Observation of narrow polar jets in the nascent wind of oxygen-rich AGB star EP Aqr
Résumé
Using ALMA observations of 12CO(2-1), 28SiO(5-4), and 32SO2(166,10-175,13) emissions of the circumstellar envelope of AGB star EP Aqr, we describe the morpho-kinematics governing the nascent wind. Main results are as follows: (1) Two narrow polar structures, referred to as jets, launched from less than 25 au away from the star, build up between ∼20 and ∼100 au to a velocity of ∼20 km s-1. They fade away at larger distances and are barely visible in CO data. (2) SO2, SiO, and CO emissions explore radial ranges reaching, respectively, ∼30, 250, and 1000 au from the star, preventing the jets to be detected in SO2 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 SO2 line profile (∼7.5 km s-1 full width at half-maximum). (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 ∼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 12C/13C abundance ratio is measured as 9 ± 2. (8) Plausible interpretations are discussed, in particular assuming the presence of a companion.
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