Optical/IR studies of Be stars in NGC 6834 with emphasis on two specific stars

TL;DR

This study combines optical and infrared observations to analyze two Be stars in the NGC 6834 cluster, revealing their spectral properties, possible binarity, and evolutionary status, with new photometric data and detailed spectral analysis.

Contribution

It provides new infrared spectra, compares classification schemes, and offers UBV photometry to better understand the nature and evolution of Be stars in NGC 6834.

Findings

NGC 6834(1) is a binary star.

NGC 6834(2) may be a gamma Cas-like variable.

New UBV photometry helps determine the evolutionary stage.

Abstract

We present optical and infrared photometric and spectroscopic studies of two Be stars in the 70--80-Myr-old open cluster NGC 6834. NGC 6834(1) has been reported as a binary from speckle interferometric studies whereas NGC 6834(2) may possibly be a gamma Cas-like variable. Infrared photometry and spectroscopy from the United Kingdom Infrared Telescope (UKIRT), and optical data from various facilities are combined with archival data to understand the nature of these candidates. High signal-to-noise near-IR spectra obtained from UKIRT have enabled us to study the optical depth effects in the hydrogen emission lines of these stars. We have explored the spectral classification scheme based on the intensity of emission lines in the $H$ and $K$ bands and contrasted it with the conventional classification based on the intensity of hydrogen and helium absorption lines. This work also presents hitherto unavailable UBV CCD photometry of NGC 6834, from which the evolutionary state of the Be stars is identified.