Pham Tuan Anh

12CO emission from the Red Rectangle

Observations of an unprecedented quality made by ALMA on the Red Rectangle of CO(3–2) and CO(6–5) emissions are analysed jointly with the aim of obtaining as simple as possible a description of the gas morphology and kinematics. Evidence is found for polar conical outflows and for a broad equatorial torus in rotation and expansion. Simple models of both are proposed. Comparing CO(6–5) and CO(3–2) emissions provides evidence for a strong temperature enhancement over the polar outflows. Continuum emission (dust) is seen to be enhanced in the equatorial region. Observed asymmetries are briefly discussed.

The Vatly Radio Telescope: Performance Study

A detailed account of the performance of the VATLY radio telescope, operated in Ha Noi on and near the 21 cm HI line, is given. Drift scans across the Sun are used to measure the dependence of the gain on frequency and power, revealing small nonlinearities at or below the percent level. Interferences associated with the electromagnetic pollution in the Ha Noi environment are described. The sensitivity of the instrument is discussed and demonstrated with the detection of the Crab. The reliability of the measurement of the spectral flux density is illustrated by comparing solar flux data measured in Ha Noi and at the Australian observatory of Learmonth.

Mapping Atomic Hydrogen in the Disk of the Milky Way

The VATLY radio telescope has been used to draw the map of atomic hydrogen gas in the disk of the Milky Way. Effects resulting from its differential rotation, its cloud and arm structure and the presence of a dark matter halo have been observed.

Morphology and kinematics of the gas envelope of the variable AGB star π^1 Gruis

Observations of the12CO(3–2) emission from the circumstellar envelope(CSE) of the variable star π1Gru using the compact array of the ALMA observatory have been recently made accessible to the public. An analysis of the morphology and kinematics of the CSE is presented with a result very similar to that obtained earlier for12CO(2–1) emission using the Submillimeter Array. A quantitative comparison is made using their flared disk model. A new model is presented that provides a significantly better description of the data, using radial winds and smooth evolutions of the radio emission and wind velocity from the stellar equator to the poles.

Sensitivity Limit of The VATLY Radio Telescope: Observing the Moon

The Moon has been observed using the VATLY radio telescope at frequencies of 1420.4 and 1417.6 MHz in order to study the behaviour of the instrument in a domain of flux density close to the limit of its sensitivity. Drift scans have revealed a Moon flux density of 0.83±0.16 kJy corresponding to a Moon black body temperature of 207±40 K. From these results, a limit sensitivity of ∼ 300 Jy has been inferred in agreement with earlier coarser estimates.

Evidence for Polarized Solar Flare Emission From Simultaneous Radio Observations in Australia and Vietnam

A sample of 34 solar flares recorded in Hanoi using the VATLY radio telescope between April 2012 and January 2014 at frequencies of 1415 and 1417.6 MHz is compared with the corresponding observations made at 1415 MHz by the solar observatory of Learmonth (Australia). While good overall agreement is obtained, a few differences are noted and studied in some detail. In particular, the use of different feeds in Hanoi and Learmonth reveals a case of very large polarization of the flare emission.

Gravitationally lensed extended sources： the case of QSO RXJ0911

After a brief reminder of the mechanism of gravitational lensing of extended sources, the particular case of the host galaxy of QSO RXJ0911, a high redshift ( z ~ 2.8) quadruply imaged quasar, is explored. The non linearity of the problem, together with the proximity of the source to a cusp of the lens inner caustic, has important consequences on the dependence of the image appearance on the size and shape of the source. Their expected main features and their interpretation in terms of source extension and shape are investigated in a spirit of simplicity and in preparation for the analysis of high sensitivity and spatial resolution images that will soon be within reach with the completion of the Atacama Large Millimeter/submillimeter Array (ALMA). In particular, the information on source size carried by relative image brightness is discussed. Extension of the results to other types of quadruply imaged quasars is briefly considered.

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

Detailed studies of the response of the VATLY water Cherenkov detector, a replica of those used in the ground array of the Pierre Auger Observatory, are presented with emphasis on the response to low amplitude signals. The method used is to detect decay electrons from muons stopping in the water volume. Results include properties of the detection process as well as of the atmospheric cosmic ray flux.

On the Role of Magnetic Field Fluctuations in Diffusive Shock Acceleration

A simple numerical simulation of the mechanism of diffusive shock acceleration, responsible for the acceleration of cosmic rays in the environment of young Super Nova Remnants, is presented. The relative roles of a uniform magnetic field component, inherited from the parent collapsed star, and of magnetic turbulences, known to be present in the vicinity of the shock, are investigated. It is shown that a uniform magnetic field allows for only doubling the energy of the cosmic particle. Important accelerations require the simultaneous presence of magnetic field turbulences at a scale commensurable with its Larmor radius.