Central Bureau for Astronomical Telegrams
IAUC 3648: NGC 4151; N IN LMC
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Circular No. 3648
Central Bureau for Astronomical Telegrams
INTERNATIONAL ASTRONOMICAL UNION
Postal Address: Central Bureau for Astronomical Telegrams
Smithsonian Astrophysical Observatory, Cambridge, MA 02138, U.S.A.
TWX 710-320-6842 ASTROGRAM CAM Telephone 617-864-5758
NGC 4151
C. Lloyd and M. V. Penston communicate: "The Herstmonceux
photographic monitoring program (cf. Selmes, Tritton and Wordsworth
1975, M.N.R.A.S. 170, 15) shows that the Seyfert galaxy NGC 4151
has remained fainter than B ~ 13.0 since 1981 April, its normal
magnitude range being 12.1 < B < 13.1. The most recent observation on
Nov. 13 shows the nucleus at B ~ 13.0. Such a minimum is unprecedented
in both depth and duration during the 13 years of optical
monitoring. NGC 4151 is a known variable at infrared (Lebofsky and
Rieke 1980, Nature 284, 410), ultraviolet (Penston et al. 1981,
M.N.R.A.S. 196, 857), x-ray (Lawrence 1980, ibid. 192, 83) and
gamma-ray (White et al. 1980, Nature 284, 608) wavelengths. The response
of the infrared continuum and optical and ultraviolet emission
lines to the withdrawal of heating and ionizing flux, respectively,
is capable of giving important information on the regions containing
dust and gas around the nucleus. The duration of the minimum
is approaching or exceeds the light-travel time across the sizes
usually ascribed to these regions. When the object brightens, any
delay in the response of the infrared or emission lines to the optical
continuum will indicate the size of the relevant emitting regions.
In the case of the broad emission lines, the spread of illumination
through the broad-line regions will convey kinematic and
geometrical information. We shall continue monitoring NGC 4151
until the current minimum ends. Other observers who wish to be
notified when this occurs are invited to contact us at the address:
Royal Greenwich Observatory, Herstmonceux Castle, Hailsham, East
Sussex BN27 1RP, England."
NOVA IN LARGE MAGELLANIC CLOUD
A. D. Mallama, Computer Sciences Corporation, writes that his
observations of this object (cf. IAUC 3641) at Cerro Tololo
Interamerican Observatory gave, after correction for extinction: Nov.
1.290 UT, V = 14.18, B-V = -0.30. Rapid fluctuations, such as those
that sometimes are found in cataclysmic stars, were not detected:
observed fluctuations (with the B filter) did not exceed the square
root of the photon counts expected from statistical arguments. The
integration times and respective rms noise were: 100 s, 0.34 percent;
10 s, 1.0 percent; and 1 s, 3.4 percent.
1981 December 14 (3648) Daniel W. E. Green
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