Central Bureau for Astronomical Telegrams
IAUC 4257: 4U 1820-30; N Cyg 1986; N Vul 1984 No. 2
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Circular No. 4257
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
J. P. Norris, P. Hertz, and K. S. Wood, Naval Research Laboratory,
report: "We confirm the periodicity in the x-ray burst source
4U 1820-30 reported by Priedhorsky et al. (IAUC 4247). A periodicity
of 691.5 +/- 2.0 (1 sigma) s is seen in 4.3 hr of data obtained
during a 10-hr pointed observation on 1978 Oct. 6 with HEAO A-1. At
least three harmonics of the fundamental frequency are seen in a
power spectrum of the data. The folded light curve appears sharply
peaked (peak has < 25 percent duty cycle) with a 3-percent peak-to-
peak modulation; however, the shape of the light curve may be
affected by uncertainties in the satellite aspect. During the
observation, the source was in a non-bursting state (fx = 200 UFU, Lx =
3 x 10**37 erg/s). 4U 1820-30 is a known QPO (IAUC 4117); we did
not observe any QPO activity during our observation (rms modulation
< 1 percent between 0.4-50 Hz). The period difference of 6.3 +/- 2.1
s between the HEAO A-1 and EXOSAT observations implies a possible
long-term period decrease of approximately 1 s/yr (P-dot/P = 3 x 10E-8)
from 1978-1985. A binary orbital period would not be expected to decay
this fast; however, short-term fluctuations in the period can not be
excluded at this time."
NOVA CYGNI 1986
Further visual magnitude estimates: Aug. 28.83 UT, 10.3 (E.
Schweitzer, Strasbourg, France); 29.83, 10.3 (A. Perez, Paris,
France); 30.8, 10.6 (A. Mizser, Budapest, Hungary); 31.18, 10.7 (S.
O'Meara, Cambridge, MA); 31.83, 10.5 (W. Hasubick, Buchloe, West
Germany); Sept. 1.08, 10.3 (J. E. Bortle, Stormville, NY); 2.83,
10.6 (Hasubick); 3.81, 10.0 (S. Baroni, Milan, Italy); 4.88, 10.7
(G. M. Hurst, Basingstoke, England); 5.85, 10.7 (R. Monella, Covo,
Italy); 6.80, 10.2 (Hasubick); 7.11, 10.1 (Bortle); 8.06, 10.1
(Bortle); 8.82, 10.2 (Hasubick); 10.88, 10.8 (Monella).
NOVA VULPECULAE 1984 No. 2
Further visual magnitude estimates (cf. IAUC 4164, 4221): June
3.95 UT, 10.7 (R. Monella, Covo, Italy); 4.96, 10.7 (Monella);
7.95, 10.8 (Monella); 12.93, 10.6 (S. Korth, Monheim, W. Germany);
24.99, 10.8 (Korth); 26.96, 10.9 (Korth); 29.96, 10.7 (Korth);
30.94, 10.8 (Korth); July 11.92, 10.9 (Korth); 13.94, 10.7 (Korth);
Aug. 5.1, 11.1 (A. Mizser, Amherst, NH).
1986 September 17 (4257) Daniel W. E. Green
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