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IAUC 4261: 1986L; SU UMa; 4U 1820-30

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                                                  Circular No. 4261
Central Bureau for Astronomical Telegrams
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

     R. H. McNaught, Siding Spring Observatory, telexes the following
precise position for SN 1986L, from a U.K. Schmidt plate taken
by D. Waldron on Oct. 7.71 UT: R.A. = 4h16m53s00, Decl. = -62deg54'19"1
(equinox 1950.0); the SN is 44" west and 4" south of the galaxy's
nucleus, in a bright knot on the outer edge of a spiral arm.  Visual
magnitude estimates by McNaught:  Oct. 7.62, 13.7; 7.64, 13.6;
7.72, 13.8.

     E. O. Waagen, AAVSO, reports that this dwarf nova is apparently
undergoing a supermaximum, as indicated by these visual magnitude
estimates:  Oct. 6.08 UT, 13.3 (M. Bernstrom, Eden Prairie,
MN); 6.21, 12.6 (Bernstrom); 6.25, 12.1 (G. Dyck, N. Dartmouth,
MA); 6.98, 11.6 (Dyck); 8.13, 11.0 (Dyck); 8.25, 11.5 (Bernstrom);
8.39, 11.1 (Dyck).  Observers are urged to search for superhumps by
observing every 10 minutes for 2-3 hr or more when possible.

4U 1820-30
     E. H. Morgan and R. A. Remillard, Massachusetts Institute of
Technology; W. Priedhorsky, Los Alamos National Laboratory; L.
Stella and N. E. White, EXOSAT Observatory; and M. Garcia, Center
for Astrophysics, write: "The SAS-3 observations of this source in
1976-77 (cf. IAUC 4254) provide a unique determination of the period
as 685.0124 +/- 0.0005 (1 sigma) s.  The period is constant in these
observations, with a 3-sigma upper limit of -3 < P-dot < 5 ms/yr.  Using
this period, we have phased together the 1984-85 EXOSAT observations
(IAUC 4247) and the 1979 Einstein MPC observation (IAUC 4259)
to yield a period of 685.01184 +/- 0.00003 (1 sigma) s.  The epoch of
maximum intensity is JDE 2443050.94541.  The epochs originally
published by Stella, Priedhorsky, and White (1986, EXOSAT Preprint 32)
are in error.  The period is constant, with a 3-sigma upper limit of P-dot
< 0.11 ms/yr, which corresponds to P-dot/P < 1.6 x 10**-7 yr**-1.  If the
binary-star system contains a neutron star and a He white dwarf
(0.07 solar mass; cf. IAUC 4247) with a mass-transfer rate of 5 x 10**-9
Mo/yr, then we would expect P-dot/P is approximately 7 x 10**-8 yr**-1
(Rappaport, Joss, and Webbink 1984, Ap.J. 254, 616)."

1986 October 9                 (4261)            Daniel W. E. Green

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