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Preparing the COROT space mission: Incidence and characterisation of pulsation in the lower instability strip
By pursuing the goal to find new variables in the COROT field-of-view wecharacterised a sample of stars located in the lower part of theinstability strip. Our sample is composed of stars belonging to the diskpopulation in the solar neighbourhood. We found that 23% of the starsdisplay multiperiodic light variability up to a few mmag in amplitude,i.e., easily detectable on a single night of photometry. uvbybetaphotometry fixed most of the variables in the middle of the instabilitystrip and high-resolution spectroscopy established that they have vsin i>100 km s-1. An analysis of the Rodríguez &Breger (\cite{Rodr01}) sample (delta Sct stars in the whole Galaxy)shows slightly different features, i.e., most delta Sct stars have a0.05-mag redder (b-y)0 index and lower vsin i values.Additional investigation in the open cluster NGC 6633 confirms the sameincidence of variability, i.e., around 20%. The wide variety ofpulsational behaviours of delta Sct stars (including unusual objectssuch as a variable beyond the blue edge or a rapidly rotatinghigh-amplitude pulsator) makes them very powerful asteroseismic tools tobe used by COROT. Being quite common among bright stars, delta Sctstars are suitable targets for optical observations from space.Based on observations collected at the S. Pedro Martír, SierraNevada, La Silla, Haute-Provence, South African and Roque de LosMuchachos observatories.
| A spectroscopic survey for lambda Bootis stars. II. The observational data
lambda Bootis stars comprise only a small number of all A-type stars andare characterized as nonmagnetic, Population i, late B to early F-typedwarfs which show significant underabundances of metals whereas thelight elements (C, N, O and S) are almost normal abundant compared tothe Sun. In the second paper on a spectroscopic survey for lambda Bootisstars, we present the spectral classifications of all program starsobserved. These stars were selected on the basis of their Strömgrenuvbybeta colors as lambda Bootis candidates. In total, 708 objects insix open clusters, the Orion OB1 association and the Galactic field wereclassified. In addition, 9 serendipity non-candidates in the vicinity ofour program stars as well as 15 Guide Star Catalogue stars were observedresulting in a total of 732 classified stars. The 15 objects from theGuide Star Catalogue are part of a program for the classification ofapparent variable stars from the Fine Guidance Sensors of the HubbleSpace Telescope. A grid of 105 MK standard as well as ``pathological''stars guarantees a precise classification. A comparison of our spectralclassification with the extensive work of Abt & Morrell(\cite{Abt95}) shows no significant differences. The derived types are0.23 +/- 0.09 (rms error per measurement) subclasses later and 0.30 +/-0.08 luminosity classes more luminous than those of Abt & Morrell(\cite{Abt95}) based on a sample of 160 objects in common. The estimatederrors of the means are +/- 0.1 subclasses. The characteristics of oursample are discussed in respect to the distribution on the sky, apparentvisual magnitudes and Strömgren uvbybeta colors. Based onobservations from the Observatoire de Haute-Provence, OsservatorioAstronomico di Padova-Asiago, Observatório do Pico dosDias-LNA/CNPq/MCT, Chews Ridge Observatory (MIRA) and University ofToronto Southern Observatory (Las Campanas).
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