CCD photometry of 23 minor planets

We present CCD photometric observations of 23 main-belt asteroids, of which 8 have never been observed before; thus, the data of these objects are the first in the literature. The majority showed well-detectable light variations, exceeding 0^m1. We have determined synodic periods for 756 Lilliana (936), 1270 Datura (34), 1400 Tirela (1336), 1503 Kuopio (998), 3682 Welther (359), 7505 Furushu (414) and 11436 1969 QR (123), while uncertain period estimates were possible for 469 Argentina (123), 546 Herodias (104) and 1026 Ingrid (53). The shape of the lightcurves of 3682 Welther changed on a short time-scale and showed dimmings that might be attributed to eclipses in a binary system. For the remaining objects, only lower limits of the periods and amplitudes were concluded.     

Orbits and masses of Saturn's coorbital and F-ring shepherding satellites

We have obtained numerically integrated orbits for Saturn's coorbital satellites, Janus and Epimetheus, together with Saturn's F-ring shepherding satellites, Prometheus and Pandora. The orbits are fit to astrometric observations acquired with the Hubble Space Telescope and from Earth-based observatories and to imaging data acquired from the Voyager spacecraft. The observations cover the 38 year period from the 1966 Saturn ring plane crossing to the spring of 2004. In the process of determining the orbits we have found masses for all four satellites. The densities derived from the masses for Janus, Epimetheus, Prometheus, and Pandora in units of g cm⁻³ are , , , and , respectively.     

Near infrared imaging spectroscopy of Venus with the Anglo-Australian Telescope

We have obtained full-disk spatially resolved spectra of the Venus nightside at near-infrared wavelengths during July 2007 using the Anglo-Australian Telescope and Infrared Imager and Spectrograph 2 (IRIS2). The data have been used to map the intensity and rotational temperature of the O₂(a¹Δ_g) airglow band at . The temperatures agree with those obtained in earlier IRIS2 observations and are significantly higher than expected from the Venus International Reference Atmosphere (VIRA) profile. We also report the detection of the corresponding ν=0-1O₂ airglow band at with a similar spatial distribution to the ν=0-0 band. Observations in the thermal window have been used to image surface topography using two different methods of cloud correction. We have also obtained images that can be used to study cloud motion.     

Optical and thermal infrared observations of six near-Earth asteroids in 2002

We present thermal infrared photometry and spectrophotometry of six Near-Earth Asteroids (NEAs) using the 3.8 m United Kingdom Infrared Telescope (UKIRT) together with quasi-simultaneous optical observations of five NEAs taken at the 1.0 m Jacobus Kapteyn Telescope (JKT). For Asteroid (6455) 1992 HE we derive a rotational period P=2.736±0.002 h, and an absolute visual magnitude H=14.32±0.24. For Asteroid 2002 HK₁₂ we derive . The Standard Thermal Model (STM), the Fast Rotating Model (FRM) and the Near-Earth Asteroid Thermal Model (NEATM) have been fitted to the measured fluxes to derive albedos and effective diameters. The derived geometric albedos and effective diameters are (6455) 1992 HE: pv=0.26±0.08, Deff=3.55±0.5 km; 1999 HF₁: pv=0.18±0.07, ; 2000 ED₁₀₄: pv=0.18±0.05, Deff=1.21±0.2 km; 2002 HK₁₂: , Deff=0.62±0.2 km; 2002 NX₁₈: pv=0.031±0.009, Deff=2.24±0.3 km; 2002 QE₁₅: , Deff=1.94±0.4 km. The limitations of using the NEATM to observe NEAs at high phase angles are discussed.     

Tvashtar awakening detected in April 2006 with OSIRIS at the W.M. Keck Observatory

We detected a volcanic outburst in Io's northern hemisphere on 17 April 2006 with the OSIRIS imaging spectrometer at Keck, and confirmed it was still erupting on 2 June 2006. The eruption, which we name 060417A, was located in Tvashtar Paterae, ∼100 km southeast of the February 2000 eruption. The observed temperature was , over a surface area of , providing a total thermal output of .     

Venus wind map at cloud top level with the MTR/THEMIS visible spectrometer, I: Instrumental performance and first results

Solar light gets scattered at cloud top level in Venus’ atmosphere, in the visible range, which corresponds to the altitude of 67 km. We present Doppler velocity measurements performed with the high resolution spectrometer MTR of the Solar telescope THEMIS (Teide Observatory, Canary Island) on the sodium D2 solar line . Observations lasted only 49 min because of cloudy weather. However, we could assess the instrumental velocity sensitivity, per pixel of 1 arcsec, and give a value of the amplitude of zonal wind at equator at .     

Calculation of the enrichment of the giant planet envelopes during the “late heavy bombardment”

The giant planets of our solar system possess envelopes consisting mainly of hydrogen and helium but are also significantly enriched in heavier elements relatively to our Sun. In order to better constrain how these heavy elements have been delivered, we quantify the amount accreted during the so-called “late heavy bombardment”, at a time when planets were fully formed and planetesimals could not sink deep into the planets. On the basis of the “Nice model”, we obtain accreted masses (in terrestrial units) equal to for Jupiter, and for Saturn. For the two other giant planets, the results are found to depend mostly on whether they switched position during the instability phase. For Uranus, the accreted mass is with an inversion and without an inversion. Neptune accretes in models in which it is initially closer to the Sun than Uranus, and otherwise. With well-mixed envelopes, this corresponds to an increase in the enrichment over the solar value of 0.033±0.001 and 0.074±0.007 for Jupiter and Saturn, respectively. For the two other planets, we find the enrichments to be 2.1±1.4 (w/ inversion) or 1.2±0.7 (w/o inversion) for Uranus, and 2.0±1.2 (w/ inversion) or 2.7±1.6 (w/o inversion) for Neptune. This is clearly insufficient to explain the inferred enrichments of ∼4 for Jupiter, ∼7 for Saturn and ∼45 for Uranus and Neptune.     

The orbit, mass, size, albedo, and density of (65489) Ceto/Phorcys: A tidally-evolved binary Centaur

Hubble Space Telescope observations of Uranus- and Neptune-crossing object (65489) Ceto/Phorcys (provisionally designated 2003 FX₁₂₈) reveal it to be a close binary system. The mutual orbit has a period of 9.554±0.011 days and a semimajor axis of 1840±48 km. These values enable computation of a system mass of (5.41±0.42)×¹⁰¹⁸ kg. Spitzer Space Telescope observations of thermal emission at 24 and 70 μm are combined with visible photometry to constrain the system's effective radius and geometric albedo . We estimate the average bulk density to be , consistent with ice plus rocky and/or carbonaceous materials. This density contrasts with lower densities recently measured with the same technique for three other comparably-sized outer Solar System binaries (617) Patroclus, (26308) 1998 SM₁₆₅, and (47171) 1999 TC₃₆, and is closer to the density of the saturnian irregular satellite Phoebe. The mutual orbit of Ceto and Phorcys is nearly circular, with an eccentricity ?0.015. This observation is consistent with calculations suggesting that the system should tidally evolve on a timescale shorter than the age of the Solar System.     

3782 Celle: Discovery of a binary system within the Vesta family of asteroids

Photometric observations of the minor planet (3782) Celle, which has been associated both dynamically and spectroscopically with the Vesta asteroid family, were obtained using the 1.8-m Vatican Advanced Technology Telescope during September 2001 and December 2002-January 2003. Analysis of these data reveals a normal rotational lightcurve (, amplitude =0.10-0.15 mag). During the 2002-2003 run, anomalous attenuation events were observed lasting for about 2.6-3.5 h that varied in amplitude from 0.15-0.3 mag. The attenuations were of two distinct types that can clearly be identified as primary and secondary occultation/eclipses similar to those that have been previously observed in known minor planet binary systems (Pravec et al., 2000). We therefore interpret our data as clear evidence that (3782) Celle is actually an asynchronous binary system with an orbital period of (Ryan et al., 2003). A preliminary model, based on spherical components, yields a primary-to-secondary diameter ratio of 0.43±0.01 and a combined bulk density of for the two components. Because these objects are likely to be composed of basaltic fragments, this density is indicative of a moderate to a highly fractured internal structure for at least one, if not both, of the binary components. Since the Vesta family is believed to have been created via a cratering event, this finding has important implications for understanding possible ejecta re-accumulation and satellite formation in subcatastrophic collisions.     

Thermal infrared and optical observations of four near-Earth asteroids

We present thermal infrared photometry and spectrophotometry of four near-Earth asteroids (NEAs), namely (433) Eros, (66063) 1998 RO₁, (137032) 1998 UO₁, and (138258) 2000 GD₂, using the United Kingdom Infrared Telescope (UKIRT) in 2002. For two objects, i.e. (433) Eros and (137032) 1998 UO₁, quasi-simultaneous optical observations were also obtained, using the Jacobus Kapteyn Telescope (JKT). For (127032) 1998 UO₁, we obtain a rotation period P=3.0±0.1 h and an absolute visual magnitude HV=16.7±0.4. The Standard Thermal Model (STM), Fast Rotating Model (FRM) and near-Earth asteroid Thermal Model (NEATM) have been fitted to the IR fluxes to determine effective diameters Deff, geometric albedos pv, and beaming parameters η. The derived values are (433) Eros: Deff=23.3±3.5 km (at lightcurve maximum), pv=0.24±0.07, η=0.95±0.19; (66063) 1998 RO₁: , ; (137032) 1998 UO₁: Deff<1.13 km, pv>0.29; (138258) 2000 GD₂: Deff=0.27±0.04 km, , η=0.74±0.15. (66063) 1998 RO₁ is a binary asteroid from lightcurve characteristics [Pravec, P., and 56 colleagues, 2006. Icarus 181, 63-93] and we estimate the effective diameter of the primary (Dp) and secondary (Ds) components: and . The diameter and albedo of (138258) 2000 GD₂ are consistent with the trend of decreasing diameter for S- and Q-type asteroids found by Delbó et al. [Delbó, M., Harris, A.W., Binzel, R.P., Pravec, P., Davies, J.K., 2003. Icarus 166, 116-130]. A possible trend of increasing beaming parameter with diameter for small (less than about 3 km) S- and Q-type asteroids is found.