73 research outputs found
The massive star population of the Virgo Cluster galaxy NGC 4535
We analyzed the massive star population of the Virgo Cluster galaxy NGC 4535
using archival Hubble Space Telescope Wide Field Planetary Camera 2 images in
filters F555W and F814W, equivalent to Johnson V and Kron-Cousins I. We
performed high precision point spread function fitting photometry of 24353
sources including 3762 candidate blue supergiants, 841 candidate yellow
supergiants and 370 candidate red supergiants. We estimated the ratio of blue
to red supergiants as a decreasing function of galactocentric radius. Using
Modules for Experiments in Stellar Astrophysics isochrones at solar
metallicity, we defined the luminosity function and estimated the star
formation history of the galaxy over the last 60 Myrs. We conducted a
variability search in the V and I filters using three variability indexes: the
median absolute deviation, the interquartile range and the inverse von-Neumann
ratio. This analysis yielded 120 new variable candidates with absolute
magnitudes ranging from M = 4 to 11 mag. We used the MESA
evolutionary tracks at solar metallicity, to classify the variables based on
their absolute magnitude and their position on the color-magnitude diagram.
Among the new candidate variable sources are eight candidate variable red
supergiants, three candidate variable yellow supergiants and one candidate
luminous blue variable, which we suggest for follow-up observations.Comment: Accepted by A&A, 7 pages, 7 Tables, 53 figure
HST WFPC2 Observations of the Peculiar Main Sequence of the Double Star Cluster NGC 2011 in the Large Magellanic Cloud
We report the serendipitous discovery of a peculiar main sequence in archived
Hubble Space Telescope WFPC2 observations of the young star cluster NGC 2011 in
the Large Magellanic Cloud. The bright part of this main sequence exhibits a
prominent double, fork-like feature, as if it consists of twin main sequences,
one of them being redder. The color-magnitude diagram, constructed from the
stars found in the only available WFPC2 field of the cluster, is used to
distinguish the stars according to their membership to each of these sequences
and to study their spatial distribution. We find that there are two well
distinguished populations in the sense that the redder main sequence is
dominated by stars that belong to the main body of the cluster, while the stars
of the bluer main sequence belong to the surrounding region. Providing that NGC
2011 is a verified binary cluster, with the second companion unfortunately not
observed, and taking into account the general region where this cluster is
located, we discuss the possible scenarios from both star formation, and early
dynamical evolution point-of-view that might explain this unique discovery.Comment: Astrophysical Journal Letters, in press. Figures in higher resolution
available upon request to D. Gouliermis ([email protected]
A close look at the Centaurus A group of galaxies IV. Recent star formation histories of late-type dwarfs around CenA
We study a sample of 5 dwarf irregular galaxies in the CenA/M83 group, which
are companions to the giant elliptical CenA. We aim at deriving their physical
properties over their lifetime and compare them to those of dwarfs located in
different environments. We use archival HST/ACS data and apply synthetic
color-magnitude diagram fitting in order to reconstruct the past star formation
activity of the target galaxies. The average star formation rate for the
studied galaxies ranges from 10^{-3} up to \sim 7x10^{-2} M_odot/yr, and their
mean metallicities correlate with their luminosities (from [Fe/H]\sim -1.4 up
to \sim -1.0). The form of the star formation histories varies across the
sample, with quiescent periods alternating with intermittent enhancements in
the star formation (from a few up to several times the average lifetime value).
The dwarfs in this sample formed ~35% to ~60% of their stellar content prior to
~5 Gyr ago. The resulting star formation histories for the CenA companions are
similar to those found for comparable Local Group and M81 group dwarfs. We
consider this sample of dwarfs together with 5 previously studied M83 dwarf
irregular companions. We find no trend of the average star formation rate with
tidal index or distance from the main galaxy of the group. However, dwarfs with
higher baryonic masses do show higher average star formation rates, underlining
the importance of intrinsic properties in governing the evolution of these
galaxies. On the other hand, there is also a clear trend when looking at the
recent (~0.5-1 Gyr) level of activity. Namely, dwarfs within a denser region of
the group appear to have had their star formation quenched while dwarfs located
in the group outskirts show a wide range of possible star formation rates, thus
indicating that external processes play a fundamental role, complementary to
mass, in shaping the star formation histories of dwarf galaxies.Comment: 16 pages, 10 figures; A&A accepte
A detailed questionnaire for the evaluation of health management in dairy sheep and goats
The objective of this work was to develop, use and present a detailed questionnaire for the evaluation of health management in dairy small ruminants; it includes 442 questions organised in seven sections: general, infrastructure, animals, production characteristics, health management, nutrition, human resources. Consistency of replies was evaluated in 27 farmers, interviewed twice. Inconsistent replies were given by all farmers to 30 different questions (Cronbach’s coefficient alpha: 0.987). Then, interviews were performed in 444 farms around Greece. Mean duration of an interview was 63.6 min. Clarifications were requested by 273 farmers to 22 different questions (maximum per farmer: 8). The experience of the investigator, the primary language of farmers and asking clarifications by the farmers affected the duration of the interview. The questionnaire can be used for research work in the field, to record details in the farms under study. In accord with the needs of a particular study, it can be modified, by adding more specific questions or omitting others deemed of less importance. Moreover, it can also be used for routine monitoring purposes, as a useful means to record and maintain details of farms during clinical work. To the best of our knowledge, the questionnaire is the most extensive and detailed one available internationally for dairy small ruminants
Primary choriocarcinoma of the renal pelvis presenting as intracerebral hemorrhage: a case report and review of the literature
<p>Abstract</p> <p>Introduction</p> <p>A choriocarcinoma is a malignant neoplasm normally arising in the gestational trophoblast, gonads and, less frequently, the retroperitoneum, mediastinum and pineal gland. Primary choriocarcinomas of the renal pelvis are extremely rare.</p> <p>Case presentation</p> <p>We report a case of primary choriocarcinoma of the renal pelvis in a 38-year-old Greek woman of reproductive age, presenting with a sudden development of intracerebral hemorrhage due to metastatic lesions. The diagnosis was established with a renal biopsy, along with an elevated serum level of beta-human chorionic gonadotropin. An extensive diagnostic work up confirmed the origin of the choriocarcinoma to be the renal pelvis.</p> <p>Conclusion</p> <p>Extragonadal choriocarcinomas are rare neoplasms that require extensive laboratory and imaging studies to exclude a gonadal origin. Moreover, this is the first case of severe intracerebral hemorrhage as the initial presentation of primary choriocarcinoma of the renal pelvis. Nonetheless, choriocarcinomas should be considered in the differential diagnosis of women of reproductive age.</p
Multi-year chemical composition of the fine-aerosol fraction in Athens, Greece, with emphasis on the contribution of residential heating in wintertime
In an attempt to take effective action towards mitigating pollution episodes
in Athens, precise knowledge of PM2.5 composition and its sources is a
prerequisite. Thus, a 2-year chemical composition dataset from aerosol
samples collected in an urban background site in central Athens from
December 2013 to March 2016 has been obtained and a positive matrix
factorization (PMF) was applied in order to identify and apportion fine
aerosols to their sources. A total of 850 aerosol samples were collected on
a 12 to 24 h basis and analyzed for major ions, trace elements, and organic and
elemental carbon, allowing us to further assess the impact of residential
heating as a source of air pollution over Athens.The ionic and carbonaceous components were found to constitute the major
fraction of the PM2.5 aerosol mass. The annual contribution of the ion
mass (IM), particulate organic mass (POM), dust, elemental carbon (EC), and
sea salt (SS) was calculated at 31 %, 38 %, 18 %, 8 %, and
3 %, respectively, and exhibited considerable seasonal variation. In
winter, the share of IM was estimated down to 23 %, with POM + EC being the dominant component accounting for 52 % of the PM2.5 mass,
while in summer, IM (42 %) and carbonaceous aerosols (41 %)
contributed almost equally.Results from samples collected on a 12 h basis (day and night) during the
three intensive winter campaigns indicated the impact of heating on the
levels of a series of compounds. Indeed, PM2.5, EC, POM,
NO3−, C2O42−, non sea salt (nss) K+ and selected trace metals
including Cd and Pb were increased by up to a factor of 4 in the night
compared to the day, highlighting the importance of heating on air quality in
Athens. Furthermore, in order to better characterize wintertime aerosol
sources and quantify the impact of biomass burning on PM2.5 levels,
source apportionment was performed. The data can be interpreted on the basis
of six sources, namely biomass burning (31 %), vehicular emissions
(19 %), heavy oil combustion (7 %), regional secondary (21 %),
marine aerosols (9 %), and dust particles (8 %). Regarding
night-to-day patterns their contributions shifted from 19 %, 19 %,
8 %, 31 %, 12 %, and 10 % of the PM2.5 mass during day
to 39 %, 19 %, 6 %, 14 %, 7 %, and 7 % during the
night, underlining the significance of biomass burning as the main
contributor to fine particle levels during nighttime in winter.</p
Reddening and metallicity maps of the Milky Way Bulge from VVV and 2MASS. I.The method and minor axis maps
We present a method to obtain reddening maps and to trace structure and
metallicity gradients of the bulge using data from the recently started ESO
public survey Vista Variables in the Via Lactea (VVV). We derive the mean J-Ks
color of the red clump (RC) giants in 1835 subfields in the Bulge region with
-8<b<-0.4 and 0.2<l<1.7, and compare it to the color of RC stars in Baade's
Window for which we adopt E(B-V)=0.55. This allows us to derive the reddening
map on a small enough scale to minimize the problems arising from differential
extinction. The dereddened magnitudes are then used to build the bulge
luminosity function in regions of 0.4 x 0.4 deg to obtain the mean RC
magnitudes. These are used as distance indicator in order to trace the bulge
structure. Finally, for each subfield we derive photometric metallicities
through interpolation of red giant branch colors on a set of empirical ridge
lines. The photometric metallicity distributions are compared to metallicity
distributions obtained from high resolution spectroscopy in the same regions.
The reddening determination is sensitive to small scale variations which are
clearly visible in our maps. The luminosity function clearly shows the double
RC recently discovered in 2MASS and OGLE III datasets, hence allowing to trace
the X-shape morphology of the bulge. Finally, the mean of the derived
photometric metallicity distributions are in remarkable agreement with those
obtained from spectroscopy. The VVV survey presents a unique tool to map the
bulge properties by means of the consistent method presented here. The
remarkable agreement between our results and those presented in literature for
the minor axis allows us to safely extend our method to the whole region
covered by the survey.Comment: Accepted for publication in A&
Listeria monocytogenes in Milk Products
peer-reviewedMilk and milk products are frequently identified as vectors for transmission of Listeria monocytogenes. Milk can be contaminated at farm level either by indirect external contamination from the farm environment or less frequently by direct contamination of the milk from infection in the animal. Pasteurisation of milk will kill L. monocytogenes, but post-pasteurisation contamination, consumption of unpasteurised milk and manufacture of unpasteurised milk products can lead to milk being the cause of outbreaks of listeriosis. Therefore, there is a concern that L. monocytogenes in milk could lead to a public health risk. To protect against this risk, there is a need for awareness surrounding the issues, hygienic practices to reduce the risk and adequate sampling and analysis to verify that the risk is controlled. This review will highlight the issues surrounding L. monocytogenes in milk and milk products, including possible control measures. It will therefore create awareness about L. monocytogenes, contributing to protection of public health
The difference in metallicity distribution functions of halo stars and globular clusters as a function of galaxy type: A tracer of globular cluster formation and evolution
Observations of globular clusters (GCs) and field stars in the halos of the giant elliptical galaxy Cen A and the spiral galaxy M31 show a large range of cluster-to-star number ratios ('specific frequencies'). The cluster-to-star ratio decreases with increasing metallicity by a factor of 100-1000, at all galactocentric radii and with a slope that does not seem to depend on radius. In dwarf galaxies, the GCs are also more metal-poor than the field stars on average. These observations indicate a strong dependence of either the cluster formation efficiency or the cluster destruction rate on metallicity and environment. We aim to explain these trends by considering various effects that may influence the observed cluster-to-star ratio as a function of metallicity, environment and cosmological history. We show that both the cluster formation efficiency and the maximum cluster mass increase with metallicity, so they cannot explain the observed trend. Destruction of GCs by tidal stripping and dynamical friction destroy clusters over too small a range of galactocentric radii. We show that cluster destruction by tidal shocks from giant molecular clouds in the high-density formation environments of GCs becomes increasingly efficient towards high galaxy masses and, hence, towards high metallicities. The predicted cluster-to-star ratio decreases by a factor 100-1000 towards high metallicities and should only weakly depend on galactocentric radius due to orbital mixing during hierarchical galaxy merging, consistent with the observations. The observed, strong dependence of the cluster-to-star ratio on metallicity and the independence of its slope on galactocentric radius can be explained by cluster destruction and hierarchical galaxy growth. As a result, we find that the metallicity-dependence of the cluster-to-star ratio does not reflect a GC formation efficiency, but a survival fraction. (Abridged
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