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Hidden subluminous stars among the FAUST UV sources towards Ophiuchus
We present results of an analysis of a UV image in the direction ofOphiuchus, obtained with the FAUST instrument. The image contains 228 UVsources. Most of these are identified as normal early-type stars throughcorrelations with catalogued objects. For the first time in this projectwe identify UV sources as such stars by selecting suitable candidates incrowded fields as the bluest objects in colour-colour diagrams usingobservations from the Wise Observatory. These candidates are thenstudied using low-resolution spectroscopy, which allows thedetermination of spectral types to an accuracy of about one-half class,for 60 stars. Synthetic photometry of spectral data is performed inorder to predict the expected UV emission, on the basis of thephotometric information. These results are used along with the Hipparcos/Tycho information, to search for subluminous stars. The comparison ofthe predicted emission with the FAUST measured magnitudes allows us toselect 12 stars as highly probable evolved hot stars. Highsignal-to-noise spectra are obtained for nine of these stars, and Balmerline profiles are compared with the prediction of atmosphere models andwith the spectrum of real stellar atmospheres. Among the ninecandidates, six are classified as previously unrecognized sdB stars, andtwo as white dwarfs. Our result indicates that indeed more brightsubluminous stars are still unrecognized in the existing samples.
| A catalog of far-ultraviolet point sources detected with the fast FAUST Telescope on ATLAS-1
We list the photometric measurements of point sources made by the FarUltraviolet Space Telescope (FAUST) when it flew on the ATLAS-1 spaceshuttle mission. The list contains 4698 Galactic and extragalacticobjects detected in 22 wide-field images of the sky. At the locationssurveyed, this catalog reaches a limiting magnitude approximately afactor of 10 fainter than the previous UV all-sky survey, TDl. Thecatalog limit is approximately 1 x 10-14 ergs A sq cm/s,although it is not complete to this level. We list for each object theposition, FUV flux, the error in flux, and where possible anidentification from catalogs of nearby stars and galaxies. Thesecatalogs include the Michigan HD (MHD) and HD, SAO, the HIPPARCOS InputCatalog, the Position and Proper Motion Catalog, the TD1 Catalog, theMcCook and Sion Catalog of white dwarfs, and the RC3 Catalog ofGalaxies. We identify 2239 FAUST sources with objects in the stellarcatalogs and 172 with galaxies in the RC3 catalog. We estimate thenumber of sources with incorrect identifications to be less than 2%.
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Observation and Astrometry data
| Constellation: | Ophiuchus |
| Right ascension: | 17h34m46.98s |
| Declination: | -16°37'25.9" |
| Apparent magnitude: | 8.764 |
| Distance: | 320.513 parsecs |
| Proper motion RA: | 5.3 |
| Proper motion Dec: | -13.3 |
| B-T magnitude: | 8.77 |
| V-T magnitude: | 8.765 |
Catalogs and designations:
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