2008AJ....135.1681T

The light variations of 11 selected single-peaked OH/IR stars have been monitored in the JHK bands from 2000 to 2005. They are found to have periods of variation between 200 and 700 days, located at the short-period end of normal OH/IR stars. Their amplitudes of variation in the K band are less than 2 mag, which is relatively small and consistent with relatively short periods. These stars exist between the Miras and OH/IR stars from the viewpoint of light variation. In addition, analysis of the infrared color indices J - H, H - K, [12]-[25], and K-[12], as well as spectroscopy from 6000 Å to 9200 Å, reveals that these stars have relatively hot and thin circumstellar shells. We suggest that the phenomenon of being sometimes single-peaked OH maser emitters can be explained by the weakness of the unseen component resulting from the short amplification path. The distances to these stars are calculated from the well-defined period-luminosity relation in the K band. In addition, two stars are found to show a long secondary variation.