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1995Apjs ... 96. .461B the Astrophysical Journal The Astrophysical Journal Supplement Series, 96:461-544, 1995 February .461B © 1995. The American Astronomical Society. All rights reserved. Printed in U.S.A. 96. ... A CATALOG OF FAR-ULTRAVIOLET POINT SOURCES DETECTED 1995ApJS WITH THE FAUST TELESCOPE ON ATLAS-1 Stuart Bowyer, Timothy P. Sasseen, Xiaoyi Wu, and Michael Lampton Center for EUV Astrophysics, University of California, Berkeley, Berkeley, CA 94720 Received 1993 September 27; accepted 1994 July 6 ABSTRACT We list the photometric measurements of point sources made by the Far Ultraviolet Space Telescope ( FAUST ) when it flew on the ATLAS-1 space shuttle mission. The list contains 4698 Galactic and extragalactic objects detected in 22 wide-field images of the sky. At the locations surveyed, this catalog reaches a limiting magnitude approximately a factor of 10 fainter than the previous UV all-sky survey, TD 1. The catalog limit is approximately 1 X 10-14 ergs s-1 cm2 Á, although it is not complete to this level. We list for each object the position, FUV flux, the error in flux, and where possible an identification from catalogs of nearby stars and galaxies. These catalogs include the Michigan HD (MHD) and HD, SAO, the HIPPARCOS Input Catalog, the Position and Proper Motion Catalog, the TD1 Catalog, the McCook and Sion Catalog of white dwarf stars, and the RC3 Catalog of Galaxies. We identify 2239 FAUST sources with objects in the stellar catalogs and 172 with galaxies in the RC3 catalog. We estimate the number of sources with incorrect identifications to be less than 2%. Subject headings: catalogs — techniques: photometric — ultraviolet: galaxies — ultraviolet: stars 1. THE FAUST EXPERIMENT We estimate the number of false detections via a Monte The Far Ultraviolet Space Telescope (FAUST) experiment Carlo technique of generating a set of images with only random photon noise and totaling the number of “stars” detected at was designed to perform photometry of diffuse and point the level of significance accepted for inclusion in the catalog. sources in the far ultraviolet. In this paper, we catalog the pho- tometry for 4698 point sources detected by FAUST during its The artificial images were chosen to have a range of back- flight in 1992 March on board the space shuttle Atlantis during ground levels, and the results are independent of the back- the ATLAS-1 mission. The experiment, the mission, and the ground level ( as our algorithm predicts ). We find a false detec- tion rate of 0.6%, or about 25 of our 4698 sources are not real data have been described in Bowyer et al. ( 1993). Briefly, the FAUST telescope is a two-mirror Wynne camera, with a 7!6 sources. We note that these false detections only occur at the very faint end of the catalog. field of view, which images the sky in a single bandpass cover- ing 1400-1800 Á. The full width half-maximum of the FAUST resolution is about 3.'5. We obtained 22 wide-field images dur- 2.1. Source Locations ing the flight, covering about 4.4% of the sky. The pointings in The accuracy of source positions is limited by photon statis- 1950 coordinates of each image are listed in Bowyer et al. tics, the point-spread function of the instrument, and irregu- ( 1993) and here in Tables 1A and IB. A detailed discussion of larities in the imaging properties of the detector. This last error the sensitivity of each observation is given in Cohen, Sasseen, is dominant for this catalog. We determine the overall uncer- & Bowyer (1994). tainty in the source locations by comparing the measured source positions with the known positions for a sample of stars 2. POINT SOURCES from the MHD catalog. The distribution is shown in Figure 1. Each image was searched for point sources using an auto- From this distribution we estimate that 82% of the sources we mated star detection routine described in Bowyer et al. ( 1993 ). have identified are within 2' of our measured position. Basically, the program tests the hypothesis that each pixel con- tains a source by summing counts within the point-spread 2.2. Source Identification function around it and subtracting a background from an area- weighted annular surrounding region. The flux uncertainty We have searched a wide variety of catalogs of nearby stars was determined using Poisson statistics. A detection was listed and galaxies for possible identifications of the FAUST sources. if its flux exceeded 4 a. We viewed this limit as conservative The catalogs we searched include the Michigan HD catalog with few resultant spurious sources, though it did have the un- (Houk & Cowley 1975, hereafter MHD), the HIPPARCOS fortunate consequence of omitting from the table some well- Input Catalog (Guyenne & Hunt 1985, hereafter HIC), the known sources from the catalog (e.g., the QSO 3C 273, which Position and Proper Motion Catalog (Roeser & Bastien 1991, was detected at 3.5 d). In this way, we keep a constant statisti- hereafter PPM), the SAO Catalog (SAO 1966), the HD cata- cal significance for source detections across an image where the log (Cannon 1924 and 1936), the TD1 Catalog (Thompson et sensitivity and exposure vary. The maximum pixel within the al. 1978), the McCook & Sion (1987) list of white dwarf stars, point-spread function of a pixel thus identified is chosen as the and the Third Reference Catalogue of Galaxies (de Vaucoule- point source center. urs et al. 1991, hereafter RC3 ). 461 © American Astronomical Society • Provided by the NASA Astrophysics Data System .461B 462 BOWYER ET AL. Vol. 96 96. TABLE IA FAUST Pointings ... Number R.A. Decl. Remarks 1 0h40m —72!5 Small MageUanic Cloud 1995ApJS 2 4 16 -56.3 Dorado galaxy cluster 3 5 10 -70.0 Large Magellanic Cloud 4 7 37 5.3 Alignment pointing 5 , 7 45 -19.2 PKS0745 6 8 21 -59.4 Alignment pointing 7 12 0 -18.6 NGC 4038/39 8 , 12 2 17.9 Near north Galactic pole 9 12 28 12.7 Virgo cluster 10 , 12 28 15.7 Virgo cluster 11 , 12 28 9.7 Virgo cluster 12 . 12 39 -1.2 Alignment pointing 13 . 12 40 22.0 Near north Galactic pole 14 . 12 46 -41.0 Centaurus galaxy cluster 15 , 12 57 28.3 Coma galaxy cluster Distance (arcmin) 16 . 13 34 -29.6 M83 17 . 17 20 -20.0 Ophiucus molecular cloud Fig 1.—The distribution of distances from FAUST sources to the near- 18 . 19 0 -60.1 NGC 6752 est SAO or MHD star. 19 . 20 12 —46.7 Telescopium galaxy cluster the flux is likely from only one of the stars via a simple discrim- We identify a FAUST source with a catalog object if these inator based on the relationship of FAUST flux, V magnitude, objects lie within 3' of each other. This associates 2411 FAUST and spectral type of the cataloged object. We plot in Figure 2 sources with catalog objects. We list the distance from the the ratio of the FAUST flux in log form to the V magnitude of FAUST source to the catalog object, the spectral type, and V an object versus the spectral type (in numerical form, where magnitude. We use the MHD catalog as the source for these ST = 0 for OO, 10 for B0, etc.). The line shown is the best fit to quantities where possible. If there is not an MHD object listed, points between spectral types O and G5. We use this line to these quantities are taken from one of the other catalogs with estimate the FAUST flux for an object as the following preference: MHD, HIPPARCOS, PPM, SAO, HD. We also list identifications with members of RC3 if the o ST b — FAUST flux = 10 (1) FAUST source lies within 3' of the galaxy. Further identifica- Z5 tions for objects in field 13 may be found in Brosch et al. (1994). We have not made an attempt to identify FAUST where <2 = 0.196 and b = 9.28, and FAUST flux is in units of sources in the direction of the Magellanic Clouds because of photons s-1 cm-2 A-1. When the flux from one star, according the difficulty in discriminating between Galactic stars and Ma- to this estimator, is at least a factor of 6 greater than that of the gellanic Cloud stars given the limited resolution of the FAUST instrument. We simply note the sources detected in these di- rections. A detailed study of these fields is underway (Courtes et al. 1994). Because of the modest imaging capabilities, it is not possible to use angular extent as a discriminant for extragalactic sources. A range of criteria have been investigated by Dehar- veng et al. ( 1994 ) to identify and characterize extragalactic ob- jects in the FAUST fields. 2.3. Source Confusion There are 142 cases where more than one stellar object is within 3' of the FAUST source. We have removed cases where TABLE IB FAUST Pointings and Scans, 1950 Coordinates Number R.A.-Decl. Remarks 20 \0P0m, —10! to 1 lh40m, —20! Low Galactic emission region in Hydra Fig. 2.—The relationship between FAUST flux, V magnitude, and 21 14 0, -30. to 12 40, -20. Low Galactic emission spectral type. The line is the best fit to stellar types between OO and G5. region in Hydra Points have been jittered slightly to separate identical spectral types, and the spectral type label is at the center of the range. © American Astronomical Society • Provided by the NASA Astrophysics Data System PQ No. 2, 1995 FAR-UV POINT SOURCES 463 In general, the uncertainty in these flux measurements is a result of photon statistics in the source and background, labo- ratory measurement uncertainties, and the overall uncertainty in IUE measurements that were used for the in-flight compar- ison calibration.
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