FTP, name these stars used as a standard candle in making astronomical distance measurements, one of the major classes of variable stars.
Delta Scuti is sometimes called a "dwarf" type of them.  Photon pressure causes them to rapidly expand in size; however, when the star has expanded, the pressure gradient is then too weak to counteract gravity, leading to contraction.  Their classical or Type I variety is the generally thought to be the most useful after Henrietta Leavitt discovered their period-luminosity relationship.  FTP, name these stars used as a standard candle in making astronomical distance measurements, one of the major classes of variable stars.
Delta Scuti is sometimes called a "dwarf" type of them.  Photon pressure causes them to rapidly expand in size; however, when the star has expanded, the pressure gradient is then too weak to counteract gravity, leading to contraction.  
Cepheid variables