15 research outputs found
Models of the formation of the planets in the 47 UMa system
Formation of planets in the 47 UMa system is followed in an evolving
protoplanetary disk composed of gas and solids. The evolution of the disk is
calculated from an early stage, when all solids, assumed to be high-temperature
silicates, are in the dust form, to the stage when most solids are locked in
planetesimals. The simulation of planetary evolution starts with a solid embryo
of ~1 Earth mass, and proceeds according to the core accretion -- gas capture
model. Orbital parameters are kept constant, and it is assumed that the
environment of each planet is not perturbed by the second planet. It is found
that conditions suitable for both planets to form within several Myr are easily
created, and maintained throughout the formation time, in disks with . In such disks, a planet of 2.6 Jupiter masses (the minimum for
the inner planet of the 47 UMa system) may be formed at 2.1 AU from the star in
\~3 Myr, while a planet of 0.89 Jupiter masses (the minimum for the outer
planet) may be formed at 3.95 AU from the star in about the same time. The
formation of planets is possible as a result of a significant enhancement of
the surface density of solids between 1.0 and 4.0 AU, which results from the
evolution of a disk with an initially uniform gas-to-dust ratio of 167 and an
initial radius of 40 AU.Comment: Accepted for publication in A&A. 10 pages, 10 figure
Formation of giant planets around stars with various masses
We examine the predictions of the core accretion - gas capture model
concerning the efficiency of planet formation around stars with various masses.
First, we follow the evolution of gas and solids from the moment when all
solids are in the form of small grains to the stage when most of them are in
the form of planetesimals. We show that the surface density of the planetesimal
swarm tends to be higher around less massive stars. Then, we derive the minimum
surface density of the planetesimal swarm required for the formation of a giant
planet both in a numerical and in an approximate analytical approach. We
combine these results by calculating a set of representative disk models
characterized by different masses, sizes, and metallicities, and by estimating
their capability of forming giant planets. Our results show that the set of
protoplanetary disks capable of giant planet formation is larger for less
massive stars. Provided that the distribution of initial disk parameters does
not depend too strongly on the mass of the central star, we predict that the
percentage of stars with giant planets should increase with decreasing stellar
mass. Furthermore, we identify the radial redistribution of solids during the
formation of planetesimal swarms as the key element in explaining these
effects.Comment: Accepted for publication in A&A. 9 pages, 9 figure
Formation of giant planets in disks with different metallicities
We present the first results from simulations of processes leading to planet
formation in protoplanetary disks with different metallicities. For a given
metallicity, we construct a two-dimensional grid of disk models with different
initial masses and radii (, ). For each disk, we follow the evolution
of gas and solids from an early evolutionary stage, when all solids are in the
form of small dust grains, to the stage when most solids have condensed into
planetesimals. Then, based on the core accretion - gas capture scenario, we
estimate the planet-bearing capability of the environment defined by the final
planetesimal swarm and the still evolving gaseous component of the disk. We
define the probability of planet-formation, , as the normalized fractional
area in the (, ) plane populated by disks that have formed
planets inside 5 AU. With such a definition, and under the assumption that the
population of planets discovered at 5 AU is not significantly
contaminated by planets that have migrated from 5 AU, our results agree
fairly well with the observed dependence between the probability that a star
harbors a planet and the star's metal content. The agreement holds for the disk
viscosity parameter ranging from to , and it
becomes much poorer when the redistribution of solids relative to the gas is
not allowed for during the evolution of model disks.Comment: Accepted for publication in A&A. 6 pages, 6 figure
An alternative look at the snowline in protoplanetary disks
We have calculated an evolution of protoplanetary disk from an extensive set
of initial conditions using a time-dependent model capable of simultaneously
keeping track of the global evolution of gas and water-ice. A number of
simplifications and idealizations allows for an embodiment of gas-particle
coupling, coagulation, sedimentation, and evaporation/condensation processes.
We have shown that, when the evolution of ice is explicitly included, the
location of the snowline has to be calculated directly as the inner edge of the
region where ice is present and not as the radius where disk's temperature
equals the evaporation temperature of water-ice. The final location of the
snowline is set by an interplay between all involved processes and is farther
from the star than implied by the location of the evaporation temperature
radius. The evolution process naturally leads to an order of magnitude
enhancement in surface density of icy material.Comment: Accepted for publication in A&A. 8 pages, 4 figure
The anomalous accretion disk of the Cataclysmic Variable RW Sextantis
Synthetic spectra covering the wavelength range 900\AA~to 3000\AA~provide an
accurate fit, established by a analysis, to a combined
observed spectrum of RW Sextantis. Two separately calibrated distances to the
system establish the synthetic spectrum comparison on an absolute flux basis
but with two alternative scaling factors, requiring alternative values of
for final models. Based on comparisons for a range of
values, the observed spectrum does not follow the standard model. Rather than
the exponent 0.25 in the expression for the radial temperature profile, a value
close to 0.125 produces a synthetic spectrum with an accurate fit to the
combined spectrum. A study of time-series spectra shows that a proposed
warped or tilted disk is not supported by the data; an alternative proposal is
that an observed non-axisymmetric wind results from an interaction with the
mass transfer stream debris.Comment: 56 pages, 15 figures, 11 tables. Accepted for The Astrophysical
Journa
Orbital and physical parameters of eclipsing binaries from the ASAS catalogue - IV. A 0.61 + 0.45 M_sun binary in a multiple system
We present the orbital and physical parameters of a newly discovered low-mass
detached eclipsing binary from the All-Sky Automated Survey (ASAS) database:
ASAS J011328-3821.1 A - a member of a visual binary system with the secondary
component separated by about 1.4 seconds of arc. The radial velocities were
calculated from the high-resolution spectra obtained with the 1.9-m
Radcliffe/GIRAFFE, 3.9-m AAT/UCLES and 3.0-m Shane/HamSpec
telescopes/spectrographs on the basis of the TODCOR technique and positions of
H_alpha emission lines. For the analysis we used V and I band photometry
obtained with the 1.0-m Elizabeth and robotic 0.41-m PROMPT telescopes,
supplemented with the publicly available ASAS light curve of the system.
We found that ASAS J011328-3821.1 A is composed of two late-type dwarfs
having masses of M_1 = 0.612 +/- 0.030 M_sun, M_2 = 0.445 +/- 0.019 M_sun and
radii of R_1 = 0.596 +/- 0.020 R_sun, R_2 = 0.445 +/- 0.024 R_sun, both show a
substantial level of activity, which manifests in strong H_alpha and H_beta
emission and the presence of cool spots. The influence of the third light on
the eclipsing pair properties was also evaluated and the photometric properties
of the component B were derived. Comparison with several popular stellar
evolution models shows that the system is on its main sequence evolution stage
and probably is more metal rich than the Sun. We also found several clues which
suggest that the component B itself is a binary composed of two nearly
identical ~0.5 M_sun stars.Comment: 12 pages, 7 figures, 7 tables, to appear in MNRA
2-D models of layered protoplanetary discs: I. The ring instability
In this work we use the radiation hydrodynamic code TRAMP to perform a
two-dimensional axially symmetric model of the layered disc. Using this model
we follow the accumulation of mass in the dead zone due to the radially varying
accretion rate. We found a new type of instability which causes the dead zone
to split into rings. This "ring instability" works due to the positive feedback
between the thickness of the dead zone and the mass accumulation rate.
We give an analytical description of this instability, taking into account
non-zero thickness of the dead zone and deviations from the Keplerian
rotational velocity. The analytical model agrees reasonably well with results
of numerical simulations. Finally, we speculate about the possible role of the
ring instability in protoplanetary discs and in the formation of planets.Comment: 9 pages, 5 figures, accepted for publication in MNRA
Orbital and physical parameters of eclipsing binaries from the All-Sky Automated Survey catalogue - IV. A 0.61 + 0.45 M⊙ binary in a multiple system
We present the orbital and physical parameters of a newly discovered low-mass detached eclipsing
binary from the All-Sky Automated Survey (ASAS) data base: ASAS J011328–3821.1 A,
which is a member of a visual binary system with the secondary component separated by about
1.4 arcsec. The radial velocities have been calculated from the high-resolution spectra obtained
with the 1.9-m Radcliffe telescope/Grating Instrument for Radiation Analysis with a Fibre-Fed
Echelle (GIRAFFE) spectrograph, the 3.9-m Anglo-Australian Telescope (AAT)/University
College London Echelle Spectrograph (UCLES) and the 3.0-m Shane telescope/Hamilton
Spectrograph (HamSpec) on the basis of the TODCOR technique and the positions of the Hα
emission lines. For the analysis, we have used V- and I-band photometry obtained with the
1.0-m Elizabeth telescope and the 0.41-m Panchromatic Robotic Optical Monitoring and
Polarimetry Telescopes (PROMPT), supplemented with the publicly available ASAS light
curve of the system.
We have found that ASAS J011328–3821.1 A is composed of two late-type dwarfs, which
have masses of M1 = 0.612 ± 0.030 M⊙ and M2 = 0.445 ± 0.019 M⊙ and radii of R1 =
0.596 ± 0.020 R⊙ and R2 = 0.445 ± 0.024 R⊙. Both show a substantial level of activity,
which manifests in strong Hα and Hβ emission and the presence of cool spots. The influence
of the third light on the eclipsing pair properties has also been evaluated and the photometric
properties of component B have been derived. A comparison with several popular stellar
evolution models shows that the system is on its main-sequence evolution stage and that it
is probably more metal-rich than the Sun. We have also found several clues to suggest that
component B itself is a binary composed of two nearly identical ∼0.5-M⊙ stars
Diversity of planetary systems from evolution of solids in protoplanetary disks
We have developed and applied a model designed to track
simultaneously the evolution of gas and solids in protoplanetary disks
from an early stage, when all solids are in the dust form, to the
stage when most solids are in the form of a planetesimal swarm. The
model is computationally efficient and allows for a global,
comprehensive approach to the evolution of solid particles due to
gas-solid coupling, coagulation, sedimentation, and
evaporation/condensation. The co-evolution of gas and solids is
calculated for 107 yr for several evolution regimes and starting
from a comprehensive domain of initial conditions. The output of a
single evolutionary run is a spatial distribution of mass locked in a
planetesimal swarm. Because swarm's mass distribution is related to the
architecture of a nascent planetary system, diversity of swarms is
taken as a proxy for a diversity of planetary systems. We have found
that disks with low values of specific angular momentum are bled out
of solids and do not form planetary systems. Disks with high and
intermediate values of specific angular momentum form diverse
planetary systems. Solar-like planetary systems form from disks with
initial masses ≤0.02 and angular momenta ≤
g cm2 s-1. Planets more massive than Jupiter can form
at locations as close as AU from the central star according to
our model