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Question

SLPaper 2

The data for the star Eta Aquilae A are given in the table.

Show by calculation that Eta Aquilae A is not on the main sequence.

[2]

Verified

Solution

« $\frac{L}{L_\odot}=\frac{M^{3.5}}{M_\odot^{3.5}}=5.70^{3.5}=»$ 442 1 mark

the luminosity of Eta $(2630 L_\odot)$ is very different «so it is not main sequence» 1 mark

Estimate, in pc, the distance to Eta Aquilae A using the parallax angle in the table.

[1]

Verified

Solution

$d «=\frac{1}{2.36 \times 10^{-3}}»=424$ «pc» 1 mark

Estimate, in pc, the distance to Eta Aquilae A using the luminosity in the table, given that $L_⊙ = 3.83 × 10^26$ W.

[3]

Verified

Solution

Use of $d=\sqrt{\frac{L}{4\pi b}}$ 1 mark

$=\sqrt{\frac{2630 \times 3.83 \times 10^{26}}{4\pi \times 7.20 \times 10^{-10}}}$ 1 mark

$«=\frac{1.055 \times 10^{19}}{3.26 \times 9.46 \times 10^{15}}»=342$ «pc» 1 mark

Suggest why your answers to (i) and (b)(ii) are different.

[2]

Verified

Solution

parallax angle in milliarc seconds/very small/at the limits of measurement 1 mark

uncertainties/error in measuring $L$ or $b$ or $\theta$ 1 mark

values same order of magnitude, so not significantly different 1 mark

2 marks max

Eta Aquilae A is a Cepheid variable. Explain why the brightness of Eta Aquilae A varies.

[3]

Verified

Solution

reference to change in size 1 mark

reference to change in temperature 1 mark

reference to periodicity of the process1 mark

reference to transparency / opaqueness 1 mark

3 marks max

The data for the star Eta Aquilae A are given in the table.