The Hvar survey for roAp stars: II. Final results (Research Note)

The 60 known rapidly oscillating Ap (roAp) stars are excellent laboratories to test pulsation models in the presence of stellar magnetic fields. Our survey is dedicated to search for new group members in the Northern Hemisphere. We attempt to increase the number of known chemically peculiar stars that are known to be pulsationally unstable. About 40 h of new CCD photometric data of 21 roAp candidates, observed at the 1m Austrian-Croatian Telescope (Hvar Observatory) are presented. We carefully analysed these to search for pulsations in the frequency range of up to 10mHz. No new roAp star was detected among the observed targets. The distribution of the upper limits for roAp-like variations is similar to that of previoius similar efforts using photomultipliers and comparable telescope sizes. In addition to photometric observations, we need to consolidate spectroscopic information to select suitable targets.Comment: 8 pages, 5 figures, accepted by Astronomy & Astrophysic

Search for variability of five central stars of planetary nebulae

The central stars of planetary nebulae are interesting objects which are important to understand the very late stages of stellar evolution. They exhibit variability due to binarity, stellar winds, and pulsation. We searched for variability in five of such objects and found only upper limits. However, also this null result is important for the understanding of these stars

New Variable Stars in Open Clusters I: Methods and Results for 20 Open Clusters

We present high precision CCD photometry of 1791 objects in 20 open clusters with an age from 10 Myr to 1 Gyr. These observations were performed within the Delta a photometric system which is primarily used to detect chemically peculiar stars of the upper main sequence. Time bases range between 30 minutes and up to 60 days with data from several nights. We describe the way of time series analysis reaching a detection limit of down to 0.006 mag. In total, we have detected 35 variable objects from which four are not members of their corresponding clusters. The variables cover the entire Hertzsprung-Russell-diagram, hence they are interesting targets for follow-up observations.Comment: 4 pages, 2 figures, accepted by A&

New spectroscopic classifications of 35 chemically peculiar candidate stars

The chemically peculiar (CP) stars of the upper main sequence are perfect tracers for several astrophysical processes.Their study especially in open clusters further helps to establish their evolutionary status. The latter is most important tounderstand the origin and evolution of the CP phenomenon, i.e. the connection between diffusion and a stellar magneticfield. There are two important topics, we cover with this paper. First of all, we investigate the reliability of the CCDa photometry for fainter objects in open clusters. The latter method is able to detect CP stars very efficiently, butstill a spectroscopic verification is needed to verify the photometric candidates. On the other hand, already publishedspectral classifications on the basis of photographic plates and prismtechnology have to be tested withmodern instruments.Classification resolution spectroscopy is presented for thirty five bona-fide CP candidates. Twenty six of them are locatedwithin the boundaries of fourteen open clusters, for which we also investigated their membership probabilities. Apart fromfive objects, they seem to be members of the respective clusters. The objects were classified in the framework of a refinedMorgan-Keenan system with the extension of well established CP star spectra. We confirm the CP nature of all but onetarget. The results of a photometry and the spectral classifications are in excellent agreement. For the cluster memberswe find a continuous sequence of CP stars from 10 to 850Myr, the whole range of investigated cluster ages.Fil: Paunzen, E.. Institut für Astronomie der Universität Wien; AustriaFil: Netopil, M.. Institut für Astronomie der Universität Wien; Austria. Masaryk University; República ChecaFil: Pintado, Olga Ines. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Tucumán. Instituto Superior de Correlación Geológica. Universidad Nacional de Tucumán. Facultad de Ciencias Naturales e Instituto Miguel Lillo. Departamento de Geología. Cátedra Geología Estructural. Instituto Superior de Correlación Geológica; ArgentinaFil: Rode Paunzen, M.. Institut für Astronomie der Universität Wien; Austri

CCD photometric search for peculiar stars in open clusters

The search for chemically peculiar (CP) stars in open clusters using photoelectric photometry sampling the presence of the characteristic flux depression feature at 5200 Å via the $\Delta a$-system (Maitzen 1976) has so far delivered data for objects usually no more distant than 1000 pc from the Sun. A series of fourteen papers (first: Maitzen & Hensberge 1981; for the time being last: Maitzen 1993) were devoted to 1240 stars in 38 open cluster fields.
If one intends to study the presence of CP stars at larger distances from the Sun, classical photometry has to be replaced by CCD photometry. We have therefore initialized in 1995 a new survey in open clusters and the Large Magellanic Cloud using the CCD technology.
As a first step, we have presented new $\Delta a$-photometry of 22 CP2 stars in the galactic field to prove the capability of CCD photometry for our aim (Maitzen et al. 1997).
In the first paper of a new series devoted to CCD photometry, we present data on NGC 2169 (13 stars investigated), Melotte 105 (114 stars), and NGC 6250 (48 stars). NGC 2169 was used to test our results with those of classical photometry which yields excellent agreement.
For NGC 6250 we find two new definite CP2 (according to the definition by Preston 1974) stars ($\Delta a$ = 0.065 and 0.026 mag) and two λ Bootis candidates. Twelve objects with only marginally peculiar $\Delta a$-values for Melotte 105 were detected. Additional spectroscopic and photometric evidence is needed to substantiate their peculiarity.