27 research outputs found
A study of contact binaries with large temperature differencies between components
We present an extensive analysis of new light and radial-velocity (RV)
curves, as well as high-quality broadening-function (BF) profiles of twelve
binary systems for which a contact configuration with large temperature
differencies between components has been reported in the literature. We find
that six systems (V1010 Oph, WZ Cyg, VV Cet, DO Cas, FS Lup, V747 Cen) have
near-contact configurations. For the remaining systems (CX Vir, FT Lup, BV Eri,
FO Hya, CN And, BX And), our solutions of the new observations once again
converge in a contact configuration with large temperature differencies between
the components. However, the bright regions discovered in the BFs for V747 Cen,
CX Vir, FT Lup, BV Eri, FO Hya, and CN And, and further attributed to hot
spots, shed new light on the physical processes taking place between the
components and imply the possibility that the contact configurations obtained
from light- and RV-curve modelling are a spurious result.Comment: Submited to Acta Astronomic
A photometric and spectroscopic study of WW And - an Algol-type, long period binary system with an accretion disc
We have analyzed the available spectra of WW And and for the first time
obtained a reasonably well defined radial velocity curve of the primary star.
Combined with the available radial velocity curve of the secondary component,
these data led to the first determination of the spectroscopic mass ratio of
the system at q-spec = 0.16 +/- 0.03. We also determined the radius of the
accretion disc from analysis of the double-peaked H-alpha emission lines. Our
new, high-precision, Johnson VRI and the previously available Stromgren vby
light curves were modelled with stellar and accretion disc models. A consistent
model for WW And - a semidetached system harbouring an accretion disc which is
optically thick in its inner region, but optically thin in the outer parts -
agrees well with both spectroscopic and photometric data.Comment: Accepted by New Astronom
Is there a circumbinary planet around NSVS 14256825?
The cyclic behaviour of (O-C) residuals of eclipse timings in the sdB+M
eclipsing binary NSVS 14256825 was previously attributed to one or two
Jovian-type circumbinary planets. We report 83 new eclipse timings that not
only fill in the gaps in those already published but also extend the time span
of the (O-C) diagram by three years. Based on the archival and our new data
spanning over more than 17 years we re-examined the up to date system (O-C).
The data revealed systematic, quasi-sinusoidal variation deviating from an
older linear ephemeris by about 100 s. It also exhibits a maximum in the (O-C)
near JD 2,456,400 that was previously unknown. We consider two most credible
explanations of the (O-C) variability: the light propagation time due to the
presence of an invisible companion in a distant circumbinary orbit, and
magnetic cycles reshaping one of the binary components, known as the Applegate
or Lanza-Rodono effect. We found that the latter mechanism is unlikely due to
the insufficient energy budget of the M-dwarf secondary. In the framework of
the third-body hypothesis, we obtained meaningful constraints on the Keplerian
parameters of a putative companion and its mass. Our best-fitting model
indicates that the observed quasi-periodic (O-C) variability can be explained
by the presence of a brown dwarf with the minimal mass of 15 Jupiter masses
rather than a planet, orbiting the binary in a moderately elliptical orbit (~
0.175) with the period of ~ 10 years. Our analysis rules out two planets model
proposed earlier.Comment: 17 pages, 9 figures, 4 tables, accepted to A
Modeling of Charge Transfer Inefficiency in a CCD with High Speed Column Parallel Readout
Charge Coupled Devices (CCDs) have been successfully used in several high
energy physics experiments over the past two decades. Their high spatial
resolution and thin sensitive layers make them an excellent tool for studying
short-lived particles. The Linear Collider Flavour Identification (LCFI)
collaboration is developing Column-Parallel CCDs (CPCCDs) for the vertex
detector of a future Linear Collider. The CPCCDs can be read out many times
faster than standard CCDs, significantly increasing their operating speed. An
Analytic Model has been developed for the determination of the charge transfer
inefficiency (CTI) of a CPCCD. The CTI values determined with the Analytic
Model agree largely with those from a full TCAD simulation. The Analytic Model
allows efficient study of the variation of the CTI on parameters like readout
frequency, operating temperature and occupancy.Comment: 5 pages, 13 figures, presented on behalf of the LCFI Collaboration,
proceedings IEEE 2008 Nuclear Science Symposium, Dresden, Germany, and 11th
Topical Seminar on Innovative Particle and Radiation Detectors (IPRD08) 2008,
Siena, Ital
Status of the Micro Vertex Detector of the Compressed Baryonic Matter Experiment
The CBM experiment will investigate heavy-ion collisions at beam energies from 8 to 45 AGeV
at the future accelerator facility FAIR. The goal of the experiment is to study the QCD phase
diagram in the vincinity of the QCD critical point. To do so, CBM aims at measuring rare probes
among them open charm. In order to identify those rare and short lived particles despite the
rich combinatorial background generated in heavy ion collisions, a micro vertex detector (MVD)
providing an unprecedented combination of high rate capability and radiation hardness, very light
material budget and excellent granularity is required. In this work, we will discuss the concept of
this detector and summarize the status of the R&D
Two-particle correlations in azimuthal angle and pseudorapidity in inelastic p + p interactions at the CERN Super Proton Synchrotron
Results on two-particle ΔηΔϕ correlations in inelastic p + p interactions at 20, 31, 40, 80, and 158 GeV/c are presented. The measurements were performed using the large acceptance NA61/SHINE hadron spectrometer at the CERN Super Proton Synchrotron. The data show structures which can be attributed mainly to effects of resonance decays, momentum conservation, and quantum statistics. The results are compared with the Epos and UrQMD models.ISSN:1434-6044ISSN:1434-605
Development of radiation hardened pixel sensors for charged particle detection
CMOS Pixel Sensors are being developed since a few years to equip vertex detectors for future high-energy physics experiments with the crucial advantages of a low material budget and low production costs. The features simultaneously required are a short readout time, high granularity and high tolerance to radiation. This thesis mainly focuses on the radiation tolerance studies. To achieve the targeted readout time (tens of microseconds), the sensor pixel readout was organized in parallel columns restricting in addition the readout to pixels that had collected the signal charge. The pixels became then more complex, and consequently more sensitive to radiation. Different in-pixel architectures were studied and it was concluded that the tolerance to ionizing radiation was limited to 300 krad with the 0.35- m fabrication process currently used, while the targeted value was several Mrad. Improving this situation calls for implementation of the sensors in processes with a smaller feature size which naturally improve the radiation tolerance while simultaneously accommodate all the inpixel microcircuitry in small pixels. Another aspect addressed in this thesis was the tolerance to non ionizing radiation, with a targeted value of >1013 neq/cm2. Different CMOS technologies featuring an enhanced signal collection were therefore investigated. It was demonstrated that this tolerance could be improved to 3·1013 neq/cm2 by the means of a high-resistivity epitaxial layer. This achievement triggered a new age of the CMOS pixel sensors and showed that their development is on a good track to meet the requirements of the particularly demanding CBM experiment
Développement de capteurs à pixels résistants aux rayonnements intenses pour la détection de particules chargées
Les capteurs CMOS sont développés depuis une décennie en vue d'équiper les détecteurs de vertex des expériences de physique des particules à venir, avec les avantages d'un faible budget de matière et de bas coûts de production. Les caractéristiques recherCMOS Pixel Sensors are being developed since a few years to equip vertex detectors for future high-energy physics experiments with the crucial advantages of a low material budget and low production costs. The features simultaneously required are a short