77 research outputs found
A photometric investigation of the young open cluster Trumpler 15
In this paper we present and analyze new CCD photometry down to
21 in the region of the young open cluster Trumpler~15, located in
the Carina spiral feature. The cluster is rather compact and has a core radius
of about 2, which translates in about 1 pc at the distance of the
cluster. We provide the first CCD investigation and update its fundamental
parameters. We identify 90 candidate photometric members on the base of the
position in the color-color and color-magnitude diagrams. This sample allows us
to obtain a distance of 2.40.3 kpc from the Sun and a reddening
E=0.52. We confirm that the cluster is young, and fix a upper
limit of 6 million yrs to its age . In addition, we draw the attention on the
lower part of the Main Sequence (MS) suggesting that some stars can be in
contracting phase and on a gap in the MS, that we show to be a real feature,
the gap found in other young open clusters. We finally study in details
the extinction toward Trumpler~15 concluding that it is normal and suggesting a
value of 2.890.19 for the ratio of total to selective absorption .\Comment: 11 pages, 13 eps figures, accepted for publication in MNRA
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Small-molecule targeting of translation initiation for cancer therapy
Translation initiation plays a critical role in the regulation of cell growth and tumorigenesis. We report here that inhibiting translation initiation through induction of eIF2α phosphorylation by small-molecular-weight compounds restricts the availability of the eIF2·GTP·Met-tRNAi ternary complex and abrogates the proliferation of cancer cells in vitro and tumor growth in vivo. Restricting the availability of the ternary complex preferentially down-regulates the expression of growth-promoting proteins and up-regulates the expression of ER stress response genes in cancer cells as well as in tumors excised from either animal models of human cancer or cancer patients. These findings provide the first direct evidence for translational control of gene-specific expression by small molecules in vivo and indicate that translation initiation factors are bona fide targets for development of mechanism-specific anti-cancer agents
A Search for Variable Stars and Planetary Occultations in NGC 2301 II: Variability
We performed R-band time series observations of the young, metal rich open
cluster NGC 2301 for 12 nights in Feb. 2004. B images were also obtained and
color magnitude diagrams, having limits of R=19.5 and B=21.5, were produced.
Only asmall effort was made to determine cluster membership as our magnitude
limits are far deeper than previously published values. Our photometric
precision, for the brightest 5 magnitudes of sources, is 1-2 mmag. We determine
that for the 4000 stars which have time-series data, 56% are variable and
of these, approximately 13% are observed to exhibit periodic light curves
ranging from tens of minutes to days. We present some examples of the light
curves obtained and produce cuts in variability space based on parameters such
as color and amplitude. The percentage of variability is approximately equal
across all colors with the majority of variables having amplitudes of 0.15
magnitudes or less. In general, redder stars show larger variability
amplitudes. We find a smooth decline in the number of periodic variables toward
longer period. This decline is probably due to a transition from intrinsic to
extrinsic variability and, in part, to our limited observing period of 12
nights. Essentially all the A and F main sequence stars in our sample are
variable (2 mmag and larger) and most present complex light curves
containing multiple periods suggestive of their inclusion in the Sct
and Dor classes. A variable non-cluster member giant and two variable
white dwarf candidates are discussed. Our equational description of variability
is shown to be an excellent predictive tool for determining the cumulative
fraction of variables that will be observed in a photometric survey. Our entire
dataset is available electronically.Comment: 25 pages, 21 figures Accepted to PAS
The structure and dynamics of young star clusters: King 16, NGC 1931, NGC 637 and NGC 189
In this paper, using 2MASS photometry, we study the structural and dynamical
properties of four young star clusters viz. King 16, NGC 1931, NGC 637 and NGC
189. For the clusters King 16, NGC 1931, NGC 637 and NGC 189, we obtain the
limiting radii of 7', 12', 6' and 5' which correspond to linear radii of 3.6
pc, 8.85 pc, 3.96 pc and 2.8 pc respectively. The reddening values
obtained for the clusters are 0.85, 0.65--0.85, 0.6 and 0.53 and their true
distances are 1786 pc, 3062 pc, 2270 pc and 912 pc respectively. Ages of the
clusters are 6 Myr, 4 Myr, 4 Myr and 10 Myr respectively. We compare their
structures, luminosity functions and mass functions () to the parameter to study the star
formation process and the dynamical evolution of these clusters. We find that,
for our sample, mass seggregation is observed in clusters or their cores only
when the ages of the clusters are comparable to their relaxation times (). These results suggest mass seggregation due to dynamical effects. The
values of , which characterise the overall mass functions for the
clusters are 0.96 0.11, 1.16 0.18, 0.55 0.14 and 0.66
0.31 respectively. The change in as a function of radius is a good
indicator of the dynamical state of clusters.Comment: Accepted for publication in Astrophysics & Space Scienc
A Chandra ACIS Study of the Young Star Cluster Trumpler 15 in Carina and Correlation with Near-infrared Sources
Using the highest-resolution X-ray observation of the Trumpler 15 star
cluster taken by the Chandra X-ray Observatory, we estimate the total size of
its stellar population by comparing the X-ray luminosity function of the
detected sources to a calibrator cluster, and identify for the first time a
significant fraction (~14%) of its individual members. The highest-resolution
near-IR observation of Trumpler 15 (taken by the HAWK-I instrument on the VLT)
was found to detect most of our X-ray selected sample of cluster members, with
a K-excess disk frequency of 3.8+-0.7%. The near-IR data, X-ray luminosity
function, and published spectral types of the brightest members support a
cluster age estimate (5-10 Myr) that is older than those for the nearby
Trumpler 14 and Trumpler 16 clusters, and suggest that high-mass members may
have already exploded as supernovae. The morphology of the inner ~0.7 pc core
of the cluster is found to be spherical. However, the outer regions (beyond 2
pc) are elongated, forming an `envelope' of stars that, in projection, appears
to connect Trumpler 15 to Trumpler 14; this morphology supports the view that
these clusters are physically associated. Clear evidence of mass segregation is
seen. This study appears in a Special Issue of the ApJS devoted to the Chandra
Carina Complex Project (CCCP), a 1.42 square degree Chandra X-ray survey of the
Great Nebula in Carina.Comment: Accepted for the ApJS Special Issue on the Chandra Carina Complex
Project (CCCP), scheduled for publication in May 2011. All 16 CCCP Special
Issue papers are available at
http://cochise.astro.psu.edu/Carina_public/special_issue.html through 2011 at
least. 30 pages; 8 figures; 3 table
Analysing the database for stars in open clusters I. General methods and description of the data
We present an overview and statistical analysis of the data included in
WEBDA. This database includes valuable information such as coordinates,
rectangular positions, proper motions, photometric as well as spectroscopic
data, radial and rotational velocities for objects of open clusters in our
Milky Way. It also contains miscellaneous types of data like membership
probabilities, orbital elements of spectroscopic binaries and periods of
variability for different kinds of variable stars. Our final goal is to derive
astrophysical parameters (reddening, distance and age) of open clusters based
on the major photometric system which will be presented in a follow-up paper.
For this purpose we have chosen the Johnson UBV, Cousins VRI and Stroemgren
uvbybeta photometric systems for a statistical analysis of published data sets
included in WEBDA. Our final list contains photographic, photoelectric and CCD
data for 469820 objects in 573 open clusters. We have checked the internal
(data sets within one photometric system and the same detector technique) and
external (different detector technique) accuracy and conclude that more than
97% of all investigated data exhibit a sufficient accuracy for our analysis.
The way of weighting and averaging the data is described. In addition, we have
compiled a list of deviating measurements which is available to the community
through WEBDA.Comment: 8 pages, 4 figures, accepted by A&
Photometric survey of marginally investigated open clusters: I. Basel 11b, King 14, Czernik 43
To progress in galactic studies based on open clusters, e.g. cluster
formation rate or kinematical properties, one needs to improve the number of
open clusters observed. However, only half of the 1700 known galactic open
clusters have been properly observed so far, making any statistical
investigation insignificant, especially at larger distances from the Sun. We
study marginally investigated or neglected open clusters with Bessell CCD BVR
photometry, whose data were used to fit isochrones to the individual
color-magnitude diagrams. We examined the galactic clusters Basel 11b, King 14
and Czernik 43, the last being observed for the first time to this extent. As
well as a careful comparison to available photometry, their parameters such as
age, interstellar reddening, distance and apparent diameter were determined.
The obtained cluster properties were verified by near infrared 2MASS data. The
three investigated intermediate age clusters are all located in the galactic
disk with distances between 1.8 and 3.0kpc from the Sun.Comment: A&A accepted, 7 pages, 5 figure
Epidemiology, patterns of care, and mortality for patients with acute respiratory distress syndrome in intensive care units in 50 countries
IMPORTANCE: Limited information exists about the epidemiology, recognition, management, and outcomes of patients with the acute respiratory distress syndrome (ARDS).
OBJECTIVES: To evaluate intensive care unit (ICU) incidence and outcome of ARDS and to assess clinician recognition, ventilation management, and use of adjuncts-for example prone positioning-in routine clinical practice for patients fulfilling the ARDS Berlin Definition.
DESIGN, SETTING, AND PARTICIPANTS:The Large Observational Study to Understand the Global Impact of Severe Acute Respiratory Failure (LUNG SAFE) was an international, multicenter, prospective cohort study of patients undergoing invasive or noninvasive ventilation, conducted during 4 consecutive weeks in the winter of 2014 in a convenience sample of 459 ICUs from 50 countries across 5 continents.
EXPOSURES:Acute respiratory distress syndrome.
MAIN OUTCOMES AND MEASURES: The primary outcome was ICU incidence of ARDS. Secondary outcomes included assessment of clinician recognition of ARDS, the application of ventilatory management, the use of adjunctive interventions in routine clinical practice, and clinical outcomes from ARDS.
RESULTS: Of 29,144 patients admitted to participating ICUs, 3022 (10.4%) fulfilled ARDS criteria. Of these, 2377 patients developed ARDS in the first 48 hours and whose respiratory failure was managed with invasive mechanical ventilation. The period prevalence of mild ARDS was 30.0% (95% CI, 28.2%-31.9%); of moderate ARDS, 46.6% (95% CI, 44.5%-48.6%); and of severe ARDS, 23.4% (95% CI, 21.7%-25.2%). ARDS represented 0.42 cases per ICU bed over 4 weeks and represented 10.4% (95% CI, 10.0%-10.7%) of ICU admissions and 23.4% of patients requiring mechanical ventilation. Clinical recognition of ARDS ranged from 51.3% (95% CI, 47.5%-55.0%) in mild to 78.5% (95% CI, 74.8%-81.8%) in severe ARDS. Less than two-thirds of patients with ARDS received a tidal volume 8 of mL/kg or less of predicted body weight. Plateau pressure was measured in 40.1% (95% CI, 38.2-42.1), whereas 82.6% (95% CI, 81.0%-84.1%) received a positive end-expository pressure (PEEP) of less than 12 cm H2O. Prone positioning was used in 16.3% (95% CI, 13.7%-19.2%) of patients with severe ARDS. Clinician recognition of ARDS was associated with higher PEEP, greater use of neuromuscular blockade, and prone positioning. Hospital mortality was 34.9% (95% CI, 31.4%-38.5%) for those with mild, 40.3% (95% CI, 37.4%-43.3%) for those with moderate, and 46.1% (95% CI, 41.9%-50.4%) for those with severe ARDS.
CONCLUSIONS AND RELEVANCE: Among ICUs in 50 countries, the period prevalence of ARDS was 10.4% of ICU admissions. This syndrome appeared to be underrecognized and undertreated and associated with a high mortality rate. These findings indicate the potential for improvement in the management of patients with ARDS
Optical and near-IR photometric study of the open cluster NGC 637 and NGC 957
We present UBVRI CCD photometry in the region of the open clusters NGC 637
and NGC 957. The radii are found to be 4.2 arcmin and 4.3 arcmin. Their
reddenings E(B-V) are 0.64+/-0.05 mag and 0.71+/-0.05 mag and their distances,
from main sequence fitting are 2.5+/-0.2 kpc and 2.2+/-0.2 kpc. Comparison with
Z=0.02 isochrones leads to an age of 10+/-5 Myr for both clusters. Combining
our photometry with 2MASS JHK shows the reddening law in these directions to be
normal. Mass function slopes of x=1.65+/-0.20 and 1.31+/-0.50 are derived for
the clusters, both of which are found to be dynamically relaxed. Spectral and
photometric characteristics of three Be stars, two in NGC 957 and one (newly
discovered) in NGC 637 indicate them to be of Classical Be type.Comment: Accepted for publication in MNRA
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