Question : 11) The helium flash increases the star's luminosity. 12) The luminosity : 1828913

11) The helium flash increases the star's luminosity.

12) The luminosity of the red giant during its second trip to the upper right on the H-R diagram is less than before the helium flash expansion.

13) A star may undergo two or more red giant expansion stages.

14) The helium flash shows up on the H-R diagram on the way to the horizontal branch.

15) Our Sun will fade in luminosity as its supply of hydrogen drops in a billion years.

16) A typical star burns helium for about the same amount of time it burns hydrogen.

17) Low-mass stars may become hundreds of times more luminous as giants than they were on the main sequence.

18) All stars have roughly the same luminosity after the helium flash.

19) Our Sun should become a planetary nebula in another five billion years.

20) A star system may undergo two or more nova outbursts.