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

Abstract

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 ∼ 20 au 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) SO 2 , SiO and CO emissions explore radial ranges reaching respectively ∼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 (∼ 7.5 km s −1 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 ∼ 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±2. 8) Plausible interpretations are discussed, in particular assuming the presence of a companion.

How to disentangle geometry and mass-loss rate from AGB-star spectral energy distributions

“…Table 1 summarises its properties. There have been several recent investigations of the CSE around EP Aqr (Nhung et al 2015;Homan et al 2018;Tuyet Nhung et al 2019;Hoai et al 2019;Tuan-Anh et al 2019), most of them of the CO lines with ALMA. Tuan-Anh et al (2019) found jets extending from 25 to 1000 au.…”

“…References. Gontcharov (2012) observations (Tuyet Nhung et al 2019;Homan et al 2018;Hoai et al 2019;Tuan-Anh et al 2019) which point at spiral arms embedded in a disc-like geometry, as seen nearly face-on. This paper has the following structure.…”

Astrophysics research at DAP

“…Evolved stars often feature a bipolar molecular outflow. A number of evolved stars at different stages of evolution and different orientations in space have been studied at DAP using observations of the high resolution continuum and line emissions from dust grains and gas molecules [8][9][10][11][12][13][14][15]. Methods to study and reconstruct in space axisymmetric radio sources (a common feature of young and old stars) have been developed to this effect [16,17].…”

On the origin of high Doppler velocity wings in the spectra of O-rich AGB stars

“…The high velocity streams are present in CO emission but weaker than in SiO emission (Figure 4), suggesting that they slow down and/or diverge at large distances from the star. These streams are very narrow (~10 o ), launched from less than 25 au from the star on the line of sight direction and build up between ~20 au and ~100 au to a velocity of ~ 20 km s −1 [3]. The mechanism governing the launching of the observed streams remains unknown.…”

“…Recently, the availability of high angular resolution ALMA (Atacama Large Millimeter/sub millimeter Array) observations of several oxygen rich AGB stars like EP Aqr, R Dor, L 2 Pup and Mira Ceti have shed a new light on this issue [3][4][5][6]. However, the origin of these high velocities is still unclear.…”