1,680 research outputs found
The IACOB project: A grid-based automatic tool for the quantitative spectroscopic analysis of O-stars
We present the IACOB grid-based automatic tool for the quantitative
spectroscopic analysis of O-stars. The tool consists of an extensive grid of
FASTWIND models, and a variety of programs implemented in IDL to handle the
observations, perform the automatic analysis, and visualize the results. The
tool provides a fast and objective way to determine the stellar parameters and
the associated uncertainties of large samples of O-type stars within a
reasonable computational time.Comment: 8 pages, 2 figures, 1 table. Proceedings of the "GREAT-ESF Stellar
Atmospheres in the Gaia Era Workshop
Asymmetric scattering by non-hermitian potentials
The scattering of quantum particles by non-hermitian (generally nonlocal)
potentials in one dimension may result in asymmetric transmission and/or
reflection from left and right incidence. Eight generalized symmetries based on
the discrete Klein's four-group (formed by parity, time reversal, their
product, and unity) are used together with generalized unitarity relations to
determine the possible and/or forbidden scattering asymmetries. Six basic
device types are identified when the scattering coefficients (squared moduli of
scattering amplitudes) adopt zero/one values, and transmission and/or
reflection are asymmetric. They can pictorially be described as a one-way
mirror, a one-way barrier (a Maxwell pressure demon), one-way (transmission or
reflection) filters, a mirror with unidirectional transmission, and a
transparent, one-way reflector. We design potentials for these devices and also
demonstrate that the behavior of the scattering coefficients can be extended to
a broad range of incident momenta
OB stars at the lowest Local Group metallicity: GTC-OSIRIS observations of Sextans A
Our aim is to find and classify OB stars in Sextans A, to later determine
accurate stellar parameters of these blue massive stars in this low metallicity
region .
Using UBV photometry, the reddening-free index Q and GALEX imaging, we built
a list of blue massive star candidates in Sextans A. We obtained low resolution
(R 1000) GTC-OSIRIS spectra for a fraction of them and carried out
spectral classification. For the confirmed O-stars we derive preliminary
stellar parameters.
The target selection criteria and observations were successful and have
produced the first spectroscopic atlas of OB-type stars in Sextans A. From the
whole sample of 18 observed stars, 12 were classified as early OB-types,
including 5 O-stars. The radial velocities of all target stars are in agreement
with their Sextans A membership, although three of them show significant
deviations. We determined the stellar parameters of the O-type stars using the
stellar atmosphere code FASTWIND, and revisited the sub-SMC temperature scale.
Two of the O-stars are consistent with relatively strong winds and enhanced
helium abundances, although results are not conclusive. We discuss the position
of the OB stars in the HRD. Initial stellar masses run from slightly below 20
up to 40 solar masses.
The target selection method worked well for Sextans A, confirming the
procedure developed in Garcia \& Herrero (2013). The stellar temperatures are
consistent with findings in other galaxies. Some of the targets deserve
follow-up spectroscopy because of indications of a runaway nature, an enhanced
helium abundance or a relatively strong wind. We observe a correlation between
HI and OB associations similar to the irregular galaxy IC1613, confirming the
previous result that the most recent star formation of Sextans A is currently
on-going near the rim of the H\,{\sc I} cavity
Oxygen and silicon abundances in Cygnus OB2: Chemical homogeneity in a sample of OB slow rotators
Cygnus OB2 is a rich OB association in the Galaxy which has experienced
intense star formation in the last 20-25 Myr. Its stellar population shows a
correlation between age and Galactic longitude. Exploring the chemical
composition of its stellar content we will be able to check the degree of
homogeneity of the natal molecular cloud and possible effects of
self-enrichment processes. Our aim is to determine silicon and oxygen
abundances for a sample of eight early-type slow rotators in Cygnus OB2 in
order to check possible inhomogeneities across the whole association and
whether there exists a correlation of chemical composition with Galactic
longitude. We have performed a spectroscopic analysis of a sample of late O and
early B stars with low rotational velocity, which have been chosen so as to
cover the whole association area. We have carried out an analysis based on
equivalent widths of metal lines, the wings of the H Balmer lines and FASTWIND
stellar atmosphere models to determine their stellar fundamental parameters as
well as the silicon and oxygen surface abundances. We derive a rather
homogeneous distribution of silicon and oxygen abundances across the region,
with average values of 12+log(Si/H)=7.530.08 dex and
12+log(O/H)=8.650.12 dex. We find a homogeneous chemical composition in
Cygnus OB2 with no clear evidence for significant chemical self-enrichment,
despite indications of strong stellar winds and possible supernovae during the
history of the region. Comparison with different scenarios of chemical
enrichment by stellar winds and supernovae point to star forming efficiencies
not significantly above 10%. The degree of homogeneity that we find is
consistent with the observed Milky Way oxygen gradient based on HII regions. We
also find that the oxygen scatter within Cygnus OB2 is at least of the same
order than among HII regions at similar Galactocentric distance.Comment: 15 pages, 7 figures, accepted for publication in Astronomy &
Astrophysic
Household water consumption in Spain: disparities between region
This paper studies the regional consumption of household water in Spain in the period 2000–2018. The use of the methodology proposed by Phillips and Sul allows us to conclude that there is no single pattern of behavior across the Spanish regions. By contrast, we can determine the existence of three convergence clubs, confirming serious regional disparities in water consumption. Navarra, País Vasco, La Rioja, and Cataluña are included in the convergence club that shows the lowest levels of household water consumption, while the Islas Canarias, Comunidad Valenciana, Castilla y León and Cantabria belong to that with the highest consumption. The determinants of the forces that drive these convergence clubs are difficult to identify because the demographic, economic and structural variables of the network interact in different ways. Nevertheless, we can select a group of explanatory variables that help to explain the formation of the convergence clubs. These are regional household income, the birth rate in the regions, and the regional spending on environmental protection. Increments in the levels of these variables are helpful for reducing household water consumption. © 2022 by the authors. Licensee MDPI, Basel, Switzerland
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