Central Bureau for Astronomical Telegrams
IAUC 5461: N Cyg 1992
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Circular No. 5461
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 CYGNI 1992
G. Sonneborn, Goddard Space Flight Center, NASA; S. N. Shore,
Goddard High Resolution Spectrograph team and Computer Sciences
Corporation; S. G. Starrfield, Arizona State University; and R.
Gonzalez-Riestra, IUE Observatory, European Space Agency, Madrid,
report: "Observations of Nova Cyg 1992 with the International
Ultraviolet Explorer (IUE) satellite have been made daily since Feb.
20. The ultraviolet behavior in the early-outburst phase of this
nova has been unique. On Feb. 21.9 UT, 24 hr after the first IUE
observation (cf. IAUC 5456), the ultraviolet flux shortward of 200
nm had faded by an order of magnitude. Subsequently, the nova again
brightened in the ultraviolet, and by Feb. 28.0 reached flux levels
comparable with that on Feb. 20. During this time the appearance of
the nova's ultraviolet spectrum has changed very little. Between
Feb. 26.0 and 27.9, the Mg II (280 nm) flux doubled and the continuum
flux increased by 35-50 percent across the 120- to 320-nm band,
indicating that the ultraviolet opacity, caused by the large number
of overlapping Fe II lines, is declining. The rapid evolution of
Nova Cyg 1992 indicates that the transition to the nebular phase may
occur soon. The visual magnitude, as measured by the IUE Fine Error
Sensor, was steady at about 4.5 until Feb. 26, when it faded to
about 5.0. The ultraviolet fluxes (units 10E-12 erg cmE-2 sE-1
AE-1) and V magnitudes are: Feb. 20.9, F(190 nm) = 11.0, F(300 nm)
= 40.0, V = 4.86; Feb. 21.9, 1.3, 12.0, 4.48; Feb. 22.8, 2.5, 28.0,
4.53; Feb. 23.9, 7.4, 50.0, 4.48; Feb. 24.2, 7.5, -, 4.53; Feb.
25.1, 7.0, 45.0, 4.65; Feb. 26.1, 8.0, 39.0, 5.02; Feb. 28.0, 12.0,
51.0, 4.92."
B. Skiff, Lowell Observatory, reports that the field surrounding
N Cyg 1992 is not crowded with stars, and that there is only one
potential candidate for the nova's precursor readily visible on the
Palomar Sky Survey prints. This candidate appears at mag about 18
on the blue print and about 17 on the red print. The average of the
measurements of both prints yields the following position for equinox
J2000.0 (epoch 1952 July 31.4 UT): R.A. = 20h30m31s.58, Decl. =
+52 37'53".4; the corresponding B1950.0 position is R.A. =
20h29m07s.03, Decl. = +52 27'44".0.
Further selected visual magnitude estimates: Feb. 28.51 UT,
5.0 (P. Collins, Boulder, CO); 28.60, 4.8 (K. Krisciunas, Mauna Kea,
HI); 28.74, 5.1 (K. G. Andersson, Solna, Sweden); 28.97, 4.9 (M.
Villi and G. Cortini, Mt. Colombo, Italy); 29.62, 5.1 (Krisciunas).
1992 February 29 (5461) Daniel W. E. Green
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