1,694 research outputs found
The S2N2 metallicity calibrator and the abundance gradient of M 33
We introduce the log(Ha/[SII]6717+6731) vs. log(Ha/[NII]6583) (S2N2)
diagnostic diagram as metallicity and ionisation parameter indicator for HII
regions in external galaxies. The location of HII regions in the S2N2 diagram
was studied both empirically and theoretically. We found that, for a wide range
of metallicities, the S2N2 diagram gives single valued results in the
metallicity-ionisation parameter plane. We demonstrate that the S2N2 diagram is
a powerful tool to estimate metallicities of high-redshift (z ~ 2) HII
galaxies. Finally, we derive the metallicity for 76 HII regions in M33 from the
S2N2 diagram and calculate an O/H abundance gradient for this galaxy of -0.05
(+-0.01) dex kpc^-1.Comment: 10 pages, 3 figures and 2 tables. Accepted for publication in MNRA
RF and IF mixer optimum matching impedances extracted by large-signal vectorial measurements
This paper introduces a new technique that allows us to measure the admittance conversion matrix of a two-port device,using a Nonlinear Vector Network Analyzer.This method is applied to extract the conversion matrix of a 0.2 µµµµm pHEMT,driven by a 4.8 GHz pump signal,at different power levels,using an intermediate frequency of 600 MHz.The issue on data inconsistency due to phase randomization among different measurements is discussed and a proper pre- processing algorithm is proposed to fix the problem. The output of this work consists of a comprehensive experimental evaluation of up-and down-conversion maximum gain,stability,and optimal RF and IF impedances
Weathering Effects on Engineering Geological Properties of Trachydacitic Volcanic Rocks from the Monte Amiata (Southern Tuscany, Italy)
Variability in lithology and weathering degree affects physical and mechanical properties
of rocks. In this study, we investigated the relationships between weathering degree and engineering
geological properties of trachydacitic volcanic rocks from Monte Amiata (central Italy) by coupling
field and laboratory analyses. We collected in situ Schmidt hammer tests in the field. We evaluated
weathering quantifying the percentage of secondary minerals through thermal analysis in the
laboratory. We also determined dry density (rd), specific gravity of solids (Gs), porosity (n) and
two-dimensional (2D) porosity as resulted from scanning electron microscopy investigations. The
results of our study indicate a negative linear correlation between Schmidt hammer rebound values
and secondary mineral percentage. This correlation provides a tool to quantitatively estimate the
deterioration of rock uniaxial compressive strength (UCS) as weathering increases. Moreover, thermal
analysis turned out to be a quantitative and reproducible method to evaluate weathering degree of
magmatic rocks
HII regions within a compact high velocity cloud. A nearly star-less dwarf galaxy?
Within the SECCO survey we identified a candidate stellar counterpart to the
Ultra Compact High Velocity Cloud (UCHVC) HVC274.68+74.70-123, that was
suggested by Adams et al. (2013) as a possible mini-halo within the Local Group
of galaxies. The spectroscopic follow-up of the brightest sources within the
candidate reveals the presence of two HII regions whose radial velocity is
compatible with physical association with the UVHVC. The available data does
not allow us to give a definite answer on the nature of the newly identified
system. A few alternative hypotheses are discussed. However, the most likely
possibility is that we have found a new faint dwarf galaxy residing in the
Virgo cluster of galaxies, which we name SECCO-1. Independently of its actual
distance, SECCO-1 displays a ratio of neutral hydrogen mass to V luminosity of
M_{HI}/L_V>= 20, by far the largest among local dwarfs. Hence, it appears as a
nearly star-less galaxy and it may be an example of the missing links between
normal dwarfs and the dark mini halos that are predicted to exist in large
numbers according to the currently accepted cosmological model.Comment: Accepted for publication in ApJ Letters. Pdflatex, emulateapj.cls. 6
pages, 3 figures, 2 table
A catalog of planetary nebula candidates and HII regions in NGC 3109
Images obtained with the ESO VLT and FORS1 in [O III] 5007 on- and off-band
as well as r_Gunn filters are analyzed to search for Planetary Nebula (PN)
candidates in the dwarf irregular NGC 3109. In the continuum-subtracted [O III]
5007 on-band images, a large number of emission-line regions were detected. We
describe the criteria employed in order to distinguish PN candidates from
compact HII regions, finding that the sizes and the properties of the ionizing
stars are the most unambiguous discriminators for separating the two classes.
Based upon these criteria, we have found 20 PN candidates for which we present
coordinates, nebular [O III] fluxes, and stellar magnitudes. The cumulative
luminosity function for these PNe is discussed. A catalog of HII regions
listing coordinates, nebular [O III] fluxes, stellar magnitudes and other
characteristics is also presented. We find that HII regions are rather
concentrated towards the disk of the galaxy, while PNe are found also above and
below this structure, consistent with their belonging to an older stellar
population.Comment: 8 pages, including 4 figures and 3 tables. Accepted in A&A. Replaced
with the final versio
Global access to affordable direct oral anticoagulants
Poor control of cardiovascular disease accounts for a substantial proportion of the disease burden in developing countries, but often essential anticoagulant medicines for preventing strokes and embolisms are not widely available. In 2019, direct oral anticoagulants were added to the World Health Organization's WHO Model list of essential medicines. The aims of this paper are to summarize the benefits of direct oral anticoagulants for patients with cardiovascular disease and to discuss ways of increasing their usage internationally. Although the cost of direct oral anticoagulants has provoked debate, the affordability of introducing these drugs into clinical practice could be increased by: price negotiation; pooled procurement; competitive tendering; the use of patent pools; and expanded use of generics. In 2017, only 14 of 137 countries that had adopted national essential medicines lists included a direct oral anticoagulant on their lists. This number could increase rapidly if problems with availability and affordability can be tackled. Once the types of patient likely to benefit from direct oral anticoagulants have been clearly defined in clinical practice guidelines, coverage can be more accurately determined and associated costs can be better managed. Government action is required to ensure that direct oral anticoagulants are covered by national budgets because the absence of reimbursement remains an impediment to achieving universal coverage. Tackling cardiovascular disease with the aid of direct oral anticoagulants is an essential component of efforts to achieve the World Health Organization's target of reducing premature deaths due to noncommunicable disease by 25% by 2025
Discovery of true, likely and possible symbiotic stars in the dwarf spheroidal NGC 205
In this paper we discuss the photometric and spectroscopic observations of
newly discovered (symbiotic) systems in the dwarf spheroidal galaxy NGC 205.
The Gemini Multi-Object Spectrograph on-off band [O III] 5007 A emission
imaging highlighted several [O III] line emitters, for which optical spectra
were then obtained (Gon\c{c}alves et al. 2014). The detailed study of the
spectra of three objects allow us to identify them as true, likely and possible
symbiotic systems (SySts), the first ones discovered in this galaxy. SySt-1 is
unambiguously classified as a symbiotic star, because of the presence of unique
emission lines which belong only to symbiotic spectra, the well known O VI
Raman scattered lines. SySt-2 is only possibly a SySt because the Ne VII Raman
scattered line at 4881 A, recently identified in a well studied Galactic
symbiotic as another very conspicuous property of symbiotic, could as well be
identified as N III or [Fe III]. Finally, SySt-3 is likely a symbiotic binary
because in the red part of the spectrum it shows the continuum of a late giant,
and forbidden lines of moderate- to high-ionization, like [Fe v] 4180 A. The
main source for skepticism on the symbiotic nature of the latter systems is
their location in the PN region in the [O III] 4363/H\gamma\ vs [O III]
5007/H\beta\ diagnostic diagram (Gutierrez-Moreno et al. 1995). It is worth
mentioning that at least another two confirmed symbiotics, one of the Local
Group dwarf spheroidal IC 10 and the other of the Galaxy, are also misplaced in
this diagram.Comment: 8 pages, 5 figures, accepted for publication in MNRAS
Planetary nebulae in M33: probes of AGB nucleosynthesis and ISM abundances
We have obtained deep optical spectrophotometry of 16 planetary nebulae in
M33, mostly located in the central two kpc of the galaxy, with the Subaru and
Keck telescopes. We have derived electron temperatures and chemical abundances
from the detection of the [OIII]4363 line for the whole sample. We have found
one object with an extreme nitrogen abundance, 12+log(N/H)=9.20, accompanied by
a large helium content. After combining our data with those available in the
literature for PNe and HII regions, we have examined the behavior of nitrogen,
neon, oxygen and argon in relation to each other, and as a function of
galactocentric distance. We confirm the good correlation between Ne/H and O/H
for PNe in M33. Ar/H is also found to correlate with O/H. This strengthens the
idea that at the metallicity of the bright PNe analyzed in M33, which is
similar to that found in the LMC, these elements have not been significantly
modified during the dredge-up processes that take place during the AGB phase of
their progenitor stars. We find no significant oxygen abundance offset between
PNe and HII regions at any given galactocentric distance, despite the fact that
these objects represent different age groups in the evolution of the galaxy.
Combining the results from PNe and HII regions, we obtain a representative
slope of the ISM alpha-element (O, Ar, Ne) abundance gradient in M33 of -0.025
+/- 0.006 dex/kpc. Both PNe and HII regions display a large abundance
dispersion at any given distance from the galactic center. We find that the N/O
ratio in PNe is enhanced, relative to the HII regions, by approximately 0.8
dex.Comment: 21 pages, 20 figures. Accepted for publication in MNRA
THE SAN PIETRO MARTIRE TRIPTYCH BY BEATO ANGELICO: MATERIALS CHARACTERIZATION BY MEANS OF INTEGRATED NON-INVASIVE SPECTROSCOPIC MEASUREMENTS.
Gas accretion as the origin of chemical abundance gradients in distant galaxies
It has recently been suggested that galaxies in the early Universe can grow
through the accretion of cold gas, and that this may have been the main driver
of star formation and stellar mass growth. Because the cold gas is essentially
primordial, it has a very low abundance of elements heavier than helium
(metallicity). As it is funneled to the centre of a galaxy, it will lead the
central gas having an overall lower metallicity than gas further from the
centre, because the gas further out has been enriched by supernovae and stellar
winds, and not diluted by the primordial gas. Here we report chemical
abundances across three rotationally-supported star-forming galaxies at z~3,
only 2 Gyr after the Big Bang. We find an 'inverse' gradient, with the central,
star forming regions having a lower metallicity than less active ones, opposite
to what is seen in local galaxies. We conclude that the central gas has been
diluted by the accretion of primordial gas, as predicted by 'cold flow' models.Comment: To Appear in Nature Oct 14, 2010; Supplementary Information included
her
- …