I. Williams - Academia.edu (original) (raw)

Papers by I. Williams

Research paper thumbnail of Division Iii: Planetary System Sciences

Proceedings of The International Astronomical Union, 2007

Division III gathers astronomers engaged in the study of a comprehensive range of phenomena in th... more Division III gathers astronomers engaged in the study of a comprehensive range of phenomena in the solar system and its bodies, from the major planets via comets to meteorites and interplanetary dust.

Research paper thumbnail of Astronomical locomotives

Astronomy & Geophysics

Iwan Williams examines the surprising range of astronomical names given to steam locomotives of t... more Iwan Williams examines the surprising range of astronomical names given to steam locomotives of the 19th century.

Research paper thumbnail of The formation and evolution of meteor streams

International Astronomical Union Colloquium

The physical processes which may affect the evolution of meteor streams are discussed and a revie... more The physical processes which may affect the evolution of meteor streams are discussed and a review is then given of the work carried out to date on the evolution of meteor streams. It is clear that they evolve principally due to the effect of planetary perturbations and radiation pressure. The formation of streams from the breakup of a comet is also discussed. All the evidence, including the recent, discovery of 1983TB points to the correctness of this hypothesis.

Research paper thumbnail of The Evolution of Meteoroid Streams

International Astronomical Union Colloquium

The existence of meteoroid streams is indicated by the regular appearance of coherent meteor acti... more The existence of meteoroid streams is indicated by the regular appearance of coherent meteor activity at specified times during the year. Since it is the interaction of the meteoroid with the atmosphere that is detected, the meteoroid has to be greater than about 100 micrometers in radius. Observation of these interactions gives information on individual meteoroids as well as collective phenomena. It is generally agreed that streams form through the ejection of dust particles from the surfaces of comets and asteroids at speeds considerably lower than the orbital speed. The subsequent motion of these particles is affected by gravitational perturbations from the planets and the effects of solar radiation forces. This review is intended to present an overview of the development of the subject and of our current state of knowledge.

Research paper thumbnail of The Quadrantid Stream, Chaos or Not?

Symposium - International Astronomical Union

The Quadrantid stream covers a region of space which contains many strong resonances and commensu... more The Quadrantid stream covers a region of space which contains many strong resonances and commensurabilities with the Jovian orbit. We have numerically integrated the orbital evolution of over one hundred actual meteoroids backwards to BC 5000. The evolution is quit complex, but most of the meteoroids are quite well behaved with rapid but smooth changes in the orbital elements. One meteoroid however shows sharp sudden changes in its orbital parameters and these changes are generally indicative of the presence of chaos.

Research paper thumbnail of The velocity of meteoroids

Atmospheric Chemistry and Physics Discussions

Determining the velocity of meteoroids as they enter the Earth's atmosphere is very important sin... more Determining the velocity of meteoroids as they enter the Earth's atmosphere is very important since the value is fundamental in calculating the orbit of the meteoroid and hence eventually its origin. We describe early attempts at this determination and highlight problems that exist today.

Research paper thumbnail of The orbital evolution of the Quadrantid meteor stream between AD 1830 and 2030

Monthly Notices of the Royal Astronomical Society

Research paper thumbnail of The Quadrantid meteoroid stream and Comet 1491I

Monthly Notices of the Royal Astronomical Society

Research paper thumbnail of On the Quadrantid meteoroid stream complex

Monthly Notices of the Royal Astronomical Society

Research paper thumbnail of Optical Imaging and Spectroscopy of the Interaction With Jupiter of Comet Shoemaker-Levy 9

Research paper thumbnail of The theoretical HR diagram for a cluster of stars with mass accretion

Monthly Notices of the Royal Astronomical Society

ABSTRACT

Research paper thumbnail of Gaps in the distribution of semimajor axes of the Perseid meteors

Monthly Notices of the Royal Astronomical Society

Gaps have been found in the distribution of the reciprocal semimajor axes of 442 Perseid meteor o... more Gaps have been found in the distribution of the reciprocal semimajor axes of 442 Perseid meteor orbits extracted from the catalogue of the IAU meteor data centre in Lund. These gaps are located at positions corresponding to mean motion resonances with the planets. A numerical integration of 11000 test meteoroids over 1000 yr shows that these gaps can form because of gravitational perturbation from the major planets. A longer integration over 100000 yr for 10 meteoroids shows that particles frequently move from one resonant region to another, often passing through a chaotic phase.

Research paper thumbnail of The hierarchical stability of satellite systems

Monthly Notices of the Royal Astronomical Society

Research paper thumbnail of The origin and evolution of meteor showers and meteoroid streams

Research paper thumbnail of Investigations of D-type asteroids

Monthly Notices of the Royal Astronomical Society

Research paper thumbnail of Comet Hale-Bopp jets into view

Research paper thumbnail of Collisions between the nucleus of Comet Halley and dust from its own meteoroid stream

Monthly Notices of the Royal Astronomical Society

ABSTRACT As Comet Halley orbits the Sun it continuously ploughs through its own meteoroid stream.... more ABSTRACT As Comet Halley orbits the Sun it continuously ploughs through its own meteoroid stream. We show that the collision velocity between the stream meteoroids and the surface of the cometary nucleus is far from negligible, the mean value being about 4.0 km/s. Half of the collisions occur when the comet is close to perihelion. The total amount of its own dust hit by Comet Halley per orbit is around 17 g, and this damages a mere 8 x 10 exp -8 percent of the surface of the nucleus.

Research paper thumbnail of Detection of Thermal Emission from 1993 SC - First Results

We report on observations of the Kuiper-Belt Objects, 1993 SC and 1996 TL66 using the European Sp... more We report on observations of the Kuiper-Belt Objects, 1993 SC and 1996 TL66 using the European Space Agency’s Infrared Space Observatory. The measurements indicate a first detection of 1993 SC at 90 microns and yield a measurement of the radius of 164 ( ±</font >\pm 35) km and a geometric albedo of 0.022 ( ±</font >\pm 0.013). For 1996 TL66, an effective radius of 316( ±</font >\pm 49) km and a geometric albedo of 0.030( ±</font >\pm 0.015) have been derived although, in this case, it cannot be ruled out that the signal is not actually from the KBO. This paper represents a brief report of an article published more fully elsewhere [13].

Research paper thumbnail of Halley's Comet

Research paper thumbnail of VizieR Online Data Catalog: Saturn's satellites in 1995/97 (Harper+ 1999)

Vizier Online Data Catalog, Apr 1, 1999

In this paper, we publish measurements of 1514 positions of the major satellites of Saturn made i... more In this paper, we publish measurements of 1514 positions of the major satellites of Saturn made in 1995 and 1997 using CCD detectors attached to the 1-metre Jacobus Kapteyn Telescope on the island of La Palma. Analysis of the data as inter-satellite positions shows that the observations of Tethys, Dione, Rhea and Titan have root-mean-square residuals of 0.08 arc-seconds in

Research paper thumbnail of Division Iii: Planetary System Sciences

Proceedings of The International Astronomical Union, 2007

Division III gathers astronomers engaged in the study of a comprehensive range of phenomena in th... more Division III gathers astronomers engaged in the study of a comprehensive range of phenomena in the solar system and its bodies, from the major planets via comets to meteorites and interplanetary dust.

Research paper thumbnail of Astronomical locomotives

Astronomy & Geophysics

Iwan Williams examines the surprising range of astronomical names given to steam locomotives of t... more Iwan Williams examines the surprising range of astronomical names given to steam locomotives of the 19th century.

Research paper thumbnail of The formation and evolution of meteor streams

International Astronomical Union Colloquium

The physical processes which may affect the evolution of meteor streams are discussed and a revie... more The physical processes which may affect the evolution of meteor streams are discussed and a review is then given of the work carried out to date on the evolution of meteor streams. It is clear that they evolve principally due to the effect of planetary perturbations and radiation pressure. The formation of streams from the breakup of a comet is also discussed. All the evidence, including the recent, discovery of 1983TB points to the correctness of this hypothesis.

Research paper thumbnail of The Evolution of Meteoroid Streams

International Astronomical Union Colloquium

The existence of meteoroid streams is indicated by the regular appearance of coherent meteor acti... more The existence of meteoroid streams is indicated by the regular appearance of coherent meteor activity at specified times during the year. Since it is the interaction of the meteoroid with the atmosphere that is detected, the meteoroid has to be greater than about 100 micrometers in radius. Observation of these interactions gives information on individual meteoroids as well as collective phenomena. It is generally agreed that streams form through the ejection of dust particles from the surfaces of comets and asteroids at speeds considerably lower than the orbital speed. The subsequent motion of these particles is affected by gravitational perturbations from the planets and the effects of solar radiation forces. This review is intended to present an overview of the development of the subject and of our current state of knowledge.

Research paper thumbnail of The Quadrantid Stream, Chaos or Not?

Symposium - International Astronomical Union

The Quadrantid stream covers a region of space which contains many strong resonances and commensu... more The Quadrantid stream covers a region of space which contains many strong resonances and commensurabilities with the Jovian orbit. We have numerically integrated the orbital evolution of over one hundred actual meteoroids backwards to BC 5000. The evolution is quit complex, but most of the meteoroids are quite well behaved with rapid but smooth changes in the orbital elements. One meteoroid however shows sharp sudden changes in its orbital parameters and these changes are generally indicative of the presence of chaos.

Research paper thumbnail of The velocity of meteoroids

Atmospheric Chemistry and Physics Discussions

Determining the velocity of meteoroids as they enter the Earth's atmosphere is very important sin... more Determining the velocity of meteoroids as they enter the Earth's atmosphere is very important since the value is fundamental in calculating the orbit of the meteoroid and hence eventually its origin. We describe early attempts at this determination and highlight problems that exist today.

Research paper thumbnail of The orbital evolution of the Quadrantid meteor stream between AD 1830 and 2030

Monthly Notices of the Royal Astronomical Society

Research paper thumbnail of The Quadrantid meteoroid stream and Comet 1491I

Monthly Notices of the Royal Astronomical Society

Research paper thumbnail of On the Quadrantid meteoroid stream complex

Monthly Notices of the Royal Astronomical Society

Research paper thumbnail of Optical Imaging and Spectroscopy of the Interaction With Jupiter of Comet Shoemaker-Levy 9

Research paper thumbnail of The theoretical HR diagram for a cluster of stars with mass accretion

Monthly Notices of the Royal Astronomical Society

ABSTRACT

Research paper thumbnail of Gaps in the distribution of semimajor axes of the Perseid meteors

Monthly Notices of the Royal Astronomical Society

Gaps have been found in the distribution of the reciprocal semimajor axes of 442 Perseid meteor o... more Gaps have been found in the distribution of the reciprocal semimajor axes of 442 Perseid meteor orbits extracted from the catalogue of the IAU meteor data centre in Lund. These gaps are located at positions corresponding to mean motion resonances with the planets. A numerical integration of 11000 test meteoroids over 1000 yr shows that these gaps can form because of gravitational perturbation from the major planets. A longer integration over 100000 yr for 10 meteoroids shows that particles frequently move from one resonant region to another, often passing through a chaotic phase.

Research paper thumbnail of The hierarchical stability of satellite systems

Monthly Notices of the Royal Astronomical Society

Research paper thumbnail of The origin and evolution of meteor showers and meteoroid streams

Research paper thumbnail of Investigations of D-type asteroids

Monthly Notices of the Royal Astronomical Society

Research paper thumbnail of Comet Hale-Bopp jets into view

Research paper thumbnail of Collisions between the nucleus of Comet Halley and dust from its own meteoroid stream

Monthly Notices of the Royal Astronomical Society

ABSTRACT As Comet Halley orbits the Sun it continuously ploughs through its own meteoroid stream.... more ABSTRACT As Comet Halley orbits the Sun it continuously ploughs through its own meteoroid stream. We show that the collision velocity between the stream meteoroids and the surface of the cometary nucleus is far from negligible, the mean value being about 4.0 km/s. Half of the collisions occur when the comet is close to perihelion. The total amount of its own dust hit by Comet Halley per orbit is around 17 g, and this damages a mere 8 x 10 exp -8 percent of the surface of the nucleus.

Research paper thumbnail of Detection of Thermal Emission from 1993 SC - First Results

We report on observations of the Kuiper-Belt Objects, 1993 SC and 1996 TL66 using the European Sp... more We report on observations of the Kuiper-Belt Objects, 1993 SC and 1996 TL66 using the European Space Agency’s Infrared Space Observatory. The measurements indicate a first detection of 1993 SC at 90 microns and yield a measurement of the radius of 164 ( ±</font >\pm 35) km and a geometric albedo of 0.022 ( ±</font >\pm 0.013). For 1996 TL66, an effective radius of 316( ±</font >\pm 49) km and a geometric albedo of 0.030( ±</font >\pm 0.015) have been derived although, in this case, it cannot be ruled out that the signal is not actually from the KBO. This paper represents a brief report of an article published more fully elsewhere [13].

Research paper thumbnail of Halley's Comet

Research paper thumbnail of VizieR Online Data Catalog: Saturn's satellites in 1995/97 (Harper+ 1999)

Vizier Online Data Catalog, Apr 1, 1999

In this paper, we publish measurements of 1514 positions of the major satellites of Saturn made i... more In this paper, we publish measurements of 1514 positions of the major satellites of Saturn made in 1995 and 1997 using CCD detectors attached to the 1-metre Jacobus Kapteyn Telescope on the island of La Palma. Analysis of the data as inter-satellite positions shows that the observations of Tethys, Dione, Rhea and Titan have root-mean-square residuals of 0.08 arc-seconds in