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IAUC 4803: Occn OF 28 Sgr BY TITAN; G29-38

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IAUC number

                                                 Circular No. 4803
Central Bureau for Astronomical Telegrams
Postal Address: Central Bureau for Astronomical Telegrams
Smithsonian Astrophysical Observatory, Cambridge, MA 02138, U.S.A.
Telephone 617-495-7244/7440/7444 (for emergency use only)
TWX 710-320-6842 ASTROGRAM CAM     EASYLINK 62794505

     The following additional reports have been received (cf. IAUC
4801; given as UT + July 3d22h; t1, t4 are beginning and end times
of the star's fading, and t2, t3 are beginning and end times of the

Observer           t1           t2        flash        t3          t4
Elliott          39m10s       40m30s     42m00s      43m50s      44m50s
Kidger           38 40        39 33                  41 25       42 33

A. Elliott (Reading, England).  Long. = -0 56'39.7, Lat. =
  +51 25'08.6.  0.25-m reflector + image intensifier.  Central flash
  lasted from 42m00s to 42m15s.  Communicated by D. W. Dunham, IOTA.
M. Kidger, R. Casas, L. Sanchez, A. Gomez, and A. Jones (Tenerife).
  0.50-m telescope + V filter.  At t1, a shallow fading (0.33 mag) of
  duration 7 s occurred; a similar event, of duration 3 s, occurred
  51 s after t3.  A complete obscuration of duration 12 s was seen
  at 38m52s; a deep fading of duration 9 s was also seen at 42m02s.
  Another complete obscuration, of duration 18 s, occurred at 39m11s.
  For the final 4 s before occultation, the star was virtually
  undimmed.  After t3, a slow rise over 21 s to maximum brightness
  was seen.  A post-occultation decline to nearly complete
  disappearance was seen at t4; no equivalent event was seen prior
  to occultation.

     R. E. Nather, Department of Astronomy, University of Texas,
writes:  "High-speed photometry of the white dwarf variable G29-38,
obtained by the Whole Earth Telescope sites at McDonald Observatory,
Mauna Kea, Anglo-Australian Observatory, Kavalur, South African
Astronomical Observatory, Haute Provence, LNA (Brazil), and European
Southern Observatory, shows that the pulse arrival times of the
615.15-s pulsation display systematic variations best explained
by light travel time effects produced by reflex motion about an unseen
orbital companion.  Our best fitting model to the observations yield
an orbital eccentricity of 0.71, a minimum mass of 0.5 M solar mass,
a projected semi-major axis of 0.22 A.U., and a time of periastron
passage given by T(periastron) = JD 2447474 + 115 (+/- 16) E.  The
pulsation data suggest a low inclination for the orbit, implying that
the unseen companion is either a neutron star or black hole.  Velocity
variations of up to 40 km/s can be expected."

1989 July 6                    (4803)             Daniel W. E. Green

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