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Pseudocepheids. III - The low-mass stars
Light and color curves in four-color, H-beta, and (RI) photometricsystems are presented for 20 low-mass pseudocepheids. Members of theWolf 630 group and the cluster M67 are used to establish the positionsof both variable and nonvariable giants with near solar abundance in theluminosity-temperature plane for old disk population stars, whilemembers of Omega Cen and of Kapteyn's Star Group are used for the lowmetal abundance halo giants. The low-mass pseudocepheids discussed aredivided into two main categories, based on the amplitude of lightvariation. The smaller amplitude stars, characterized by R CrB and RYSgr in the old disk population, show the R CrB syndrome of occasionaldeep light minima, as does UW Cen. The small amplitude variables in thehalo population, BL Tel and LN Hya, do not show the R CrB syndrome andtheir periods are longer than those of old disk stars. Large amplitudevariables, with periods ranging from 10 to 150 days, are all haloobjects with stability of period and form of light curve an obviousfunction of the period. Cen and BL Tel are members of Kapteyn's StarGroup, and the spectroscopic orbital elements of the latter indicate amass near 0.5 solar mass for the pseudocepheid and 1 solar mass for thelate-type giant companion. Far-infrared observations are important inexploring the correlations between the presence and character ofcircumstellar dust shells and other post-AGB star parameters.
| The S201 far-ultraviolet imaging survey. III - A field in Sagittarius
Far-ultraviolet imagery of a 20 deg diameter field in Sagittarius,centered near (1950) R.A. 18 h 34 m, decl. -30 deg 25 arcmin, wasobtained by the S201 far-ultraviolet camera during the Apollo 16mission. In a 10-minute exposure covering the 1250-1600 A wavelengthrange, 1034 star images are detectable, with a limiting ultravioletmagnitude of about 10. Most of these objects are identified withearly-type stars listed in the Smithsonian Astrophysical ObservatoryStar Catalog, the Catalog of Stellar Identifications, or both, but 203objects remain unidentified or are identified with late-type stars. Thephotometric measurements appear to be in reasonable agreement with thoseof the International Ultraviolet Explorer for stars in common, and withexpectations for A0 stars. A detailed photometric study was made of theMessier 8 region, and it is concluded that dust-scattered starlightcontributes about half of the total radiation observed from the centralregion of M8.
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Osservazione e dati astrometrici
| Costellazione: | Sagittario |
| Ascensione retta: | 18h59m53.81s |
| Declinazione: | -24°23'54.5" |
| Magnitudine apparente: | 8.462 |
| Distanza: | 675.676 parsec |
| Moto proprio RA: | -2.7 |
| Moto proprio Dec: | -7.2 |
| B-T magnitude: | 8.513 |
| V-T magnitude: | 8.467 |
Cataloghi e designazioni:
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