A CCD Search for Variable Stars in the Open Cluster NGC 6611

TL;DR

This study conducted a comprehensive variability survey of the young open cluster NGC 6611, identifying 95 variable stars, including pre-main sequence stars, eclipsing binaries, and δ Scuti candidates, with many confirmed as cluster members via Gaia data.

Contribution

It provides the first extensive variability catalog for NGC 6611, combining optical, infrared, and Gaia data to classify and confirm cluster membership of variable stars.

Findings

95 variable stars identified, including PMS, eclipsing binaries, and δ Scuti candidates.

Most variables are cluster members with high membership probability.

Discovered 8 new δ Scuti candidates and 17 eclipsing binaries.

Abstract

We present the results of the $UBVI_C$ variability survey in the young open cluster NGC 6611 based on observations obtained during 34 nights spanning one year. In total, we found 95 variable stars. Most of these stars are classified as periodic and irregular pre-main sequence (PMS) stars. The analysis of the $JHK_S$ 2MASS photometry and four-colour IRAC photometry revealed 165 Class II young stellar sources, 20 of which are irregular variables and one is an eclipsing binary. These classifications, complemented by $JHK$ UKIDSS photometry and $riH\alpha$ VPHAS photometry, were used to identify 24 candidates for classical T Tauri stars and 30 weak-lined T Tauri stars. In addition to the PMS variables, we discovered eight $\delta$ Scuti candidates. None of these were previously known. Furthermore, we detected 17 eclipsing binaries where two were previously known. Based on the proper motions provided by the Gaia EDR3 catalogue, we calculated the cluster membership probabilities for 91 variable stars. For 61 variables, a probability higher than 80% was determined, which makes them cluster members. Only 25 variables with a probability less than 20% were regarded to be non-members.