Cau Giay, Vietnam
Cau Giay, Vietnam

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Hiep N.V.,VATLY Institute | Nhung P.T.,VATLY Institute | Darriulat P.,VATLY Institute | Diep P.N.,VATLY Institute | And 4 more authors.
Solar Physics | Year: 2014

The VATLY radio telescope, operating at 1.415 GHz in Ha Noi, has been used to track the Sun in the summer - autumn months in 2012. Evidence has been obtained for solar activity, including occasional flares and variable oscillations with amplitudes at the percent level and periods of about 6 min. Comparison with data collected at the same frequency by the Learmonth Observatory in Australia suggests that the observed oscillations were associated with solar activity. A joint analysis of both data sets is presented, evaluating the correlations between them. We describe the common and different main features. © 2013 Springer Science+Business Media Dordrecht.

Hoai D.T.,Paris Observatory | Hoai D.T.,VATLY Institute | Matthews L.D.,Massachusetts Institute of Technology | Winters J.M.,Grenoble Institute of Technology | And 6 more authors.
Astronomy and Astrophysics | Year: 2014

We present a detailed study of the circumstellar gas distribution and kinematics of the semi-regular variable star RS Cnc on spatial scales ranging from ∼1′′ (∼150 AU) to ∼6′ (∼0.25 pc). Our study utilizes new CO1-0 data from the Plateau de Bure Interferometer and new H i 21 cm line observations from the Jansky Very Large Array (JVLA), in combination with previous observations. New modeling of CO1-0 and CO2-1 imaging observations leads to a revised characterization of RS Cnc's previously identified axisymmetric molecular outflow. Rather than a simple disk-outflow picture, we find that a gradient in velocity as a function of latitude is needed to fit the spatially resolved spectra, and in our preferred model, the density and the velocity vary smoothly from the equatorial plane to the polar axis. In terms of density, the source appears quasi-spherical, whereas in terms of velocity the source is axisymmetric with a low expansion velocity in the equatorial plane and faster outflows in the polar directions. The flux of matter is also larger in the polar directions than in the equatorial plane. An implication of our model is that the stellar wind is still accelerated at radii larger than a few hundred AU, well beyond the radius where the terminal velocity is thought to be reached in an asymptotic giant branch star. The JVLA H i data show the previously detected head-tail morphology, and also supply additional details about the atomic gas distribution and kinematics. We confirm that the head seen in H i is elongated in a direction consistent with the polar axis of the molecular outflow, suggesting that we are tracing an extension of the molecular outflow well beyond the molecular dissociation radius (up to ∼0.05 pc). The 6′-long H i tail is oriented at a PA of 305°, consistent with the space motion of the star. The tail is resolved into several clumps that may result from hydrodynamic effects linked to the interaction with the local interstellar medium. We measure a total mass of atomic hydrogen MHI 0.0055 M⊙ and estimate a lower limit to the timescale for the formation of the tail to be ∼6.4 × 104 years. © 2014 ESO.

Hoai D.T.,VATLY Institute | Diep P.N.,VATLY Institute | Darriulat P.,VATLY Institute | Anh P.T.,VATLY Institute | And 4 more authors.
Astroparticle Physics | Year: 2012

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 18to 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.© 2012 Elsevier B.V. All rights reserved.

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