Searching for new yellow symbiotic stars: positive identification of StHa63

TL;DR

This study identifies a new yellow symbiotic star, StHa63, through spectroscopic analysis, and proposes the WISE W3-W4 index as an effective tool for selecting such stars.

Contribution

The paper reports the discovery of a new yellow symbiotic star and introduces the WISE W3-W4 index as a novel method for candidate selection.

Findings

StHa63 confirmed as a yellow symbiotic star based on spectrum and emission lines.

WISE W3-W4 index effectively separates K-giants from yellow symbiotic stars.

Three candidates rejected due to lack of emission lines or Balmer-only emission.

Abstract

Yellow symbiotic stars are useful targets to probe whether mass transfer has happened in these binary systems. However, the number of known yellow symbiotic stars is very scarce. We report spectroscopic observations of five candidate yellow symbiotic stars selected by their position in the 2MASS (J-H) vs. (H-Ks) diagram and included in some emission-line catalogs. Among the five candidates, only StHa63 is identified as a new yellow symbiotic star because of its spectrum and its position in the [TiO]1-[TiO]2 diagram that indicates a K4-K6 spectral type. In addition, the derived electron density (10E8.4 cm-3) and several emission line intensity ratios provide further support for that classification. The other four candidates are rejected as symbiotic stars because three of them actually do not show emission lines and the fourth one shows only Balmer emission lines. We also found that the WISE W3-W4 index clearly separates normal K-giants from yellow symbiotic stars and, therefore, can be used as an additional tool to select candidate yellow symbiotic stars.