Searching for Be Stars in the Open Cluster NGC 663

TL;DR

This study identifies Be star candidates in the open cluster NGC 663 using H-alpha imaging, revealing their spectral distribution, membership status, and prevalence, to better understand their role in stellar evolution.

Contribution

The paper presents a new method of identifying Be stars in NGC 663 through H-alpha imaging and confirms their membership, providing insights into their spectral distribution and prevalence.

Findings

Discovered 4 new Be stars in NGC 663.

Be star fraction in NGC 663 is 3.5%.

Be stars show bimodal spectral type distribution at B0--B2 and B5--B7.

Abstract

We present Be star candidates in the open cluster NGC\,663, identified by H$\alpha$ imaging photometry with the Palomar Transient Factory Survey, as a pilot program to investigate how the Be star phenomena, the emission spectra, extended circumstellar envelopes, and fast rotation, correlate with massive stellar evolution. Stellar membership of the candidates was verified by 2MASS magnitudes and colors, and by proper motions. We discover 4 new Be stars and exclude one known Be star from being a member due to its inconsistent proper motions. The fraction of Be stars to member stars [N(Be)/N(members)] in NGC\,663 is 3.5\%. The spectral type of the 34 Be stars in NGC\,663 shows bimodal peaks at B0--B2 and B5--B7, which is consistent with the statistics in most star clusters. Additionally, we also discover 23 emission-line stars of different types, including non-member Be stars, dwarfs, and giants.