1,231 research outputs found
New Cepheid variables in the young open clusters Berkeley 51 and Berkeley 55
As part of a wider investigation of evolved massive stars in Galactic open clusters, we have spectroscopically identified three candidate classical Cepheids in the little-studied clusters Berkeley 51, Berkeley 55 and NGC 6603. Using new multi-epoch photometry, we confirm that Be 51 #162 and Be 55 #107 are bona fide Cepheids, with pulsation periods of 9.83±0.01 d and 5.850±0.005 d respectively, while NGC 6603 star W2249 does not show significant photometric variability. Using the period-luminosity relationship for Cepheid variables, we determine a distance to Be 51 of 5.3 +1.0 −0.8 kpc and an age of 44 +9 −8 Myr, placing it in a sparsely-attested region of the Perseus arm. For Be 55, we find a distance of 2.2±0.3 kpc and age of 63 +12 −11 Myr, locating the cluster in the Local arm. Taken together with our recent discovery of a long-period Cepheid in the starburst cluster VdBH222, these represent an important increase in the number of young, massive Cepheids known in Galactic open clusters. We also consider new Gaia (data release 2) parallaxes and proper motions for members of Be 51 and Be 55; the uncertainties on the parallaxes do not allow us to refine our distance estimates to these clusters, but the well-constrained proper motion measurements furnish further confirmation of cluster membership. However, future final Gaia parallaxes for such objects should provide valuable independent distance measurements, improving the calibration of the period-luminosity relationship, with implications for the distance ladder out to cosmological scales
A quantitative examination of the impact of featured articles in Wikipedia
This paper presents a quantitative examination of the impact of the presentation of featured articles as quality content in the main page of several Wikipedia editions. Moreover, the paper also presents the analysis performed to determine the number of visits received by the articles promoted to the featured status. We have analyzed the visits not only in the month when articles awarded the promotion or were included in the main page, but also in the previous and following ones. The main aim for this is to assess the attention attracted by the featured content and the different dynamics exhibited by each community of users in respect to the promotion process. The main results of this paper are twofold: it shows how to extract relevant information related to the use of Wikipedia, which is an emerging research topic, and it analyzes whether the featured articles mechanism achieve to attract more attention
Temporal characterization of the requests to Wikipedia
This paper presents an empirical study about the temporal patterns
characterizing the requests submitted by users to Wikipedia.
The study is based on the analysis of the log lines registered by the
Wikimedia Foundation Squid servers after having sent the appropriate
content in response to users' requests. The
analysis has been conducted regarding the ten most visited editions of
Wikipedia and has involved more than 14,000 million log lines
corresponding to the traffic of the entire year 2009. The conducted methodology
has mainly consisted in the parsing and filtering
of users' requests according to the study directives. As a result, relevant information
fields have been finally stored in a database for persistence and further
characterization. In this way, we, first, assessed, whether the traffic to Wikipedia could serve
as a reliable estimator of the overall traffic to all the Wikimedia Foundation
projects. Our subsequent analysis of the temporal evolutions corresponding to
the different types of requests to Wikipedia revealed interesting differences
and similarities among them that can be related to the users' attention to the Encyclopedia.
In addition, we have performed separated characterizations of each Wikipedia edition
to compare their respective evolutions over time
NGC 3105: a young open cluster with low metallicity
NGC 3105 is a young open cluster hosting blue, yellow and red supergiants.
This rare combination makes it an excellent laboratory to constrain
evolutionary models of high-mass stars. It is poorly studied and fundamental
parameters such as its age or distance are not well defined. We intend to
characterize in an accurate way the cluster as well as its evolved stars, for
which we derive for the first time atmospheric parameters and chemical
abundances. We identify 126 B-type likely members within a radius of
2.70.6 arcmin, which implies an initial mass, 4100
M. We find a distance of 7.20.7 kpc for NGC 3105, placing it at
=10.01.2 kpc. Isochrone fitting supports an age of 286 Ma,
implying masses around 9.5 M for the supergiants. A high fraction of
Be stars (25 %) is found at the top of the main sequence down to
spectral type b3. From the spectral analysis we estimate for the cluster a
=+46.90.9 km s and a low metallicity,
[Fe/H]=-0.290.22. We also have determined, for the first time, chemical
abundances for Li, O, Na, Mg, Si, Ca, Ti, Ni, Rb, Y, and Ba for the evolved
stars. The chemical composition of the cluster is consistent with that of the
Galactic thin disc. An overabundance of Ba is found, supporting the enhanced
-process. NGC 3105 has a low metallicity for its Galactocentric distance,
comparable to typical LMC stars. It is a valuable spiral tracer in a very
distant region of the Carina-Sagittarius spiral arm, a poorly known part of the
Galaxy. As one of the few Galactic clusters containing blue, yellow and red
supergiants, it is massive enough to serve as a testbed for theoretical
evolutionary models close to the boundary between intermediate and high-mass
stars.Comment: 18 pages, 13 figures. Accepted for publication in A&
Testing the chemical tagging technique with open clusters
Context. Stars are born together from giant molecular clouds and, if we
assume that the priors were chemically homogeneous and well-mixed, we expect
them to share the same chemical composition. Most of the stellar aggregates are
disrupted while orbiting the Galaxy and most of the dynamic information is
lost, thus the only possibility of reconstructing the stellar formation history
is to analyze the chemical abundances that we observe today.
Aims. The chemical tagging technique aims to recover disrupted stellar
clusters based merely on their chemical composition. We evaluate the viability
of this technique to recover co-natal stars that are no longer gravitationally
bound.
Methods. Open clusters are co-natal aggregates that have managed to survive
together. We compiled stellar spectra from 31 old and intermediate-age open
clusters, homogeneously derived atmospheric parameters, and 17 abundance
species, and applied machine learning algorithms to group the stars based on
their chemical composition. This approach allows us to evaluate the viability
and efficiency of the chemical tagging technique.
Results. We found that stars at different evolutionary stages have distinct
chemical patterns that may be due to NLTE effects, atomic diffusion, mixing,
and biases. When separating stars into dwarfs and giants, we observed that a
few open clusters show distinct chemical signatures while the majority show a
high degree of overlap. This limits the recovery of co-natal aggregates by
applying the chemical tagging technique. Nevertheless, there is room for
improvement if more elements are included and models are improved.Comment: accepted for publication in Astronomy and Astrophysics. Corrected
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Evaluating trifluridine + tipiracil hydrochloride in a fixed combination (TAS-102) for the treatment of colorectal cancer
Introduction: Despite major progress in treating advanced colorectal cancer (CRC), prognosis in this population after progression on standard treatment remains dismal and the development of new drugs represents an unmet need. Historically, fluoropyrimidines have played a major role in the treatment of metastatic CRC. TAS-102, a novel combination of trifluridine and tipiracil hydrochloride, has demonstrated improvement in overall survival in the refractory CRC setting, with a safe toxicity profile. Areas covered: A literature review of published clinical studies was performed. Herein, the authors review the pharmacological and clinical data of TAS-102 when used in metastatic CRC, both as a single agent as well as in novel combinations under investigation. Expert opinion: The addition of TAS-102 to the therapeutic armamentarium of metastatic CRC is an encouraging breakthrough considering the demonstrated survival benefit and favorable tolerability profile. Combinations with other agents are under clinical investigation in different settings in an attempt to widen its use. To optimize treatment in today’s era of molecular oncology, efforts should be focused on understanding primary and secondary resistance mechanisms, along with the identification of potential biomarkers of response
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