Bibcode
Vaduvescu, O.
Bibliographical reference
PhD Thesis, Babes-Bolyai University, Cluj-Napoca, Romania
Advertised on:
8
1997
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Description
The number of minor bodies in the Solar System is continuing to
increase. More than 30,000 asteroids have been discovered by 1996, and
about 7,000 have been catalogued. About 855 comets had known orbits by
1994. The number of known planetary satellites reached 60 (1996). All
these minor bodies require improved astrometry, also more accurate
physical parameters (sizes, masses, albedo, etc) to ensure accurate
determination of their orbits. Some rapid dynamical phenomena could
bring valuable information in this sense.
Occultations and appulses (close approaches) of stars by asteroids
represent the most accurate phenomena to determine or constraint sizes
and shape of the asteroids. Given a fixed place, such events are very
rare. Moreover, their prediction could be quite inaccurate, due to the
reduced accuracy in both stellar and asteroid positions. Coordinated
international campaigns, such as those lead by EAON (European Asteroidal
Occultation Network) and IOTA (International Occultation Timing
Association) could determine sizes and shapes of the asteroids. Some
events could also lead to the discovery of double or triple asteroids
systems. Four appulses involving PPM catalog stars and the minor planets
(7) Iris, (297) Caecilia, (382) Dodona, and (824) Anastasia were
observed by the author using the F=6m/D=0.38m refractor of the
Astronomical Institute of the Romanian Academy (AIRA) in Bucharest. None
were recorded as occultations, but their reduced astrometry (~0.01
arcsec) brought valuable information about the time of minimum approach
and the minimum distance between the start and the asteroid, leading to
some constraints about their sizes.
Mutual phenomena in the systems of satellites of Jupiter and Saturn
could bring valuable information about planetary and satellite masses,
also about their moons orbits. Such phenomena are eclipses, occultations
and passages between a satellite and the planet, and mutual eclipses and
occultations between two satellites. Such events took place in 1995-1996
in the system of Saturn, when Earth passed through the plane of the ring
of Saturn, allowing increased accuracy in timing and astrometry of the
events, via photometry. Some contributions have been made by AIRA part
of the international campaign PHESAT95 lead by Bureau des Longitudes in
Paris, in which the author was involved part of a small team (3 people).
Astrometry of a small CCD field (<5 arcmin) from a light polluted
place (such as Bucharest) can be challenging, due to the few number of
stars in the field, also to the low density of the astrometric catalogs
(e.g., PPM). Most of the times only one or two stars in the field can be
used for astrometry. The orientation of the CCD camera on the sky has to
be determined for every observation, due to the flexure of the F=6m
refractor which was determined to be different given various positions
of the telescope during the night. A catalog of double, triple and
multiple PPM stars in a small field (5x5 arcmin) was built in order to
allow the observation of an orientation field close to every science
field observed during the night.
Some contributions to the astronomical software library of AIRA and its
Astronomical Yearbook were made by the author in conjunction with this
thesis. Other software were written to assist the observing runs and
data reduction. We note here the following: CELESTIAL MAPS 5.0, MAPSAT,
APRPPM, TOP, INTTOP, ORIENT, RELCCD, ABSCCD, PARGEO, SEPAD, EPHEMERID,
LAPLACE, etc.
Some contributions to the correlation of the orbital elements of the
asteroids (semimajor axis, eccentricity, inclination, longitude of the
ascending node and longitude of the perihelium) were made using the
ASTEROIDS II database using the principal component analysis. A curious
distribution of perihelion longitudes of the asteroids showing symmetry
of the number of asteroids around perihelion longitude 180 deg was found
using the IRAS database. This could be attributed to perturbations from
Jupiter.
Scanned thesis in pdf format available online at
http://ovidiuvh.tripod.com/Teza-Romania/ (200 pags, 9 MB)