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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.
| Interstellar extinction in the vicinity of the North America and Pelican Nebulae. II
The results of photoelectric photometry of 564 stars in the Vilniusseven-color system in three areas near the North America and PelicanNebulae are given. Photometric spectral types, absolute magnitudes,color excesses, interstellar extinction,s and distances to the stars aredetermined. We find that the dark cloud separating both nebulae is at580 pc distance. A number of stars immersed in the dark cloud have beenfound. It seems that the dark cloud extends south down to 40 degdeclination. The area southwest of alpha Cygni in the declination zones42 deg and 43 deg is comparatively transparent at least up to 1 kpc.
| The spectra, magnitudes and colours of O-A type stars in an area of the Milky Way, with the Center alpha = 20h16m, delta = +42 D 30'.
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Observation and Astrometry data
| Constellation: | はくちょう座 |
| Right ascension: | 20h30m31.36s |
| Declination: | +43°27'48.8" |
| Apparent magnitude: | 7.596 |
| Distance: | 423.729 parsecs |
| Proper motion RA: | 3.7 |
| Proper motion Dec: | -13.1 |
| B-T magnitude: | 7.82 |
| V-T magnitude: | 7.615 |
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