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 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 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 Pulsation of PMS 1.8 M⊙ Stars: A Theoretical Investigation

1998 ◽  
Vol 185 ◽  
pp. 397-398 ◽  
Author(s):  
Doru Marian Suran
Keyword(s):  
Instability Strip ◽  
Before And After ◽  
Deep Layers ◽  
Nuclear Burning ◽  
Similar Range ◽  
M Stars ◽  
Herbig Ae Stars ◽  
Pms Stars ◽  
Scuti Stars ◽  
Δ Scuti Stars

Herbig Ae stars are pre-main sequence of masses ~2M⊙. As they trace their course toward the ZAMS, they cross the classical instability strip. At this stage, their evolution has considerably slowed down. Their structure differs from that of stars evolving after the ZAMS (δ Scuti stars) in the very deep layers where nuclear burning has only recently started. But the outer layers for stars before and after the ZAMS are expected to be similar. As these layers drive the pulsation of δ Scuti stars, it is reasonable to expect that PMS stars in the instability strip also are destabilized by the κ mechanism with a similar range of unstable modes. Indeed, recently a Herbig Ae star has been reported as a variable (Kurtz and Marang 1995).

scholarly journals Asteroseismic Analysis of δ Scuti Components of Binary Systems: The Case of KIC 8504570

Galaxies ◽  
2020 ◽  
Vol 8 (4) ◽  
pp. 75
Author(s):  
Alexios Liakos ◽  
Panagiotis Niarchos
Keyword(s):  
Light Curve ◽  
Binary Systems ◽  
Theoretical Models ◽  
Primary Component ◽  
Physical Parameters ◽  
Pulsation Period ◽  
Oscillation Modes ◽  
Scuti Star ◽  
Scuti Stars ◽  
Δ Scuti Stars

The present work concerns the Asteroseismology of the Kepler-detached eclipsing binary KIC 8504570. Particularly, it focuses on the pulsational behaviour of the oscillating component of this system and the estimation of its physical parameters in order to enrich the so far poor sample of systems of this kind. Using spectroscopic observations, the spectral type of the primary component was determined and used to create accurate light curve models and estimate its absolute parameters. The light curve residuals were subsequently analysed using Fourier transformation techniques to obtain the pulsation models. Theoretical models of δ Scuti stars were employed to identify the oscillation modes of the six detected independent frequencies of the pulsator. In addition, more than 385 combination frequencies were also detected. The absolute and the pulsational properties of the δ Scuti star of this system are discussed and compared with all the currently known similar cases. Moreover, using a recent(empirical) luminosity–pulsation period relationship for δ Scuti stars, the distance of the system was estimated.

scholarly journals Asteroseismology of δ Scuti Stars: Observations

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.

scholarly journals High-resolution spectroscopy and abundance analysis of δ Scuti stars near the γ Doradus instability strip

2017 ◽  
Vol 470 (4) ◽  
pp. 4408-4420 ◽  
Author(s):  
F. Kahraman Aliçavuş ◽  
E. Niemczura ◽  
M. Polińska ◽  
K. G. Hełminiak ◽  
P. Lampens ◽  
...  
Keyword(s):  
High Resolution ◽  
High Resolution Spectroscopy ◽  
Instability Strip ◽  
Scuti Stars ◽  
Δ Scuti Stars

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 CCD Studies of δ Scuti Stars in Open Clusters

2000 ◽  
Vol 176 ◽  
pp. 415-420
Author(s):  
Hans Kjeldsen
Keyword(s):  
Theoretical Models ◽  
Open Clusters ◽  
Composition Gradient ◽  
Simple Task ◽  
Nonradial Oscillation ◽  
Cluster Properties ◽  
Oscillation Frequencies ◽  
Scuti Stars ◽  
Δ Scuti Stars ◽  
Eigenfrequency Spectrum

AbstractAsteroseismology on δ Scuti stars has until now produced very few convincing results – if we aim at doing strong tests of details of stellar modelling. The main reason for the lack of success is probably that these stars often rotate, which split nonradial oscillation frequencies into many more frequencies. These many frequencies and the fact that the more evolved δ Scuti stars contain a strong chemical composition gradient at the edge of the convective core, produce a very complicated eigenfrequency spectrum. In contrast to this, we expect, in principle, seismological studies of δ Scuti stars to be a very simple task: One has to compare theoretical oscillations in model stars with the observed oscillations. However, in order to produce convincing asteroseismological results, we need to do three things: (1) Detect as many eigenfrequencies as possible at high precision, (2) identify the eigenmodes and (3) improve the theoretical models. By observing δ Scuti stars in open clusters using CCDs, we have a possibility to improve on (1) and (2) as well as providing an opening for an improvement in the theoretical models by doing accurate calibrations of the basic cluster properties. In this paper I shall describe some of the results from CCD studies of δ Scuti stars in open clusters and identify some future prospects for this technique.

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.

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