The companion object to HD114762

We obtained 28 independent radial velocity measurements on the star HD114762, and are now able to derive orbit solution. We confirm the existence of a companion object in an orbit with a semimajor axis about 0.4 au. The new orbit solution is discussed. The result show that the companion is not a planet, but instead is a brown dwarf or a low mass star in a system viewed nearly pole-on

Radial velocity detection of extra-solar planetary systems

The goal of this program was to detect planetary systems in orbit around other stars through the ultra high precision measurement of the orbital motion of the star around the star-planet barycenter. The survey of 33 nearby solar-type stars is the essential first step in understanding the overall problem of planet formation. The program will accumulate the necessary statistics to determine the frequency of planet formation as a function of stellar mass, age, and composition

Finite type invariants of 3-manifolds

A theory of finite type invariants for arbitrary compact oriented 3-manifolds is proposed, and illustrated through many examples arising from both classical and quantum topology. The theory is seen to be highly non-trivial even for manifolds with large first betti number, encompassing much of the complexity of Ohtsuki's theory for homology spheres. (For example, it is seen that the quantum SO(3) invariants, though not of finite type, are determined by finite type invariants.) The algebraic structure of the set of all finite type invariants is investigated, along with a combinatorial model for the theory in terms of trivalent "Feynman diagrams".Comment: Final version for publication, with figures. The most significant changes from the original posted version are in the exposition of section 3 (on the Conway polynomial) and section 4 (on quantum invariants

On the Nature of the Radial Velocity Variability of Aldebaran: A Search for Spectral Line Bisector Variations

The shape of the Ti I 6303.8 A spectral line of Aldebaran as measured by the line bisector was investigated using high signal-to-noise, high resolution data. The goal of this study was to understand the nature of the 643-day period in the radial velocity for this star reported by Hatzes and Cochran. Variations in the line bisector with the radial velocity period would provide strong evidence in support of rotational modulation or stellar pulsations as the cause of the 643-day period. A lack of any bisector variability at this period would support the planet hypothesis. Variations in the line asymmetries are found with a period of 49.93 days. These variations are uncorrelated with 643-day period found previously in the radial velocity measurements. It is demonstrated that this 50-day period is consistent with an m=4 nonradial sectoral g-mode oscillation. The lack of spectral variability with the radial velocity period of 643 days may provide strong evidence in support of the hypothesis that this variability stems from the reflex motion of the central star due to a planetary companion having a mass of 11 Jupiter masses. However, this long-period variability may still be due to a low order (m=2) pulsation mode since these would cause bisector variations less than the error measurement.Comment: LaTeX, 8 pages, 10 figures. Accepted in Monthly Notices of the Royal Astronomical Societ

Gravitational Instabilities In A Protoplanetary Disk Including The Effects Of Magnetic-Fields

We investigate the gravitational instability of a thin, Keplerian protoplanetary disk including the effects of a largely azimuthal magnetic field. The model follows that of our previous work (Noh, Vishniac, & Cochran 1991) except for the inclusion of a magnetic field. The disk is assumed to consist of neutral and ionized gas and neutral dust which are coupled by gravity and friction. The growth rates and eigenfunctions are calculated numerically using nonaxisymmetric linear perturbation methods. The results show that the growth rate has a maximum at some intermediate azimuthal number m, but for each value of m it is reduced relative to the unmagnetized case. The effects of the magnetic field appear more strongly on small scales. As the strength of the equilibrium magnetic field increases the growth rates decrease, and the maximum instability occurs at a lower value of m due to the increasing magnetic pressure. The response of each component to the magnetic field is discussed using the behavior of the eigenfunctions in the radial direction. With the inclusion of the magnetic field, the effects of the ionization fraction and friction on the growth rates also appear to be important for high m modes. Increasing the ionization fraction or the friction suppresses instability, but only slightly changes the maximally unstable azimuthal scales. The enhanced growth rates due to a dust component for which thermal pressure is negligible are somewhat reduced by the inclusion of a magnetic field. The effects of different boundary conditions (reflecting and transmitting) on the growth rates are also shown.NASA NAGW 2418Astronom

Physical observations of comets: Their composition, origin and evolution

Observations of Comet P/Schwassmann-Wachmann 1 (SW1) during one observing run each in 1989 and 1990 are discussed, and the new significant information that was obtained is presented. Also discussed are near-UV observations of comets. The near-UV is a mostly unexplored spectral region for comets since it is not visible to spacecraft such as IUE and most ground-based detectors and spectrographs are not sensitive in the near-UV