618 research outputs found
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
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
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
Physical observations of comets: Their composition, origin and evolution
The composition, origins, and evolution of comets were studied. The composition was studied using spectroscopic observations of primarily brighter comets at moderate and high resolution for the distribution of certain gases in the coma. The origins was addressed through an imaging search for the Kuiper belt of comets. The evolution was addressed by searching for a link between comets and asteroids using an imaging approach to search for an OH coma
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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
Observations of O (1S) and O (1D) in Spectra of C/1999 S4 (LINEAR)
We report on high spectral resolution observations of comet C/1999 S4
(LINEAR) obtained at McDonald Observatory in June and July 2000. We report
unequivocal detections of the O (1S) and O (1D) metastable lines in emission in
the cometary spectrum. These lines are well separated from any telluric or
cometary emission features. We have derived the ratio of the two red doublet
lines and show they are consistent with the predictions of the branching ratio.
We also derived a ratio of 0.06+/-0.01 for the green line flux to the sum of
the red line fluxes. This ratio is consistent with H2O as the dominant parent
for atomic oxygen. We have measured the widths of the lines and show that the
widths imply that there must be some parent of atomic oxygen in addition to the
H2O.Comment: 26 pages includes 6 figures and 3 tables; accepted for Icaru
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