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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.
| UBVRI photometry of FKSZ stars. II
The results of UBVRI photometry for 169 stars of the Faint FundamentalStars Catalog (Zverev, 1957) in the declination zone lambda of between-30 and -60 deg are presented. Observations were obtained between May1984 and February 1987 using the 50-cm ESO telescope at La Silla.Tabular data presented include the number of the star in the E-regions,the V magnitude, the (B-V), (U-B), (V-R), and (R-I) colors, and thespectral types.
| Further photometry and spectroscopy in the young cluster region TR 24/Sco OB 1
Further photometric and spectroscopic observations in the Tr 24/Sco OB 1area are presented. The new data support our earlier suggestion that Tr24 and Sco OB1 form one stellar aggregate. A high percentage (greater 70percent) of suspected pre-main sequence stars from photometry showspectral evidence for young age and/or variability. It seems now firmlyestablished that a subclustering containing 29 stars is a spatialrelated, coevally born concentration of pre-main sequence stars. Largediscrepancies in recent distance determinations of Sco OB 1 are pointedout and discussed. No real reconciliation is found, but it is suggestedthat the stars traditionally assigned to Sco OB 1 may in fact be apartial overlap of two associations.
| UBV photometry of TR 24 and its relation to SCO OB1
In an area of 1.3 x 0.3 deg centered on Tr 24 UBV photometry down toabout 14m has been obtained. From color-magnitude and color-colordiagrams a distance of 2300 pc, a foreground reddening of Av = 1.10m anda cluster with an age of less than 10 to the 7th yr is derived. Tr 24and Sco OB1 form one large cluster containing many pre-main sequencestars. The existence of a small (8 x 3 pc) subgroup is pointed out whichcontains more than 20 stars and could be a T Tau-association embedded inTr 24.
| Variable polarization in X-ray binaries - HD 153919 (= 4U1700 - 37) and HD 152667 (= OAO1653 - 40?)
Variable linear polarization has been observed in the optical radiationfrom two presumed X-ray binary systems, HD 153919 (= 4U1700 - 37) and HD152667 (probably not OAO1653 - 40). This intrinsic polarization appearscorrelated with the orbital phase of the binary, but the polarimetriclight curve shows variations from year to year. The Stokes parameter q,u light curves are consistent with the polarization being caused by theRayleigh scattering of light from the primary by gas streams in thevicinity of the secondary. Several orbital and physical parameters ofthe binary systems are derived from the polarimetric observations.
| Determination of proper motions in the region of the association Scorpius OB1
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