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Long term photometric monitoring with the Mercator telescope. Frequencies and mode identification of variable O-B stars
Aims. We selected a large sample of O-B stars that were considered as(candidate) slowly pulsating B, β Cep, and Maia stars after theanalysis of their hipparcos data. We analysed our new seven passbandgeneva data collected for these stars during the first three years ofscientific operations of the mercator telescope. We performed afrequency analysis for 28 targets with more than 50 high-qualitymeasurements to improve their variability classification. For thepulsating stars, we tried both to identify the modes and to search forrotationally split modes. Methods: . We searched for frequenciesin all the geneva passbands and colours by using two independentfrequency analysis methods and we applied a 3.6 S/N-level criterion tolocate the significant peaks in the periodograms. The modes wereidentified by applying the method of photometric amplitudes for which wecalculated a large, homogeneous grid of equilibrium models to perform apulsational stability analysis. When both the radius and the projectedrotational velocity of an object are known, we determined a lower limitfor the rotation frequency to estimate the expected frequency spacingsin rotationally split pulsation modes. Results: . We detected 61frequencies, among which 33 are new. We classified 21 objects aspulsating variables (7 new confirmed pulsating stars, including 2 hybridβ Cep/SPB stars), 6 as non-pulsating variables (binaries or spottedstars), and 1 as photometrically constant. All the Maia candidates werereclassified into other variability classes. We performed modeidentification for the pulsating variables for the first time. The mostprobable ℓ value is 0, 1, 2, and 4 for 1, 31, 9, and 5 modes,respectively, including only 4 unambiguous identifications. For 7 starswe cannot rule out that some of the observed frequencies belong to thesame rotationally split mode. For 4 targets we may begin to resolveclose frequency multiplets. Based on observations collected with the p7 photometer attached to theFlemish 1.2-m mercator telescope situated at the Roque de los Muchachosobservatory on La Palma (Spain). Section [see full textsee full text],including Figs. is only available in electronic form athttp://www.aanda.org, and Tables 2 and 3 are only available inelectronic form at the CDS via anonymous ftp to cdsarc.u-strasbg.fr(130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/463/243
| New periodic variables from the Hipparcos epoch photometry
Two selection statistics are used to extract new candidate periodicvariables from the epoch photometry of the Hipparcos catalogue. Theprimary selection criterion is a signal-to-noise ratio. The dependenceof this statistic on the number of observations is calibrated usingabout 30000 randomly permuted Hipparcos data sets. A significance levelof 0.1 per cent is used to extract a first batch of candidate variables.The second criterion requires that the optimal frequency be unaffectedif the data are de-trended by low-order polynomials. We find 2675 newcandidate periodic variables, of which the majority (2082) are from theHipparcos`unsolved' variables. Potential problems with theinterpretation of the data (e.g. aliasing) are discussed.
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