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FAUST observations of ultraviolet sources in the directions of NGC 4038-39 and 6752
Analysis of ultraviolet (UV) observations with the FAUST shuttle-bornetelescope toward the Antennae and NGC 6752 celestial regions resulted inthe detection of 46 and 221 candidate sources respectively, for asignal-to-noise ratio of 8. We discuss the source detection process andthe identification of UV sources with optical counterparts. Usingcorrelations with existing catalogues, we present reliableidentifications for approximately 60 per cent of the sources. We findthat most identified objects are B, A and F stars. The remainingidentified objects are galaxies, a white dwarf in a binary system, andtwo K-type stars. Nearly all of the remaining unidentified objects haveassigned optical counterparts but, lacking additional information, wegive these only as best estimates. With help from new diagnosticdiagrams, we suggest that these unclassified objects are main-sequence(or giant) stars within the local spiral arm or halo; or other hotevolved objects within the local spiral arm. We discuss the nature ofthe objects found and compare our results with those predicted fromspectral and Galactic models.
| Voyager Far-Ultraviolet Observations of Globular Clusters
We report on the observations of nine globular clusters carried out bythe Voyager ultraviolet spectrometers (UVSs). Three of the observedclusters, M13, NGC 6752, and M70, exhibit an intense far-ultraviolet(FUV) spectrum down to the Lyman limit. However, the spectrum obtainedfor NGC 6752 is heavily contaminated by the nearby star HD 177999 forwavelengths longward of 1200 Å. For M70 the Voyager spectrum iscompletely dominated by the B3 star HD 172535. The FUV spectral energydistribution of M13 confirms results from the Ultraviolet ImagingTelescope that the main contributors to the FUV emission are hot sdBstars. M13's integrated spectrum resembles that of an sdB star ofT_eff~28,000 K. For two clusters, M92 and M5, UVS detected a weaksignal, making it difficult to reach any conclusion on the underlyinghot components of the systems. Four clusters, M15, NGC 2298, NGC 6656,and NGC 6793, were observed but not detected. In some cases it waspossible to identify a weak stellar spectrum, which, however, verylikely originates from foreground FUV emitters not related to thesystems. For the nondetected clusters we provide upper limits on the FUVflux.
| Ultraviolet Imagery of NGC 6752: A Test of Extreme Horizontal Branch Models
We present a 1620 A image of the nearby globular cluster NGC 6752obtained with the Ultraviolet Imaging Telescope (UIT) during the Astro-2mission of the Space Shuttle Endeavour in 1995 March. Anultraviolet-visible color-magnitude diagram (CMD) is derived for 216stars matched with the visible photometry of Buonanno et al. This CMDprovides a nearly complete census of the hot horizontal-branch (HB)population with good temperature and luminosity discrimination forcomparison with theoretical tracks. The observed data show goodagreement with the theoretical zero-age horizontal branch (ZAHB) ofSweigart for an assumed reddening of E(B - V) = 0.05 and a distancemodulus of 13.05. The observed HB luminosity width is in excellentagreement with the theoretical models and supports the single-starscenario for the origin of extreme horizontal branch (EHB) stars.However, only four stars can be identified as post-EHB stars, whereasalmost three times this many are expected from the HB number counts. Ifthis effect is not a statistical anomaly, then some noncanonical effectmay be decreasing the post-EHB lifetime. The recent noncanonical modelsof Sweigart, which have helium-enriched envelopes due to mixing alongthe red giant branch, cannot explain the deficit of post-EHB stars, butmight be better able to explain their luminosity distribution.
| 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%.
| Broad-band photometry of selected southern ultraviolet-bright stars.
Not Available
| The main sequence of the globular cluster NGC 6752
UBV photoelectric and photographic photometry of the southern globularcluster NGC 6752 are presented. The photoelectric sequence is extendedto a point about 1 mag below the main-sequence turnoff. A clustercolor-magnitude diagram, uncorrected for reddening, is plotted whichshows that: (1) the RR Lyrae gap is unpopulated except for oneshort-period W Vir star that lies above the horizontal branch; (2) thehorizontal-branch stars apparently lie mostly to the blue of theinstability strip; (3) the slope of the giant branch is about 5.0,implying an intermediate metal deficiency; (4) the main-sequence turnoffoccurs at V = 17.30 + or - 0.05 and B-V = 0.425 + or - 0.010; (5) themain sequence appears to be very broad, probably as a result of errorsin the photographic photometry; and (6) the normalized UV excess of themain-sequence stars is 0.22 mag, indicative of a metallicity (Fe/H) ofabout -1.5.
| Photometry of southern globular clusters II. Bright stars in NGC 6752
Abstract image available at:http://adsabs.harvard.edu/abs/1973MNRAS.162..227C
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