The classification of intrinsic variables. IV. Very-small-amplitude, very-short-period red variables

Photometry over extended intervals of eight red giants of the old disk population has (1) shown these objects to be very-small-amplitude (less than 0.2 mag visual) and very-short-period (2() 40 days) variables and (2) indicated that the blue boundary of the red-variable instability region, previously found to be near R - I = + 1.0 mag, is nearer 0.9 mag. A list of candidates for even shorter period, smaller amplitude, and hotter variables of this type, which might be called "a Lib" variables, is included. Subject headings: late-type stars - variable stars