$\eta$ Carinae: high angular resolution continuum, H30$\alpha$ and He30$\alpha$ ALMA images

TL;DR

This paper presents high-resolution ALMA images of $ta$ Carinae revealing detailed structures in recombination lines and continuum, identifying compact sources, and providing insights into their motions and physical conditions.

Contribution

First high-resolution ALMA imaging of $ta$ Carinae's recombination lines and continuum, revealing unresolved sources, their motions, and line identifications with detailed modeling.

Findings

Resolved continuum into a core and extended structure.

Identified sources with ejection times near periastron.

Detected He30$\u03b1$ line with similar velocity to H30$\u03b1$.

Abstract

We present images of $\eta$ Carinae in the recombination lines H30$\alpha$ and He30$\alpha$ and the underlying continuum with 50~mas resolution (110 AU), obtained with ALMA. For the first time, the 230 GHz continuum image is resolved into a compact core, coincident with the binary system position, and a weaker extended structure to the NW of the compact source. Iso-velocity images of the H30$\alpha$ recombination line show at least 16 unresolved sources with velocities between -30 and -65 km s$^{-1}$ distributed within the continuum source. A NLTE model, with density and temperature of the order $10^7$ cm$^{-3}$ and $10^4$ K, reproduce both the observed H30$\alpha$ line profiles and their underlying continuum flux densities. Three of these sources are identified with Weigelt blobs D, C and B; estimating their proper motions, we derive ejection times (in years) of 1952.6, 1957.1, and 1967.6, respectively, all of which are close to periastron passage. Weaker H30$\alpha$ line emission is detected at higher positive and negative velocities, extending in the direction of the Homunculus axis. The He30$\alpha$ recombination line is also detected with the same velocity of the narrow H30$\alpha$ line. Finally, the close resemblance of the H30$\alpha$ image with that of an emission line that was reported in the literature as HCO$^+$(4-3) led us to identify this line as H40$\delta$ instead, an identification that is further supported by modeling results. Future observations will enable to determine the proper motions of all the compact sources discovered in the new high-angular resolution data of $\eta$ Carinae.