Runaway Dwarf Carbon Stars as Candidate Supernova Ejecta

TL;DR

This paper investigates high-velocity dwarf carbon stars, suggesting they may be ejected supernova remnants, with new observations indicating some stars have velocities exceeding typical galactic escape speeds.

Contribution

It presents new proper motion and spectroscopic data for dwarf carbon stars, proposing a novel scenario of supernova ejection as their origin.

Findings

Several dwarf carbon stars have extreme galactocentric velocities.

High velocities are unlikely due to Galactic center passage.

Supernova ejection is a plausible origin for these stars.

Abstract

The dwarf carbon (dC) star SDSS J112801.67+004034.6 has an unusually high radial velocity, 531$\pm 4$ km s$^{-1}$. We present proper motion and new spectroscopic observations which imply a large Galactic rest frame velocity, 425$\pm 9$ km s$^{-1}$. Several other SDSS dC stars are also inferred to have very high galactocentric velocities, again each based on both high heliocentric radial velocity and also confidently detected proper motions. Extreme velocities and the presence of $C_2$ bands in the spectra of dwarf stars are both rare. Passage near the Galactic center can accelerate stars to such extreme velocities, but the large orbital angular momentum of SDSS J1128 precludes this explanation. Ejection from a supernova in a binary system or disruption of a binary by other stars are possibilities, particularly as dC stars are thought to obtain their photospheric $C_2$ via mass transfer from an evolved companion.