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Tuan P.A.,Vietnam National Satellite Center | Phuong V.V.,Vietnam National Satellite Center
Proceedings of the International Astronautical Congress, IAC | Year: 2013

The Vietnam National Satellite Center (VNSC), a national research agency under Vietnam Academy of Science and Technology (VAST), was established in 2011 by the Decision of the Prime Minister. Its tasks are to research and develop earth observation satellites and to apply, especially in remote sensing, GIS and GPS; to establish infrastructure for space technology; to promote education and training activities; and to explore international cooperation. VNSC is also an executing organization involved in implementation and management of Vietnam Space Center Project. ©2013 by the International Astronautical Federation. All rights reserved.


Nhung P.T.,Paris Observatory | Nhung P.T.,Vietnam National Satellite Center | Hoai D.T.,Paris Observatory | Hoai D.T.,Vietnam National Satellite Center | And 7 more authors.
Astronomy and Astrophysics | Year: 2015

The CO(1-0) and (2-1) emission of the circumstellar envelope of the asymptotic giant branch (AGB) star EP Aqr has been observed in 2003 using the IRAM Plateau-de-Bure Interferometer and in 2004 with the IRAM 30-m telescope at Pico Veleta. The line profiles reveal the presence of two distinct components centred on the star velocity, a broad component extending up to ∼10 km s-1 and a narrow component indicating an expansion velocity of only ∼2 km s-1. An early analysis of these data was performed under the assumption of isotropic winds. The present study revisits this interpretation, instead assuming a bipolar outflow nearly aligned with the line of sight. A satisfactory description of the observed flux densities is obtained with a radial expansion velocity increasing from ∼2 km s-1 at the equator to ∼10 km s-1 near the poles. The mass-loss rate is ∼1.2 × 10-7 M yr-1. The angular aperture of the bipolar outflow is ∼ 45° with respect to the star axis, which makes an angle of ∼ 13° with the line of sight. A detailed study of the CO(1-0) to CO(2-1) flux ratio reveals a significant dependence of the temperature on the stellar latitude, smaller and steeper at the poles than at the equator at large distances from the star (>2′′ 1.0 × 10-3 pc). Under the hypothesis of radial expansion of the gas and of rotation invariance about the star axis, the effective density was evaluated in space as a function of star coordinates (longitude, latitude, and distance from the star). Evidence is found for an enhancement of the effective density in the northern hemisphere of the star at angular distances in excess of ∼ 3′′ and covering the whole longitudinal range. The peak velocity of the narrow component is observed to vary slightly with position on the sky, a variation consistent with the model and understood as the effect of the inclination of the star axis with respect to the line of sight. This variation is inconsistent with the assumption of a spherical wind and strengthens our interpretation in terms of an axisymmetric outflow. While the phenomenological model presented here reproduces well the general features of the observations, not only qualitatively but also quantitatively, significant differences are also revealed, which would require a better spatial resolution to be properly described and understood. © ESO, 2015.


Anh P.T.,Vietnam National Satellite Center | Diep P.N.,Vietnam National Satellite Center | Hoai D.T.,Vietnam National Satellite Center | Nhung P.T.,Vietnam National Satellite Center | And 3 more authors.
Research in Astronomy and Astrophysics | Year: 2015

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. © 2015 National Astronomical Observatories, Chinese Academy of Sciences and IOP Publishing Ltd.


Nhung P.T.,Vietnam National Satellite Center | Hoai D.T.,Vietnam National Satellite Center | Diep P.N.,Vietnam National Satellite Center | Phuong N.T.,Vietnam National Satellite Center | And 3 more authors.
Research in Astronomy and Astrophysics | Year: 2016

Observations of the 12CO(3-2) emission from the circumstellar envelope (CSE) of the variable star π1 Gru 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 for 12CO(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. © 2016 National Astronomical Observatories, Chinese Academy of Sciences and IOP Publishing Ltd.


Nhung P.T.,Vietnam National Satellite Center | Hoai D.T.,Vietnam National Satellite Center | Diep P.N.,Vietnam National Satellite Center | Phuong N.T.,Vietnam National Satellite Center | And 3 more authors.
Monthly Notices of the Royal Astronomical Society | Year: 2016

Observations of 12CO(3-2) emission of the circumbinary envelope of Mira Ceti, made by Atacama Large Millimetre/sub-millimetre Array, are analysed. The observed Doppler velocity distribution is made of three components: a blueshifted south-eastern arc, which can be described as a ring in slow radial expansion, ∼1.7 km s-1, making an angle of ∼50° with the plane of the sky and born some 2000 years ago; a few arcs, probably born at the same epoch as the blueshifted arc, all sharing Doppler velocities redshifted by approximately 3±2 km s-1 with respect to the main star; thirdly, a central region dominated by the circumbinary envelope, displaying two outflows in the south-western and north-eastern hemispheres. At short distances from the star, up to ∼1.5 arcsec, these hemispheres display very different morphologies: the south-western outflow covers a broad solid angle, expands radially at a rate between 5 and 10 km s-1 and is slightly redshifted; the north-eastern outflow consists of two arms, both blueshifted, bracketing a broad dark regionwhere emission is suppressed. At distances between ∼1.5 and ∼2.5 arcsec the asymmetry between the two hemispheres is significantly smaller and detached arcs, particularly spectacular in the north-eastern hemisphere are present. Close to the stars, we observe a mass of gas surrounding Mira B, with a size of a few tens of au, and having Doppler velocities with respect to Mira B reaching ±1.5 km s-1, which we interpret as gas flowing from Mira A towards Mira B. © 2016 The Authors. Published by Oxford University Press on behalf of The Royal Astronomical Society.

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