150 research outputs found
NGC 6302: high-ionization permitted lines. Applying X-SSN synthesis to VLT-UVES spectra
A preliminary VLT-UVES spectrum of NGC 6302 (Casassus et al. 2002, MN), which
hosts one of the hottest PN nuclei known (Teff ~ 220000 K; Wright et al. 2011,
MN), has been recently analysed by means of X-SSN, a spectrum synthesis code
for nebulae (Morisset and P\'equignot). Permitted recombination lines from
highly-ionized species are detected/identified for the first time in a PN, and
some of them probably for the first time in (Astro)Physics. The need for a
homogeneous, high signal-to-noise UVES spectrum for NGC 6302 is advocated.Comment: Poster contribution (2 pages, 1 figure) to IAU Symposium 283:
"Planetary Nebulae: An Eye to the Future" held in Puerto de la Cruz,
Tenerife, Spain in July 25th-29th 201
Cooling in the shade of warped transition disks
The mass of the gaseous reservoir in young circumstellar disks is a crucial
initial condition for the formation of planetary systems, but estimates vary by
orders of magnitude. In some disks with resolvable cavities, sharp inner disk
warps cast two-sided shadows on the outer rings; can the cooling of the gas as
it crosses the shadows bring constraints on its mass? The finite cooling
timescale should result in dust temperature decrements shifted ahead of the
optical/IR shadows in the direction of rotation. However, some systems show
temperature drops, while others do not. The depth of the drops and the
amplitude of the shift depend on the outer disk surface density Sigma through
the extent of cooling during the shadow crossing time, and also on the
efficiency of radiative diffusion. These phenomena may bear observational
counterparts, which we describe with a simple one-dimensional model. An
application to the HD142527 disk suggests an asymmetry in its shadows, and
predicts a >~10deg shift for a massive gaseous disk, with peak Sigma > 8.3
g/cm2. Another application to the DoAr44 disk limits the peak surface density
to Sigma < 13g/cm2Comment: accepted to MNRAS Letter
Protoplanetary disks including radiative feedback from accreting planets
While recent observational progress is converging on the detection of compact
regions of thermal emission due to embedded protoplanets, further theoretical
predictions are needed to understand the response of a protoplanetary disk to
the planet formation radiative feedback. This is particularly important to make
predictions for the observability of circumplanetary regions. In this work we
use 2D hydrodynamical simulations to examine the evolution of a viscous
protoplanetary disk in which a luminous Jupiter-mass planet is embedded. We use
an energy equation which includes the radiative heating of the planet as an
additional mechanism for planet formation feedback. Several models are computed
for planet luminosities ranging from to Solar luminosities.
We find that the planet radiative feedback enhances the disk's accretion rate
at the planet's orbital radius, producing a hotter and more luminous
environement around the planet, independently of the prescription used to model
the disk's turbulent viscosity. We also estimate the thermal signature of the
planet feedback for our range of planet luminosities, finding that the emitted
spectrum of a purely active disk, without passive heating, is appreciably
modified in the infrared. We simulate the protoplanetary disk around HD 100546
where a planet companion is located at about 68 au from the star. Assuming the
planet mass is 5 Jupiter masses and its luminosity is , we find that the radiative feedback of the planet increases the
luminosity of its au circumplanetary disk from (without feedback) to , corresponding to an
emission of in band after radiative transfer
calculations, a value that is in good agreement with HD 100546b observations.Comment: 12 pages, 12 figures. Accepted for publication in The Astrophysical
Journa
Spiral waves triggered by shadows in transition disks
Circumstellar asymmetries such as central warps have recently been shown to
cast shadows on outer disks. We investigate the hydrodynamical consequences of
such variable illumination on the outer regions of a transition disk, and the
development of spiral arms. Using 2D simulations, we follow the evolution of a
gaseous disk passively heated by the central star, under the periodic forcing
of shadows with an opening angle of 28. With a lower pressure
under the shadows, each crossing results in a variable azimuthal acceleration,
which in time develops into spiral density waves. Their pitch angles evolve
from at the onset, to 11-14,
over 65~AU to 150~AU. Self-gravity enhances the density contrast of the
spiral waves, as also reported previously for spirals launched by planets. Our
control simulations with unshadowed irradiation do not develop structures,
except for a different form of spiral waves seen at later times only in the
gravitationally unstable control case. Scattered light predictions in the
-band show that such illumination spirals should be observable. We suggest
that spiral arms in the case-study transition disk HD~142527 could be explained
as a result of shadowing from the tilted inner disk.Comment: 6 pages, 4 figures, 1 table. Accepted for publication in ApJ
Modelling the spinning dust emission from LDN 1780
We study the anomalous microwave emission (AME) in the Lynds Dark Nebula
(LDN) 1780 on two angular scales. Using available ancillary data at an angular
resolution of 1 degree, we construct an SED between 0.408 GHz to 2997 GHz. We
show that there is a significant amount of AME at these angular scales and the
excess is compatible with a physical spinning dust model. We find that LDN 1780
is one of the clearest examples of AME on 1 degree scales. We detected AME with
a significance > 20. We also find at these angular scales that the
location of the peak of the emission at frequencies between 23-70 GHz differs
from the one on the 90-3000 GHz map. In order to investigate the origin of the
AME in this cloud, we use data obtained with the Combined Array for Research in
Millimeter-wave Astronomy (CARMA) that provides 2 arcmin resolution at 30 GHz.
We study the connection between the radio and IR emissions using morphological
correlations. The best correlation is found to be with MIPS 70m, which
traces warm dust (T50K). Finally, we study the difference in radio
emissivity between two locations within the cloud. We measured a factor
of difference in 30 GHz emissivity. We show that this variation can
be explained, using the spinning dust model, by a variation on the dust grain
size distribution across the cloud, particularly changing the carbon fraction
and hence the amount of PAHs.Comment: 14 pages, 11 figures, submitted to MNRA
Observability of planet-disc interactions in CO kinematics
Empirical evidence of planets in gas-rich circumstellar discs is required to
constrain giant planet formation theories. Here we study the kinematic patterns
which arise from planet-disc interactions and their observability in CO
rotational emission lines. We perform three-dimensional hydrodynamical
simulations of single giant planets, and predict the emergent intensity field
with radiative transfer. Pressure gradients at planet-carved gaps, spiral wakes
and vortices bear strong kinematic counterparts. The iso-velocity contours in
the CO(2-1) line centroids reveal large-scale perturbations,
corresponding to abrupt transitions from below sub-Keplerian to super-Keplerian
rotation along with radial and vertical flows. The increase in line optical
depth at the edge of the gap also modulates , but this is a mild
effect compared to the dynamical imprint of the planet-disc interaction. The
large-scale deviations from the Keplerian rotation thus allow the planets to be
indirectly detected via the first moment maps of molecular gas tracers, at ALMA
angular resolutions. The strength of these deviations depends on the mass of
the perturber. This initial study paves the way to eventually determine the
mass of the planet by comparison with more detailed models.Comment: 6 pages, 3 color figures. 1 animation (Figure 3, Adobe Reader
recommended). Accepted for publication in MNRAS Letter
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