Catching the Butterfly and the Homunculus of η Carinae with ALMA

Abstract

The nature and origin of the molecular gas component located in the circumstellar vicinity of η Carinae are still far from being completely understood. Here, we present Atacama Large Millimeter/submillimeter Array CO(3−2) observations with a high angular resolution (∼0.″15) and a great sensitivity that are employed to reveal the origin of this component in η Carinae. These observations reveal much higher velocity (−300 to +270 km s−1) blue- and redshifted molecular thermal emission than previously reported, which we associate with the lobes of the Homunculus Nebula, and which delineates very well the innermost contours of the red- and blueshifted lobes likely due to limb brightening. The inner contour of the redshifted emission was proposed to be a disrupted torus, but here we reveal that it is at least part of the molecular emission originating from the lobes and/or the expanding equatorial skirt. On the other hand, closer to systemic velocities (±100 km s−1), the CO molecular gas traces an inner butterfly-shaped structure that is also revealed at near-IR and mid-IR wavelengths as the region in which the shielded dust resides. The location and kinematics of the molecular component indicate that this material has formed after the different eruptions of η Carinae.

First Detection of Silicon-bearing Molecules in η Car

“…This ring, disrupted toward the NW-its near side, coincident with the projected direction of the orbit's major axis-delineates the bright rims of the so-called "butterfly" nebula (Chesneau et al 2005), a region of efficient dust processing where emission from several other species has been resolved, such as HCN and HCO + (Bordiu & Rizzo 2019, hereafter BR19). Interestingly, a thorough recalibration of CO ALMA data by Zapata et al (2022), significantly improving sensitivity, has revealed higher velocity components that may be tracing the walls of the polar lobes of the Homunculus by means of limb brightening.…”