264 research outputs found
Pursuing the planet-debris disk connection: Analysis of upper limits from the Anglo-Australian Planet Search
Solid material in protoplanetary discs will suffer one of two fates after the
epoch of planet formation; either being bound up into planetary bodies, or
remaining in smaller planetesimals to be ground into dust. These end states are
identified through detection of sub-stellar companions by periodic radial
velocity (or transit) variations of the star, and excess emission at mid- and
far-infrared wavelengths, respectively. Since the material that goes into
producing the observable outcomes of planet formation is the same, we might
expect these components to be related both to each other and their host star.
Heretofore, our knowledge of planetary systems around other stars has been
strongly limited by instrumental sensitivity. In this work, we combine
observations at far-infrared wavelengths by IRAS, Spitzer, and Herschel with
limits on planetary companions derived from non-detections in the 16-year
Anglo-Australian Planet Search to clarify the architectures of these
(potential) planetary systems and search for evidence of correlations between
their constituent parts. We find no convincing evidence of such correlations,
possibly owing to the dynamical history of the disk systems, or the greater
distance of the planet-search targets. Our results place robust limits on the
presence of Jupiter analogs which, in concert with the debris disk
observations, provides insights on the small-body dynamics of these nearby
systems.Comment: Accepted for publication in A
An Orbital Stability Study of the Proposed Companions of SW Lyncis
We have investigated the dynamical stability of the proposed companions
orbiting the Algol type short-period eclipsing binary SW Lyncis (Kim et al.
2010). The two candidate companions are of stellar to sub-stellar nature, and
were inferred from timing measurements of the system's primary and secondary
eclipses. We applied well-tested numerical techniques to accurately integrate
the orbits of the two companions and to test for chaotic dynamical behaviour.
We carried out the stability analysis within a systematic parameter survey
varying both the geometries and orientation of the orbits of the companions, as
well as their masses. In all our numerical integrations we found that the
proposed SW Lyn multi-body system is highly unstable on time-scales on the
order of 1000 years. Our results cast doubt on the interpretation that the
timing variations are caused by two companions. This work demonstrates that a
straightforward dynamical analysis can help to test whether a best-fit
companion-based model is a physically viable explanation for measured eclipse
timing variations. We conclude that dynamical considerations reveal that the
propsed SW Lyncis multi-body system most likely does not exist or the
companions have significantly different orbital properties as conjectured in
Kim et al. (2010).Comment: 9 pages, 6 figures, 2 tables. Submitted to and accepted by JASS --
Journal for Astronomy and Space Sciences (using JKAS LaTeX style file
Gap formation in a self-gravitating disk and the associated migration of the embedded giant planet
We present the results of our recent study on the interactions between a
giant planet and a self-gravitating gas disk. We investigate how the disk's
self-gravity affects the gap formation process and the migration of the giant
planet. Two series of 1-D and 2-D hydrodynamic simulations are performed. We
select several surface densities and focus on the gravitationally stable
region. To obtain more reliable gravity torques exerted on the planet, a
refined treatment of disk's gravity is adopted in the vicinity of the planet.
Our results indicate that the net effect of the disk's self-gravity on the gap
formation process depends on the surface density of the disk. We notice that
there are two critical values, \Sigma_I and \Sigma_II. When the surface density
of the disk is lower than the first one, \Sigma_0 < \Sigma_I, the effect of
self-gravity suppresses the formation of a gap. When \Sigma_0 > \Sigma_I, the
self-gravity of the gas tends to benefit the gap formation process and enlarge
the width/depth of the gap. According to our 1-D and 2-D simulations, we
estimate the first critical surface density \Sigma_I \approx 0.8MMSN. This
effect increases until the surface density reaches the second critical value
\Sigma_II. When \Sigma_0 > \Sigma_II, the gravitational turbulence in the disk
becomes dominant and the gap formation process is suppressed again. Our 2-D
simulations show that this critical surface density is around 3.5MMSN. We also
study the associated orbital evolution of a giant planet. Under the effect of
the disk's self-gravity, the migration rate of the giant planet increases when
the disk is dominated by gravitational turbulence. We show that the migration
timescale associates with the effective viscosity and can be up to 10^4 yr.Comment: 24 pages, 13 figures, accepted by RA
Searching for Earth-mass planets around Centauri: precise radial velocities from contaminated spectra
This work is part of an ongoing project which aims to detect terrestrial
planets in our neighbouring star system Centauri using the Doppler
method. Owing to the small angular separation between the two components of the
Cen AB binary system, the observations will to some extent be
contaminated with light coming from the other star. We are accurately
determining the amount of contamination for every observation by measuring the
relative strengths of the H- and NaD lines. Furthermore, we have
developed a modified version of a well established Doppler code that is
modelling the observations using two stellar templates simultaneously. With
this method we can significantly reduce the scatter of the radial velocity
measurements due to spectral cross-contamination and hence increase our chances
of detecting the tiny signature caused by potential Earth-mass planets. After
correcting for the contamination we achieve radial velocity precision of for a given night of observations. We have also
applied this new Doppler code to four southern double-lined spectroscopic
binary systems (HR159, HR913, HR7578, HD181958) and have successfully recovered
radial velocities for both components simultaneously.Comment: accepted for publication in the International Journal of Astrobiology
(published by Cambridge University Press); will appear in a revised form,
subsequent to editorial input by Cambridge University Pres
The Weihai Observatory search for close-in planets orbiting giant stars
Planets are known to orbit giant stars, yet there is a shortage of planets
orbiting within ~0.5 AU (P<100 days). First-ascent giants have not expanded
enough to engulf such planets, but tidal forces can bring planets to the
surface of the star far beyond the stellar radius. So the question remains: are
tidal forces strong enough in these stars to engulf all the missing planets? We
describe a high-cadence observational program to obtain precise radial
velocities of bright giants from Weihai Observatory of Shandong University. We
present data on the planet host Beta Gem (HD 62509), confirming our ability to
derive accurate and precise velocities; our data achieve an rms of 7.3 m/s
about the Keplerian orbit fit. This planet-search programme currently receives
~100 nights per year, allowing us to aggressively pursue short-period planets
to determine whether they are truly absent.Comment: Accepted for publication in PAS
The PanâPacific Planet Search: A Southern Hemisphere Search for Planets Orbiting Evolved Massive Stars
The vast majority of known extrasolar planets orbit stars with a narrow range of masses (0.7â1.3âMâ). Little is known about the properties of planetary systems with host stars significantly more massive than the Sun. Planet formation models predict that giant planets are more common around higherâmass stars (M* >1.5âMâ ). However, these types of stars pose severe observational challenges while on the main sequence, resulting in a strong bias against them in current planet searches. Fortunately, it is possible to obtain highâprecision Doppler velocities for these massive stars as they evolve off the main sequence and cool as subâgiants. We describe the PanâPacific Planet Search, a survey of 170 subâgiant stars using the 3.9 m Australian Astronomical Telescope. In collaboration with J. Johnsonâs Keck survey of Northern âretired A stars,â we are monitoring nearly every subgiant brighter than Vâ=â8. This survey will provide critical statistics on the frequency and characteristics of planetary systems formed around higherâmass stars
News From The Gamma Cephei Planetary System
The Gamma Cephei planetary system is one of the most interesting systems due
to several reasons: 1.) it is the first planet candidate detected by precise
radial velocity (RV) measurements that was discussed in the literature
(Campbell et al. 1988); 2.) it is a tight binary system with a ~ 20AU; and 3.)
the planet host star is an evolved K-type star. In Hatzes et al. (2003) we
confirmed the presence of the planetary companion with a minimum mass of 1.7
M_Jup at 2 AU. In this paper we present additional eight years of precise RV
data from the Harlan J. Smith 2.7 m Telescope and its Tull Coude spectrograph
at McDonald Observatory. The 900 d signal, that is interpreted as the presence
of the giant planetary companion, is strongly confirmed by adding the new data.
We present an updated orbital solution for the planet, which shows that the
planet is slightly more massive and the orbit more circular than previous
results have suggested. An intensive high-cadence week of RV observations in
2007 revealed that Gamma Cep A is a multi-periodic pulsator. We discuss this
issue within the context of searching for additional planets in this system.Comment: Part of PlanetsbeyondMS/2010 proceedings
http://arxiv.org/html/1011.660
A Second Giant Planet in 3:2 Mean-Motion Resonance in the HD 204313 System
We present 8 years of high-precision radial velocity (RV) data for HD 204313
from the 2.7 m Harlan J. Smith Telescope at McDonald Observatory. The star is
known to have a giant planet (M sin i = 3.5 M_J) on a ~1900-day orbit, and a
Neptune-mass planet at 0.2 AU. Using our own data in combination with the
published CORALIE RVs of Segransan et al. (2010), we discover an outer Jovian
(M sin i = 1.6 M_J) planet with P ~ 2800 days. Our orbital fit suggests the
planets are in a 3:2 mean motion resonance, which would potentially affect
their stability. We perform a detailed stability analysis, and verify the
planets must be in resonance.Comment: Accepted for publication in Ap
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