Central Bureau for Astronomical Telegrams
IAUC 5518: EC 04552-2812 = RE 0457-28 = MCT 0455-2812; 1992d
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Circular No. 5518
Central Bureau for Astronomical Telegrams
INTERNATIONAL ASTRONOMICAL UNION
Postal Address: Central Bureau for Astronomical Telegrams
Smithsonian Astrophysical Observatory, Cambridge, MA 02138, U.S.A.
Telephone 617-495-7244/7440/7444 (for emergency use only)
TWX 710-320-6842 ASTROGRAM CAM EASYLINK 62794505
MARSDEN@CFA or GREEN@CFA (.SPAN, .BITNET or .HARVARD.EDU)
EC 04552-2812 = RE 0457-28 = MCT 0455-2812
M. A. Barstow, University of Leicester; F. Wesemael, G.
Fontaine, S. Demers, R. Lamontagne, and P. Bergeron, Universite de
Montreal; M. J. Irwin, Institute for Astronomy, Cambridge; S. O.
Kepler, Universidade Federal do Rio Grande do Sul, Brazil; S.
Vennes, Center for EUV Astrophysics, Berkeley; J. B. Holberg,
University of Arizona; D. Buckley, D. O'Donoghue, and D. Kilkenny,
University of Cape Town; and R. Stobie, Royal Observatory, Edinburgh,
communicate: "We report the observation of a bright new extreme
ultraviolet (EUV) source in the 50- to 91.2-nm band. A hot
DA white dwarf, discovered independently by the Edinburgh-Cape (EC
04552-2812), the ROSAT EUV Wide Field Camera (RE 0457-28), and the
Montreal-Cambridge-Tololo surveys (MCT 0455-2812), was observed
between 1991 Sept. 5 and 8 with the Voyager 2 ultraviolet spectrometer.
The detection of significant EUV flux below the Lyman limit
at 91.2 nm (comparable to that of HZ 43) is indicative of an
extremely low line-of-sight column density. A detailed analysis
gives a value of 1.3 x 10E17 atoms cmE-2 to this star, compared to
the lowest previously measured column density of 3.9 x 10E17 along
the line-of-sight to the prototype EUV source HZ 43 (Holberg et al.
1980, Ap.J. 242, L119). With an estimated distance of 93 pc to the
white dwarf, this translates into an volume density of 0.0005 atoms
cmE-3, two orders of magnitude below the local average of 0.007
atoms cmE-3 (Paresce 1984, A.J. 89, 1022). The galactic coordinates
of the field (l = 229.3, b = -36.2) place it well within the
low-density 'third quadrant' reported by Paresce (ibid.) in his
study of the distribution of interstellar material. The apparent
void may have been swept out by an ancient supernova or could be
the result of photo-ionisation of the interstellar medium by EUV
flux from RE 0457-28 in conjunction with EUV emission from three
additional hot white dwarfs which share the same 1-deg ROSAT field
as the Voyager target."
COMET TANAKA-MACHHOLZ (1992d)
Total visual magnitude estimates: Apr. 28.09 UT, 7.9 (M.
Lehky, Hradec Kralove, Czechoslovakia, 10x80 binoculars); 29.35,
8.2 (J. E. Bortle, Stormville, NY, 10x50 binoculars); 30.09, 8.1
(A. Diepvens, Balen, Belgium, 0.15-m refractor); May 4.02, 8.3 (H.
Luthen, Hamburg, Germany, 0.10-m reflector); 10.00, 8.2 (B. H.
Granslo, Fjellhamar, Norway, 0.20-m reflector); 11.44, 7.7 (A.
Hale, Las Cruces, NM, 10x50 binoculars).
1992 May 11 (5518) Daniel W. E. Green
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