Central Bureau for Astronomical Telegrams
IAUC 6935: MICROLENSING EVENT; 1998 KY26
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Circular No. 6935
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)
BMARSDEN@CFA.HARVARD.EDU or DGREEN@CFA.HARVARD.EDU (science)
URL http://cfa-www.harvard.edu/iau/cbat.html
Phone 617-495-7244/7440/7444 (for emergency use only)
MICROLENSING EVENT
A. Becker, on behalf of the MACHO Collaboration (cf. IAUC
6845), reports the discovery of a likely exotic gravitational
microlensing event in progress toward the Small Magellanic Cloud:
"The star in question is located at R.A. = 0h45m35s.2, Decl. =
-72o52'34" (equinox 2000.0). The star was constant at R = 21.7, V
= 21.8 during 1993-1998 and was observed to have brightened
significantly on 1998 May 25. Follow-up observations taken with
the Cerro Tololo 0.9-m telescope indicate a strong deviation from
standard microlensing occuring near June 5, where the star
brightened from a magnification of 3 to > 13. This is thought to
have been a caustic crossing due to a binary lensing system.
Preliminary binary microlensing fits by the MACHO team and S. Rhie
indicate that a second caustic crossing will occur within about 2
weeks, possibly between June 21 and 27, although the date is
extremely uncertain. This will consist of a sharp rise and fall in
brightness of > 2 mag within a few hours. Very frequent photometry
(hourly or more often) during the second caustic crossing will
provide valuable information on the transverse velocity of the
lensing system, which helps to constrain the lens mass and
distance. Spectroscopy of the brightened star will also be
important for estimating the source angular diameter. A finding
chart and additional information are available by anonymous ftp at
darkstar.astro.washington.edu:/macho/Alerts/98-SMC-1 or at the
MACHO Web site (cf. IAUC 6312, 6720). Observers are asked to
contact macho@astro.washington.edu, A. Becker at telephone
206-543-9205, or D. Bennett at telephone 219-631-8298, to
coordinate observations."
1998 KY26
S. Ostro, L. Benner, J. Giorgini, K. Rosema, and D. Yeomans,
Jet Propulsion Laboratory, write: "We have detected Goldstone
(8510-MHz, 3.5-cm) radar echoes from 1998 KY26 (MPEC 1998-L02) on
June 6-8 that have a bandwidth > 11 Hz, providing the constraint P
< 0.55D, where P is rotation period in min and D is the diameter in
m (Ostro et al. 1995, Science 270, 80). Delay-Doppler images with
a range resolution of 19 m do not resolve the asteroid, suggesting
a diameter no greater than 40 m and therefore P < 22 min."
(C) Copyright 1998 CBAT
1998 June 9 (6935) Daniel W. E. Green
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