276 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
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A search for multi-planet systems
textI report the results of a three-year intensive radial-velocity survey of 22 planet-host stars in search of the low-amplitude (K ~5-10 m s⁻¹) signals from additional planets which may be "hiding" in the residuals of the known planet orbital solution. On average, more than 40 radial-velocity observations were obtained for each target using the High-Resolution Spectrograph at the 9.2m Hobby-Eberly Telescope (HET). These high-precision data can be used to rule out additional planets in some of these systems to a detection limit of M sin i ~10-20 Earth masses at a = 0:05 AU. Jupiter-mass planets can be excluded at the 99% level for orbital separations a < 2 AU. No additional planets are evident, and our data do not confirm the planets HD 20367b, HD 74156d, and 47 UMa c. Test particle simulations of these systems with the SWIFT N-body integrator reveal the regions where additional planets could reside in stable orbits. Further simulations with Saturn-mass bodies in these regions are also performed. We note a lack of short-period giant planets in any of these 22 systems, despite dynamical feasibility. The frequency of inner giant planets may be much lower than what was expected based on early discoveries of such objects in systems containing jovian-mass planets. Terrestrial-mass planets may be present in these systems but as yet undetectable. These results suggest that planet formation and migration processes do not favor systems containing both "hot" and "cold" Jupiters. Hence, as detection methods become sensitive to terrestrial-mass planets, systems with architectures like our own Solar system may yet be commonplace.Astronom
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
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
The McDonald Observatory Planet Search: New Long-Period Giant Planets, and Two Interacting Jupiters in the HD 155358 System
We present high-precision radial velocity (RV) observations of four
solar-type (F7-G5) stars - HD 79498, HD 155358, HD 197037, and HD 220773 -
taken as part of the McDonald Observatory Planet Search Program. For each of
these stars, we see evidence of Keplerian motion caused by the presence of one
or more gas giant planets in long-period orbits. We derive orbital parameters
for each system, and note the properties (composition, activity, etc.) of the
host stars. While we have previously announced the two-gas-giant HD 155358
system, we now report a shorter period for planet c. This new period is
consistent with the planets being trapped in mutual 2:1 mean-motion resonance.
We therefore perform an in-depth stability analysis, placing additional
constraints on the orbital parameters of the planets. These results demonstrate
the excellent long-term RV stability of the spectrometers on both the Harlan J.
Smith 2.7 m telescope and the Hobby-Eberly telescope.Comment: 38 pages, 10 figures, 6 tables. Accepted for publication in Ap
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