A large number of particle detectors employ liquid argon as their target material owing to its high scintillation yield and its ability to drift ionization charge over large distances. Scintillation ...light from argon is peaked at 128 nm and a wavelength shifter is required for its efficient detection. In this work, we directly compare the light yield achieved in two identical liquid argon chambers, one of which is equipped with polyethylene naphthalate (PEN) and the other with tetraphenyl butadiene (TPB) wavelength shifter. Both chambers are lined with enhanced specular reflectors and instrumented with SiPMs with a coverage fraction of approximately 1%, which represents a geometry comparable to the future large scale detectors. We measured the light yield of the PEN chamber to be 39.4
±
0.4(stat)
±
1.9(syst)% of the yield of the TPB chamber. Using a Monte Carlo simulation this result is used to extract the wavelength shifting efficiency of PEN relative to TPB equal to 47.2
±
5.7%. This result paves the way for the use of easily available PEN foils as a wavelength shifter, which can substantially simplify the construction of future liquid argon detectors.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
ABSTRACT
Eclipse timing variations (ETVs) have been a successful tool for detecting circumbinary companions to eclipsing binaries (EBs). While TESS and Kepler have been prolific for ETV searches, ...they sometimes can be limited by time and sky coverage, a limitation that can be addressed by specialized ground-based ETV surveys. We present the initial results from the Solaris photometric survey, which uses four 0.5-m robotic telescopes in the Southern hemisphere to look for circumbinary companions. We present the method of light-curve extraction, detrending, and EB modelling using observations from the Solaris network. Using these light curves, we extract precise eclipse timings for seven EBs and look for companions using a Lomb–Scargle periodogram search. We find two possible periodic signals for the target GSC 08814–01026. With the system having strong activity, we check for the feasibility of orbital solutions at these two periods. We find that the 245 ± 1 d period is due to an M dwarf-mass companion. This makes GSC 08814–01026 a candidate compact hierarchical triple system. The other periodic signal at 146 ± 1 d is an artefact of stellar activity.
We report a new hot post-asymptotic giant branch (PAGB) star in the Galactic globular cluster (GC) E3, which is one of the first of the identified PAGB stars in a GC to show a binary signature. The ...star stands out as the brightest source in E3 in the Astrosat/UVIT images. We confirmed its membership with the cluster E3 using Gaia DR3 kinematics and parallax measurements. We supplemented the photometric observations with radial velocities (RVs) from high-resolution spectroscopic observations at two epochs and with ground- and space-based photometric observations from 0.13 μm to 22 μm. We find that the RVs vary over ∼6 km s −1 between the two epochs. This is an indication of the star being in a binary orbit. A simulation of possible binary systems with the observed RVs suggests a binary period of either 39.12 days or 17.83 days with mass ratio q ≥ 1.0. The Fe/H derived using the high-resolution spectra is ∼−0.7 dex, which closely matches the cluster metallicity. The spectroscopic and photometric measurements suggest T eff and log g of the star as 17 500 ± 1000 K and 2.37 ± 0.20 dex, respectively. Various PAGB evolutionary tracks on the Hertzsprung–Russell (H–R) diagram suggest a current mass of the star in the range 0.51–0.55 M ⊙ . The star is enriched with C and O abundances, showing similar CNO abundances compared to the other PAGB stars in GCs with the evidence of the third dredge-up on the AGB phase.
ABSTRACT
We present results of the analysis of light and radial velocity (RV) curves of eight detached eclipsing binaries observed by the All-Sky Automated Survey, which we have followed up with ...high-resolution spectroscopy, and were later observed by the Keplersatellite as part of the K2mission. The RV measurements came from spectra obtained with OAO-188/HIDES, MPG-2.2 m/FEROS, SMARTS 1.5 m/CHIRON, Euler/CORALIE, ESO-3.6 m/HARPS, and OHP-1.93/ELODIE instruments. The K2 time-series photometry was analysed with the jktebop code, with out-of-eclipse modulations of different origin taken into account. Individual component spectra were retrieved with the fd3 code, and analysed with the code ispec in order to determine effective temperatures and metallicities. Absolute values of masses, radii, and other stellar parameters are calculated, as well as ages, found through isochrone fitting. For five systems, such analysis has been done for the first time. The presented sample consists of a variety of stars, from low-mass dwarfs, through G- and F-type main sequence objects, to evolved active sub-giants, one of which is found to be crossing the Hertzsprung gap. One target may contain a γ Dor-type pulsator, two more are parts of higher-order multiples, and spectra of their tertiaries were also retrieved and used to constrain the properties of these systems.
ABSTRACT
The pulsating eclipsing binaries are remarkable systems that provide an opportunity to probe the stellar interior and to determine the fundamental stellar parameters precisely. Especially ...the detached eclipsing binary systems with (a) pulsating component(s) are significant objects to understand the nature of the oscillations since the binary effects in these systems are negligible. Recent studies based on space data have shown that the pulsation mechanisms of some oscillating stars are not completely understood. Hence, comprehensive studies of a number of pulsating stars within detached eclipsing binaries are important. In this study, we present a detailed analysis of the pulsating detached eclipsing binary system AI Hya which was studied by two independent groups with different methods. We carried out a spectroscopic survey to estimate the orbital parameters via radial velocity measurements and the atmospheric parameters of each binary component using the composite and/or disentangled spectra. We found that the more luminous component of the system is a massive, cool and chemically normal star while the hotter binary component is a slightly metal-rich object. The fundamental parameters of AI Hya were determined by the analysis of binary variations and subsequently used in the evolutionary modelling. Consequently, we obtained the age of the system as 850 ± 20 Myr and found that both binary components are situated in the δ Scuti instability strip. The frequency analysis revealed pulsation frequencies between 5.5 and 13.0 d−1 and we tried to estimate which binary component is the pulsating one. However, it turned out that those frequencies could originate from both binary components.
ABSTRACT
We use photometric and spectroscopic observations of four detached eclipsing binaries in the globular cluster NGC 3201 to derive masses, radii, and luminosities of the component stars. ...Spanning across almost three magnitudes in the colour–magnitude diagram, the components offer a unique possibility to test the theory of stellar evolution. Their masses, radii, and luminosities range from 0.66 to 0.84 M⊙, 0.68 to 2.46 R⊙, and 0.38 to 5.56 L⊙, respectively. The distance to the cluster measured from the distance moduli of the component stars amounts to 4.54$^{+0.11}_{-0.14}$ kpc and agrees with the recent estimate based on Gaia parallaxes. By comparing the M − R and M − L diagrams of the component stars and the colour–magnitude diagram of NGC 3201 to Dartmouth model isochrones, we estimate the most probable age of the cluster to be 11.5 ± 0.5 Gyr. This estimate is based on three binaries only, as the fourth one seems to evolve along a different path, probably due to non-standard chemical composition and/or history. We confirm the tendency, observed in earlier CASE papers, for the age indicated by the M − R diagram to be younger than that implied by the colour–magnitude diagram.
Integration of large wind farms may get constrained owing to the available transfer capacity of existing transmission networks. This transmission capacity may be enhanced by incorporating series ...compensation. However, series capacitors are known to cause subsynchronous resonance (SSR) oscillations in synchronous generators. In this study, the potential of SSR is investigated with series-compensated lines connected to wind farms based on single-cage self-excited induction generators. Eigenvalue analysis is performed through MATLAB at various operating points. This is validated by detailed time-domain simulation through an electromagnetic transient simulation software EMTDC/PSCAD for a three-phase-to-ground fault at the remote end of the compensated line. An equivalent circuit analysis is performed to examine the impact of a similar fault at the terminals of the wind farm. It is shown from detailed non-linear simulation that even at a realistic level of series compensation a three-phase fault at generator terminals for low levels of wind farm power generation may subject the generator shafts to potentially dangerous magnitudes.
This paper presents a hybrid approach for tracking the amplitude, phase, frequency, and harmonic content of power quality disturbance signals occurring in power networks using an unscented Kalman ...filter (UKF) and swarm intelligence. The UKF is a novel extension of the well-known extended Kalman filter (EKF) using an unscented transformation to overcome the difficulties of linearization and derivative calculations of signals with a low signal-to-noise ratio (SNR). Further, the model and measurement error covariance matrices Q and R , along with the UKF parameters, are selected using a modified particle swarm optimization (PSO) algorithm for accurate tracking of signal parameters. To circumvent the problem of premature convergence and local minima in conventional PSO, a dynamically varying inertia weight based on the variance of the population fitness is used. This results in a better local and global searching ability of the particles, which improves the convergence of the velocity, and in a better accuracy of the UKF parameters. Various simulation results for nonstationary sinusoidal signals occurring in power networks with varying amplitudes, phases, and harmonic contents corrupted with noise having a low SNR reveal significant improvements in noise rejection and speed of convergence and accuracy.
Abstract
In this work we will document the design and the performances of a SiPM-based photo-detector with a surface area of 100 cm
2
conceived to operate as a replacement for PMTs. The signals from ...94 SiPMs are summed up to produce an aggregated output that exhibits in liquid nitrogen a dark count rate (DCR) lower than 100 cps over the entire surface, a signal to noise ratio better than 13, and a timing resolution better than 5.5 ns. The module feeds about 360 mW at 5 V with a dynamic range in excess of 500 photo-electrons on a 100 Ω differential line. The unit can also operate at room temperature, at the cost of an increase of DCR to 10
8
cps.
SiPM-based readouts are becoming the standard for light detection in particle detectors given their superior resolution and ease of use with respect to vacuum tube photo-multipliers. However, the ...contributions of noise detection such as the dark rate, cross-talk, and after-pulsing (AP) may significantly impact their performance. In this work, we present the development of highly reflective single-phase argon chambers capable of displaying light yields up to 32 photo-electrons per keV, with approximately 12 being primary photo-electrons generated by the argon scintillation, while the rest are accounted by optical cross-talk. Furthermore, the presence of compound processes results in a generalized Fano factor larger than 2 already at an over-voltage of 5 V. Finally, we present a parametrization of the optical cross-talk for the FBK NUV-HD-Cryo SiPMs at 87 K that can be extended to future detectors with tailored optical simulations.
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