scholarly journals The subgiant HR 7322 as an asteroseismic benchmark star

2019 ◽  
Vol 489 (1) ◽  
pp. 928-940 ◽  
Author(s):  
Amalie Stokholm ◽  
Poul Erik Nissen ◽  
Víctor Silva Aguirre ◽  
Timothy R White ◽  
Mikkel N Lund ◽  
...  
Keyword(s):  
Oscillation Mode ◽  
Stellar Radius ◽  
Avoided Crossing ◽  
Depth Analysis ◽  
Fitting Algorithm ◽  
Dipole Oscillation ◽  
Standard Models ◽  
Oscillation Frequencies ◽  
Gaia Dr2 ◽  
Good Agreement

Abstract We present an in-depth analysis of the bright subgiant HR 7322 (KIC 10005473) using Kepler short-cadence photometry, optical interferometry from CHARA, high-resolution spectra from SONG, and stellar modelling using garstec grids, and the Bayesian grid-fitting algorithm basta. HR 7322 is only the second subgiant with high-quality Kepler asteroseismology for which we also have interferometric data. We find a limb-darkened angular diameter of 0.443 ± 0.007 mas, which, combined with a distance derived using the parallax from Gaia DR2 and a bolometric flux, yields a linear radius of 2.00 ± 0.03 R⊙ and an effective temperature of 6350 ± 90 K. HR 7322 exhibits solar-like oscillations, and using the asteroseismic scaling relations and revisions thereof, we find good agreement between asteroseismic and interferometric stellar radius. The level of precision reached by the careful modelling is to a great extent due to the presence of an avoided crossing in the dipole oscillation mode pattern of HR 7322. We find that the standard models predict a stellar radius systematically smaller than the observed interferometric one and that a sub-solar mixing length parameter is needed to achieve a good fit to individual oscillation frequencies, interferometric temperature, and spectroscopic metallicity.

Anomalous transitions in two-level systems driven by the ac Stark effect

2001 ◽  
Vol 79 (2-3) ◽  
pp. 533-545 ◽  
Author(s):  
W L Meerts ◽  
I Ozier ◽  
J T Hougen
Keyword(s):  
Molecular Beam ◽  
Stark Effect ◽  
Electric Resonance ◽  
Avoided Crossing ◽  
Different Types ◽  
Two Level Systems ◽  
Experimental Findings ◽  
Ac Stark Effect ◽  
Unusual Type ◽  
Good Agreement

An unusual type of nonresonant absorption signal produced by the ac Stark effect has been observed in a two-level avoided-crossing system. The theory for these anomalous transitions has been developed. The nonresonant signals have been shown to be caused by the perturbation by the oscillating field of the dephasing of the two-level system at the avoided crossing. A series of measurements of these anomalous transitions has been carried out using the avoided-crossing molecular-beam electric-resonance technique. In addition, different types of resonant multiphoton transitions have been investigated. Results are reported for the AE-barrier anticrossing with J = 1 in CH3SiH3. The experimental findings are in good agreement with the theory developed. PACS Nos.: 33.20Bx, 33.80Be, 42.50Hz

scholarly journals Asteroseismology of 36 Kepler subgiants – I. Oscillation frequencies, linewidths, and amplitudes

2020 ◽  
Vol 495 (2) ◽  
pp. 2363-2386 ◽  
Author(s):  
Yaguang Li ◽  
Timothy R Bedding ◽  
Tanda Li ◽  
Shaolan Bi ◽  
Dennis Stello ◽  
...  
Keyword(s):  
Monte Carlo ◽  
Oscillation Mode ◽  
Monte Carlo Algorithm ◽  
Scaling Relations ◽  
Mass Dependence ◽  
Seismic Parameters ◽  
Theoretical Predictions ◽  
Mixed Modes ◽  
Oscillation Frequencies ◽  
Spectrum Model

ABSTRACT The presence of mixed modes makes subgiants excellent targets for asteroseismology, providing a probe for the internal structure of stars. Here we study 36 Kepler subgiants with solar-like oscillations and report their oscillation mode parameters. We performed a so-called peakbagging exercise, i.e. estimating oscillation mode frequencies, linewidths, and amplitudes with a power spectrum model, fitted in the Bayesian framework and sampled with a Markov chain Monte Carlo algorithm. The uncertainties of the mode frequencies have a median value of 0.180 μHz. We obtained seismic parameters from the peakbagging, analysed their correlation with stellar parameters, and examined against scaling relations. The behaviour of seismic parameters (e.g. Δν, νmax, ϵp) is in general consistent with theoretical predictions. We presented the observational p–g diagrams, namely γ1–Δν for early subgiants and ΔΠ1–Δν for late subgiants, and demonstrate their capability to estimate stellar mass. We also found a log g dependence on the linewidths and a mass dependence on the oscillation amplitudes and the widths of oscillation excess. This sample will be valuable constraints for modelling stars and studying mode physics such as excitation and damping.

scholarly journals Torque Characteristics of the Revolving Vane Air Expander

Machines ◽  
2020 ◽  
Vol 8 (3) ◽  
pp. 58
Author(s):  
Kuan Thai Aw ◽  
Alison Subiantoro ◽  
Kim Tiow Ooi
Keyword(s):  
High Efficiency ◽  
Clean Energy ◽  
Compressed Air ◽  
Generic Model ◽  
Alternative Source ◽  
Output Torque ◽  
Depth Analysis ◽  
Rotary Machines ◽  
Rotational Vibration ◽  
Good Agreement

The use of compressed air as an alternative source of clean energy requires an air expander to extract work. A new design, known as the revolving vane mechanism, has been proposed in an effort to develop high efficiency rotary machines. This paper provides an in-depth analysis by including the vibration characteristics of the revolving vane air expander to evaluate the steady-state operating output torque. A generic model for describing the revolving vane rotational vibration is first derived and subsequently modified to describe the prototype tested. Measurements show that the output torque is bimodal; arising from a tolerance gap between the vane and its slot during fabrication. This effect was found to be less pronounced at high operating speeds. The model is found to be in good agreement with the measured output torques. Further analysis with the validated model showed that extracting shaft work from the cylinder would result in better performance.

scholarly journals Some Insights into Stellar Structure from Nonlinear Pulsations

1993 ◽  
Vol 134 ◽  
pp. 231-233
Author(s):  
M. J. Goupil
Keyword(s):  
Amplitude Equation ◽  
Second Order ◽  
Stellar Structure ◽  
Static Structure ◽  
Stellar Radius ◽  
Stellar Pulsation ◽  
Oscillation Frequencies ◽  
Mass Level ◽  
Marginal Mode ◽  
Second Order Of Approximation

Efficient tools of investigation of stellar pulsation are the integral relations which link oscillation frequencies to the static structure of stellar models, as provided by the linear theory of pulsation (for a review, see Saio, this conference).Similarly, oscillation amplitudes and phases, which arise from nonlinear processes, can be related to the stellar structure by means of amplitude equation formalisms (for a review, see Buchler, this conference).For the simple case of a monoperiodic oscillation, involving only one unstable marginal mode, such a formalism shows that the (limit cycle) radius variations, at time t and mass level m, can be approximated, up to second order of approximation, (Buchler and Goupil, 1984; Buchler and Kovàca, 1986) by:where A, R, Ω, ĸ, £r(m) respectively are the amplitude, stellar radius, linear nonadiabatic frequency, growth rate, radius eigenfunction. Second order nonlinearities generated first harmonic oscillations and change in equilibrium radius about which the star oscillates, as represented by the last two terms in (la) respectively. Analogous expressions are obtained for velocity and light variations, that can be compared with observations.

scholarly journals Multiplicity among the cool supergiants in the Magellanic Clouds

2021 ◽  
Author(s):  
R Dorda ◽  
L R Patrick
Keyword(s):  
Binary Systems ◽  
Magellanic Clouds ◽  
High Mass ◽  
Intrinsic Variability ◽  
Long Baseline ◽  
Star Evolution ◽  
Massive Star Evolution ◽  
Over 40 Years ◽  
Gaia Dr2 ◽  
Good Agreement

Abstract The characterisation of multiplicity among of high-mass stars is of fundamental importance to understand their evolution, the diversity of observed core-collapse supernovae and the formation of gravitational wave progenitor systems. Despite that, until recently, one of the final phases of massive star evolution – the cool supergiant phase – has received comparatively little attention. In this study we aim to explore the multiplicity among the cool supergiant (CSG) population in the Large and Small Magellanic Clouds (LMC and SMC, respectively). To do this we compile extensive archival radial velocity (RV) measurements for over 1000 CSGs from the LMC and SMC, spanning a baseline of over 40 years. By statistically correcting the RV measurements of each stellar catalogue to the Gaia DR2 reference frame we are able to effectively compare these diverse observations. We identify 45 CSGs where RV variations cannot be explained through intrinsic variability, and are hence considered binary systems. We obtain a minimum binary fraction of $15\pm 4{{\ \rm per\ cent}}$ for the SMC and of $14\pm 5{{\ \rm per\ cent}}$ for the LMC, restricting our sample to objects with at least 6 and 5 observational epochs, respectively. Combining these results, we determine a minimum binary fraction of $15\pm 3{{\ \rm per\ cent}}$ for CSGs. These results are in good agreement with previous results which apply a correction to account for observational biases. These results add strength to the hypothesis that the binary fraction of CSGs is significantly lower than their main-sequence counterparts. Going forward, we stress the need for long-baseline multi-epoch spectroscopic surveys to cover the full parameter space of CSG binary systems.

scholarly journals Experimental and numerical investigation of thermal and flow conditions inside a large pharmaceutical storage after the ventilation system failure

2021 ◽  
pp. 346-346
Author(s):  
Ilija Tabasevic ◽  
Rastko Jovanovic ◽  
Dragan Milanovic
Keyword(s):  
Temperature Distribution ◽  
Flow Field ◽  
Flow Rate ◽  
Ventilation System ◽  
Pharmaceutical Products ◽  
System Failure ◽  
Flow Conditions ◽  
Cfd Simulations ◽  
Depth Analysis ◽  
Good Agreement

Safe storage of pharmaceutical products is of great importance due to potential hazards for human health. The aim of this study was to assess the ability of pharmaceutical storage to recover design temperature during ventilation system recovery. The performed CFD simulations showed good agreement with experimental temperature measurements. Numerical results allowed in-depth analysis of flow field and temperature distribution inside the storage. It was discovered that the flow field is highly non-uniform, which consequently leads to an uneven temperature distribution of pallets with products. However, a high inlet mass flow rate ensured that all pallets reach the designed temperature.

scholarly journals To estimate the curing time of epoxy oligomer during nonisothermal polymerization process

2021 ◽  
pp. 30-36
Author(s):  
S. V. Rusakov ◽  
◽  
V. G. Gilev ◽  
Keyword(s):  
Temperature Change ◽  
Oscillation Mode ◽  
Epoxy Oligomer ◽  
Polymerization Process ◽  
Model Parameters ◽  
Curing Process ◽  
The Cauchy Problem ◽  
Rheological Method ◽  
Main Model ◽  
Good Agreement

The results of an experimental study and numerical modeling of the curing process of an epoxy binder under conditions of non-isothermal polymerization are presented. Object of research: twocomponent composition of "cold curing": epoxy resin L and hardener EPH 161, certified as a binder for aerospace composite materials. The measurements were performed on a Physica MCR 501 rotary rheometer in the oscillation mode under conditions of a programmable temperature change. The Cauchy problem for an ordinary differential equation describing the behavior of an oligomer during the curing process was used as the main model. The values of the material parameters necessary for performing the calculation operations were obtained by the rheological method, analyzing the dependence of the binder viscosity on the polymerization time and the rate of temperature change. Estimates of the model parameters obtained as a result of processing full-scale experiments aregiven. The effective values of the kinetic parameters are determined, at which the calculated yield loss time is in good agreement with the experimental one.

Experimental Study of the Faraday Effect in 1D-Photonic Crystal in Millimeter Waveband

2012 ◽  
Vol 190 ◽  
pp. 365-368 ◽  
Author(s):  
A.A. Girich ◽  
S.Y. Polevoy ◽  
Sergey I. Tarapov ◽  
A.M. Merzlikin ◽  
A.B. Granovsky ◽  
...  
Keyword(s):  
Experimental Study ◽  
Photonic Crystal ◽  
Faraday Effect ◽  
Metal Layer ◽  
Oscillation Mode ◽  
Surface Oscillation ◽  
Thin Metal Layer ◽  
1D Photonic Crystal ◽  
Experimental Structure ◽  
Good Agreement

The paper is devoted to experimental study of Faraday Effect enhancement. The experimental structure consists of photonic crystal, loaded with ferrite, which in turn is covered by thin metal layer or wire medium. An analysis of the transmission/reflection spectra for both unloaded and loaded photonic crystals shows that the surface oscillation mode (the surface state) is formed in the crystal band gap. A good agreement exists between experimental data and numerical calculations.

scholarly journals Physical properties of AM CVn stars: New insights from Gaia DR2

2018 ◽  
Vol 620 ◽  
pp. A141 ◽  
Author(s):  
G. Ramsay ◽  
M. J. Green ◽  
T. R. Marsh ◽  
T. Kupfer ◽  
E. Breedt ◽  
...  
Keyword(s):  
Gravitational Wave ◽  
White Dwarfs ◽  
Large Population ◽  
Mass Transfer Rate ◽  
Absolute Magnitude ◽  
Wave Radiation ◽  
Compact Binaries ◽  
Standard Models ◽  
Value Sets ◽  
Gaia Dr2

AM CVn binaries are hydrogen deficient compact binaries with an orbital period in the 5–65 min range and are predicted to be strong sources of persistent gravitational wave radiation. Using Gaia Data Release 2, we present the parallaxes and proper motions of 41 out of the 56 known systems. Compared to the parallax determined using the HST Fine Guidance Sensor we find that the archetype star, AM CVn, is significantly closer than previously thought. This resolves the high luminosity and mass accretion rate which models had difficulty in explaining. Using Pan-STARRS1 data we determine the absolute magnitude of the AM CVn stars. There is some evidence that donor stars have a higher mass and radius than expected for white dwarfs or that the donors are not white dwarfs. Using the distances to the known AM CVn stars we find strong evidence that a large population of AM CVn stars has yet to be discovered. As this value sets the background to the gravitational wave signal of LISA this is of wide interest. We determine the mass transfer rate for 15 AM CVn stars and find that the majority has a rate significantly greater than expected from standard models. This is further evidence that the donor star has a greater size than expected.

scholarly journals Merger-inspired rotation laws and the low-T/W instability in neutron stars

2020 ◽  
Vol 498 (4) ◽  
pp. 5904-5915
Author(s):  
A Passamonti ◽  
N Andersson
Keyword(s):  
Oscillation Mode ◽  
Growth Time ◽  
Qualitative Behaviour ◽  
Dynamical Equations ◽  
Binary Neutron Star ◽  
Pattern Speed ◽  
Instability Growth ◽  
Oscillation Frequencies ◽  
The Impact ◽  
Fast Rotating

ABSTRACT Implementing a family of differential rotation laws inspired by binary neutron-star merger remnants, we consider the impact of the rotation profile on the low-T/W instability. We use time evolutions of the linearized dynamical equations, in Newtonian gravity, to study non-axisymmetric oscillations and identify the unstable modes. The presence and evolution of the low-T/W instability is monitored with the canonical energy and angular momentum, while the growth time is extracted from the evolved kinetic energy. The results for the new rotation laws highlight similarities with the commonly considered j-constant law. The instability sets in when an oscillation mode corotates with the star (i.e. whenever there is a point at which the mode’s pattern speed matches the bulk angular velocity) and grows faster deep inside the co-rotation region. However, the new profiles add features, like an additional co-rotation point, to the problem, and these affect the onset of instability. The rotation laws have the most drastic influence on the oscillation frequencies of the l = m = 2 f mode in fast-rotating models, but affect the instability growth time at some level for any rotation rate. We also identify models where the low-T/W instability appears to be triggered by inertial modes. We discuss to what extent the inferred qualitative behaviour is likely to be of observational relevance.

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