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Archival light curves from the Bamberg Sky Patrol: CF Octantis, 1964-76
We use the archive of the Bamberg Sky Patrol to obtain light curves ofthe active K subgiant CF Octantis (HD 196818) for the interval 1964-76.Digitized images of the field near CF Oct were obtained with a flat-bedscanner. Aperture photometry was performed of photo-positives of theseimages. Using a transformation to second order in plate magnitude, andfirst order in B-V, for nine field stars for each plate, the Bmagnitudes of CF Oct were obtained for just over 350 plates. Theestimated precision of an individual determination of the B magnitude ofCF Oct is 0.05 mag. Analysis of the resulting data reveals the known 20d rotational variation of this star, and shows the evolution of thelight curves from year to year. We obtain light curves with good phasecoverage for 1964 to 1969 inclusive, partial light curves for 1970 and1976, and a few data points from 1971. The amplitude of variation rangesfrom ~0.2 to ~0.4 mag. There is evidence that the characteristicrotation period of the star in the 1960s was slightly less than thatmeasured from photoelectric photometry in the 1980s.
| An Historical Light Curve of CF Octantis from Digitised Images of the Bamberg Plate Archive
Digital images were made of Bamberg Observatory Sky Patrol plates of thefield surrounding the active-chromosphere star CF Octantis (HD 196818).These images, taken with an inexpensive camera, were analysed usingstandard aperture photometry techniques. Good agreement was found withcatalogued photographic magnitudes for stars in the range mpg~8.5 to ~10.5. The root-mean-square deviations in themeasured differences for non-variable field stars was found to be oforder 0.10mag, although a small number of larger differences occurred.For CF Oct, a period search of data from 1966 recovered the known 20dvariation due to starspot rotational modulation, with a range ofvariation of order 0.5mag photographic. For active-chromosphere starswith moderately large photometric variations (>~0.3mag), and moderateto long rotation periods (>~1 week), careful analysis of similarlyobtained digital copies of archive plates may provide valuable insightsinto historical actvity.
| 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.
| CF Octantis, an RS CVn-type variable with a prominent activity cycle
Photoelectric photometry has been obtained for CF Octantis on 39 nights.The object is a member of the RS CVn class and has a highly activechromosphere. A 20.15 + or - 0.06 d period has been found from the B andV magnitudes which is interpreted as the rotational modulation of thelight from a nonuniformly spotted star. The amplitude of this spot waveis observed to vary slowly between Delta V of about 0.1 to 0.3 mag,which may be evidence for an activity cycle of 9 + or - 3 years.
| UBV(RI)c photometry for CaII emission stars. II - Observations at Mt. John University Observatory and at Mt. Stromlo
UBV(RI)c data are given for 17 stars with strong Ca II H and K emission.Techniques of observation and reduction are described briefly.
| B and V Photometry of the Southern RS CVn Candidate HD 196818
Not Available
| Local photometric standards for CaII emission stars
UBV data are given for 108 stars which are suitable local standards for52 stars with strong Ca2 emissions. An additional eight stars wererejected as possible standards because of suspected variability.
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Observation and Astrometry data
| Constellation: | Oktant |
| Right ascension: | 20h47m36.35s |
| Declination: | -79°51'13.1" |
| Apparent magnitude: | 7.605 |
| Distance: | 177.305 parsecs |
| Proper motion RA: | -13.3 |
| Proper motion Dec: | 5.9 |
| B-T magnitude: | 8.965 |
| V-T magnitude: | 7.718 |
Catalogs and designations:
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