The Stability of Planets in the Alpha Centauri system

This paper investigates the long-term orbital stability of small bodies near the central binary of the Alpha Centauri system. Test particles on circular orbits are integrated in the field of this binary for 32000 binary periods or approximately 2.5 Myr. In the region exterior to the binary, particles with semi-major axes less than roughly three times the binary's semi-major axis are unstable. Inside the binary, particles are unstable if further than 0.2 binary semimajor axes from the primary, with stablility closer in a strong function of inclination: orbits inclined near 90 degrees are unstable in as close as 0.01 binary semimajor axes from either star.Comment: 13 pages, 6 Postscript figures (uses psfig.sty

The return of the Andromedids meteor shower

The Andromedid meteor shower underwent spectacular outbursts in 1872 and 1885, producing thousands of visual meteors per hour and described as `stars fell like rain' in Chinese records of the time. The shower originates from comet 3D/Biela whose disintegration in the mid-1800's is linked to the outbursts, but the shower has been weak or absent since the late 19th Century. This shower returned in December 2011 with a zenithal hourly rate of approximately 50, the strongest return in over a hundred years. Some 122 probable Andromedid orbits were detected by the Canadian Meteor Orbit Radar. The shower outburst occurred during 2011 Dec 3-5. The radiant at RA +$18\degree$ and Dec +$56\degree$ is typical of the `classical' Andromedids of the early 1800's, whose radiant was actually in Cassiopeia. The orbital elements indicate that the material involved was released before 3D/Biela's breakup prior to 1846. The observed shower in 2011 had a slow geocentric speed (16 km s$^{-1}$) and was comprised of small particles: the mean measured mass from the radar is $\sim5 \times 10^{-7}$ kg corresponding to radii of 0.5 mm at a bulk density of 1000 kg/m$^3$. Numerical simulations of the parent comet indicate that the meteoroids of the 2011 return of the Andromedids shower were primarily ejected during 3D/Biela's 1649 perihelion passage. The orbital characteristics, radiant, timing as well as the absence of large particles in the streamlet are all consistent with simulations. Predictions are made regarding other appearances of the shower in the years 2000-2047 based on our numerical model. We note that the details of the 2011 return can, in principle, be used to better constrain the orbit of 3D/Biela prior to the comets first recorded return in 1772.Comment: submitted to the Astronomical Journal Sep 22 201

Finding Long Lost Lexell's Comet: The Fate of the First Discovered Near-Earth Object

Jupiter-family Comet D/1770 L1 (Lexell) was the first discovered Near-Earth Object (NEO), and passed the Earth on 1770 Jul 1 at a recorded distance of 0.015 au. The comet was subsequently lost due to unfavorable observing circumstances during its next apparition followed by a close encounter with Jupiter in 1779. Since then, the fate of D/Lexell has attracted interest from the scientific community, and now we revisit this long-standing question. We investigate the dynamical evolution of D/Lexell based on a set of orbits recalculated using the observations made by Charles Messier, the comet's discoverer, and find that there is a $98\%$ chance that D/Lexell remains in the Solar System by the year of 2000. This finding remains valid even if a moderate non-gravitational effect is imposed. Messier's observations also suggest that the comet is one of the largest known near-Earth comets, with a nucleus of $\gtrsim 10$ km in diameter. This implies that the comet should have been detected by contemporary NEO surveys regardless of its activity level if it has remained in the inner Solar System. We identify asteroid 2010 JL$_{33}$ as a possible descendant of D/Lexell, with a $0.8\%$ probability of chance alignment, but a direct orbital linkage of the two bodies has not been successfully accomplished. We also use the recalculated orbit to investigate the meteors potentially originating from D/Lexell. While no associated meteors have been unambiguously detected, we show that meteor observations can be used to better constrain the orbit of D/Lexell despite the comet being long lost.Comment: AJ in press; animation version of Figure 2 at http://www.astro.uwo.ca/~wiegert/Lexell/Lexell.mp

A numerical comparison with the Ceplecha analytical meteoroid orbit determination method

Abstract-Analytic methods by Ceplecha have long been used for the determination of meteoroid heliocentric orbits. These methods include both the derivation of an initial atmospheric contact position and velocity state, and the calculation of an orbit at infinity based on zenithal attraction assumptions. Herein, we describe a numerical integration-based verification for a portion of the Ceplecha methods, a verification driven by the need for an accurate meteoroid ephemeris in the hours before atmospheric contact. We show a close correspondence in analytic and numerical results, with a previously undocumented minor correction to a meteoroid's longitude of the ascending node