Central Bureau for Astronomical Telegrams
IAUC 3108: Occns BY URANIAN RINGS; Cir X-1; 4U 1608-52; MXB1730-335; V1017 Sgr
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Read IAUC 3109
Circular No. 3108
Central Bureau for Astronomical Telegrams
INTERNATIONAL ASTRONOMICAL UNION
Postal Address: Central Bureau for Astronomical Telegrams
Smithsonian Astrophysical Observatory, Cambridge, MA 02138, U.S.A.
Cable Address: SATELLITES, NEWYORK Telex: 921428
Telephone: (617) 864-5758
OCCULTATIONS BY URANIAN RINGS
A. R. Klemola, Lick Observatory, provides the following positional
measurements of two stars that will be occulted by the rings
of Uranus in December. The B, V and R magnitudes are by W. Liller,
Center for Astrophysics; the estimated I magnitudes and occultation
depths (in magnitudes; I band; combined light of Uranus and the
star; epsilon ring) are by J. L. Elliot, Cornell University.
1977 UT R. A. (1950) Decl. B V R I Depth
Dec. 5.62 14 45 03.98 -15 33 19.2 14.8 13.8 13.0 12.5 0.004
23.31 14 48 44.66 -15 49 47.9 11.9 10.4 9.3 8.4 0.14
The following local circumstances for the minimum separations of
star and the center of Uranus and the approximate predicted (UT)
times of occultation by the leading (epsilon-A) and following (epsilon-B)
edges of the epsilon ring are by the undersigned:
Location Sep. epsilon-A epsilon-B
Mauna Kea 3"1 Dec. 5d14h39m: Dec. 5d15h00m:
Herstmonceux 0.8 Dec. 23 06 55 -
La Plata 0.1 23 06 54 Dec. 23 07 46
La Serena 0.1 - 23 07 46
The second star will be occulted by Uranus itself for 32 min around
Dec. 23d07h20m UT (at all three stations). Although observations
will be somewhat difficult to make in the dawn sky, it should be
pointed out that the Dec. 23 star is by far the brightest (in R and
I) of the 12 predicted to be occulted by the Uranian rings during
the next three years (Klemola and Marsden 1977, Cent. Astrophys.
Prepr. No. 788 and Astron. J. in press; Liller 1977, Astron. J. in
press; Elliot, submitted to Astron. J.); Elliot points out that the
signal-to-noise ratio will be down by a factor of 3 to 4 from the
Mar. 10 event (SAO 158687 having an I magnitilde of 7.2).
CIRCINUS X-1
L. J. Kaluzienski and S. S. Holt, Goddard Space Flight Center,
report the detection of a strong increase in x-ray flux from Cir
X-1 on Sept. 10.1 +/- 0.1 UT, the 3-6 keV flux increasing to that of
the Crab Nebula on Sept. 11.3 (integrations over ~ 0.3 day). Fine-mode
observations on Sept. 9.6 and again on Sept. 12.2 yield upper
limits of approximately 0.08 times the Crab. This flare is significant
in that it represents the first positive detection of the
source at high levels (> 0.2 times the Crab) early in the phase of
the 16.6-day cycle (turn-on was at phase ~ 0.3) since Ariel 5 was
launched in Oct. 1974. This behavior is reminiscent of that observed
by Uhuru in 1971-72 and suggests a possible return to the
source conditions prevailing at that epoch.
4U 1608-52
Kaluzienski and Holt also report that the flaring source 4U
1608-52 was still bright in early September (cf. IAUC 3099),
factor-of-two variations in flux on timescales of hours to days being
evident. Ariel 5 observations yielded 3-6 keV fluxes (half-day
averages) of 0.68 +/- 0.07 and 0.35 +/- 0.07 times the Crab on Sept. 3
and 5, respectively.
M. Duldig, J. Greenhill and R. Thomas, University of Tasmania;
R. Haynes and L. Simons, C.S.I.R.O. Radiophysics; and P. Murdin,
Anglo-Australian Observatory, observing during a 13-min interval on
Aug. 20.4 UT with the Parkes 64-m telescope at a wavelength of 2 cm,
obtained an upper limit (2-sigma) of 16 mJy for any radio source in the
x-ray error box.
MXB1730-335
P. C. Joss, G. Ricker, W. Mayer and J. Hoffman, SAS-3 Group,
Massachusetts Institute of Technology, report that the rapid burster
MXB1730-335 has again started to emit x-ray bursts. The burst
pattern is similar to that observed in Mar. 1976 (Lewin et al. 1976,
Astrophys. J. 207, L95). There is a large spread (a factor of ~
100) in total burst energy, and the delay until the next burst increases
with increasing total energy of each burst.
V1017 SAGITTARII
F. M. Bateson, Variable Star Section, Royal Astronomical Society
of New Zealand, reports that R.A.S.N.Z. observations show this
recurrent nova to have been near visual magnitude 13.5 in July. On
Aug. 4.5 UT T. A. Cragg, observing with the 380-cm Anglo-Australian
telescope, failed to detect the star down to magnitude 15.7, and it
was still faint on Aug. 30. Comparison with T CrB in 1945-46
(Webbink 1976, J. AAVSO 5, 26) suggests that this decline may be
the prelude to a considerable flare. Previous outbursts were observed
in 1901, 1919 and 1973, maximum brightness being mpg 10.8,
6.2 and 10.5, respectively.
1977 September 16 (3108) Brian G. Marsden
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