Showing papers by "Alan Fitzsimmons published in 2008"

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

Abstract: 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 1.846 834 ± 0.000 002 d. 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 and find it to have T eff = 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 MJ and radius 1.31 +0.07 −0.14 RJ 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.

Optical observations of 23 distant Jupiter Family Comets, including 36P/Whipple at multiple phase angles

Abstract: We present photometry on 23 Jupiter Family Comets (JFCs) observed at large heliocentric distance, primarily using the 2.5-m Isaac Newton Telescope (INT). Snapshot images were taken of 17 comets, of which five were not detected, three were active and nine were unresolved and apparently inactive. These include 103P/ Hartley 2, the target of the NASA Deep Impact extended mission, EPOXI. For six comets we obtained time-series photometry and use this to constrain the shape and rotation period of these nuclei. The data are not of sufficient quantity or quality to measure precise rotation periods, but the time-series do allow us to measure accurate effective radii and surface colours. Of the comets observed over an extended period, 40P/Vaisala 1, 47P/Ashbrook-Jackson and P/2004 H2 (Larsen) showed faint activity which limited the study of the nucleus. Light curves for 94P/Russell 4 and 121P/Shoemaker-Holt 2 reveal rotation periods of around 33 and 10 h, respectively, although in both cases these are not unique solutions. 94P was observed to have a large range in magnitudes implying that it is one of the most elongated nuclei known, with an axial ratio a/b≥ 3. 36P/ Whipple was observed at five different epochs, with the INT and ESO's 3.6-m NTT, primarily in an attempt to confirm the preliminary short rotation period apparent in the first data set. The combined data set shows that the rotation period is actually longer than 24 h. A measurement of the phase function of 36P's nucleus gives a relatively steep β= 0.060 ± 0.019. Finally, we discuss the distribution of surface colours observed in JFC nuclei, and show that it is possible to trace the evolution of colours from the Kuiper Belt Object (KBO) population to the JFC population by applying a ‘dereddening’ function to the KBO colour distribution.

Surface properties of Rosetta's targets (21) Lutetia and (2867) Steins from ESO observations

Abstract: Aims. The aim of this work is to constrain the size, composition and surface properties of asteroids (2867) Steins and (21) Lutetia, targets of the Rosetta mission. Rosetta is en route to rendezvous with comet 67P/Churyumov-Gerasimenko. Methods. Thermal-Infrared N-band observations for Lutetia and Steins were obtained using, respectively, TIMMI2 on the ESO 3.6-m telescope at La Silla and VISIR at the UT3 VLT telescope on Cerro Paranal; visible light curves for Steins were obtained using NTT+SUSI2, while R-band photometry for Lutetia was obtained with the 2.0-m Faulkes Telescope North on Haleakala. For Steins, the NEATM model was used to constrain its visible geometric albedo and beaming parameter. A detailed thermophysical model was implemented and used to analyze our set of observations of Lutetia as well as previous reported measurements. Results. The visible photometry of Steins was used along with data from the literature to yield a slope parameter of G = 0.32 +0.14 −0.11 . Problems during the observations led to the loss of measurements on two of the three N-band filters requested for Steins. Using the remaining data and the polarimetric albedo recently published, we were able to constrain the thermal beaming parameter as η> 1.2, which is more similar to near-Earth asteroids and suggests either high thermal inertia or a very rough surface. For Lutetia, the best fit visible geometric albedo obtained with our model and the reported observation is pv = 0.129, significantly lower than that obtained if one applies the same model to previously reported measurements. The discrepancy cannot be explained solely by assuming inhomogeneities in the surface properties and we suggest that the most plausible explanation is the presence of one or more large craters on the northern hemisphere. For both sets of measurements, the implied single scattering albedo of Lutetia is compatible with laboratory measurements of carbonaceous chondrite meteorites.

Kuiper Belt Objects in the Planetary Region: The Jupiter-Family Comets

Abstract: Jupiter-family comets (JFCs) are a dynamically distinct group with low orbital inclinations and orbital periods ?20 yr. Their origin has been shown computationally to be the Kuiper belt region beyond Neptune. Therefore studying the nuclei of these comets, as well as their coma species, can provide valuable insights into the nature of the kilometer-sized Kuiper belt ob- jects (KBOs). These include their size distribution, internal structure, and composition, as well as some hints at their likely surface features. Although JFCs are much closer to the Sun than KBOs, they are still very difficult to observe due to their intrinsic faintness and outgassing comae. However, observational studies are advancing rapidly and we are now starting to place valuable constraints on the bulk physical properties of these nuclei. In this chapter, we review some of the more important findings in this field and their relevance to KBO studies.

SuperWASP‐N extrasolar planet candidates from fields 06h < RA < 16h

Abstract: 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 extrasolar planets, asteroids, and transient events. Here, we present results from a transit-hunting observing campaign using SuperWASP-N covering a right ascension (RA) range of 06 h < RA < 16 h . 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, six stars were found to have events consistent with the signature of a transiting extrasolar planet based on 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.

Optical Observations of Comet McNaught from La Silla

Abstract: Fitzsimmons, Emmanuel Jehin, Jean Manfroid, Damien Hutsemekers. European Southern Observatory, Chile (csnodgra@eso.org), Queen’s University Belfast, UK, Universite de Liege, Belgium Comet C/2006 P1 (McNaught) has rightly earned the title of a ‘Great Comet’; one so bright in the sky that such an occurrence could be expected once in a generation. Observers from both hemispheres saw the impressive tail as the comet passed within 0.3 AU of the Sun and became highly active, but those in the Southern Hemisphere got the most spectacular views after perihelion. We report on our optical observations from the European Southern Observatory’s La Silla site, in Chile[1].