94 research outputs found
High-resolution spectroscopic view of planet formation sites
Theories of planet formation predict the birth of giant planets in the inner,
dense, and gas-rich regions of the circumstellar disks around young stars.
These are the regions from which strong CO emission is expected. Observations
have so far been unable to confirm the presence of planets caught in formation.
We have developed a novel method to detect a giant planet still embedded in a
circumstellar disk by the distortions of the CO molecular line profiles
emerging from the protoplanetary disk's surface. The method is based on the
fact that a giant planet significantly perturbs the gas velocity flow in
addition to distorting the disk surface density. We have calculated the
emerging molecular line profiles by combining hydrodynamical models with
semianalytic radiative transfer calculations. Our results have shown that a
giant Jupiter-like planet can be detected using contemporary or future
high-resolution near-IR spectrographs such as VLT/CRIRES or ELT/METIS. We have
also studied the effects of binarity on disk perturbations. The most
interesting results have been found for eccentric circumprimary disks in
mid-separation binaries, for which the disk eccentricity - detectable from the
asymmetric line profiles - arises from the gravitational effects of the
companion star. Our detailed simulations shed new light on how to constrain the
disk kinematical state as well as its eccentricity profile. Recent findings by
independent groups have shown that core-accretion is severely affected by disk
eccentricity, hence detection of an eccentric protoplanetary disk in a young
binary system would further constrain planet formation theories.Comment: IAU Symposium 276 (contributed talk
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
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
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
\textit{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 onto the core. On the other hand, a
large amount of pebbles () 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.Comment: 6 pages, 3 figures, This article has been accepted for publication in
MNRAS Letters Published by Oxford University Press on behalf of the Royal
Astronomical Societ
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
Double neutron star formation via consecutive type II supernova explosions
Since the discovery of the first double neutron star (DNS) system, the number
of these exotic binaries has reached fifteen. Here we investigate a channel of
DNS formation in binary systems with components above the mass limit of type II
supernova explosion (SN II), i.e. 8 MSun. We apply a spherically symmetric
homologous envelope expansion model to account for mass loss, and follow the
dynamical evolution of the system numerically with a high-precision integrator.
The first SN occurs in a binary system whose orbital parameters are
pre-defined, then, the homologous expansion model is applied again in the newly
formed system. Analysing 1 658 880 models we find that DNS formation via
subsequent SN II explosions requires a fine-tuning of the initial parameters.
Our model can explain DNS systems with a separation greater than 2.95 au. The
eccentricity of the DNS systems spans a wide range thanks to the orbital
circularisation effect due to the second SN II explosion. The eccentricity of
the DNS is sensitive to the initial eccentricity of the binary progenitor and
the orbital position of the system preceding the second explosion. In agreement
with the majority of the observations of DNS systems, we find the system
centre-of mass velocities to be less than 60 km/s. Neutron stars that become
unbound in either explosion gain a peculiar velocity in the range of 0.02 - 240
km/s. In our model, the formation of tight DNS systems requires a
post-explosion orbit-shrinking mechanism, possibly driven by the ejected
envelopes.Comment: Accepted for publication in MNRA
Outbursts in Global Protoplanetary Disk Simulations
While accreting through a circumstellar disk, young stellar objects are
observed to undergo sudden and powerful accretion events known as FUor or EXor
outbursts. Although such episodic accretion is considered to be an integral
part of the star formation process, the triggers and mechanisms behind them
remain uncertain. We conducted global numerical hydrodynamics simulations of
protoplanetary disk formation and evolution in the thin-disk limit, assuming
both magnetically layered and fully magnetorotational instability (MRI)-active
disk structure. In this paper, we characterize the nature of the outbursts
occurring in these simulations. The instability in the dead zone of a typical
layered disk results in "MRI outbursts". We explore their progression and their
dependence on the layered disk parameters as well as cloud core mass. The
simulations of fully MRI-active disks showed an instability analogous to the
classical thermal instability. This instability manifested at two
temperatures--above approximately 1400 K and 3500 K--due to the steep
dependence of Rosseland opacity on the temperature. The origin of these
thermally unstable regions is related to the bump in opacity resulting from
molecular absorption by water vapor and may be viewed as a novel mechanism
behind some of the shorter duration accretion events. Although we demonstrated
local thermal instability in the disk, more investigations are needed to
confirm that a large-scale global instability will ensue. We conclude that the
magnetic structure of a disk, its composition, as well as the stellar mass, can
significantly affect the nature of episodic accretion in young stellar objects.Comment: 16 figure
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