193 research outputs found
Wide angle search for extrasolar planets by the transit method
The transit method is considered to be one of the most promising for discovering extrasolar planets.
However, the method requires photometric precision of better than
∼
1%. If we are able to
achieve this kind of accuracy, then we are set to discover extrasolar planets. The uniqueness of my
experiment will lead to the discovery of transiting planets around the brightest and most important
stars quicker than the competitors in the field. The importance of the transit method stems from
being able to supply many more planetary parameters than other methods, which plays a crucial
role in testing planet formation theories. This thesis is divided into eight chapters.
The first chapter provides a general background about transits and their theory. We discuss
other methods of extrasolar planet detection, recent developments, future space missions, and
what we have learned so far about properties of hot Jupiters. The second chapter details the theory
of signals and noise on CCDs followed by the design of the PASS0 experiment. The third chapter
reports on the difference imaging data pipeline that we developed and applied to a set of PASS0
data to search for transiting planets. The fourth chapter shows how we apply the PASS0 pipeline to
SuperWASP data and improve on the accuracy obtained with their aperture photometry pipeline.
The fifth chapter reports on the search for variable stars from the PASS0 and SuperWASP data sets
that we consider in this thesis. In the sixth chapter we perform a transit search on the PASS0 and
SuperWASP data sets and report the results. In the seventh chapter we use the PASS0 pipeline to
process a full season of observing data from 2007 for two recent planet discoveries, WASP-7b and
WASP-8b, that have not yet been announced. We analyse their lightcurves and predict their radii.
Finally we conclude in the eighth chapter
Solving the intractable problem: optimal performance for worst case scenarios in XML twig pattern matching
In the history of databases, eXtensible Markup Language (XML) has been thought of as the standard format to store and exchange semi-structured data. With the advent of IoT, XML technologies can play an important role in addressing the issue of processing a massive amount of data generated from heterogeneous devices. As the number and complexity of such datasets increases there is a need for algorithms which are able to index and retrieve XML data efficiently even for complex queries. In this context twig pattern matching , finding all occurrences of a twig pattern query (TPQ), is a core operation in XML query processing. Until now holistic joins have been considered the state-of-the-art TPQ processing algorithms, but they fail to guarantee an optimal evaluation except at the expense of excessive storage costs which limit their scope in large datasets. In this article, we introduce a new approach which significantly outperforms earlier methods in terms of both the size of the intermediate storage and query running time. The approach presented here uses Child Prime Labels (Alsubai & North, 2018) to improve the filtering phase of bottom-up twig matching algorithms and a novel algorithm which avoids the use of stacks, thus improving TPQs processing efficiency. Several experiments were conducted on common benchmarks such as DBLP, XMark and TreeBank datasets to study the performance of the new approach. Multiple analyses on a range of twig pattern queries are presented to demonstrate the statistical significance of the improvements
Difference image analysis: The interplay between the photometric scale factor and systematic photometric errors
Context: Understanding the source of systematic errors in photometry is
essential for their calibration. Aims: We investigate how photometry performed
on difference images can be influenced by errors in the photometric scale
factor. Methods: We explore the equations for difference image analysis (DIA)
and we derive an expression describing how errors in the difference flux, the
photometric scale factor and the reference flux are propagated to the object
photometry. Results: We find that the error in the photometric scale factor is
important, and while a few studies have shown that it can be at a significant
level, it is currently neglected by the vast majority of photometric surveys
employing DIA. Conclusions: Minimising the error in the photometric scale
factor, or compensating for it in a post-calibration model, is crucial for
reducing the systematic errors in DIA photometry.Comment: Accepted A&
A Prime Number Approach to Matching an XML Twig Pattern including Parent-Child Edges
Twig pattern matching is a core operation in XML query processing because it is how all the occurrences
of a twig pattern in an XML document are found. In the past decade, many algorithms have been proposed
to perform twig pattern matching. They rely on labelling schemes to determine relationships between
elements corresponding to query nodes in constant time. In this paper, a new algorithm TwigStackPrime is
proposed, which is an improvement to TwigStack (Bruno et al., 2002). To reduce the memory consumption and
computation overhead of twig pattern matching algorithms when Parent-Child (P-C) edges are involved, TwigStackPrime
efficiently filters out a tremendous number of irrelevant elements by introducing a new labelling
scheme, called Child Prime Label (CPL). Extensive performance studies on various real-world and artificial
datasets were conducted to demonstrate the significant improvement of CPL over the previous indexing and
querying techniques. The experimental results show that the new technique has a superior performance to the
previous approaches
A Prototype for the PASS Permanent All Sky Survey
A prototype system for the Permanent All Sky Survey (PASS) project is
presented. PASS is a continuous photometric survey of the entire celestial
sphere with a high temporal resolution. Its major objectives are the detection
of all giant-planet transits (with periods up to some weeks) across stars up to
mag 10.5, and to deliver continuously photometry that is useful for the study
of any variable stars. The prototype is based on CCD cameras with short focal
length optics on a fixed mount. A small dome to house it at Teide Observatory,
Tenerife, is currently being constructed. A placement at the antarctic Dome C
is also being considered. The prototype will be used for a feasibility study of
PASS, to define the best observing strategies, and to perform a detailed
characterization of the capabilities and scope of the survey. Afterwards, a
first partial sky surveying will be started with it. That first survey may be
able to detect transiting planets during its first few hundred hours of
operation. It will also deliver a data set around which software modules
dealing with the various scientific objectives of PASS will be developed. The
PASS project is still in its early phase and teams interested in specific
scientific objectives, in providing technical expertise, or in participating
with own observations are invited to collaborate.Comment: Accepted for Astronomische Nachrichten (special issue for 3rd Potsdam
Thinkshop 'Robotic Astronomy' in July 2004). 4 pages, 4 fig
Child Prime Label Approaches to Evaluate XML Structured Queries
The adoption of the eXtensible Markup Language (XML) as the standard format to store and exchange semi-structure data has been gaining momentum. The growing number of XML documents leads to the need for appropriate XML querying algorithms which are able to retrieve XML data efficiently. Due to the importance of twig pattern matching in XML retrieval systems, finding all matching occurrences of a tree pattern query in an XML document is often considered as a specific task for XML databases as well as a core operation in XML query processing. This thesis presents a design and implementation of a new indexing technique, called the Child Prime Label (CPL) which exploits the property of prime numbers to identify Parent-Child (P-C) edges in twig pattern queries (TPQs) during query evaluation. The CPL approach can be incorporated efficiently within the existing labelling schemes. The major contributions of this thesis can be seen as a set of novel twig matching algorithms which apply the CPL approach and focus on reducing the overhead of storing useless elements and performing unnecessary computations during the output enumeration. The research presented here is the first to provide an efficient and general solution for TPQs containing ordering constraints and positional predicates specified by the XML query languages. To evaluate the CPL approaches, the holistic model was implemented as an experimental prototype in which the approaches proposed are compared against state-of-the-art holistic twig algorithms. Extensive performance studies on various real-world and artificial datasets were conducted to demonstrate the significant improvement of the CPL approaches over the previous indexing and querying methods. The experimental results demonstrate the validity and improvements of the new algorithms over other related methods on common various subclasses of TPQs. Moreover, the scalability tests reveal that the new algorithms are more suitable for processing large XML datasets
RR Lyrae Stars In The GCVS Observed By The Qatar Exoplanet Survey
We used the light curve archive of the Qatar Exoplanet Survey (QES) to
investigate the RR Lyrae variable stars listed in the General Catalogue of
Variable Stars (GCVS). Of 588 variables studied, we reclassify 14 as eclipsing
binaries, one as an RS Canum Venaticorum-type variable, one as an irregular
variable, four as classical Cepheids, and one as a type II Cepheid, while also
improving their periods. We also report new RR Lyrae sub-type classifications
for 65 variables and improve on the GCVS period estimates for 135 RR Lyrae
variables. There are seven double-mode RR Lyrae stars in the sample for which
we measured their fundamental and first overtone periods. Finally, we detect
the Blazhko effect in 38 of the RR Lyrae stars for the first time and we
successfully measured the Blazhko period for 26 of them.Comment: Accepted IBV
TwigStackPrime: A Novel Twig Join Algorithm Based on Prime Numbers
The growing number of XML documents leads to the need for appropriate XML querying algorithms which are able to utilize the specific characteristics of XML documents. A labelling scheme is fundamental to processing XML queries efficiently. They are used to determine structural relationships between elements corresponding to query nodes in twig pattern queries (TPQs). This article presents a design and implementation of a new indexing technique which exploits the property of prime numbers to identify Parent-Child (P-C) relationships in TPQs during query evaluation. The Child Prime Label (CPL, for short) approach can be efficiently incorporated within the existing labelling schemes. Here, we propose a novel twig matching algorithm based on the well known TwigStack algorithm [3], which applies the CPL approach and focuses on reducing the overhead of storing useless elements and performing unnecessary join operations. Our performance evaluation demonstrates that the new algorithm significantly outperforms the previous approaches
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