Mon. Not. R. Astron. Soc. 324, 580±598 (2001)

FAUST observations of ultraviolet sources in the directions of NGC 4038±39 and 6752

Julian Daniels,1,2w Noah Brosch,1 Elchanan Almoznino,1 Ohad Shemmer,1 Stuart Bowyer3 and Michael Lampton3 1The Wise Observatory and the School of Physics and Astronomy, Raymond and Beverly Sackler Faculty of Exact Sciences, Tel Aviv University, Tel Aviv 69978, Israel 2Department of Geography and Environmental Development, Ben Gurion University, Beer Sheva 84105, Israel 972-8-6472017 3Space Sciences Laboratory and Center for EUV Astrophysics, University of California, Berkeley, CA 94720, USA

Accepted 2000 December 29. Received 2000 December 29; in original form 2000 September 6

ABSTRACT Analysis of ultraviolet (UV) observations with the FAUST shuttle-borne telescope toward the Antennae and NGC 6752 celestial regions resulted in the detection of 46 and 221 candidate sources respectively, for a signal-to-noise ratio of 8. We discuss the source detection process and the identification of UV sources with optical counterparts. Using correlations with existing catalogues, we present reliable identifications for approximately 60 per cent of the sources. We find that most identified objects are B, A and F stars. The remaining identified objects are galaxies, a white dwarf in a binary system, and two K-type stars. Nearly all of the remaining unidentified objects have assigned optical counterparts but, lacking additional information, we give these only as best estimates. With help from new diagnostic diagrams, we suggest that these unclassified objects are main-sequence (or giant) stars within the local spiral arm or halo; or other hot evolved objects within the local spiral arm. We discuss the nature of the objects found and compare our results with those predicted from spectral and Galactic models. Key words: Galaxy: stellar content ± ultraviolet: galaxies ± ultraviolet: stars.

b 2258:63 : The study of UV sources in this part of the 1 INTRODUCTION Milkyˆ Way may† help the understanding of the morphology of the The ultraviolet (UV) region of the electromagnetic spectrum is an disc and halo regions of our Galaxy. excellent tool for identifying and quantifying active star formation There is a general lack of information about the nature of UV (SF) regions (Donas et al. 1987). It is also a sensitive probe of sources fainter than the completeness limit of the TD-1 all-sky evolved hot stellar populations (Burstein et al. 1988; Dorman & survey conducted during 1972 to 1974. A description of the UV O'Connell 1996). Furthermore, UV observations of galaxies are sky survey telescope on TD-1 was presented by Boksenberg et al. important for the following reasons. First, this wavelength range is (1973). For point sources, the S2/68 experiment on TD-1 provided shifted into the visible for high-redshift objects, and UV <300-AÊ broad-band flux measurements at 2740 and <330-AÊ , observations are expected to provide templates for evaluating wide-band photometry at 1565, 1965 and 2365 AÊ . The photo- evolution effects. Secondly, the UV contrasts the hot stellar metric accuracy over the short-wave band was claimed to be <10 population of a galaxy against the contribution from cooler stars, per cent (Jamar et al. 1976). and should provide new insight on galaxy stellar content. Previous The results of the TD-1 survey were published in the form of a UV observations of galaxies and their current interpretations have catalogue (Thompson et al. 1978) that contains approximately been reviewed by O'Connell (1990, 1992, 1999). 31 000 stars detected with S=N $ 10; corresponding to a flux 212 21 22  21 In this paper we study the population of Galactic UV stars density limit of 10 erg s cm A or about m1600 < 9: We and extragalactic sources detected in UV images of the sky in use here monochromatic magnitudes defined here as m 22:5 l ˆ  the directions of the Antennae or NGC 4038-39 l 2868:97; log f 2 21:75; where f is in cgs units. An extended version of ˆ l† l b 428:46 and the globular cluster NGC 6752 l 3368:50; the TD-1 catalogue contains 58012 stars (Landsman 1984). In the ˆ † ˆ 1565-AÊ band, the full TD-1 catalogue (henceforth TD1F) is w E-mail: [email protected] complete to <8.5 mag. Gondhalekar (1990) discussed the TD1F

q 2001 RAS Ultraviolet sources in the directions of NGC 4038±39 and 6752 581 catalogue, and mentions that the experiment is not linear for predicted from the Bahcall±Soneira model of the Galaxy (Bahcall sources fainter than 10212 erg s21 cm22 A 21. Thus, although the & Soneira 1980) and modifications therein (Brosch 1991; Bilenko, TD1F contains 58 012 stars, only 47 039 of them are brighter than private communication). We examine FAUST colour±magnitude the linearity limit in at least one band. diagrams to suggest morphological types for unclassified objects. The TD-1 catalogue shows only 19 objects1 for the Antennae We compare colour±colour plots with those predicted (Shemi et al. field and 50 objects1 for NGC 6752 field. Since the TD-1 mission 1994, and modifications therein). The colours of metallic-line there has been no further complete surveys of the UV sky. In stars in our fields are investigated, and individual sources of note particular, for the two fields studied here, only limited regions of are discussed. Finally, we discuss the extragalactic content of both the sky have been observed with space platforms such as HST and fields. UIT. One of the more extended partial surveys was by the FAUST experiment (see below), which operated on board the Space 2 FAUST OBSERVATIONS TOWARDS THE Shuttle (STS) Atlantis in 1992 March and April as part of the ANTENNAE AND NGC 6752 ATLAS-1 mission. During this flight, 19 pointed exposures were FAUST is a wide-field (78.6 field of view) all-reflecting two- obtained, of which three were short exposures for pointing checks. mirror Wynne camera with a bandpass between 1400 and 1800 AÊ The other fixed-pointing images were exposed for 12 to 18 min. In and an angular resolution of 3.5 arcmin. It utilizes a microchannel addition, two approximately 308-long scans of the sky were plate detector with wedge-and-strip anode, which records the obtained by rolling the STS during the exposure. A catalogue of position of each detected photon. A description of FAUST and its 4660 FAUST sources (FSC) was published by Bowyer et al. operation aboard ATLAS-1 on the Space Shuttle was given by (1995). This was produced using a uniform thresholding algorithm Lampton et al. (1993). Details of the image construction and for source detection, and the identifications were obtained from subsequent reductions are given in Bowyer et al. (1993), these nearest-object correlations against catalogues mostly from SIM- include: removing the effects of shuttle drift during the exposure; BAD [Set of Identifications, Measurements and Bibliography for correcting for airglow, aurora and South Atlantic Anomaly effects; Astronomical Data created and maintained by the Centre de removing optical and detector distortions; and correcting for DonneeÂs Astronomiques de Strasbourg (CDS), Strasbourg]. detector quantum efficiency variations. The FAUST images are being examined systematically at Tel The Antennae region was imaged by a single FAUST exposure Aviv University to identify sources using astrophysical criteria and pointed at 12:01, 218:18. The total exposure time was 863.4 s, perform, where possible, ground-based follow-up studies. In this and the image covers 67.5 deg2. Because of spacecraft motion, the context, we have already presented results from eight sky regions: sky covered by FAUST during pointed observations is slightly the North Galactic Pole, Brosch et al. (1995); the Virgo cluster larger than the instrumental field of view, and is typically 108 in region, Brosch et al. (1997); the direction of the Coma cluster, diameter. The NGC 6752 region was also imaged by a single Brosch et al. (1998); four regions of the Fourth Galactic Quadrant, FAUST exposure pointed at 19:02, 260:15. The total exposure Brosch et al. (2000a); and toward a second area near the North time was 1122.1 s, and the image covers 64.0 deg2. Shuttle drift Galactic Pole, Brosch et al. (2000b). results in a non-uniform exposure across both images. The Antennae and NGC 6752 fields were also observed by the The sky area covered by each image was calculated from FAUST telescope. The Antennae region is well suited for studies the total number of non-zero exposure pixels and by assuming of the UV stellar population and UV-bright galaxies, because of its that each pixel is a square of 1.1-arcmin sides. This is an low extinction. Measurements of H i from Dickey & Lockman approximation, because electrostatic distortions of the image (1990) using a rectangular region 88.4 long, covering the FAUST caused by the detector change slightly the area imaged by each field and centred at l 2868:97 and b 428:46; give column ˆ ˆ 2 pixel. densities of 3:3±8:0 (mean 4:3 1020 cm 2: With a standard †Â Count images of both regions in counts per detector pixel were extinction law and dust-to-gas ratio, this would imply a Galactic divided by the corresponding exposure images to produce counts extinction at 1660 AÊ of 0:2±0:5 mag (mean 0.3). per pixel per second. For a similar reason, NGC 6752 is also well suited for studies of the UV stellar population and UV-bright galaxies. Measurements of H i (Dickey & Lockman 1990) using a rectangular region 88.2 2.1 Source detection long, covering the FAUST field and centred at l 3368:5 and ˆ b 2258:63; give H i column densities of 7:3±11:5 (mean 8:9 An automatic detection technique was developed to provide ˆ 2 †Â 1020 cm 2: With a standard extinction law and dust-to-gas ratio, impartial source detection. A typical stellar point spread function this would imply a Galactic extinction at 1660 AÊ of 0:4±0:7 mag of FAUST extends for more than a single pixel, and so a square (mean 0.5). Note that N(H i) values from Dickey & Lockman were box three pixels wide, referred to as a source-box, was translated derived assuming optically thin emission; also, the N(H i) given across the FAUST image in single pixel steps. The median of all should be considered a lower limit when the N(H i) is greater than nine pixels was adopted as the typical source-box count rate. This several times 1020. was compared with the typical neighbourhood background count In this paper we describe FAUST imaging, source detection, rate evaluated as follows. source astrometry, source photometry, identification of the UV The mean and standard deviation of each of eight square boxes, sources with catalogued objects, and observations from the Wise six pixels wide distributed symmetrically around the source box, Observatory. We then discuss the stellar content of the fields, were calculated. Sky boxes with any pixels outside the image field comparing observed differential star counts and colours with those were rejected. The median of all eight box means and the median of all box standard deviations were adopted as the most significant 1 Excluding a few possible objects within 25 arcmin of each of the FAUST background level and typical deviation from this level. Sky boxes image field boundaries. for which the mean count rate deviated by more than two typical q 2001 RAS, MNRAS 324, 580±598 582 J. Daniels et al.

Figure 1. FAUST image of the Antennae showing detected sources. deviation intervals from the background were rejected. All locations of the objects) and corresponding J2000 celestial relevant pixels within the remaining sky boxes were considered coordinates were input to the iraf2 routine ccmap which evaluates at this stage, and their mean and standard deviation were a 2D quadratic polynomial surface fit (using a tangential sky calculated to represent the neighbourhood count rate and the projection for the celestial coordinates) that converts image pixel neighbourhood standard deviation s b. As relevant pixels we coordinates to celestial J2000 coordinates; it then re-evaluates the considered only those with non-zero count rate values. A source celestial J2000 coordinates, using the 2D quadratic polynomial was detected if the median pixel value from the source box was surface fit, for all bright FAUST objects. Those FAUST bright $ S=N p9 s ; where S=N is the effective signal-to-noise objects whose coordinates showed a deviation larger than 1 arcmin ‰ †Â ŠÂ b ratio, adopted here as S=N 8: from their catalogue positions were rejected. The 2D quadratic ˆ The size of the sky box, the deviation size for rejection of polynomial surface fit was then re-evaluated using the more background boxes and the signal-to-noise level were all set to accurately registered objects. The final accuracy at the last stage ensure the maximum number of source detections whilst avoiding of coordinate transformations was better than 1 arcmin. The iraf spurious noise detections. Such a routine is designed for the routine cctrans was then used for each field to transform pixel detection of faint sources, and therefore when encountering a coordinates to celestial J2000 coordinates for all sources. bright object, it initially detects it at the object periphery and subsequently at its centre. Further processing retains a single entry 2.3 Source photometry of these multiple detections. The algorithm identified 46 candidate sources for the Antennae field and 221 candidate sources for the The photon flux from each detected source was measured by NGC 6752 field: these are indicated in Figs 1 and 2. integrating all count rates within a simulated round aperture centred on the location of the object and subtracting the local background. The circular aperture of diameter 16 pixels, 2.2 Source astrometry

More than 20 bright objects in each field were first identified in 2 Image Reduction and Analysis Facility, a general purpose software predicted UV images, which were created with data from the system for the reduction and analysis of astronomical data. iraf is written Hipparcos Input and SAO catalogue stars, together with the and supported by the iraf programming group at the National Optical algorithm for predicting the UV magnitude using the visual Astronomy Observatories (NOAO) in Tucson, Arizona. NOAO is operated magnitude and spectral type of stars (Shemi et al. 1994, and by the Association of Universities for Research in Astronomy (AURA) modifications therein). The pixel coordinates (at the centroid Inc. under cooperative agreement with the National Science Foundation.

q 2001 RAS, MNRAS 324, 580±598 Ultraviolet sources in the directions of NGC 4038±39 and 6752 583

Figure 2. FAUST image of NGC 6752 showing detected sources. equivalent to 17.8 arcmin, was used for all non-saturated sources; and source background. The systematic errors (resulting from the the aperture is shown in Figs 1 and 2. This aperture is much larger intrinsic errors of the IUE photometric scale and a systematic error than the resolution of FAUST, and it allows for the collection of in flux resulting from the laboratory calibration of FAUST) were virtually all the UV photons from a source. The local background estimated by Bowyer et al. (1993) to be 15.8 per cent of the was determined using an annulus of 10 pixels wide starting in the measured flux, corresponding to an additional error of 0.17 mag to region immediately (0.1 pixels) outside the source aperture. The the monochromatic magnitude used here. The total photometric mode rather than the mean of the background pixels was error was calculated by combining in quadrature the instrumental evaluated, as this gives photometry with a smaller error. For and systematic errors. very bright (saturated) sources an aperture of diameter 80 pixels Table 1 shows the sources detected in both the Antennae and (88.8 arcmin) was used with a background annulus of 10 pixels. NGC 6752 fields. The first column is the source number detected, FAUST was calibrated before flight in Berkeley, but there was prefixed by FA for Antennae sources, and by FN for NGC 6752 no post-flight calibration of the instrument. Bowyer et al. (1993) sources. Columns 2 and 3 are the (a, b) coordinates of the source used 16 objects that appear on FAUST images and were observed as determined from the astrometric transformation described by IUE to establish an in-flight calibration for converting earlier. Column 4 is the monochromatic flux at 1660 AÊ , and FAUST apparent source brightness counts per second to column 5 the total photometric error. Column 6 is the FSC photon s21 cm22 A 21; shown as fig. 2 in Bowyer et al. (1994). catalogue number. The positional uncertainty is 3 arcmin for Using this figure, a relation was derived that converts counts per sources in the FSC; see Bowyer et al. (1995). Using 2 arcmin second (SN), measured for any object in the FAUST image, to UV ( 2s) for our astrometric accuracy, the errors are added in ˆ monochromatic magnitudes (called here F1660) ± whilst assuming quadrature, and therefore any FSC object within 3.7 arcmin of that the energy is distributed with constant power per unit our source coordinates is considered the same source. Table 1 wavelength (Brosch et al. 1995): indicates two possible FSC counterparts for FN22, with FSC 4465 marginally closer. Sources indicated with an asterisk are saturated. F 11:62 2 2:5 log SN : 1 1660 ˆ  † † The faintest sources we found for each field are FN32 and FA1. 2 The iraf routine radprof was used to evaluate the count rate FN32 has a net count rate of 0.046 count s 1, corresponding to for each source (using the aperture size and background annulus <27 counts collected by FAUST during the exposure, and FA1 2 described above), and to convert this to a FAUST monochromatic measured 0.102 counts s 1, corresponding to <33 counts collected magnitude, F1660, using equation (1). The instrumental errors were during the exposure. evaluated for each source from the photon statistics of the source The FSC includes 17 sources for the Antennae field and 68 q 2001 RAS, MNRAS 324, 580±598 584 J. Daniels et al.

Table 1. Detected UV sources and FSC counterparts. Table 1 ± continued

Object a(J2000) d(J2000) F1660 DF1660 FSC no. Object a(J2000) d(J2000) F1660 DF1660 FSC no. FA1 12 6 8.64 222 51 59.8 14.10 2.16 3006 FN26 19 33 1.74 261 6 22.9 12.96 0.47 4524 FA2 12 4 15.33 222 54 5.5 11.36 0.23 2998 FN27 19 19 58.4 257 58 39 11.02 0.18 4482 FA3 12 8 1.97 222 15 36.1 10.94 0.23 FN28 19 19 27.2 257 45 53.9 12.71 0.32 4477 FA4 12 14 24.96 221 22 0.5 11.90 0.44 FN29 19 23 39.42 259 6 13 11.19 0.18 4492 FA5 12 10 6.55 221 41 46.8 11.30 0.27 3022 FN30 19 21 13.48 258 39 40 11.40 0.19 4487 FA6 12 6 6.69 221 52 46.7 11.77 0.34 3007 FN31 19 24 47.25 259 38 45.1 11.56 0.19 4500 FA7 12 20 2.06 220 0 42.8 11.07 0.28 FN32 19 32 21.17 261 20 39 14.96 2.69 4522 FA8 12 9 28.7 221 3 6.2 9.55 0.17 3018 FN33 19 9 10.33 255 48 49.9 7.34 0.17 4418 FA9 12 16 40.58 220 16 40.9 8.84 0.17 3060 FN34 19 17 37.86 258 11 38.7 12.27 0.23 4466 FA10 12 0 30.4 221 52 24.2 10.00 0.18 2978 FN35 19 26 35.65 260 30 38.7 11.60 0.19 4509 FA11 11 56 11.6 222 16 34 11.19 0.25 2964 FN36 19 23 59.11 259 55 22.5 12.84 0.32 4494 FA12 12 4 36.45 221 20 33.7 10.91 0.19 3002 FN37 19 12 34.82 257 0 21.1 9.35 0.17 4437 FA13 12 13 45.47 220 19 55.5 10.97 0.20 3045 FN38 19 28 48.12 261 3 56.7 13.44 0.51 4515 FA14 11 55 8.45 222 11 41.2 11.41 0.27 2958 FN39 19 13 57.86 257 37 46 8.50 0.17 4446 FA15 12 20 2.75 219 29 49.7 11.46 0.34 FN40 19 18 19.77 258 52 20.1 9.52 0.17 4471 FA16 12 4 16.51 221 1 32.3 10.19 0.17 3000 FN41 19 16 3.61 258 23 59.1 10.93 0.18 4456 FA17 12 19 26.97 219 7 41.3 12.32 0.62 3084 FN42 19 11 25.56 257 2 11.3 10.53 0.17 4431 FA18 12 21 35.33 218 53 40.8 9.57 0.20 FN43 19 19 39.45 259 22 5.6 11.02 0.18 4478 FA19 12 2 1.05 220 47 45.4 9.50 0.17 2988 FN44 19 21 5.71 259 41 47.2 13.86 0.72 4486 FA20 12 1 20.63 220 49 34.7 10.52 0.18 2985 FN45 19 9 52.8 256 40 42.9 11.82 0.23 4423 FA21 11 51 33.3 221 38 3 11.27 0.21 2942 FN46 19 25 25 260 56 46 11.84 0.20 4502 FA22 12 15 10.99 219 14 23 11.61 0.26 3050 FN47 19 9 31.62 256 51 30.5 8.92 0.17 4422 FA23 12 20 53.95 218 33 50.5 11.36 0.53 FN48 19 27 4.06 261 34 8 10.25 0.17 4511 FA24 12 0 53.95 220 37 22.7 10.56 0.19 2982 FN49 19 9 59.24 257 3 32.5 11.07 0.18 4425 FA25 11 52 38.59 220 50 1.9 8.79 0.17 2946 FN50 19 19 43.53 260 1 11.9 11.54 0.19 4479 FA26 11 50 49.36 221 0 33.4 10.06 0.23 2940 FN51 19 18 43.95 259 46 5.7 10.99 0.18 4473 FA27 12 2 36.62 219 40 47.2 8.98 0.17 2991 FN52 19 14 38.05 258 52 43.2 14.60 1.55 4451 FA28 11 54 2.16 220 34 20.8 12.29 0.36 2952 FN53 19 13 19.78 258 40 59.8 12.21 0.24 4444 FA29* 12 0 35.84 219 40 15.5 ,4.85 20.17 2981 FN54 19 16 58.27 259 49 1.3 11.54 0.19 4464 FA30 12 8 43.6 218 26 48.7 11.31 0.23 3015 FN55 19 16 14.01 259 43 0.6 11.65 0.19 4457 FA31 11 59 27.81 219 16 32.1 9.99 0.19 2975 FN56 19 12 58.68 258 51 25.1 11.46 0.19 4438 FA32* 12 15 30.68 217 31 57.4 ,3.86 20.17 3054 FN57 19 6 38.93 257 5 53.8 11.29 0.19 4401 FA33 12 1 52.48 218 52 2.9 10.35 0.19 2987 FN58 19 18 23.57 260 29 12.5 12.24 0.23 4472 FA34 12 0 6.28 219 1 55.2 8.99 0.17 2976 FN59 19 25 44.63 262 12 24.4 12.21 0.24 4504 FA35 12 1 5.97 218 47 33.9 11.72 0.34 2984 FN60 19 13 47.71 259 29 6.1 11.84 0.20 4445 FA36 12 9 33.46 217 35 0.2 8.36 0.17 3020 FN61 19 16 18 260 11 8.1 12.44 0.25 4459 FA37 12 1 2.24 218 31 15.6 10.79 0.19 2983 FN62 19 9 29.05 258 25 56.1 11.59 0.19 FA38 12 17 4.31 216 41 15.4 7.13 0.17 3062 FN63 19 14 57.26 260 6 56.2 12.10 0.23 4453 FA39 12 12 17.88 217 13 31.9 10.16 0.20 3037 FN64 19 9 36.74 258 39 13.2 11.01 0.18 4421 FA40 11 52 14.65 219 12 55.5 10.22 0.18 2944 FN65 19 14 5.75 259 55 16 11.48 0.20 4447 FA41 12 10 27.1 217 13 10.4 8.75 0.17 3024 FN66 19 25 14.73 262 35 30.1 11.44 0.20 4501 FA42 11 56 30.73 218 6 31.7 10.97 0.19 2965 FN67 19 8 46.09 258 31 39.3 11.32 0.18 4412 FA43 11 55 22 218 6 51.1 11.38 0.23 2959 FN68 19 24 41.97 262 41 43.2 11.20 0.19 4496 FA44 11 54 9.55 217 58 22.2 10.52 0.18 2953 FN69 19 17 51.83 261 17 56.3 9.39 0.17 4467 FA45 12 3 7.79 216 27 40.7 9.17 0.17 2994 FN70 19 0 32.79 256 13 59.3 9.85 0.17 4374 FA46 11 55 59.14 217 9 19.9 5.57 0.17 2962 FN71 19 6 26.5 258 9 41.2 10.60 0.17 4399 FN1 19 35 59.34 258 17 15.7 11.18 0.25 FN72 19 24 17.04 263 0 42.6 10.52 0.18 4495 FN2 19 35 48.07 258 50 54.8 11.36 0.23 4527 FN73 19 23 7.94 262 49 49.6 11.54 0.21 4490 FN3 19 25 56.86 256 33 49 9.75 0.18 4508 FN74 19 3 43.9 257 40 50.8 9.90 0.17 4389 FN4 19 36 58.6 259 15 52.2 10.01 0.18 4529 FN75 19 8 47.99 259 20 9.8 9.71 0.17 4414 FN5 19 35 43.85 259 6 56.3 12.31 0.43 4526 FN76 19 19 58.63 262 14 59.8 11.84 0.20 4480 FN6 19 25 25.18 256 45 19.2 10.77 0.20 4505 FN77 19 16 13.67 261 20 58.4 12.21 0.23 FN7 19 22 48.7 256 23 49.6 10.21 0.19 4491 FN78 19 10 35.95 260 3 2.2 5.80 0.17 4428 FN8 19 20 46.32 256 27 53.6 10.44 0.20 4485 FN79 19 10 21.79 259 45 43.6 10.00 0.17 FN9 19 18 42.99 256 9 4 6.47 0.17 4474 FN80 19 4 59.38 258 18 15.4 7.32 0.17 4393 FN10 19 30 41.45 259 12 22.8 6.69 0.17 4519 FN81 19 17 5.75 261 48 48.6 10.48 0.17 4461 FN11 19 21 17.94 256 50 30.6 11.77 0.25 4488 FN82 19 7 58.99 259 18 26.5 9.81 0.17 FN12 19 22 7.05 257 8 41.3 12.30 0.32 4489 FN83 19 5 16.19 258 30 11.6 10.02 0.17 4394 FN13 19 34 9.88 260 12 23.9 12.32 0.31 4525 FN84 19 9 22.48 259 52 12.9 9.64 0.17 FN14 19 23 39.01 257 52 33.5 12.00 0.23 4493 FN85 19 3 47.5 258 32 28.2 10.27 0.17 4390 FN15 19 17 52.18 256 23 12.1 8.69 0.17 4468 FN86 19 16 22.73 262 0 7.1 12.30 0.25 4458 FN16 19 29 15.94 259 20 38.6 10.14 0.17 4517 FN87 19 19 26.72 262 40 3.7 11.62 0.19 4476 FN17 19 20 43.6 257 18 19.2 11.78 0.22 4484 FN88 19 19 33.73 262 45 46.9 11.91 0.21 FN18 19 16 50.52 256 20 45.4 9.10 0.17 4463 FN89 19 11 17.42 260 50 19.1 12.14 0.23 4430 FN19 19 32 15.41 260 15 56.1 8.20 0.17 4521 FN90 19 13 11.71 261 21 50 13.91 0.71 4440 FN20 19 25 58.75 258 42 41.9 12.78 0.33 4507 FN91 19 14 44.95 261 45 20.8 9.81 0.17 4450 FN21 19 18 1.47 256 43 56.6 11.22 0.23 FN92 19 20 12.28 263 12 13.7 10.60 0.18 4481 FN22 19 16 54.45 256 38 29.7 10.41 0.18 4465, 4462 FN93 19 18 20.27 262 41 9.4 11.52 0.19 4469 FN23 19 32 42.24 260 45 54.9 11.72 0.21 4523 FN94 19 7 34.1 259 54 22.9 12.26 0.26 4406 FN24 19 27 38.77 259 54 0.2 8.56 0.17 4512 FN95 19 14 33.46 261 53 55.9 9.01 0.17 4449 FN25 19 24 54.19 259 9 57.1 11.16 0.18 4499 FN96 19 8 39.5 260 29 46.1 7.60 0.17 4410

q 2001 RAS, MNRAS 324, 580±598 Ultraviolet sources in the directions of NGC 4038±39 and 6752 585

Table 1 ± continued Table 1 ± continued

Object a(J2000) d(J2000) F1660 DF1660 FSC no. Object a(J2000) d(J2000) F1660 DF1660 FSC no. FN97 19 3 38.21 258 55 49.9 12.66 0.31 4388 FN168 18 59 41.91 263 53 44.2 11.54 0.24 4366 FN98 19 7 41.26 260 9 25.4 12.73 0.41 4408 FN169 18 51 33.73 261 19 30.7 10.46 0.19 FN99 19 16 6.21 262 35 24.4 11.67 0.19 4455 FN170 18 49 13.22 260 43 54 11.86 0.23 4315 FN100 19 14 34.17 262 14 34.2 13.22 0.46 4488 FN171 18 57 21.59 263 23 28.6 8.31 0.17 4360 FN101 19 11 49.02 261 39 44.7 12.44 0.25 4433 FN172 18 44 48.64 259 14 35.4 10.93 0.18 4304 FN102 19 10 34.94 261 21 52.6 12.72 0.30 4427 FN173 18 43 48.51 258 51 19.1 11.46 0.20 4302 FN103 18 55 19.69 256 42 18 11.32 0.19 4349 FN174 18 47 24.97 260 22 35.4 7.27 0.17 4310 FN104 19 0 1.74 258 20 45.9 11.89 0.21 4370 FN175 18 45 9.49 259 39 50.8 10.15 0.17 4306 FN105 18 58 48.94 258 14 38.8 11.29 0.18 4364 FN176 18 55 5.56 262 55 57.7 10.23 0.19 4344 FN106 19 10 7.27 261 43 12.1 11.81 0.20 4424 FN177 18 55 26.61 263 5 15.9 10.43 0.18 4348 FN107 18 56 59.49 257 39 54.3 11.69 0.20 4359 FN178* 18 52 4.51 262 14 2.9 ,4.09 20.17 4333 FN108 19 1 0.03 259 9 41.5 11.91 0.21 4376 FN179 18 55 14.25 263 18 46.8 12.05 0.34 4345 FN109 19 12 26.58 262 46 54.3 10.21 0.17 4434 FN180 18 40 23.08 258 29 50.5 10.65 0.18 4290 FN110 19 8 47.47 261 48 6.3 13.62 0.62 4409 FN181 18 51 33.45 262 38 31.6 7.68 0.17 4326 FN111 18 57 11.88 258 35 15 11.00 0.18 4361 FN182 18 40 58.13 258 54 21.4 9.73 0.17 4293 FN112 19 7 27.08 261 41 16.6 12.87 0.35 4405 FN183 18 40 25.76 258 45 36 10.52 0.18 4288 FN113 18 59 35.76 259 24 26.8 11.90 0.21 4367 FN184 18 51 23.67 262 50 2.2 9.11 0.17 4325 FN114 18 51 48.92 256 44 45 10.16 0.17 4331 FN185 18 47 28.4 261 57 49 8.50 0.17 4309 FN115 19 9 25.65 262 22 29.2 10.24 0.17 4417 FN186 18 38 4.58 258 23 45.9 11.90 0.27 4279 FN116 18 55 53.77 258 14 28.7 11.69 0.20 4351 FN187 18 52 46.14 263 44 16.1 10.04 0.18 4334 FN117 18 56 58.94 258 41 53.7 11.13 0.18 FN188 18 51 49.97 263 49 42.2 9.59 0.17 4327 FN118 18 52 25.93 257 12 0.5 7.26 0.17 4337 FN189 18 44 9.81 261 27 9.7 10.90 0.18 4303 FN119 18 53 43.6 257 44 48.3 10.77 0.18 4340 FN190 18 49 7.06 263 17 3.7 9.18 0.17 4314 FN120 19 1 46.04 260 23 36.2 10.47 0.17 4380 FN191 18 35 57.18 258 33 38.7 11.66 0.25 4271 FN121 18 59 49.3 260 0 34.6 11.46 0.19 4369 FN192 18 38 25.52 259 54 4.5 10.55 0.18 4280 FN122 19 7 18.28 262 9 28 12.09 0.23 4403 FN193 18 38 34.75 260 11 23.8 8.36 0.17 4281 FN123 19 0 12.73 260 12 5 8.92 0.17 4372 FN194 18 36 25.31 259 19 43.6 11.14 0.19 4272 FN124 19 3 6.51 261 6 35.6 11.32 0.18 4386 FN195 18 41 1.57 261 24 4.1 9.49 0.17 4292 FN125 19 13 9.98 263 52 11.1 9.55 0.17 4439 FN196 18 39 4.08 260 35 46.5 11.73 0.23 4284 FN126 18 54 41.48 258 35 23.8 11.43 0.19 4343 FN197 18 47 57.37 263 49 56.5 10.19 0.18 4311 FN127 19 7 25.77 262 28 24.8 11.81 0.21 4404 FN198 18 43 1.85 262 8 42 11.24 0.22 4298 FN128 18 51 58.2 257 55 55.6 8.01 0.17 4332 FN199 18 35 56.01 259 31 22.7 9.90 0.17 4270 FN129 19 1 0.25 260 41 30.9 14.12 0.98 4375 FN200 18 37 44.1 260 23 32.9 9.72 0.17 4276 FN130 18 49 35.18 256 58 16.9 11.52 0.21 4322 FN201 18 41 37.61 261 49 50.5 11.58 0.23 4294 FN131 19 9 36.24 263 14 20.8 12.11 0.25 4419 FN202 18 39 35.52 261 9 45.9 11.62 0.21 4285 FN132 19 5 37.64 262 7 17.2 12.54 0.32 4396 FN203 18 43 53.33 262 42 41.5 12.21 0.38 4301 FN133 18 54 2.33 258 39 48.3 11.34 0.18 4341 FN204 18 37 32.95 260 45 0.2 8.72 0.17 4275 FN134 18 55 57.95 259 29 1.4 8.14 0.17 4352 FN205 18 35 31.95 259 47 28.7 11.63 0.24 4268 FN135 19 7 49.45 263 1 55.1 11.14 0.18 4407 FN206 18 36 1.03 260 22 16.2 8.51 0.17 4269 FN136 18 57 3.07 259 51 28.1 13.64 0.65 4358 FN207 18 40 14.27 262 7 23.8 7.89 0.17 4287 FN137 19 1 31.28 261 36 20.3 9.94 0.17 4378 FN208 18 35 11.35 260 13 40.1 9.23 0.17 4267 FN138 19 3 29 262 19 27.2 9.77 0.17 4387 FN209 18 37 45.76 261 8 47.7 12.13 0.29 4277 FN139 18 49 24.38 257 33 12.1 10.81 0.18 4319 FN210 18 37 53.85 261 23 37.9 11.48 0.21 4278 FN140 19 9 47.76 263 50 35.6 8.95 0.17 4420 FN211 18 33 22.8 259 44 29.6 10.09 0.17 4261 FN141 19 1 55.37 261 53 32.1 9.80 0.17 4381 FN212 18 35 9.72 260 27 53.2 9.06 0.17 4266 FN142 19 1 30.08 261 46 13.7 9.77 0.17 4379 FN213 18 37 9.32 261 29 34.8 11.36 0.21 4273 FN143 18 54 46.09 259 35 44.1 10.62 0.17 FN214 18 33 22.85 260 14 9.6 10.41 0.18 4262 FN144 18 56 47.99 260 31 11.6 12.97 0.38 4357 FN215 18 31 59.03 259 33 56.2 11.95 0.33 4259 FN145 18 49 7.83 257 47 27 11.69 0.21 4316 FN216 18 33 50.25 260 25 42.5 10.83 0.20 4264 FN146 18 49 36.63 258 22 15.9 11.39 0.19 4321 FN217 18 40 12.3 262 53 2.9 11.18 0.22 4286 FN147 19 0 37.43 262 3 13.1 11.99 0.31 4373 FN218 18 31 16.1 259 57 33.3 10.05 0.18 4258 FN148 19 5 58.39 263 44 10.8 6.72 0.17 4397 FN219 18 32 14.42 260 54 0.7 9.76 0.17 4260 FN149 18 49 34.89 258 57 0.6 8.52 0.17 4320 FN220 18 30 7.26 260 40 45.8 10.23 0.20 4255 FN150 18 52 39.14 260 13 26.7 7.56 0.17 4336 FN221 18 29 48.57 261 2 37.8 9.22 0.17 4254 FN151 19 3 22.24 263 23 50.5 11.31 0.20 4384 FN152 18 59 55.23 262 35 14.3 8.85 0.17 4368 2 FN153 19 2 18.04 63 12 13.4 11.64 0.21 4383 sources for the NGC 6752 field that were not detected by our FN154 19 4 8.68 263 46 59.6 6.36 0.17 4391 FN155 18 49 26.16 259 25 37.3 10.51 0.17 4317 algorithm. Visual inspection indicated that these were virtually all FN156 18 56 24.82 261 49 4.7 9.55 0.17 4355 either noise artefacts or sources too close to the field edges to be FN157 18 52 42.73 260 59 20.5 10.10 0.17 4335 picked up by our source detection algorithm. Table 1 includes six FN158 18 46 11.9 258 30 59.3 10.84 0.18 4308 sources for the Antennae Field, and 12 sources for the NGC 6752 FN159 18 52 15.28 260 54 29.9 9.58 0.17 FN160 18 53 41.7 261 26 35.4 9.71 0.17 4338 field detected here but not appearing in the FSC. FN161 18 50 40.46 260 31 14.6 11.77 0.21 4324 FN162 18 51 34.94 260 53 42 9.79 0.17 4328 FN163 18 53 7.44 261 25 56.5 9.64 0.17 4338 2.4 Source identification FN164 18 55 14.01 262 12 21.4 8.10 0.17 4347 FN165 18 52 3.75 261 11 2.7 10.91 0.20 4330 The identification of each source with a counterpart from a list of FN166 18 58 29.12 263 16 25 9.56 0.17 4362 catalogue objects within a 2-arcmin radius was based upon the FN167 18 48 1 260 5 13.1 11.74 0.21 4313 following criteria: blueness, blue magnitude; distance from the q 2001 RAS, MNRAS 324, 580±598 586 J. Daniels et al.

Table 2. Proposed counterparts of FAUST sources with photometric properties.

Object ID Type F BVRF2 BB2 V *B 2 R 1660 1660 † FA1 TYC6667-109-1 F0 14.10 10.70 10.24 3.40 0.47 FA2 TYC6667-527-1 A1III 11.36 10.43 10.28 0.93 0.15 FA3 TYC6101-70-1 A2mV 10.94 8.77 8.49 2.17 0.28 FA4 TYC6101-1612-1 A7IV 11.90 10.51 10.12 1.39 0.39 FA5 TYC6101-399-1 A5IV 11.30 9.62 9.35 1.68 0.27 FA6 TYC6101-743-1 ? 11.77 11.39 11.44 0.38 20.05 FA7 US0675-11998696 ? 11.07 17.08BJ 26.01 *u0.6 FA8 TYC6101-597-1 A3V 9.55 8.20 7.99 1.35 0.21 FA9 US0675-11972813 ? 8.84 13.21BJ 24.37 *u0.3 FA10 TYC6100-1816-1 A3IV 10.00 8.76 8.55 1.24 0.21 FA11 US0675-11794652 ? 11.19 12.10BJ 20.91 *u20.2 FA12 TYC6100-802-1 A4III 10.91 8.68 8.42 2.23 0.26 FA13 TYC6101-1455-1 F2V 10.97 8.01 7.63 2.96 0.38 FA14 US0675-11783673 ? 11.41 13.17BJ 21.76 *u20.8 FA15 US0675-11999846 ? 11.46 14.24BJ 22.78 *u0.1 FA16 TYC6100-988-1 A2II 10.19 8.21 7.87 1.98 0.34 FA17 US0675-11993797(1) ? 12.32 **u24.3 *u20.9 FA18 NO CANDIDATE ? 9.57 FA19 TYC6100-1251-1 A3IV/V 9.50 7.98 7.79 1.52 0.19 FA20 TYC6100-877-1 A9/FOIV 10.52 10.51 10.40 0.01 0.11 FA21 TYC6099-966-1 F3V 11.27 8.04 7.61 3.23 0.44 FA22 US0675-11960509 ? 11.61 12.11BJ 20.50 *u20.4 FA23 US0675-12006965 ? 11.36 12.11BJ 20.75 *u0.9 FA24 TYC6100-374-1 A3III 10.56 8.75 8.52 1.81 0.23 FA25 TYC6099-1337-1 B8/B9II/III 8.79 10.50 10.59 21.70 20.09 FA26 TYC6099-1499-1 A5/A6V 10.06 8.49 8.23 1.57 0.26 FA27 US0675-11857164 ? 8.98 14.42BJ 25.44 *u20.6 FA28 NGC3956 SA(s)c 12.29 12.99BTC 11.85RTC 20.7 *1.14 FA29 TYC6097-1648-1 B2IV 4.85 5.02 5.24 20.17 20.22 FA30 TYC6098-818-1 F5IV/V 11.31 7.64 7.18 3.67 0.46 FA31 NGC4027 SB(s)dm 9.99 11.71BTC 11.12VT 10.60RTC 21.72 0.59 FA32 TYC6098-1754-1 B8III 3.86 2.49 2.57 1.37 20.08 FA33 Antennae 10.35 10.25BTC 9.00RTC 0.10 *1.25 NGC4038 SB(s)mpec 10.94BTC 9.74RTC *1.20 NGC4039 SA(s)mpec 11.06BTC 9.77RTC *1.29 FA34 US0675-11833064 ? 8.99 13.57BJ 24.58 *u0.1 FA35 US0675-11842723 ? 11.72 15.34BJ 23.62 *u20.1 FA36 HD105604 B9V 8.36 9.70 9.70 21.34 0.00 FA37 TYC6097-844-1 A5IV 10.79 9.20 8.84 1.59 0.36 FA38 TYC6102-1712-1 A2V 7.13 6.19 6.07 0.94 0.12 FA39 TYC6095-1418-1 A3m 10.16 8.84 8.55 1.32 0.29 FA40 TYC6096-1499-1 A9V 10.22 7.75 7.46 2.47 0.29 FA41 TYC6095-300-1 A0V 8.75 8.31 8.20 0.44 0.11 FA42 TYC6097-144-1 A3IV 10.97 9.75 9.53 1.23 0.22 FA43 TYC6097-804-1 A1/A2IV 11.38 9.68 9.47 1.70 0.19 FA44 TYC6096-1880-1 A2V 10.52 9.24 8.97 1.28 0.27 FA45 TYC6094-619-1 A2V 9.17 8.47 8.27 0.70 0.20 FA46 TYC6094-1532-1 A0V 5.57 5.14 5.17 0.43 20.03 FN1 US0300-35920609 ? 11.18 16.33BJ 25.15 *u0.6 FN2 US0300-35920183 ? 11.36 16.82BJ 25.46 *u0.5 FN3 REJ1925-563 UvES 9.75 FN4 TYC8786-1818-1 ? 10.01 11.43 11.24 21.42 0.19 FN5 US0300-35915166 ? 12.31 14.08BJ 21.77 *u1.1 FN6 TYC8769-1708-1 Fm 10.77 8.96 8.61 1.81 0.35 FN7 TYC8769-1696-1 A3IV 10.21 9.30 9.09 0.91 0.21 FN8 US0300-35647513 ? 10.44 12.38BJ 21.94 *u0.0 FN9 TYC8764-2333-1 B2V 6.47 6.59 6.78 20.12 20.19 FN10 TYC8773-967-1 B8/B9V 6.69 7.92 7.99 21.23 20.07 FN11 US0300-35656647 ? 11.77 15.00BJ 23.23 *u20.4 FN12 US0300-35670839 ? 12.30 13.82BJ 21.52 *u21.3 FN13 US0225-30197510 ? 12.32 15.24BJ 22.92 *u20.2 FN14 US0300-35701282 ? 12.00 **u21.9 *u20.3 FN15 US0300-35592867 ? 8.69 12.50BJ 23.81 *u0.0 FN16 US0300-35804284 ? 10.14 16.57BJ 26.43 *u0.4 FN17 US0300-35643963 ? 11.78 12.60BJ 20.82 *u20.6 FN18 TYC8768-1861-1 A6V 9.10 8.70 8.46 0.41 0.24 FN19 TYC9084-582-1 A3IV 8.20 7.34 7.20 0.86 0.14 FN20 US0300-35744377 ? 12.78 14.06BJ 21.28 *u0.3 FN21 US0300-35591593 ? 11.22 **u21.3 *u21.7 FN22 US0300-35570871 ? 10.41 14.86BJ 24.45 *u0.2 FN23 US0225-30181606 ? 11.72 15.82BJ 24.10 *u0.5

q 2001 RAS, MNRAS 324, 580±598 Ultraviolet sources in the directions of NGC 4038±39 and 6752 587

Table 2 ± continued

Object ID Type F BVRF2 BB2 V *B 2 R 1660 1660 † FN24 TYC8773-796-1 A1V 8.56 8.38 8.27 0.18 0.11 FN25 US0300-35725172 ? 11.16 14.82BJ 23.66 *u0.0 FN26 TYC9084-845-1 F0V 12.96 10.77 10.39 2.19 0.37 FN27 TYC8768-841-1 A1mV 11.02 9.00 8.67 2.02 0.34 FN28 US0300-35619097 ? 12.71 12.61BJ 0.10 *u20.4 FN29 US0300-35701956 ? 11.19 14.69BJ 23.50 *u1.0 FN30 ESO141-G055 Sc, Sy1 11.40 14.36BTC 14.00VJ 13.28RTC 22.96 0.36 FN31 US0300-35723864 ? 11.56 13.23BJ 21.67 *u0.3 FN32 US0225-30177965 ? 14.96 15.79BJ 20.83 *u0.0 FN33 TYC8764-2235-1 B9.5Vn 7.34 8.16 8.13 20.82 0.02 FN34 TYC8772-184-1 F0V 12.27 10.11 9.87 2.16 0.24 FN35 TYC9084-1024-1 F0V 11.60 10.261 9.87 1.34 0.39 FN36 NGC6782 (R _1)SB(r)0/a 12.84 12.70BTC 11.84VT 11.27RTC 0.14 0.86 FN37 US0300-35480541 ? 9.35 10.83BJ 21.48 *u20.4 FN38 US0225-30134009 ? 13.44 16.21BJ 22.77 *u20.2 FN39 TYC8768-961-1 A1V 8.50 8.46 8.39 0.04 0.07 FN40 TYC8772-84-1 A6V 9.52 8.15 7.95 1.38 0.20 FN41 US0300-35554285 ? 10.93 13.36BJ 22.43 *u0.7 FN42 NGC6753 (R )SA(r)b 10.53 11.84BTC 11.14VT 10.31RTC 21.31 0.70 FN43 TYC-8772-1231-1 F0V 11.02 8.98 8.68 2.04 0.30 FN44 US0300-35652778 ? 13.86 13.88BJ 20.02 *u0.2 FN45 US0300-35419948 ? 11.82 11.99BJ 20.17 *u20.1 FN46 TYC9071-781-1 A2mV 11.84 10.09 9.73 1.75 0.36 FN47 US0300-35411766 ? 8.92 10.87BJ 21.95 *u20.6 FN48 TYC9084-108-1 A0V 10.25 10.78 10.71 20.52 0.07 FN49 US0300-35422639 ? 11.07 14.74BJ 23.67 *u20.9 FN50 TYC9071-476-1 A4III/IV 11.54 10.20 9.87 1.34 0.33 FN51 US0300-35607291 ? 10.99 13.26BJ 22.27 *u0.1 FN52 US0300-35526133 ? 14.60 **u0.0 *u0.3 FN53 US0300-35498614 ? 12.21 13.51BJ 21.30 *u0.1 FN54 US0300-35572077 ? 11.54 13.90BJ 22.36 *u20.4 FN55 TYC8772-603-1 A8V 11.65 10.53 10.20 1.12 0.33 FN56 TYC8772-1824-1 ? 11.46 11.22 11.07 0.24 0.15 FN57 TYC8767-123-1 A7/A8IV 11.29 8.67 8.37 2.59 0.33 FN58 12.24 11.63BTC 11.09VT 10.29RTC 0.61 0.54 NGC6769 (R )SA(r)b 12.33BTC 11.75VT 10.93RTC 0.58 NGC6770 SB(rs)b 12.44BTC 11.94VT 11.16RTC 0.50 FN59 TYC9088-1001-1 F5/F6V 12.21 8.17 7.69 4.04 0.48 FN60 TYC8772-1603-1 A7III/IV 11.84 10.41 10.06 1.43 0.35 FN61 IC4836 SA(s)c 12.44 13.40BTC 12.65VT 12.16RTC 20.96 0.75 FN62 US0300-35412697 ? 11.59 15.11BJ 23.52 *u20.1 FN63 US0225-29963588 ? 12.10 13.92BJ 21.82 *u0.2 FN64 US0300-35415465 ? 11.01 13.02BJ 22.01 *u0.1 FN65 TYC-8772-213-1 F2III 11.48 9.31 8.91 2.17 0.40 FN66 TYC-9075-1668-1 FO 11.44 10.48 10.16 0.96 0.32 FN67 US0300-35394840 ? 11.32 14.55BJ 23.23 *u0.7 FN68 TYC9075-1979-1 A5IV 11.20 9.82 9.57 1.38 0.26 FN69 TYC9071-1227-1 A0V 9.39 9.84 9.76 20.45 0.08 FN70 TYC8763-1330-1 A2V 9.85 9.22 9.02 0.63 0.20 FN71 TYC8771-131-1 ? 10.60 10.97 10.86 20.37 0.11 FN72 TYC9075-1919-1 F3/F5V 10.52 7.06 6.64 3.46 0.43 FN73 TYC9075-1485-1 A7/A8V 11.54 10.24 9.99 1.30 0.25 FN74 TYC8767-649-1 A2V 9.90 9.88 9.66 0.02 0.22 FN75 TYC8772-1847-1 A8/A9V 9.71 8.07 7.80 1.64 0.27 FN76 TYC9075-1473-1 A8 11.84 10.62 10.34 1.23 0.27 FN77 US0225-29980501 ? 12.21 13.38BJ 21.17 *u0.2 FN78 TYC9071-2141-1 B9II/III 5.80 7.52 7.56 21.72 20.03 FN79 TYC8772-359-1 ? 10.00 10.93 10.50 20.93 0.43 FN80 TYC8771-253-1 B9.5IV 7.32 8.22 8.24 20.90 20.02 FN81 TYC9071-84-1 F0/F2V 10.48 7.74 7.37 2.74 0.36 FN82 TYC8772-1092-1 ? 9.81 11.19 10.85 21.38 0.34 FN83 TYC8771-239-1 A7 10.02 10.93 10.47 20.91 0.46 FN84 US0300-35411297 ? 9.64 **u23.9 *u20.6 FN85 TYC8771-1844-1 A3V 10.27 9.45 9.27 0.82 0.18 FN86 TYC9075-1292-1 A9V 12.30 10.29 9.93 2.01 0.36 FN87 TYC9075-1087-1 FO 11.62 10.32 9.86 1.31 0.45 FN88 TYC9075-230-1 F3/F5V 11.91 10.39 9.90 1.52 0.48 FN89 TYC9071-1479-1 F2IV 12.14 9.68 9.30 2.47 0.37 FN90 US0225-29940382 ? 13.91 13.90BJ 0.01 *u0.8 FN91 TYC9071-32-1 ? 9.81 11.18 11.00 21.37 0.18 FN92 TYC9075-712-1 A7III 10.60 8.78 8.50 1.82 0.28 q 2001 RAS, MNRAS 324, 580±598 588 J. Daniels et al.

Table 2 ± continued

Object ID Type F BVRF2 BB2 V *B 2 R 1660 1660 † FN93 US0225-30005027 ? 11.52 16.13BJ 24.61 *u0.2 FN94 TYC8772-415-1 F0V 12.26 10.09 9.72 2.17 0.37 FN95 US0225-29958462 ? 9.01 12.59BJ 23.58 *u20.1 FN96 TYC9071-739-1 B9V 7.60 8.77 8.74 21.17 0.03 FN97 TYC8771-1209-1 ? 12.66 11.57 11.26 1.09 0.32 FN98 TYC9070-1024-1 F0 12.73 10.76 10.31 1.97 0.44 FN99 TYC9075-1641-1 ? 11.67 10.79 10.49 0.88 0.29 FN100 TYC9075-770-1 F7V 13.22 9.02 8.49 4.20 0.53 FN101 TYC9071-2055-1 F0 12.44 10.70 10.33 1.74 0.38 FN102 TYC9071-903-1 F0 12.72 10.23 9.90 2.49 0.33 FN103 US0300-35091119 ? 11.32 16.16BJ 24.84 *u20.2 FN104 TYC8771-785-1 A9IV 11.89 9.92 9.50 1.97 0.42 FN105 US0300-35168553 ? 11.29 12.84BJ 21.55 *u20.2 FN106 TYC9071-1676-1 F2III 11.81 8.97 8.54 2.84 0.43 FN107 US0300-35124703 ? 11.69 12.61BJ 20.92 *u0.5 FN108 US0300-35218933 ? 11.91 14.03BJ 22.12 *u0.3 FN109 US0225-29929615 ? 10.21 14.19BJ 23.98 *u0.3 FN110 US0225-29879192 ? 13.62 **u22.4 *u0.0 FN111 US0300-35130666 ? 11.00 13.25BJ 22.25 *u0.3 FN112 TYC9070-444-1 F0 12.87 10.71 10.42 2.16 0.29 FN113 US0300-35187385 ? 11.90 11.53BJ 0.37 *u0.2 FN114 TYC8766-1829-1 A3V 10.16 9.01 8.81 1.15 0.21 FN115 US0225-29887591 ? 10.24 13.23BJ 22.99 *u0.2 FN116 TYC8771-565-1 F3IV/V 11.69 8.78 8.35 2.91 0.43 FN117 TYC8771-1425-1 F0IV 11.13 9.53 9.13 1.60 0.41 FN118 TYC8766-879-1 B9/B9.5V 7.26 8.26 8.19 21.00 0.07 FN119 US0300-35048922 ? 10.77 12.43BJ 21.66 *u20.2 FN120 US0225-29782307 ? 10.47 13.26BJ 22.79 *u20.1 FN121 US0225-29755579 ? 11.46 12.74BJ 21.28 *u0.5 FN122 TY9074-44-1 F5V 12.09 8.54 8.07 3.55 0.47 FN123 TYC9070-832-1 K0III+ 8.92 7.64 6.96 1.28 0.67 FN124 TYC9070-1898-1 F3V 11.32 9.04 8.63 2.28 0.41 FN125 TYC9079-353-1 A7V 9.55 8.23 8.00 1.32 0.23 FN126 TYC8771-933-1 ? 11.43 10.90 10.64 0.53 0.27 FN127 TYC9074-1516-1 F0IV 11.81 9.15 8.81 2.66 0.34 FN128 TYC8766-572-1 A0V 8.01 7.96 7.90 0.05 0.06 FN129 TYC9070-1192-1 ? 14.12 10.96 10.63 3.16 0.34 FN130 TYC8766-1160-1 A5IV 11.52 9.87 9.59 1.65 0.28 FN131 TYC9075-30-1 A8 12.11 10.90 10.59 1.21 0.31 FN132 US0225-29835798 ? 12.54 12.93BJ 20.39 *u0.4 FN133 TYC8771-1019-1 A5III/IV 11.34 10.01 9.65 1.33 0.36 FN134 TYC8771-1288-1 A0IV/V 8.14 8.83 8.81 20.69 0.03 FN135 TYC9074-1437-1 ? 11.14 11.57 11.25 20.43 0.32 FN136 US0300-35127442 ? 13.64 13.63BJ 0.01 *u0.5 FN137 TYC9070-192-1 B9.5V 9.94 10.03 9.84 20.09 0.18 FN138 TYC9074-1705-1 A1V 9.77 9.34 9.16 0.43 0.18 FN139 TYC8766-1004-1 Fm 10.81 8.65 8.32 2.16 0.33 FN140 NGC6744 SAB(r)bc 8.95 9.28BTC 9.54VJ 8.10RTC 20.33 20.26 FN141 TYC9074-344-1 A1V 9.80 10.07 9.87 20.27 0.21 FN142 TYC8883-128-1 K1IV/V 9.77 9.62 9.37 0.16 0.24 FN143 US0300-35072405 ? 10.62 14.25BJ 23.63 *u20.2 FN144 TYC9070-451-1 F2 12.97 10.00 9.59 2.97 0.41 FN145 TYC8766-468-1 F0 11.69 10.52 10.13 1.17 0.39 FN146 US0300-34945665 ? 11.39 13.68BJ 22.29 *u0.0 FN147 USN0225-29766917 Ellip 11.99 11.80BJ 0.19 *u20.1 FN148 TYC9074-133-1 A0V 6.72 7.45 7.49 20.78 20.04 FN149 TYC8770-225-1 ApV 8.52 8.01 7.92 0.51 0.09 FN150 TYC9070-1449-1 A0V 7.56 8.17 8.14 20.61 0.03 FN151 US0225-29804869 B 11.31 15.44BJ 24.13 *u0.0 FN152 TYC9074-1684-1 A3V 8.85 8.45 8.36 0.40 0.09 FN153 US0225-29789810 ? 11.64 15.94BJ 24.30 *u0.4 FN154 6.36 6.51 6.57 20.15 20.06 TYC9078-1193-1 ? 7.06 7.11 20.05 TYC9078-1193-2 B9V 7.50 7.59 20.09 FN155 TYC8770-319-1 A3III/IV 10.51 9.28 9.00 1.23 0.28 FN156 TYC9070-32-1 F3/F5IV 9.55 7.57 7.14 1.98 0.43 FN157 US0225-29652723 ? 10.10 13.75BJ 23.65 *u0.3 FN158 TYC8770-816-1 F0IV/V 10.84 9.36 9.05 1.48 0.32 FN159 US0225-29646263 ? 9.58 12.31BJ 22.73 *u20.1 FN160 TYC9070-1765-1 A1IV 9.71 10.13 9.98 20.42 0.15 FN161 TYC9069-847-1 A3IV 11.77 9.96 9.78 1.81 0.18

q 2001 RAS, MNRAS 324, 580±598 Ultraviolet sources in the directions of NGC 4038±39 and 6752 589

Table 2 ± continued

Object ID Type F BVRF2 BB2 V *B 2 R 1660 1660 † FN162 TYC9070-843-1 F0/F2IV/V 9.79 7.79 7.47 2.00 0.32 FN163 US0225-29656940 ? 9.64 13.45BJ 23.81 *u0.8 FN164 US0225-29689711 ? 8.10 13.28BJ 25.18 *u20.5 FN165 TYC9070-1183-1 F2 10.91 10.48 10.08 0.43 0.40 FN166 TYC9074-168-1 ? 9.56 10.55 10.53 20.99 0.02 FN167 TYC9069-279-1 ? 11.74 11.17 10.92 0.57 0.25 FN168 US0225-29752538 ? 11.54 **u23.7 *u20.9 FN169 TYC9070-1767-1 F0V 10.46 10.02 9.63 0.44 0.39 FN170 US0225-29598915 ? 11.86 13.44BJ 21.58 *u0.4 FN171 TYC9074-429-1 B9V 8.31 9.07 9.05 20.76 0.02 FN172 TYC8770-565-1 A1mV 10.93 8.86 8.62 2.07 0.24 FN173 TYC8770-1304-1 A8 11.46 10.22 9.98 1.24 0.24 FN174 TYC9069-2515-1 A0V 7.27 7.50 7.47 20.23 0.03 FN175 TYC8770-1688-1 A0 10.15 10.20 10.09 20.05 0.11 FN176 US0225-29687216 ? 10.23 15.41BJ 25.18 *u20.1 FN177 US0225-29691954 ? 10.43 14.48BJ 24.05 *u20.4 FN178 TYC9074-2203-1 B2II-IIIe 4.09 4.02 4.192 0.07 20.17 FN179 TYC9074-804-1 ? 12.05 10.40 10.17 1.65 0.24 FN180 US0300-34699023 ? 10.65 14.67BJ 24.02 *u20.4 FN181 TYC9074-1773-1 A2V 7.68 7.74 7.62 20.06 0.12 FN182 TYC8770-309-1 A0 9.73 10.34 10.14 20.61 0.19 FN183 US0300-34697352 ? 10.52 13.19BJ 22.67 *u22.1 FN184 TYC9073-1066-1 A3 9.11 10.08 9.77 20.97 0.31 FN185 TYC9073-1625-1 A0V 8.50 9.30 9.18 20.80 0.12 FN186 US0300-34641736 ? 11.90 11.88BJ 0.02 *u0.0 FN187 TYC9074-106-1 A7 10.04 10.02 9.74 0.02 0.28 FN188 TYC9078-1651-1 A3V 9.59 8.62 8.45 0.97 0.17 FN189 TYC9069-840-1 A9/F0III 10.90 8.38 8.04 2.52 0.34 FN190 TYC9073-935-1 A2mV 9.18 7.64 7.43 1.54 0.21 FN191 TYC8757-1958-1 A4:mV 11.66 9.46 9.06 2.20 0.40 FN192 TYC8757-443-1 ? 10.55 10.74 10.68 20.19 0.06 FN193 TYC9069-1734-1 A 8.36 9.39 9.44 21.03 20.05 FN194 TYC8757-2220-1 F0IV/V 11.14 8.95 8.60 2.19 0.35 FN195 TYC9069-182-1 A0V 9.49 9.66 9.55 20.16 0.11 FN196 TYC9069-765-1 F0 11.73 9.37 8.99 2.36 0.39 FN197 US0225-29576742 ? 10.19 12.48BJ 22.29 *u0.7 FN198 TYC9073-586-1 A1III/IV 11.24 10.25 9.92 0.99 0.33 FN199 TYC8757-489-1 A4IV 9.90 8.98 8.68 0.98 0.23 FN200 US0225-29396328 ? 9.72 12.76BJ 23.04 *u20.2 FN201 TYC9069-900-1 A2 11.58 10.91 10.86 0.68 0.05 FN202 TYC9069-610-1 ? 11.62 11.40 11.14 0.22 0.26 FN203 US0225-29502917 ? 12.21 14.57BJ 22.36 *u0.4 FN204 TYC9069-1787-1 A0 8.72 9.37 9.17 20.65 0.19 FN205 US0300-34559172 ? 11.63 12.69BJ 21.06 *u20.6 FN206 TYC9069-1744-1 A2IV 8.51 8.10 7.96 0.41 0.13 FN207 TYC9073-1493-1 B9Vn 7.89 8.68 8.63 20.79 0.05 FN208 TYC9069-1851-1 A2IV 9.23 9.29 9.15 20.06 0.14 FN209 US0225-29396776 ? 12.13 14.79BJ 22.66 *u20.7 FN210 TYC9069-1792-1 F0III/IV 11.48 8.79 8.43 2.69 0.35 FN211 TYC8757-1309-1 ? 10.09 11.20 11.42 21.11 20.21 FN212 TYC9069-2188-1 A2 9.06 10.28 10.14 21.22 0.14 FN213 TYC9069-1872-1 F0IV 11.36 9.18 8.83 2.18 0.35 FN214 TYC9068-1767-1 A4 10.41 9.49 9.25 0.93 0.23 FN215 TYC8757-571-1 F3IV/V 11.95 8.27 7.82 3.68 0.46 FN216 US0225-29326441 ? 10.83 12.70BJ 21.87 *u20.9 FN217 US0225-29440038 ? 11.18 12.29BJ 21.11 *u0.3 FN218 US0300-34431394 ? 10.05 12.75BJ 22.70 *u20.7 FN219 TYC9068-2257-1 A0 9.76 10.30 10.25 20.54 0.05 FN220 TYC9068-2825-1 A2V 10.23 9.34 9.15 0.89 0.18 FN221 TYC9068-1183-1 A0 9.22 9.94 9.83 20.72 0.11 Note. ± Description of morphological type coding for above galaxies is from de Vaucouleurs et al. (1976), Sandage & Tamman (1981), Makenty (1990) and Buta (1995): SA Ordinary spiral; SB Barred spiral; SAB Mixed Spiral; O/a, b, c, dm, m Intermediate spiral classes; the presence of an inner ring structure is indicated by (r) following the spiral subclass, those spirals where the arms spring from the ends of the bar or are traced into the centre are indicated by (s), intermediate cases are designated with (rs); Pseudo-outer rings surrounding the galaxy are indicated by R preceding the type with subclass, R _1, a type where the outer arms wind 1808 with respect to the bar end and subclass, R _2, a type where the arms wind 2708 with respect to the bar ends; pec peculiar; Sy1 Seyfert Type 1. Description of photometric descriptors from de Vaucouleurs et al. (1991): BT total (asymptotic) magnitude in the B band; BTC is the face-on-corrected total magnitude in the B band; BJ is the B magnitude on the Johnson system;ˆ UT is the total magnitude in the U band; VT is the total magnitude in the V band; VJ is the V magnitude on the Johnson system; RTC is the face-on-corrected total magnitude in the R band.

q 2001 RAS, MNRAS 324, 580±598 590 J. Daniels et al. source, the measured source F1660 2 B magnitude; and, if known, from the USNO-A2.0 catalogue is given and is indicated by the the candidate counterpart spectral class, luminosity class and B 2 symbol *u. *uu indicates that the B value from the USNO-A2.0 V colour. The bluer, brighter and closer the object, the more likely catalogue was used to evaluate F1660 2 B; as there was no it is to be the counterpart. In addition, where some or all of the COSMOS counterpart. BJ indicates the Cosmos BJ magnitude. spectral, luminosity and B 2 V colour are available, the object is The summary of extragalactic detections is given in Table 3: more likely to be the counterpart if its predicted F1660 magnitude column 1 is the source identifier as before; column 2 gives the (using the colour relationships of Shemi et al. 1994, and catalogue identifier; column 3 the morphological type; columns modifications therein) approximates the measured F1660 magni- 4±7 the apparent F1660, U, B and V magnitudes; and columns 8, 9 tude. Finally, the measured source F1660 2 B magnitude of the and 10 the F1660 2 B; B 2 V and B 2 R colours respectively. object must fall within the expected range #26:0 of known † astrophysical objects. 2.5 Wise observations The majority of the bright sources were identified using the main part of the Tycho catalogue (Hog et al. 1998) for stellar Follow-up observations were made with the 1-m telescope at the sources and the NASA=IPAC Extragalactic Data base (NED) for Wise Observatory (WO). Observations were possible only for the extragalactic sources. Fainter sources were identified using the US Antennae Field, as NGC 6752 is located too far south to be Naval Observatory two-colour catalogue, USNO-A2.0 (Monet et observable from Israel. The seeing conditions at the WO are al. 1998), and the COSMOS3 (Yentis et al. 1992) catalogue. The <2 arcsec. Two source locations indicated by an asterisk in USNO-A2.0 catalogue, containing both stellar and non-stellar column 1 in Table 1 were examined with CCD imaging, and one sources, is based upon a re-reduction of the Precision Measuring source indicated by an `s' in column 1 in Table 1 was examined Machine (PMM) scans from the Palomar Observatory Sky Survey with spectroscopy. The additional information obtained from the I (POSS-I) O and E plates and the UK Science Research Council WO assisted in the identification and confirmation of catalogue SRC-J survey plates and European Southern Observatory ESO-R counterparts. plates. The COSMOS catalogue data, also containing both stellar Some Antennae sources which could not be safely identified and non-stellar sources, consist of a set of scans on the SRC-J with known objects were observed with the WO Tektronix 1024 2Â1 plates for all objects detected to BJ (where J refers to the J plate) 1024 CCD in imaging mode. The pixel scale is 0.7 arcsec pixel <21.5 mag, but with a smaller machine scanning aperture than and the overall field of view of the CCD is 11:95 11:95 arcmin2: USNO-A2.0 and a better photometric accuracy. Two source locations were observed during the period 1999 April The USNO-A2.0 photometric accuracy is reported to be 0.15- 22±24 with B, V and R filters. Flat-field and bias measurements mag internal error and up to 0.5 mag due to systematic effects. The were taken and used in the reduction process to remove instrument absolute values of the blue and red magnitudes are not accurate, background. The reduction also included corrections for atmo- but a local (radius 2 arcmin) comparison of objects for each UV spheric extinction. Photometry was performed using the iraf source gives the bluest and brightest candidate which, when cross- radprof package. Results are discussed in Section 3.2.1 on correlated with corresponding COSMOS objects and visual individual sources, FA9 and FA11. inspection of images from the Digitized Sky Survey, yields the The Faint-Object Spectrograph and Camera (FOSC) was used best counterpart. for spectroscopic observations of FA36 (from Table 1), a multiple Additional catalogue searching was undertaken with the Deep star system, on 1999 April 30. The FOSC in spectroscopic mode Near Infra-red Survey of the Southern sky, DENIS (Epchtein et al. consists of a focal-reducer camera with a collimated beam section 1999), the HEArsarc data base (viz., FAUST, Palomar Green, and a 10-arcsec-wide long-slit focal plane entrance aperture. A ROSAT, McCook and Sion Catalogue of White Dwarf Stars, TD-1, grism with 600 line mm21 was inserted into the collimated beam IRAS and all the major multicatalogues), the Multi-Archive at the section in order to disperse the incoming light; and a wedged Space Telescope, MAST (the Multimission Archive at StscI being window as a beam steerer was used to centre the desired spectral developed to support a variety of astronomical data archives, with region on to a Tektronix back-illuminated CCD chip with the primary focus on scientifically related data sets in the optical, Metachrome II coating to enhance its blue±ultraviolet response. UV, and near-infrared parts of the spectrum; MAST is funded by The CCD has a 1024 1024 pixel format, but for spectral  NASA's Office of Space Science through a grant from NASA and observations only the relevant part of the chip containing the other grants and contracts) the HST, ASTRO, IUE, Copernicus, spectrum of the object and that of the nearby sky was read out. EUVE catalogues, the Washington Visual Double Star Catalogue The FOSC spectra, in configuration chosen for the two FA36 (Worley & Douglass 1997) and the TD1F Catalogue. candidates, cover the region from ,4000 to ,7800 AÊ with 3.75 AÊ Table 2 gives the identification of UV Sources: repeating the per pixel, resulting in ,8-AÊ resolution. source identifier from Table 1 in column 1; a catalogue identifier4 During the spectroscopic observations the spectrograph's 10- in column 2; spectral type/luminosity class (if known) for stars arcsec-wide long slit was aligned at PA 1678 in order to include obtained from SIMBAD or morphological type for galaxies from simultaneously both objects. In thisˆ manner a maximum NED in column 3; the F1660 magnitude in column 4; the apparent separation between the spectra of two objects is achieved, B magnitude in column 5; the apparent V magnitude in column 6; minimizing the possibility of light from one object contaminating the apparent R magnitude in column 7; F1660 2 B in column 8; the other. The spectra were extracted after debiasing, calibration and B 2 V in column 9 ± where B 2 V is not available, B 2 R and flat-fielding. Reduction of all spectra was conducted using the iraf specred package. Since no spectroscopic standards 3 COSMOS Coordinates, Orientations, Sizes, Magnitudes, and Shapes. were observed when the spectra of the stars were taken, the ˆ 4 Catalogue ID abbreviations are: TYC Tycho; US USNO-A2.0; spectrum was flux-calibrated using the WO standard coefficients. ˆ ˆ NGC New General Catalogue; IC Index Catalogue; ESO European These generally do not change significantly from night to ˆ ˆ ˆ Southern Observatory; HD Henry Draper; REJ ROSAT satellite night. Results are discussed in Section 3.2.1 on individual sources, ˆ ˆ Extreme UV. FA36.

q 2001 RAS, MNRAS 324, 580±598 Ultraviolet sources in the directions of NGC 4038±39 and 6752 591

Table 3. Extragalactic FAUST sources with photometric properties.

Object ID Type F1660 UB VRF1660 2 BB2 VB2 R FA28 NGC3956 SA(s)c 12.29 12.99 11.85 20.70 1.14 FA31 NGC4027 SB(s)dm 9.99 11.62 11.71 11.12 10.60 21.72 0.59 1.11 FA33 Antennae 10.35 10.25 9.00 0.10 1.25 NGC4038 SB(s)mpec 10.94 9.74 1.20 NGC4039 SA(s)mpec 11.06 9.77 1.29 FN30 ESO141-G055 Sc, Sy1 11.40 14.36 14.00 13.28 22.96 0.36 1.08 FN36 NGC6782 (RÂ _1)SB(r)0/a 12.84 12.70 11.84 11.27 0.14 0.86 1.43 FN42 NGC6753 (RÂ )SA(r)b 10.53 12.00 11.84 11.14 10.31 21.31 0.70 1.53 FN58 12.24 11.63 11.09 10.29 0.61 0.54 0.34 NGC6769 (RÂ )SA(r)b 12.33 11.75 10.93 0.58 0.40 NGC6770 SB(rs)b 13.17 12.44 11.94 11.16 0.50 1.28 FN140 NGC6744 SAB(r)bc 8.95 9.28 9.54 8.10 20.33 20.26 1.18 FN147 USN0225-29766917 Ellip 11.99 11.80BJ 29.9 10.8u 0.19 *u20.1

the UV stellar density was evaluated as 0.85 star deg22 for the 3 DISCUSSION 2 Antennae and 4.45 star deg 2 for NGC 6752. Table 4 gives the summary of results with respect to source type. Figs 5 and 6 show the F1660 2 B colour distribution for the The number of unknown sources in the Antennae is ,28 per cent Antennae and NGC 6752 fields respectively, with along the compared to ,55 per cent in NGC 6752. We noted earlier that the predicted curves from our UV model. The predicted curves were exposure for NGC 6752 was longer than that for the Antennae; generated using a limiting faintness of F1660 12 mag; where the consequently, more faint sources were detected, and most of these FAUST source detection begins to drop sharply.ˆ The curves were are unclassified. then scaled to the peak stellar count/colour bin for each figure. In Fig. 5 the x 2 probability for the predicted curve describing the data, over the region F1660 2 B $23:0; is 51 per cent, indicating a very good fit. The discrepancy between the predicted curve and 3.1 Stars data for F1660 2 B ,23:0 is possibly due to those hot evolved Tables 5 and 6 bin sources by both F1660 magnitude and spectral objects (e.g., ZAHB, EHB, post-EHB and subdwarf stars) that type for the Antennae and NGC 6752 fields respectively. our UV model does not include. In Fig. 6 the discrepancy starts Assuming that all unclassified objects are stars, the proportion already at F1660 2 B , 0: Amongst our detections in the NGC of B, A and F stars is 67 per cent of the stellar population for 6752 field, there are many more unclassified objects in the colour the Antennae, and 46 per cent of the stellar population for NGC range 23:0 # F1660 , 0:0 compared to the detections in the 6752. Antennae field ± see Fig. 10 compared to Fig. 8. These Both tables indicate a notable deficiency in hot evolved stars unclassified objects could include many of the afore-mentioned (HES); only one identified HES object (the hot white dwarf hot evolved objects and hence explain the discrepancy starting at a REJ1925 2 563 was found in the NGC 6752 field. This is far redder colour. We also note that in Fig. 8, for the region F1660 2 † fewer than in other FAUST fields: 11 HES in the Coma cluster B $ 0:0; the predicted curve only roughly (within 2s) describes (Brosch et al. 1998), 10 HES in the North Galactic Pole (Brosch the data; the reason for this is not known at present. et al. 1995), and seven HES in the Virgo cluster (Brosch et al. We have plotted colour±magnitude diagrams for both fields: 1997). As we will discuss later, Figs 7±10 indicate that many of Antennae (Figs 7 and 8) and NGC 6752 (Figs 9 and 10), and use the unclassified objects in Tables 5 and 6 may be HES. This can them as diagnostic diagrams to establish the likely types of stars only be verified by follow-up spectroscopic observations of all that are FAUST sources. We have also plotted in Figs 7 and 9 the these objects. main sequences for different distances. These have been evaluated A comparison with the predicted differential star density from using data from Fanelli et al. (1992). Specifically, we calculated our UV model (Brosch 1991, and modifications therein; Bilenko, M1700 and M17002B from MV, 1700 2 V and B 2 V given in their private communication) for the Antennae and NGC 6752 regions tables 5 and 7. The M1700 band defined there is very similar to the is given in Figs 3 and 4. The UV model does not include FAUST sensitivity band, so a direct comparison is valid. In Figs 8 subdwarfs, horizontal branch stars, post-asymptotic giant branch and 10, we have also plotted the canonical zero-age horizontal 2 or post-horizontal branch stars. Fig. 3 shows a marked lack of stars branch (ZAHB) (for a scaled-solar metallicity of Z 5 10 4 ˆ  for all F magnitudes .7.0 (e.g., at F 9:5; there is a .4s and a main-sequence helium abundance of Y 0:23 at varying 1660 1660 ˆ † difference between the model and theˆ observations). The distances. The ZAHB was derived from fig. 2 of Landsman et al. agreement in Fig. 4 is very good up until F 10:0; when (1996) and the B 2 V data (table 7) of Fanelli et al. In Figs 8 and 1660 ˆ the expected drop in detected stars starts to occur as the faintness 10 we have also plotted cooling curves for 0.6- and 1.0-M( white detection limit of FAUST is approached. To evaluate the detected stellar densities in Figs 3 and 4, we took the effective exposure of Table 4. Summary of results. each FAUST field as all pixels with a value .25 per cent of the peak exposure, where objects can be reliably found, giving a field Field Detections Extragalactic Stellar Unclassified of 42.8 deg2 for the Antennae, and 43.6 deg2 for NGC 6752. Using these field areas and the total number of stars from Tables 5 and 6, Antennae 46 3 30 13 NGC 6752 221 7 93.5 120.5 TOTAL 267 10 122.5 134.5 5 ftp://kepler.pss.fit.edu/pub/wd. q 2001 RAS, MNRAS 324, 580±598 592 J. Daniels et al.

Table 5. Binning of stars by type and magnitude in the Antennae field.

Mag. B A F G K2M D. Sd. Spi. Ell. Unc. Tot. ,7.0 2 1 0 0 0 0 0 0 0 0 3 7.0±7.9 0 1 0 0 0 0 0 0 0 0 1 8.0±8.9 2 1 0 0 0 0 0 0 0 3 6 9.0±9.9 0 3 0 0 0 0 0 1 0 1 5 10.0±10.9 0 12 1 0 0 0 0 1 0 0 14 11.0±11.9 0 4 2 0 0 0 0 0 0 8 14 12.0±12.9 0 0 0 0 0 0 0 1 0 1 2 13.0±13.9 0 0 0 0 0 0 0 0 0 0 0 14.0±14.9 0 0 1 0 0 0 0 0 0 0 1 TOTALS 4 22 4 0 0 0 0 3 0 13 46

Note. ± Key: D Hot White Dwarf; Sd Subdwarf; Spi Spiral; Ell Elliptical; Unc Unclassified; Tot Total. ˆ ˆ ˆ ˆ ˆ ˆ dwarfs for different distances from the data of Wood (1995) The diagnostic diagrams in Figs 7±10 allow a tentative available on the WWW.5 The models were transformed from assignment of spectral types to the unclassified sources. These [log(Teff); log L*=L( to the colour±magnitude units used here consist of hot white dwarfs within a few hundred parsecs from the via the spectral type,†Š 1700 2 V to B 2 V transformations of Sun, ZAHB/EHB stars within 4 kpc, and main-sequence stars Fanelli et al., and the standard bolometric corrections from Snow within 2 kpc. The direction of NGC 6752 seems to be particularly & Brownsberger (1997, table 14.5). The cooling curves start at rich in unclassified sources. As the F1660-bright objects do not <3.7 Myr (for 0.6 M() and <14.4 Myr (for 1.0 M() and for the appear to concentrate particularly near the globular cluster, the 10 pc curves end at <7±8 Gyr: In Figs 7±10 we have added the UV objects are probably not cluster members. This is probably reddening vector, assuming the standard Savage & Mathis (1979) some disc population of WD or ZAHB/EHB stars, which shows extinction law for E B 2 V 0:3: This represents a moderate up more prominently due to the lower Galactic latitude of this amount of extinction to the objects,†ˆ as shown in the Introduction. pointing direction. The very bright objects labelled 29, 32, 38 and 46, the faint red The FAUST sample allows the evaluation of the accuracy of object labelled 1, and the blue object labelled 25 in Fig. 7 are inferring the UV brightness of stars while relying on optical discussed in Section 3.2.1 on individual sources. In a similar colours only. Figs 11 and 12 are F1660 2 V versus B 2 V colour manner the very bright identified object labelled 178 in Fig. 9 and plots for the Antennae and NGC 6752 images respectively. All the very blue object labelled 151 in Figs 9 and 10 are also classified stars with known luminosities are plotted; in addition, discussed in that section. four very B 2 V red objects (FN83, FN87, FN165 and FN184) We now discuss the nature of the unclassified sources in with unknown luminosities have been added for discussion in Figs 7±10. For both the Antennae and NGC 6752 the view Section 3.2.1 on individual sources. The curves are the modified direction is through the nearby disc and Galactic halo. The relationships of Shemi et al. (1994) which were evaluated using unclassified objects in the Antennae image (referring to Figs 7 and IUE spectral data sets, data from the Hipparcos Input Catalogue, 8) with F1660 2 B .24:0; could be ZAHB stars closer than and measurements from the TD-1 satellite. Both figures 2 kpc, white dwarfs within 500 pc, and main-sequence (or giant) demonstrate that the above method of inference is reliable, giants at distances .1 kpc. For F1660 2 B ,24:0; subdwarfs are considering the uncertainties in the quadratic relationships and any the only known candidates. The unclassified objects in the NGC extinction associated with each star. The method is applicable to 6752 image (referring to Figs 9 and 10) with F1660 2 B .24:0 all luminosity classes and spectral types (B, A, F and K) detected could be: ZAHB stars ,4 kpc, white dwarfs within 500 pc, and by FAUST; only those numbered stars (4, 37 and 46 in Fig. 11, and main-sequence (or giant) stars more distant than 300 pc. For 9, 83, 87, 88, 123, 165, 169 and 184 in Fig. 12) are significantly F1660 2 B ,24:0; subdwarfs are the only known candidates. We distant from the predicted curves, and are discussed in Section also note from fig. 3 of Landsman et al. (1996) that EHB and post- 3.2.1. Fig. 12 shows that most sources in the NGC 6752 image lie EHB stars are possible candidates for unclassified objects with to the right of the theoretical relationships. This is true for all 25 , F1660 2 B , 0: luminosity classes, and indicates a general behaviour of UV

Table 6. Binning of stars by type and magnitude in the NGC 6752 field.

Mag. B A F G K2M D. Sd. Spi. Ell. Sy. Unc. Tot. ,7.0 4.5 1 0 0 0 0 0 0 0 0 0.5 6 7.0±7.9 5 3 0 0 0 0 0 0 0 0 0 8 8.0±8.9 1 11 0 0 1 0 0 1 0 0 3 17 9.0±9.9 1 20 2 0 1 1 0 0 0 0 9 34 10.0±10.9 0 13 7 0 0 0 0 1 0 0 23 44 11.0±11.9 1 17 17 0 0 0 0 0 1 1 36 73 12.0±12.9 0 2 11 0 0 0 0 3 0 0 14 30 13.0±13.9 0 0 1 0 0 0 0 0 0 0 5 6 14.0±14.9 0 0 0 0 0 0 0 0 0 0 3 3 TOTALS 12.5 67 38 0 2 1 0 5 1 1 93.5 221

Note. ± Key: D Hot White Dwarf; Sd Subdwarf; Spi Spiral; Ell Elliptical; Sy Seyfert; Unc Unclassified; Tot Total. ˆ ˆ ˆ ˆ ˆ ˆ ˆ q 2001 RAS, MNRAS 324, 580±598 Ultraviolet sources in the directions of NGC 4038±39 and 6752 593

Figure 3. Differential star counts in the Antennae field versus the UV sky Figure 5. Colour distribution in the Antennae field versus the predictions 2 model (solid line) for a 42.8 deg area at the coordinates of the FAUST of the UV sky model (solid line). The prediction was scaled to match the image centre. The star counts include all the sources (solid objects) actual count rates at F1660 2 B 1:0: identified as stars, and unclassified objects all assumed to be stars. The ˆ vertical bars are 1s Poisson deviates.

Figure 4. Differential star counts in NGC 6752 field versus predictions of the UV sky model for a 43.6 deg2 area at the coordinates of the FAUST image centre. The star counts include all the sources (solid objects) Figure 6. Colour distribution in NGC 6752 field versus the predictions of identified as stars, and unclassified objects all assumed to be stars. The the UV sky model (solid line). The prediction was scaled to match the vertical bars are 1s Poisson deviates. actual count rates at F 2 B 0:0: 1660 ˆ q 2001 RAS, MNRAS 324, 580±598 594 J. Daniels et al.

sources in this region. We plotted in the figures the influence of a moderate amount of extinction: this shows that the UV sources in this field could be reddened by dust. We further tested the proposition of Brosch et al. (2000a) that the UV properties of A stars can be used to identify possible candidate Am or Ap stars. Fig. 13 shows a F1660 2 B versus B 2 V colour plot for all A stars in both FAUST images. Metallic A and F stars (both indicated by filled triangles) are clearly UV-faint when compared to early A stars (open triangles). Of the nine `m' stars, two are F stars. The UV deficiency is probably due to line blanketing of their spectral energy distributions. This deficiency has been noted before by van Dijk et al. (1978), mostly in regard to Ap stars. Our results agree with Brosch et al. (2000a) that UV faintness in loosely classified A stars is an indicator of possible metallicity. Fig. 13 also includes an Ap star, two nebular B stars, and a BII±III emission star (FN178 saturated in the FAUST image).

3.2 Individual sources Here we discuss individual sources that merit attention due to their unusual location in the colour±magnitude diagrams of Figs 7±10 and/or the colour±colour diagrams of Figs 11 and 12. In addition, objects observed at the WO are discussed.

Figure 7. UV colour±magnitude diagram for objects identified as stars in 3.2.1 Stars the Antennae image with the main-sequence branch at different distances derived from Fanelli et al. (1992). Fiducial error bars are indicated at the FA1 This object appears extremely dim and red in Figs 7 and 8. lower-left corner for classified and unclassified stars. The giant-branch This can be explained by the very large error in F1660 14:1 ^ ˆ curves are not shown, as they do not differ notably in location from the 2:16: main-sequence branch. The colour±magnitude shift due to a typical colour FA4 In Fig. 11 this object it appears redder in both colours than excess of E B 2 V 0:3 is shown as a vector. †ˆ predicted. This could be a result of reddening by dust of an A star, as indicated by the spectroscopic typing.

Figure 8. UV colour±magnitude diagram for objects identified as stars in the Antennae image with WD cooling curves at different distances and masses from Wood (1995) and zero-age horizontal-branch (ZAHB) stars at different distances from Landsman et al. (1996). Fiducial error bars are indicated at the lower- left corner for classified and unclassified stars. The colour±magnitude shift due to a typical colour excess of E B 2 V 0:3 is shown as a vector. †ˆ q 2001 RAS, MNRAS 324, 580±598 Ultraviolet sources in the directions of NGC 4038±39 and 6752 595

brighter and bluer than shown. It is a variable star, and the parallax measurement from SIMBAD places it at 51 ^ 2pc: FA36 This is the brightest object, F 8:36 ^ 0:17; in the 1660 ˆ Antennae image lacking a Tycho identification. The best counterpart was found to be USNOA-2.0 0675-11972813. Examination of the SIMBAD data base revealed a double or multiple star system listing a B9V star HD 105604 with B and V 9:7 and an unclassified object BD-16 3399B with a V magnitudeˆ of 11.6. Both stars are also identified in the Washington Double Star Catalogue WDS J1209:6 2 1734 that indicates the presence of a triple system. We examined the two SIMBAD listed stars at the WO, and confirmed that HD 105604 is a B9V star. The second candidate is probably an F or G star. HD 105604 is therefore the hotter of the two objects (as well as the brighter in V), and is thus identified as the correct counterpart UV object. FA37 In Fig. 11, this object appears F1660 2 B bluer and B 2 V redder than predicted. This could be the result of dust reddening of an A star, as indicated by the assigned spectral type. The parallax 87 measurement from SIMBAD indicates a distance of 2402‡51 pc: FA38 The parallax measurement from SIMBAD indicates a 26 distance of 1662‡19 pc; confirming its location in Fig. 7 as a nearby source. FA46 This is a variable star, and the parallax measurement from SIMBAD indicates a distance of 88 ^ 6pc; confirming its location in Fig. 7 as a nearby source. FN9 The colours are F 2 B 20 12 ^ 0 17 and B 2 V Figure 9. 1660 : : UV colour±magnitude diagram for objects identified as stars in 2 ^ 2 ˆ ˆ the NGC 6752 image with the main-sequence branch at different distances 0:19 0:01: The F1660 B colour is much redder than derived from Fanelli et al. (1992). Fiducial error bars are indicated at the lower-left corner. The colour±magnitude shift due to a typical colour excess of E B 2 V 0:3 is shown as a vector. †ˆ

FA9 This is the second brightest object, F1660 8:84 ^ 0:17; in the Antennae image without a reliable identification.ˆ The best counterpart USNOA-2.0 0675-11972813, given in Table 2, was verified with UBV observations at the WO: USNOA-2.0 0675-11972813 is the bluest source present in the U 2 B versus B 2 V plot. The F1660 2 B of this source is 24:37 ^ 0:23 and F1660 is 8:84 ^ 0:17: From our discussions of Figs 7 and 8, this would indicate a subdwarf, a very distant (.15 kpc) main- sequence or giant B star in the Galactic halo or a ZAHB/EHB star at under 1 kpc. Follow-up spectral observations are essential to determine its nature. FA11 The best counterpart USNOA-2.0 0675-11794652 was observed in U, B and V at the WO: USNOA-2.0 0675-11794652 was found to be the bluest source present. F 2 B 20:91 ^ 1660 ˆ 0:29 and F 11:19 ^ 0:25: Possible types of counterparts are 1660 ˆ a ZAHB/EHB at between 1±2 kpc; a main-sequence or giant star at <2 kpc, or a very nearby hot white dwarf at <10 pc. The last possibility is rather unlikely, as it would have implied a measurable parallax. Follow-up spectral observations are essential to determine its nature. FA25 Fig. 7 places this object at <2 kpc, the most distant Tycho counterpart in the Antennae field. FA29 This object is saturated in the FAUST image of the Figure 10. UV colour±magnitude diagram for objects identified as stars in Antennae Field, and so its true location in Figs 7 and 8 should be the NGC 6752 image with WD cooling curves at different distances and brighter and bluer than shown. The counterpart is a spectroscopic masses from Wood (1995) and zero-age horizontal-branch (ZAHB) stars at binary and the parallax measurement quoted in SIMBAD places it different distances from Landsman et al. (1996). Fiducial error bars are 379 at 5382‡158 pc: indicated at the lower-left corner for classified and unclassified stars. The FA32 This object is saturated in the FAUST image of the colour±magnitude shift due to a typical colour excess of E B 2 V 0:3 †ˆ Antennae Field, and so its true location in Figs 7 and 8 should be is shown as a vector. q 2001 RAS, MNRAS 324, 580±598 596 J. Daniels et al.

Figure 11. Measured F1660 2 B versus B 2 V colour for the Antennae Image, showing that the method of deriving properties from optical ones is valid. The fiducial error bar is indicated towards the upper-left corner. The colour±colour shift due to a typical colour excess of E B 2 V 0:3 is shown as a vector. †ˆ predicted in Fig. 12. SIMBAD gives a radial velocity of 21 59 151 km s , and the distance from the parallax is 2442‡40 pc: The motion perpendicular to the line of sight, evaluated from proper motion measurements in SIMBAD and the parallax distance, is <39 km s21. The spatial velocity is thus <156 km s21, a fairly high-velocity star. It has a companion star HD 180183B, a K0V star, with V 12:0 ˆ FN78 This is a double or multiple star; on sky projection it is within 1 arcmin of the globular cluster NGC 6752 and outshines it at F1660. FN83 The colours are F 2 B 20:91 ^ 0:18 and B 2 V 1660 ˆ ˆ 0:46 ^ 0:08; much redder than predicted (Shemi et al. 1994, and modifications therein) for an A7 star of any luminosity class. This could be the result of very high dust extinction, E B 2 V < 0:5: † FN87 The colours are F 2 B 1:31 ^ 0:19 and B 2 V 1660 ˆ ˆ 0:45 ^ 0:04: These colours are redder than predicted for an F0 star of any luminosity class. This could be the result of high dust extinction. FN88 In Fig. 12 this object appears much redder than predicted. This could be the result of high dust extinction. FN123 The distance derived from the SIMBAD parallax is 80 2602‡ pc: Its F 2 B 1:28 ^ 0:17 and B 2 V 0:67 ^ 40 1660 ˆ ˆ 0.01. The F1660 2 B colour is much bluer than predicted by its type. Brosch (2000a) indicates that K stars are expected to have F1660 2 B < 3:2±7:4; but some stars in this class are more UV- bright than this, possibly because of some form of coronal activity (see, e.g., Jordan et al. 1987), or because of the presence of a hot secondary such as a hot white dwarf. FN151 This source is identified with a star spectrally classified as B. If main-sequence, it should be at <30 kpc ± putting it far Figure 12. Measured F1660 2 B versus B 2 V colour for the NGC 6752 beyond the accepted Galactic boundaries. If, on the other hand, we image. The fiducial error bar is indicated towards the upper-left corner. assume it to be a WD (perhaps a DA dwarf), it could be as close as The colour±colour shift due to a typical colour excess of E B 2 V 0:3 †ˆ <100 pc. is shown as a vector.

q 2001 RAS, MNRAS 324, 580±598 Ultraviolet sources in the directions of NGC 4038±39 and 6752 597

FA33 This corresponds to both Antennae galaxies, NGC 4038 and 4039. Both have very long tidal tails. NGC 4038 is a barred spiral [SB(s)mpec] with a heliocentric radial velocity of 1642 ^ 12 km s21: The northern part of the Antennae, it has very bright knotty areas. NGC 4039 is a barred spiral [SA(s)mpec] with a heliocentric radial velocity of 1641 ^ 9kms21: The southern part of the Antennae, it shows both loops and plumes, presumably the result of tidal interactions. FN30 This is the Seyfert [Sc, Sy1] ESO 141-G055 with a heliocentric radial velocity of 10 793 ^ 90 km s21: Marginal evidence for spectral flattening has been found at high energies. It was observed by the HST Goddard High Resolution Spectro- graph (GHRS), and also by the IUE. The F16602B colour of 22.96 is the bluest of the FAUST galaxies detected here. There were seven observations by the IUE over the period 1980 October 2 to 1990 September 14; the variation in F1660 was 11:13 ^ 0:05 to 11:88 ^ 0:10: This compares with the FAUST measurement of F1660 11:40 ^ :09; this suggests that all the F1660 emission originatesˆ from the nucleus. FN36 This is the barred spiral R 2 1 SB s r O=a NGC 6782 ‰ † † † Š2 with a heliocentric radial velocity of 3736 ^ 37 km s 1: It has a double bar structure and a very bright nucleus. The outer arms form an R 2 1 outer pseudoring in blue light. FN42  Figure 13. F1660 2 B versus B 2 V colour comparison plot between This is the spiral R SA r b NGC 6753 with a ‰ † † Š 21 regular A stars and metallic (and other non-normal) stars from both heliocentric radial velocity of 3124 ^ 26 km s : The ellipticity FAUST images. The colour±colour shift due to a typical colour excess of and PA profiles of this galaxy show several small peaks related E B 2 V 0:3 is shown as a vector. probably to the presence of star forming regions. H ii regions and †ˆ diffuse emission concentrate in the nuclear ring-lens. FN165 The colours are F 2 B 0:43 ^ 0:20 and B 2 V FN58 This corresponds to the interacting pair of galaxies NGC 1660 ˆ ˆ 0:40 ^ 0:05; much redder than predicted for an F2 star of any 6769 and 6770. There is a bridge between the two galaxies. NGC luminosity class. This could be the result of high dust reddening. 6769 is a spiral [(R )SA(r)b] with a heliocentric radial velocity of 2 FN169 In Fig. 12 this object appears much redder than 3686 ^ 46 km s 1: There is a dark lane in the disc and an H ii predicted. This could be the result of high reddening. region evident. NGC 6770 is a barred spiral [SB(rs)b] with a 21 FN178 This object is saturated in the FAUST image of the heliocentric radial velocity of 3813 km s . There are streamers, Antennae field, and so its true location in Figs 9 and 10 should be plumes, loops and one arm with H ii regions. There are two dark brighter and bluer than shown. lanes. FN184 The colours are F1660 2 B 20:97 ^ 0:17 and B 2 FN140 This is the mixed spiral [SAB(r)bc] LINER NGC 6744 ˆ 21 V 0:31 ^ 0:04; much redder than predicted for an A3 star of with a heliocentric radial velocity of 841 ^ 5kms : The region anyˆ luminosity class. This could be the result of very high dust dominated by the bar is very extended and quite clean of gas. extinction. Many knots are evident. Two arms in particular contain a bunch of For all those spectrally unclassified sources in Table 2, we have adjoining giant H ii regions where most of the massive star already discussed the nature of possible counterparts with formation must currently be taking place. NGC 6744, with F 8:95; is the brightest of the FAUST galaxies observed in reference to Figs 7±10. 1660 ˆ the NGC 6752 and the Antennae fields. FN147 This is not identified with any known galaxy; however, the USNOA-2.0 catalogue gives USN0A-2.0 0225-29766917 as 3.2.2 Galaxies the bluest object in this field with B 2 R 0:1: Examination of the ˆ We detected a total of 11 galaxies: 10 are known objects, and one Digitized Sky Survey image shows USN0A-2.0 0225-29766917 to is the best candidate from the USNO-A 2.0 and COSMOS be an elliptical galaxy with dimensions 50 arcsec by 34 arcsec. Catalogues. Two galaxies show forms of nuclear activity; one is a There is a galactic triplet, IC 4803 at 1.3 arcmin from USN0A-2.0 Seyfert, and the other is a LINER. The origin of the UV emission 0225-29766917, which may contribute to the F1660 flux. FN147 is in the nine other objects is presumably general star formation. the bluest object among our FAUST-detected galaxies. This is supported by the high fraction of barred galaxies among the 10 objects. An extensive discussion of galaxies observed by FAUST was given by Deharveng et al. (1994). We now discuss 4 CONCLUSIONS each object listed in Table 3. All data are from the NED data base. FA28 This is the spiral [SA(s)c] NGC 3956 with a heliocentric We have analysed two UV images from the FAUST experiment: radial velocity of 1645 ^ 5kms21: It has patchy arms with many the Antennae region covering 67.5 deg2, and NGC 6752 region knots. covering 64.0 deg2. A total of 227 sources were detected, of which FA31 This is the barred spiral [SB(s)dm] NGC 4027 with a approximately 60 per cent have reliable identifications: most are heliocentric radial velocity of 1671 ^ 6kms21: It is an asym- B, A and F stars; the remaining objects are 11 galaxies, two K metric spiral with very bright knotty arms. stars and a white dwarf in a binary system. The remaining <40 per q 2001 RAS, MNRAS 324, 580±598 598 J. Daniels et al. cent have assigned optical counterparts from the USNO-A2.0 Brosch N., Almoznino E., Engels D., Bowyer S., Lampton M., 2000b, catalogue, and these objects could plausibly be white dwarfs, MNRAS, 316, 58 subdwarfs, horizontal branch stars or main-sequence (or giant) Burstein D., Bertola F., Buson L. M., Faber S. M., Lauer T. R., 1988, ApJ, 328, 440 stars. Only one bright F1660 9:57 object has no assigned optical counterpart. A comparison ˆ of† the star counts with the Buta R., 1995, ApJS, 96, 39 Deharveng J. M., Sasseen T. P., Buat V., Bowyer S., Lampton M., Xu X., predictions of a model for the galactic UV stellar populations 1994, A&A, 289, 715D shows good agreement for the NGC 6752 field but there is a de Vaucouleurs G. H., de Vaucouleurs A., Corwin H. G., Jr, 1976, Second marked shortage of stellar objects in the Antennae field. We have Reference Catalogue of Bright Galaxies. Univ. Texas, Austin demonstrated that metallic A stars are UV-faint compared to de Vaucouleurs G. H., de Vaucouleurs A., Corwin H. G., Jr, Buta R. J., normal early A stars, and shown that in most instances it is valid to Paturel G., Fouque P., 1991, Third Reference Catalogue of Bright infer the UV brightness of stars given the B and V colours only. Galaxies. Springer-Verlag, New York Follow-up spectroscopic measurements of the <40 per cent Dickey J. M., Lockman F. J., 1990, ARA&A, 28, 215 unclassified objects are essential to determine their true nature. Donas J., Deharvent J. M., Milliard B., Laget M., Huguenin D., 1987, The entire sample of UV measured objects from the FAUST flight A&A, 180, 12 will allow firmer statistical conclusions on the distribution of UV Dorman B., O'Connell R. W., 1996, in Leitherer C., Fritze-v.Alvensleben U., Huchra J., eds, ASP Conf. Ser. Vol. 98, From Stars to Galaxies. bright stars and possibly the identification of additional peculiar Astron. Soc. Pac., San Francisco, p. 105 UV sources. Epchtein N. et al., 1999, A&A, 349, 236 Fanelli M. N., O'Connell R. W., Burstein D., Wu C. C., 1992, ApJS, 82, 197 ACKNOWLEDGMENTS Gondhalekar P. M., 1990, in Bowyer S., Liebert C., eds, The Galactic and The UV astronomy effort at Tel Aviv is supported by special grants Extragalactic Background Radiation. Kluwer, Dordrecht, p. 49 to develop a space UV astronomy experiment (TAUVEX) from the Hog E., Kuzmin A., Bastian U., Fabricius C., Kuimov K., Lindegren L., Ministry of Science and from the Austrian Friends of Tel Aviv Makarov V. V., Roeser S., 1998, A&A, 335, L65 University. This research has made use of the NASA/IPAC Jamar C., Macau-Hercot D., Monfils A., Thompson G. I., Houziaux L., Wilson R., 1976, Ultraviolet Bright-Star Spectrophotometric Cata- Extragalactic Data base (NED), which is operated by the Jet logue. ESA, SR-27 Propulsion Laboratory, California Institute of Technology, under Jordan C., Ayres T. R., Brown A., Linsky J. L., Simon T., 1987, MNRAS, contract with the National Aeronautics and Space Administration. 225, 903 This research has also made use of High Energy Science Archive Lampton M., Sasseen T. P., Wu X., Bowyer S., 1993, Geophys. Res. Lett., Research Center (HEArsarc) data base provided by NASA's 20, 539 Goddard Space Flight Center. In addition, this research has also Landsman W. B., 1984, PhD thesis, Johns Hopkins Univ. made use of the COSMOS/UKST Southern Sky Catalogue Landsman W. B., Sweigart A. V., Bohlin R. C., Neff S. G., O'Connell supplied by the Anglo-Australian Observatory. We also appreciate R. W., Roberts M. S., Smith A. M., Stecher T. P., 1996, ApJ, 472, L93 the assistance of Eran O. Ofek for his assistance in the processing Makenty J. W., 1990, ApJS, 72, 231 of WO photometric data. JD thanks both the Leverhulme Monet D., et al., 1998, USNO-A2.0 Catalogue. Washington DC, U.S. Naval Observatory Flagstaff Station (USNOFS) and Universities Space Foundation of the United Kingdom, and Roger Smith in Research Association (USRA) stationed at USNOFS, association with the Adult Education HELP facility at Eastfield O'Connell R. W., 1990, in Fabbiano G. et al., eds, Windows on Galaxies. School, Hull, UK for initiating his post-doctoral career in UV Kluwer, Dordrecht, p. 39 astronomy. NB acknowledges support from the US-Israel Bi- O'Connell R. W., 1992, in Barley B., Renzini A., eds, IAU Symp. 149, The national Science Foundation and from the Austrian Friends of Tel stellar population of galaxies. Kluwer, Dordrecht, p. 233 Aviv University. 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