Amor asteroid 1990 TR was monitored during three nights shortly after discovery. Obtained lightcurves did not reveal a repeatable curve with two maxima and two minima. However, some features suggest periodicity, and a synodic rotational period P = 6.25 hours was determined. Individual and composite lightcurves are presented. The colors are best represented by the class S

Wisniewski, Wieslaw Z.

English

NASA Technical Reports Server

Asteroids, Comets, Meteors 1991, pp. 653-656
Lunar and Planetary Institute, Houston, 1992
THE UNUSUAL LIGHTCURVE OF 1990 TR
653
Wieslaw Z. Wisniewski, Space Sciences Bld. Lunar and Planetary Laboratory,
University of Arizona, Tucson, Arizona 85721, USA
ABSTRACT
Amor asteroid 1990 TR was monitored during three nights shortly after discovery.
Obtained lightcurves did not reveal a repeatable curve with two maxima and two
minima. However, some features suggest periodicity, and a synodic rotational period
P = 6.25 hours was determined. Individual and composite lightcurves are presented.
The colors are best represented by the class S.
INTRODUCTION
When monitoring lightcurves of asteroids we usually expect to observe two maxima
and two minima, reflecting an elongated shape for the observed object. There
are just a few known objects, e.g. 29 Amphitrite, 51 Namausa, 75 Euridike, 287
Nepthys, and 471 Papagena which show 3 maxima and 3 minima in their lightcurves.
471 Papagena had been extensively studied by several researches with unambiguous
results. (Lustig 1977, Scaltriti and Zappala 1978, Surdej and Surdej 1977, Di Martino
and Cacciatori 1984). Such lightcurves with multiple extrema are interpreted as
caused by irregular shapes and/or by albedo spots on the objects surface. To this list
we may add Earth Approching asteroid 1990 TR.
Asteroid 1990 TR was discovered by S. Ueda and H. Kaneda (IAU Circ. #5121) and
independently by A. V. Tarasova and L. I. Chernykh (IAU Circ. #5137). The ephemeris
based on the discovery predicted the object to be as bright as 12.9 magnitude
in Oct 1990 and still as bright as 14.4 at the end of November.
OBSERVATIONS AND RESULTS
Amor asteroid 1990 TR was monitored during the nights of Nov 13 and 18,1990.
Color measurements were obtained during the night of Nov 19. The data presented
here were obtained with a photoelectric photometer equipped with a Hamamatsu
photomultipier R943-02 on the 1.5 meter telescope at the University of Arizona
Observatory on Mt. Lemmon in the Catalina Mountain range of Tucson. When
monitoring visual lightcurves, two comparison stars in the vicinity of the asteroid were
measured regularly. The ubvwx "subset" f'llters of the eight-color asteroid filters
(Tedesco et al. 1982) were used. Comparison stars' standartization and color
transformation was done during the night of Nov 19. The aspect data and physical
parameters are presented in Table I and Table II respectively.
https://ntrs.nasa.gov/search.jsp?R=19930010076 2020-03-17T08:17:30+00:00Z
654 Asteroids, Comets, Meteors 1991
Unexpectedly, the observations turned out to be quite challenging, as 1990 TR
appeared to be about 1.5 mag fainter (V = 15.2 at maximum) than predicted by the
initial ephemeris. The 5.5 hours of monitoring during the ftrst night reveal_a-_!_ _
complex lightcurve with two maxima and two minima followed by a semi-plateau
(Fig. 1). To be certain that the lightcurve is not modulated by faint stars, the
asteroid path was checked against a Hubble Telescope Guide Star plate. The path i _-._ _
seems to be clear to the best of my knowledge. On Nov 18 a plateau was observed
again (Fig. 2). Assuming that this is the same as the one from Nov 13, the composite
lightcurve was plotted as seen in Fig. 3, from which a synodic period of rotation P =
6hr 15m was determin_i However a period of 7hr 54min _ match both
lightcurves and single measurements from the night of Nov 19 as well.
At present there is not enough data to differentiate between the interpretations of
irregular shape or albedo spots. Perhaps a local topography fike craters _dflat areas
should be taken into consideration. There are small asteroids with lightcurves having_: _: :_
"bump" visible only on occasion. Fig. 4 shows such l_ghtcurve for 1917 t2uyo
observed in Oct 1989. Similarly, Fig. 5 shows two pronounced bumEs (0r 3_908_1980pA. :
A well known asteroid with three maxima, 1580 Betuiia, laas at times a "normal" _6
maxima lightcurve as observed in May 1989 (Fig. 6). There is just a hint of maximum
splitting. If this were the only observation of Betulia we would treat it as a typical asteroid.
As 1990 TR appears to be an interesting candidate for future studies, !calcula_ted
its ephemeris for the next 10 years. In Table III the favorable oppositions are listed.
The +1.5 mag correction to the V magnitude was applied. A t its best, the oqa]ect may
be observed from the southern hemisphere, being 17.1 magnitude at its brightest. _ _
This calls for a CCD camera and a telescope larger than 1 meter. _
With so much successful activity in discoveries of Earth Approaching asteroids,
reaching to fainter and fainter ones - read shorter and shorter observability windows -
the follow up is falling behind. A much better organized, concentrated, effort is
needed. This doesn't mean necessarily an increase in current total observing time.
One or two nights of observations from telescopes well spaced in longitude__!l :_ _
produce by far more complete data than hundreds of hours of observirig at one site
(weather permitting such a long run). This is particularly true if an object turns out
to be a slow rotator, with a period of several days.
ACKNOWLEDGMENTS
Support by Space Engineering Research Center at the University of Arizona and by
NASA Grant NAGW-716 is gratefully acknowledged.
Asteroids,Cornets,Meteors1991 655
Date RA
UT
yr/mo/day h m
90/11/13 Ol 56
90/11/18 01 55
90/11/19 01 55
TABLE I
Aspect data for 1990 TR
Dec Long Lat r _ Phase
(1950) (1950) (1950) (AU) (AU)
26 47 36.55 13.91 1.405 0.432 13.4
27 03 36.45 14.25 1.429 0.467 15.9
27 06 36 45 14.26 1.434 0.474 16.1
Date
9o/11/19
U--V
m
0.81
b-v
m
0.12
TABLE II
Physical Parameters for 1990 TR
V v-w v-x Period amp.
m m m h m
15.22 0.13 0.07 6.15 0.19
H CLASS
m
16.05 S
TABLE III
Favorable oppositions for 1990 TR
Date Dec V mag.
1993 May-Aug -40 17.1 - 18
1996 Apr-Jun -25 18.3 - 19
REFERENCES
Di Martino M., and Caclatori S. (1984) Photoelectric Photometry of 14 Asteroids.
Icarus. 60. 75-82.
Lusdg G. (1977) Die Rotations Periode und die Photoelektdsche [/chtkurve des
Planetoiden 471 Papagena. Astron. & AstroDhvs. Suppl.. 30. I17-I19
Scaltriti F. and Zapalla V. (1978) Photoelectric Photometry of Asteroids 37, 80, 97,
216, 270, 313 and 471. _ 34. 428-435.
Surdej A. and Surdej J. (1977) Rotation Period and Photoelectric I/ghtcurves of
Asteroid 471 Papagena. Astron. & Astrophys. Suppl., 30. 121-124.
Tarasova A. V. and Chemykh L. I. (1990) 1990 TIL IAU Circ. #5137.
Tedesco E. F., Tholen D. J., and ZeIlner B. (1982) The Eight Color Survey: Standard
Stars. Astron. J., 87. 1585-1592.
Ueda S., and Kaneda H. (1990) 1990 TR. IAU Circ. #5121.
656 Asteroids, Comets, Meteors 1991
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184
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166
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I 16.v
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Fig. 4. klghlcnr_ o( 1917 Cuyo olxaJ_,,don Oct 7. 1989. i
xi
0
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2
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4
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lit 1989 Msy 25
!_8, 6. l.i|Ncurve of 1580Retulimoblalnedon M.y 24-25, 1989.
13.4
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10


The unusual lightcurve of 1990 TR

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