19,534 research outputs found
Faint emission lines in the Galactic H II regions M16, M20 and NGC 3603
We present deep echelle spectrophotometry of the Galactic {\hii} regions M16,
M20 and NGC 3603. The data have been taken with the Very Large Telescope
Ultraviolet-Visual Echelle Spectrograph in the 3100 to 10400 \AA range. We have
detected more than 200 emission lines in each region. Physical conditions have
been derived using different continuum and line intensity ratios. We have
derived He, C and O abundances from pure recombination
lines as well as abundances from collisionally excited lines for a large number
of ions of different elements. We have obtained consistent estimations of the
temperature fluctuation parameter, {\ts}, using different methods. We also
report the detection of deuterium Balmer lines up to D (M16) and to
D (M20) in the blue wings of the hydrogen lines, which excitation
mechanism seems to be continuum fluorescence. The temperature fluctuations
paradigm agree with the results obtained from optical CELs and the more
uncertain ones from far IR fine structure CELs in NGC 3603, although, more
observations covering the same volume of the nebula are necessary to obtain
solid conclusions.Comment: 22 pages, 13 Tables, 7 Figures. Accepted for publication by MNRA
Insights into the Carbon chemistry of Mon R2
Aiming to learn about the chemistry of the dense PDR around the ultracompact
(UC) HII region in Mon R2, we have observed a series of mm-wavelength
transitions of C3H2 and C2H. In addition, we have traced the distribution of
other molecules, such as H13CO+, SiO, HCO, and HC3N. These data, together with
the reactive ions recently detected, have been considered to determine the
physical conditions and to model the PDR chemistry. We then identified two kind
of molecules. The first group, formed by the reactive ions (CO+, HOC+) and
small hydrocarbons (C2H, C3H2), traces the surface layers of the PDR and is
presumably exposed to a high UV field (hence we called it as "high UV", or
HUV). HUV species is expected to dominate for visual absorptions 2 < Av < 5
mag. A second group (less exposed to the UV field, and hence called "low UV",
or LUV) includes HCO and SiO, and is mainly present at the edges of the PDR (Av
> 5 mag). While the abundances of the HUV molecules can be explained by gas
phase models, this is not the case for the studied LUV ones. Although some
efficient gas-phase reactions might be lacking, grain chemistry sounds like a
probable mechanism able to explain the observed enhancement of HCO and SiO.
Within this scenario, the interaction of UV photons with grains produces an
important effect on the molecular gas chemistry and constitutes the first
evidence of an ionization front created by the UC HII region carving its host
molecular cloud. The physical conditions and kinematics of the gas layer which
surrounds the UC HII region were derived from the HUV molecules. Molecular
hydrogen densities > 4 10^6 cm^(-3) are required to reproduce the observations.
Such high densities suggest that the HII region could be pressure-confined by
the surrounding high density molecular gas.Comment: 32 pages, 8 figures. Accepted by Astrophysical Journa
An upgraded drift-diffusion model for evaluating the carrier lifetimes in radiation-damaged semiconductor detectors
P10-13. Increased production of alpha-defensins 1–3 by dendritic cells in HIV-infected individuals is associated with a slower disease progression rate
Comparative study of the environmental footprints of marinas on European Islands
Ports have been key elements in Europe's economic development. This situation is even more relevant on islands, which are highly dependent on the maritime sector. Consequently, over the years, ports with diverse functionalities have been established both in mainland Europe and on its outlying islands. This article discusses the environmental impact of leisure marinas on European islands, especially as they are closely linked to economic development through tourism. The aim is to study the environmental impact of these infrastructures by determining the carbon and water footprints of marinas on European islands in the Atlantic and the Mediterranean. The results obtained enable the authors to make recommendations in order to reduce the overall environmental footprint of marinas on islands, considering that these territories are much more vulnerable to climate change than mainland locations in Europe
- …