Locating Red Supergiants in the Galaxy NGC 6822

Abstract

Using archival near-IR photometry, we identify 51 of the K-band brightest red supergiants (RSGs) in NGC 6822 and compare their physical properties with stellar evolutionary model predictions. We first use Gaia parallax and proper motion values to filter out foreground Galactic red dwarfs before constructing a J - K vs. K color-magnitude diagram to eliminate lower-mass asymptotic giant branch star contaminants in NGC 6822. We then cross-match our results to previously spectroscopically confirmed RSGs and other NGC 6822 content studies and discuss our overall completeness, concluding that radial velocity alone is an insufficient method of determining membership in NGC 6822. After transforming the J and K magnitudes to effective temperatures and luminosities, we compare these physical properties with predictions from both the Geneva single-star and Binary Population and Spectral Synthesis (BPASS) single and binary star evolution tracks. We find that our derived temperatures and luminosities match the evolutionary model predictions well, however the BPASS model that includes the effects of binary evolution provides the best overall fit. This revealed the presence of a group of cool RSGs in NGC 6822, suggesting a history of binary interaction. We hope this work will lead to further comparative RSG studies in other Local Group galaxies, opportunities for direct spectroscopic follow-up, and a better understanding of evolutionary model predictions.

arXiv commentAJ, accepted

References in corpus (19)

• Maps of Dust IR Emission for Use in Estimation of Reddening and CMBR Foregrounds
• Color Transformations for the 2MASS Second Incremental Data Release
• Binary Population and Spectral Synthesis Version 2.1: construction, observational verification and new results
• Gaia Data Release 2: Kinematics of globular clusters and dwarf galaxies around the Milky Way
• Reevaluating Old Stellar Populations
• A Survey of Local Group Galaxies Currently Forming Stars: II. UBVRI Photometry of Stars in Seven Dwarfs and a Comparison of the Entire Sample
• The impact of mass-loss on the evolution and pre-supernova properties of red supergiants
• A dusty veil shading Betelgeuse during its Great Dimming
• Red Supergiant Stars as Cosmic Abundance Probes: KMOS Observations in NGC 6822
• Betelgeuse Just Isn't That Cool: Effective Temperature Alone Cannot Explain the Recent Dimming of Betelgeuse
• Grids of stellar models with rotation VI: Models from 0.8 to 120 $M_{\odot }$ at a metallicity Z = 0.006
• Spectral Types of Red Supergiants in NGC 6822 and the Wolf-Lundmark-Melotte Galaxy
• The Luminosity Function of Red Supergiants in M31
• The Red Supergiant Content of M31 and M33
• Exploring the Mass Loss Histories of the Red Supergiants
• Red Supergiants in M31 and M33 I. The Complete Sample
• Evolved Massive Stars at Low-metallicity III. A Source Catalog for the Large Magellanic Cloud
• Evolved Massive Stars at Low-metallicity II. Red Supergiant Stars in the Small Magellanic Cloud
• Evolved Massive Stars at Low-metallicity IV. Using 1.6 $\mu$m "H-bump" to identify red supergiant stars: a case study of NGC 6822