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uvby-Hβ CCD photometry of NGC 1817 and NGC 1807
We have investigated the area of two NGC entries, NGC 1817 and NGC 1807,with deep CCD photometry in the uvby-Hβintermediate-band system. The photometric analysis of a selected sampleof stars of the open cluster NGC 1817 yields a reddening value of E(b-y)= 0.19±0.05, a distance modulus of V0-MV =10.9±0.6, a metallicity of [Fe/H] = -0.34±0.26 and an ageof log t = 9.05±0.05. Our measurements allow us to confirm thatNGC 1807 is not a physical cluster.Figure \ref{map} and Tables \ref{log} and \ref{chips} are only availablein electronic form at http://www.edpsciences.orgTables 4 and 5 are only available in electronic form at the CDS viaanonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/426/827
| New membership determination and proper motions of NGC 1817. Parametric and non-parametric approach
We have calculated proper motions and re-evaluated the membershipprobabilities of 810 stars in the area of two NGC objects, NGC 1817 andNGC 1807. We have obtained absolute proper motions from 25 plates in thereference system of the Tycho-2 Catalogue. The plates have a maximumepoch difference of 81 years; and they were taken with the doubleastrograph at Zo-Sèstation of Shanghai Observatory, which has anaperture of 40 cm and a plate scale of 30 arcsec mm-1. Theaverage proper motion precision is 1.55 mas yr-1. Theseproper motions are used to determine the membership probabilities ofstars in the region, based on there being only one very extendedphysical cluster: NGC 1817. With that aim, we have applied and comparedparametric and non-parametric approaches to cluster/field segregation.We have obtained a list of 169 probable member stars.Table 5 is only available in electronic form at the CDS via anonymousftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/426/819Tables 1, 2 and 4 and Fig. 1 are only available in electronic form athttp://www.edpsciences.org
| Determination of proper motions and membership of the open clusters NGC 1817 and NGC 1807
Relative proper motions, their corresponding observed errors andmembership probabilities of 722 stars in the old open cluster NGC 1817region are determined from PDS measurements of 12 plate pairs. Theplates have the maximum epoch difference of 81 years and were taken withthe double astrograph at Zǒ-Sè station of ShanghaiObservatory, which has an aperture of 40 cm, a focal length of 6.9 m anda plate scale of 30''/mm. The average proper motion accuracy is 1.6mas/yr. These proper motions are used to determine the membershipprobabilities of stars in the region. The existence of two clusters inthe region (NGC 1817, NGC 1807) is discussed. The number of stars withmembership probability higher than 0.7 is 416 for NGC 1817 and 14 forNGC 1807. Table 5 is only available in electronic form from CDS viaanonymous ftp 130.79.128.5, and by e-mail request tolbalague@pchpc3.am.ub.es
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Observation and Astrometry data
| Constellation: | Ταύρος |
| Right ascension: | 05h11m10.50s |
| Declination: | +16°35'39.6" |
| Apparent magnitude: | 9.762 |
| Proper motion RA: | 1.3 |
| Proper motion Dec: | -6 |
| B-T magnitude: | 9.946 |
| V-T magnitude: | 9.778 |
Catalogs and designations:
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