– 1 –1. Some Relevant Conventional Notation Used in Astronomy[X] = log(X)(for the object) – log(X)(for the Sun)In describing abundances, one can use [A/B], which is the ratio of element A to B,relative to that ratio for the Sun, expressed as log10.The absolute abundance of a species X is oft en denoted by ǫ(X), where the normalizationis such that ǫ(H) =1012. Thus a species K which has log[ǫ(K)] = 1 .0 dex has a ration(K)/n(H) of 10−11.brightness of objects – magnitude scale,apparent magnitude = A − 2.5 × log(Flux at Earth), brightest stars in sky haveapparent mag −1.Absolute mag = apparent mag of the object at a standard distance, fixed at 10 pc,where 1 pc is the distance at which the Earth’s orbit around the Sun subtends an angle o f1 arcsec, 1 pc = 3.08 × 1018cm.z refers to redshift. Z refers to the abundance by mass of elements other than H or He.X is the abundance by mass of H, Y is that of He.Stages of stellar evolution for stars in mass range about 1 to 3M⊙: MS = main sequence(H burning in core), followed by RGB = red giant branch, H exhausted in core, H burningin shell, stellar core contracting, envelope expanding, followed by He flash (ignition of Heburning in a degenerate core), leading to HB (horizontal branch) - He burning in core,followed by AGB (asymptotic giant branch) He exhausted in core, He and H burning shells,– 2 –eventually pulsational instability with substantial mass loss, planetary nebulae, cooling toa white dwarf.Higher mass stars ignite He in a non-degenerate core, so no He flash. by AGB(asymptotic giant