Occultations of stars by planets, satellites, planetary ring systems, asteroids, and comets provide valuable opportunities to probe the Solar System in ways otherwise impossible from the surface of the earth. For example, one can precisely measure the size and shape of objects which are much too small to be resolved directly, accurately map the structure and transparency of ring systems, and detect the faintest trace of an atmosphere. In this investigation, researchers identify upcoming occultations through wide-ranging computer searches, provide accurate predictions for the more important events, and observe selected occultations with our specially designed portable photometric equipment. During the past year, researchers produced accurate predictions for an occultation of AG+40 degrees 0783 by 324 Bamberga on 8 December 1987 and coordinated efforts to observe this event. The occultation was successfully observed at 13 sites including two manned by Lowell Observatory astronomers

Millis, Robert L.

English

The planetary occultation program began at Lowell Observatory in 1973 with a worldwide campaign to observe mutual occultations and eclipses of the Galilean Satellites. Then the temperature profile of the Martian atmosphere was measured from data taken during the occultation of epsilon Geminorum, the Rings of Uranus were discovered as they occulted SAO 158687, and the dimensions of Pallas were measured when that minor planet occulted SAO 85009. In 1979 the present grant was initiated, providing funds for portable photometric instrumentation used to observe occultations by asteroids as well as by Uranus and Neptune. Software for predicting occultations of catalog stars by asteroids, planets, and comets was written in 1983. Lowell currently provides most of the available predictions for asteroid occultations. Realizing in 1983 that the lack of a high-quality astrometric telescope dedicated to occultation work was limiting progress, an 18-inch, F/8 lens was acquired and adapted to an existing mounting at Lowell. Although acquisition of the lens and implementation of the new telescope has been accomplished primarily with non-grant funds, the instrument makes a major contribution to occultation research

NASA Technical Reports Server

FLAGSTAFF, ARIZONA 86001 
, /I /  - .s 7 PLANETARY RESEARCH CENTER - /  -e< 
LOWELL OBSERVATORY 
5-3 5- 37 
NASA GRANT NSG-7603 - 
OCCULTATION STUDIES O F  THE SOLAR SYSTEM 
Semi-Annual Status Report No. 15 
1 July 1986 through 31 December 1986 
SUBMITTED: 18 February 1987 
INASA-Ci3-180143) OCCULTAXlCN STUDIES OF THE N87-167 29 
S C L A f i  SYSTEM SeEiannual  S t a t u s  &€port ,  1 
Jul. - 3 1  Dec. 14FO (Lowell Ctservatory)  
4 P  CSCL 03A U n c l a s  
G3/89 43481 
Robert L. Millis 
Principal Investigator 
https://ntrs.nasa.gov/search.jsp?R=19870007287 2020-03-20T12:11:13+00:00Z
Page 2 
INTRODUCTION 
The planetary occultation program began at Lowell Observatory in 1973 when 
Brinkmann and Millis (1973) coordinated a worldwide campaign to  observe mutual 
occultations and eclipses of the Galilean Satellites. Subsequently the temperature 
structure of the Martian atmosphere was measured from data taken during the oc- 
cultation of e Geminorum (Wasserman, Millis, and Williamon 1977); the Rings of 
Uranus were discovered as they occulted SA0  158687 (Millis, Wasserman, and Birch 
1977); and the dimensions of Pallas were measured when that minor planet occulted 
SA0 85009 (Wasserman e t  al. 1979). In 1979 the present grant was initiated and 
has supported our occultation research since that time. The grant provided funds 
for portable photometric instrumentation which we have used to  observe occulta- 
tions by asteroids as well as occultations by Uranus and Neptune (e.g., Millis e t  al. 
1981, 1983, 1984 and 1985). Software for predicting occultations of catalog stars by 
asteroids, planets, and comets was written in 1983. We currently provide most of 
the available predictions for asteroid occultations (Wasserman, Bowell, and Millis 
1983 and 1985). Realizing in 1983 that the lack of a high-quality astrometric tele- 
scope dedicated to  occultation work was limiting progress in this field, we acquired 
an 18-inch, F/8 lens and adapted i t  t o  an existing mounting at Lowell. Although ac- 
quisition of the lens and implementation of the new telescope has been accomplished 
primarily with non-grant funds, the instrument is making a major contribution to  
this research. 
Occultation research is inherently an opportunistic endeavor. We attempt to  
take an integrated approach in our program with attention to  long-range identifica- 
tion of upcoming opportunities, intensive prediction refinement efforts for important 
events, and, most importantly, observation of occultations using portable or fixed 
telescopes around the world. The focus of our research will necessarily shift from 
year to year depending on what occultations are available. In the past year, we have 
concentrated on analysis of existing observations and on bringing the astrograph to  
its full potential. Few attractive occultations occurred in the United States. Only 
one occultation expedition' was launched by our group during the year, and i t  was 
unsuccessful because of poor weather. In 1987 the observational side of our program 
will pick up as we bring the astrograph into full use and pursue the asteroid and 
Pluto occultations that have already been identified. 
ACCOMPLISHMENTS O F  THE PAST SIX MONTHS 
Two and a half years ago we observed an occultation of a star by Ceres using 
portable gear along the west coast of Mexico. This occultation was also observed by 
colleagues at  the University of Arizona, the Massachusetts Institute of Technology, 
the Florida Institute of Technology, the University of Maryland, and others. The 
analysis of the total data set from this occultation was undertaken by our group 
and turned out t o  be a lengthy study. Inconsistencies in the various data sets 
had to be iesolved and mdtitudinous co!!ab=rators consulted z.s the investination 0 
Page 3 
progressed. Only within the last few weeks was the job completed and the resulting 
paper accepted for publication in Icarus (Millis e t  al. 1987). We believe that the 
results justify the investment of our time. The dimensions of Ceres were determined 
with an uncertainty of only about 2%, the bulk density of the asteroid computed to 
within 5%, and its shape shown to be that of an object in hydrostatic equilibrium. 
In 1982 Millis observed an occultation of a star by Uranus and the Rings with 
the 1.5-meter Infrared Flux Collector at Teide Observatory in the Canary Islands. 
During the reporting period, Millis and Wasserman in collaboration with Richard 
French of MIT completed an anlysis of those data. The results of that study were 
recently published in Icarus (Millis, Wasserman, and French 1987). Using Elliot e t  
aL’s (1984) square-well model, midtimes, widths, and optical depths of the individual 
rings were determined. Because this occultation was observed “simultaneously” 
from Chile, Pic du Midi, and the Canary Islands, the data helped provide strong 
constraints on ring orbital elements. It was also possible from our data to  derive 
the atmospheric temperature profile for the planet. 
A review paper by Millis (1986) entitled “Occultation Studies with Small Tele- 
scopes” was recently published. Also appearing in 1986 was the abstract of a paper 
discussing the results from an occultation by Antigone (Wasserman, Millis, and 
Franz 1986). 
Franz and Nye have devoted much effort in the past year to  understanding 
and improving the performance of the 18-inch astrograph. A new right ascension 
drive was installed, and high-quality glass filters were obtained to replace the in- 
ferior gelatin and plexiglass filters used in the past. It is now possible to take 
well-guided exposures in which the filter does not limit the attainable astrometric 
accuracy. The telescope has been used regularly since the fall of 1986 and is being 
mid-January 1987 an occultation by Hygiea was observed at  Table Mountain Ob- 
servatory (Harris 1987). Prediction refinement for that event was done entirely with 
our telescope. As we continue to improve the 18-inch astrograph and refine our plate 
reduction procedures, we expect that this telescope will play an increasing role in 
the progress of occultation research. Already plates have been taken to extend Mink 
and Klemola’s (1985) predictions for Pluto occultations to fainter magnitude limits. 
Photometry by Bosh e t  al. (1986) has shown that all of the stars identified by Mink 
and Klemola are significantly brighter than required to give an occultation with an 
adequate signal-to-noise ratio. We have taken plates covering Pluto’s path in the 
sky during 1987 and 1988. These plates were scanned by Anita Killian of MIT, and 
many potential occultation candidates missing from Mink and Kiemola’s list were 
found. 
routilicly applied io ~ i c i i l t a t i ~ i i  ijidictioii work. T ~ c  r s d t s  are e z ~ ~ ~ r a g i ~ g .  In 
During 1986, Millis, in his role as Chairman, orchestrated a reorganization of 
the IAU Commission 20 Working Group on Occultations. Regional coordinators 
have been recruited who are responsible for funneling information to observers in 
Page 4 
their areas. Additionally, 16 occultations occurring in 1987 have been targeted for 
special attention. The Lowell and Lick astrographs are being used to  provide refined 
predictions for these events. Of the three events that  have occurred so far this year, 
one was successfully observed. The track of one of the other two moved off the Earth, 
while that of the third drifted south into Central America, where few observers are 
available. We expect that by concentrating prediction efforts on a limited number 
of occultations, the observational success rate will be improved. 
B I B L I O G R A P H Y  (papers published or in press during the past six months) 
1. Millis, R. L., Wasserman, L. H., and French, R. G. 1987. Observations of the 22 
April 1982 Stellar Occultation by Uranus. Icarus 69, 176-184. 
2. Millis, R. L., et al. 1987. The size, shape, density, and albedo of Ceres from its 
\ occultation of BDS8'471. I c a r m ,  in press. 
3. Millis, R. L. 1986. Occultation studies with small telescopes. In Instrumenta- 
tion and Research Programmes for Small Telescopes (J. B. Hearnshaw and P. L. 
Cottrell, Eds.) Reidel, Dordrecht. 
4. Wasserman, L. H., Millis, R. L., and Franz, 0. G. 1986. T.he Occultation of 
AG+20°1138 by 129 Antigone on 11 April 1985. Bull. Amer. Astron. SOC. 18, 
797. 
BUDGET 
Expenditures during the reporting period under this grant were closely in line 
with the proposal budget. 


Occultation studies of the Solar System

N89-16671 i - 
N A T I O N A L  AERONAUTICS A N D  SPACE ADMINISTRATION 
RESEARCH AND TECHNOLOGY RESUME 
O c c u l t a t i o n  S t u d i e s  o f  t h e  S o l a r  Sys t em 
NASA G r a n t  NSG-7603 
L o w e l l  O b s e r v a t o r y  
1 4 0 0  W e s t  Mars Hill Road 
F l a g s t a f f ,  A r i z o n a  8 6 0 0 1  
T I T L E  1 
PERFORMING O R G A N I Z A T I O N  
INVESTIGATOR'S N A M E  
Robert L .  M i l l i s  
DESCRIPTION la. Llricf rtalcment on rhatepy of  inuerligalion; b. Progress and occomplishmcntr o f p r i o r  year, c. What wl l l  be occomplirhed 
t h u  year. or well or how and w h y ;  and d. Summary bibliography) 
a. Strategy. Occultations of stars by planets, satellites, planetary ring systems, asteroids, and 
comets provide valuable opportunities to probe the Solar System in ways otherwise impossible from 
the surface of the Earth. For example, one can precisely measure the size and shape of objects which 
are much too small to be resolved directly, accurately map the structure and transparency of ring 
systems, and detect the faintest trace of an atmosphere. In this investigation, we identify upcoming 
occultations through wide-ranging computer searches, provide accurate predictions for the more 
important events, and observe selected occultations with our specially designed portable photmetric 
equipment. 
b. Accomplishments. During the past year, we produced accurate predictions for an occultation of 
AG+40°0783 by 324 Bamberga on 8 December 1987 and coordinated efforts to observe this event. 
The occultation was successfully observed at 13 sites including two manned by Lowell Observatory 
astronomers. We presented a preliminary analysis of the data at the Asteroids I I  Conference held in 
Tucson in March 1988. We also have devoted a lot of time to producing an accurate prediction for the 
9 June 1988 occultation of a star by Pluto. Prediction of this important occultation is complicated by 
the presence of Pluto's satellite, Charon. We have worked closely with astronomers at MIT, Lick 
Observatory, and the U.S. Naval Observatory, in the application of a variety of astrometric 
approaches to this problem. If the occultation is successfully observed, there will be a major advance 
in our knowledge of the most distant planet. Finally, Millis, in collaboration with Dr. David Dunham, 
has recently completed a lengthy review paper on occultation studies of asteroids. 
c. Expected Accomplishments. Next year we expect to complete an analysis of existing 
observations of occultations by the asteroids 47 Aglaja and 324 Bamberga. We expect to participate 
fully in the analysis of observations of the 9 June Pluto occultation, should we or our collaborators 
succeed in observing it. Additionally, 1989 will be a banner year for occultation observers, with 
outstanding occultations involving Saturn, Vesta, Ceres, Kleopatra, Bamberga, and Brixia predicted to 
occur. We intend to observe most, if not all of these. The Saturn occultation provides an opportunity 
to probe that planet's rings with a resolution approaching that achieved by the Voyager spacecraft. 
Kleopatra is believed, on the basis of radar observations, to be extremely elongated. Occultation 
observations can check that result. Vesta is the one remaining asteroid whose mass is well known, 
but whose size is not. We plan to measure the size and thereby determine Vestals density, which in 
turn gives a direct clue to this unusual asteroid's composition. 
ORIGINAL PAGE IS 
OF POOR QUALITY 
93 
https://ntrs.nasa.gov/search.jsp?R=19890007300 2020-03-20T03:23:08+00:00Z
SUMMARY BIBLIOGRAPHY 
Millis, R. L., and Dunham, D. W.: Precise Measurement of Asteroid Sizes and Shapes 
from Occultations. In Asteroids / I  (T. Gehrels and R. Binzel, eds.), University of 
Arizona Press, submitted 1988. 
Millis, R. L., Wasserman, L. H., Franz, 0. G., Nye, R. A., Oliver, R. C., Kreidl, T. J., 
Jones, S. E., Hubbard, W., Lebofsky, L., Goff, R., Marcialis, R., Sykes, M., 
Frecker, J., Hunten, D., Zellner, B., Reitsema, H., Schneider, G., Dunham, E., 
Klavetter, J., Meech, K., Oswalt, T., Rafert, J., Strother, E., Smith, J., 
Povenmire, H., Jones, B., Kornbluh, D., Reed, L., Izor, K., A'Hearn, M. F., 
Schnurr, R., Osborn, W., Parker, D., Douglas, W. T., Beish, J. D., Klemola, 
A. R., Rios, M., Sanchez, A., Piironen, J., Mooney, M., Ireland, R. S., and Leibow, 
D.: The Size, Shape, Density, and Albedo of Ceres from Its Occultation of 
BD+8"471. /carus 72, 507-51 8, 1987. 
Wasserman, L. H., Bowell, E., and Millis, R. L.: Occultations of Stars by Solar System 
Objects. VII. Occultations of Catalog Stars by Asteroids in 1988 and 1989. 
Astrun. J. 94, 1364-1372, 1987. 
Hubbard, W. B., Nicholson, P. D., Lellouch, E., Sicardy, B., Brahic, A., Vilas, F., 
Bouchet, P., McLaren, R. A., Millis, R. L., Wasserman, L. H., Elias, J. H., 
Matthews, K., and McGill, J. D.: Oblateness, Radius, and Mean Stratospheric 
Temperature of Neptune from the 1985 August 20 Occultation. lcarus 72, 
635-646. 1987. 
94 


Occultation studies of the solar system

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