The Role of Binarity and Stellar Rotation in the Split Main Sequence of NGC 2422

In addition to the extended main-sequence turnoffs widely found in young and intermediate-age (∼600 Myr to 2 Gyr old) star clusters, some younger clusters even exhibit split main sequences (MSs). Different stellar rotation rates are proposed to account for the bifurcated MS pattern, with red and blu...

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Bibliographic Details
Published in:The Astrophysical journal 2022-10, Vol.938 (1), p.42
Main Authors: He, Chenyu, Sun, Weijia, Li, Chengyuan, Li, Lu, Shao, Zhengyi, Zhong, Jing, Chen, Li, Grijs, Richard de, Tang, Baitian, Qin, Songmei, Randriamanakoto, Zara
Format: Article
Language:English
Subjects:
Astrophysics
Bifurcations
Binary stars
Color
Companion stars
Galactic clusters
Open star clusters
Photometry
Radial velocity
Rotational spectra
Spectral energy distribution
Star clusters
Stars
Stellar rotation
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Summary:In addition to the extended main-sequence turnoffs widely found in young and intermediate-age (∼600 Myr to 2 Gyr old) star clusters, some younger clusters even exhibit split main sequences (MSs). Different stellar rotation rates are proposed to account for the bifurcated MS pattern, with red and blue MSs (rMS and bMS) populated by fast and slowly rotating stars, respectively. Using photometry from Gaia Early Data Release 3, we report a Galactic open cluster with a bifurcated MS, NGC 2422 (∼90 Myr). We exclude the possibilities that the bifurcated MS pattern is caused by photometric noise or differential reddening. We aim to examine if stellar rotation can account for the split MS. We use spectra observed with the Canada–France–Hawaii Telescope and the Southern African Large Telescope and directly measured v sin i , the projected rotational velocities, for stars populating the bMS and rMS. We find that their v sin i values are weakly correlated with their loci in the color–magnitude diagram because of contamination caused by a large fraction of rMS stars with low projected rotational velocities. Based on the spectral energy distribution fitting method, we suggest that these slowly rotating stars at the rMS may hide a binary companion, which breaks the expected v sin i –color correlation. Future time-domain studies focusing on whether these slowly rotating stars are radial velocity variables are crucial to test the roles of stellar rotation and binarity in generating the split MSs.
ISSN:0004-637X
1538-4357
DOI:10.3847/1538-4357/ac8b08