4,483 research outputs found
MSUO Information Technology and Geographical Information Systems: Common Protocols & Procedures. Report to the Marine Safety Umbrella Operation
The Marine Safety Umbrella Operation (MSUO) facilitates the cooperation between Interreg
funded Marine Safety Projects and maritime stakeholders. The main aim of MSUO is to
permit efficient operation of new projects through Project Cooperation Initiatives, these
include the review of the common protocols and procedures for Information Technology (IT)
and Geographical Information Systems (GIS).
This study carried out by CSA Group and the National Centre for Geocomputation (NCG)
reviews current spatial information standards in Europe and the data management
methodologies associated with different marine safety projects.
International best practice was reviewed based on the combined experience of spatial data
research at NCG and initiatives in the US, Canada and the UK relating to marine security
service information and acquisition and integration of large marine datasets for ocean
management purposes.
This report identifies the most appropriate international data management practices that could
be adopted for future MSUO projects
Nucler star formation in NGC 6240
We have made use of archival HST BVIJH photometry to constrain the nature of
the three discrete sources, A1, A2 and B1, identified in the double nucleus of
NGC 6240. STARBURST99 models have been fitted to the observed colours, under
the assumption, first, that these sources can be treated as star clusters (i.e.
single, instantaneous episodes of star formation), and subsequently as
star-forming regions (i.e. characterised by continuous star formation). For
both scenarios, we estimate ages as young as 4 million years, integrated masses
ranging between 7x10^6 Msun (B1) and 10^9 Msun (A1) and a rate of 1 supernova
per year, which, together with the stellar winds, sustains a galactic wind of
44 Msun/yr. In the case of continuous star formation, a star-formation rate has
been derived for A1 as high as 270 Msun/yr, similar to what is observed for
warm Ultraluminous Infrared Galaxies (ULIRGs) with a double nucleus. The A1
source is characterised by a mass density of about 1200 Msun/pc^3 which
resembles the CO molecular mass density measured in cold ULIRGs and the stellar
density determined in ``elliptical core'' galaxies. This, together with the
recent discovery of a supermassive binary black hole in the double nucleus of
NGC 6240, might indicate that the ongoing merger could shape the galaxy into a
core elliptical.Comment: 14 pages, 5 postscript figures, accepted by A&
A near-infrared survey for Galactic Wolf-Rayet stars
Initial results, techniques, and rationale for a near-infrared survey of
evolved emission-line stars toward the Galactic Center are presented. We use
images taken through narrow-band emission-line and continuum filters to select
candidates for spectroscopic follow-up. The filters are optimized for the
detection of Wolf-Rayet stars and other objects which exhibit emission-lines in
the 2 micron region. Approximately three square degrees along the Galactic
plane have been analyzed in seven narrow-filters (four emission-lines and three
continuum). Four new Wolf-Rayet stars have been found which are the subject of
a following paper.Comment: 10 pages, 2 figures, accepted for publication in A&
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
SPIDER X - Environmental effects in central and satellite early-type galaxies through the stellar fossil record
A detailed analysis of how environment affects the star formation history of
early-type galaxies (ETGs) is undertaken via high signal to noise ratio stacked
spectra obtained from a sample of 20,977 ETGs (morphologically selected) from
the SDSS-based SPIDER survey. Two major parameters are considered for the
study: the central velocity dispersion (sigma), which relates to local drivers
of star formation, and the mass of the host halo, which relates to
environment-related effects. In addition, we separate the sample between
centrals (the most massive galaxy in a halo) and satellites. We derive trends
of age, metallicity, and [alpha/Fe] enhancement, with sigma. We confirm that
the major driver of stellar population properties in ETGs is velocity
dispersion, with a second-order effect associated to the central/satellite
nature of the galaxy. No environmental dependence is detected for satellite
ETGs, except at low sigma - where satellites in groups or in the outskirts of
clusters tend to be younger than those in the central regions of clusters. In
contrast, the trends for centrals show a significant dependence on halo mass.
Central ETGs in groups (i.e. with a halo mass >10^12.5 M_Sun) have younger
ages, lower [alpha/Fe], and higher internal reddening, than "isolated" systems
(i.e. centrals residing in low-mass, <10^12.5 M_Sun, halos). Our findings imply
that central ETGs in groups formed their stellar component over longer time
scales than "isolated" centrals, mainly because of gas-rich interactions with
their companion galaxies.Comment: 22 pages, 19 figures, accepted for publication in MNRA
IMF and [Na/Fe] abundance ratios from optical and NIR Spectral Features in Early-type Galaxies
We present a joint analysis of the four most prominent sodium-sensitive
features (NaD, NaI8190, NaI1.14, and NaI2.21), in the optical and Near-Infrared
spectral range, of two nearby, massive (sigma~300km/s), early-type galaxies
(named XSG1 and XSG2). Our analysis relies on deep VLT/X-Shooter long-slit
spectra, along with newly developed stellar population models, allowing for
[Na/Fe] variations, up to 1.2dex, over a wide range of age, total metallicity,
and IMF slope. The new models show that the response of the Na-dependent
spectral indices to [Na/Fe] is stronger when the IMF is bottom heavier. For the
first time, we are able to match all four Na features in the central regions of
massive early-type galaxies, finding an overabundance of [Na/Fe], in the range
0.5-0.7dex, and a bottom-heavy IMF. Therefore, individual abundance variations
cannot be fully responsible for the trends of gravity-sensitive indices,
strengthening the case towards a non-universal IMF. Given current limitations
of theoretical atmosphere models, our [Na/Fe] estimates should be taken as
upper limits. For XSG1, where line strengths are measured out to 0.8Re, the
radial trend of [Na/Fe] is similar to [Mg/Fe] and [C/Fe], being constant out to
0.5Re, and decreasing by 0.2-0.3dex at 0.8Re, without any clear correlation
with local metallicity. Such a result seems to be in contrast with the
predicted increase of Na nucleosynthetic yields from AGB stars and TypeII SNe.
For XSG1, the Na-inferred IMF radial profile is consistent, within the errors,
with that derived from TiO features and the Wing-Ford band, presented in a
recent paper.Comment: 22 pages, 8 figure, accepted for publication in MNRAS. The new
Na-enhanced models will be available soon at http://miles.iac.es
LA IONIA DI CALLIMACO. UN CAPITOLO DI GEOGRAFIA E STORIA DELLA POESIA CALLIMACHEA.
The present work investigates Callimachus\u2019 literary purposes and his method by focusing on the recurring presence of Ionia in his poetic production. Different reasons can explain the diffuse presence of Ionia in Callimachus\u2019 work: the geopolitical interests in the region by the Ptolemies \u2013 Callimachus\u2019 protectors - on the one hand, and the crucial role of Ionia in the foundation of Greek civilization and culture, on the other. In order to understand what Ionia was in the eyes of Callimachus, this thesis follows several research directions. It starts from identifying all references to Ionia, its places, cults and myths \u2013 the so called Ionik\ue1 - in Callimachus\u2019s work, and it then investigates the importance of Ionic literary models (Mimnermus and Hipponax, in particular) in Callimachus\u2019 poetic production.
After an introduction to Ionia and its influence on the Greeks\u2019 collective imagination and on Hellenic history, the thesis proposes a review of all Ionik\ue1 present in Callimachus\u2019 opera and of all references to Mimnermus and Hipponax, the two poets chosen by Callimachus as models for his project of renovating the traditional genres of elegy and iambus. Finally, the thesis proposes a synthesis of the collected data in order to identify which sources and stimuli are at the base of the literary representation of Ionia in Callimachus\u2019 poetry and to highlight his creative and compositional manners
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