4U 1820-30
Abstract
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)."
- Publication:
-
International Astronomical Union Circular
- Pub Date:
- October 1986
- Bibcode:
- 1986IAUC.4261....3M