80 research outputs found
Petersen Diagram Revolution
Over the recent years, the Petersen diagram for classical pulsators, Cepheids
and RR Lyr stars, populated with a few hundreds of new multiperiodic variables.
We review our analyses of the OGLE data, which resulted in the significant
extension of the known, and in the discovery of a few new and distinct forms of
multiperiodic pulsation. The showcase includes not only radial mode pulsators,
but also radial-non-radial pulsators and stars with significant modulation
observed on top of the beat pulsation. First theoretical models explaining the
new forms of stellar variability are briefly discussed.Comment: 5 pages; to be published in the proceedings of the 22nd Los Alamos
Stellar Pulsation Conference "Wide-field variability surveys: a 21st-century
perspective", San Pedro de Atacama, Chile, Nov. 28 - Dec. 2, 201
Evaluation of the robustness of optical density as a tool for estimation of biomass in microalgal culture:the effects of growth conditions and physiological state
Everything that glitters is not gold: V1315 Cas is not a dormant black hole
The quest for quiet or dormant black holes has been ongoing since several
decades. Ellipsoidal variables possibly indicate the existence of a very
high-mass invisible companion and are thought to be one of the best ways to
find such dormant black holes. This, however, is not a panacea as we show here
with one example. We indeed report the discovery of a new semi-detached
interacting binary, V1315 Cas, discovered as an ellipsoidal variable. Using
data from photometric surveys (ASAS-SN, TESS) and high-resolution spectroscopy,
we derived a nearly circular orbit with an orbital period of
=34.54 d. The binary system consists of an evolved F-type star
primary that is likely still filling its Roche lobe and a B-type star
secondary. Using \textsc{phoebe}2, we derived the following masses and radii:
for the primary, and ; for the secondary, and . Modeling the evolution of
the system with MESA, we found an age of 7.7e7 years. The system is at
the end of a period of rapid non-conservative mass transfer that reversed its
mass ratio, while significantly widening its orbit. The primary shows carbon
depletion and nitrogen overabundance, indicative of CNO processed material
being exposed due to mass transfer. An infrared excess as well as stationary
H emission suggest the presence of a circumstellar or circumbinary
disc. V1315 Cas will likely become a detached stripped star binary.Comment: Accepted in MNRA
Knowledge Graph of Design Rules for a Context-Aware Cognitive Design Assistant
[Context] The design of a system shall comply with many design rules that help industrial designers to create high quality design in an efficient way. Nowadays, design rules try to consider all product lifecycle’s phases leading to an ever-increasing growth. This context makes the management of design rules a difficult but essential task. This is why many research and industrial works try to automate this task [1, 3, 4]. [Problem] The processing of design rules, which are natural language sentences stored in unstructured documents, requires expert software. Moreover, existing tools interrupt the design workflow and slow down the design process. [Proposition] We propose a Context-Aware Cognitive Design Assistant (CACDA) to support designers who have to satisfy some design rules among “Big Data”. First, we describe the CACDA from the user’s perspective. Second, we detail the process for modelling unstructured design rules into a com-putable knowledge graph that will feed the cognitive design assistant. [Future Work] Once our knowledge graph of design rules will be operational, we will concentrate on its processing to retrieve, recommend, and verify design rules. Experiments will also help to determine pros and cons of the design assistant.En partenariat avec Capgemini DEM
A generic travelling wave solution in dissipative laser cavity
A large family of cosh-Gaussian travelling wave solution of a complex Ginzburg–Landau equation (CGLE), that describes dissipative semiconductor laser cavity is derived. Using perturbation method, the stability region is identified. Bifurcation analysis is done by smoothly varying the cavity loss coefficient to provide insight of the system dynamics. He’s variational method is adopted to obtain the standard sech-type and the notso-explored but promising cosh-Gaussian type, travelling wave solutions. For a given set of system parameters, only one sech solution is obtained, whereas several distinct solution points are derived for cosh-Gaussian case. These solutions yield a wide variety of travelling wave profiles, namely Gaussian, near-sech, flat-top and a cosh-Gaussianwith variable central dip. A split-step Fourier method and pseudospectral method have been used for direct numerical solution of the CGLE and travelling wave profiles identical to the analytical profiles have been obtained. We also identified the parametric zone that promises an extremely large family of cosh-Gaussian travelling wave solutions with tunable shape. This suggests that the cosh-Gaussian profile is quite generic and would be helpful for further theoretical as well as experimental investigation on pattern formation, pulse dynamics andlocalization in semiconductor laser cavity
Pulsating stars in SuperWASP
Abstract. SuperWASP is one of the largest ground-based surveys for transiting exoplan- ets. To date, it has observed over 31 million stars. Such an extensive database of time resolved photometry holds the potential for extensive searches of stellar variability, and provide solid candidates for the upcoming TESS mission. Previous work by e.g. [15], [5], [12] has shown that the WASP archive provides a wealth of pulsationally variable stars. In this talk I will provide an overview of the SuperWASP project, present some of the published results from the survey, and some of the on-going work to identify key targets for the TESS mission
Science with a small two-band UV-photometry mission II: Observations of stars and stellar systems
We outline the impact of a small two-band UV-photometry satellite mission on
the field of stellar physics, magnetospheres of stars, binaries, stellar
clusters, interstellar matter, and exoplanets. On specific examples of
different types of stars and stellar systems, we discuss particular
requirements for such satellite missions in terms of specific mission
parameters such as bandpass, precision, cadence, and mission duration. We show
that such a mission may provide crucial data not only for hot stars that emit
most of their light in UV, but also for cool stars, where UV traces their
activity. This is important, for instance, for exoplanetary studies, because
the level of stellar activity influences habitability. While the main asset of
the two-band UV mission rests in time-domain astronomy, an example of open
clusters proves that such a mission would be important also for the study of
stellar populations. Properties of the interstellar dust are best explored when
combining optical and IR information with observations in UV. It is well known
that dust absorbs UV radiation efficiently. Consequently, we outline how such a
UV mission can be used to detect eclipses of sufficiently hot stars by various
dusty objects and study disks, rings, clouds, disintegrating exoplanets or
exoasteroids. Furthermore, UV radiation can be used to study the cooling of
neutron stars providing information about the extreme states of matter in the
interiors of neutron stars and used for mapping heated spots on their surfaces.Comment: Submitted to Space Science Review
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