δ Scuti, 2300 γ Doradus, and 114 roAp candidates. Whereas it has been assumed that high-frequency pulsations among B-type main-sequence stars are confined to the early B-type β Cephei stars, the observations indicate that high frequencies are to be found over the whole B-star range, eventually merging with δ Scuti stars. The cool B stars pulsating in high frequencies are called Maia variables. It is shown that Maia variables are not rapidly rotating and thus cannot be β Cephei pulsators that appear to have lower temperatures due to gravity darkening. In the region where β Cephei variables are found, the proportion of pulsating stars is larger and amplitudes are higher and a considerable fraction pulsate in a single mode and low rotation rate. There is no distinct region of slowly pulsating B stars (SPB stars). Stars pulsating solely in low frequencies are found among all B stars. At most, only one-third of B stars appear to pulsate. These results, as well as the fact that a large fraction of A and B stars show rotational modulation, indicate a need for a revision of current ideas regarding stars with radiative envelopes.

scholarly journals 35. Commission De La Constitution Des Etoiles

1950 ◽  
Vol 7 ◽  
pp. 367-368
Author(s):  
M. H. N. Russell
Keyword(s):  
Main Sequence ◽  
Successive Approximations ◽  
Atomic Composition ◽  
The Past ◽  
Convective Core ◽  
Internal Constitution ◽  
The Mean ◽  
Present Summary ◽  
Mean Molecular Weight ◽  
Uniform Composition

The study of the internal constitution of the stars has advanced rapidly in the past few years, especially for those of the main sequence. The present summary is necessarily brief.For a star of uniform composition, whose interior is in radiative equilibrium, with or without a convective core, the constitution can be completely determined by successive approximations by quadratures, if there are given(a)the atomic composition(b)the equation of state, defining the mean molecular weight μ(c)the equation defining the opacity for the outflowing radiation(d)the equation defining the rate of liberation of energy per gram.

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