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The region of Collinder 121
The distribution of bright B-type stars in a field with a radius of5° centred at the Galactic open cluster Cr 121 is studied utilizingStrömgren and Hβ photometry. All PPM stars earlier thanspectral type A0 are used, revealing a loose nearby structure at adistance of 660-730pc, and a compact more distant group, which appearsto be a genuine cluster: Cr 121. Based on similar coordinates, distancesand positions on the colour-magnitude (CM) and Hertzsprung-Russell (HR)diagrams, 11 photometric cluster members are selected at a mean distanceof 1085(+/-41 standard error) pc. The results are discussed in the lightof both classical and Hipparcos points of view.
| A Photometric and Spectrophotometric Study of MR Cygni
A self-consistent, physically accurate program suite has been used in anaccurate simulation of new spectroscopy and photometry of MR Cygni.Analysis of both the spectroscopic and photometric data used spectrumsynthesis techniques and a synthetic photometry augmentation of a lightsynthesis program package. The theoretical light curves closely fit theobservational data. The same self-consistent parameters from the lightsynthesis solution produced synthetic spectra precisely fitting theobserved spectra at all orbital phases. The IRAF-reduced spectroscopyhas produced an accurate double-lined radial velocity curve. The derivedmass ratio differs greatly from photometric mass ratios in theliterature. New UBV photometry closely replicates existing data andindicates photometric stability of the binary system. A syntheticspectrum fitted to IUE data established the primary component Teff. Thelight curve solution determined a single set of system parameters usedto calculate U, B, and V light curves. We conclude that MR Cygni is amember of the relatively rare class of hot Algol systems defined byPopper. It is likely that mass transfer still is in progress, but thereis no evidence, either from orbital period variation or from a brightspot on the mass gainer, for its existence. The lack of H alpha emissionin any of our spectra, including one at phase 0.063, suggests a smallcurrent rate of mass transfer. The fact that our computationallyself-consistent procedure has successfully represented both thephotometry and the spectroscopy for a binary system whose components areappreciably distorted demonstrates the overall power of the procedure.
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