2,235 research outputs found
Microlensing towards M31 with MDM data
We report the final analysis of a search for microlensing events in the
direction of the Andromeda galaxy, which aimed to probe the MACHO composition
of the M31 halo using data collected during the 1998-99 observational campaign
at the MDM observatory. In a previous paper, we discussed the results from a
first set of observations. Here, we deal with the complete data set, and we
take advantage of some INT observations in the 1999-2000 seasons. This merging
of data sets taken by different instruments turns out to be very useful, the
study of the longer baseline available allowing us to test the uniqueness
characteristic of microlensing events. As a result, all the candidate
microlensing events previously reported turn out to be variable stars. We
further discuss a selection based on different criteria, aimed at the detection
of short--duration events. We find three candidates whose positions are
consistent with self--lensing events, although the available data do not allow
us to conclude unambiguously that they are due to microlensing.Comment: Accepted for publication in Astronomy and Astrophysic
The POINT-AGAPE survey II: An Unrestricted Search for Microlensing Events towards M31
An automated search is carried out for microlensing events using a catalogue
of 44554 variable superpixel lightcurves derived from our three-year monitoring
program of M31. Each step of our candidate selection is objective and
reproducible by a computer. Our search is unrestricted, in the sense that it
has no explicit timescale cut. So, it must overcome the awkward problem of
distinguishing long-timescale microlensing events from long-period stellar
variables. The basis of the selection algorithm is the fitting of the
superpixel lightcurves to two different theoretical models, using variable star
and blended microlensing templates. Only if microlensing is preferred is an
event retained as a possible candidate. Further cuts are made with regard to
(i) sampling, (ii) goodness of fit of the peak to a Paczynski curve, (iii)
consistency of the microlensing hypothesis with the absence of a resolved
source, (iv) achromaticity, (v) position in the colour-magnitude diagram and
(vi) signal-to-noise ratio. Our results are reported in terms of first-level
candidates, which are the most trustworthy, and second-level candidates, which
are possible microlensing but have lower signal-to-noise and are more
questionable. The pipeline leaves just 3 first-level candidates, all of which
have very short full-width half-maximum timescale (<5 days) and 3 second-level
candidates, which have timescales of 31, 36 and 51 days respectively. We also
show 16 third-level lightcurves, as an illustration of the events that just
fail the threshold for designation as microlensing candidates. They are almost
certainly mainly variable stars. Two of the 3 first-level candidates correspond
to known events (PA 00-S3 and PA 00-S4) already reported by the POINT-AGAPE
project. The remaining first-level candidate is new.Comment: 22 pages, 18 figures, MNRAS, to appea
Recommended from our members
Early symptoms and sensations as predictors of lung cancer: a machine learning multivariate model.
The aim of this study was to identify a combination of early predictive symptoms/sensations attributable to primary lung cancer (LC). An interactive e-questionnaire comprised of pre-diagnostic descriptors of first symptoms/sensations was administered to patients referred for suspected LC. Respondents were included in the present analysis only if they later received a primary LC diagnosis or had no cancer; and inclusion of each descriptor required ≥4 observations. Fully-completed data from 506/670 individuals later diagnosed with primary LC (n = 311) or no cancer (n = 195) were modelled with orthogonal projections to latent structures (OPLS). After analysing 145/285 descriptors, meeting inclusion criteria, through randomised seven-fold cross-validation (six-fold training set: n = 433; test set: n = 73), 63 provided best LC prediction. The most-significant LC-positive descriptors included a cough that varied over the day, back pain/aches/discomfort, early satiety, appetite loss, and having less strength. Upon combining the descriptors with the background variables current smoking, a cold/flu or pneumonia within the past two years, female sex, older age, a history of COPD (positive LC-association); antibiotics within the past two years, and a history of pneumonia (negative LC-association); the resulting 70-variable model had accurate cross-validated test set performance: area under the ROC curve = 0.767 (descriptors only: 0.736/background predictors only: 0.652), sensitivity = 84.8% (73.9/76.1%, respectively), specificity = 55.6% (66.7/51.9%, respectively). In conclusion, accurate prediction of LC was found through 63 early symptoms/sensations and seven background factors. Further research and precision in this model may lead to a tool for referral and LC diagnostic decision-making
The POINT-AGAPE Survey: Comparing Automated Searches of Microlensing Events toward M31
Searching for microlensing in M31 using automated superpixel surveys raises a
number of difficulties which are not present in more conventional techniques.
Here we focus on the problem that the list of microlensing candidates is
sensitive to the selection criteria or "cuts" imposed and some subjectivity is
involved in this. Weakening the cuts will generate a longer list of
microlensing candidates but with a greater fraction of spurious ones;
strengthening the cuts will produce a shorter list but may exclude some genuine
events. We illustrate this by comparing three analyses of the same data-set
obtained from a 3-year observing run on the INT in La Palma. The results of two
of these analyses have been already reported: Belokurov et al. (2005) obtained
between 3 and 22 candidates, depending on the strength of their cuts, while
Calchi Novati et al. (2005) obtained 6 candidates. The third analysis is
presented here for the first time and reports 10 microlensing candidates, 7 of
which are new. Only two of the candidates are common to all three analyses. In
order to understand why these analyses produce different candidate lists, a
comparison is made of the cuts used by the three groups...Comment: 28 pages, 24 figures, 9 table
Gene expression changes related to immune processes associate with cognitive endophenotypes of schizophrenia
Schizophrenia is a heterogeneous disorder characterized by a spectrum of symptoms and many different underlying causes. Thus, instead of using the broad diagnosis, intermediate phenotypes can be used to possibly decrease the underlying complexity of the disorder. Alongside the classical symptoms of delusions and hallucinations, cognitive deficits are a core feature of schizophrenia. To increase our understanding of the biological processes related to these cognitive deficits, we performed a genome-wide gene expression analysis. A battery of 14 neuropsychological tests was administered to 844 individuals from a Finnish familial schizophrenia cohort. We grouped the applied neuropsychological tests into five factors for further analysis. Cognitive endophenotypes, whole blood mRNA, genotype, and medication use data were studied from 47 individuals. Expression level of several RNA probes were significantly associated with cognitive performance. The factor representing Verbal Working Memory was associated with altered expression levels of 11 probes, of which one probe was also associated with a specific sub-measure of this factor (WMS-R Digit span backward). While, the factor Processing speed was related to one probe, which additionally associated among 55 probes with a specific sub-measure of this factor (WAIS-R Digit symbol). Two probes were associated with the measure recognition memory performance. Enrichment analysis of these differentially expressed probes highlighted immunological processes. Our findings are in line with genome-wide genetic discoveries made in schizophrenia, suggesting that immunological processes may be of biological interest for future drug design towards schizophrenia and the cognitive dysfunctions that underlie it.Peer reviewe
The importance of clinical and labour market histories in psychiatric disability retirement : analysis of the comprehensive Finnish national-level RETIRE data
Objectives Despite the stable incidence of mental disorders in Finland and Europe, mental health-related occupational disability has been increasing. We unveiled the paths to permanent psychiatric disability, recovery, or death, by analysing sequences of labour market participation. Methods The RETIRE register database includes information regarding all persons (n = 42,170) awarded an ICD-10 psychiatric disability pension between 2010 and 2015 in Finland. We identified clusters of typical paths of pre-retirement labour market history. Controlling for major mental disorders, age, and sex, we evaluated factors associated with returning to work (RTW), or death, over a 5-year follow-up period. Results Only 10.5% of the disabled subjects returned to work within the follow-up. Half of them ended up with a permanent disability pension. Seven distinguishable paths to disability were identified. Subjects in the cluster characterized by steady employment were relatively often females, lost their work ability due to affective disorders, and had the highest rate of returning to work (16.3%). Mortality was highest (9%) among the cluster characterized by long-term unemployment. Distributions of major diagnostic groups, as well as age and sex, differed between clusters. After their adjustment in the analysis of RTW or death, the identified labour market history paths prior to losing work ability remained as important independent prognostic factors for both outcomes. Conclusions The complex retirement process involves identifiable clinical and contextual associating factors. Labour market history patterns associate with varying prognoses after psychiatric retirement. Prolonged unemployment appears as a predictor of relatively poor prognoses, whereas employment indicates the opposite.Peer reviewe
Cosmic shear requirements on the wavelength-dependence of telescope point spread functions
Cosmic shear requires high precision measurement of galaxy shapes in the
presence of the observational Point Spread Function (PSF) that smears out the
image. The PSF must therefore be known for each galaxy to a high accuracy.
However, for several reasons, the PSF is usually wavelength dependent,
therefore the differences between the spectral energy distribution of the
observed objects introduces further complexity. In this paper we investigate
the effect of the wavelength-dependence of the PSF, focusing on instruments in
which the PSF size is dominated by the diffraction-limit of the telescope and
which use broad-band filters for shape measurement.
We first calculate biases on cosmological parameter estimation from cosmic
shear when the stellar PSF is used uncorrected. Using realistic galaxy and star
spectral energy distributions and populations and a simple three-component
circular PSF we find that the colour-dependence must be taken into account for
the next generation of telescopes. We then consider two different methods for
removing the effect (i) the use of stars of the same colour as the galaxies and
(ii) estimation of the galaxy spectral energy distribution using multiple
colours and using a telescope model for the PSF. We find that both of these
methods correct the effect to levels below the tolerances required for per-cent
level measurements of dark energy parameters. Comparison of the two methods
favours the template-fitting method because its efficiency is less dependent on
galaxy redshift than the broad-band colour method and takes full advantage of
deeper photometry.Comment: 10 pages, 8 figures, version accepted for publication in MNRA
Classical novae from the POINT-AGAPE microlensing survey of M31 -- I. The nova catalogue
The POINT-AGAPE survey is an optical search for gravitational microlensing
events towards the Andromeda Galaxy (M31). As well as microlensing, the survey
is sensitive to many different classes of variable stars and transients. Here
we describe the automated detection and selection pipeline used to identify M31
classical novae (CNe) and we present the resulting catalogue of 20 CN
candidates observed over three seasons. CNe are observed both in the bulge
region as well as over a wide area of the M31 disk. Nine of the CNe are caught
during the final rise phase and all are well sampled in at least two colours.
The excellent light-curve coverage has allowed us to detect and classify CNe
over a wide range of speed class, from very fast to very slow. Among the
light-curves is a moderately fast CN exhibiting entry into a deep transition
minimum, followed by its final decline. We have also observed in detail a very
slow CN which faded by only 0.01 mag day over a 150 day period. We
detect other interesting variable objects, including one of the longest period
and most luminous Mira variables. The CN catalogue constitutes a uniquely
well-sampled and objectively-selected data set with which to study the
statistical properties of classical novae in M31, such as the global nova rate,
the reliability of novae as standard-candle distance indicators and the
dependence of the nova population on stellar environment. The findings of this
statistical study will be reported in a follow-up paper.Comment: 21 pages, 13 figures, re-submitted for publication in MNRAS, typos
corrected, references updated, figures 5-9 made cleare
- …