1
PHOTOMETRY OF THE MARS CROSSING ASTEROIDS
3800 KARAYUSUF AND 1951 LICK
William H. Ryan and Eileen V. Ryan
Magdalena Ridge Observatory, New Mexico Institute of Mining
and Technology, Socorro, NM 87801
bryan@nmt.edu
Robert Godfrey and Garrett Wright1
Eastern Arizona College, Thatcher, Arizona
Carlos T. Martinez
Department of Physics and Astronomy, University of New
Mexico, Albuquerque, NM 87131
1
Current address: Raytheon Corporation, Tucson, Arizona
(Received:
Revised: )
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The Mars-crossing asteroids 3800 Karayusuf and 1951 Lick were
the primary targets of an undergraduate student observing project
supported by the Arizona Space Grant Program at Eastern Arizona
College in the Spring of 1998. Additional data for Karayusuf were
collected in January and July of 2000.
Observations
The images were obtained using the 1.8-meter Vatican Advanced
Technology Telescope at Mt. Graham International Observatory.
The Harris R was used for most of the frames with exposure times
that ranged from 60-180 seconds. The observational circumstances
are given in Table I. This table includes the UT date of midobservation, target name, solar phase angle, mean R magnitudes,
reduced to unit heliocentric and geocentric distances, and
observer's initials. The data for the March 1998 run were obtained
during full moon conditions and through thin clouds. Since this
resulted in very high sky background, approximately one-quarter
of the images had to be discarded since the object signals
exceeded the linearity limit of the detector. The data obtained in
2000 was obtained under photometric to light cirrus conditions.
(Calibration frames for the March 98 run were taken . . . .)
Reductions and Analysis
The images were processed and aperture photometry was
performed using IRAF (Tody, 1993). Differential magnitudes were
calculated between the asteroid and an ensemble of 2-5
comparison stars yielding typical errors on the order of 0.02 mag
for the March 1998 run and less than 0.01 mag for the 2000 runs.
Additionally, BVRI sequences taken during 2000 and were
calibrated using Landolt (1992) standards. (Calibration frames for
the March 98 run were taken . . . .) Lightcurves were generated for
using either the heliocentric and geocentric distance corrected R
magnitudes, or simply differential magnitudes if no calibration we
available. These data were then analyzed using the standard
technique described by Harris and Lupishko (1989) and Harris, et
al (1989) to generate composite lightcurves.
Results for Individual Objects
1951 Lick
1951 Lick has been identified as an A type asteroid (Bus and
Binzel, 2002) and has been observed previously to have a
rotational period of 5.3 hours (Pravec, 1998) It was observed for
the present work on March 9 and 13, 1998. The resulting
composite lightcurve is shown in Figure 1 and displays a
rotational period of 5.2980.002 hours. (The data were calibrated
with frames from 2005 and assuming a V-R of XXX, which was
generated synthetically using SMASS spectra)
3800 Karayusuf
This is an S type asteroid (Bus and Binzel, 2002) with no previous
published rotational period. The composite lightcurve generated
from data obtained on March 11-12, 1998 is shown in Figure 2
and displays a period of 2.2350.003 hours. The additional data
that was discarded was also consistent with this period. However,
the errors were much larger, typically of magnitude 0.05 or more,
due to the high sky background and the object counts extending
into the non-linearity region of the chip. Therefore, these data
were not included in the quantitative analysis.
Approximately 3 hours of data were obtained on January 6, 2000
during a gap in another observing project with the resulting
composite lightcurve shown in Figure 3. Although the duration of
the observations was ~1.3 cycles, interference due to a field star
resulted in only about 80% phase coverage. Unfortunately, this
gap occurred at a critical time when Karayusuf was beginning to
display the tri-modal behavior that was only hinted at in the 1998
data. Since, in the context of the incomplete phase coverage, this
behavior would lead one to the interpretation that the lightcurve
had a shorter period, data from the two subsequent rotational
cycles are plotted with different symbols to elucidate the
2.220.02 hour period. The time between the primary minima is
also consistent with the asymmetric nature of the March 1998
composite curve. The analysis of two BVRI color sequences from
this night yielded the following observed (not corrected for solar
colors) color indices for 3800 Karayusuf: B-V=0.900.01, VR=0.490.02, and V-I=0.860.07, which are consistent with its
classification as a S type asteroid (Shevchenko and Lupishko,
1998). The asteroid was again observed briefly on July 4-5, 2000.
The resulting composite lightcurve, assuming a period of
2.2330.003 hours, is shown in Figure 4. Again, although only
~80% rotational phase coverage was obtained, the trimodal nature
of the lightcurve is apparent.
Acknowledgements
This work was supported by the Arizona Space Grant Consortium
(NASA) and is based on observations with the VATT: the Alice P.
Lennon telescope and the Thomas J. Bannan Astrophysics
Facility.
Minor Planet Bulletin xx (xxxx)
2
References
Bus, S.J, and Binzel, R. P. (2002). "Phase II of the Small MainBelt Asteroid Spectroscopic Survey: A Feature-Based
Taxonomy", Icarus 158, 146-177
Harris, A.W. and Lupishko, D.F. (1989). “Photometric lightcirve
observation and reduction techniques.” In Asteroids II (R. P.
Binzel, M. Matthews, and T. Gehrels, eds.) pp 39-53. Univ.
Arizona Press, Tucson.
Harris, A.W., Young, J.W., Bowell, E., Martin, L. J., Millis, R. L.,
Poutanen, M., Scaltriti, F., Zappala, V., Schober, H. J.,
Debehogne, H, and Zeigler, K. (1989).
“Photoelectric
Observations of Asteroids 3, 24, 60, 261, and 863.” Icarus 77,
171-186.
Landolt, A.U. (1992). "UBVRI photometric standard stars in the
magnitude range 11.5<V<16.0 around the celestial equator",
Astron. J., 104, 340-371
Pravec, P., personal communication and (website)
Shevchenko, V.G. and Lupishko, D.F. (1998). "Optical Properties
of Asteroids from Photometric Data", Solar System Research 32,
220-232
Tody, D. (1993). "IRAF in the Nineties", In Astronomical Data
Analysis Software and Systems II, A.S.P Conference Ser., Vol 52,
eds. Hanisch, R.J., Brissenden, R.J.V., and Barnes, J., 173.
-------------tables and figure captions----------------------------------Table I: Observational circumstances
UT
1998
1998
1998
1998
2000
2000
2000
Date
Asteroid
Mar 9.4
1951
Mar 11.3
3800
Mar 12.3
3800
Mar 13.3
1951
Jan 6.5
3800
Jul 4.2
3800
Jul 5.2
3800
Phase Rmean
38.2
30.7
31.2
39.9
28.5 16.05
43.3 (maybe)
43.2 (maybe)
Observers
WHR,EVR,GW
WHR,EVR
WHR,EVR,RG
WHR,EVR,RG
WHR,EVR
WHR,EVR,CTM
WHR,EVR,CTM
Figure 1. Composite lightcurve for 1951 Lick from March 1998.
Figure 2. Composite lightcurve for 3800 Karayusuf from March
1998.
Figure 3. Composite lightcurve for Karayusuf 3800 from the
single night of 6 January 2000. Note that data taken during
different rotational cycles are plotted with different symbols.
Figure 4. Composite lightcurve for Karayusuf 3800 from July
2000.
Minor Planet Bulletin xx (xxxx)