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 Oscillation Patterns of SX Phœnicis Variables in Globular Clusters

2000 ◽  
Vol 176 ◽  
pp. 497-498
Author(s):  
J. O. Petersen ◽  
M. Quaade ◽  
M. I. Andersen ◽  
L. M. Freyhammer
Keyword(s):  
Life History ◽  
Globular Clusters ◽  
Open Clusters ◽  
Light Curves ◽  
Standard Field ◽  
Blue Straggler ◽  
Scuti Stars ◽  
Δ Scuti Stars

AbstractBased on new analyses of light curves of SX Phœnicis variables in globular clusters and on results taken from the literature, an overview of oscillation patterns in this subgroup of δ Scuti variables is given. Belonging to the Blue Straggler stars, they are expected to have a more complicated life history than “normal” δ Scuti stars in the field or in open clusters. The overall picture is that the patterns found in this SX Phe group seem to be similar to the patterns that are well established for standard field δ Set stars.

scholarly journals The pulsation properties of λ bootis stars I. the southern TESS sample

2020 ◽  
Vol 495 (2) ◽  
pp. 1888-1912
Author(s):  
S J Murphy ◽  
E Paunzen ◽  
T R Bedding ◽  
P Walczak ◽  
D Huber
Keyword(s):  
Stellar Evolution ◽  
Fundamental Mode ◽  
Eclipsing Binaries ◽  
Light Curves ◽  
Mode Identification ◽  
Regular Sequences ◽  
Stellar Ages ◽  
Scuti Stars ◽  
Δ Scuti Stars ◽  
Gaia Dr2

ABSTRACT We analyse TESS light curves for 70 southern λ Boo stars to identify binaries and to determine which of them pulsate as δ Scuti stars. We find two heartbeat stars and two eclipsing binaries among the sample. We calculate that 81 per cent of λ Boo stars pulsate as δ Sct variables, which is about twice that of normal stars over the same parameter space. We determine the temperatures and luminosities of the λ Boo stars from photometry and Gaia DR2 parallaxes. A subset of 40 λ Boo stars have 2-min TESS data, reliable temperatures and luminosities, and δ Sct pulsation. We use Petersen diagrams (period ratios), échelle diagrams, and the period–luminosity relation to identify the fundamental mode in 20 of those 40 stars and conclude that a further 8 stars are not pulsating in this mode. For the remaining 12, the fundamental mode cannot be unambiguously identified. Further mode identification is possible for 12 of the fundamental mode pulsators that have regular sequences of pulsation overtones in their échelle diagrams. We use stellar evolution models to determine statistically that the λ Boo stars are only superficially metal weak. Simple pulsation models also better fit the observations at a metallicity of Z = 0.01 than at Z = 0.001. The TESS observations reveal the great potential of asteroseismology on λ Boo stars, for determining precise stellar ages and shedding light on the origin(s) of the λ Boo phenomenon.

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 The first view of δ Scuti and γ Doradus stars with the TESS mission

2019 ◽  
Vol 490 (3) ◽  
pp. 4040-4059 ◽  
Author(s):  
V Antoci ◽  
M S Cunha ◽  
D M Bowman ◽  
S J Murphy ◽  
D W Kurtz ◽  
...  
Keyword(s):  
Theoretical Models ◽  
Instability Strip ◽  
Mixing Processes ◽  
Data Set ◽  
Intermediate Mass Stars ◽  
Kepler Mission ◽  
Blue Straggler ◽  
First Time ◽  
Scuti Stars ◽  
Δ Scuti Stars

ABSTRACT We present the first asteroseismic results for δ Scuti and γ Doradus stars observed in Sectors 1 and 2 of the TESS mission. We utilize the 2-min cadence TESS data for a sample of 117 stars to classify their behaviour regarding variability and place them in the Hertzsprung–Russell diagram using Gaia DR2 data. Included within our sample are the eponymous members of two pulsator classes, γ Doradus and SX Phoenicis. Our sample of pulsating intermediate-mass stars observed by TESS also allows us to confront theoretical models of pulsation driving in the classical instability strip for the first time and show that mixing processes in the outer envelope play an important role. We derive an empirical estimate of 74 per cent for the relative amplitude suppression factor as a result of the redder TESS passband compared to the Kepler mission using a pulsating eclipsing binary system. Furthermore, our sample contains many high-frequency pulsators, allowing us to probe the frequency variability of hot young δ Scuti stars, which were lacking in the Kepler mission data set, and identify promising targets for future asteroseismic modelling. The TESS data also allow us to refine the stellar parameters of SX Phoenicis, which is believed to be a blue straggler.

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 Luminosity of δ Scuti Stars After Hipparcos Satellite

1998 ◽  
Vol 11 (1) ◽  
pp. 567-567
Author(s):  
E. Antonello ◽  
L. Mantegazza ◽  
E. Poretti
Keyword(s):  
Globular Clusters ◽  
Rotational Velocity ◽  
High Amplitude ◽  
Empirical Dependence ◽  
Trigonometric Parallaxes ◽  
Nearby Stars ◽  
Observational Errors ◽  
Absolute Magnitudes ◽  
Scuti Stars ◽  
Δ Scuti Stars

The absolute magnitudes of δ Scuti stars derived from parallaxes measured by the Hipparcos satellite were compared with the previous estimates based on photometric uvby² indices, and significant differences were found which are related to photometric effects of metallicity and rotational velocity. A reliable calibration of Mv in terms of the photometric indices shall include an estimate of these effects. It is important also to take into account the possible presence of unresolved close companions in order to fully exploit the accuracy of Mv of nearby stars derived from the trigonometric parallaxes. The Mv of few bright SX Phe stars support the period-luminosity relation obtained with ground based observations of globular clusters, while it does not seem to confirm the empirical dependence of this relation on the metallicity. Some high amplitude δ Scuti stars with intermediate or normal metallicity and small and uncertain parallax have apparently a very low luminosity. Simulations of Mv determinations from observed parallaxes based on the discussion of observational errors by Lutz and Kelker (1973) have shown that the low luminosity could be an effect related to these errors.

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 Fractal analysis applied to light curves of δ Scuti stars★

2018 ◽  
Author(s):  
S de Franciscis ◽  
J Pascual-Granado ◽  
J C Suárez ◽  
A García Hernández ◽  
R Garrido
Keyword(s):  
Fractal Analysis ◽  
Light Curves ◽  
Scuti Stars ◽  
Δ Scuti Stars

scholarly journals Bulge δ Scuti stars in the MACHO database

1997 ◽  
Vol 189 ◽  
pp. 293-298
Author(s):  
D. Minniti ◽  
C. Alcock ◽  
D.R. Alves ◽  
T.S. Axelrod ◽  
A.C. Becker ◽  
...  
Keyword(s):  
Spatial Distribution ◽  
High Amplitude ◽  
Light Curves ◽  
Evolutionary Status ◽  
Absolute Magnitudes ◽  
Scuti Stars ◽  
Δ Scuti Stars

We describe the search for δ Scuti stars in the MACHO database of bulge fields. Concentrating on a sample of high amplitude δ Scutis, we examine the light curves and pulsation modes. We also discuss their spatial distribution and evolutionary status using mean colors and absolute magnitudes.

scholarly journals Pulsations of Ob-Stars: New Observations

1998 ◽  
Vol 185 ◽  
pp. 347-354 ◽  
Author(s):  
Dietrich Baade
Keyword(s):  
Main Sequence ◽  
Physical Parameters ◽  
Be Stars ◽  
Instability Strip ◽  
Ob Stars ◽  
Analysis Strategies ◽  
The Galaxy ◽  
Order Line ◽  
Nonradial Pulsation ◽  
Radial Pulsations

Improved observing and data analysis strategies have initiated a considerable expansion of the empirical knowledge about the pulsations of OB stars. Possible correlations between physical parameters and associated pulsation characteristics are becoming more clearly perceivable. This starts to include the asteroseismologically fundamental areas of g-modes and rapid rotation. The β Cephei instability strip continues to be the only locus where radial pulsations occur (but apparently not in all stars located in that strip). Except for spectral types B8/B9 near the main sequence, where pulsations are hardly detected even at low amplitudes, any major group of stars in the Galaxy that are obviously not candidate pulsators still remains to be identified. However, the incidence and amplitudes of OB star pulsations decrease steeply with metallicity. The behaviour of high-luminosity stars is less often dominated by very few modes. In broad-lined stars the moving-bump phenomenon is more common than low-order line-profile variability. But its relation to nonradial pulsation is not clear. The beating of low-ℓ nonradial pulsation modes that have identical angular mode indices may be the clockwork of the outbursts of at least some Be stars. The physics of this episodic mass loss process remains to be identified.

Sign in / Sign up

Export Citation Format

Share Document