J. C. Suárez

OBSERVATIONAL Δ ν –

Delta Scuti (δ Sct) stars are intermediate-mass pulsators, whose intrinsic oscillations have been studied for decades. However, modeling their pulsations remains a real theoretical challenge, thereby even hampering the precise determination of global stellar parameters. In this work, we used space photometry observations of eclipsing binaries with a δ Sct component to obtain reliable physical parameters and oscillation frequencies. Using that information, we derived an observational scaling relation between the stellar mean density and a frequency pattern in the oscillation spectrum. This pattern is analogous to the solar-like large separation but in the low order regime. We also show that this relation is independent of the rotation rate. These findings open the possibility of accurately characterizing this type of pulsator and validate the frequency pattern as a new observable for δ Sct stars.

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In the present work, we study correlations between stellar fundamental parameters and the oscillation amplitude for Scuti stars. We present this study for a sample of 17 selected Scuti stars belonging to 5 young open clusters. Taking advantage of properties of Scuti stars in clusters, we correct the photometric parameters of our objects for the eects of fast rotation. We confirm the benefit of applying such corrections in this kind of studies. In addition, the technique used for this correction allows us to obtain an estimate of stellar parameters such as the angle of inclination and the rotation rate, usually not accessible. A significant correlation between the parameter i 0 (estimation of the angle of inclination of the star) and the oscillation amplitude is found. A discussion and interpretation of these a priori surprising results is proposed, in terms of a possible selection rule for oscillation modes of Scuti stars.

RELATION FOR δ Sct STARS USING ECLIPSING BINARIES AND SPACE PHOTOMETRY

The present work focuses on the discussion of the λ Bootis nature of the multiperiodic δ Scuti star HDxa0192640 (29 Cyg), through a comprehensive asteroseismic modeling. Some of the most recent asteroseismic tools are used to check whether the observed low metallicity is internal, i.e., intrinsic, present throughout the star, or due to superficial processes as accretion, diffusive settling, radiative levitation, mass loss, etc. The modeling method uses some of the most recent tools, including: (1) effects of rotation on equilibrium models, on the adiabatic oscillation spectrum, and its influence in multicolor observables, (2) nonadiabatic stability of radial and nonradial modes, (3) inclusion of the atmosphere-pulsation interaction for a more accurate multicolor mode identification, and (4) ratio between radial modes n = 4 and n = 5 in the framework of Petersen diagrams. The analysis performed reveals that the models fulfilling all the constraints are those in the middle of the main sequence (MS), with subsolar metallicity, except some other unlikely possibilities. Therefore, this study does not support the idea of the λ Bootis stars being zero-age MS or pre-MS stars interacting with their primordial cloud of gas and dust, but suggest the explanation of their nature as submetallic MS objects. Nevertheless, more accurate multicolor photometric observations are required for a more conclusive study using the procedure presented here, since the observational errors are too large for a definitive rejection of any of the possible explanations.

A study of correlation between the oscillation amplitude and stellar parameters of delta Scuti stars in open clusters - Toward selection rules for delta Scuti star oscillations

New observations of V534 Tau were performed during the STEPHI IX campaign in November 1998. An overall run of 285 h of data has been collected from three sites over a period of 23 days. Period analysis reveals a rich oscillation spectrum with nine frequencies above the 99% confidence level. This oscillation spectrum spans a large range of frequencies, from 179 to 525 µHz (15.52 to 45.36 cycles per day). A preliminary comparison with models suggests that the observed modes would lie in the range of modes from g1 or g2 to p4 or p5, depending on the rotation rate considered for V534 Tau.

Asteroseismological Modeling of the Multiperiodic λ Bootis Star 29 Cygni

Asteroseismology is witnessing a revolution thanks to high-precise asteroseismic space data (MOST, CoRoT, Kepler, BRITE), and their large ground-based follow-up programs. Those instruments have provided an unprecedented large amount of information, which allows us to scrutinize its statistical properties in the quest for hidden relations among pulsational and/or physical observables. This approach might be particularly useful for stars whose pulsation content is difficult to interpret. This is the case of intermediate-mass classical pulsating stars (i.e. gamma Dor, delta Scuti, hybrids) for which current theories do not properly predict the observed oscillation spectra. Here we establish a first step in finding such hidden relations from Data Mining techniques for these stars. We searched for those hidden relations in a sample of delta Scuti and hybrid stars observed by CoRoT and Kepler (74 and 153, respectively). No significant correlations between pairs of observables were found. However, two statistically significant correlations emerged from multivariable correlations in the observed seismic data, which describe the total number of observed frequencies and the largest one, respectively. Moreover, three different sets of stars were found to cluster according to their frequency density distribution. Such sets are in apparent agreement with the asteroseismic properties commonly accepted for A-F pulsating stars.

9+ frequencies for V534 Tauri, a delta Scuti variable in the Pleiades - Results of the STEPHI IX campaign

Using ultra-precise data from space instrumentation, we found that the underlying functions of stellar light curves from some AF pulsating stars are non-analytic, and consequently their Fourier expansion is not guaranteed. This result demonstrates that periodograms do not provide a mathematically consistent estimator of the frequency content for this type of variable stars. More importantly, this constitutes the first counterexample against the current paradigm, which considers that any physical process is described by a continuous (band-limited) function that is infinitely differentiable.

Semi-empirical seismic relations of A-F stars from COROT and Kepler legacy data

Inspired by the so appealing example of red giants, where going from a handful of stars to thousands revealed the structure of the eigenspectrum, we inspected a large homogeneous set of around 1860 δ Scuti stars observed with CoRoT. This unique data set reveals a common regular pattern which appears to be in agreement with island modes featured by theoretical non-perturbative treatments of fast rotation. The comparison of these data with models and linear stability calculations suggests that spectra can be fruitfully characterized to first order by a few parameters which might play the role of seismic indices for δ Scuti stars, as Δ v and v max do for red giants. The existence of this pattern offers an observational support for guiding further theoretical works on fast rotation. It also provides a framework for further investigation of the observational material collected by CoRoT ([1]) and Kepler ([2]). Finally, it sketches out the perspective of using δ Scuti stars pulsations for ensemble asteroseismology

Limits in the application of harmonic analysis to pulsating stars

The work reported here demonstrates that it is possible to accurately determine surface gravities of

What CoRoT tells us about δ Scuti stars - Existence of a regular pattern and seismic indices to characterize stars

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Precise surface gravities of δ Scuti stars from asteroseismology

Sct stars using the frequency content from high precision photometry and a measurement of the parallax. Using a sample of 10 eclipsing binary systems with a