Alan Fitzsimmons | Queen's University Belfast (original) (raw)

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Papers by Alan Fitzsimmons

The Astronomical Journal, 2014

We present the results of a search for the reactivation of active asteroid 176P/LINEAR during its... more We present the results of a search for the reactivation of active asteroid 176P/LINEAR during its 2011 perihelion passage using deep optical observations obtained before, during, and after that perihelion passage. Deep composite images of 176P constructed from data obtained between June 2011 and December 2011 show no visible signs of activity, while photometric measurements of the object during this period also show no significant brightness enhancements similar to that observed for 176P between November 2005 and December 2005 when it was previously observed to be active. An azimuthal search for dust emission likewise reveals no evidence for directed emission (i.e., a tail, as was previously observed for 176P), while a one-dimensional surface brightness profile analysis shows no indication of a spherically symmetric coma at any time in 2011. We conclude that 176P did not in fact exhibit activity in 2011, at least not on the level on which it exhibited activity in 2005, and suggest that this could be due to the devolatization or mantling of the active site responsible for its activity in 2005.

The Karin cluster is by far the youngest known family of main-belt asteroids, dating back to a co... more The Karin cluster is by far the youngest known family of main-belt asteroids, dating back to a collisional event only 5.8+/-0.2 Myr ago. We propose to sample the thermal continua of 17 Karin cluster asteroids of different sizes, down to the smallest members discovered so far, in order to derive accurate sizes and study the physical properties of their surfaces. Our aims include a study of trends in thermal inertia and albedo with size. The analysis will be based on sophisticated thermal models that will provide important insight into thermal inertia and regolith coverage. The widely used 'standard thermal model' leads to serious errors in thermal studies of small asteroids and is not adequate for a detailed study of the physical characteristics of Karin cluster members. The following questions are amongst those addressed by this program: 1. Are the distributions of sizes and albedos compatible with the Karin cluster being the result of a single catastrophic collision 5.8+/...

The Astrophysical Journal, 2012

Main belt asteroid (300163) 2006 VW 139 (later designated P/2006 VW 139 ) was discovered to exhib... more Main belt asteroid (300163) 2006 VW 139 (later designated P/2006 VW 139 ) was discovered to exhibit comet-like activity by the Pan-STARRS1 survey telescope using automated point-spread-function analyses performed by PS1's Moving Object Processing System. Deep follow-up observations show both a short (∼ 10 ) antisolar dust tail and a longer (∼ 60 ) dust trail aligned with the object's orbit plane, similar to the morphology observed for another main-belt comet, P/2010 R2 (La Sagra), and other well-established comets, implying the action of a long-lived, sublimation-driven emission event.

Icarus, 2013

We present an analysis of comet activity based on the Spitzer Space Telescope component of the Su... more We present an analysis of comet activity based on the Spitzer Space Telescope component of the Survey of the Ensemble Physical Properties of Cometary Nuclei. We show that the survey is well suited to measuring the activity of Jupiter-family comets at 3-7 AU from the Sun. Dust was detected in 33 of 89 targets (37 ± 6%), and we conclude that 21 comets (24 ± 5%) have morphologies that suggest ongoing or recent cometary activity. Our dust detections are sensitivity limited, therefore our measured activity rate is necessarily a lower limit. All comets with small perihelion distances (q < 1.8 AU) are inactive in our survey, and the active comets in our sample are strongly biased to post-perihelion epochs. We introduce the quantity f ρ, intended to be a thermal emission counterpart to the often reported Af ρ, and find that the comets with large perihelion distances likely have greater dust production rates than other comets in our survey at 3-7 AU from the Sun, indicating a bias in the discovered Jupiter-family comet population. By examining the orbital history of our survey sample, we suggest that comets perturbed to smaller perihelion distances in the past 150 yr are more likely to be active, but more study on this effect is needed.

Icarus, 2004

Our goal is to determine whether or not the observed sudden termination of the Edgeworth-Kuiper b... more Our goal is to determine whether or not the observed sudden termination of the Edgeworth-Kuiper belt can be the result of perturbations from a hypothetical planet. We investigate the effects that such an object would produce on the primordial orbital distribution if the trans-neptunian objects, for a range of masses and orbital parameters of the hypothetical planet. In this numerical investigation, the motion of the hypothetical planet was influenced by the existing planets but not by its interaction with the disk. We find that no set of parameters produce results that match the observed data. Dynamical interaction with the disk is likely to be important so that the orbit of the hypothetical planet changes significantly during the integration interval. This is also discussed. The overall conclusion is that none of the models for the hypothetical planet that were investigated can reproduce the observed features of the Edgeworth-Kuiper belt starting from any probable primordial distribution.

The peculiar object P/2010 A2 was discovered by the LINEAR near-Earth asteroid survey in January ... more The peculiar object P/2010 A2 was discovered by the LINEAR near-Earth asteroid survey in January 2010 and given a cometary designation due to the presence of a trail of material, although there was no central condensation or coma. The appearance of this object, in an asteroidal orbit (small eccentricity and inclination) in the inner main asteroid belt attracted attention as a potential new member of the recently recognized class of 'Main Belt Comets' (MBCs). If confirmed, this new object would greatly expand the range in heliocentric distance over which MBCs are found. Here we present observations taken from the unique viewing geometry provided by ESA's Rosetta spacecraft, far from the Earth, that demonstrate that the trail is due to a single event rather than a period of cometary activity, in agreement with independent results from the Hubble Space Telescope (HST). The trail is made up of relatively large particles of millimetre to centimetre size that remain close to the parent asteroid. The shape of the trail can be explained by an initial impact ejecting large clumps of debris that disintegrated and dispersed almost immediately. We determine that this was an asteroid collision that occurred around February 10, 2009.

The Astronomical Journal, 2014

We present the results of a search for the reactivation of active asteroid 176P/LINEAR during its... more We present the results of a search for the reactivation of active asteroid 176P/LINEAR during its 2011 perihelion passage using deep optical observations obtained before, during, and after that perihelion passage. Deep composite images of 176P constructed from data obtained between June 2011 and December 2011 show no visible signs of activity, while photometric measurements of the object during this period also show no significant brightness enhancements similar to that observed for 176P between November 2005 and December 2005 when it was previously observed to be active. An azimuthal search for dust emission likewise reveals no evidence for directed emission (i.e., a tail, as was previously observed for 176P), while a one-dimensional surface brightness profile analysis shows no indication of a spherically symmetric coma at any time in 2011. We conclude that 176P did not in fact exhibit activity in 2011, at least not on the level on which it exhibited activity in 2005, and suggest that this could be due to the devolatization or mantling of the active site responsible for its activity in 2005.

The Karin cluster is by far the youngest known family of main-belt asteroids, dating back to a co... more The Karin cluster is by far the youngest known family of main-belt asteroids, dating back to a collisional event only 5.8+/-0.2 Myr ago. We propose to sample the thermal continua of 17 Karin cluster asteroids of different sizes, down to the smallest members discovered so far, in order to derive accurate sizes and study the physical properties of their surfaces. Our aims include a study of trends in thermal inertia and albedo with size. The analysis will be based on sophisticated thermal models that will provide important insight into thermal inertia and regolith coverage. The widely used 'standard thermal model' leads to serious errors in thermal studies of small asteroids and is not adequate for a detailed study of the physical characteristics of Karin cluster members. The following questions are amongst those addressed by this program: 1. Are the distributions of sizes and albedos compatible with the Karin cluster being the result of a single catastrophic collision 5.8+/...

The Astrophysical Journal, 2012

Main belt asteroid (300163) 2006 VW 139 (later designated P/2006 VW 139 ) was discovered to exhib... more Main belt asteroid (300163) 2006 VW 139 (later designated P/2006 VW 139 ) was discovered to exhibit comet-like activity by the Pan-STARRS1 survey telescope using automated point-spread-function analyses performed by PS1's Moving Object Processing System. Deep follow-up observations show both a short (∼ 10 ) antisolar dust tail and a longer (∼ 60 ) dust trail aligned with the object's orbit plane, similar to the morphology observed for another main-belt comet, P/2010 R2 (La Sagra), and other well-established comets, implying the action of a long-lived, sublimation-driven emission event.

Icarus, 2013

We present an analysis of comet activity based on the Spitzer Space Telescope component of the Su... more We present an analysis of comet activity based on the Spitzer Space Telescope component of the Survey of the Ensemble Physical Properties of Cometary Nuclei. We show that the survey is well suited to measuring the activity of Jupiter-family comets at 3-7 AU from the Sun. Dust was detected in 33 of 89 targets (37 ± 6%), and we conclude that 21 comets (24 ± 5%) have morphologies that suggest ongoing or recent cometary activity. Our dust detections are sensitivity limited, therefore our measured activity rate is necessarily a lower limit. All comets with small perihelion distances (q < 1.8 AU) are inactive in our survey, and the active comets in our sample are strongly biased to post-perihelion epochs. We introduce the quantity f ρ, intended to be a thermal emission counterpart to the often reported Af ρ, and find that the comets with large perihelion distances likely have greater dust production rates than other comets in our survey at 3-7 AU from the Sun, indicating a bias in the discovered Jupiter-family comet population. By examining the orbital history of our survey sample, we suggest that comets perturbed to smaller perihelion distances in the past 150 yr are more likely to be active, but more study on this effect is needed.

Icarus, 2004

Our goal is to determine whether or not the observed sudden termination of the Edgeworth-Kuiper b... more Our goal is to determine whether or not the observed sudden termination of the Edgeworth-Kuiper belt can be the result of perturbations from a hypothetical planet. We investigate the effects that such an object would produce on the primordial orbital distribution if the trans-neptunian objects, for a range of masses and orbital parameters of the hypothetical planet. In this numerical investigation, the motion of the hypothetical planet was influenced by the existing planets but not by its interaction with the disk. We find that no set of parameters produce results that match the observed data. Dynamical interaction with the disk is likely to be important so that the orbit of the hypothetical planet changes significantly during the integration interval. This is also discussed. The overall conclusion is that none of the models for the hypothetical planet that were investigated can reproduce the observed features of the Edgeworth-Kuiper belt starting from any probable primordial distribution.

The peculiar object P/2010 A2 was discovered by the LINEAR near-Earth asteroid survey in January ... more The peculiar object P/2010 A2 was discovered by the LINEAR near-Earth asteroid survey in January 2010 and given a cometary designation due to the presence of a trail of material, although there was no central condensation or coma. The appearance of this object, in an asteroidal orbit (small eccentricity and inclination) in the inner main asteroid belt attracted attention as a potential new member of the recently recognized class of 'Main Belt Comets' (MBCs). If confirmed, this new object would greatly expand the range in heliocentric distance over which MBCs are found. Here we present observations taken from the unique viewing geometry provided by ESA's Rosetta spacecraft, far from the Earth, that demonstrate that the trail is due to a single event rather than a period of cometary activity, in agreement with independent results from the Hubble Space Telescope (HST). The trail is made up of relatively large particles of millimetre to centimetre size that remain close to the parent asteroid. The shape of the trail can be explained by an initial impact ejecting large clumps of debris that disintegrated and dispersed almost immediately. We determine that this was an asteroid collision that occurred around February 10, 2009.