A Few Binary Star Puzzles for Roberto on the Occasion of His Birthday

TL;DR

This paper analyzes radial velocity data over 16 years for several CEMP stars, revealing small velocity amplitudes and discussing the challenges in detecting companions, with insights into binary star period distributions and accretion effects.

Contribution

It provides new orbital data for CEMP stars and discusses the implications of binary separation on accreted mass and companion detection.

Findings

Small velocity amplitude for CS 22881-036

No velocity variation in three other CEMP stars

Disparity in period distribution explained by accretion decline

Abstract

Radial velocity observations accumulated during the past 16 years are used to derive a preliminary orbit for the CEMP star CS 22881-036. The velocity amplitude is very small. No velocity variation is found for three additional CEMP stars observed over roughly the same time interval. Searches for companions of two CEMP double-lined spectroscopic binaries and of the RR Lyrae star TY Gruis are reviewed. A disparity between the period distribution of disk carbon-star binaries and that of their parent population of normal binaries can be attributed qualitatively to a decline in accreted mass with increasing binary separation. Finally, possible reasons for failure to find expected companions of CEMP stars are discussed.