L. Fox Machado

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

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.

A seismological analysis of delta Scuti stars in the Pleiades cluster

A comparison between the oscillation frequencies of six multi-periodic 6 Scuti stars of the Pleiades cluster and the eigenfrequencies of rotating stellar models that match the corresponding stellar parameters has been carried out. The assumption that all the stars considered have some common parameters, such as metallicity, distance or age, is imposed as a constraint. As a result, we have a best fit solution associated with a cluster metallicity of [Fe/H] = 0.067, an age between 70 × 10 6 and 100 x 10 6 yr and a distance modulus of m V - M V = 5.60-5.70 mag. All the stars were found to oscillate mainly in non-radial, low degree, low order p modes. Estimates of mass and rotation rates for each star are also obtained.

Pulsational frequencies of the eclipsing δ Scuti star HD 172189. Results of the STEPHI XIII campaign

Context. The eclipsing δ Scuti star HD 172189 is a probable member of the open cluster IC 4756 and a promising candidate target for the CoRoT mission. Aims. The detection of pulsation modes is the first step in the asteroseismological study of the star. Further, the calculation of the orbital parameters of the binary system allows us to make a dynamical determination of the mass of the star, which works as an important constraint to test and calibrate the asteroseismological models. Methods. We performed a detailed frequency analysis of 210 hours of photometric data of HD 172189 obtained from the STEPHI XIII campaign �� . Results. We have identified six pulsation frequencies with a confidence level of 99% and a seventh with a 65% confidence level of 65%, in the range between 100−300 µHz. In addiction, three eclipses were observed during the campaign, allowing us to improve the determination of the orbital period of the system.

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

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.

New

We report here the discovery of very low amplitude oscillations in the Pleiades star HD 23628. The 14-nights high quality light curve designates HD 23628 as a new member of the Scuti stars class. Amplitude spectra indicate a multi-periodic pulsation behaviour, and four pulsation frequencies have been detected so far. The frequency distribution suggests the presence of nonradial modes. Pulsation constant values of the four modes are distributed in the range corresponding to fundamental f to p4 radial modes.

\delta

As a continuation of the study of the Delta Scuti stars 7 Aql and 8 Aql; new CCD photometric data were acquired in 2007. We present a period analysis on these data that confirm the dominant modes detected in each star in the framework of the STEPHI XII campaign in 2003.