scholarly journals Astrophysical Applications of Delta Scuti Stars

1995 ◽  
Vol 155 ◽  
pp. 70-80
Author(s):  
Michel Breger
Keyword(s):  
Main Sequence ◽  
Statistical Significance ◽  
Instability Strip ◽  
Short Period ◽  
Scuti Star ◽  
Systematic Behaviour ◽  
Delta Scuti ◽  
F Stars ◽  
Available Information ◽  
Scuti Stars

AbstractThe δ Scuti stars pulsate with a large number of low-order radial and nonradial p-modes. There also exists some evidence for the presence of g-modes.The pulsational variability outside the classical δ Scuti star instability strip (A1V - F0V on the main sequence) is examined. New measurements do not confirm the short-period variability of the hot B9p star ET And. However, a number of cool, early-F stars shows variability around one day: the γ Dor variables. An explanation involving nonradial g modes appears the most promising.An examination of available information on the multi-periodicity of δ Scuti stars shows no systematic behaviour in which pulsation modes axe excited to an observable level with luminosity and temperature. The asteroseismological potential of δ Scuti vaxiables is briefly examined.So far, the period changes of five luminous Pop. I δ Scuti variables have been studied. While stellar evolution predicts period increases, decreases have been observed and reported for all five stars. The statistical significance of this result and alternative explanations axe briefly examined.

scholarly journals Frequency Oscillations in the Delta Scuti Star V534 Tauri: Preliminary Results of the STEPHI IX Campaign

2000 ◽  
Vol 176 ◽  
pp. 477-478
Author(s):  
L. Fox Machado ◽  
Z. P. Li ◽  
E. Michel ◽  
M. Alvarez ◽  
M. M. Hernández ◽  
...  
Keyword(s):  
Main Sequence ◽  
Class Iii ◽  
Significant Progress ◽  
Instability Strip ◽  
Preliminary Results ◽  
Scuti Star ◽  
Delta Scuti Star ◽  
Delta Scuti ◽  
Scuti Stars ◽  
Made In

The δ Scuti stars are pulsating variables located in the lower part of the Cepheid instability strip with spectral types from A2 to F0 on the main sequence, and from A3 to F5 at luminosity class III. These variables show short periods (< 0.3day) and luminosity amplitudes ranging from a few thousandths of a magnitude to several tenths. Over the last few years, significant progress has been made in the detection of pulsating modes in the framework of the multisite campaigns, e.g. STACC (Frandsen et al. 1996), DSN (Breger et al. 1998), STEPHI (Michel et al. 2000). For the 1998 STEPHI IX photometry campaign, the δ Scuti star V534 Tau of the Pleiades cluster (see Table 1) was monitored during a three week, three continent run. Preliminary results are reported here.

scholarly journals Amplitudes and Frequencies of δ Scuti Stars: Systematics

1980 ◽  
Vol 5 ◽  
pp. 463-466 ◽  
Author(s):  
Michel Breger
Keyword(s):  
Main Sequence ◽  
Light Curves ◽  
Interior Structure ◽  
Minimum Requirement ◽  
Short Period ◽  
Delta Scuti ◽  
F Stars ◽  
Scuti Stars ◽  
Δ Scuti Stars

Delta Scuti stars are short-period pulsating A/F stars situated on or above the main sequence. They often pulsate with two more excited modes. The knowledge of the period lengths and period ratios is very important to deduce the nature of the pulsation modes, e.g. is the pulsation radial or nonradial? Furthermore, these values provide valuable information on the interior structure of these stars.The determination of the period ratios from the light curves is difficult, since only a few cycles can be covered during a night. The small amplitudes of about 0.01 mag in some variables also makes the multiperiod analysis difficult. While every star should be considered on its own merit, a rough estimate of about 5 nights per deduced period appears to be a minimum requirement. Even then different analyses can give different results. A recent example is the star 38 Cnc (=BT Cnc). An excellent set of observations by Guerrero, Mantegazza and Scardia (1979) gave three periods with nonradial period ratios and a good fit. Our subsequent analysis of the same data gave three radial periods with an even better fit!

scholarly journals The Delta Scuti Network: Steps Towards Successful Asteroseismology of Delta Scuti Stars

2002 ◽  
Vol 185 ◽  
pp. 598-599
Author(s):  
W. Zima ◽  
M. Breger ◽  
K. Bischof ◽  
F. Rodler ◽  
A. Stankov ◽  
...  
Keyword(s):  
High Precision ◽  
Main Sequence ◽  
Scientific Research ◽  
Mode Identification ◽  
Short Period ◽  
Delta Scuti ◽  
The Moment ◽  
Identification Techniques ◽  
Scuti Stars ◽  
Nonradial Oscillations

AbstractThe Delta Scuti Network (DSN) is a collaboration of astronomers all around the globe who study and observe short-period variables. The field of scientific research includes high-precision photometric and Spectroscopic global campaigns, mode identification techniques, and asteroseismological pulsation modeling. We present results for three stars that are receiving the most attention at the moment: 4 CVn, BI CMi, and 44 Tau. Our results demonstrate that a large number of simultaneously excited nonradial oscillations in stars on and above the main sequence can be detected by conventional means.

scholarly journals A Photometric Search for Circumstellar Shell Variability and Pre-Main Sequence Delta Scuti Variables

1971 ◽  
Vol 15 ◽  
pp. 85-89
Author(s):  
M. Breger ◽  
J. Hardorp
Keyword(s):  
Main Sequence ◽  
Color Variation ◽  
Sequence Band ◽  
Short Period ◽  
Circumstellar Shell ◽  
Delta Scuti ◽  
F Stars ◽  
Variability Study ◽  
Light Variability ◽  
Selective Extinction

AbstractA light variability study in NGC 2264 shows that about 25 % of the pre-main sequence A and F stars show irregular short-period variability and/or brightness changes since 1953. There exists a good correlation between this variability and (other) shell indicators. The scatter in the pre-main sequence band in the color-magnitude diagram can be partially explained by shells and an age spread between 1 and 3 × 106 years is indicated. W 90, a star below the main sequence, has brightened by half a magnitude to V = 12.5 since 1953. The corresponding color variation suggests a ratio of total to selective extinction of about 9.

scholarly journals Hd 24975: A New Delta Scuti Star? (Or A Mild Ap Star with Short Photometric Variations?)

1986 ◽  
Vol 90 ◽  
pp. 253-256
Author(s):  
C. Megessier ◽  
P. North ◽  
M. Burnet
Keyword(s):  
Clear Correlation ◽  
Comparison Star ◽  
Instability Strip ◽  
Precise Location ◽  
Short Period ◽  
Scuti Star ◽  
Delta Scuti Star ◽  
Delta Scuti ◽  
Ap Stars ◽  
Hr Diagram

Looking in the literature for short period variations of Ap stars, we found the puzzling case of HD 24975. Used as a comparison star by Weiss (1978), it had been found then to present variations with a peak-to-peak amplitude of 0.01 in U, B and V with a period of about 45mn, but with no clear correlation between the three passbands.HD 24975 has the same spectral type A2 as 21 Com which seems to present photometric variations with P ⋍ 31mn and Δ V < 0,02m (Percy, 1973, 1975). Both stars are near the blue edge of the δ Scuti instability strip in the HR diagram. The lack of photo metric data, however, prevented the precise location of HD 24975 from being found on the HR diagram.

scholarly journals High- and Low-Degree Modes in Delta Scuti Stars: 1- and 2-D Fourier Analyses Of τ Peg

1993 ◽  
Vol 137 ◽  
pp. 743-745 ◽  
Author(s):  
Edward J. Kennelly ◽  
Jaymie M. Matthews ◽  
Gordon A.H. Walker
Keyword(s):  
Radial Velocity ◽  
Time Evolution ◽  
Main Sequence ◽  
Velocity Measurements ◽  
Low Degree ◽  
Delta Scuti ◽  
Stellar Seismology ◽  
F Stars ◽  
High Degree ◽  
Scuti Stars

Stellar seismology of δ Scuti stars offers the best prospect for determining the interior properties of normal non-magnetic A-F stars on or near the main sequence. The discovery of rich eigenfrequency spectra in the light variations of several δ Scuti stars (e.g., θ2 Tau: Breger et al. 1989; GX Peg: Michel et al. 1990) should make this possible for low-degree modes (l ≤ 4). However, due to cancellation effects, modes of higher l cannot be studied through photometry or radial velocity measurements.The detection of rapid line-profile variations among rapidly rotating δ Scuti stars (e.g., Walker et al. 1987; Kennelly et al. 1992) has extended our sensitivity to much higher modes. These variations are consistent with moderate- to high-degree modes, where |m| ~ l. (In the simplest case, they could be pure sectorial modes with |m| = l and pulsation amplitudes strongly confined to the stellar equator.) To use these data effectively, we need an objective way to identify the modes and their time evolution.

scholarly journals The Delta Scuti Star GX Pegasi: A Theoretical Investigation of its Power Spectrum

1993 ◽  
Vol 134 ◽  
pp. 181-183
Author(s):  
E. Michel ◽  
M. J. Goupil ◽  
Y. Lebreton ◽  
A. Baglin
Keyword(s):  
Power Spectrum ◽  
Theoretical Investigation ◽  
Main Sequence ◽  
Main Sequence Star ◽  
Mode Identification ◽  
Star Models ◽  
Convective Core ◽  
Scuti Star ◽  
Delta Scuti Star ◽  
Delta Scuti

Target of a STEPHI multisite campaign, the Delta Scuti star GX Pegasi has been found to oscillate with at least five simultaneous, close frequencies (table I).Mode identification together with informations about the star that such an identification can provide are outlined below (see also Michel et al, 1992b).The mode identification is carried out by means of a comparison between the observed frequencies and the adiabatic frequencies of models appropriate to this star. Models that match GX Peg’s position in a Hertzsprung-Russell diagram have masses in the range 1.9 – M⊙. When included, convective core overshoot is handled as in Maeder and Meynet (1989). According to these models, GX Peg is a rather evolved, main sequence star.

scholarly journals Is Delta Scuti Star Seismology Possible?

1989 ◽  
Vol 111 ◽  
pp. 271-271
Author(s):  
G. Kovacs
Keyword(s):  
Sampling Rate ◽  
Efficient Tool ◽  
Scuti Star ◽  
Delta Scuti Star ◽  
Delta Scuti ◽  
Stellar Seismology ◽  
Ap Stars ◽  
Scuti Stars ◽  
Δ Scuti Stars ◽  
Nonradial Pulsation

AbstractThe direct fit of theoretical pulsation frequencies to the observations (i.e. stellar seismology) proved to be a very efficient tool in the study of solar oscillations. In the case of other multiperiodic variables, like δ Scuti stars, Ap stars and white dwarfs the method suffers from the disturbing abundance of possible nonradial modes. Colour and/or radial velocity (or line profile) measurements can narrow down the number of possibilities, but these kinds of data are not often available with the desired accuracy and sampling rate. Since pulsational frequencies are the most readily and accurately computed and measured quantities of pulsation, we address the question of the accurate fit of the nonradial pulsation frequencies to the observations in the case of δ Scuti stars.

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