7,372 research outputs found
Modeling dust emission in PN IC 418
We investigated the infrared (IR) dust emission from PN IC 418, using a
detailed model controlled by a previous determination of the stellar properties
and the characteristics of the photoionized nebula, keeping as free parameters
the dust types, amounts and distributions relative to the distance of the
central star. The model includes the ionized region and the neutral region
beyond the recombination front (Photodissociation region, or PDR), where the
[OI] and [CII] IR lines are formed. We succeeded in reproducing the observed
infrared emission from 2 to 200~\mm. The global energy budget is fitted by
summing up contributions from big grains of amorphous carbon located in the
neutral region and small graphite grains located in the ionized region (closer
to the central star).
Two emission features seen at 11.5 and 30~\mm are also reproduced by assuming
them to be due to silicon carbide (SiC) and magnesium and iron sulfides
(MgFeS), respectively. For this, we needed to consider ellipsoidal
shapes for the grains to reproduce the wavelength distribution of the features.
Some elements are depleted in the gaseous phase: Mg, Si, and S have sub-solar
abundances (-0.5 dex below solar by mass), while the abundance of C+N+O+Ne by
mass is close to solar. Adding the abundances of the elements present in the
dusty and gaseous forms leads to values closer to but not higher than solar,
confirming that the identification of the feature carriers is plausible. Iron
is strongly depleted (3 dex below solar) and the small amount present in dust
in our model is far from being enough to recover the solar value. A remaining
feature is found as a residue of the fitting process, between 12 and 25~\mm,
for which we do not have identification.Comment: Accepted for publication in Astronomy & Astrophysics. V2: adding
reference
Modeling the dust emission from PN IC418
We construct a detailed model for the IR dust emission from the PN IC 418. We
succeed to reproduce the emission from 2 to 200m. We can determine the
amount of emitting dust as well as its composition, and compare to the
depletion of elements determined for the photoionized region.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 2011. Few typos correcte
On the frequency dependence of p-mode frequency shifts induced by magnetic activity in Kepler solar-like stars
The variations of the frequencies of the low-degree acoustic oscillations in
the Sun induced by magnetic activity show a dependence with radial order. The
frequency shifts are observed to increase towards higher-order modes to reach a
maximum of about 0.8 muHz over the 11-yr solar cycle. A comparable frequency
dependence is also measured in two other main-sequence solar-like stars, the
F-star HD49933, and the young 1-Gyr-old solar analog KIC10644253, although with
different amplitudes of the shifts of about 2 muHz and 0.5 muHz respectively.
Our objective here is to extend this analysis to stars with different masses,
metallicities, and evolutionary stages. From an initial set of 87 Kepler
solar-like oscillating stars with already known individual p-mode frequencies,
we identify five stars showing frequency shifts that can be considered reliable
using selection criteria based on Monte Carlo simulations and on the
photospheric magnetic activity proxy Sph. The frequency dependence of the
frequency shifts of four of these stars could be measured for the l=0 and l=1
modes individually. Given the quality of the data, the results could indicate
that a different physical source of perturbation than in the Sun is dominating
in this sample of solar-like stars.Comment: Accepted for publication in A&
Birth, death and diffusion of interacting particles
Individual-based models of chemical or biological dynamics usually consider
individual entities diffusing in space and performing a birth-death type
dynamics. In this work we study the properties of a model in this class where
the birth dynamics is mediated by the local, within a given distance, density
of particles. Groups of individuals are formed in the system and in this paper
we concentrate on the study of the properties of these clusters (lifetime,
size, and collective diffusion). In particular, in the limit of the interaction
distance approaching the system size, a unique cluster appears which helps to
understand and characterize the clustering dynamics of the model.Comment: 15 pages, 6 figures, Iop style. To appear in Journal of Physics A:
Condensed matte
A test for asymptotic giant branch evolution theories: Planetary Nebulae in the Large Magellanic Cloud
We used a new generation of asymptotic giant branch (AGB) stellar models that
include dust formation in the stellar winds to find the links between
evolutionary models and the observed properties of a homogeneous sample of
Large Magellanic Cloud (LMC) planetary nebulae (PNe). Comparison between the
evolutionary yields of elements such as CNO and the corresponding observed
chemical abundances is a powerful tool to shed light on evolutionary processes
such as hot bottom burning (HBB) and third dredge-up (TDU). We found that the
occurrence of HBB is needed to interpret the nitrogen-enriched (log(N/H)+12>8)
PNe. In particular, N-rich PNe with the lowest carbon content are nicely
reproduced by AGB models of mass M >=6 Mo, whose surface chemistry reflects the
pure effects of HBB. PNe with log(N/H)+12<7.5 correspond to ejecta of stars
that have not experienced HBB, with initial mass below about 3 Mo. Some of
these stars show very large carbon abundances, owing to the many TDU episodes
experienced. We found from our LMC PN sample that there is a threshold to the
amount of carbon accumulated at AGB surfaces, log(C/H)+12<9. Confirmation of
this constraint would indicate that, after the C-star stage is reached,AGBs
experience only a few thermal pulses, which suggests a rapid loss of the
external mantle, probably owing to the effects of radiation pressure on
carbonaceous dust particles present in the circumstellar envelope. The
implications of these findings for AGB evolution theories and the need to
extend the PN sample currently available are discussed.Comment: 12 pages, 4 figures, 1 table, accepted for publication in MNRAS (2015
July 13; in original form 2015 June 9
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