The morpho-kinematics of the circumstellar envelope around the AGB star EP Aqr

ALMA observations of CO(1-0) and CO(2-1) emissions of the circumstellar envelope of EP Aqr, an oxygen-rich AGB star, are reported. A thorough analysis of their properties is presented using an original method based on the separation of the data-cube into a low velocity component associated with an equatorial outflow and a faster component associated with a bipolar outflow. A number of important and new results are obtained concerning the distribution in space of the effective emissivity, the temperature, the density and the flux of matter. A mass loss rate of (1.6$\pm$0.4)10$^{-7}$ solar masses per year is measured. The main parameters defining the morphology and kinematics of the envelope are evaluated and uncertainties inherent to de-projection are critically discussed. Detailed properties of the equatorial region of the envelope are presented including a measurement of the line width and a precise description of the observed inhomogeneity of both morphology and kinematics. In particular, in addition to the presence of a previously observed spiral enhancement of the morphology at very small Doppler velocities, a similarly significant but uncorrelated circular enhancement of the expansion velocity is revealed, both close to the limit of sensitivity. The results of the analysis place significant constraints on the parameters of models proposing descriptions of the mass loss mechanism, but cannot choose among them with confidence.Comment: 26 pages, 31 figures, accepted for publication in MNRA

Observation of narrow polar jets in the nascent wind of oxygen-rich AGB star EP Aqr

Using ALMA observations of $^{12}$CO(2-1), $^{28}$SiO(5-4) and $^{32}$SO$_2$(16$_{6,10}$-17$_{5,13}$) emissions of the circumstellar envelope of AGB star EP Aqr, we describe the morpho-kinematics governing the nascent wind. Main results are: 1) Two narrow polar structures, referred to as jets, launched from less than 25 au away from the star, build up between $\sim$ 20 au and $\sim$ 100 au to a velocity of $\sim$ 20 \kms. They fade away at larger distances and are barely visible in CO data. 2) SO$_2$, SiO and CO emissions explore radial ranges reaching respectively $\sim$30 au, 250 au and 1000 au from the star, preventing the jets to be detected in SO$_2$ data. 3) Close to the star photosphere, rotation (undetected in SiO and CO data) and isotropic radial expansion combine with probable turbulence to produce a broad SO$_2$ line profile ($\sim$ 7.5 \kms\ FWHM). 4) A same axis serves as axis of rotation close to the star, as jet axis and as axi-symmetry axis at large distances. 5) A radial wind builds up at distances up to $\sim$ 300 au from the star, with larger velocity near polar than equatorial latitudes. 6) A sharp depletion of SiO and CO emissions, starting near the star, rapidly broadens to cover the whole blue-western quadrant, introducing important asymmetry in the CO and particularly SiO observations. 7) The $^{12}$C/$^{13}$C abundance ratio is measured as 9$\pm$2. 8) Plausible interpretations are discussed, in particular assuming the presence of a companion.Comment: 18 pages, 16 figures, MNRAS accepte

A quasi-3D theory for vibration and buckling of functionally graded sandwich beams

This paper presents a finite element model for free vibration and buckling analyses of functionally graded (FG) sandwich beams by using a quasi-3D theory in which both shear deformation and thickness stretching effects are included. Sandwich beams with FG skins-homogeneous core and homogeneous skins-FG core are considered. By using the Hamilton’s principle, governing equations of motion for coupled axial–shear–flexural–stretching response are derived. The resulting coupling is referred to as fourfold coupled vibration and buckling. Numerical examples are carried out to investigate the thickness stretching effect on natural frequencies and critical buckling loads as well as mode shapes of sandwich beams for various power-law indexes, skin–core–skin thickness ratios and boundary conditions

A nonlocal sinusoidal shear deformation beam theory with application to bending, buckling, and vibration of nanobeams

This paper presents a nonlocal sinusoidal shear deformation beam theory for the bending, buckling, and vibration of nanobeams. The present model is capable of capturing both small scale effect and transverse shear deformation effects of nanobeams, and does not require shear correction factors. Based on the nonlocal differential constitutive relations of Eringen, the equations of motion as well as the boundary conditions of the beam are derived using Hamilton’s principle. Analytical solutions for the deflection, buckling load, and natural frequency are presented for a simply supported beam, and the obtained results are compared with those predicted by the nonlocal Timoshenko beam theory. The comparison firmly establishes that the present beam theory can accurately predict the bending, buckling, and vibration responses of short nanobeams where the small scale and transverse shear deformation effects are significant

Finite element model for vibration and buckling of functionally graded sandwich beams based on a refined shear deformation theory

Finite element model for vibration and buckling of functionally graded sandwich beams based on a refined shear deformation theory is presented. The core of sandwich beam is fully metal or ceramic and skins are composed of a functionally graded material across the depth. Governing equations of motion and boundary conditions are derived from the Hamilton’s principle. Effects of power-law index, span-to-height ratio, core thickness and boundary conditions on the natural frequencies, critical buckling loads and load–frequency curves of sandwich beams are discussed. Numerical results show that the above-mentioned effects play very important role on the vibration and buckling analysis of functionally graded sandwich beams