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Colour excesses of F-G supergiants and Cepheids from Geneva photometry.
A reddening scale for F-G supergiants and Cepheids is presented.Supergiants with low reddenings or in clusters form the basis of thecalibration. In this sense, it is entirely empirical. The data have beenobtained in the Geneva photometric system. Comparisons with otherreddening scales show no disagreement. The only problem is with Fernie'sscale for Cepheids (1990), where a systematic trend exists. Its originis not clear. It is suggested to extend the number of supergiants withindependently obtained colour excesses in order to test the existence ofa possible luminosity dependence of the calibration. A period-colourrelation for Cepheids is deduced, on the basis of the present reddeningcorrections. It gives strong support for V473 Lyr being a secondovertone pulsator.
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Observation and Astrometry data
| Constellation: | Οκτάς |
| Right ascension: | 17h45m52.05s |
| Declination: | -86°17'54.4" |
| Apparent magnitude: | 9.689 |
| Proper motion RA: | 28.4 |
| Proper motion Dec: | -13.6 |
| B-T magnitude: | 10.268 |
| V-T magnitude: | 9.737 |
Catalogs and designations:
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