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HD 81804


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Five-colour photometry of early-type stars in the direction of galactic X-ray sources
The results of five-color (Walraven system) photometry of 551 O- andB-type stars located in 17 fields of a few square degrees aroundgalactic X-ray sources are presented. From a comparison ofreddening-free combinations of color indices with theoretical values,calculated for model atmospheres of Kurucz (1979), effective temperatureand surface gravity for these stars are derived. In addition theirabsolute magnitude are determined by combining these parameters with theresults of evolutionary calculations of massive stars. These effectivetemperatures are in good agreement with the temperature scale ofBohm-Vitense (1981) for stars of luminosity classes II to V. For thesupergiants the effective temperatures are about 40 percent higher. Forstars of luminosity classes III to V the absolute magnitudes agree wellwith the results of independent luminosity calibrations of spectraltypes, but for brighter stars they deviate systematically. Thephotometric data are also used to study the interstellar reddening inthe direction of the X-ray sources.

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Сазвежђа:Једра
Ректацензија:09h25m45.45s
Deклинација:-55°17'16.5"
Apparent магнитуда:8.994
Даљина:10000000 parsecs
Proper motion RA:-7.4
Proper motion Dec:5.8
B-T magnitude:9.018
V-T magnitude:8.996

Каталог и designations:
Proper имена   (Edit)
HD 1989HD 81804
TYCHO-2 2000TYC 8588-2819-1
USNO-A2.0USNO-A2 0300-06907687
HIPHIP 46251

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