1,062 research outputs found
No temperature fluctuations in the giant HII region H 1013
While collisionally excited lines in HII regions allow one to easily probe
the chemical composition of the interstellar medium in galaxies, the possible
presence of important temperature fluctuations casts some doubt on the derived
abundances. To provide new insights into this question, we have carried out a
detailed study of a giant HII region, H 1013, located in the galaxy M101, for
which many observational data exist and which has been claimed to harbour
temperature fluctuations at a level of t^2 = 0.03-0.06. We have first
complemented the already available optical observational datasets with a
mid-infrared spectrum obtained with the Spitzer Space Telescope. Combined with
optical data, this spectrum provides unprecedented information on the
temperature structure of this giant HII region. A preliminary analysis based on
empirical temperature diagnostics suggests that temperature fluctuations should
be quite weak. We have then performed a detailed modelling using the pyCloudy
package based on the photoionization code Cloudy. We have been able to produce
photoionization models constrained by the observed Hb surface brightness
distribution and by the known properties of the ionizing stellar population
than can account for most of the line ratios within their uncertainties. Since
the observational constraints are both strong and numerous, this argues against
the presence of significant temperature fluctuations in H 1013. The oxygen
abundance of our best model is 12 + log O/H = 8.57, as opposed to the values of
8.73 and 8.93 advocated by Esteban et al. (2009) and Bresolin (2007),
respectively, based on the significant temperature fluctuations they derived.
However, our model is not able to reproduce the intensities of the oxygen
recombination lines . This cannot be attributed to observational uncertainties
and requires an explanation other than temperature fluctuations.Comment: accepted in Astronomy & Astrophysic
Metal abundances in extremely distant Galactic old open clusters. II. Berkeley 22 and Berkeley 66
We report on high resolution spectroscopy of four giant stars in the Galactic
old open clusters Berkeley~22 and Berkeley~66 obtained with HIRES at the Keck
telescope. We find that and for
Berkeley~22 and Berkeley~66, respectively. Based on these data, we first revise
the fundamental parameters of the clusters, and then discuss them in the
context of the Galactic disk radial abundance gradient. We found that both
clusters nicely obey the most updated estimate of the slope of the gradient
from \citet{fri02} and are genuine Galactic disk objects.Comment: 20 pages, 6 eps figures, accepted for publication in the Astronomical
Journa
Silence superoxide dismutase 1 (SOD1): a promising therapeutic target for amyotrophic lateral sclerosis (ALS)
Introduction: Amyotrophic lateral sclerosis (ALS) is a progressive and incurable neurodegenerative disorder that targets upper and lower motor neurons and leads to fatal muscle paralysis. Mutations in the superoxide dismutase 1 (SOD1) gene are responsible for 15% of familial ALS cases, but several studies have indicated that SOD1 dysfunction may also play a pathogenic role in sporadic ALS. SOD1 induces numerous toxic effects through the pathological misfolding and aggregation of mutant SOD1 species, hence a reduction of the levels of toxic variants appears to be a promising therapeutic strategy for SOD1-related ALS. Several methods are used to modulate gene expression in vivo; these include RNA interference, antisense oligonucleotides (ASOs) and CRISPR/Cas9 technology. Areas covered: This paper examines the current approaches for gene silencing and the progress made in silencing SOD1 in vivo. It progresses to shed light on the key results and pitfalls of these studies and highlights the future challenges and new perspectives for this exciting research field. Expert opinion: Gene silencing strategies targeting SOD1 may represent effective approaches for familial and sporadic ALS-related neurodegeneration; however, the risk of off-target effects must be minimized, and effective and minimally invasive delivery strategies should be fine-tuned
The ARAUCARIA project: Grid-Based Quantitative Spectroscopic Study of Massive Blue Stars in NGC55
The quantitative study of the physical properties and chemical abundances of
large samples of massive blue stars at different metallicities is a powerful
tool to understand the nature and evolution of these objects. Their analysis
beyond the Milky Way is challenging, nonetheless it is doable and the best way
to investigate their behavior in different environments. Fulfilling this task
in an objective way requires the implementation of automatic analysis
techniques that can perform the analyses systematically, minimizing at the same
time any possible bias.
As part of the ARAUCARIA project we carry out the first quantitative
spectroscopic analysis of a sample of 12 B-type supergiants in the galaxy NGC55
at 1.94 Mpc away. By applying the methodology developed in this work, we derive
their stellar parameters, chemical abundances and provide a characterization of
the present-day metallicity of their host galaxy.
Based on the characteristics of the stellar atmosphere/line formation code
FASTWIND, we designed and created a grid of models for the analysis of massive
blue supergiant stars. Along with this new grid, we implemented a spectral
analysis algorithm. Both tools were specially developed to perform fully
consistent quantitative spectroscopic analyses of low spectral resolution of
B-type supergiants in a fast and objective way.
We present the main characteristics of our FASTWIND model grid and perform a
number of tests to investigate the reliability of our methodology. The
automatic tool is applied afterward to a sample of 12 B-type supergiant stars
in NGC55, deriving the stellar parameters and abundances. The results indicate
that our stars are part of a young population evolving towards a red supergiant
phase. The derived chemical composition hints to an average metallicity similar
to the one of the Large Magellanic Cloud, with no indication of a spatial trend
across the galaxy.Comment: 19 pages, 12 figures and 9 tables. Accpeted for publication in A&
Carbon and oxygen in HII regions of the Magellanic Clouds: abundance discrepancy and chemical evolution
We present C and O abundances in the Magellanic Clouds derived from deep
spectra of HII regions. The data have been taken with the Ultraviolet-Visual
Echelle Spectrograph at the 8.2-m VLT. The sample comprises 5 HII regions in
the Large Magellanic Cloud (LMC) and 4 in the Small Magellanic Cloud (SMC). We
measure pure recombination lines (RLs) of CII and OII in all the objects,
permitting to derive the abundance discrepancy factors (ADFs) for O^2+, as well
as their O/H, C/H and C/O ratios. We compare the ADFs with those of other HII
regions in different galaxies. The results suggest a possible metallicity
dependence of the ADF for the low-metallicity objects, but more uncertain for
high-metallicity objects. We compare nebular and B-type stellar abundances and
we find that the stellar abundances agree better with the nebular ones derived
from collisionally excited lines (CELs). Comparing these results with other
galaxies we observe that stellar abundances seem to agree better with the
nebular ones derived from CELs in low-metallicity environments and from RLs in
high-metallicity environments. The C/H, O/H and C/O ratios show almost flat
radial gradients, in contrast with the spiral galaxies where such gradients are
negative. We explore the chemical evolution analysing C/O vs. O/H and comparing
with the results of HII regions in other galaxies. The LMC seems to show a
similar chemical evolution to the external zones of small spiral galaxies and
the SMC behaves as a typical star-forming dwarf galaxy.Comment: Accepted for publication in MNRAS, 17 pages, 11 figures, 8 table
[ArIII]/[OIII] and [SIII]/[OIII]: well-behaved oxygen abundance indicators for HII regions and star forming galaxies
We propose two statistical methods to derive oxygen abundances in HII regions
and star forming galaxies and calibrate them with a sample of several hundred
giant HII regions in spiral and blue compact galaxies as well as of galaxies
from the Sloan Digital Sky Survey. We show the advantages of our new abundance
indicators over previous ones.Comment: accepted as Letter to Astronomy & Astrophysic
Glial cells involvement in spinal muscular atrophy: Could SMA be a neuroinflammatory disease?
Spinal muscular atrophy (SMA) is a severe, inherited disease characterized by the progressive degeneration and death of motor neurons of the anterior horns of the spinal cord, which results in muscular atrophy and weakness of variable severity. Its early-onset form is invariably fatal in early childhood, while milder forms lead to permanent disability, physical deformities and respiratory complications. Recently, two novel revolutionary therapies, antisense oligonucleotides and gene therapy, have been approved, and might prove successful in making long-term survival of these patients likely. In this perspective, a deep understanding of the pathogenic mechanisms and of their impact on the interactions between motor neurons and other cell types within the central nervous system (CNS) is crucial. Studies using SMA animal and cellular models have taught us that the survival and functionality of motor neurons is highly dependent on a whole range of other cell types, namely glial cells, which are responsible for a variety of different functions, such as neuronal trophic support, synaptic remodeling, and immune surveillance. Thus, it emerges that SMA is likely a non-cell autonomous, multifactorial disease in which the interaction of different cell types and disease mechanisms leads to motor neurons failure and loss. This review will introduce the different glial cell types in the CNS and provide an overview of the role of glial cells in motor neuron degeneration in SMA. Furthermore, we will discuss the relevance of these findings so far and the potential impact on the success of available therapies and on the development of novel ones
Decidability and complexity of the fragments of the modal logic of Allen's relations over the rationals
Interval temporal logics provide a natural framework for temporal
reasoning about interval structures over linearly
ordered domains, where intervals are taken as first-class
citizens. Their expressive power and computational behaviour
mainly depend on two parameters: the set of modalities they feature and
the linear orders over which they are interpreted. In this paper, we consider
all fragments of Halpern and Shoham's interval temporal logic hs
with a decidable satisfiability problem over the rationals,
and we provide a complete classification of them in
terms of their expressiveness and computational complexity by solving the last few
open problems
Faint Supernovae and Supernova Impostors: Case studies of SN2002kg/NGC2403-V37 and SN 2003gm
Photometric and spectroscopic observations of the faint Supernovae (SNe)
2002kg and 2003gm, and their precursors, in NGC 2403 and NGC 5334 respectively,
are presented. The properties of these SNe are discussed in the context of
previously proposed scenarios for faint SNe: low mass progenitors producing
under-energetic SNe; SNe with ejecta constrained by a circumstellar medium; and
outbursts of massive Luminous Blue Variables (LBVs). The last scenario has been
referred to as ``Type V SNe'', ``SN impostors'' or ``fake SNe.'' The faint SN
2002kg reached a maximum brightness of , much fainter than
normal type II SNe. The precursor of SN 2002kg is confirmed to be, as shown in
previous work, the LBV NGC2403-V37. Strong lines are observed
in the spectra of SN 2002kg, similar to both the LBV NGC2363-V1 and the type
IIn SN 1995G. The spectrum of SN 2002kg does show strong resolved at 6549,6583\ang. The identified progenitor of SN 2003gm
is a bright yellow star, consistent with a F5-G2 supergiant. SN 2003gm, at the
epoch of discovery, was of similar brightness to the possible fake SN 1997bs.
Photometrically SN 2003gm shows the same decrease in brightness, over the same
time period as SN 1997bs. The early time spectra of SN 2003gm are dominated by
Balmer emission lines, which at the observed resolution, appear similar to SN
2000ch. On the basis of the post-discovery photometric and spectroscopic
observations presented here we suggest that SN 2003gm is a similar event to SN
1997bs. The presence of strong lines, near
, is suggested as a possible means of identifying objects
such as SN 2002kg/NGC2403-V37 as being LBVs - although not as a general
classification criterion of all LBVs masquerading as SNe (abridged).Comment: 17 pages, 17 figures (4 jpg), MNRAS accepted, 4 typos correcte
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