27 research outputs found
Increased isolation mass for pebble accreting planetary cores in pressure maxima of protoplanetary discs
The growth of a pebble accreting planetary core is stopped when reaching its isolation mass that is due to a pressure maximum emerging at the outer edge of the gap opened in gas. This pressure maximum traps the inward drifting pebbles stopping the accretion of solids on to the core. On the other hand, a large amount of pebbles ( \\sim \\! 100\\, {\\mathrm{ M}}_\\oplus ) should flow through the orbit of the core until reaching its isolation mass. The efficiency of pebble accretion increases if the core grows in a dust trap of the protoplanetary disc. Dust traps are observed as ring-like structures by ALMA suggesting the existence of global pressure maxima in discs that can also act as planet migration traps. This work aims to reveal how large a planetary core can grow in such a pressure maximum by pebble accretion. In our hydrodynamic simulations, pebbles are treated as a pressureless fluid mutually coupled to the gas via drag force. Our results show that in a global pressure maximum the pebble isolation mass for a planetary core is significantly larger than in discs with power-law surface density profile. An increased isolation mass shortens the formation time of giant planets
Hunting for binary Cepheids using lucky imaging technique
Detecting companions to Cepheids is difficult. In most cases the bright
pulsator overshines the fainter secondary. Since Cepheids play a key role in
determining the cosmic distance scale it is crucial to find binaries among the
calibrating stars of the period-luminosity relation. Here we present an ongoing
observing project of searching for faint and close companions of Galactic
Cepheids using lucky imaging technique.Comment: 4 pages, 2 figures, published in AN. Proceedings for the 6th Workshop
of Young Researchers in Astronomy and Astrophysic
Water delivery to the TRAPPIST-1 planets
Three of the seven rocky planets (e, f, and g) in TRAPPIST-1 system orbit in the habitable zone of the host star. Therefore, water can be in liquid state at their surface being essential for life. Recent studies suggest that these planets formed beyond the snow line in a water-rich region. The initial water reservoir can be lost during the planet formation due to the stellar activity of the infant low-mass star. However, a potential subsequent water delivery event, like the late heavy bombardment (LHB) in the Solar system, can replenish planetary water reservoirs. To study this water delivery process, we set up a simple model in which an additional 5 -50 M⊕ planet is embedded in a water-rich asteroid belt beyond the snow line of TRAPPIST-1. Asteroids perturbed out from the chaotic zone of the putative planet can enter into the inner system and accreted by the known planets. Our main finding is that the larger is the orbital distance of planet, the higher is the amount of water delivered to the planet by an LHB-like event
Interpreting Brightness Asymmetries in Transition Disks: Vortex at Dead Zone or Planet-carved Gap Edges?
Recent sub-millimeter observations show non-axisymmetric brightness
distributions with a horseshoe-like morphology for more than a dozen transition
disks. The most accepted explanation for the observed asymmetries is the
accumulation of dust in large-scale vortices. Protoplanetary disks vortices can
form by the excitation of Rossby-wave instability in the vicinity of a steep
pressure gradient, which can develop at the edges of a giant planet carved gap
or at the edges of an accretionally inactive zone. We studied the formation and
evolution of vortices formed in these two distinct scenarios by means of
two-dimensional locally isothermal hydrodynamic simulations. We found that the
vortex formed at the edge of a planetary gap is short-lived, unless the disk is
nearly inviscid. In contrast, the vortex formed at the outer edge of a dead
zone is long-lived. The vortex morphology can be significantly different in the
two scenarios: the vortex radial and azimuthal extensions are ~1.5 and ~3.5
times larger for the dead zone edge compared to gap models. In some particular
cases, the vortex aspect ratios can be similar in the two scenarios, however,
the vortex azimuthal extensions can be used to distinguish the vortex formation
mechanisms. We calculate predictions for vortex observability in the
sub-millimeter continuum with ALMA. We found that the azimuthal and radial
extent of brightness asymmetry correlates with vortex formation process, within
the limitations of alpha-viscosity prescription.Comment: 13 pages, 10 figures, accepted for publication in Ap
Dynamics of Haumea’s dust ring
The particle dynamics of the recently observed ring around dwarf planet Haumea is numerically
investigated. The point mass gravitational force, a second degree and order gravity field, and
the solar radiation pressure as the main perturbations are considered. The quasi-stationary
state of the ring varies for different micron-sized grains and depends also on the spin–orbit
resonances between the rotation rate of the main body and the orbital period of the dust
particles. The simulations confirm the variable radial width of the ring observed during the
transit ingress and egress. Results show that the micron-sized grains, initially on circular orbits,
become eccentric and form an apse-aligned ring at the observed radial distance near to the
3:1 spin–orbit resonance. It is also demonstrated that this coincidence is only apparent and
independent of 3:1 resonance
HAT-P-13: a multi-site campaign to detect the transit of the second planet in the system
A possible transit of HAT-P-13c has been predicted to occur on 2010 April 28.
Here we report on the results of a multi-site campaign that has been organised
to detect the event. CCD photometric observations have been carried out at five
observatories in five countries. We reached 30% time coverage in a 5 days
interval centered on the suspected transit of HAT-P-13c. Two transits of
HAT-P-13b were also observed. No transit of HAT-P-13c has been detected while
the campaign was on. By a numerical experiment with 10^5 model systems we
conclude that HAT-P-13c is not a transiting exoplanet with a significance level
from 65% to 72%, depending on the planet parameters and the prior assumptions.
We present two times of transit of HAT-P-13b ocurring at BJD 2455141.5522 +-
0.0010 and BJD 2455249.4508 +- 0.0020. The TTV of HAT-P-13b is consistent with
zero within 0.001 days. The refined orbital period of HAT-P-13b is 2.916293 +-
0.000010 days.Comment: 5 pages, 4 figures, to be accepted by A&
Tidal and rotational effects in the perturbations of hierarchical triple stellar systems. II. Eccentric systems - the case of AS Camelopardalis
We study the perturbations of a relatively close third star on a tidally
distorted eccentric eclipsing binary. We consider both the observational
consequences of the variations of the orbital elements and the interactions of
the stellar rotation with the orbital revolution in the presence of
dissipation. We concentrate mainly on the effect of a hypothetical third
companion on both the real, and the observed apsidal motion period. We
investigate how the observed period derived mainly from some variants of the
O-C relates to the real apsidal motion period. We carried out both analytical
and numerical investigations and give the time variations of the orbital
elements of the binary both in the dynamical and the observational reference
frames. We give the direct analytical form of an eclipsing O-C affected
simultaneously by the mutual tidal forces and the gravitational interactions
with a tertiary. We also integrated numerically simultaneously the orbital and
rotational equations for the possible hierarchical triple stellar system AS
Camelopardalis. We find that there is a significant domain of the possible
hierarchical triple system configurations, where both the dynamical and the
observational effects tend to measure longer apsidal advance rate than is
expected theoretically. This happens when the mutual inclination of the close
and the wide orbits is large, and the orbital plane of the tertiary almost
coincides with the plane of the sky. We also obtain new numerical results on
the interaction of the orbital evolution and stellar rotation in such triplets.
The most important fact is that resonances might occur as the stellar
rotational rate varies during the dissipation-driven synchronization process...Comment: 33 pages, 12 figures (reduced quality!), accepted for publication for
Astronomy and Astrophysic
Spectral signatures of disk eccentricity in young binary systems: I. Circumprimary case
Star formation occurs via fragmentation of molecular clouds, which means that
the majority of stars born are a members of binaries. There is growing evidence
that planets might form in circumprimary disks of medium-separation binaries.
The tidal forces caused by the secondary generally act to distort the
originally circular disk to an eccentric one. To infer the disk eccentricity
from high-res NIR spectroscopy, we calculate the fundamental band emission
lines of the CO molecule emerging from the atmosphere of the disk. We model
circumprimary disk evolution under the gravitational perturbation of the
orbiting secondary using a 2D grid-based hydrodynamical code, assuming
alpha-type viscosity. The hydrodynamical results are combined with our spectral
code based on the double-layer disk model to calculate the CO molecular line
profiles. We find that the orbital velocity distribution of the gas parcels
differs significantly from the circular Keplerian fashion, thus the line
profiles are asymmetric in shape. The magnitude of asymmetry is insensitive to
the binary mass ratio, the magnitude of viscosity, and the disk mass. In
contrast, the disk eccentricity, thus the level of the line profile asymmetry,
is influenced significantly by the binary eccentricity and the disk geometrical
thickness. We demonstrate that the disk eccentricity profile in the
planet-forming region can be determined by fitting the high-resolution CO line
profile asymmetry using a simple 2D spectral model that accounts for the
velocity distortions caused by the disk eccentricity. Thus, with our novel
approach the disk eccentricity can be inferred with high-resolution near-IR
spectroscopy prior to the era of high angular resolution optical or radio
direct-imaging. By determining the disk eccentricity in medium-separation young
binaries, we might be able to constrain the planet formation theories.Comment: 15 pages, 10 figures. Accepted by A&
Near-infrared spectroscopy of EX Lupi in outburst
EX Lup is the prototype of the EXor class of young eruptive stars: objects
showing repetitive brightenings due to increased accretion from the
circumstellar disk to the star. In this paper, we report on medium-resolution
near-infrared spectroscopy of EX\,Lup taken during its extreme outburst in
2008, as well as numerical modeling with the aim of determining the physical
conditions around the star. We detect emission lines from atomic hydrogen,
helium, and metals, as well as first overtone bandhead emission from carbon
monoxide. Our results indicate that the emission lines are originating from gas
located in a dust-free region within ~ 0.2 AU of the star. The profile of the
CO bandhead indicates that the CO gas has a temperature of 2500 K, and is
located in the inner edge of the disk or in the outer parts of funnel flows.
The atomic metals are probably co-located with the CO. Some metallic lines are
fluorescently excited, suggesting direct exposure to ultraviolet photons. The
Brackett series indicates emission from hot (10000 K) and optically thin gas.
The hydrogen lines display a strong spectro-astrometric signal, suggesting that
the hydrogen emission is probably not coming from an equatorial boundary layer;
a funnel flow or disk wind origin is more likely. This picture is broadly
consistent with the standard magnetospheric accretion model usually assumed for
normally accreting T Tauri stars. Our results also set constraints on the
eruption mechanism, supporting a model where material piles up around the
corotation radius and episodically falls onto the star.Comment: 12 pages, 8 figures, 1 table, accepted for publication in Ap