球状星团M4中另一颗周期约一天的小变幅新红变星

Another New Small-amplitude Red Variable Star with Period of about One Day in the Globular Cluster M4

A66是位于球状星团M4红巨星支最底部(近亚巨星支顶部)的一颗红星．按其在C-M图上的位置,A66可能是星团成员．目前尚无自行或视线速度的测定．发现A66为一小变幅的新变星,周期约一天, v波段的总变幅约0．05等．但是,如果自行或视线速度测定证实为其成员星,那么变光的原因也许不是脉动．因为按照熊氏理论,这样低光度的红星其脉动周期不可能长于0．1天．对于A66这样的周期和变幅,又很难想像变光原因是黑子星的自转或EW型双星的交食．或者,A66不是星团成员．

A66 is a red star located at the lowest end of the red giant branch （near the top of the sub-giant branch） of the globular cluster M4. According to its location on the C-M diagram, A66 may be a cluster member. No proper motion and radial velocity determinations are available up to date. It is discovered that A66 is a small-amplitude new variable star with a period of about one day and the peak to peak amplitude is about 0.05 mag in V. However, if its membership can be confirmed by proper motion and radial velocity determinations, the cause of light variation may not be pulsation. This is because according to Xiong＇s theory, a red star at such low luminosity can not pulsate at a period longer than 0.1 day. But with the amplitude and period of A66 , it is difficult to imagine that the cause of variability is due to EW type eclipsing of a binary or rotation of a spotted star. Otherwise A66 is not a cluster member.