328 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
Excitation of emission lines by fluorescence and recombination in IC 418
We predict intensities of lines of CII, NI, NII, OI and OII and compare them
with a deep spectroscopic survey of IC 418 to test the effect of excitation of
nebular emission lines by continuum fluorescence of starlight. Our calculations
use a nebular model and a synthetic spectrum of its central star to take into
account excitation of the lines by continuum fluorescence and recombination.
The NII spectrum is mostly produced by fluorescence due to the low excitation
conditions of the nebula, but many CII and OII lines have more excitation by
fluorescence than recombination. In the neutral envelope, the NI permitted
lines are excited by fluorescence, and almost all the OI lines are excited by
recombination. Electron excitation produces the forbidden optical lines of OI,
but continuum fluorescence excites most of the NI forbidden line intensities.
Lines excited by fluorescence of light below the Lyman limit thus suggest a new
diagnostic to explore the photodissociation region of a nebula.Comment: 2 pages, 4 figures, to appear in proceedings of the IAU Symposium
283: "Planetary Nebulae: An Eye to the Future", Eds.: A. Manchado, L.
Stanghellini and D. Schoenberne
Impact of using a privacy model on smart buildings data for CO2 prediction
There is a constant trade-off between the utility of the data collected and
processed by the many systems forming the Internet of Things (IoT) revolution
and the privacy concerns of the users living in the spaces hosting these
sensors. Privacy models, such as the SITA (Spatial, Identity, Temporal, and
Activity) model, can help address this trade-off. In this paper, we focus on
the problem of prediction, which is crucial for health monitoring but
can be used to monitor occupancy, which might reveal some private information.
We apply a number of transformations on a real dataset from a Smart Building to
simulate different SITA configurations on the collected data. We use the
transformed data with multiple Machine Learning (ML) techniques to analyse the
performance of the models to predict levels. Our results show that,
for different algorithms, different SITA configurations do not make one
algorithm perform better or worse than others, compared to the baseline data;
also, in our experiments, the temporal dimension was particularly sensitive,
with scores decreasing up to between the original and the transformed
data. The results can be useful to show the effect of different levels of data
privacy on the data utility of IoT applications, and can also help to identify
which parameters are more relevant for those systems so that higher privacy
settings can be adopted while data utility is still preserved
The impact of strong recombination on temperature determination in planetary nebulae
The long-standing difference in chemical abundances determined from optical
recombination lines and collisionally excited lines raises questions about our
understanding of atomic physics, as well as the assumptions made when
determining physical conditions and chemical abundances in astrophysical
nebulae. Here, we study the recombination contribution of [O III] 4363 and the
validity of the line ratio [O III] 4363/4959 as a temperature diagnostic in
planetary nebulae with a high abundance discrepancy. We derive a fit for the
recombination coefficient of [O III] 4363 that takes into account the radiative
and dielectronic recombinations, for electron temperatures from 200 to 30,000
K. We estimate the recombination contribution of [O III] 4363 for the planetary
nebulae Abell 46 and NGC 6778 by subtracting the collisional contribution from
the total observed flux. We find that the spatial distribution for the
estimated recombination contribution in [O III] 4363 follows that of the O II
4649 recombination line, both peaking in the central regions of the nebula,
especially in the case of Abell 46 which has a much higher abundance
discrepancy. The estimated recombination contribution reaches up to 70% and 40%
of the total [O III] 4363 observed flux, for Abell 46 and NGC 6778,
respectively.Comment: Accepted in MNRAS Letter
MUSE crowded field 3D spectroscopy in NGC 300 III. Characterizing extremely faint HII regions and diffuse ionized gas
There are known differences between the physical properties of HII and
diffuse ionized gas (DIG), but most of the studied regions in the literature
are relatively bright. We compiled a faint sample of 390 HII regions with
median =34.7 in the spiral galaxy NGC300, derived their
physical properties in terms of metallicity, density, extinction, and
kinematics, and performed a comparative analysis of the properties of the DIG.
We used MUSE data of nine fields in NGC300, covering a galactocentric distance
of zero to ~450 arcsec (~4 projected kpc), including spiral arm and inter-arm
regions. We binned the data in dendrogram leaves and extracted all strong
nebular emission lines. We identified HII and DIG regions and compared their
electron densities, metallicity, extinction, and kinematic properties. We also
tested the effectiveness of unsupervised machine-learning algorithms in
distinguishing between the HII and DIG regions. The gas density in the HII and
DIG regions is close to the low-density limit in all fields. The average
velocity dispersion in the DIG is higher than in the HII regions, which can be
explained by the DIG being 1.8 kK hotter than HII gas. The DIG manifests a
lower ionization parameter than HII gas, and the DIG fractions vary between
15-77%, with strong evidence of a contribution by hot low-mass evolved stars
and shocks to the DIG ionization. Most of the DIG is consistent with no
extinction and an oxygen metallicity that is indistinguishable from that of the
HII gas.We observe a flat metallicity profile in the central region, without a
sign of a gradient. The differences between extremely faint HII and DIG regions
follow the same trends and correlations as their much brighter cousins. HII and
DIG are so heterogeneous, however, that the differences within each class are
larger than the differences between the two classes.Comment: Accepted in A&
Recommended from our members
MUSE crowded field 3D spectroscopy in NGC 300: III. Characterizing extremely faint HII regions and diffuse ionized gas
Context. There are known differences between the physical properties of H II and diffuse ionized gas (DIG). However, most of the studied regions in the literature are relatively bright, with log10 L(Hα)[erg s-1] âł37. Aims. We compiled an extremely faint sample of 390 H II regions with a median Hα luminosity of 34.7 in the flocculent spiral galaxy NGC 300, derived their physical properties in terms of metallicity, density, extinction, and kinematics, and performed a comparative analysis of the properties of the DIG. Methods. We used MUSE data of nine fields in NGC 300, covering a galactocentric distance of zero to ~450 arcsec (~4 projected kpc), including spiral arm and inter-arm regions. We binned the data in dendrogram leaves and extracted all strong nebular emission lines. We identified H II and DIG regions and compared their electron densities, metallicity, extinction, and kinematic properties. We also tested the effectiveness of unsupervised machine-learning algorithms in distinguishing between the H II and DIG regions. Results. The gas density in the H II and DIG regions is close to the low-density limit in all fields. The average velocity dispersion in the DIG is higher than in the H II regions, which can be explained by the DIG being 1.8 kK hotter than H II gas. The DIG manifests a lower ionization parameter than H II gas, and the DIG fractions vary between 15-77%, with strong evidence of a contribution by hot low-mass evolved stars and shocks to the DIG ionization. Most of the DIG is consistent with no extinction and an oxygen metallicity that is indistinguishable from that of the H II gas. We observe a flat metallicity profile in the central region of NGC 300, without a sign of a gradient. Conclusions. The differences between extremely faint H II and DIG regions follow the same trends and correlations as their much brighter cousins. Both types of objects are so heterogeneous, however, that the differences within each class are larger than the differences between the two classes
Highly Significant Impact of HLA-DRB3 and -DRB4 Matching on Different Unrelated allo-HSCT Outcomes: New Perspectives in the Unrelated Donor Selection
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