904 research outputs found
Is the interstellar gas of starburst galaxies well mixed?
The extent to which the ISM in galaxies is well mixed is not yet settled.
Measured metal abundances in the diffuse neutral gas of star--forming gas--rich
dwarf galaxies are deficient with respect to that of the ionized gas. The
reasons, if real, are not clear and need to be based on firm grounds. Far-UV
spectroscopy of giant HII regions such as NGC604 in the spiral galaxy M33 using
FUSE allows us to investigate possible systematic errors in the metallicity
derivation. We still find underabundances of nitrogen, oxygen, argon, and iron
in the neutral phase by a factor of~6. This could either be explained by the
presence of less chemically evolved gas pockets in the sightlines or by dense
clouds out of which HIIregions form. Those could be more metallic than the
diffuse medium.Comment: 4 pages, 2 figures;contribution to Starbursts: from 30 Dor to Lyman
Break Galaxies, 6 -10 September 2004, Institute of Astronomy, University of
Cambridge, U
Chemical abundances and radial velocities in the extremely metal-poor galaxy DDO 68
We present chemical abundances and radial velocities of six HII regions in
the extremely metal-poor star-forming dwarf galaxy DDO 68. They are derived
from deep spectra in the wavelength range 3500 - 10,000 {\AA}, acquired with
the Multi Object Double Spectrograph (MODS) at the Large Binocular Telescope
(LBT). In the three regions where the [O III]4363 {\AA} line was
detected, we inferred the abundance of He, N, O, Ne, Ar, and S through the
"direct" method. We also derived the oxygen abundances of all the six regions
adopting indirect method calibrations. We confirm that DDO 68 is an extremely
metal-poor galaxy, and a strong outlier in the luminosity - metallicity
relation defined by star-forming galaxies. With the direct-method we find
indeed an oxygen abundance of 12+log(O/H)=7.140.07 in the northernmost
region of the galaxy and, although with large uncertainties, an even lower
12+log(O/H)=6.960.09 in the "tail". This is, at face value, the most
metal-poor direct abundance detection of any galaxy known. We derive a radial
oxygen gradient of -0.060.03 dex/kpc (or -0.30 dex ) with the
direct method, and a steeper gradient of -0.120.03 dex/kpc (or -0.59 dex
) from the indirect method. For the -element to oxygen
ratios we obtain values in agreement with those found in other metal-poor
star-forming dwarfs. For nitrogen, instead, we infer much higher values,
leading to log(N/O), at variance with the suggested existence of a
tight plateau at in extremely metal poor dwarfs. The derived helium mass
fraction ranges from Y=0.2400.005 to Y=0.250.02, compatible with
standard big bang nucleosynthesis. Finally, we measured HII region radial
velocities in the range 479522 km/s from the tail to the head of the
"comet", consistent with the rotation derived in the HI.Comment: Accepted for publication in MNRA
HST resolves stars in a tiny body falling on the dwarf galaxy DDO 68
We present new Hubble Space Telescope (HST) imaging of a stream-like system
associated with the dwarf galaxy DDO 68, located in the Lynx-Cancer Void at a
distance of D12.65 Mpc from us. The stream, previously identified in deep
Large Binocular Telescope images as a diffuse low surface brightness structure,
is resolved into individual stars in the F606W (broad V) and F814W (I)
images acquired with the Wide Field Camera 3. The resulting V, I
color-magnitude diagram (CMD) of the resolved stars is dominated by old
(age1-2 Gyr) red giant branch (RGB) stars. From the observed RGB tip,
we conclude that the stream is at the same distance as DDO 68, confirming the
physical association with it. A synthetic CMD analysis indicates that the large
majority of the star formation activity in the stream occurred at epochs
earlier than 1 Gyr ago, and that the star formation at epochs more recent
than 500 Myr ago is compatible with zero. The total stellar mass of the
stream is , about 1/100 of that of DDO~68. This is a
striking example of hierarchical merging in action at the dwarf galaxy scales.Comment: ApJ in pres
Feedback in the local LBG Analog Haro 11 as probed by far-UV and X-ray observations
We have re-analyzed FUSE data and obtained new Chandra observations of Haro
11, a local (D_L=88 Mpc) UV luminous galaxy. Haro 11 has a similar far-UV
luminosity (10^10.3 L_\odot), UV surface brightness (10^9.4 L_\odot kpc^-2),
SFR, and metallicity to that observed in Lyman Break Galaxies (LBGs). We show
that Haro 11 has extended, soft thermal (kT~0.68 keV) X-ray emission with a
luminosity and size which scales with the physical properties (e.g. SFR,
stellar mass) of the host galaxy. An enhanced alpha/Fe, ratio of ~4 relative to
solar abundance suggests significant supernovae enrichment. These results are
consistent with the X-ray emission being produced in a shock between a
supernovae driven outflow and the ambient material. The FUV spectra show strong
absorption lines similar to those observed in LBG spectra. A blueshifted
absorption component is identified as a wind outflowing at ~200-280 km/s.
OVI\lambda\lambda1032,1038 emission, the dominant cooling mechanism for coronal
gas at T~10^5.5 K is also observed. If associated with the outflow, the
luminosity of the OVI emission suggests that <20% of the total mechanical
energy from the supernovae and solar winds is being radiated away. This implies
that radiative cooling through OVI is not significantly inhibiting the growth
of the outflowing gas. In contradiction to the findings of Bergvall et al 2006,
we find no convincing evidence of Lyman continuum leakage in Haro 11. We
conclude that the wind has not created a `tunnel' allowing the escape of a
significant fraction of Lyman continuum photons and place a limit on the escape
fraction of f_{esc}<2%. Overall, both Haro 11 and a previously observed LBG
analogue VV 114, provide an invaluable insight into the X-ray and FUV
properties of high redshift LBGs.Comment: Accepted for publication in ApJ, 40 pages, 17 figure
Morphoâphysiological classification of italian tomato cultivars (Solanum lycopersicum l.) according to drought tolerance during vegetative and reproductive growth
Irrigation is fundamental for agriculture but, as climate change becomes more persistent, there is a need to conserve water and use it more efficiently. It is therefore crucial to identify cultivars that can tolerate drought. For economically relevant crops, such as tomatoes, this purpose takes on an even more incisive role and local agrobiodiversity is a large genetic reservoir of promising cultivars. In this study, nine local Italian cultivars of tomatoes plus four widely used commercial cultivars were considered. These experienced about 20 d of drought, either at vegetative or reproductive phase. Various physioâmorphological parameters were monitored, such as stomatal conductance (gs), photosynthesis (A), water use efficiency (WUE), growth (GI) and soil water content (SWC). The different responses and behaviors allowed to divide the cultivars into three groups: tolerant, susceptible, and intermediate. The classification was also confirmed by a principal component analysis (PCA). The study, in addition to deepening the knowledge of local Italian tomato cultivars, reveals how some cultivars perform better under stress condition than commercial ones. Moreover, the different behavior depends on the genotype and on the growth phase of plants. In fact, the Perina cultivar is the most tolerant during vegetative growth while the Quarantino cultivar is mostly tolerant at reproductive stage. The results suggest that selection of cultivars could lead to a more sustainable agriculture and less wasteful irrigation plans
The Resolved Stellar Populations in NGC 1705
We present HST photometry of the resolved stellar population in the dwarf
irregular galaxy NGC 1705. The galaxy has been observed with both WFPC2 and
NICMOS, and successful images have been obtained in the F555W, F814W, F110W and
F160W bands. The optical fields cover most of the galaxy, while the infrared
field (NIC2) maps only its central regions. The optical photometry provides
\~20000 objects down to m_F555W ~ 29 in the PC field of view and ~ 20000 in the
three WFCs. In the infrared we have been able to resolve ~ 2400 stars down to
m_{F110W}, m_{F160W} ~ 26. A subsample of 1834 stars have been unambiguously
measured in all the four bands. The corresponding color-magnitude diagrams
(CMDs) confirm the existence of an age gradient, showing that NGC 1705 hosts
both young (a few Myr old) and very old (up to 15 Gyr old) stars, with the
former strongly concentrated toward the galactic center and the latter present
everywhere, but much more easily visible in the external regions. The tip of
the red giant branch (TRGB) is clearly visible both in the optical and in the
infrared CMDs and allows us to derive the galaxy distance. Taking into account
the uncertainties related to both the photometry and the TRGB magnitude --
distance relation, we find that the distance modulus of NGC 1705 is
(m-M)_0=28.54 +- 0.26, corresponding to a distance D=5.1 +- 0.6 Mpc.Comment: aastex, 37 pages, 13 (reduced resolution) .ps figures. Accepted by
AJ. Full resolution figures are available upon request to the first autho
How to combine CTA, 99mTc-WBC SPECT/CT, and [18F]FDG PET/CT in patients with suspected abdominal vascular endograft infections?
Purpose - We aimed at comparing Tc-99m-HMPAO white blood cells (Tc-99m-WBC) scintigraphy, 18fluorine-fluorodeoxyglucose ([F-18]FDG) positron emission tomography/computed tomography (PET/CT) and CT angiography (CTA) in patients with suspected abdominal vascular graft or endograft infection (VGEI). Moreover, we attempted to define a new visual score for interpreting [F-18]FDG PET/CT scans aiming at increasing its specificity. Methods - We prospectively compared Tc-99m-WBC SPECT/CT, [F-18]FDG PET/CT, and CTA in 26 patients with suspected abdominal VGEI. WBC scans were performed and interpreted according to EANM recommendations. [F-18]FDG PET/CT studies were assessed with both qualitative (Sah's scale and new visual score) and semi-quantitative analyses. CTA images were interpreted according to MAGIC criteria. Microbiology, histopathology or a clinical follow-up of at least 24 months were used to achieve final diagnosis. Results - Eleven out of 26 patients were infected. [F-18]FDG PET/CT showed 100% sensitivity and NPV, with both scoring systems, thus representing an efficient tool to rule out the infection. The use of a more detailed scoring system provided statistically higher specificity compared to the previous Sah's scale (p = 0.049). Tc-99m-WBC SPECT/CT provided statistically higher specificity and PPV than [F-18]FDG PET/CT, regardless the interpretation criteria used and it can be, therefore, used in early post-surgical phases or to confirm or rule out a PET/CT finding. Conclusions - After CTA, patients with suspected late VGEI should perform a [F-18]FDG PET/CT given its high sensitivity and NPV. However, given its lower specificity, positive results should be confirmed with Tc-99m-WBC scintigraphy. The use of a more detailed scoring system reduces the number of Tc-99m-WBC scans needed after [F-18]FDG PET/CT. Nevertheless, in suspected infections within 4 months from surgery, Tc-99m-WBC SPECT/CT should be performed as second exam, due to its high accuracy in differentiating sterile inflammation from infection
Airborne Pollen, Allergens, and Proteins: A Comparative Study of Three Sampling Methods
Nowadays, there is a wide range of different methods available for the monitoring of pollen and allergens, but their relative efficiency is sometimes unclear, as conventional pollen monitoring does not thoroughly describe pollen allergenicity. This study aims to evaluate airborne pollen, allergen, and protein levels, associating them with meteorological and chemical parameters. The sampling was performed in Bologna (Italy) during the grass flowering period, with three different devices: a Cyclone sampler (CS), a Dicothomous sampler (DS), and a Berner impactor (BI). Total proteins were extracted from aerosol samples, and grass allergens Phl p 1 and Phl p 5 were quantified by ELISA. Airborne Poaceae pollen concentrations were also evaluated, using a Hirst-type trap. Proteins and allergens collected by CS resulted about ten times higher than those collected by the other two instruments, possibly due to their different cut-offs, while DS and BI results appeared consistent only for the total proteins collected in the fine fraction (1.3 vs. 1.6 mu g/m(3)). Airborne proteins correlated neither with Poaceae pollen nor with its aeroallergens, while aeroallergens correlated with pollen only in the coarse particulate, indicating the presence of pollen-independent aeroallergens in the fine particulate, promoted by high wind speed
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