923 research outputs found
Stellar variability in open clusters. I. A new class of variable stars in NGC 3766
Aims. We analyze the population of periodic variable stars in the open
cluster NGC 3766 based on a 7-year multi-band monitoring campaign conducted on
the 1.2 m Swiss Euler telescope at La Silla, Chili.
Methods. The data reduction, light curve cleaning and period search
procedures, combined with the long observation time line, allow us to detect
variability amplitudes down to the milli-magnitude level. The variability
properties are complemented with the positions in the color-magnitude and
color-color diagrams to classify periodic variable stars into distinct
variability types.
Results. We find a large population (36 stars) of new variable stars between
the red edge of slowly pulsating B (SPB) stars and the blue edge of delta Sct
stars, a region in the Hertzsprung-Russell (HR) diagram where no pulsation is
predicted to occur based on standard stellar models. The bulk of their periods
ranges from 0.1 to 0.7 d, with amplitudes between 1 and 4 mmag for the majority
of them. About 20% of stars in that region of the HR diagram are found to be
variable, but the number of members of this new group is expected to be higher,
with amplitudes below our milli-magnitude detection limit.
The properties of this new group of variable stars are summarized, and
arguments set forth in favor of a pulsation origin of the variability, with
g-modes sustained by stellar rotation. Potential members of this new class of
low-amplitude periodic (most probably pulsating) A and late-B variables in the
literature are discussed.
We additionally identify 16 eclipsing binary, 13 SPB, 14 delta Sct and 12
gamma Dor candidates, as well as 72 fainter periodic variables. All are new
discoveries.
Conclusions. We encourage to search for the existence of this new class of
variables in other young open clusters, especially in those hosting a rich
population of Be stars.Comment: Accepted for publication in A&A. Size of pdf file ~7Mo. Figures 12,
13, 14 and in the Appendix are of lower quality. Full quality images
published in A&
New Periodic Variables from the Hipparcos Epoch Photometry
Two selection statistics are used to extract new candidate periodic variables
from the epoch photometry of the Hipparcos catalogue. The primary selection
criterion is a signal to noise ratio. The dependence of this statistic on the
number of observations is calibrated using about 30 000 randomly permuted
Hipparcos datasets. A significance level of 0.1% is used to extract a first
batch of candidate variables. The second criterion requires that the optimal
frequency be unaffected if the data are de-trended by low order polynomials. We
find 2675 new candidate periodic variables, of which the majority (2082) are
from the Hipparcos "unsolved" variables. Potential problems with the
interpretation of the data (e.g. aliasing) are discussed.Comment: 18 pages, 9 figures, accepted for publication in MNRA
On Machine-Learned Classification of Variable Stars with Sparse and Noisy Time-Series Data
With the coming data deluge from synoptic surveys, there is a growing need
for frameworks that can quickly and automatically produce calibrated
classification probabilities for newly-observed variables based on a small
number of time-series measurements. In this paper, we introduce a methodology
for variable-star classification, drawing from modern machine-learning
techniques. We describe how to homogenize the information gleaned from light
curves by selection and computation of real-numbered metrics ("feature"),
detail methods to robustly estimate periodic light-curve features, introduce
tree-ensemble methods for accurate variable star classification, and show how
to rigorously evaluate the classification results using cross validation. On a
25-class data set of 1542 well-studied variable stars, we achieve a 22.8%
overall classification error using the random forest classifier; this
represents a 24% improvement over the best previous classifier on these data.
This methodology is effective for identifying samples of specific science
classes: for pulsational variables used in Milky Way tomography we obtain a
discovery efficiency of 98.2% and for eclipsing systems we find an efficiency
of 99.1%, both at 95% purity. We show that the random forest (RF) classifier is
superior to other machine-learned methods in terms of accuracy, speed, and
relative immunity to features with no useful class information; the RF
classifier can also be used to estimate the importance of each feature in
classification. Additionally, we present the first astronomical use of
hierarchical classification methods to incorporate a known class taxonomy in
the classifier, which further reduces the catastrophic error rate to 7.8%.
Excluding low-amplitude sources, our overall error rate improves to 14%, with a
catastrophic error rate of 3.5%.Comment: 23 pages, 9 figure
Les microARNs
MiRNAs are small non-coding RNAs ensuring the post-transcriptional regulation of gene expression. Their expression is tissue-specific and some miRNAs have diagnostic and / or prognostic value for tumor classes. MiRNAs are involved in tumorigenesis by two mechanisms: amplification or deletion of chromosomal regions containing clusters of genes encoding miRNAs (quantitative effect) or modification of the effects of miRNAs on their target genes by mutation in the region of interaction with the mRNA (qualitative effect). Their specificity, the possibility for miRNA measurement in blood, must now lead to consider miRNAs as markers for therapeutic management. A better understanding of the different regulatory mechanisms involving miRNAs will also consider new therapeutic approaches
Photo-responsive polymer with erasable and reconfigurable micro- and nano-patterns: An in vitro study for neuron guidance
The interaction of cells with nanoscale topography has proven to be an important modality in controlling cell responses. Topographic parameters on material surfaces play a role in cell growth. We have synthesized a new bio compatible polymer containing photoswitching molecules. Stripepatterned (groove/ridge pattern) were patterned and erased with ease on this bio azopolymer with two different set-ups: one with the projection of an optical interference pattern and the other one by molecular self-organization with one single laser beam. These two set-ups allow the re-writing of pattern after erasing and its inscription in vitro. PC12 cells were cultured on the bio-photoswitching patterned polymer and compared with PC12 cells growing on a well know substrate: poly-L-lysine. This result is of interest for facilitating contact guidance and designing reconfigurable scaffold for neural network formation in vitro. (C) 2011 Elsevier B.V. All rights reserve
From Hipparcos to Gaia
The measurement of the positions, distances, motions and luminosities of
stars represents the foundations of modern astronomical knowledge. Launched at
the end of the eighties, the ESA Hipparcos satellite was the first space
mission dedicated to such measurements. Hipparcos improved position accuracies
by a factor of 100 compared to typical ground-based results and provided
astrometric and photometric multi-epoch observations of 118,000 stars over the
entire sky. The impact of Hipparcos on astrophysics has been extremely valuable
and diverse. Building on this important European success, the ESA Gaia
cornerstone mission promises an even more impressive advance. Compared to
Hipparcos, it will bring a gain of a factor 50 to 100 in position accuracy and
of a factor of 10,000 in star number, collecting photometric,
spectrophotometric and spectroscopic data for one billion celestial objects.
During its 5-year flight, Gaia will measure objects repeatedly, up to a few
hundred times, providing an unprecedented database to study the variability of
all types of celestial objects. Gaia will bring outstanding contributions,
directly or indirectly, to most fields of research in astrophysics, such as the
study of our Galaxy and of its stellar constituents, the search for planets
outside the solar system.Comment: 6 pages. New Horizons in Time Domain Astronomy Proceedings IAU
Symposium No. 285, 2012, E. Griffin, B. Hanisch & R. Seaman, ed
An Entry/Gateway® cloning system for general expression of genes with molecular tags in Drosophila melanogaster
<p>Abstract</p> <p>Background</p> <p>Tagged fusion proteins are priceless tools for monitoring the activities of biomolecules in living cells. However, over-expression of fusion proteins sometimes leads to the unwanted lethality or developmental defects. Therefore, vectors that can express tagged proteins at physiological levels are desirable tools for studying dosage-sensitive proteins. We developed a set of Entry/Gateway<sup>® </sup>vectors for expressing fluorescent fusion proteins in <it>Drosophila melanogaster</it>. The vectors were used to generate fluorescent CP190 which is a component of the <it>gypsy </it>chromatin insulator. We used the fluorescent CP190 to study the dynamic movement of related chromatin insulators in living cells.</p> <p>Results</p> <p>The Entry/Gateway<sup>® </sup>system is a timesaving technique for quickly generating expression constructs of tagged fusion proteins. We described in this study an Entry/Gateway<sup>® </sup>based system, which includes six P-element destination vectors (P-DEST) for expressing tagged proteins (eGFP, mRFP, or myc) in <it>Drosophila melanogaster </it>and a TA-based cloning vector for generating entry clones from unstable DNA sequences. We used the P-DEST vectors to express fluorecent <it>CP190 </it>at tolerable levels. Expression of <it>CP190 </it>using the UAS/Gal4 system, instead, led to either lethality or underdeveloped tissues. The expressed eGFP- or mRFP-tagged CP190 proteins are fully functional and rescued the lethality of the homozygous <it>CP190 </it>mutation. We visualized a wide range of CP190 distribution patterns in living cell nuclei, from thousands of tiny particles to less than ten giant ones, which likely reflects diverse organization of higher-order chromatin structures. We also visualized the fusion of multiple smaller insulator bodies into larger aggregates in living cells, which is likely reflective of the dynamic activities of reorganization of chromatin in living nuclei.</p> <p>Conclusion</p> <p>We have developed an efficient cloning system for expressing dosage-sensitive proteins in <it>Drosophila melanogaster</it>. This system successfully expresses functional fluorescent CP190 fusion proteins. The fluorescent CP190 proteins exist in insulator bodies of various numbers and sizes among cells from multiple living tissues. Furthermore, live imaging of the movements of these fluorescent-tagged proteins suggests that the assembly and disassembly of insulator bodies are normal activities in living cells and may be directed for regulating transcription.</p
Investigating Cepheid Carinae's Cycle-to-cycle Variations via Contemporaneous Velocimetry and Interferometry
Baade-Wesselink-type (BW) techniques enable geometric distance measurements
of Cepheid variable stars in the Galaxy and the Magellanic clouds. The leading
uncertainties involved concern projection factors required to translate
observed radial velocities (RVs) to pulsational velocities and recently
discovered modulated variability. We carried out an unprecedented observational
campaign involving long-baseline interferometry (VLTI/PIONIER) and spectroscopy
(Euler/Coralie) to search for modulated variability in the long-period (P
35.5 d) Cepheid Carinae. We determine highly precise angular diameters
from squared visibilities and investigate possible differences between two
consecutive maximal diameters, . We characterize the
modulated variability along the line-of-sight using 360 high-precision RVs.
Here we report tentative evidence for modulated angular variability and confirm
cycle-to-cycle differences of Carinae's RV variability. Two successive
maxima yield = 13.1 0.7 (stat.) {\mu}as for
uniform disk models and 22.5 1.4 (stat.) {\mu}as (4% of the total angular
variation) for limb-darkened models. By comparing new RVs with 2014 RVs we show
modulation to vary in strength. Barring confirmation, our results suggest the
optical continuum (traced by interferometry) to be differently affected by
modulation than gas motions (traced by spectroscopy). This implies a previously
unknown time-dependence of projection factors, which can vary by 5% between
consecutive cycles of expansion and contraction. Additional interferometric
data are required to confirm modulated angular diameter variations. By
understanding the origin of modulated variability and monitoring its long-term
behavior, we aim to improve the accuracy of BW distances and further the
understanding of stellar pulsations.Comment: Accepted for publication in MNRAS. 19 pages, 13 figures, 10 table
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