Central Bureau for Astronomical Telegrams
IAUC 6402: 1996 JA1
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Circular No. 6402
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)
1996 JA1
MPEC 1996-K01 gives word of the discovery, by T. Spahr at the
University of Arizona on May 14.4 UT, of a bright asteroidal object
rapidly approaching the earth. The extensive follow-up observations
(published also on MPEC 1996-K03 and -K04) show that the object
(a = 2.53 AU, e = 0.70, i = 22 deg) will pass only 0.00303 AU from
the center of the earth on May 19.690 UT. With absolute visual
magnitude H = 21.0, 1996 JA1 is probably the largest such object
ever observed to approach the earth so closely. The object should
brighten to about V = 11, and it will be necessary for observers to allow
for parallax in their ephemerides; a facility for computing topocentric
ephemerides at UT intervals as short as 10 min is available in the WWW
at http://cfa-www.harvard.edu/cfa/ps/NEO/1996JA1.html.
D. J. Tholen, University of Hawaii, reports that his single-filter
photometry with the 2.2-m reflector showed 1996 JA1 to brighten by
about 0.75 mag between May 17.254 UT and what was a fairly broad maximum
around May 17.311. The object was almost 0.5 mag fainter by May 17.353,
indicating that the rotation period was rather more than 5.5 hr. On the
following night, he observed a broad maximum around May 18.297 and
a sharp minimum on May 18.338, suggesting eight cycles between the
maxima, i.e., a rotation period of 5.92 hr. By May 18.353 there had
again been brightening by 0.3 mag. The 0.75-mag range between the May 18
maximum and minimum suggests that the object was very close to minimum
when first observed on May 17.254; nine cycles between then and May 18.338
correspond to a revolution period of 5.78 hr, in plausible agreement
with the value established from the maxima. Calibration using a set
of solar-color Landolt standards confirmed that the adopted H = 21.0
(with slope parameter G = 0.15) is close to the object's mean value.
M. Hicks and J. Collins, Lunar and Planetary Laboratory, University
of Arizona, report: "CCD spectra (range 0.55-1.05 microns, resolution 1.5 nm)
were obtained with the Catalina Station 1.54-m telescope on May 17 and 18.
Preliminary reductions of the first night's data indicate that 1996 JA1
is of Tholen's V type (Tholen and Barucci 1989, Asteroids II, p. 298;
Binzel and Xu 1993, Science 260, 186). The relative depth of the pyroxene
absorption band centered at 0.92-0.94 micron is 0.75 for 1996 JA1, compared
to 0.72 for (4) Vesta. The spectrum also shows the characteristic reddish
slope, increasing by 18 percent over the range 0.55-0.70 micron."
(C) Copyright 1996 CBAT
1996 May 18 (6402) Brian G. Marsden
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