Figure 5 : Location of the BLAPs in the Hertzsprung–Russell diagram.

From: Blue large-amplitude pulsators as a new class of variable stars

Figure 5

The zero-age main sequence (thick solid line), evolutionary tracks for 1, 2, 4 and 8M (thin solid lines23), edges of the classical instability strip and instability domain for radial pulsations in the upper main sequence (dashed lines20) are presented for the metallicity of Z = 0.02. Hatched regions show locations of various types of known pulsating stars in which pulsations are driven by the presence of the He ii bump (δ Cep, δ Sct and RR Lyrae-type stars) and Z bump in the opacity (β Cep-type, SPB stars, sdO, slowly (s) and rapidly (r) pulsating sdB variables). Different shading represents different types of mode: backslash (\) shading is for pressure modes whereas slash (/) shading is for gravity modes. Positions of two known radially pulsating extreme helium stars (BX Cir and V652 Her) are also marked (small circles). BLAPs are located in a region not occupied by any known pulsating variables.