Question

Select all that are correct: 14. Brown Dwarfs: a. are plotted at the extreme lower left-hand corner of an HR diagram. b. are all main sequence stars. c. are actually Òfailed stars.Ó d. include Jupiter. e. are all thought to be the final evolutionary state of the lowest mass Main Sequence stars. 20. During post main sequence evolution: a. elements heavier than helium can be produced. b. the remaining lifetime is much shorter than the same star's main sequence lifetime had been. c. all stars will become extreme Population I stars in their surface spectrum. d. some stars still continue to burn hydrogen in their innermost cores. e. all stars tend to increase their masses slightly.

Answer 1

14. a. INCORRECT. Reason : Brown Dwarfs are plotted at the extreme lower right-hand corner of an HR diagram, where HR diagram refers to the Hertzsprung Russell diagram.

b. INCORRECT. Reason : Brown dwarfs are not massive enough to sustain nuclear fusion of hydrogen ¹H to helium ²He in their cores. But this is a characteristic feature of the Main Sequence stars. Thus it cannot be called so.

c. CORRECT. Reason : Brown dwarfs' masses are usually between 15 times the mass of Jupiter and 75 times the mass of Jupiter. In this range, as previously mentioned, Brown dwarfs are not massive enough to sustain nuclear fusion within their cores. Thus, they are often referred to as "failed stars".

d. INCORRECT. Reason : A planet usually refers to an astronomical body whose mass is less than 10 times the mass of Jupiter, the largest planet in our Solar System. An astronomical body with masses larger than 15 times the mass of Jupiter can be called a Brown Dwarf, if the other requirements are met. Jupiter is a planet, while Brown dwarfs are not.

e. INCORRECT. Reason : A White Dwarf is considered as the final stage of the low mass main sequence star, not a Brown Dwarf.