Compact Radio Sources within 30" of Sgr A*: Proper Motions, Stellar Winds and the Accretion Rate onto Sgr A*

TL;DR

This study uses radio and near-IR observations to analyze stellar proper motions, winds, and accretion rates near Sgr A*, revealing new insights into the dynamics and mass loss of stars in the Galactic center.

Contribution

It provides the first detailed comparison of IR and radio proper motions near Sgr A* and estimates stellar wind mass-loss rates, refining the understanding of accretion onto Sgr A*.

Findings

Proper motions from IR data show varying accuracy when predicting radio positions.

Mass-loss rates of radio stars are about half of those from model atmospheres, suggesting wind clumpiness.

Reduced stellar wind mass-loss implies a lower accretion rate onto Sgr A*.

Abstract

Recent broad-band 34 and 44 GHz radio continuum observations of the Galactic center have revealed 41 massive stars identified with near-IR counterparts, as well as 44 proplyd candidates within 30" of Sgr A*. Radio observations obtained in 2011 and 2014 have been used to derive proper motions of eight young stars near Sgr A*. The accuracy of proper motion estimates based on near-IR observations by Lu et al. and Paumard et al. have been investigated by using their proper motions to predict the 2014 epoch positions of near-IR stars and comparing the predicted positions with those of radio counterparts in the 2014 radio observations. Predicted positions from Lu et al. show an rms scatter of 6 mas relative to the radio positions, while those from Paumard et al. show rms residuals of 20 mas, which is mainly due to uncertainties in the IR-based proper motions. Under the assumption of homogeneous ionized winds, we also determine the mass-loss rates of 11 radio stars, finding rates that are on average $\sim$2 times smaller than those determined from model atmosphere calculations and near-IR data. Clumpiness of ionized winds would reduce the mass loss rate of WR and O stars by additional factors of 3 and 10, respectively. One important implication of this is a reduction in the expected mass accretion rate onto Sgr A* from stellar winds by nearly an order of magnitude to a value of few$\times10^{-7}$ \msol\ yr$^{-1}$. Finally, we present the positions of 318 compact 34.5 GHz radio sources within 30\arcs\ of Sgr A*. At least 45 of these have stellar counterparts in the near-IR $K_s$ (2.18 $\mu$m) and $L'$ (3.8$\mu$m) bands.