# Investigation of long-period variables in the Catalina Southern catalog: new carbon stars and false objects

## TL;DR

This study analyzes long-period variables in the Catalina Southern catalog, identifying new carbon stars and revealing that many faint LPVs are false detections caused by contamination from nearby bright Miras, emphasizing the need for careful data interpretation.

## Contribution

It provides the first spectral classification of LPVs in the Catalina Southern catalog and uncovers the prevalence of false positives due to instrumental contamination.

## Key findings

- Only 2 new carbon stars identified among the classified LPVs.
- Many faint LPVs are actually artifacts caused by nearby bright Miras.
- Contamination significantly affects the reliability of faint LPV detections.

## Abstract

As part of our ongoing study of the evolved giants in the galactic halo, we consider the sample of 1286 long-period variables (LPVs) in the southern hemisphere provided by the Catalina Sky Survey experiment. These LPVs have periods P larger than 80 days and amplitudes over 0.2 mag. First, by using the Hamburg-ESO spectral survey, we aim to determine the spectral type as either M-type or C-type for objects located in the imprint of this survey, $|b| > 30$ degrees. Of 135 LPVs obeying this selection, we classified 93, and found only 2 new carbon stars. Secondly, we consider faint LPVs. We discovered that many lie at about 1 arcmin from a bright Mira catalogued in the General Catalog of Variable Stars, with identical period. We study these suspicious cases in detail, and conclude that, for as many as 56 faint Catalina LPVs, their variability is due to contamination by light from the bright, neighbouring GCVS Mira: an instrumental artefact. We conclude that when dealing with distant, faint Miras in the Catalina catalog, researchers should pay attention to the polluting effects of neighbouring bright and variable objects.