141 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
Population gradients and photometric metallicities in early- and transition-type dwarf galaxies: Clues from the Sculptor group
We focus on the resolved stellar populations of one early- and four
transition-type dwarf galaxies in the Sculptor group, with the aim to examine
the potential presence of population gradients and place constraints on their
mean metallicities. We use deep HST images to construct CMDs, from which we
select stellar populations that trace different evolutionary phases in order to
constrain their range of ages and metallicities, as well as to examine their
spatial distribution. In addition, we use the resolved stars in the RGB in
order to derive photometric metallicities. All studied dwarfs contain
intermediate-age stars with ages of ~1Gyr and older as traced by the luminous
asymptotic giant branch and red clump stars, while the transition-type dwarfs
contain also stars younger than ~1Gyr as traced by a young main sequence and
vertical red clump stars. Moreover, the spatial distribution of the stars that
trace different evolutionary phases shows a population gradient in all
transition-type dwarfs. The derived error-weighted mean metallicities, assuming
purely old stellar populations, range from -1.5dex for ESO294-G010 to -1.9dex
for Scl-dE1, and should be considered as lower limits to their true
metallicities. Assuming intermediate-age stellar populations to dominate the
dwarfs, we derive upper limits for the metallicities that are 0.3 to 0.2 dex
higher than the metallicities derived assuming purely old populations. We
discuss how photometric metallicity gradients are affected by the
age-metallicity degeneracy, which prevents strong conclusions regarding their
actual presence. Finally, the transition-type dwarfs lie beyond the virial
radius of their closest bright galaxy, as also observed for the LG
transition-type dwarfs. Scl-dE1 is the only dSph in our sample and is an
outlier in a potential morphology-distance relation, similar as the two
isolated dSphs of the LG, Tucana and Cetus.Comment: A&A published; 21 pages, 16 figures, 3 appendices; replaced to match
the published versio
The first maps of Îșd - the dust mass absorption coefficient - in nearby galaxies, with DustPedia
The dust mass absorption coefficient, Îșd is the conversion function used to infer physical dust masses from observations of dust emission. However, it is notoriously poorly constrained, and it is highly uncertain how it varies, either between or within galaxies. Here we present the results of a proof-of-concept study, using the DustPedia data for two nearby face-on spiral galaxies M 74 (NGC 628) and M 83 (NGC 5236), to create the first ever maps of Îșd in galaxies. We determine Îșd using an empirical method that exploits the fact that the dust-to-metals ratio of the interstellar medium is constrained by direct measurements of the depletion of gas-phase metals. We apply this method pixel-by-pixel within M 74 and M 83, to create maps of Îșd. We also demonstrate a novel method of producing metallicity maps for galaxies with irregularly sampled measurements, using the machine learning technique of Gaussian process regression. We find strong evidence for significant variation in Îșd. We find values of Îșd at 500 ÎŒm spanning the range 0.11-0.25 m^{2 kg^{-1}} in M 74, and 0.15-0.80 m^{2 kg^{-1}} in M 83. Surprisingly, we find that Îșd shows a distinct inverse correlation with the local density of the interstellar medium. This inverse correlation is the opposite of what is predicted by standard dust models. However, we find this relationship to be robust against a large range of changes to our method - only the adoption of unphysical or highly unusual assumptions would be able to suppress it
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 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 (Cronbachâs 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 +Â 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,
NO3â, C2O42â, 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 PM2.5âmass 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
DustPedia: Multiwavelength photometry and imagery of 875 nearby galaxies in 42 ultraviolet-microwave bands
Aims. The DustPedia project is capitalising on the legacy of the Herschel Space Observatory, using cutting-edge modelling techniques to study dust in the 875 DustPedia galaxies â representing the vast majority of extended galaxies within 3000âkmâs-1 that were observed by Herschel. This work requires a database of multiwavelength imagery and photometry that greatly exceeds the scope (in terms of wavelength coverage and number of galaxies) of any previous local-Universe survey.
Methods. We constructed a database containing our own custom Herschel reductions, along with standardised archival observations from GALEX, SDSS, DSS, 2MASS, WISE, Spitzer, and Planck. Using these data, we performed consistent aperture-matched photometry, which we combined with external supplementary photometry from IRAS and Planck.
Results. We present our multiwavelength imagery and photometry across 42 UV-microwave bands for the 875 DustPedia galaxies. Our aperture-matched photometry, combined with the external supplementary photometry, represents a total of 21â857 photometric measurements. A typical DustPedia galaxy has multiwavelength photometry spanning 25 bands. We also present the Comprehensive & Adaptable Aperture Photometry Routine (CAAPR), the pipeline we developed to carry out our aperture-matched photometry. CAAPR is designed to produce consistent photometry for the enormous range of galaxy and observation types in our data. In particular, CAAPR is able to determine robust cross-compatible uncertainties, thanks to a novel method for reliably extrapolating the aperture noise for observations that cover a very limited amount of background. Our rich database of imagery and photometry is being made available to the community
Genetic and Diet-Induced Animal Models for Non-Alcoholic Fatty Liver Disease (NAFLD) Research
A rapidly increasing incidence of non-alcoholic fatty liver disease (NAFLD) is noted worldwide due to the adoption of western-type lifestyles and eating habits. This makes the understanding of the molecular mechanisms that drive the pathogenesis of this chronic disease and the development of newly approved treatments of utmost necessity. Animal models are indispensable tools for achieving these ends. Although the ideal mouse model for human NAFLD does not exist yet, several models have arisen with the combination of dietary interventions, genetic manipulations and/or administration of chemical substances. Herein, we present the most common mouse models used in the research of NAFLD, either for the whole disease spectrum or for a particular disease stage (e.g., non-alcoholic steatohepatitis). We also discuss the advantages and disadvantages of each model, along with the challenges facing the researchers who aim to develop and use animal models for translational research in NAFLD. Based on these characteristics and the specific study aims/needs, researchers should select the most appropriate model with caution when translating results from animal to human
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