A study of binary constraints for seismology of delta Scuti stars

Seismology of single delta Scuti stars has mainly been inhibited by failing to detect many of the theoretically predicted pulsation modes, resulting in difficulties with mode identification. Theoretical and observational advances have, however, helped to overcome this problem, but the following questions then remain: do we know enough about the star to either use the (few) identified mode(s) to probe the structure of the star? or improve the determination of the stellar parameters? It is now generally accepted that for the observed frequencies to be used successfully as seismic probes for these objects, we need to concentrate on stars where we can constrain the number of free parameters in the problem, such as in binary systems or open clusters. The work presented here, investigates how much is gained in our understanding of the star, by comparing the information we obtain from a single star with that of an eclipsing binary system. Singular Value Decomposition is the technique used to explore the precision we expect in terms of stellar parameters (such as mass, age and chemical composition).Comment: v2: error in equation corrected. HELAS II Conference: Helioseismology, Asteroseismology and MHD Connections, August 2007 Goettingen, German

KIC 9533489: a genuine γ Doradus – δ Scuti Kepler hybrid pulsator with transit events

Context Several hundred candidate hybrid pulsators of type A–F have been identified from space-based observations. Their large number allows both statistical analyses and detailed investigations of individual stars. This offers the opportunity to study the full interior of the genuine hybrids, in which both low-radial-order p- and high-order g-modes are self-excited at the same time. However, a few other physical processes can also be responsible for the observed hybrid nature, related to binarity or to surface inhomogeneities. The finding that most δ Scuti stars also show long-period light variations represents a real challenge for theory. Aims We aim at determining the pulsation frequencies of KIC 9533489, to search for regular patterns and spacings among them, and to investigate the stability of the frequencies and the amplitudes. An additional goal is to study the serendipitously detected transit events: is KIC 9533489 the host star? What are the limitations on the physical parameters of the involved bodies? Methods Fourier analysis of all the available Kepler light curves. Investigation of the frequency and period spacings. Determination of the stellar physical parameters from spectroscopic observations. Modelling of the transit events. Results The Fourier analysis of the Kepler light curves revealed 55 significant frequencies clustered into two groups, which are separated by a gap between 15 and 27 d −1. The light variations are dominated by the beating of two dominant frequencies located at around 4 d −1 . The amplitudes of these two frequencies show a monotonic long-term trend. The frequency spacing analysis revealed two possibilities: the pulsator is either a highly inclined moderate rotator (v ≈ 70 km s −1 , i > 70 ◦ ) or a fast rotator (v ≈ 200 km s −1 ) with i ≈ 20 ◦ . The transit analysis disclosed that the transit events, which occur with a ≈ 197 d period may be caused by a 1.6 R_Jup body orbiting a fainter star, which would be spatially coincident with KIC 9533489

KIC 6951642: confirmed Kepler γ\gamma Doradus-δ\delta Scuti star with intermediate to fast rotation in a possible single-lined binary system

KIC 6951642 has been reported as a candidate hybrid pulsator of type-$\gamma$ Doradus-$\delta$ Scuti from observations of the first quarters of the Kepler mission. We aim to investigate the pulsating nature of KIC 6951642 and to search for the signature of rotation and/or activity in the light curves. We performed an iterative frequency search of both Fourier spectra, and searched for regular patterns in them. We applied spectrum synthesis to determine the atmospheric stellar parameters. Since KIC 6951642 was reported to belong to a spectroscopic binary system, we fitted the time delays derived from the light curves with the radial velocities obtained from published as well as new spectra in an attempt to improve the quality of the first orbit. Follow-up spectroscopy showed that KIC 6951642 is a fast-rotating F0-type star in a possible single-lined binary with a period of $\sim$4.8 yr. In the low-frequency regime, we identified the frequencies of 0.721 d$^{-1}$ as well as of 0.0087 d$^{-1}$. We attribute the first frequency to stellar rotation and the second one to stellar activity with a cycle. We also detected $g$ modes, with the strongest mode located at 2.238 d$^{-1}$, as well as three asymmetric multiplets (with a mean spacing of 0.675$\pm$0.044 d$^{-1}$). In the high-frequency regime, we detected frequencies of type-$\delta$ Scuti, with the strongest mode located at 13.96 d$^{-1}$, as well as seven asymmetric multiplets (with a mean spacing of 0.665$\pm$0.084 d$^{-1}$). We subsequently identified a few more frequencies that appear to be combinations of a $g$ or $p$ mode and one of the higher cited frequencies not due to pulsations. We propose that KIC 6951642 accommodates for a fast-rotating $\gamma$ Dor-$\delta$ Sct hybrid star with various rotationally split multiplets of $g$ and $p$ modes and that it also displays a cycle lasting years of (possible) stellar activity

Multicolour CCD Measurements of Visual Double and Multiple Stars. III

Recent CCD observations were performed in the period 1998-2004 for a large sample of visual double and multiple stars selected from the Hipparcos Catalogue and/or from the Gliese Catalogue of Nearby Stars. Accurate astrometric and photometric data allowing to characterize the individual components are provided. These data are confronted to Hipparcos data or to data from an older epoch in order to assess the nature of the observed systems. We simultaneously apply a Moffat-Lorentz profile with a similar shape to all detected components and adjust the profile parameters from which we obtain the relative astrometric position (epoch, position angle, angular separation) as well as differential multi-colour photometry (filters (B)VRI). We thus acquired recent data for 71 visual systems of which 6 are orbital binaries, 27 are nearby and 30 are multiple systems. In three cases, the systems remained unresolved. 23 new components were detected and measured. Two new visual double stars of intermediate separation were also found. The estimated accuracies in relative position are 0.04 deg and 0.01" respectively, while those in differential photometry are of the order of 0.01-0.02 mag in general. The nature of the association of 55 systems is evaluated. New basic binary properties are derived for 20 bound systems. Component colours and masses are provided for two orbital binaries.Comment: 7 pages, 2 Postscript figures, 1 appendix, 1 annex containing 3 tables. Appendix A and Tables~4-6 are only available in electronic form. Astronomy and Astrophysics, in press (2006