The series of astrometric observations of the satellites of the trans-martian planets re-established at the McDonald Observatory in 1972 is continued. The positions deduced from photographic observations of the jovian system obtained during the 1975-76 opposition are presented together with the discovery positions of four asteroids found on these plates

Benedict, G. F.

Mulholland, J. D.

Shelus, P. J.

English

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https://ntrs.nasa.gov/search.jsp?R=19790009598 2020-03-22T01:25:20+00:00Z
WASTROMETRIC OBSERVATIONS OF THE FAINT SATELLI;-- S OF JUPITER
DURING THE 1975-1976 OPPOSITION
J. Derral Mulholland, Peter J. Shelus, and G. F. Benedict
McDonald Observatory and Department of Astronomy
University of Texas 3t Austin
Austin, Texas 78712 U.S.A.
(NASA-CF-158105)	 ASTFCMETFIC OBSEFVATICNS
nF THE FA14T SATELLITES OF JUEITEF DOFING
THE 1975 - 1S76 OPPOSITICN (McDonald
Observatory, Austin, Tex.)	 6 p HC A02/MF
A01	 CSCL 03A G3/89
N79-17769
Unclas
14032
ABSTRACT
Precise positions for the faint satellites VI•
. XII of	 'l
Jupiter during the 1975-76 opposition have been obtained from plates
taken with the 2.1 m Otto Struve reflector of the McDonald Observatory.
Positions of several asteroids were secured incidental to those of
the satellites, and these are given also.
^	 r Jed Jay
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Mulholland et al, p. 2
1. INTRODUCTION
This paper continues the series of astroit.1tric observations
of the satellites of the trans-martian planets re-established at the
McDonald Observatory in 1972. We present here the positions deduced
from photographic observations of the jovian system obtained during the
1975-76 opposition, together with the discovery positions of four
asteroids found on these plates.
II. OBSERVATIONS
During the five months be g inning 1975 October, a total of
25 plates were exposed on the faint satellites of Jupiter, using the 2.1
meter Otto Struve reflector of the McDonald Observatory at Mt. Locke.
These included unsuccessful attempts at obtaining measurable images of
Amalthea (Jupiter V) and the suspected fourteenth satellite (1975J1)
discovered by K.owal during September of that same opposition. The
remaining plates contained a total of 18 images of satellites VI-XIII,
as well as images of four asteroidal objects. All of these exposures
were made on Kodak 103aD plates sensitized by pre-flashing, with no
filters or magnitude compensation. Some were manually guided, while
others were guided with the aid of the Rybski autoguider, with successful
exposures ranging up to 120-minute duration (the attempt at 1975J1 was
180 minutes, guided manually). Tracking at satellite rate was accomplished
by offsetting the plate holder from the camera at the appropriate
predicted rate, with the offset direction established by rotation of the
telescope tailpiece collar. Due to the special interest in the then
rMulholland et al, p. 3
newly-discovered thirteenth satellite, the six successful observations
of that object have already been published outside the chronological
sequence (Mulholland and Shelus 1977; Benedict, Shelus and Mulholland 1978,
hereafter r^ferred to as Paper I), and they are not included in the list
presented here.
III. REDUCTION PROCEDURE
The observations presented below were measured and
reduced with the quasi-automatic PDS rricrodensitorneter system described
in Paper I, to which readers are directed for all pertinent details.
IV. DISCUSSION OF RESULTS
the results of the plate reductions are given in Table 1,
in a form homogeneous with the data of Paper I. That is, the positions
are given as topocentric astrometric (i.e. no E-term correction.) right
ascension and declination in the fixed coordinate system of the mean
equator and equinox of 61950.0, based on the coordinate frame defined by
the SAO catalogue. The stated uncertainties (E a , E d ) are formal
standard deviations from the solutions in the two coordinates, computed
as the quadratic sums of the formal standard deviations for the plate
solutions for the PSS field and for the observation plate. The uncertainty
in the determination of the centroids of the individual images is much
smaller than these contributions (typically 10-20 microdegrees) and has
thus been neglected. Of course, systematic errors in the catalogue are
not represented in these values. The number of SAO stars used in the
determination of the secondary reference frame is given as * 1 and the
Mulholland et al, p. 4
number of secondary stars used in the actual observation plate reduction
is*2 . Except as indicated in the notes, all positions are based on
single exposures. For a discussion of the rationale of the data format,
see Abbot, Mulholland and Shelus (1975).
ACKNO14LEDGEMENTS
We are grateful to our measurers M. A. Dritschel, J.
Higdon and R. Wilbourn for their diligent 6 forts with the PDS machine.
This work is supported by the National Aeronautics and Space Administration,
under grant NGR 44-012-282.
REFERENCES
Abbot, R. I., Mulholland, J. D., and Shelus, P. J. (1975): Astron. J. 80,
723.
Benedict, G. F., Shelus, P. J., and Mulholland, J. D. (1978): Astron. J.
83, 999.
Mulholland, J. D., and Shelus, P. J. (1977): Astron. J. 82, 238.
Mulholland et al, p. 4
number of secondary stars used in the actual observation plate reduction
is *2 . Except as indicated in the notes, all positions are hased on
single exposures. For a discussion of the rationale of the data format,
see Abbot, Mulholland and Shelus (1975).
ACKNO14LEDGEMENTS
We are grateful to our measurers M. A. Dritschel, J.
Higdon and R. Wilbourn for their diligent c7forts with the PDS machine.
This work is supported by the National Aeronautics and Space Administration,
under grant NGR 44-012-282.
REFERENCES
Abbot, R. I., Mulholland, J. D., and Shelus, P. J. (1975):	 Astron. J. 80,
723.
Benedict, G. F., Shelus, P. J., and Mulholland, J. D. (1978):	 Astron. J.
83, 999.
Mulholland, J. D., and Shelus, P. J. (1977):	 Astron. J. 82, 238.
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Astrometric observations of the faint satellites of Jupiter during the 1975 - 1976 opposition

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