arXiv subjects

A. Fitzsimmons

Publications and source records attributed to A. Fitzsimmons.

At least 37 records · Page 2Linked to original sources

arXiv2013

Thermal Properties, Sizes, and Size Distribution of Jupiter-Family Cometary Nuclei

We present results from SEPPCoN, an on-going Survey of the Ensemble Physical Properties of Cometary Nuclei. In this report we discuss mid-infrared measurements of the thermal emission from 89 nuclei of Jupiter-family comets (JFCs). All data were obtained in 2006 and 2007 with the Spitzer Space Telescope. For all 89 comets, we present new effective radii, and for 57 comets we present beaming parameters. Thus our survey provides the largest compilation of radiometrically-derived physical properties of nuclei to date. We conclude the following. (a) The average beaming parameter of the JFC population is 1.03+/-0.11, consistent with unity, and indicating low thermal inertia. (b) The known JFC population is not complete even at 3 km radius, and even for comets with perihelia near ~2 AU. (c) We find that the JFC nuclear cumulative size distribution (CSD) has a power-law slope of around -1.9. (d) This power-law is close to that derived from visible-wavelength observations, suggesting that there is no strong dependence of geometric albedo with radius. (e) The observed CSD shows a hint of structure with an excess of comets with radii 3 to 6 km. (f) Our CSD is consistent with an intrinsic distribution that lacks many sub-kilometer objects.

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arXiv2012

Physical and dynamical characterisation of low Delta-V NEA (190491) 2000 FJ10

We investigated the physical properties and dynamical evolution of Near Earth Asteroid (NEA) (190491) 2000 FJ10 in order to assess the suitability of this accessible NEA as a space mission target. Photometry and colour determination were carried out with the 1.54 m Kuiper Telescope and the 10 m Southern African Large Telescope during the object's recent favourable apparition in 2011-12. During the earlier 2008 apparition, a spectrum of the object in the 6000-9000 Angstrom region was obtained with the 4.2 m William Herschel Telescope. Interpretation of the observational results was aided by numerical simulations of 1000 dynamical clones of 2000 FJ10 up to 10^6 yr in the past and in the future. The asteroid's spectrum and colours determined by our observations suggest a taxonomic classification within the S-complex although other classifications (V, D, E, M, P) cannot be ruled out. On this evidence, it is unlikely to be a primitive, relatively unaltered remnant from the early history of the solar system and thus a low priority target for robotic sample return. Our photometry placed a lower bound of 2 hrs to the asteroid's rotation period. Its absolute magnitude was estimated to be 21.54+-0.1 which, for a typical S-complex albedo, translates into a diameter of 130+-20 m. Our dynamical simulations show that it has likely been an Amor for the past 10^5 yr. Although currently not Earth-crossing, it will likely become so during the period 50 - 100 kyr in the future. It may have arrived from the inner or central Main Belt > 1 Myr ago as a former member of a low-inclination S-class asteroid family. Its relatively slow rotation and large size make it a suitable destination for a human mission. We show that ballistic Earth-190491-Earth transfer trajectories with Delta-V < 2 km s^-1 at the asteroid exist between 2052 and 2061.

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arXiv2011

On the alignment of debris disks and their host stars' rotation axis -implications for spin-orbit misalignment in exoplanetary systems

It has been widely thought that measuring the misalignment angle between the orbital plane of a transiting exoplanet and the spin of its host star was a good discriminator between different migration processes for hot-Jupiters. Specifically, well-aligned hot-Jupiter systems (as measured by the Rossiter-McLaughlin effect) were thought to have formed via migration through interaction with a viscous disk, while misaligned systems were thought to have undergone a more violent dynamical history. These conclusions were based on the assumption that the planet-forming disk was well-aligned with the host star. Recent work by a number of authors has challenged this assumption by proposing mechanisms that act to drive the star-disk interaction out of alignment during the pre-main sequence phase. We have estimated the stellar rotation axis of a sample of stars which host spatially resolved debris disks. Comparison of our derived stellar rotation axis inclination angles with the geometrically measured debris-disk inclinations shows no evidence for a misalignment between the two.

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arXiv2011

The size distribution of Jupiter Family comet nuclei

We present an updated cumulative size distribution (CSD) for Jupiter Family comet (JFC) nuclei, including a rigourous assessment of the uncertainty on the slope of the CSD. The CSD is expressed as a power law, N(>r_N) \propto r_N^{-q}, where r_N is the radius of the nuclei and q is the slope. We include a large number of optical observations published by ourselves and others since the comprehensive review in the "Comets II" book (Lamy et al. 2004), and make use of an improved fitting method. We assess the uncertainty on the CSD due to all of the unknowns and uncertainties involved (photometric uncertainty, assumed phase function, albedo and shape of the nucleus) by means of Monte Carlo simulations. In order to do this we also briefly review the current measurements of these parameters for JFCs. Our final CSD has a slope q=1.92\pm 0.20 for nuclei with radius r_N \ge 1.25 km.

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arXiv2009

Spitzer observations of the asteroid-comet transition object and potential spacecraft target 107P (4015) Wilson-Harrington

Context. Near-Earth asteroid-comet transition object 107P/ (4015) Wilson-Harrington is a possible target of the joint European Space Agency (ESA) and Japanese Aerospace Exploration Agency (JAXA) Marco Polo sample return mission. Physical studies of this object are relevant to this mission, and also to understanding its asteroidal or cometary nature. Aims. Our aim is to obtain significant new constraints on the surface thermal properties of this object. Methods. We present mid-infrared photometry in two filters (16 and 22 microns) obtained with NASA's Spitzer Space Telescope on February 12, 2007, and results from the application of the Near Earth Asteroid Thermal Model (NEATM).We obtained high S/N in two mid-IR bands allowing accurate measurements of its thermal emission. Results. We obtain a well constrained beaming parameter (eta = 1.39 +/- 0.26) and obtain a diameter and geometric albedo of D = 3.46 +/- 0.32 km, and pV = 0.059 +/- 0.011. We also obtain similar results when we apply this best-fitting thermal model to single-band mid-IR photometry reported by Campins et al. (1995), Kraemer et al. (2005) and Reach et al. (2007). Conclusions. The albedo of 4015 Wilson-Harrington is low, consistent with those of comet nuclei and primitive C-, P-, D-type asteorids. We establish a rough lower limit for the thermal inertia of W-H of 60 Jm^-2s^(-0.5)K^-1 when it is at r=1AU, which is slightly over the limit of 30 Jm^-2s^(-0.5)K-1 derived by Groussin et al. (2009) for the thermal inertia of the nucleus of comet 22P/Kopff.

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arXiv2007

The 2003 Nov 14 occultation by Titan of TYC 1343-1865-1. II. Analysis of light curves

We observed a stellar occultation by Titan on 2003 November 14 from La Palma Observatory using ULTRACAM with three Sloan filters: u', g', and i' (358, 487, and 758 nm, respectively). The occultation probed latitudes 2 degrees S and 1 degrees N during immersion and emersion, respectively. A prominent central flash was present in only the i' filter, indicating wavelength-dependent atmospheric extinction. We inverted the light curves to obtain six lower-limit temperature profiles between 335 and 485 km (0.04 and 0.003 mb) altitude. The i' profiles agreed with the temperature measured by the Huygens Atmospheric Structure Instrument [Fulchignoni, M. et al., 2005. Nature 438, 785-791] above 415 km (0.01 mb). The profiles obtained from different wavelength filters systematically diverge as altitude decreases, which implies significant extinction in the light curves. Applying an extinction model [Elliot, J.L., Young, L.A., 1992. Astron. J. 103, 991-1015] gave the altitudes of line of sight optical depth equal to unity: 396 +/- 7 km and 401 +/- 20 km (u' immersion and emersion); 354 +/- 7 km and 387 +/- 7 km (g' immersion and emersion); and 336 +/- 5 km and 318 +/- 4 km (i' immersion and emersion). Further analysis showed that the optical depth follows a power law in wavelength with index 1.3 +/- 0.2. We present a new method for determining temperature from scintillation spikes in the occulting body's atmosphere. Temperatures derived with this method are equal to or warmer than those measured by the Huygens Atmospheric Structure Instrument. Using the highly structured, three-peaked central flash, we confirmed the shape of Titan's middle atmosphere using a model originally derived for a previous Titan occultation [Hubbard, W.B. et al., 1993. Astron. Astrophys. 269, 541-563].

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arXiv2007

SuperWASP-N Extra-solar Planet Candidates from Fields 06hr < RA < 16hr

The Wide Angle Search for Planets (WASP) survey currently operates two installations, designated SuperWASP-N and SuperWASP-S, located in the northern and southern hemispheres respectively. These installations are designed to provide high time-resolution photometry for the purpose of detecting transiting extra-solar planets, asteroids, and transient events. Here we present results from a transit-hunting observing campaign using SuperWASP-N covering a right ascension range of 06hr < RA < 16hr. This paper represents the fifth and final in the series of transit candidates released from the 2004 observing season. In total, 729,335 stars from 33 fields were monitored with 130,566 having sufficient precision to be scanned for transit signatures. Using a robust transit detection algorithm and selection criteria, 6 stars were found to have events consistent with the signature of a transiting extra-solar planet based upon the photometry, including the known transiting planet XO-1b. These transit candidates are presented here along with discussion of follow-up observations and the expected number of candidates in relation to the overall observing strategy.

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arXiv2007

WASP-3b: a strongly-irradiated transiting gas-giant planet

We report the discovery of WASP-3b, the third transiting exoplanet to be discovered by the WASP and SOPHIE collaboration. WASP-3b transits its host star USNO-B1.0 1256-0285133 every 1.846834+-0.000002 days. Our high precision radial-velocity measurements present a variation with amplitude characteristic of a planetary-mass companion and in-phase with the light-curve. Adaptive optics imaging shows no evidence for nearby stellar companions, and line-bisector analysis excludes faint, unresolved binarity and stellar activity as the cause of the radial-velocity variations. We make a preliminary spectroscopic analysis of the host star finding it to have Teff = 6400+-100 K and log g = 4.25+-0.05 which suggests it is most likely an unevolved main sequence star of spectral type F7-8V. Our simultaneous modelling of the transit photometry and reflex motion of the host leads us to derive a mass of 1.76 +0.08 -0.14 M_J and radius 1.31 +0.07-0.14 R_J for WASP-3b. The proximity and relative temperature of the host star suggests that WASP-3b is one of the hottest exoplanets known, and thus has the potential to place stringent constraints on exoplanet atmospheric models.

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arXiv2007

SuperWASP-North Extra-solar Planet Candidates between 3hr < RA < 6hr

The Wide Angle Search for Planets (WASP) photometrically surveys a large number of nearby stars to uncover candidate extrasolar planet systems by virtue of small-amplitude lightcurve dips on a < 5-day timescale typical of the ``Hot-Jupiters.'' Observations with the SuperWASP-North instrument between April and September 2004 produced a rich photometric dataset of some 1.3 billion datapoints from 6.7 million stars. Our custom-built data acquisition and processing system produces ~0.02 mag photometric precision at V=13. We present the transit-candidates in the 03h-06h RA range. Of 141,895 lightcurves with sufficient sampling to provide adequate coverage, 2688 show statistically significant transit-like periodicities. Of these, 44 pass visual inspection of the lightcurve, of which 24 are removed through a set of cuts on the statistical significance of artefacts. All but 4 of the remaining 20 objects are removed when prior information at higher spatial-resolution from existing catalogues is taken into account. Of the four candidates remaining, one is considered a good candidate for follow-up observations with three further second-priority targets. We provide detailed information on these candidates, as well as a selection of the false-positives and astrophysical false-alarms that were eliminated, and discuss briefly the impact of sampling on our results.

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arXiv2007

SuperWASP-North Extrasolar Planet Candidates. Candidates from Fields 17hr < RA < 18hr

We have performed photometric observations of nearly 7 million stars with 8 < V < 15 with the SuperWASP-North instrument from La Palma between 2004 May-September. Fields in the RA range 17-18hr, yielding over 185,000 stars with sufficient quality data, have been searched for transits using a modified box least-squares (BLS) algorithm. We find a total of 58 initial transiting candidates which have high S/N in the BLS, show multiple transit-like dips and have passed visual inspection. Analysis of the blending and inferred planetary radii for these candidates leaves a total of 7 transiting planet candidates which pass all the tests plus 4 which pass the majority. We discuss the derived parameters for these candidates and their properties and comment on the implications for future transit searches.

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arXiv2007

SuperWASP-N Extra-solar Planet Candidates Between 18hr < RA < 21hr

The SuperWASP-I instrument observed 6.7 million stars between 8-15 mag from La Palma during the 2004 May-September season. Our transit-hunting algorithm selected 11,626 objects from the 184,442 stars within the range RA 18hr-21hr. We describe our thorough selection procedure whereby catalogue information is exploited along with careful study of the SuperWASP data to filter out, as far as possible, transit mimics. We have identified 35 candidates which we recommend for follow-up observations.

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arXiv2006

WASP-1b and WASP-2b: Two new transiting exoplanets detected with SuperWASP and SOPHIE

We have detected low-amplitude radial-velocity variations in two stars, USNO-B1.0 1219-0005465 (GSC 02265-00107 = WASP-1) and USNO-B1.0 0964-0543604 (GSC 00522-01199 = WASP-2). Both stars were identified as being likely host stars of transiting exoplanets in the 2004 SuperWASP wide-field transit survey. Using the newly-commissioned radial-velocity spectrograph SOPHIE at the Observatoire de Haute-Provence, we found that both objects exhibit reflex orbital radial-velocity variations with amplitudes characteristic of planetary-mass companions and in-phase with the photometric orbits. Line-bisector studies rule out faint blended binaries as the cause of either the radial-velocity variations or the transits. We perform preliminary spectral analyses of the host stars, which together with their radial-velocity variations and fits to the transit light curves, yield estimates of the planetary masses and radii. WASP-1b and WASP-2b have orbital periods of 2.52 and 2.15 days respectively. Given mass estimates for their F7V and K1V primaries we derive planet masses 0.80 to 0.98 and 0.81 to 0.95 times that of Jupiter respectively. WASP-1b appears to have an inflated radius of at least 1.33 R_Jup, whereas WASP-2b has a radius in the range 0.65 to 1.26 R_Jup.

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arXiv2006

A fast hybrid algorithm for exoplanetary transit searches

We present a fast and efficient hybrid algorithm for selecting exoplanetary candidates from wide-field transit surveys. Our method is based on the widely-used SysRem and Box Least-Squares (BLS) algorithms. Patterns of systematic error that are common to all stars on the frame are mapped and eliminated using the SysRem algorithm. The remaining systematic errors caused by spatially localised flat-fielding and other errors are quantified using a boxcar-smoothing method. We show that the dimensions of the search-parameter space can be reduced greatly by carrying out an initial BLS search on a coarse grid of reduced dimensions, followed by Newton-Raphson refinement of the transit parameters in the vicinity of the most significant solutions. We illustrate the method's operation by applying it to data from one field of the SuperWASP survey, comprising 2300 observations of 7840 stars brighter than V=13.0. We identify 11 likely transit candidates. We reject stars that exhibit significant ellipsoidal variations indicative of a stellar-mass companion. We use colours and proper motions from the 2MASS and USNO-B1.0 surveys to estimate the stellar parameters and the companion radius. We find that two stars showing unambiguous transit signals pass all these tests, and so qualify for detailed high-resolution spectroscopic follow-up.

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arXiv2006

The WASP Project and the SuperWASP Cameras

The SuperWASP Cameras are wide-field imaging systems sited at the Observatorio del Roque de los Muchachos on the island of La Palma in the Canary Islands, and the Sutherland Station of the South African Astronomical Observatory. Each instrument has a field of view of some ~482 square degrees with an angular scale of 13.7 arcsec per pixel, and is capable of delivering photometry with accuracy better than 1% for objects having V ~ 7.0 - 11.5. Lower quality data for objects brighter than V ~15.0 are stored in the project archive. The systems, while designed to monitor fields with high cadence, are capable of surveying the entire visible sky every 40 minutes. Depending on the observational strategy, the data rate can be up to 100GB per night. We have produced a robust, largely automatic reduction pipeline and advanced archive which are used to serve the data products to the consortium members. The main science aim of these systems is to search for bright transiting exo-planets systems suitable for spectroscopic followup observations. The first 6 month season of SuperWASP-North observations produced lightcurves of ~6.7 million objects with 12.9 billion data points.

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arXiv2006

The SuperWASP wide-field exoplanetary transit survey: Candidates from Fields 23hr < RA < 03hr

Photometric transit surveys promise to complement the currently known sample of extra-solar planets by providing additional information on the planets and especially their radii. Here we present extra-solar planet (ESP) candidates from one such survey called, the Wide Angle Search for Planets (WASP) obtained with the SuperWASP wide-field imaging system. Observations were taken with SuperWASP-North located in La Palma during the April to October 2004 observing season. The data cover fields between 23hr and 03hr in RA at declinations above +12. This amounts to over $\approx$400,000 stars with V magnitudes 8 to 13.5. For the stars brighter than 12.5, we achieve better than 1 percent photometric precision. Here we present 41 sources with low amplitude variability between $\approx$ 1 and 10 mmag, from which we select 12 with periods between 1.2 and 4.4 days as the most promising extrasolar planet candidates. We discuss the properties of these ESP candidates, the expected fraction of transits recovered for our sample, and implications for the frequency and detection of hot-Jupiters.

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arXiv2005

The nuclei of comets 7P/Pons-Winnecke, 14P/Wolf and 92P/Sanguin

Jupiter Family comets (JFCs) are short period comets which have recently entered the inner solar system, having previously orbited in the Kuiper Belt since the formation of the planets. We used two nights on the 3.6m New Technology Telescope (NTT) at the European Southern Observatory, to obtain VRI photometry of three JFCs; 7P/Pons-Winnecke, 14P/Wolf and 92P/Sanguin. These were observed to be stellar in appearance. We find mean effective radii of 2.24 \pm 0.02 km for 7P, 3.16 \pm 0.01 km for 14P and 2.08 \pm 0.01 km for 92P, assuming a geometric albedo of 0.04. From light-curves for each comet we find rotation periods of 7.53 \pm 0.10 and 6.22 \pm 0.05 hours for 14P and 92P respectively. 7P exhibits brightness variations which imply a rotation period of 6.8 \le P_rot \le 9.5 hours. Assuming the nuclei to be ellipsoidal the measured brightness variations imply minimum axial ratios a/b of 1.3 \pm 0.1 for 7P and 1.7 \pm 0.1 for both 14P and 92P. This in turn implies minimum densities of 0.23 \pm 0.08 g cm^{-3} for 7P, 0.32 \pm 0.02 g cm^{-3} for 14P and 0.49 \pm 0.06 g cm^{-3} for 92P. Finally, we measure colour indices of (V-R) = 0.40 \pm 0.05 and (R-I) = 0.41 \pm 0.06 for 7P/Pons-Winnecke, (V-R) = 0.57 \pm 0.07 and (R-I) = 0.51 \pm 0.06 for 14P/Wolf, and (V-R) = 0.54 \pm 0.04 and (R-I) = 0.54 \pm 0.04 for 92P/Sanguin.

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arXiv2004

Current Status of the SuperWASP Project

We present the current status of the SuperWASP project, a Wide Angle Search for Planets. SuperWASP consists of up to 8 individual cameras using ultra-wide field lenses backed by high-quality passively cooled CCDs. Each camera covers 7.8 x 7.8 sq degrees of sky, for nearly 500 sq degrees of sky coverage. SuperWASP I, located in LaPalma, is currently operational with 5 cameras and is conducting a photometric survey of a large numbers of stars in the magnitude range ~7 to 15. The collaboration has developed a custom-built reduction pipeline and aims to achieve better than 1 percent photometric precision. The pipeline will also produce well sampled light curves for all the stars in each field which will be used to detect: planetary transits, optical transients, and track Near-Earth Objects. Status of current observations, and expected rates of extrasolar planetary detections will be presented. The consortium members, institutions, and further details can be found on the web site at: http://www.superwasp.org.

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arXiv2002

SuperWASP: Wide Angle Search for Planets

SuperWASP is a fully robotic, ultra-wide angle survey for planetary transits. Currently under construction, it will consist of 5 cameras, each monitoring a 9.5 x 9.5 deg field of view. The Torus mount and enclosure will be fully automated and linked to a built-in weather station. We aim to begin observations at the beginning of 2003.

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