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The Kepler characterization of the variability among A- and F-type stars. I. General overview
Context. The Kepler spacecraft is providing time series of photometricdata with micromagnitude precision for hundreds of A-F type stars. Aims: We present a first general characterization of the pulsationalbehaviour of A-F type stars as observed in the Kepler light curves of asample of 750 candidate A-F type stars, and observationally investigatethe relation between ? Doradus (? Dor), ? Scuti(? Sct), and hybrid stars. Methods: We compile a databaseof physical parameters for the sample stars from the literature and newground-based observations. We analyse the Kepler light curve of eachstar and extract the pulsational frequencies using different frequencyanalysis methods. We construct two new observables, "energy" and"efficiency", related to the driving energy of the pulsation mode andthe convective efficiency of the outer convective zone, respectively. Results: We propose three main groups to describe the observedvariety in pulsating A-F type stars: ? Dor, ? Sct, andhybrid stars. We assign 63% of our sample to one of the three groups,and identify the remaining part as rotationally modulated/active stars,binaries, stars of different spectral type, or stars that show no clearperiodic variability. 23% of the stars (171 stars) are hybrid stars,which is a much higher fraction than what has been observed before. Wecharacterize for the first time a large number of A-F type stars (475stars) in terms of number of detected frequencies, frequency range, andtypical pulsation amplitudes. The majority of hybrid stars showfrequencies with all kinds of periodicities within the ? Dor and? Sct range, also between 5 and 10 d-1, which is achallenge for the current models. We find indications for the existenceof ? Sct and ? Dor stars beyond the edges of the currentobservational instability strips. The hybrid stars occupy the entireregion within the ? Sct and ? Dor instability strips andbeyond. Non-variable stars seem to exist within the instability strips.The location of ? Dor and ? Sct classes in the(Teff, log g)-diagram has been extended. We investigate twonewly constructed variables, "efficiency" and "energy", as a means toexplore the relation between ? Dor and ? Sct stars. Conclusions: Our results suggest a revision of the current observationalinstability strips of ? Sct and ? Dor stars and imply aninvestigation of pulsation mechanisms to supplement the ?mechanism and convective blocking effect to drive hybrid pulsations.Accurate physical parameters for all stars are needed to confirm thesefindings.
| CHARM2: An updated Catalog of High Angular Resolution Measurements
We present an update of the Catalog of High Angular ResolutionMeasurements (CHARM, Richichi & Percheron \cite{CHARM}, A&A,386, 492), which includes results available until July 2004. CHARM2 is acompilation of direct measurements by high angular resolution methods,as well as indirect estimates of stellar diameters. Its main goal is toprovide a reference list of sources which can be used for calibrationand verification observations with long-baseline optical and near-IRinterferometers. Single and binary stars are included, as are complexobjects from circumstellar shells to extragalactic sources. The presentupdate provides an increase of almost a factor of two over the previousedition. Additionally, it includes several corrections and improvements,as well as a cross-check with the valuable public release observationsof the ESO Very Large Telescope Interferometer (VLTI). A total of 8231entries for 3238 unique sources are now present in CHARM2. Thisrepresents an increase of a factor of 3.4 and 2.0, respectively, overthe contents of the previous version of CHARM.The catalog is only available in electronic form at the CDS viaanonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/431/773
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