Contributions of Rotation, Expansion and Line Broadening to the Morphology and Kinematics of the Inner CSE of Oxygen-rich AGB Star R Hya

Abstract

We use archival ALMA observations of the CO(2-1) and SiO(5-4) molecular line emissions of AGB star R Hya to illustrate the relative contributions of rotation, expansion and line broadening to the morphology and kinematics of the circumstellar envelope (CSE) within ~70 au (~0.5 arcsec) from the centre of the star. We give evidence for rotation and important line broadening to dominate the inner region, within ~ 14 au (~100 mas) from the centre of the star. The former is about an axis that projects a few degrees west of north and has a projected rotation velocity of a few km s−1 . The latter occurs within some 7-14 au (50-100 mas) from the centre of the star, the line width reaching two to three times its value outside this region. We suggest that it is caused by shocks induced by stellar pulsations and convective cell granulation. We show the importance of properly accounting for the observed line broadening when discussing rotation and evaluating the radial dependence of the rotation velocity.

On the nascent wind of oxygen-rich AGB stars: scrutiny of a sample of nearby stars

“…Their ALMA observation was first mentioned by Decin et al [6] and early attempts at interpreting them as bipolar gas streams flowing along the line of sight in the case of EP Aqr [66] or as the effect of rotation in the case of L 2 Pup [20,61] have been published. However, it has been later understood, following the study of other stars, that they are in fact confined to the close neighbourhood of the star and are essentially radial, although occasionally combining with rotation [53,67]. As first remarked by Decin et al [6], it is the high sensitivity of ALMA observations, rather than their high angular resolution, which made it possible to reveal their presence.…”

“…Similarly, the possible presence of expansion in this radial range complicates the analysis of the line broadening and needs to be properly taken into account. A detailed discussion of disentangling the effects of line broadening, rotation and expansion has been given by Nhung et al [67] using the case of R Hya as an illustration.…”

A Pre-explosion Effervescent Zone for the Circumstellar Material in SN 2023ixf

“…For the wind parameters used here the density of the clumps at R eff is The value of l b is not determined. The model assumes that very large convective cells that move outward, acting together with the pulsation modes, e.g., Freytag et al (2017) and Nhung et al (2023) for AGB stars, eject clumps (blobs) with sizes of ;0.2-0.5 R * . Shortly after it is formed and before it cools, a clump expands in all directions due to its high pressure.…”

Is Betelgeuse Really Rotating? Synthetic ALMA Observations of Large-scale Convection in 3D Simulations of Red Supergiants

“…Despite theoretical expectations, cool stars with rotation rates exceeding these predictions have been observed across the Hertzsprung-Russell diagram. These include several hundred red giants, about 1% of the total population of red giants (e.g., Patton et al 2024, and references therein), and a few asymptotic giant branch (AGB) stars (Barnbaum et al 1995;Vlemmings et al 2018;Brunner et al 2019;Nhung et al 2021Nhung et al , 2023. For RSGs, so far only one has been claimed to rotate rapidly: α Orionis, better known as Betelgeuse (Uitenbroek et al 1998;Harper & Brown 2006;Kervella et al 2018), which recently has drawn wide attention after the sudden Great Dimming (Guinan et al 2019;Montargès et al 2021) and subsequent rebrightening (Guinan et al 2020;Dupree et al 2022).…”