6,179 research outputs found
PopStar Evolutionary Synthesis Models II: Optical emission-line spectra from Giant H{\sc ii} regions
This is the second paper of a series reporting the results from the PopStar
evolutionary synthesis models. Here we present synthetic emission line spectra
of H{\sc ii} regions photoionized by young star clusters, for seven values of
cluster masses and for ages between 0.1 and 5.2 Myr. The ionizing Spectral
Energy Distributions (SEDs) are those obtained by the PopStar code
\citep*{mgb09} for six different metallicities, with a very low metallicity
set, Z=0.0001, not included in previous similar works. We assume that the
radius of the H{\sc ii} region is the distance at which the ionized gas is
deposited by the action of the mechanical energy of the winds and supernovae
from the central ionizing young cluster. In this way the ionization parameter
is eliminated as free argument, since now its value is obtained from the
cluster physical properties (mass, age and metallicity) and from the gaseous
medium characteristics (density and abundances). We discuss our results and
compare them with those from previous models and also with a large and data set
of giant H{\sc ii} regions for which abundances have been derived in a
homogeneous manner. The values of the [OIII] lines (at 4363,
4959, 5007\AA) in the lowest metallicity nebulae are found to be very weak and
similar to those coming from very high metallicity regions (solar or
over-solar). Thus, the sole use of the oxygen lines is not enough to
distinguish between very low and very high metallicity regions. In these cases
we emphasize the need of the additional support of alternative metallicity
tracers, like the [SIII] lines in the near-\textit{IR}.Comment: 20 pages, 26 figures, accepted for publication in MNRAS Main Journa
Mapping the ionized gas of the metal-poor HII galaxy PHL 293B with MEGARA
Here we report the first spatially resolved spectroscopic study for the
galaxy PHL293B using the high-resolution GTC/MEGARA IFU. PHL293B is a local,
extremely metal-poor, high ionization galaxy. This makes PHL 293B an excellent
analogue for galaxies in the early Universe. The MEGARA aperture (~12.5''x
11.3'') covers the entire PHL 293B main body and its far-reaching ionized gas.
We created and discussed maps of all relevant emission lines, line ratios and
physical-chemical properties of the ionized ISM. The narrow emission gas
appears to be ionized mainly by massive stars according to the observed
diganostic line ratios, regardless of the position across the MEGARA aperture.
We detected low intensity broad emission components and blueshifted absorptions
in the Balmer lines (H,H) which are located in the brightest
zone of the galaxy ISM. A chemically homogeneity, across hundreds of parsecs,
is observed in O/H. We take the oxygen abundance 12+log(O/H)=7.64 0.06
derived from the PHL293B integrated spectrum as the representative metallicity
for the galaxy. Our IFU data reveal for the first time that the nebular
HeII4686 emission from PHL 293B is spatially extended and coincident with the
ionizing stellar cluster, and allow us to compute its absolute HeII ionizing
photon flux. Wolf-Rayet bumps are not detected excluding therefore Wolf-Rayet
stars as the main HeII excitation source. The origin of the nebular HeII4686 is
discussed.Comment: 14 pages, 9 Figures, 3 Tables; Accepted for publication in MNRA
The 2HWC HAWC Observatory Gamma Ray Catalog
We present the first catalog of TeV gamma-ray sources realized with the
recently completed High Altitude Water Cherenkov Observatory (HAWC). It is the
most sensitive wide field-of-view TeV telescope currently in operation, with a
1-year survey sensitivity of ~5-10% of the flux of the Crab Nebula. With an
instantaneous field of view >1.5 sr and >90% duty cycle, it continuously
surveys and monitors the sky for gamma ray energies between hundreds GeV and
tens of TeV.
HAWC is located in Mexico at a latitude of 19 degree North and was completed
in March 2015. Here, we present the 2HWC catalog, which is the result of the
first source search realized with the complete HAWC detector. Realized with 507
days of data and represents the most sensitive TeV survey to date for such a
large fraction of the sky. A total of 39 sources were detected, with an
expected contamination of 0.5 due to background fluctuation. Out of these
sources, 16 are more than one degree away from any previously reported TeV
source. The source list, including the position measurement, spectrum
measurement, and uncertainties, is reported. Seven of the detected sources may
be associated with pulsar wind nebulae, two with supernova remnants, two with
blazars, and the remaining 23 have no firm identification yet.Comment: Submitted 2017/02/09 to the Astrophysical Journa
Climate-resilient and regenerative futures for Latin America and the Caribbean
Few events have had an impact as the global crisis caused by COVID-19. However, prior to the pandemic, Latin American and Caribbean (LAC) countries already had severe problems in terms of inequality, environmental degradation, and dysfunctional political systems. Added to this are the growing challenges that climate change poses for this highly vulnerable region. This historic turning point represents a new call to consider future studies to re-imagine and reinvent alternative futures for the LAC region. For this paper, we conducted an in-depth qualitative futures study to identify how Latin American and Caribbean countries could build long-term resilience, focusing on adaptability to climate change risks, considering existing sustainable development challenges and the detrimental effects of the COVID-19 pandemic on the economic, environmental, and social aspects. This study's findings provide recommendations for policymakers and decision-makers to achieve sustainable futures for LAC. Finally, it reflects on the value of collective action for a future-proof region
The Sensitivity of HAWC to High-Mass Dark Matter Annihilations
The High Altitude Water Cherenkov (HAWC) observatory is a wide field-of-view
detector sensitive to gamma rays of 100 GeV to a few hundred TeV. Located in
central Mexico at 19 degrees North latitude and 4100 m above sea level, HAWC
will observe gamma rays and cosmic rays with an array of water Cherenkov
detectors. The full HAWC array is scheduled to be operational in Spring 2015.
In this paper, we study the HAWC sensitivity to the gamma-ray signatures of
high-mass (multi- TeV) dark matter annihilation. The HAWC observatory will be
sensitive to diverse searches for dark matter annihilation, including
annihilation from extended dark matter sources, the diffuse gamma-ray emission
from dark matter annihilation, and gamma-ray emission from non-luminous dark
matter subhalos. Here we consider the HAWC sensitivity to a subset of these
sources, including dwarf galaxies, the M31 galaxy, the Virgo cluster, and the
Galactic center. We simulate the HAWC response to gamma rays from these sources
in several well-motivated dark matter annihilation channels. If no gamma-ray
excess is observed, we show the limits HAWC can place on the dark matter
cross-section from these sources. In particular, in the case of dark matter
annihilation into gauge bosons, HAWC will be able to detect a narrow range of
dark matter masses to cross-sections below thermal. HAWC should also be
sensitive to non-thermal cross-sections for masses up to nearly 1000 TeV. The
constraints placed by HAWC on the dark matter cross-section from known sources
should be competitive with current limits in the mass range where HAWC has
similar sensitivity. HAWC can additionally explore higher dark matter masses
than are currently constrained.Comment: 15 pages, 4 figures, version to be published in PR
Bright Stars and Recent Star Formation in the Irregular Magellanic Galaxy NGC2366
The stellar content of the Im galaxy NGC 2366 is discussed on the basis of
CCD BVR photometry. The three brightest blue and red stars have been used to
estimate its distance, obtaining a balue of 2.9 Mpc. The spatial distribution
of the young stellar population is discussed in the light of the integrated
color indices and the color-magnitude diagrams of different zones of the
galaxy. A generalized star formation burst seems to have taken place about 50
Myr ago. The youngest stars are preferentially formed in the South-West part of
the bar, where the giant HII complex NGC 2363 is located, being younger and
bluer. The bar seems to play a role favouring star formation in one of its
extremes. Self-propagation however, does not seem to be triggering star
formation at large scale. A small region, populated by very young stars has
also been found at the East of the galaxy.Comment: Astronomical Journal, accepted. This is a uuencoded, compressed, tar
file (102 Kbytes) of 1 text, 1 table postscript files. Figures are retrieved
as a separate file. One single file with all figures and tables (552Kb) also
available from http://www.ast.cam.ac.uk/~etelles/astronomy.htm
До питання проблематики розвитку логістичного аутсорсингу ринку України
Genomic imprinting, the epigenetic process by which transcription occurs from a single parental allele, is believed influence social behaviours in mammals. An important social behaviour is group living, which is enriched in Eutherian mammals relative to monotremes and marsupials. Group living facilitates resource acquisition, defence of territory and co-care of young, but requires a stable social group with complex inter-individual relationships. Co-occurring with increased group living in Eutherians is an increase in the number of imprinted loci, including that spanning the maternally expressed Cdkn1c. Using a ‘loss-of-imprinting’ model of Cdkn1c (Cdkn1cBACx1), we demonstrated that two-fold over expression of Cdkn1c results in abnormal social behaviours. Although our previous work indicated that male Cdkn1cBACx1 mice were more dominant as measured by tube-test encounters with unfamiliar wild-type males. Building upon this work, using more ecologically relevant assessments of social dominance, indicated that within their normal social group, Cdkn1cBACx1 mice did not occupy higher ranking positions. Nevertheless, we find that presence of Cdkn1cBACx1 animals within a group leads to instability of the normal social hierarchy, as indicated by greater variability in social rank within the group over time and an increase in territorial behaviour in WT cage-mates. Consequently, these abnormal behaviours led to an increased incidence of fighting and wounding within the group. Taken together these data indicate that normal expression of Cdkn1c is required for maintaining stability of the social group and suggests that the acquisition of monoallelic expression of Cdkn1c may have enhanced social behaviour in Eutherian mammals to facilitate group living
- …