Central Bureau for Astronomical Telegrams
IAUC 4259: 4U 1820-30; N Cyg 1986
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Circular No. 4259
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 617-495-7244/7440/7444
4U 1820-30
M. Garcia, R. Burg, and J. Grindlay, Center for Astrophysics,
write: "We searched Einstein Monitor Proportional Counter (MPC)
observations, made in 1979 Mar., Apr., and Sept. of the x-ray-burst
source in NGC 6624, for the 685-s period discovered by Priedhorsky
et al. (IAUC 4247). Due to sporadic variability of the source on ~
10-min timescales, we found a number of apparently significant periods.
However, on Apr. 5 and 7 the strongest periods are 683.0 +/- 9 s (1 sigma)
and 684.0 +/- 1.8 s, respectively; phasing the data over the two days
creates aliasing at delta-P = 3 s, but only one period (684.9 +/- 0.12s)
is consistent with both the SAS and EXOSAT period determinations. The
pulse fraction is 2.8 percent and the pulse shape is smooth with a
minimum lasting about 135 deg. Comparing our period to the weighted
mean of the 4 EXOSAT values reported in IAUC 4247 (685.3 +/- 0.4 s) and
the 6 SAS values reported in IAUC 4254 (684.99 +/- 0.07 s) yields
P-dot/P = 1.0 (+/- 1.0) x 10E-4 and -0.54 (+/- 0.67) x 10E-4 yrE-1,
respectively. Both are consistent with P-dot/P = 0.0 and the 3-sigma upper
limit of P-dot/P < 2.3 x 10E-4 yrE-1 reported by Morgan and Remillard
(IAUC 4254). The 691.5-s period observed 1978 Oct. 6 with the HEAO
A-1 satellite (Norris et al., IAUC 4257) does not appear consistent
with our period and P-dot/P limits (above). Comparing our period to
that derived from the HEAO A-1 observations made 6 months earlier
would imply P-dot/P = -1.9 (+/- 0.6) x 10E-2 yrE-1; this inconsistency
suggests that the HEAO A-1 period determination may be affected by
sporadic variability of the sort seen with the MPC. Our upper limits
on P-dot/P support the interpretation by Priedhorsky et al. that
685 s is the system's binary period."
NOVA CYGNI 1986
R. D. Gehrz, Department of Astronomy, University of Minnesota,
telexes: "Infrared observations made by T. J. Jones and me with
the Wyoming Infrared Telescope yield the following magnitudes: Aug.
15.4 UT, [2.3 microns] = 7.5, [3.6 microns] = 8.0; Sept. 17.4, [2.3
microns] = 9.1, [3.6 microns] = 7.8, N = 6.0 +/- 0.4. The nova appears
to have entered the optically-thin free-free emissions phase."
Further visual magnitude estimates (cf. IAUC 4257), provided
in part by E. Waagen, AAVSO: Sept. 10.97 UT, 9.9 (D. Fischer,
Koenigswinter, W. Germany); 11.17, 10.3 (R. Davidson, Las Vegas,
NV); 20.10, 10.7 (S. O'Meara, Cambridge, MA).
1986 September 24 (4259) Daniel W. E. Green
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