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IAUC 7485: MXB 1659-29; C/1996 E2, C/1997 K5, C/1997 K6, C/1998 F2

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                                                  Circular No. 7485
Central Bureau for Astronomical Telegrams
INTERNATIONAL ASTRONOMICAL UNION
Mailstop 18, Smithsonian Astrophysical Observatory, Cambridge, MA 02138, U.S.A.
IAUSUBS@CFA.HARVARD.EDU or FAX 617-495-7231 (subscriptions)
CBAT@CFA.HARVARD.EDU (science)
URL http://cfa-www.harvard.edu/iau/cbat.html  ISSN 0081-0304
Phone 617-495-7440/7244/7444 (for emergency use only)


MXB 1659-29
     R. Wijnands, Massachusetts Institute of Technology; T.
Strohmayer, Goddard Space Flight Center; and L. M. Franco,
University of Chicago, report:  "Using archival data from the PCA
instrument on the Rossi X-ray Timing Explorer, we have detected
x-ray brightness oscillations with a frequency of about 567 Hz in
five type-I x-ray bursts observed from the x-ray transient and
eclipsing binary MXB 1659-29.  This source is still active more
than a year after its reappearance in Apr. 1999 (IAUC 7138, 7139).
The oscillations have fractional rms amplitudes of 10-20 percent
and are most likely related to the spin frequency of the neutron
star in MXB 1659-29.  The oscillations are preferentially detected
between orbital phase 0.05 and 0.75 (using the orbital ephemeris
provided by Wachter et al. 2000, Ap.J. 534, 367) and only
marginally detectable during intervals of x-ray dipping activity.
This strongly suggests that the mechanism behind the x-ray dips
inhibits the detectability of the oscillations.  More observations
are needed of MXB 1659-29 outside the x-ray dips and x-ray eclipses
(i.e., between orbital phase 0.05 and 0.75) in order to study these
oscillations before the source returns to quiescence."


COMETS C/1996 E2, C/1997 K5, C/1997 K6, C/1998 F2 (SOHO)
     Further to IAUC 7480, D. Hammer and D. Biesecker have provided
measurements of four more Kreutz sungrazing comets detected by SOHO
instruments; discovery positions and citations to the MPECs
containing the reduced measurements and orbits by B. G. Marsden are
given below.  The 1997 objects (which both showed obvious tails)
were found by M. Oates in archival images, and the other two comets
were found by M. Meyer.  All four comets were seen with the C2
coronagraph, but only C/1996 E2 (which showed cometary appearance
and a tail) was also seen with C3.

  Comet         1996 UT           R.A. (2000) Decl.       MPEC
  C/1996 E2     Mar. 10.281      23 44.2      - 4 48      2000-Q18

  Comet         1997 UT           R.A. (2000) Decl.       MPEC
  C/1997 K5     May  20.264       3 46.9      +18 14      2000-Q18
  C/1997 K6          31.188       4 31.0      +20 34      2000-Q18

  Comet         1998 UT           R.A. (2000) Decl.       MPEC
  C/1998 F2     Mar. 27.879       0 33.5      + 2 06      2000-Q35

                      (C) Copyright 2000 CBAT
2000 September 1               (7485)            Daniel W. E. Green

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