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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.
| Observations of active-chromosphere stars - IV. Photometry and spectroscopy of CF Octantis (HD 196818)
We present photometry and spectroscopy of the single, K-type,active-chromosphere star CF Octantis (=HD 196818), from 1982 to 1986.The photometric data show the 20-d rotation period seen previously, andalso demonstrate that the light curve is variable on time-scales of afew months, which we ascribe to variations in the properties ofstarspots. We postulate that a temporary dimming of minimum light seenin mid-1983 was a result of the appearance and later disappearance of arelatively small spot or spot group, which had a lifetime between 10 and24 months. The main spot appeared relatively stable during the intervalof our observations, with a lifetime of at least 3 years. Our radialvelocity data are consistent with the results of other work in that novariations above observational scatter are seen. Both the Ca K andHα emission are variable, with tentative evidence for the latterthat a lower emission level occurred near the phase of photometricmaximum, although the spectroscopic and photometric data were notcontemporaneous. The lithium abundance is found to be logN(Li)=0.45+/-0.15. The star may have evolved from a rapidly rotating A-Fmain-sequence star.
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Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1985A&AS...59...15A&db_key=AST
| B and V Photometry of the Southern RS CVn Candidate HD 196818
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Osservazione e dati astrometrici
| Costellazione: | Ottante |
| Ascensione retta: | 20h38m18.60s |
| Declinazione: | -81°17'20.0" |
| Magnitudine apparente: | 5.91 |
| Distanza: | 194.932 parsec |
| Moto proprio RA: | 0.7 |
| Moto proprio Dec: | -38 |
| B-T magnitude: | 8.17 |
| V-T magnitude: | 6.104 |
Cataloghi e designazioni:
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