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Stellar Physics

# Stellar Physics - 1 This question is about the nature of...

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1. This question is about the nature of certain stars on the Hertzsprung-Russell diagram and determining stellar distance. The diagram below shows the grid of a Hertzsprung-Russell (H-R) diagram on which the positions of the Sun and four other stars A, B, C and D are shown. 1 0 1 0 1 1 0 1 0 1 0 1 0 4 2 2 4 6 6 2 5 0 0 0 1 0 0 0 0 8 0 0 0 6 0 0 0 5 0 0 0 4 0 0 0 3 0 0 0 S u r f a c e t e m p e r a t u r e ( / K ) T A B C D S u n L u m i n o s i t y ( ) ( S u n = 1 ) L L (a) State an alternative labelling of the axes, (i) x -axis ................................................................................................................. (1) (ii) y -axis ................................................................................................................. (1) 1

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(b) Complete the table below. Star Type of star A B C D (4) (c) Explain, using information from the H-R diagram, and without making any calculations, how astronomers can deduce that star B is larger than star A . ..................................................................................................................................... ..................................................................................................................................... ..................................................................................................................................... (3) (d) Using the following data and information from the H-R diagram, show that star B is at a distance of about 700 pc from Earth. Apparent visual brightness of the Sun = 1.4 × 10 3 W m –2 Apparent visual brightness of star B = 7.0 × 10 –8 W m –2 Mean distance of the Sun from Earth = 1.0 AU 1 parsec = 2.1 × 10 5 AU ..................................................................................................................................... ..................................................................................................................................... ..................................................................................................................................... ..................................................................................................................................... ..................................................................................................................................... ..................................................................................................................................... (4) 2
(e) Explain why the distance of star B from Earth cannot be determined by the method of stellar parallax. ..................................................................................................................................... ..................................................................................................................................... (1) (Total 14 marks) 2. This question is about white dwarfs and neutron stars. (a) State the property that determines whether a star ends its life as a white dwarf or as a neutron star. ..................................................................................................................................... (1) (b) Define the Chandrasekhar limit and use this concept to explain the difference between a white dwarf and neutron star. ..................................................................................................................................... ..................................................................................................................................... ..................................................................................................................................... ..................................................................................................................................... (3) (c) State the name given to a rotating neutron star. ..................................................................................................................................... (1) (Total 5 marks) 3

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3. This question is about some facts regarding some of the planets in the Solar system. Four of the planets in the Solar system are Jupiter, Earth, Mars and Pluto. (a) List these four planets in order of increasing distance from the Sun. n e a r e s t f u r t h e s t i n c r e a s i n g d i s t a n c e f r o m S u n (2) (b) List these four planets in order of increasing diameter. s m a l l e s t l a r g e s t i n c r e a s i n g d i a m e t e r (2) (Total 4 marks) 4
4. This question is about some of the properties of Barnard’s star. Barnard’s star, in the constellation Ophiuchus, has a parallax angle of 0.549 arc-second as measured from Earth. (a) With the aid of a suitable diagram, explain what is meant by parallax angle and outline how it is measured. ..................................................................................................................................... ..................................................................................................................................... ..................................................................................................................................... ..................................................................................................................................... (6) (b) Deduce that the distance of Barnard’s star from the Sun is 5.94 ly. ..................................................................................................................................... ..................................................................................................................................... ..................................................................................................................................... ..................................................................................................................................... (2) 5

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(c) The ratio Sun the of brightness apparent star s Barnard' of brightness apparent is 2.6 × 10 –14 . (i) Define the term apparent brightness . ........................................................................................................................... ........................................................................................................................... ........................................................................................................................... (2) (ii) Determine the value of the ratio Sun the of luminosity star s Barnard' of luminosity (1 ly = 6.3 × 10 4 AU). (4) (d) The surface temperature of Barnard’s star is about 3 500 K. Using this information and information about its luminosity, explain why Barnard’s star cannot be (i) a white dwarf. ........................................................................................................................... ........................................................................................................................... (1) (ii) a red giant.
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