Central Bureau for Astronomical Telegrams
IAUC 6485: MICROLENSING EVENT IN LMC; C/1996 Q1
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Circular No. 6485
Central Bureau for Astronomical Telegrams
INTERNATIONAL ASTRONOMICAL UNION
Postal Address: Central Bureau for Astronomical Telegrams
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)
Phone 617-495-7244/7440/7444 (for emergency use only)
MICROLENSING EVENT IN LARGE MAGELLANIC CLOUD
The MACHO collaboration (cf. IAUC 6312, plus D. Minniti)
reports the discovery of a likely gravitational microlensing event
in progress toward the Large Magellanic Cloud: "The star in
question is located at R.A. = 5h34m44s.4, Decl. = -70o25'07"
(equinox J2000.0). The star was constant at R = 19.6, V = 19.6
during 1993-1995 and has brightened by 0.6 mag during 1996 Sept.
The color appears unchanged. The current best microlensing fit to
Mt. Stromlo data predicts that the star should reach a peak of R
and V < 18.8 between Oct. 9 and Nov. 28, and then decline
symmetrically. This fit indicates an Einstein-diameter crossing
time of 120 +/- 30 days, which would contribute a significant
optical depth to microlensing towards the LMC. Accurate photometry
and low-resolution spectroscopy of this star at regular intervals
over the next few weeks will be valuable to test the microlensing
interpretation. Photometric measurements may possibly detect
light-curve deviations that are due to a breakdown of the usual
point-source, point-lens, or constant-velocity assumptions. If
these exotic effects are detected, it is usually possible to
estimate the distance to the lensing object. A finding chart is
available on the MACHO Alert web page (cf. IAUC 6312, 6361) or ftp
site darkstar.astro.washington.edu (directory macho/Alert/96-LMC-2).
Potential observers are requested to contact
macho@astro.washington.edu, or A. Becker at telephone 206-543-1979
or D. Bennett at telephone 219-631-8298, to coordinate observations."
COMET C/1996 Q1 (TABUR)
M. Womack and D. Suswal, Pennsylvania State University at Erie,
report on observations of HCN and CO in comet C/1996 Q1 with the
National Radio Astronomy Observatory's 12-m telescope at Kitt Peak:
"We have detected the HCN J=1-0 rotational line at 89 GHz on Oct. 6
and 7 UT. The integrated line-flux area is 0.068 +/- 0.009 K km/s
(antenna temperature scale). The FWHM linewidth is about 1.5 km/s
and the line center is not measurably shifted from the ephemeris
velocity. Assuming a rotational temperature of 50 K, we derive an
HCN-production rate of Q(HCN) approximately 2.5 x 10E25 mol/s at r
= 1 AU. The CO J=1-0 line could not be detected down to a 3-sigma
level of 0.04 K km/s."
Naked-eye m1 estimates: Sept. 27.12 UT, 5.7 (M. V. Zanotta,
Mount Generoso, Italy); Oct. 6.20, 5.3 (A. Pereira, Cabo da Roca,
Portugal); 7.20, 5.2 (C. Vitorino, Cabo da Roca, Portugal).
(C) Copyright 1996 CBAT
1996 October 8 (6485) Daniel W. E. Green
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