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IAUC 3184: HR 1099; V1500 Cyg; 4U 1538-52; Her X-1; 4U 1249-28; HDE 245770; N Sge 1977

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                                                  Circular No. 3184
Central Bureau for Astronomical Telegrams
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

HR 1099
     A. R. Taylor, University of British Columbia, reporting for
the Canadian group of radio astronomers observing with the 46-m
Algonquin telescope, informs us that the 2.8-cm flux varied over
0.2-0.7 Jy during Feb. 24-27.  From Feb. 27d18h UT until observations
ended on Mar. 1d03h UT the flux had stabilized at ~ 0.2 Jy.

     D. S. Hall, Dyer Observatory, provides the ephemeris 1975 Dec.
19.569 UT + 2.83782E, where the orbital period is that of Bopp and
Fekel (1976, Astron. J. 81, 771) and the epoch a conjunction with
the more active star in front.  He reports that recent photometric
observations, obtained mainly in Dec. 1977, show that the minimum
of the photometric wave is in the vicinity of phase 0.55-0.60.  He
also points out that the Astron. J. is planning to devote an issue
to HR 1099, with particular reference to the February outburst.
Manuscripts should be submitted to the Editors by May 15.

     J. Patterson, University of Texas, writes: "Photoelectric
observations at the McDonald Observatory show that the 3.3-hr
variation continues to be present through Dec. 1977.  During the
interval Oct. 18-Dec. 4 the period was 0.13962 +/- 0.00007 days, a 1
percent increase from the 1976 value.  The star continues to show
rapid flickering."

4U 1538-52
     G. E. Parkes, Mullard Space Science Laboratory; P. Murdin,
Anglo-Australian Observatory; and K. O. Mason, University of
California at Berkeley, report that star 12 of Cowley et al. (1977,
Astrophys. J. 218, L3) in the SAS-3 error circle of 4U 1538-52 is a
very reddened B-type star with He I and H-alpha emission.  They propose
it as the identification for the heavily cut-off and massive x-ray-source
binary, and they suggest that it should be observed for the
3.73-day orbital period of the x-ray source.

     W. Voges, W. Pietsch, C. Reppin and J. Trumper, Max-Planck-Institut
fur Extraterrestrische Physik; and R. Staubert and E.
Kendziorra, Astronomisches Institut Tubingen, report hard x-ray (>~
20 keV) balloon observations of Her X-1 for three phases of the
35-day cycle (phases being measured with respect to turn-on): (1) 1977
Sept. 3, phase 0.12 ('on' state); the existence of the 58-keV line
discovered in the pulsed (1s.24) spectrum and interpreted as a
cyclotron line (Trumper et al. 1978, Astrophys. J. 219, L105) is
confirmed with large statistical significance (>~ 10 sigma); the 1s.24
pulsations (20-50 keV) show an interpulse that is 12 times weaker than
the main pulse.  (2) 1977 Sept. 20, phase 0.61 (short 'on' state);
the intensity (20-50 kev) is a factor of 4 lower than during the
'on' state; the 1s.24 pulsations (20-50 keV) show an interpulse that
is only 2.5 times weaker than the train pulse.  (3) 1977 Oct. 18,
phase 0.41 ('off' state); the intensity (20-50 keV) is a factor of
10 lower than during the 'on' state; the 1s.24 pulsations are
detected at a 3.9-sigma level.  These results represent the first
detection of hard x-rays (> 20 keV) during the short 'on' state and the
'off' state.  It is suggested that hard-x-ray satellite and balloon
observations be made to check whether the observed significant
changes in relative strength of the pulses and interpulses are a
systematic effect of the 35-day cycle.

4U 1249-28
     H. M. Johnson, Lockheed Palo Alto Research Laboratory, notes
that the eclipsing U Gem-type variable EX Hya is in the error box
of 4U 1249-28, while the catalogued identification PKS 1252-289 is

HDE 245770
     S. Rossiger, Sonneberg Observatory, presents the following
photoelectric UBV observations of the probable counterpart of
A0535+26 for times before, during and after the x-ray flare
reported by Chartres and Li (IAUC 3154):

     1977 UT       V     B     U     1977/78 UT     V     B     U
     Mar.  1.77   8.82  9.47  8.95   Dec.  18.87   8.72  9.41  8.93
           9.86   8.89  9.45  8.93         21.09   8.87  9.45  8.93
          31.82   8.87  9.45  9.00   Jan.  15.96   8.86  9.44  8.88

Mean errors in V and B are about +/- 0.02 magnitude, in U about +/-
0.05 magnitude.  V on 1977 Dec. 18.87 is the brightest known for
this star.  The comparison star is HDE 245906 (Mitt. Veranderl.
Sterne 1976, 7, 105).

     Further visual magnitude estimates: 1977 Nov. 6.86 UT, 12.3
(G. Hurst, Northampton, England); 15.0, 12.3 (J. Bortle, Brooks
Observatory); 29.0, 12.3 (Bortle); Dec. 8.0, 12.3 (Bortle); 18.73,
12.0 (Hurst); 28.0, 12.4 (Bortle); 1978 Jan. 7.75, 12.2 (Hurst).

1978 March 7                   (3184)              Brian G. Marsden

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