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Lunar occultations of 184 stellar sources in two crowded regions toward the Galactic bulge
Context. Lunar occultations (LO) provide a unique combination of highangular resolution and sensitivity at near-infrared wavelenghts. At theESO Very Large Telescope, it is possible to achieve about 1milliarcsecond (mas) resolution and detect sources as faint as K ? 12mag. Aims: We have taken advantage of a passage of the Moon overtwo crowded and reddened regions in the direction of the inner part ofthe Galactic bulge to obtain a high number of occultation light curvesover two half nights. Our goal was to detect and characterize new binarysystems, and to investigate highly extincted and relatively unknowninfrared sources in search of circumstellar shells and similarpeculiarities. Our target list included a significant number of verylate-type stars, but the majority of the sources was without spectralclassification. Methods: An LO event requires the sampling of thelight curve at millisecond rates to permit a detailed study of thediffraction fringes. For this, we used the so-called burst mode of theISAAC instrument at the Melipal telescope. Our observing efficiency wasultimately limited by overheads for telescope pointing and data storageto about one event every three minutes. Results: We could recorduseful light curves for 184 sources. Of these, 24 were found to bebinaries or multiples, all previously unknown. The projected separationsare as small as 7.5 mas, and the magnitude differences as high as?K = 6.5 mag. Additionally we could also establish for the firsttime the resolved nature of at least two more stars, along with anindication of circumstellar emission. We were also able to put upperlimits on the angular size of about 165 unresolved stars, an informationthat combined with previous and future observations will be very helpfulin establishing a list of reliable calibrators for long baselineinterferometers. Conclusions: Many of the newly detectedcompanions are beyond the present capabilities of other high angularresolution techniques, but some could be followed up by long baselineinterferometry or adaptive optics. From estimates of the stellar densitywe conclude that statistically the influence of chance alignmentsappears to be negligible. We infer that most cases are probablygiant-dwarf pairs.Based on observations made with ESO telescopes at Paranal Observatory.
| CCD measurements of visual binaries
CCD measurements of visual double stars were obtained with the ESO 1.5 mdanish reflector. All binaries observed are candidates for the HIPPARCOSInput Catalogue. More than 400 observations have been made in four clearnights. The accuracy obtained is comparable to the accuracy of thephotographic technique, but the observing and reduction times are oneorder of magnitude smaller.
| 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: | 18h57m09.23s |
| Declinazione: | -23°51'58.4" |
| Magnitudine apparente: | 10.389 |
| Moto proprio RA: | -1.2 |
| Moto proprio Dec: | -23.4 |
| B-T magnitude: | 10.731 |
| V-T magnitude: | 10.418 |
Cataloghi e designazioni:
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