Revised classification of the SBS carbon star candidates including the discovery of a new emission line dwarf carbon star

TL;DR

This study reclassifies ten high-latitude carbon star candidates from the Second Byurakan Survey, revealing some as nearby dwarf carbon stars with emission lines, and clarifying the nature of others as giants or M-type stars.

Contribution

It provides a revised classification of these carbon star candidates using new spectra and photometry, identifying a rare emission line dwarf carbon star and challenging previous luminosity assumptions.

Findings

Two stars are confirmed N-type giants.

Four candidates are M-type stars.

One dwarf carbon star shows emission lines.

Abstract

Faint high latitude carbon stars are rare objects commonly thought to be distant, luminous giants. For this reason they are often used to probe the structure of the Galactic halo; however more accurate investigation of photometric and spectroscopic surveys has revealed an increasing percentage of nearby objects with luminosities of main sequence stars. Aiming at clarifyin the nature of the ten carbon star candidates present in the General Catalog of the Second Byurakan Survey we analyzed new optical spectra and photometry and used astronomical databases available on the web. We verified that two stars are N-type giants already confirmed by other surveys. We found that four candidates are M type stars and confirmed the carbon nature of the remaining four stars; the characteristics of three of them are consistent with an early CH giant type. The fourth candidate, SBS1310+561 identified with a high proper motion star, is a rare type of dwarf carbon showing emission lines in its optical spectrum. We estimated absolute magnitudes and distances to the dwarf carbon and the three CH stars. Our limited sample confirmed the increasing evidence that spectroscopy or colour alone are not conclusive luminosity discriminants for CH$-$type carbon stars .