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Photometric Parameters of the Dwarf Nova SS Cygni in the Quiescent State
The mean 1983 1996 UBV light curves of the dwarf nova SS Cyg are used toderive the binary parameters in the quiescent state. Solutions areobtained for a classical hot-spot model and a model with an energysource lying outside the accretion disk. Photometric and spectroscopicdata are combined to infer the masses and radii of the binarycomponents. The white dwarf in SS Cyg is one and a half times as massiveas the red dwarf, q=M wd /M rd ˜1.45, M rd ˜0.46M ȯ andM wd ˜0.66M ȯ. The orbital inclination of the system isi⋍51° 54°. The contribution of the accretion disk to thetotal flux in the quiescent state is estimated to be ˜47 49% and˜54% in the VU and B filters, respectively. The hot spotcontributes less than ˜3% to the total optical flux. In the“non-classical” hot-spot model, the disk and bulgecontributions are 27 and 2 8%, respectively, depending on the orbitalphase. The shape of the mean light curves of SS Cyg suggests asymmetricheating of the red-dwarf surface in the quiescent state byhigh-temperature radiation generated in the hot-spot region.
| Parallaxes and Proper Motions of Prototypes of Astrophysically Interesting Classes of Stars. I. R Coronae Borealis Variables
Hipparcos data were obtained under the 1982 announcement of opportunityfor the seven brightest R CrB stars then known. None of the parallaxmeasurements is different from zero in a statistically significant way,though most of the proper motions are. The body of the data neverthelesssuggest that the stars belong to two rather different populations ineither luminosity, kinematics, or both. The best-known stars (R. CrBitself, RY Sgr, and perhaps others) probably are the very luminous, Msubscript v = -4 to -5, objects they are generally accused of being, butothers may belong to a fainter class for which there is some independentevidence among stars in the Large Magellanic Cloud. Alternatively, or inaddition, the apparently fainter stars may belong to a higher-velocitypopulation that we have had rather bad luck in sampling. Of two rashassumptions, the one that all seven stars are at the same distance of1200 pc leads to a velocity ellipsoid U superscript 2 superscript 1/2, Vsuperscript 2 superscript 1/2, W superscript 2> superscript 1/2 = 41,30, 35 km sec superscript -1, which is "not inconsistent" with valuestypical of (other) old disk populations, like carbon stars, long periodvariables, and planetary nebulae. The seemingly less rash assumptionthat all stars have M subscript v = -4.5 leads to U superscript 2superscript 1/2, V superscript 2 superscript 1/2, W superscript 2superscript 1/2, = 52, 60, and 104 km sec supercript -1, resembles noknown stellar population, at least not in our galaxy. (SECTION: Stars)
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Osservazione e dati astrometrici
| Costellazione: | Cigno |
| Ascensione retta: | 21h42m20.24s |
| Declinazione: | +43°34'03.3" |
| Magnitudine apparente: | 9.757 |
| Moto proprio RA: | -4.6 |
| Moto proprio Dec: | -1.6 |
| B-T magnitude: | 10.258 |
| V-T magnitude: | 9.799 |
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INHABITED SKY
