Central Bureau for Astronomical Telegrams
IAUC 5257: N LMC 1991
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Read IAUC 5258
Circular No. 5257
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 or GREEN@CFA.BITNET MARSDEN or GREEN@CFAPS2.SPAN
NOVA IN THE LARGE MAGELLANIC CLOUD 1991
S. N. Shore, GHRS/Computer Sciences Corporation; S. G.
Starrfield, Arizona State University; and G. Sonneborn, Goddard
Space Flight Center, NASA, report: "Observations of Nova LMC 1991
with the International Ultraviolet Explorer (IUE) satellite began on
Apr. 20.7 UT. Fine Error Sensor (FES) photometry indicates that
optical maximum occurred on about Apr. 24.0. The current (Apr. 29.6)
rate of decline in the optical, also determined from FES photometry,
is nearly 0.4 mag/day. In a high-dispersion spectrum obtained on
Apr. 29.6, interstellar line profiles of Mg I 285.2-nm and Mg II
280.0-nm show characteristic LMC absorption features, which confirms
that this nova is in the Cloud. C II 133.5-nm and Mg II 280.0-nm
(FWHM 2500 km/s) appear in emission in low-dispersion spectra on Apr.
29.61. The nova is still optically thick in the ultraviolet, with
absorption from various Fe II multiplets dominating the entire IUE
spectral range (cf. IAUC 5253). However, the rapid optical decline
indicates that a nebular phase may soon develop. Integrated
ultraviolet fluxes (120-340 nm; units 1.0 x 10E-10 erg cmE-2 sE-1) are:
Apr. 20.76, 3.82; 20.82, 4.20; 22.84, 6.81; 25.70, > 6.84; 27.48,
7.73; 29.61, 5.48. The flux shortward of 190 nm showed a temporary
decrease between Apr. 25.7 and 27.48, while the longward flux continued
to increase. Therefore, as seen in other novae, optical maximum
occurs before ultraviolet maximum, in this case by about 3
days. The ultraviolet evolution of the nova is also slower than the
optical evolution. Assuming E(B-V) = 0.15 and a distance of 55 kpc
for the LMC, the peak flux corresponds to a luminosity of 1.9 x 10E5
L(sun), or about 5 times the Eddington Luminosity for a 1.0-solar-
mass white dwarf (solar composition and electron scattering opacity).
This nova is the brightest observed in the LMC and one of the most
luminous ever recorded. Our IUE observations are continuing and we
urge observations at other wavelengths."
Photometry by A. C. Gilmore (cf. IAUC 5253) with the 0.6-m
Cassegrain reflector at Mt. John Observatory (+/- 0.02 unless noted
otherwise): Apr. 30.37 UT, V = 11.48, U-B = -0.85, B-V = +0.03, V-R
= +0.97, V-I = +1.26 +/- 0.06; May 1.34, 11.95, -0.86, +0.01, +1.12,
+1.35 +/- 0.01.
Visual magnitude estimates (those by Liller are photovisual):
Apr. 22.985 UT, 9.5 (W. Liller, Vina del Mar, Chile); 23.992, 9.3
(Liller); 24.975, 9.1 (Liller); 26.68, 9.3 (A. Jones, Nelson, N.Z.);
28.33, 9.9 (Jones); May 1.49, 11.7 (A. Pearce, Scarborough, W.A.).
1991 May 2 (5257) Daniel W. E. Green
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