On the central symmetry of the circumstellar envelope of RS Cnc

We present a phenomenological study of CO(1-0) and CO(2-1) emission from the circumstellar envelope (CSE) of the Asymptotic Giant Branch (AGB) star RS\,Cnc. It reveals departures from central symmetry that turn out to be efficient tools for the exploration of some of the CSE properties. We use a wind model including a bipolar flow with a typical wind velocity of $\sim$8 km\,s$^{-1}$ decreasing to $\sim$2 km\,s$^{-1}$ near the equator to describe Doppler velocity spectral maps obtained by merging data collected at the IRAM Plateau de Bure Interferometer and Pico Veleta single dish radio telescope. Parameters describing the wind morphology and kinematics are obtained, together with the radial dependence of the gas temperature in the domain of the circumstellar envelope probed by the CO observations. Significant north-south central asymmetries are revealed by the analysis, which we quantify using a simple phenomenological description. The origin of such asymmetries is unclear.Comment: accepted for publication in Research in Astronomy and Astrophysics (RAA

Non-destructive Characteristics of Ultrasonic Waves in 1018 Low Carbon Steel

In this paper, the dependences of the velocities and the absorption coefficients of ultrasonic waves transmitted in 1018 low carbon steel on temperature ranging from 0$^{\circ}$C to 50$^{\circ}$C were investigated. It was shown that the velocities of the ultrasonic longitudinal wave and ultrasonic shear wave were decreased when the temperature increased. The transportation of the ultrasonic longitudinal wave and ultrasonic shear wave depends on temperature and its coefficient in a temperature range of (0 - 50 $^{\circ}$C) was estimated about 0.8 m/s.$^{\circ}$C and 0.44~m/s.$^{\circ}$C, respectively. These obtained results are in good agreement with the theoretical prediction. Furthermore, the absorption coefficients of the ultrasonic longitudinal wave were also studied

Observation of High Doppler Velocity Wings in the Nascent Wind of R Doradus

We study the morpho-kinematics in the nascent wind of AGB star R Doradus in the light of high Doppler velocity wings observed in the spectral lines of several species. We probe distances from the star between ∼10 and ∼100 au using ALMA observations of the emission of five different molecular lines. High Doppler velocity enhancements of the line emission are observed in the vicinity of the line of sight crossing the star, reminiscent of those recently interpreted as gas streams in the nascent wind of a similar AGB star, EP Aqr. They are present in both blue-shifted and red- shifted hemispheres but are not exactly back-to-back. They are accelerated at a typical rate of 0.7 km s$^{−1}$ au$^{−1}$ up to some 20 km s$^{−1}$. Important differences are observed between the emissions of different molecules. We exclude an effect of improper continuum subtraction. However, in contrast to EP Aqr, the line of sight plays no particular role in the R Dor morpho-kinematics, shedding doubt on the validity of a gas stream interpretation. We discuss possible interpretations in terms of stellar pulsations or of rotation of the gas in the environment of the star. We conclude that, in the state of current knowledge, no fully convincing picture of the physics governing the production of such high velocities, typically twice as large as the terminal velocity, can be reliably drawn. New high resolution analyses of observations of the nascent wind of oxygen-rich AGB stars are needed to clarify the issue

The VATLY Radio Telescope

A small radio telescope (SRT) has been installed on the roof of the Hanoi astrophysics laboratory VATLY. It is equipped with a 2.6 m diameter mobile parabolic dish remotely controlled in elevation and azimuth and with super-heterodyne detection around the 21 cm hydrogen line. First results of observations of the Sun and of the centre of the Milky Way are presented. They demonstrate the high quality of the telescope performance and are used to evaluate lobe size, signal to noise ratios, anthropogenic interferences and measurement accuracies. Particular attention is given to the measurement of the pointing accuracy. The rich measurement programme that is now at hand is briefly sketched

Simulation of proton-induced and iron-induced extensive air showers at extreme energies

The development of extensive air showers at extreme energies is studied using a simulation model much simpler and cruder, but also more transparent and flexible, than existing sophisticated codes. Evidence for its satisfactory performance is presented. As an illustration, shower elongation rates are evaluated in the $10^{18}$ to $10^{20}$ eV region and compared with recently published data. Lateral distribution functions of both muons and electrons/photons are also briefly discussed. Reliable results are obtained in the comparison between proton-induced and iron-induced showers.Comment: 22 pages, Preprint submitted to Astroparticle Physic

Response of Water Cherenkov Detectors to Small Signals: a Case Study

Detailed studies of the response of the VATLY water Cherenkovdetector, a replica of those used in the ground array of the PierreAuger Observatory, are presented with emphasis on the response to lowamplitude signals. The method used is to detect decay electrons frommuons stopping in the water volume. Results include properties of the detection process as well as of the atmospheric cosmic ray flux

Sensitivity Limit of The VATLY Radio Telescope: Observing the Moon

The Moon has been observed using the VATLY radio telescope at frequencies of 1420.4and 1417.6 MHz in order to study the behaviour of the instrument in a domain of ux densityclose to the limit of its sensitivity. Drift scans have revealed a Moon ux density of 0:83 0:16kJy corresponding to a Moon black body temperature of 207 40 K. From these results, a limitsensitivity of 300 Jy has been inferred in agreement with earlier coarser estimates

Extensive Air Showers and the LPM Effect

A very simple model of thelongitudinal development of electromagnetic showers is presented,allowing for easy calculations at the highest energies where usualsimulation codes become impracticable because of the enormousmultiplicity of secondary shower particles. Shower profiles aredescribed in terms of a few parameters having Gaussianfluctuations. The model is applied to the impact of theLandau-Pomeranchuk-Migdal effect on the shower development, whichis found negligible in practical cases