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Date May 2015 Marks available 8 Reference code 15M.3.SL.TZ1.15
Level Standard level Paper Paper 3 Time zone Time zone 1
Command term Calculate, Determine, and Outline Question number 15 Adapted from N/A

Question

This question is about a particular star called Barnard’s star.

The peak wavelength in the spectrum of Barnard’s star is 940 nm. The following data are available.

apparent brightness of Barnard's starapparent brightness of the Sun=2.5×1014

luminosity of Barnard's starluminosity of the Sun=3.8×103

(i) Show that the surface temperature of Barnard’s star is about 3000 K.

(ii) Suggest why Barnard’s star is not likely to be either a white dwarf or a red giant.

[4]
a.

(i) Determine, in astronomical units (AU), the distance between Earth and Barnard’s star.

(ii) Calculate the parallax angle for Barnard’s star as observed from Earth.

(iii) Outline how the parallax angle is measured.

[8]
b.

Markscheme

(i) T=0.0029λ;
3080/3090 (K); (more than 1 SD must be shown)

(ii) temperature too low for white dwarf;
not luminous enough for red giant;

a.

(i) L=4πd2b;
dBdS(=LBLSbSbB)=3.8×1032.5×1014;
3.9×105 AU;

(ii) conversion of AU to 1.89 pc;
0.53 (arc-seconds);

(iii) measure position of star;
with respect to fixed background;
with six months between readings;
parallax angle is half the total angle / OWTTE;
May be shown in a diagram. 
b.

Examiners report

[N/A]
a.
[N/A]
b.

Syllabus sections

Option D: Astrophysics » Option D: Astrophysics (Core topics) » D.1 – Stellar quantities
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