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Cau Giay, Vietnam

Anh P.T.,Toulouse 1 University Capitole | Anh P.T.,Roche Holding AG | Anh P.T.,Institute of Physics | Boone F.,Toulouse 1 University Capitole | And 7 more authors.
Astronomy and Astrophysics | Year: 2013

We report on high angular resolution observations of the CO(7-6) line and millimeter continuum in the host galaxy of the gravitationally lensed (z ∼ 2.8) quasar RXJ0911.4+0551 using the Plateau de Bure Interferometer. Our CO observations resolve the molecular disk of the source. Using a lens model based on HST observations, we fit source models to the observed visibilities. We estimate a molecular disk radius of 1 ± 0.2 kpc and an inclination of 69 ± 6 deg, the continuum is more compact and is only marginally resolved by our observations. The relatively low molecular gas mass, Mgas = (2.3 ± 0.5) × 109 M·, and far-infrared (FIR) luminosity, LFIR = (7.2 ± 1.5) × 1011 L·, of this quasar could be explained by its relatively low dynamical mass, Mdyn = (3.9 ± 0.9) × 109 M·. It would be a scaled-down version the quasi-stellar objects (QSOs) usually found at high-z. The FIR and CO luminosities lie on the correlation found for QSOs from low to high redshifts and the gas-to-dust ratio (45 ± 17) is similar to the one measured in the z = 6.4 QSO, SDSS J1148+5251. Differential magnification affects the continuum-to-line luminosity ratio, the line profile, and possibly the spectral energy distribution. © 2013 ESO.

Tuyet Nhung P.,VATLY | Thi Hoai D.,Paris Observatory | Martin Winters J.,Grenoble Institute of Technology | Darriulat P.,VATLY | And 2 more authors.
Research in Astronomy and Astrophysics | Year: 2015

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 properties of the CSE. We use a wind model including a bipolar flow with a typical wind velocity of ∼8 km s-1 that decreases to ∼2 km s-1 near the equator. This wind model is used 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 CSE 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. © 2015 National Astronomical Observatories, Chinese Academy of Sciences and IOP Publishing Ltd.

Hoai D.T.,VATLY | Nhung P.T.,VATLY | Anh P.T.,VATLY | Boone F.,IRAP | And 5 more authors.
Research in Astronomy and Astrophysics | Year: 2013

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. © 2013 National Astronomical Observatories of Chinese Academy of Sciences and IOP Publishing Ltd.

Diep P.N.,VATLY | Phuong N.T.,VATLY | Darriulat P.,VATLY | Nhung P.T.,VATLY | And 4 more authors.
Publications of the Astronomical Society of Australia | Year: 2014

A multipath mechanism similar to that used in Australia sixty years ago by the Sea-cliff Interferometer is shown to generate correlations between the periods of oscillations observed by two distant radio telescopes pointed to the Sun. The oscillations are the result of interferences between the direct wave detected in the main antenna lobe and its reflection on ground detected in a side lobe. A model is made of such oscillations in the case of two observatories located at equal longitudes and opposite tropical latitudes, respectively in Ha Noi (Viet Nam) and Learmonth (Australia), where similar radio telescopes are operated at 1.4 GHz. Simple specular reflection from ground is found to give a good description of the observed oscillations and to explain correlations that had been previously observed and for which no satisfactory interpretation, instrumental or other, had been found. Copyright © 2014 Astronomical Society of Australia.

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