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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.
| A study of SCO 0B1 and NGC 6231. II - A new analysis
A new analysis of the Sco 0B1 association, and the two open clusters NGC6231 and Tr 24 was undertaken, making use of the extensive amount ofpublished data for this region of the southern sky. The averageinterstellar reddening, due mostly to foreground particulate matter, isE(b - y) = 0.326 mag or E(B - V) = 0.44 mag, with a pronouncednorth-to-south variation across the association. The distance moduli ofthe three aggregates are indistinguishable from one another; their meandistance from the sun is 2.0 kpc. A logarithmic age of 6.9 +/- 0.2 yearswas derived for the systems. Photometric criteria were used to assigndifferent degrees of membership to the B-type stars. Potential variablestar candidates were noted. Contrary to previous suggestions, NGC 6231retains its role as the nucleus of Sco 0B1 and, finally, the physicalreality of Tr 24 itself is questioned and briefly discussed.
| VBLUW photometry of the association SCO OB1 (containing the open cluster NGC 6231) - A discussion on the evolutionary status of the hypergiant Zeta(1) SCO (B1Ia+)
Attention is given to VBLUW photometry obtained for nearly 190 stars inSco OB1, of which almost 60 appear to be foreground objects.Temperature, surface gravity, and individual reddenings have beenobtained. It appears that the reddening is not uniformly distributedacross the association. Virtually all reddening is due to dust in thelocal spiral arm, up to a distance of almost 700 pc from the sun. Akinematical age of about one million years, as determined by Braes(1967), is in reasonable agreement with the average evolutionary age ofabout 3.6 + or - 0.6 years for the 12 brightest stars.
| Blue Giants in the Neighborhood of NGC 6231.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1953ApJ...118..323M&db_key=AST
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Observation and Astrometry data
| Constellation: | Ophiuchus |
| Right ascension: | 16h53m50.08s |
| Declination: | +02°29'43.8" |
| Apparent magnitude: | 9.225 |
| Proper motion RA: | -0.1 |
| Proper motion Dec: | -4.9 |
| B-T magnitude: | 11.089 |
| V-T magnitude: | 9.379 |
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